metal-organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoSTRUCTURAL
CHEMISTRY
ISSN: 2053-2296

A new polymorph of bis­­[2,6-bis­­(1H-benzimidazol-2-yl-κN3)pyridinido-κN]zinc(II)

aUniversidad Nacional de la Patagonia, Sede Trelew, 9100 Trelew, Chubut, Argentina, bCenPat, CONICET, 9120 Puerto Madryn, Chubut, Argentina, cDepartamento de Química Inorgánica, Analítica y Química Física, INQUIMAE–CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina, and dGerencia de Investigación y Aplicaciones, Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica, Buenos Aires, Argentina
*Correspondence e-mail: seba@qi.fcen.uba.ar

(Received 8 November 2012; accepted 11 December 2012; online 18 December 2012)

The title compound, [Zn(C19H12N5)2], crystallizes in the tetra­gonal space group P43212, with the monomer residing on a twofold axis. The imidazole N-bound H atoms are disordered over the two positions, with refined occupancies of 0.59 (3) and 0.41 (3). The strong similarities to, and slight differences from, a reported P42212 polymorph which has a 50% smaller unit-cell volume [Harvey, Baggio, Muñoz & Baggio (2003[Harvey, M. A., Baggio, S., Muñoz, J. C. & Baggio, R. (2003). Acta Cryst. C59, m283-m285.]). Acta Cryst. C59, m283–m285], to which the present structure bears a group–subgroup relationship, are discussed.

Comment

Metal complexes incorporating benzimidazole derivatives may mimic the behaviour of metal-ion sites in biological systems, in both structure and reactivity (Alagna et al., 1984[Alagna, L., Hassnain, S. S., Piggott, B. & Williams, D. J. (1984). Biochem. J. 59, 591-595.]; Rijn et al., 1987[Rijn, J. V., Reedijk, J., Dartmann, M. & Krebs, B. (1987). J. Chem. Soc. Dalton Trans. pp. 2579-2593.]), and this fact has rendered their study increasingly attractive. One such derivative, namely 2,6-bis(benzimidazol-2-yl)pyridine (BzimpyH2), is a potentially active ligand which binds through one pyridine and two benzimidazole N atoms in a typical tridentate mode (a comprehensive review has been published recently; Boča et al., 2011[Boča, M., Jameson, R. F. & Linert, W. (2011). Coord. Chem. Rev. 255, 290-317.]). In particular, a common pattern has two tridentate ligands bound to a transition metal cation (Tr), with the planar ligands at right angles to each other, thus shielding the cation from inter­action with other species.

In these mol­ecules, the ligand can appear as the neutral unit (BzimpyH2), with both uncoordinated imidazole N atoms protonated, in which case there is a counter-ion balancing the [Tr(BzimpyH2)2]2+ charge. Many structures of this sort appear in Version 5.33 of the Cambridge Structural Database (CSD; Allen, 2002[Allen, F. H. (2002). Acta Cryst. B58, 380-388.]), viz. DURWOJ (Huang et al., 2010[Huang, X., Kou, F., Qi, B., Meng, X. & Wu, H. (2010). Acta Cryst. E66, m967.]) and DURWOJ01 (Wu, Huang, Yuan, Kou, Chen et al., 2010[Wu, H., Huang, X., Yuan, J., Kou, F., Chen, G., Jia, B., Yang, Y. & Lai, Y. (2010). Z. Naturforsch. Teil B, 65, 1334-1340.]) for NiII, EYINAB (Harvey et al., 2004[Harvey, M. A., Baggio, S., Ibañez, A. & Baggio, R. (2004). Acta Cryst. C60, m375-m381.]) for ZnII, NETBUJ (Boca et al., 1997[Boca, R., Baran, P., Dlhan, L., Fuess, H., Haase, W., Renz, F., Linert, W., Svoboda, I. & Werner, R. (1997). Inorg. Chim. Acta, 260, 129-137.]) and PAFZIF (Ruttimann et al., 1992[Ruttimann, S., Moreau, C. M., Williams, A. F., Bernardinelli, G. & Addison, A. W. (1992). Polyhedron, 11, 635-646.]) for FeII, and WUXBUN (Yan et al., 2010[Yan, Z. Z., Xu, Z. H., Dai, G. L., Liang, H. D. & Zhao, S. H. (2010). J. Coord. Chem. 63, 1097-1106.]), EZEXOX (Wu, Huang, Yuan, Kou, Jia et al., 2010[Wu, H., Huang, X., Yuan, J., Kou, F., Jia, F., Liu, B. & Wang, K. (2010). Eur. J. Med. Chem. 45, 5324-5330.]), OYAKEF (Guo et al., 2011[Guo, Y. C., Chen, S. Y., Qiu, D. F., Feng, Y. Q. & Song, W. H. (2011). Chin. J. Inorg. Chem. 27, 1517-1520.]) and BAHJOL (Wu et al., 2011[Wu, H. L., Huang, X., Liu, B., Kou, F., Jia, F., Yuan, J. & Bai, Y. (2011). J. Coord. Chem. 64, 4383-4396.]) for MnII. There are also a number of complexes in which one of these H atoms is lost, giving a monoanion (hereinafter BzimpyH) which forms neutral Tr(BzimpyH)2 units, viz. PANXAE (Shi et al., 2003[Shi, W., Li, W., Shen, P. P., Xu, Y. K., Wang, H. M., Shi, M. & Liu, Y. (2003). Chin. J. Chem. 21, 659.]), PANXAE01 (Bai & Zhang, 2009[Bai, X.-Q. & Zhang, S.-H. (2009). Acta Cryst. E65, m397.]) and TAWZOG (Rajan et al., 1996[Rajan, R., Rajaram, R., Nair, B. U., Ramasami, T. & Mandal, S. K. (1996). J. Chem. Soc. Dalton Trans. pp. 2019-2021.]) for MnII, TIBGUH (Zhang et al., 2007[Zhang, S.-H., Zeng, M.-H. & Liang, H. (2007). Acta Cryst. E63, m1055-m1056.]) for CoII, WICJOH (Wang et al., 1994[Wang, S., Cui, Y., Tan, R. & Luo, Q. (1994). Polyhedron, 13, 1661-1668.]) and WICJOH01 (Yue et al., 2006[Yue, S.-M., Xu, H.-B., Ma, J.-F., Su, Z.-M. & Kan, Y.-E. (2006). Polyhedron, 25, 635-644.]) for CdII (see footnote1), and EJEBOK (Harvey et al., 2003[Harvey, M. A., Baggio, S., Muñoz, J. C. & Baggio, R. (2003). Acta Cryst. C59, m283-m285.]) and EJEBOK01 (Yue et al., 2006[Yue, S.-M., Xu, H.-B., Ma, J.-F., Su, Z.-M. & Kan, Y.-E. (2006). Polyhedron, 25, 635-644.]) for ZnII (see footnote1).

[Scheme 1]

We present here the structure of the title complex, Zn(BzimpyH)2, (I)[link], where the ligand displays the latter behaviour. The compound appeared serendipitously in tiny amounts as a by-product of the frustrated synthesis of a Zn + BzimpyH2 + tetra­thio­nate complex (see Experimental). In addition to (I)[link], the same crystallization batch produced a second, also unexpected, compound which proved to be a known polymorph of (I)[link] [CSD refcode EJEBOK (Harvey et al., 2003[Harvey, M. A., Baggio, S., Muñoz, J. C. & Baggio, R. (2003). Acta Cryst. C59, m283-m285.]), (II)], which presents a number of noteworthy similarities to (I)[link] but some inter­esting differences as well.

Compound (I)[link] crystallizes in the tetra­gonal space group P43212 (No. 96), while (II) crystallizes in P42212 (No. 94), although the c axis of (I)[link] is doubled with respect to that of (II). The point group (422) is the same. There is a clear group–subgroup relationship, as P43212 (c′ = 2c) is a maximal non-isomorphic subgroup of P42212. Unfortunately, the scant amount of material obtained precluded any serious attempt to detect any potential phase transition linking the two structures.

Table 1[link] presents a comparison of significant parameters in (I)[link] and (II), while the slight differences introduced into the structure by symmetry relaxation will be presented below.

The structural building block in (I)[link] is a Zn(BzimpyH)2 monomer (Fig. 1[link]) lying on a single twofold axis which traverses the ZnII cation and relates the two N,N′,N′′-tri­dent­ate BzimpyH anions; thus, half of the mol­ecule is independent. In the previously reported structure of (II), the monomer is bis­ected by a second independent twofold axis, passing through ZnII but also bis­ecting the BzimpyH anion, thus rendering just one quarter of the monomer independent. In addition, in (II), there is a third symmetry-required twofold axis perpendicular to the other two diads. The symmetry differences between the two structures can be seen in Fig. 2[link], which shows a schematic representation of the symmetry elements at the origin in both space groups, where the mol­ecules lie.

The BzimpyH anion in (I) is nearly planar, with a mean deviation of 0.063 (2) Å (maximum deviation for atom N5 of 0.1684 Å); the dihedral angle between the mean planes of the symmetry-related ligands is 75.7 (2)°, compared with an angle of 75.4 (3)° for (II). The similarities – metric as well as orientational – can be seen in Fig. 3[link], which shows an overlay of (I)[link] and (II), with neither least-squares fitting nor rotations having been performed and with their relative original orientations in the unit cells preserved. The almost perfect overlap is apparent, with a mean unweighted deviation of 0.14 (8) Å for all atoms.

The double tridentate bite with five-membered chelate rings imposes a distorted geometry on the Zn coordination octa­hedron in (I), with `cis' N—Zn—N angles spanning the broad range 74.93 (7)–107.91 (7)° and `trans' angles spanning the range 141.35 (15)–173.98 (9)°. The strain in the ligand due to the triple (N,N′,N′′) bite is evidenced by the N1⋯N5 distance [4.220 (4) Å], which is significantly shorter than those reported for three (unstrained) free BzimpyH2 entities (Freire et al., 2003[Freire, E., Baggio, S., Muñoz, J. C. & Baggio, R. (2003). Acta Cryst. C59, o259-o262.]), which have a range of 4.550 (3)–4.580 (3) Å. Comparable values were observed for (II).

The Zn—N coordination distances also show the effect of symmetry relaxation (Table 1[link]). Those in (II) are divided into two groups: Zn—Ncentral and Zn—Nlateral. In (I)[link], a very similar Zn—Ncentral value is found, but the fourfold degeneracy of Zn—Nlateral is broken, splitting into two groups. It is inter­esting to note that the average of these latter bond distances [2.1775 (14) Å] agrees fairly well with those in (II) [2.181 (3) Å].

The symmetry restrictions on the disordered imidazole N—H groups impose differences on the pattern of protonation. In the case of (II), the two N atoms per ligand which can be protonated are related by symmetry, so H-atom occupancy is forced to be 0.5 per N atom to give a total charge of −1 per ligand. In the case of (I)[link], there are two independent N atoms to accommodate one or two H-atom sites in such a way that their populations sum to 1. In order to check for differences, ΔF syntheses were plotted in an orientation suitable for viewing the electron density in the neighbourhood of the imidazole N atoms (Fig. 4[link]). The expected symmetric distribution in (II) contrasts with the asymmetric pattern in (I)[link], notably biased towards atom N4. When allowed to refine, the occupancies reflected these results [0.59 (3) and 0.41 (3) for atoms N4 and N2, respectively]. These different disorder patterns for the imidazole H atoms are linked to the inter­nal symmetry and surroundings of the mol­ecule. There are examples in the literature (CSD refcode WICJOH01; Yue et al., 2006[Yue, S.-M., Xu, H.-B., Ma, J.-F., Su, Z.-M. & Kan, Y.-E. (2006). Polyhedron, 25, 635-644.]) of Tr analogues with the monomers lying on general positions for which there is no disorder in the N—H groups, with one of the two imidazole N atoms fully protonated and the second `naked' and acting as a hydrogen-bond acceptor. This leads to an ordered distribution of hydrogen bonds in space, defining a homogeneous three-dimensional hydrogen-bonded structure.

Entries 1 and 2 in Table 2[link] reflect the two different ways in which the disordered hydrogen bond in (I)[link] is formed. The first entry corresponds to the major fraction, with the H atom linked to N4, while the second, minor, component has the H atom attached to N2. This contact links monomers in two (not three) directions parallel to the tetra­gonal base, to form broad two-dimensional nets on (001). Fig. 5[link](a) shows a packing view of one of these nets, while Fig. 5[link](b) presents a perpendicular view showing the way in which these planes stack. Inter­planar inter­actions consist of much weaker C—H⋯π inter­actions (Table 2[link], entries 3 and 4). No ππ bonds linking aromatic groups are present in the structure, the rings being too far apart to have any kind of inter­action.

A final difference observed between (I)[link] and (II) is the enantio­purity revealed by the two refinements. While (II) refines with a Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]) parameter of 0.48 (3), pointing to the presence of inversion twinning with almost equal populations of both absolute structures, (I)[link] can be described as an almost enantio­pure compound, with a Flack parameter of 0.087 (14).

As stated in the footnote1, the analysis of a third Zn(BzimpyH)2 polymorph (CSD refcode EJEBOK01) has been published, but the structure as reported presents serious formal errors which mitigate against its use for detailed comparison. However, the fact that there is an isomorphous Cd complex (refcode WICJOH01) reported in the same work and apparently error-free might suggest that the analogous Zn complex does in fact exist, possibly with space group Cc, and with its Zn cation on a general position. This would be a nonsymmetric Zn(BzimpyH)2 unit, metrically similar but different in crystallographic symmetry from the two variants discussed here. Unfortunately, for the time being this is only speculative and this (potentially inter­esting) comparison must be postponed until better data are available.

[Figure 1]
Figure 1
The mol­ecular structure of (I)[link], showing the atom-labelling scheme, with displacement ellipsoids drawn at the 40% probability level. [Symmetry code: (v) y + 1, x − 1, −z.]
[Figure 2]
Figure 2
A schematic representation of the symmetry elements at the origin in space groups P43212 (No. 96) for (I)[link] and P42212 (No. 94) for (II).
[Figure 3]
Figure 3
A common-origin orientation-preserving superposition of mol­ecules (I)[link] (heavy lines) and (II) (light lines).
[Figure 4]
Figure 4
Difference maps for (a) (I)[link] and (b) (II) (H atoms have been omitted from Fcalc), showing the electron density in the neighbourhood of the imidazole N atoms. [Symmetry code: (i) y + 1, x, −z.]
[Figure 5]
Figure 5
Packing views of (I)[link]. (a) A projection down [001], showing the two-dimensional structure mediated by strong N—H⋯N hydrogen bonds. (b) A view along [010], showing the two-dimensional structures side-on.

Experimental

In a frustrated attempt to obtain zinc tetra­thio­nate [the main final product happened to be Zn(BzimpyH2)(acetate) monohydrate], tiny amounts of pyramidal crystals of the title compound, (I)[link], and bipy­rami­dal crystals of the previously published polymorph, (II), were obtained.

An aqueous solution of zinc acetate dihydrate and potassium tetra­thio­nate was allowed to diffuse slowly into a solution of BzimpyH2 in dimethyl­formamide (DMF), with all solutions equimolar (0.080 M). After the intial formation of a solid conglomerate, spontaneous dissolution occurred. When the process seemed to have finished, the diffusion system was disassembled and the resulting solution allowed to evaporate slowly. On standing (for about three weeks), three different phases were present in different amounts, viz. an overwhelming majority of the main product, Zn(BzimpyH2)(C2H3O2)2·H2O, and minor quanti­ties of (I)[link] and (II).

Crystal data (see Table 1[link])
  • Mo Kα radiation

  • μ = 0.80 mm−1

  • 0.42 × 0.38 × 0.38 mm

Data collection
  • Oxford Gemini CCD S Ultra diffractometer

  • Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]) Tmin = 0.72, Tmax = 0.74

  • 32522 measured reflections

  • 3926 independent reflections

  • 3098 reflections with I > 2σ(I)

  • Rint = 0.041

Refinement
  • R[F2 > 2σ(F2)] = 0.038

  • wR(F2) = 0.090

  • S = 1.01

  • 3926 reflections

  • 224 parameters

  • H-atom parameters constrained

  • Δρmax = 0.28 e Å−3

  • Δρmin = −0.53 e Å−3

  • Absolute structure: Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]), with 1445 Friedel pairs

  • Flack parameter: 0.087 (14)

Table 1
Comparison of relevant data for (I)[link] and (II)

Structure(I)[link](II)
Formula[Zn(C19H12N5)2][Zn(C19H12N5)2]
Mr686.04686.04
Crystal systemTetra­gonalTetra­gonal
Space groupP43212P42212
a (Å)9.7292 (2)9.7411 (8)
c (Å)34.3125 (13)17.108 (2)
V3)3247.93 (15)1623.3 (3)
Z42
T (K)298293
Flack parameter0.087 (14)0.48 (3)
Zn—Ncentral (Å)2.1054 (17) (2×)2.088 (3) (2×)
Zn—Nlateral (Å)2.1319 (19) (2×), 2.2232 (19) (2×)2.181 (3) (4×)

Table 2
Hydrogen-bond geometry (Å, °)

Cg1 and Cg2 are the centroids of the N4/C13/N5/C19/C14 and N1/C1/C6/N2/C7 rings, respectively.

D—H⋯AD—HH⋯ADAD—H⋯A
N4—H4N⋯N2i0.861.892.744 (3)171
N2—H2N⋯N4ii0.861.942.744 (3)156
C4—H4⋯Cg1iii0.932.943.579 (3)127
C16—H16⋯Cg2iv0.932.943.633 (3)132
Symmetry codes: (i) y+1, x, -z; (ii) y, x-1, -z; (iii) [y+{\script{1\over 2}}, -x+{\script{1\over 2}}, z+{\script{1\over 4}}]; (iv) [-y+{\script{3\over 2}}, x-{\script{1\over 2}}, z-{\script{1\over 4}}].

All H atoms were visible in a difference Fourier map. Those attached to C atoms were added at their expected positions (C—H = 0.93 Å) and allowed to ride. The single H atom of the BzimpyH anion was found to be distributed unequally over the two potential sites at the N atoms of different imidazole units. Their locations were further idealized and their occupancies refined to final values of 0.59 (3) and 0.41 (3). In all cases, H-atom displacement parameters were assigned as Uiso(H) = 1.2Ueq(host). Similar to what was observed for polymorph (II), where H-atom disorder was present, the outermost part of the pyridine group presents elongated displacement ellipsoids normal to the plane of the ring, due either to genuine vibration or to an uncharacterized disorder.

Data collection: CrysAlis PRO (Oxford Diffraction, 2009[Oxford Diffraction (2009). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]).

Supporting information


Comment top

Metal complexes incorporating benzimidazole derivatives may mimic the behaviour of metal-ion sites in biological systems, in both structure and reactivity (Alagna et al., 1984; Rijn et al., 1987), and this fact has rendered their study increasingly attractive. One such derivative, 2,6-bis(benzimidazol-2-yl)pyridine (BzimpyH2), is a potentially active ligand which binds through one pyridine and two benzimidazole N atoms in a typical tridentate mode (a comprehensive review has been published recently; Boča et al., 2011). In particular, a common pattern has two tridentate ligands bound to a transition metal cation (Tr), with the planar groups at right angles to each other, thus shielding the cation from interaction with other species.

In these molecules, the ligand can appear as the neutral unit (BzimpyH2), with both uncoordinated imidazole N atoms protonated, in which case there is a counterion balancing the [Tr(BzimpyH2)2]2+ charge. Many structures of this sort appear in Version 5.33 of the Cambridge Structural Database (CSD; Allen, 2002), viz. DURWOJ (Reference?) and DURWOJ01 (Reference?) for Ni, EYINAB (Reference?) for Zn, NETBUJ (Reference?) and PAFZIF (Reference?) for Fe, and WUXBUN (Reference?), EZEXOX (Reference?), OYAKEF (Reference?) and BAHJOL (Reference?) for Mn. There are also a number of complexes in which one of these H atoms is lost, giving a monoanion (hereinafter BzimpyH) which forms neutral Tr(BzimpyH)2 units, viz. PANXAE (Reference?), PANXAE01 (Reference?) and TAWZOG (Reference?) for Mn, TIBGUH (Reference?) for Co, WICJOH (Reference?) and WICJOH01 (Reference?) for Cd (see footnote), and EJEBOK (Harvey et al., 2003) and EJEBOK01 (Yue et al., 2006) for Zn (see footnote).

We present here the structure of the title complex, Zn(BzimpyH)2, (I), where the ligand displays the latter behaviour. The compound appeared serendipitously in tiny amounts, as a by-product of the frustrated synthesis of a Zn + BzimpyH2 + tetrathionate complex (see Experimental). In addition to (I), the same crystallization batch rendered a second, also unexpected, compound which proved to be a known polymorph of (I) [CSD refcode EJEBOK (Harvey et al., 2003), (II)], which presents a number of noteworthy similarities to (I) but some interesting differences as well.

Compound (I) crystallizes in the tetragonal space group P43212 (No. 96), while (II) crystallizes in P42212 (No. 94), although the c axis of (I) is doubled with respect to that of (II). The point group (422) is the same. There is a clear group–subgroup relationship, as P43212 (c' = 2c) is a maximal non-isomorphic subgroup of P42212. Unfortunately, the scant amount of material obtained precluded any serious attempt to detect any potential phase transition linking the two structures.

Table 1 presents a comparison of significant paramaters in (I) and (II), while the slight differences introduced into the structure by symmetry relaxation will be presented below.

The structural building block in (I) is a Zn(BzimpyH)2 monomer (Fig. 1) lying on a single twofold axis which traverses the ZnII cation and relates the two N,N',N''-tridentate BzimpyH anions; thus, half of the molecule is independent. In the previously reported structure of (II), the monomer is bisected by a second independent twofold axis, passing through ZnII but also bisecting the BzimpyH anion, thus rendering just 1/4 of the monomer independent. In addition, in (II) there is a third msymmetry-required twofold axis perpendicular to the other two diads. The symmetry differences between the two structures can be seen in Fig. 2, which shows a schematic representation of the symmetry elements at the origin in both space groups, where the molecules lie.

The BzimpyH anion is nearly planar, with a mean deviation of 0.063 (2) Å (maximum deviation for atom N5 of 0.1684 Å); the dihedral angle between the mean planes of the symmetry-related ligands is 75.7 (2)°, compared with an angle of 75.4 (3)° for (II). The similarities – metric as well as orientational – can be seen in Fig. 3, which shows (I) and (II) overlapped, with neither least-squares fitting nor rotations having been performed and with their original orientations preserved. The almost perfect overlap is apparent.

The double tridentate bite with five-membered chelate rings imposes a distorted geometry on the Zn coordination octahedron, with `cis' N—Zn—N angles spanning the broad range 74.93 (7)–107.91 (7)° and `trans' angles spanning the range 141.35 (15)–173.98 (9)°. The strain in the ligand due to the triple (N,N',N'') bite is evidenced by the N1···N5 distance [4.220 (4) Å], which is significantly shorter than those reported for three (unstrained) free BzimpyH2 entities (Freire et al., 2003), which have a range of 4.550 (3)–4.580 (3) Å. Comparable values had been observed for (II).

The Zn—N coordination distances also show the effect of symmetry relaxation (Table 1). Those in (II) are divided into two groups: Zn—Ncentral and Zn—Nlateral. In (I), a very similar Zn—Ncentral value is found, but the fourfold degeneracy of Zn—Nlateral is broken, splitting into two groups. It is interesting to note that the average of these latter bond distances [2.1775 (14) Å] agrees fairly well with those in (II) [2.181 (3) Å].

The symmetry restrictions on the disordered imidazole N—H groups impose differences on the pattern of protonation. In the case of (II), the two N atoms per ligand which can be protonated are related by symmetry, so H-atom occupancy is forced to be 1/2 per N atom to give a total charge of -1 per ligand. In the case of (I), there are two independent N atoms to accommodate one or two H-atom sites in such a way that their populations sum to 1. In order to check for differences, ΔF syntheses were plotted in an orientation suitable for viewing the electron density in the neighbourhood of the imidazole N atoms (Fig. 4). The expected symmetric distribution in (II) contrasts with the asymmetric pattern in (I), notably biased towards atom N4. When allowed to refine, the occupancies reflected these results [0.59 (3) and 0.41 (3) for atoms N4 and N2, respectively]. These different disorder patterns for the imidazole H atoms are linked to the internal symmetry and surroundings of the molecule. There are examples in the literature of Tr analogues with the monomers lying on general positions for which there is no disorder in the N—H groups, with one of the two imidazole N atoms fully protonated and the second `naked' and acting as a hydrogen-bond acceptor. This leads to an ordered distribution of hydrogen bonds in space, defining a homogeneous three-dimensional hydrogen-bonded structure.

Entries 1 and 2 in Table 2 reflect the two different ways in which the disordered hydrogen bond in (I) is formed. The first entry corresponds to the major fraction, with the H atom linked to N4, while the second, minor, component has the H atom attached to N2. This contact links monomers in two (not three) directions parallel to the tetragonal base, to form broad two-dimensional nets on (001). Fig. 5(a) shows a packing view of one of these nets, while Fig. 5(b) presents a perpendicular view showing the way in which these planes stack. Interplanar interactions consist of much weaker C—H···π interactions (Table 2, entries 3 and 4). No ππ bonds linking aromatic groups are present in the structure, the rings being too far apart to have any kind of interaction.

A final difference observed between (I) and (II) is the enantiopurity revealed by the two refinements. While (II) refines with a Flack (1983) parameter of 0.48 (3), pointing to almost equal populations of both absolute structures, (I) can be described as an almost enantiopure compound, with a Flack parameter of 0.087 (14).

As stated above, the analysis of a third Zn(BzimpyH)2 polymorph (CSD refcode EJEBOK01) has been published, but the structure as reported presents serious formal errors which mitigate against its use for detailed comparison. However, the fact that there is an isomorphous Cd complex (refcode WICJOH01) reported in the same work and apparently error-free might suggest that the analogous Zn complex does in fact exist, possibly with space group Cc, and with its Zn cation on a general position. This would be a nonsymmetric Zn(BzimpyH)2 unit, metrically similar but different in crystallographic symmetry from the two variants discussed here. Unfortunately, for the time being this is only speculative and this (potentially interesting) comparison must be postponed until better data are available.

Footnote Entry EJEBOK01 (Yue et al., 2006) has been reported as a ZnII structure with formula Zn(BzimpyH)2, polymorphic with both EJEBOK (Harvey et al., 2003) and the present complex, (I). In the same paper, the Cd isomorph is also reported (refcode WICJOH01). In the ZnII complex EJEBOK01, as reported (Yue et al., 2006), one of the two imidazole units in each BzimpyH anion is assigned a fully occupied N-bound H atom. Examination of the crystal packing reveals a problem with the given assignment, since it produces an intermolecular N—H···H—N contact with H···H = 1.02 Å and N···N = 2.730 (13) Å. Furthermore, according to the published model, the two `naked' imidazole N atoms make an intermolecular contact of 2.782 (14) Å with no H atom between them. While a ΔF synthesis would be needed in order to assign the correct H-atom positions (the reflection data are not available), we think that a likely possibility is that the H atoms are distributed among all possible sites, with each short intermolecular imidazole N···N contact representing a hydrogen bond. Moreover, there is a further, more serious, objection to the structure as reported, observed in a bond-valence (BV) analysis (Brown, 2002). The BV calculation gives, for the reported Zn cation, a BV sum of 1.131 valence units (v.u.), quite outside the expected range for any 2+ cation (as a rule of thumb, ~2 ± 0.025 v.u.), thus casting doubt on the cation assignment. If the metal is changed to Cd, the same calculation gives a BV sum of 2.164 v.u. In addition, the calculation for WICJOH01 (the Cd structure originally reported in the same paper) gives 2.190 v.u. for the central cation. The obvious explanation would be an erroneous cation assignment in the Zn case. These considerations advise against making comparisons using EJEBOK01, which has thus not been used in the present report. We do, however, use the apparently error-free Cd counterpart (refcode WICJOH01).

Related literature top

For related literature, see: Alagna et al. (1984); Allen (2002); Boča et al. (2011); Brown (2002); Flack (1983); Freire et al. (2003); Harvey et al. (2003); Rijn et al. (1987); Yue et al. (2006).

Experimental top

In a frustrated attempt to obtain zinc tetrathionate [the main final product happened to be Zn(BzimpyH2)(acetate) monohydrate], tiny amounts of pyramidal crystals of the title compound, (I), and bipyramidal crystals of the previously published polymorph, (II), were obtained.

An aqueous solution of zinc acetate dihydrate and potassium tetrathionate was allowed to diffuse slowly into a solution of BzimpyH2 in dimethylformamide (DMF), with all solutions equimolar (0.080 M). After the intial formation of a solid conglomerate, spontaneous dissolution occurred. When the process seemed to be finished, the diffusion system was disassembled and the resulting solution allowed to evaporate slowly. On standing (for about three weeks), three different phases were present in different amounts, viz. an overwhelming majority of the main product, Zn(BzimpyH2)(C2H3O2)2.H2O, and minor quantities of (I) and (II).

Refinement top

All H atoms were visible in a difference Fourier map. Those attached to C atoms were added at their expected positions (C—H = 0.93 Å) and allowed to ride. The single H atom of the BzimpyH anion was found to be split over two positions of different heights, bound to N atoms of different imidazole units. Their locations were further idealized and their occupancies refined to final values of 0.59 (3) and 0.41 (3). In all cases, H-atom displacement parameters were assigned as Uiso(H) = 1.2Ueq(host). Similar to what was observed for polymorph (II), where H-atom disorder was present, the outermost part of the pyridine group presents elongated displacement ellipsoids normal to the plane of the ring, due either to genuine vibration or to an uncharacterized disorder.

Computing details top

Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell refinement: CrysAlis PRO (Oxford Diffraction, 2009); data reduction: CrysAlis PRO (Oxford Diffraction, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top
Fig. 1. The molecular structure of (I), showing the atom-labelling scheme, with displacement ellipsoids drawn at the 40% probability level. [Symmetry code: (v) y + 1, x - 1, -z.]

Fig. 2. A schematic representation of the symmetry elements at the origin in space groups P43212 (No. 96) for (I) and P42212 (No. 94) for (II).

Fig. 3. A common-origin orientation-preserving superposition of molecules (I) (heavy lines?) and (II) (light lines?).

Fig. 4. Difference maps for (a) (I) and (b) (II) (H atoms omitted from Fcalc), showing the electron density in the neighbourhood of the imidazole N atoms. [Symmetry code: (i) y + 1, x, -z.]

Fig. 5. Packing views of (I). (a) A projection down [001], showing the two-dimensional structure mediated by strong N—H···N hydrogen bonds. (b) A view along [010], showing the two-dimensional structures side-on.
Bis[2,6-bis(1H-benzimidazol-2-yl- κN3)pyridinido-κN]zinc(II) top
Crystal data top
[Zn(C19H12N5)2]Dx = 1.403 Mg m3
Mr = 686.04Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P43212Cell parameters from 12073 reflections
Hall symbol: P 4nw 2abwθ = 3.5–28.5°
a = 9.7292 (2) ŵ = 0.80 mm1
c = 34.3125 (13) ÅT = 298 K
V = 3247.93 (15) Å3Pyramid, light yellow
Z = 40.42 × 0.38 × 0.38 mm
F(000) = 1408
Data collection top
Oxford Gemini CCD S Ultra
diffractometer
3926 independent reflections
Radiation source: fine-focus sealed tube3098 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.041
ω scans, thick slicesθmax = 28.5°, θmin = 3.5°
Absorption correction: multi-scan
(CrysAlis PRO; Oxford Diffraction, 2009)
h = 1212
Tmin = 0.72, Tmax = 0.74k = 1212
32522 measured reflectionsl = 4546
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.038H-atom parameters constrained
wR(F2) = 0.090 w = 1/[σ2(Fo2) + (0.0523P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.01(Δ/σ)max < 0.001
3926 reflectionsΔρmax = 0.28 e Å3
224 parametersΔρmin = 0.53 e Å3
0 restraintsAbsolute structure: Flack (1983), with 1445 Friedel pairs
Primary atom site location: structure-invariant direct methodsAbsolute structure parameter: 0.087 (14)
Crystal data top
[Zn(C19H12N5)2]Z = 4
Mr = 686.04Mo Kα radiation
Tetragonal, P43212µ = 0.80 mm1
a = 9.7292 (2) ÅT = 298 K
c = 34.3125 (13) Å0.42 × 0.38 × 0.38 mm
V = 3247.93 (15) Å3
Data collection top
Oxford Gemini CCD S Ultra
diffractometer
3926 independent reflections
Absorption correction: multi-scan
(CrysAlis PRO; Oxford Diffraction, 2009)
3098 reflections with I > 2σ(I)
Tmin = 0.72, Tmax = 0.74Rint = 0.041
32522 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.038H-atom parameters constrained
wR(F2) = 0.090Δρmax = 0.28 e Å3
S = 1.01Δρmin = 0.53 e Å3
3926 reflectionsAbsolute structure: Flack (1983), with 1445 Friedel pairs
224 parametersAbsolute structure parameter: 0.087 (14)
0 restraints
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Zn10.98271 (2)0.01729 (2)0.00000.03697 (13)
N10.83297 (18)0.0840 (2)0.04123 (6)0.0372 (5)
N20.62060 (19)0.0454 (2)0.06625 (6)0.0413 (5)
H2N0.54450.00450.07150.050*0.41 (3)
N30.83794 (17)0.14354 (17)0.00031 (6)0.0355 (4)
N41.0450 (2)0.3536 (2)0.06371 (6)0.0401 (5)
H4N1.01510.43600.06700.048*0.59 (3)
N51.06611 (19)0.13871 (18)0.04101 (6)0.0375 (5)
C10.7945 (2)0.1981 (2)0.06246 (7)0.0369 (5)
C20.8613 (3)0.3241 (3)0.06830 (9)0.0534 (8)
H20.94750.34170.05770.064*
C30.7942 (3)0.4195 (3)0.09027 (9)0.0607 (8)
H30.83500.50490.09400.073*
C40.6670 (3)0.3942 (3)0.10730 (9)0.0620 (8)
H40.62690.46130.12290.074*
C50.5997 (3)0.2721 (3)0.10152 (8)0.0514 (7)
H50.51400.25600.11260.062*
C60.6634 (2)0.1730 (3)0.07851 (7)0.0376 (6)
C70.7243 (2)0.0006 (2)0.04428 (7)0.0358 (6)
C80.7289 (3)0.1315 (3)0.02333 (9)0.0466 (6)
C90.6348 (3)0.2368 (3)0.02616 (14)0.1011 (16)
H90.55800.22870.04210.121*
C100.6571 (4)0.3536 (4)0.00489 (14)0.144 (3)
H100.59520.42610.00670.173*
C110.7691 (4)0.3655 (3)0.01895 (13)0.0995 (15)
H110.78380.44430.03370.119*
C120.8598 (3)0.2562 (3)0.02037 (9)0.0449 (6)
C130.9892 (2)0.2513 (2)0.04254 (7)0.0373 (6)
C141.1697 (3)0.3048 (2)0.07661 (7)0.0387 (6)
C151.2722 (3)0.3653 (3)0.09913 (8)0.0499 (7)
H151.26240.45360.10910.060*
C161.3887 (3)0.2888 (3)0.10593 (9)0.0591 (8)
H161.45900.32590.12100.071*
C171.4037 (3)0.1565 (3)0.09068 (9)0.0612 (8)
H171.48450.10840.09540.073*
C181.3024 (3)0.0962 (3)0.06907 (9)0.0510 (7)
H181.31320.00790.05920.061*
C191.1823 (2)0.1709 (2)0.06227 (7)0.0355 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Zn10.03085 (14)0.03085 (14)0.0492 (2)0.01051 (15)0.00121 (9)0.00121 (9)
N10.0275 (10)0.0369 (11)0.0473 (12)0.0087 (8)0.0009 (9)0.0024 (9)
N20.0222 (9)0.0405 (12)0.0610 (14)0.0074 (8)0.0033 (9)0.0051 (11)
N30.0269 (9)0.0312 (10)0.0484 (11)0.0044 (7)0.0012 (10)0.0008 (10)
N40.0394 (12)0.0255 (9)0.0552 (13)0.0073 (9)0.0028 (10)0.0030 (9)
N50.0355 (10)0.0261 (9)0.0508 (12)0.0072 (7)0.0019 (9)0.0003 (8)
C10.0276 (12)0.0378 (13)0.0452 (14)0.0057 (9)0.0024 (10)0.0022 (11)
C20.0473 (17)0.0458 (16)0.067 (2)0.0152 (14)0.0016 (14)0.0124 (14)
C30.0590 (18)0.0420 (16)0.081 (2)0.0136 (14)0.0057 (16)0.0162 (15)
C40.0606 (19)0.0528 (19)0.073 (2)0.0010 (14)0.0037 (16)0.0259 (16)
C50.0351 (14)0.0566 (18)0.0624 (19)0.0006 (13)0.0066 (13)0.0117 (14)
C60.0276 (12)0.0402 (14)0.0450 (15)0.0044 (10)0.0019 (11)0.0020 (11)
C70.0259 (10)0.0357 (15)0.0459 (14)0.0070 (10)0.0005 (9)0.0023 (11)
C80.0314 (13)0.0373 (14)0.0712 (19)0.0089 (10)0.0092 (13)0.0067 (13)
C90.063 (2)0.062 (2)0.179 (4)0.0332 (17)0.068 (3)0.052 (2)
C100.096 (3)0.080 (3)0.257 (7)0.065 (2)0.103 (4)0.088 (4)
C110.066 (2)0.056 (2)0.176 (4)0.0362 (17)0.050 (2)0.058 (2)
C120.0372 (13)0.0355 (14)0.0619 (17)0.0082 (11)0.0021 (13)0.0073 (12)
C130.0322 (14)0.0274 (11)0.0524 (15)0.0034 (10)0.0006 (11)0.0013 (10)
C140.0386 (14)0.0281 (12)0.0494 (16)0.0029 (10)0.0003 (12)0.0028 (11)
C150.0556 (17)0.0330 (13)0.0612 (19)0.0001 (13)0.0090 (14)0.0062 (13)
C160.0546 (18)0.0545 (18)0.068 (2)0.0019 (15)0.0234 (15)0.0014 (15)
C170.0493 (18)0.0579 (19)0.076 (2)0.0217 (15)0.0202 (15)0.0061 (16)
C180.0517 (16)0.0386 (15)0.0628 (19)0.0139 (13)0.0134 (14)0.0044 (13)
C190.0399 (14)0.0290 (12)0.0375 (13)0.0074 (9)0.0001 (11)0.0004 (10)
Geometric parameters (Å, º) top
Zn1—N3i2.1054 (17)C4—C51.371 (4)
Zn1—N32.1054 (17)C4—H40.9300
Zn1—N1i2.1319 (19)C5—C61.392 (4)
Zn1—N12.1319 (19)C5—H50.9300
Zn1—N5i2.2232 (19)C7—C81.463 (3)
Zn1—N52.2232 (19)C8—C91.378 (4)
N1—C71.344 (3)C9—C101.368 (4)
N1—C11.379 (3)C9—H90.9300
N2—C71.337 (3)C10—C111.367 (4)
N2—C61.376 (3)C10—H100.9300
N2—H2N0.8600C11—C121.382 (3)
N3—C121.323 (3)C11—H110.9300
N3—C81.327 (3)C12—C131.472 (3)
N4—C131.346 (3)C14—C151.392 (4)
N4—C141.376 (3)C14—C191.398 (3)
N4—H4N0.8602C15—C161.376 (4)
N5—C131.327 (3)C15—H150.9300
N5—C191.381 (3)C16—C171.396 (4)
C1—C21.402 (4)C16—H160.9300
C1—C61.411 (3)C17—C181.366 (4)
C2—C31.362 (4)C17—H170.9300
C2—H20.9300C18—C191.396 (3)
C3—C41.391 (4)C18—H180.9300
C3—H30.9300
N3i—Zn1—N3173.98 (9)C6—C5—H5121.0
N3i—Zn1—N1i76.46 (7)N2—C6—C5131.6 (2)
N3—Zn1—N1i107.91 (7)N2—C6—C1108.1 (2)
N3i—Zn1—N1107.91 (7)C5—C6—C1120.3 (2)
N3—Zn1—N176.46 (7)N2—C7—N1115.6 (2)
N1i—Zn1—N191.37 (11)N2—C7—C8126.3 (2)
N3i—Zn1—N5i74.93 (7)N1—C7—C8118.1 (2)
N3—Zn1—N5i100.50 (7)N3—C8—C9120.5 (2)
N1i—Zn1—N5i151.33 (7)N3—C8—C7113.2 (2)
N1—Zn1—N5i99.07 (8)C9—C8—C7126.3 (3)
N3i—Zn1—N5100.50 (7)C10—C9—C8118.4 (3)
N3—Zn1—N574.93 (7)C10—C9—H9120.8
N1i—Zn1—N599.07 (8)C8—C9—H9120.8
N1—Zn1—N5151.33 (7)C11—C10—C9121.0 (3)
N5i—Zn1—N584.40 (10)C11—C10—H10119.5
C7—N1—C1103.79 (19)C9—C10—H10119.5
C7—N1—Zn1113.74 (15)C10—C11—C12117.7 (3)
C1—N1—Zn1141.35 (15)C10—C11—H11121.1
C7—N2—C6104.26 (18)C12—C11—H11121.1
C7—N2—H2N127.9N3—C12—C11121.1 (3)
C6—N2—H2N127.9N3—C12—C13112.8 (2)
C12—N3—C8121.4 (2)C11—C12—C13126.1 (3)
C12—N3—Zn1120.38 (15)N5—C13—N4113.8 (2)
C8—N3—Zn1118.14 (15)N5—C13—C12119.2 (2)
C13—N4—C14105.90 (19)N4—C13—C12126.8 (2)
C13—N4—H4N128.6N4—C14—C15131.6 (2)
C14—N4—H4N125.3N4—C14—C19106.6 (2)
C13—N5—C19104.67 (19)C15—C14—C19121.8 (2)
C13—N5—Zn1112.50 (16)C16—C15—C14117.1 (2)
C19—N5—Zn1141.97 (15)C16—C15—H15121.5
N1—C1—C2130.8 (2)C14—C15—H15121.5
N1—C1—C6108.2 (2)C15—C16—C17121.4 (3)
C2—C1—C6121.0 (2)C15—C16—H16119.3
C3—C2—C1116.9 (3)C17—C16—H16119.3
C3—C2—H2121.6C18—C17—C16121.6 (3)
C1—C2—H2121.6C18—C17—H17119.2
C2—C3—C4122.6 (3)C16—C17—H17119.2
C2—C3—H3118.7C17—C18—C19118.1 (2)
C4—C3—H3118.7C17—C18—H18121.0
C5—C4—C3121.2 (3)C19—C18—H18121.0
C5—C4—H4119.4N5—C19—C18131.0 (2)
C3—C4—H4119.4N5—C19—C14109.0 (2)
C4—C5—C6118.0 (3)C18—C19—C14120.0 (2)
C4—C5—H5121.0
N3i—Zn1—N1—C7179.79 (15)Zn1—N1—C7—N2172.31 (16)
N3—Zn1—N1—C74.10 (16)C1—N1—C7—C8177.5 (2)
N1i—Zn1—N1—C7104.00 (17)Zn1—N1—C7—C86.9 (3)
N5i—Zn1—N1—C7102.80 (17)C12—N3—C8—C90.2 (4)
N5—Zn1—N1—C77.9 (2)Zn1—N3—C8—C9176.6 (3)
N3i—Zn1—N1—C115.0 (3)C12—N3—C8—C7178.9 (2)
N3—Zn1—N1—C1169.3 (3)Zn1—N3—C8—C72.5 (3)
N1i—Zn1—N1—C161.2 (2)N2—C7—C8—N3172.8 (2)
N5i—Zn1—N1—C192.0 (3)N1—C7—C8—N36.3 (3)
N5—Zn1—N1—C1173.1 (2)N2—C7—C8—C98.1 (5)
N1i—Zn1—N3—C1297.3 (2)N1—C7—C8—C9172.7 (4)
N1—Zn1—N3—C12175.7 (2)N3—C8—C9—C100.4 (6)
N5i—Zn1—N3—C1278.8 (2)C7—C8—C9—C10178.7 (4)
N5—Zn1—N3—C122.40 (19)C8—C9—C10—C110.7 (7)
N1i—Zn1—N3—C886.30 (19)C9—C10—C11—C120.9 (7)
N1—Zn1—N3—C80.72 (19)C8—N3—C12—C110.4 (4)
N5i—Zn1—N3—C897.63 (19)Zn1—N3—C12—C11176.7 (3)
N5—Zn1—N3—C8178.8 (2)C8—N3—C12—C13177.4 (2)
N3i—Zn1—N5—C13172.63 (16)Zn1—N3—C12—C131.1 (3)
N3—Zn1—N5—C133.35 (16)C10—C11—C12—N30.7 (6)
N1i—Zn1—N5—C13109.58 (17)C10—C11—C12—C13176.8 (4)
N1—Zn1—N5—C130.4 (2)C19—N5—C13—N41.1 (3)
N5i—Zn1—N5—C1399.12 (18)Zn1—N5—C13—N4172.92 (16)
N3i—Zn1—N5—C195.6 (3)C19—N5—C13—C12175.9 (2)
N3—Zn1—N5—C19170.4 (3)Zn1—N5—C13—C124.1 (3)
N1i—Zn1—N5—C1983.3 (3)C14—N4—C13—N51.0 (3)
N1—Zn1—N5—C19166.6 (2)C14—N4—C13—C12175.8 (2)
N5i—Zn1—N5—C1968.0 (2)N3—C12—C13—N52.2 (3)
C7—N1—C1—C2176.0 (3)C11—C12—C13—N5179.9 (4)
Zn1—N1—C1—C29.9 (5)N3—C12—C13—N4174.4 (2)
C7—N1—C1—C61.9 (3)C11—C12—C13—N43.3 (5)
Zn1—N1—C1—C6167.98 (19)C13—N4—C14—C15179.1 (3)
N1—C1—C2—C3178.1 (3)C13—N4—C14—C190.4 (3)
C6—C1—C2—C30.5 (4)N4—C14—C15—C16177.9 (3)
C1—C2—C3—C41.7 (5)C19—C14—C15—C161.6 (4)
C2—C3—C4—C52.5 (5)C14—C15—C16—C170.4 (5)
C3—C4—C5—C61.0 (5)C15—C16—C17—C181.4 (5)
C7—N2—C6—C5178.8 (3)C16—C17—C18—C190.3 (5)
C7—N2—C6—C10.4 (3)C13—N5—C19—C18175.9 (3)
C4—C5—C6—N2177.0 (3)Zn1—N5—C19—C188.3 (5)
C4—C5—C6—C11.2 (4)C13—N5—C19—C140.8 (3)
N1—C1—C6—N21.5 (3)Zn1—N5—C19—C14168.45 (19)
C2—C1—C6—N2176.6 (2)C17—C18—C19—N5178.1 (3)
N1—C1—C6—C5179.9 (2)C17—C18—C19—C141.6 (4)
C2—C1—C6—C52.0 (4)N4—C14—C19—N50.2 (3)
C6—N2—C7—N10.8 (3)C15—C14—C19—N5179.8 (2)
C6—N2—C7—C8178.3 (2)N4—C14—C19—C18176.9 (2)
C1—N1—C7—N21.7 (3)C15—C14—C19—C182.7 (4)
Symmetry code: (i) y+1, x1, z.
Hydrogen-bond geometry (Å, º) top
Cg1 and Cg2 are the centroids of the N4/C13/N5/C19/C14 and N1/C1/C6/N2/C7 rings, respectively.
D—H···AD—HH···AD···AD—H···A
N4—H4N···N2ii0.861.892.744 (3)171
N2—H2N···N4iii0.861.942.744 (3)156
C4—H4···Cg1iv0.932.943.579 (3)127
C16—H16···Cg2v0.932.943.633 (3)132
Symmetry codes: (ii) y+1, x, z; (iii) y, x1, z; (iv) y+1/2, x+1/2, z+1/4; (v) y+3/2, x1/2, z1/4.

Experimental details

Crystal data
Chemical formula[Zn(C19H12N5)2]
Mr686.04
Crystal system, space groupTetragonal, P43212
Temperature (K)298
a, c (Å)9.7292 (2), 34.3125 (13)
V3)3247.93 (15)
Z4
Radiation typeMo Kα
µ (mm1)0.80
Crystal size (mm)0.42 × 0.38 × 0.38
Data collection
DiffractometerOxford Gemini CCD S Ultra
diffractometer
Absorption correctionMulti-scan
(CrysAlis PRO; Oxford Diffraction, 2009)
Tmin, Tmax0.72, 0.74
No. of measured, independent and
observed [I > 2σ(I)] reflections
32522, 3926, 3098
Rint0.041
(sin θ/λ)max1)0.672
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.038, 0.090, 1.01
No. of reflections3926
No. of parameters224
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.28, 0.53
Absolute structureFlack (1983), with 1445 Friedel pairs
Absolute structure parameter0.087 (14)

Computer programs: CrysAlis PRO (Oxford Diffraction, 2009), SHELXS97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top
Cg1 and Cg2 are the centroids of the N4/C13/N5/C19/C14 and N1/C1/C6/N2/C7 rings, respectively.
D—H···AD—HH···AD···AD—H···A
N4—H4N···N2i0.861.892.744 (3)171
N2—H2N···N4ii0.861.942.744 (3)156
C4—H4···Cg1iii0.932.943.579 (3)127
C16—H16···Cg2iv0.932.943.633 (3)132
Symmetry codes: (i) y+1, x, z; (ii) y, x1, z; (iii) y+1/2, x+1/2, z+1/4; (iv) y+3/2, x1/2, z1/4.
Comparison of relevant data for (I) and (II) top
Structure(I)(II)
FormulaC38H24N10ZnC38H24N10Zn
Mr686.04686.04
Crystal systemTetragonalTetragonal
Space groupP43212P42212
a (Å)9.7292 (2)9.7411 (8)
c (Å)34.3125 (13)17.108 (2)
V3)3247.93 (16)1623.3 (3)
Z42
Flack parameter0.087 (14)0.48 (3)
Zn—Ncentral (Å)2.1054 (17) (2×)2.088 (3) (2×)
Zn—Nlateral (Å)2.1319 (19) (2×), 2.2232 (19) (2×)2.181 (3) (4×)
 

Footnotes

1CSD entry EJEBOK01 (Yue et al., 2006[Yue, S.-M., Xu, H.-B., Ma, J.-F., Su, Z.-M. & Kan, Y.-E. (2006). Polyhedron, 25, 635-644.]) has been reported as a ZnII structure with formula Zn(BzimpyH)2, polymorphic with both EJEBOK (Harvey et al., 2003[Harvey, M. A., Baggio, S., Muñoz, J. C. & Baggio, R. (2003). Acta Cryst. C59, m283-m285.]) and the present complex, (I)[link]. In the same paper, the Cd isomorph is also reported (refcode WICJOH01). As reported for the ZnII complex EJEBOK01 (Yue et al., 2006[Yue, S.-M., Xu, H.-B., Ma, J.-F., Su, Z.-M. & Kan, Y.-E. (2006). Polyhedron, 25, 635-644.]), one of the two imidazole units in each BzimpyH anion is assigned a fully occupied N-bound H atom. Examination of the crystal packing reveals a problem with the given assignment, since it produces an inter­molecular N—H⋯H—N contact with H⋯H = 1.02 Å and N⋯N = 2.730 (13) Å. Furthermore, according to the published model, the two `naked' imidazole N atoms make an inter­molecular contact of 2.782 (14) Å, with no H atom between them. While a ΔF synthesis would be needed in order to assign the correct H-atom positions (the reflection data are not available), we think that a likely possibility is that the H atoms are distributed over all possible sites, with each short inter­molecular imidazole N⋯N contact representing a hydrogen bond. Moreover, there is a further, more serious, objection to the structure as reported, observed in a bond-valence (BV) analysis (Brown, 2002[Brown, I. D. (2002). In The Chemical Bond in Inorganic Chemistry: The Bond Valence Model. Oxford University Press.]). The BV calculation gives, for the reported ZnII cation, a BV sum of 1.131 valence units (v.u.), quite outside the expected range for any 2+ cation (as a rule of thumb, ∼2±0.025 v.u.), thus casting doubt on the cation assignment. If the metal is changed to Cd, the same calculation gives a BV sum of 2.164 v.u. In addition, the calculation for WICJOH01 (the Cd structure originally reported in the same paper) gives 2.190 v.u. for the central cation. The obvious explanation would be an erroneous cation assignment in the Zn case. These considerations advise against making comparisons using EJEBOK01, which has thus not been used in the present report. We do, however, use the apparently error-free Cd counterpart (refcode WICJOH01).

Acknowledgements

The authors acknowledge ANPCyT (project No. PME 2006–01113) for the purchase of the Oxford Gemini CCD diffractometer, and the Spanish Research Council (CSIC) for the provision of a free-of-charge licence to the Cambridge Structural Database (Allen, 2002[Allen, F. H. (2002). Acta Cryst. B58, 380-388.]).

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