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Keywords:

  • Chromyl chloride;
  • Chromium;
  • Nitrogen heterocycles;
  • Chromium(V) complexes

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results
  5. Discussion
  6. Conclusions
  7. Experimental Section
  8. Acknowledgements

The reaction of CrO2Cl2 with 2, 2′-bipyridyl or 1, 10-phenanthroline (diimine) in CCl4 or anhydrous CH3CO2H solution, produces orange-brown diamagnetic [CrO2Cl2(diimine)]. The X-ray structure of [CrO2Cl2(2, 2′-bipy)] shows a six-coordinate central chromium(VI) atom with cis-dioxo groups trans to the diimine. In contrast, the diimines react with CrO3 in CH3CO2H / conc. aqueous HCl to form bright red paramagnetic CrV complexes, [CrOCl3(diimine)]. The X-ray structure of [CrOCl3(2, 2′-bipy)] shows a six-coordinate central chromium atom with mer-chlorines and the diimine trans to O/Cl. The addition of [2, 2-bipyH2]Cl2 to a solution of CrO3 in CH3CO2H saturated with HCl gas, produces the CrV anion [2, 2′-bipyH2][CrOCl4]Cl, which loses HCl on heating in vacuo to form [CrOCl3(2, 2′-bipy)]. IR, UV/Vis, and 1H NMR spectra (CrVI only) are reported for the new complexes. Attempts to extend these routes to oxygen donor ligands, including ethers and phosphine oxides, were unsuccessful. The diimine complexes are the first structurally autheticated adducts of chromium(VI) and (V) oxide-chlorides with neutral ligands.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results
  5. Discussion
  6. Conclusions
  7. Experimental Section
  8. Acknowledgements

The ability of chromyl chloride (CrO2Cl2) to oxidise hydrocarbons (the Etard reaction) has been known for well over 100 years, but elucidation of the mechanism and identification of the often complex mixture of products has remained an active research topic.15 In a series of studies Ault and co-workers explored the reactions of CrO2Cl2 with a variety of organic molecules and donor ligands at very low temperatures using matrix isolation IR spectroscopic techniques.611 More conventional coordination studies are limited and the reports contradictory. The reactions of CrO2Cl2 or of CrO3/HCl with N-donor ligands (amines or nitrogen heterocycles) were variously claimed to give CrVI complexes such as [CrO2Cl2(diimine)] (diimine = 2, 2′-bipyridyl, 4, 4′-bipyridyl, 1, 10-phenanthroline, etc.), [CrO2Cl2(py)n] (n = 1 or 2), chromium(V) complexes [CrOCl3(diimine)], or chromium(V) or CrVI oxido-chlorido anions, [diimineH2][CrOCl5], [diimineH][CrO2Cl2], or [diimineH][CrO3Cl].1220 There are major disagreements between the reports about the identity, purity and the spectroscopic properties of the products. X-ray structural authentications are completely lacking.

We recently reported the X-ray crystal structures and spectroscopic characterization of two CrV compounds, CrOCl3 and Rb2[CrOCl5],21 and during these studies we had occasion to examine some of the N-base chemistry of high valent chromium and we report these results herein.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results
  5. Discussion
  6. Conclusions
  7. Experimental Section
  8. Acknowledgements

After conducting a substantial number of trial syntheses using either CrO3 or CrO2Cl2 as starting material, we have established the key factors which need to be carefully controlled to obtain pure samples of the complexes. These are: the purity of the reagents and solvent used, the temperature, and especially the ratio of chromium reagent:ligand. The most successful solvents were anhydrous (glacial) acetic acid and CCl4, and typically the temperature was kept below ca. 280 K during the syntheses. (Although glacial acetic acid freezes at 289 K, the freezing point is reduced by dissolved reagents, and crystallization of the acid is slow, so this is not a problem over the short time of the syntheses.) Attempts to use CH2Cl2, MeCN, thf, or Et2O as solvent gave impure products or mixtures, and it seems likely that some attack on the solvent C–H functions accompanies adduct formation.

[CrO2Cl2(diimine)]

The addition of a CCl4 solution of CrO2Cl2 to a vigorously stirred CCl4 solution of 2, 2′-bipy in a 0.9:1.0 molar ratio at ca. 280 K, results in immediate precipitation of an orange-brown powder in high yield. A spectroscopically identical product was formed using anhydrous CH3CO2H as solvent, and from this solvent the product was sometimes obtained as very small needle crystals. Excess CrO2Cl2 must be avoided or highly impure products are obtained, probably due to further reaction with the carbon skeleton of the ligands (Etard type reactions). At room temperature or above, or in wet solvents, darker, impure products result. The complex has the composition [CrO2Cl2(2, 2′-bipy)], and is fairly soluble in CH2Cl2 and CH3CO2H, insoluble in CCl4, and decomposed by acetone or thf. It can be kept for some weeks in a freezer in the dark, and can be handled quickly in air when dry. On standing at room temperature it slowly decomposes, becoming dull brown, and is then insoluble in CH2Cl2. [CrO2Cl2(2, 2′-bipy)] shows two Cr=O IR stretches at 963 and 893 cm–1, a very broad Cr–Cl stretch at 360 cm–1, and a strong feature at 251 cm–1 tentatively assigned as δ(CrO2). These features are in reasonable agreement with predictions from DFT calculations,22 if one applies the usual scaling factor of 0.9 to allow for the neglect of anharmonicity. The complex is diamagnetic as expected for the d0 CrVI (The experimental value of ca. 0.2 B.M. could be due to small amounts of lower oxidation state impurities, but could also be due to temperature independent paramagnetism.), and the UV/Vis spectrum also supports the presence of the higher oxidation state. Almost all CrVI complexes, for which UV/Vis data are available are four-coordinate, except for solid CrOF4 and the [CrOF5] anion, which are six-coordinate, and show charge-transfer bands at ca. 21 000 and 27 000 cm–1 assigned as O(π) [RIGHTWARDS ARROW] Cr(t2g) and F(π) [RIGHTWARDS ARROW] Cr(t2g) respectively.23 The spectrum of powdered [CrO2Cl2(2, 2′-bipy)] has overlapping bands at 19800(sh), 23800 and 30300 cm–1 (and several ill-defined absorptions at higher energy). The bands at 19800 and 23800 cm–1 can be assigned as Cl(π) [RIGHTWARDS ARROW] Cr(t2g) and N(σ) [RIGHTWARDS ARROW] Cr(t2g) respectively, based upon the electronegativities of the donor atoms and the strong π donation expected from two oxido-groups, which significantly raise the energy of the metal t2g derived levels.24 Notably there is no absorption in the range of ca. 12000–17000 cm–1 indicating the absence of CrV.21

The 1H NMR spectrum also shows four C–H resonances of equal intensity, indicating the equivalence of the pyridyl rings and, together with the two Cr=O IR stretches, identifies the isomer present as having oxygen trans to nitrogen atoms. This was confirmed by the X-ray structure (Figure 1). The limited solution stability and poor solubility precluded the growth of X-ray quality crystals from the isolated complex, but on several occasions, some very small needle crystals were formed directly from the synthesis in glacial acetic acid. Several data sets were collected, all showing the same arrangement, and the structure determined from the best data is reported herein.

thumbnail image

Figure 1. The structure of [CrO2Cl2(2, 2′-bipyridine)] showing the atom numbering scheme. Ellipsoids are drawn at the 50 % probability level and hydrogen atoms are omitted for clarity. Selected bond lengths /Å and angles /°: Cr1–O1 = 1.605(3), Cr1–O2 = 1.620(3), Cr1–N1 = 2.187(3), Cr1–N2 = 2.181(3), Cr1–Cl1 = 2.2797(13), Cr1–Cl2 = 2.2857(14), O1–Cr1–O2 = 106.35(15), O1–Cr1–N2 = 89.36(14), O2–Cr1–N1 = 91.04(14), N2–Cr1–N1 = 73.26(13), O1–Cr1–Cl1 = 95.42(10), O2–Cr1–Cl1 = 94.65(10), N2–Cr1–Cl1 = 84.17(9), N1–Cr1–Cl1 = 82.83(9), O1–Cr1–Cl2 = 95.80(10), O2–Cr1–Cl2 = 94.36(10), N2–Cr1–Cl2 = 83.26(9), N1–Cr1–Cl2 = 82.65(9), Cl1–Cr1–Cl2 = 163.02(5).

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The structure shows a distorted octahedral arrangement at the chromium, with a small N–Cr–N angle of 73.26(13)°, reflecting the constrained chelate bite size of 2, 2′-bipy, and with the trans-Cl–Cr–Cl unit bent towards the nitrogen ligand [163.02(5)°]. The angle O–Cr–O is markedly wider at 106.35(15)° than the Cl–Cr–N or Cl–Cr–O. The Cr–O and Cr–Cl distances are slightly longer than those in the distorted tetrahedral parent species, CrO2Cl2,25 as expected due to the increased coordination number.

The corresponding [CrO2Cl2(1, 10-phen)] was made similarly, from CrO2Cl2 and the ligand in glacial CH3CO2H. The complex is very poorly soluble in CH2Cl2, but is spectroscopically similar to the 2, 2′-bipy analogue. In contrast, reaction of pyridine with CrO2Cl2 in either a 1.1 or 2.2:1.0 molar ratio in CCl4 at ambient temperature or –20 °C gave dark coloured, often sticky, materials. These were clearly mixtures from their IR spectra, with [pyH][CrOCl4]18 as a major constituent.

[CrOCl3(diimine)]

The reaction of CrO3 with conc. hydrochloric acid in glacial acetic acid solution at room temperature gave a dark purple solution with some evolution of Cl2. After about 20 min., during which a slow stream of nitrogen was bubbled through the solution, the solution was cooled in iced water, and vigorously stirred, whilst powdered 2, 2′-bipyridyl was sifted in. The solution changed to bright red, and after a further 30 min the deep crimson product was filtered off, rinsed with acetic acid and dried in vacuo. The key to obtaining a pure product appears to be to allow the initial solution to stand, to allow the reduction to CrV to proceed to completion; purging with N2 removes the evolved Cl2. The product was identified by microanalysis and spectroscopic data as [CrOCl3(2, 2′-bipy)], and from comparison of the limited data reported, is the complex first described by Saha and Ghosh.12 It is air stable when dry and very poorly soluble in CH2Cl2 or MeCN. The solid decomposes slowly at room temperature turning a dull brown. [CrOCl3(2, 2′-bipy)] is paramagnetic, μeff = 1.92 B.M., and in the IR spectrum has a single strong Cr=O stretch at 962 cm–1 and Cr–Cl stretches at 380 and 355 cm–1. The UV/Vis spectrum of the solid contains bands at 12400, 17660, 19500, 22100, 32510 cm–1, for which by comparison with other CrV complexes,18,21,26,27 the first three bands are d-d transitions, with the lowest Cl(π) [RIGHTWARDS ARROW] Cr(t2g) band at 22100 cm–1. Attempts to grow crystals of the complex from CH2Cl2 or MeCN solutions by cooling, or by vapour diffusion of Et2O, failed due to the poor solubility. However, a few crimson crystals were obtained directly from the acetic acid synthesis solution, one of which was used for the structure determination (Figure 2).

thumbnail image

Figure 2. Structure of [CrOCl3(2, 2′-bipy)] showing the atom numbering scheme. Ellipsoids are drawn at the 50 % probability level and hydrogen atoms are omitted for clarity. Selected bond lengths /Å and angles /°: Cr1–O1 = 1.599(5), Cr1–N1 = 2.090(6), Cr1–N2 = 2.199(6), Cr1–Cl3 = 2.226(4), Cr1–Cl1 = 2.278(3), Cr1–Cl2 = 2.282(3), O1–Cr1–N1 = 92.3(3), N1–Cr1–N2 = 75.0(2), O1–Cr1–Cl3 = 100.8(2), N2–Cr1–Cl3 = 91.95(18), O1–Cr1–Cl1 = 95.93(19), N1–Cr1–Cl1 = 84.31(17), N2–Cr1–Cl1 = 84.52(17), Cl3–Cr1–Cl1 = 91.47(8), O1–Cr1–Cl2 = 95.95(19), N1–Cr1–Cl2 = 89.23(16), N2–Cr1–Cl2 = 82.57(17), Cl3–Cr1–Cl2 = 92.19(8), Cl1–Cr1–Cl2 = 166.69(8).

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The structure shows a distorted octahedron, with a mer arrangement of chlorines, and the acute N1–Cr1–N2 = 75.0(2)°, with the axial chlorines bent towards the diimine C1–Cr1–Cl2 = 166.69(8)°. The corresponding bond lengths are similar to those in [CrO2Cl2(2, 2′-bipy)] (above), and to those in other CrV adducts.28 The Cr1–O1 = 1.599(5) Å, may be compared with CrOCl3 [1.543(9) Å]21 and in [CrOCl4] [1.519(12) Å],26 which are five-coordinate. The structure appears to be free from O/Cl disorder in plane and the Cr–N distances reflect the greater trans influence of the Cr=O bond.

Sarkar and Singh14 reported that [CrOCl3(2, 2′-bipy)] was formed by heating [2, 2′-BipyH2][CrOCl5] at 80 °C in carbon dioxide, and we find that on heating [2, 2′-BipyH2][CrOCl5] in vacuo at 80 °C the purple crystals transform into a bright red powder, with evolution of HCl. The product has an IR spectrum, in which the main features correspond to those of [CrOCl3(2, 2′-bipy)] (made from CH3CO2H/HCl), although some other much weaker bands are present and it is not analytically pure. This material could not be recrystallised successfully due to its poor solubility. On stronger heating, the material becomes dull brown and loses the terminal Cr=O vibration in the IR spectrum. This is replaced by a new band at 896 cm–1; this may indicate a Cr–O–Cr link. We also found that [CrOCl3(2, 2′-bipy)] can be obtained directly by reaction of 2, 2′-bipyridyl with a suspension of CrOCl3 in anhydrous MeCN, but since the synthesis of CrOCl3 requires complex apparatus29,30 the preparation from CrO3/HCl/2, 2′-bipy in CH3CO2H is much simpler. The deep red [CrOCl3(1, 10-phen)] was made from CrO3/HCl in CH3CO2H and is spectroscopically very similar to the 2, 2′-bipyridyl complex, although even less soluble in chlorocarbon solvents. Attempts to extend the syntheses from CrO3/HCl/CH3CO2H to CrV complexes of oxygen donor ligands including Ph3PO, Me3PO, Ph3AsO, and MeO(CH2)2OMe were unsuccessful.

In contrast to the above, saturation of a glacial acetic acid solution of CrO3 with hydrogen chloride at ca. 280 K, followed by addition of a solution of 2, 2′-bipyridyl in concentrated (aqueous) hydrochloric acid, and further passage of HCl gas, precipitated deep purple red crystals of[2, 2′-BipyH2][CrOCl5].12,18 As we have reported elsewhere,21 the crystal structure of this complex shows it to be[2, 2′-BipyH2][CrOCl4]Cl, containing the familiar square pyramidal CrV anion. If this reaction is conducted at room temperature or with larger amounts of water present the product contains substantial amounts of the well-known orange [CrO3Cl] anion.31

CrO2Cl2 and Other Ligands

Under rigorously anhydrous conditions, in CH2Cl2 or CH3CO2H at ca. 5 °C there was no adduct formation between CrO2Cl2 and O-donor ligands, including Ph3PO,32 Me3PO, MeO(CH2)2OMe, or 12-crown-4. On standing the solutions turn brown as decomposition occurs. Heavier donor ligands, such as Ph3P, Ph3As, Me2S, and Me2Se, immediately reduce CrO2Cl2 (a CrO2Cl2:ligand ratio of 1:2 was used to avoid/minimise any Etard-type reactions with the carbon backbones) with formation of the corresponding oxidised ligands (Ph3PO, Ph3AsO, Me2SO) identified by IR and multinuclear NMR spectra. Me2Se gives both Me2SeCl2 and Me2SeO, identified by their 77Se NMR chemical shifts (see Experimental Section). CrOCl3 also oxidised the soft donor ligands on contact, giving similar products.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results
  5. Discussion
  6. Conclusions
  7. Experimental Section
  8. Acknowledgements

The results reported above show that CrO2Cl2 is a modest Lewis acid, forming complexes with strong σ-donor nitrogen ligands, but not with weaker donor, neutral oxygen ligands. VOCl3 forms complexes with N- and O-donor ligands, and even unstable examples with neutral sulfur ligands33,34 but with VO2Cl, only N- and a limited number of O-donor examples form.35 This suggests that the presence of two strong π-donor oxido groups significantly reduces the Lewis acidity of the central metal atom, and a similar effect will be present in CrO2Cl2 (CrOCl4 is unknown, so direct comparisons cannot be made). Adduct formation requires the deformation of the stable tetrahedral CrO2Cl2 arrangement into a four coordinate fragment required in the octahedral adducts, and the energy required for this deformation needs to be recovered from the Lewis acid-base bonds formed. It is plausible that weaker Cr–OPR3 or Cr–ether linkages provide insufficient energy return. The [CrOCl3(diimine)] species are formed by reduction of CrVI under carefully controlled conditions, or by direct reaction of CrOCl3 with the ligands. [CrOCl3(2, 2′-bipy)] is the first structurally authenticated complex of a CrV oxido-halide containing a neutral ligand.28 The redox chemistry found with soft donor ligands closely resembles that of high valent vanadium species, although the chromium systems are stronger oxidants.3335

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results
  5. Discussion
  6. Conclusions
  7. Experimental Section
  8. Acknowledgements

The existence of the six-coordinate adducts of CrO2Cl2, [CrO2Cl2(diimine)] (diimine = 2, 2′-bipy, 1, 10-phen) was confirmed and full structural and spectroscopic data reported. CrO2Cl2 fails to form complexes with neutral O-donor ligands, and redox chemistry occurs with softer donor ligands. No evidence was found for [CrVO2Cl2], although [VO2Cl2] is well known.35 The characterization of the CrV complexes [CrOCl3(diimine)] was also achieved.

Experimental Section

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results
  5. Discussion
  6. Conclusions
  7. Experimental Section
  8. Acknowledgements

All manipulations were made in a dry nitrogen atmosphere using standard Schlenk, vacuum line, and glove box techniques. CrO2Cl2 (Aldrich) was freshly distilled under reduced pressure, 2, 2′-bipyridyl, 1, 10-phenanthroline, Ph3PO, Ph3P, Ph3As, and 12-crown-4 were dried by heating in vacuo. Me3PO was freshly sublimed in vacuo. Me2S and Me2Se were dried with molecular sieves, and pyridine, MeO(CH2)2OMe and thf distilled off sodium. MeCN, CH2Cl2 and CCl4 were dried by distillation from CaH2. Glacial acetic acid, CrO3, and HCl(gas) (Aldrich) were used as received.

[CARE: CrO2Cl2 and CrO3 are carcinogenic, and it is probable that the other CrVI and CrV products are also. Appropriate precautions should be taken.]

[CrO2Cl2(2, 2′-bipy)]: Method 1: 2, 2′-Bipyridyl (0.35 g, 2.2 mmol) was dissolved in glacial CH3CO2H (10 mL), the solution cooled to ca. 5 °C, and CrO2Cl2 (0.16 mL, 0.31 g, 2.0 mmol) in glacial CH3CO2H (5 mL) was added slowly, producing a dark orange-red solution. The mixture was stirred for 5 min and then concentrated to ca. 5 mL in vacuo. A deep orange-brown solid precipitated which was filtered off, rinsed with a small amount (1 mL) of CH3CO2H, and dried in vacuo. Yield 0.55 g, 78 %. The product is stable for some weeks in a freezer (–18 °C) in the dark, but decomposes slowly at room temperature or in bright light. C10H8Cl2CrN2O2 (311.1): cacld. C 38.6; H 2.6; N 9.0 %; found: C 38.0; H 2.3; N 8.7 %. 1H NMR (CD2Cl2, 293 K): δ = 9.63 (d, [H], J = 8 Hz). 8.32 (d, [H], J = 8 Hz), 8.22 (d, [H], J = 8 Hz) 7.77 (t, [H] J = 8 Hz) ppm. IR (Nujol/): equation image = 963 (s), 893 (s) ν(Cr=O), 360 (vs) ν(CrCl), 251 (m), δ(CrO2) cm–1. UV/Vis (diffuse reflectance in BaSO4): 19800(sh), 23800, 30300 cm–1. μeff = 0.2 B.M.

Method 2: 2, 2′-Bipyridyl (0.35 g, 2.25 mmol) was dissolved in anhydrous CCl4 (30 mL) and the solution cooled to 0 °C with vigorous stirring. A solution of CrO2Cl2 (0.16 mL, 0.31 g, 2.0 mmol) in CCl4 (5 mL) was added dropwise, resulting in immediate precipitation of an orange-brown powder. The solution was stirred briefly at 0 °C and then the solid filtered off, rinsed with cold CCl4 (5 mL), and dried in vacuo. Yield 0.65 g, 92 %. The product was spectroscopically identical to that from Method 1.

[CrO2Cl2(1, 10-phen)]: 1, 10-Phenanthroline (0.39 g, 2.2 mmol) was dissolved in glacial acetic acid (30 mL) and the solution cooled to ca. 5 °C. A solution of CrO2Cl2 (0.16 mL, 0.31 g, 2.0 mmol) in CH3CO2H (5 mL) was added dropwise with vigorous stirring. An orange-brown precipitate formed rapidly, which was filtered off after 10 min, washed with CH3CO2H (5 mL), and dried in vacuo. Yield 0.73 g, 95 %. C12H8Cl2CrN2O2 (335.1): calcd. C 43.0; H 2.4; N 8.4 %; found: C 42.9; H 2.3; N 8.5 %. 1H NMR (CD2Cl2, 293 K): δ = 9.46 (m [H]), 8.86 (d, [H], J = 8 Hz), 8.21 (s, [H]), 8.18 (m, [H] J = 8 Hz). IR (Nujol): equation image = 941 (s), 901 (s) Cr=O, 360 (vs) CrCl, 251 (m), δ(CrO2) cm–1. UV/Vis (diffuse reflectance in BaSO4): 20000, 23100, 32300 cm–1. μeff = 0.45 B.M.

The same product was formed from CCl4 solution, but 1, 10-phenanthroline is poorly soluble in CCl4 in the cold, making isolation of the pure product more difficult from this solvent.

[CrOCl3(2, 2′-bipy)]: CrO3 (1.0 g, 10.0 mmol) was dissolved in a mixture of glacial acetic acid (25 mL) and conc. hydrochloric acid (5 mL) at room temperature, forming a deep red solution. After stirring for 30 min, during which time a slow stream of nitrogen was bubbled through the solution, the solution was filtered to remove any undissolved solid and cooled in iced-water to ca. 5 °C. Powdered 2, 2′-bipyridyl (1.6 g, 10.0 mmol) was added slowly to the stirred solution. After 30 min the deep red microcrystalline solid was filtered off, rinsed with CH3CO2H (5 mL), and dried in vacuo. Yield 2.5 g, 76 %. C10H8Cl3CrN2O (330.5): calcd. C 36.3; H 2.4; N 8.5 %; found: C 36.6; H 2.7; N 7.8 %. IR (Nujol): equation image = 962 (s) ν(Cr=O), 380 (sh), 355 (vs) ν(CrCl) cm–1. UV/Vis (diffuse reflectance in BaSO4): 12400, 17660, 19500, 22100, 32510 cm–1. μeff = 1.92 B.M.

[CrOCl3(1, 10-phen)]: [CrOCl3(1, 10-phen)] was made similarly to the 2, 2′-bipy analogue, yield 58 %. It is a crimson powder, very poorly soluble is non-coordinating organic solvents. C12H8Cl3CrN2O·H2O (372.6): calcd. C 38.7; H 2.7, N 7.5 %; found C 38.0; H 2.3; N 7.5 %. IR (Nujol): equation image = 3500 (vbr), 1610 (w) H2O, 940 (s) ν(Cr=O), 370 (sh), 345 (vs) ν(CrCl) cm–1. UV/Vis (diffuse reflectance in BaSO4): 12000, 17200(sh), 19400, 22300, 32500 cm–1. μeff = 1.87 B.M.

[2, 2′-BipyH2][CrOCl4]Cl (for comparison, data from reference21). IR (Nujol): equation image = 1017 (m) Cr=O, 360 (br.,vs) Cr–Cl cm–1. UV/Vis (diffuse reflectance in BaSO4/cm–1): 12500, 17000, 19800, 23300, 27100 cm–1. μeff = 1.79 B.M.

CrO2Cl2 and Soft Donor Ligands. General Method: The ligand (0.02 mmol) was dissolved in either CD2Cl2 or CH3CO2H (2 mL) and a solution of CrO2Cl2 (0.01 mmol) in the same solvent added. Reaction occurred immediately, sometimes quite violently, with the formation of green or brown precipitates. The major organic products were identified by in situ 1H, 31P{1H}, or 77Se{1H} NMR spectroscopy as appropriate. For the reactions in CD2Cl2 the mixture was subsequently pumped to dryness and the identifications confirmed by IR spectroscopy after hydrolysis with “880” ammonia, extraction with CH2Cl2, and removal of the solvent. Me2Se was unusual in that both Me2SeCl2 [δ(77Se) = 446] and Me2SeO [δ(77Se) = 805] were formed.

X-ray Crystallography: Crystals were obtained directly from the syntheses as described above. Details of the crystallographic data collection and refinement parameters are given in Table 1. Data collections used a Rigaku AFC12 goniometer equipped with an enhanced sensitivity (HG) Saturn724+ detector mounted at the window of an FR-E+ SuperBright molybdenum (λ = 0.71073 Å) rotating anode generator with VHF Varimax optics (100 μm focus) with the crystal held at 100 K (N2 cryostream). Structure solution and refinement were straightforward.36,37

Table 1. X-ray crystallographic data a).
 [CrOCl3(2, 2′-bipy)][CrO2Cl2(2, 2′-bipy)]
  1. a

    a) Common items: temperature = 100 K; wavelength (Mo-Kα) = 0.71073 Å; θ(max) = 27.5°. b) R1 = Σ||Fo|–|Fc||/Σ|Fo|; wR2 = [Σw(Fo2Fc2)2wFo4]1/2.

FormulaC10H8Cl3CrN2OC10H8Cl2CrN2O2
M330.53311.08
Crystal systemmonoclinictriclinic
Space group (no.)P21/n (14)Pequation image (2)
a8.479(10)7.696(2)
b15.173(16)8.749(2)
c9.968(13)9.460(2)
α9067.268(9)
β102.86(4)86.710(14)
γ9086.999(14)
U31250(3)586.2(3)
Z42
μ(Mo-Kα) /mm–11.5381.419
F(000)660312
Total number reflections63725534
Rint0.08290.0658
Unique reflections24222683
No. of params, restraints154, 0154, 0
R1, wR2 [I > 2σ(I)] b)0.089, 0.1220.056, 0.084
R1, wR2 (all data)0.122, 0.1980.104, 0.115

Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies of the data can be obtained free of charge on quoting the depository numbers CCDC-955800 http://www.ccdc.cam.ac.uk/data_request/cif and CCDC-955801 http://www.ccdc.cam.ac.uk/data_request/cif (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results
  5. Discussion
  6. Conclusions
  7. Experimental Section
  8. Acknowledgements

We thank Dr M. Webster for assistance with the X-ray data solution, and EPSRC for support (EP/1033394/1).