Odd and Even Numbered Ferric Wheels

Abstract The structurally related odd and even numbered wheels [FeIII 11ZnII 4(tea)10(teaH)1(OMe)Cl8] (1) and [FeIII 12ZnII 4(tea)12Cl8] (2) can be synthesized under ambient conditions by reacting FeIII and ZnII salts with triethanolamine (teaH3), the change in nuclearity being dictated by the solvents employed. An antiferromagnetic exchange between nearest neighbors, J = ‐10.0 cm−1 for 1 and J = −12.0 cm−1 for 2, leads to a frustrated S = 1/2 ground state in the former and an S = 0 ground state in the latter.


Single crystal X-ray crystallography
Diffraction data for compound 1 were collected on a Bruker APEX-II CCD diffractometer.The crystals were kept at a steady temperature of T = 100.4K throughout data collection using an Oxford Cryosystems Cryostream.The dataset was truncated at 1 Å due to rapidly rising values of Rint at higher resolution.[3] Diffraction data for compound 2 were collected on a Rigaku Oxford Diffraction Xcalibur diffractometer.The crystals were kept at a steady temperature of T = 120.0K throughout data collection using an Oxford Cryosystems Cryostream.[3] CCDC 2202758-2202759.

Powder X-ray diffraction
Diffraction data for compounds 1 and 2 were collected on polycrystalline powders using a Bruker D8 ADVANCE with Cu radiation at 40 kV, 40 mA and a Johansson monochromator, 2 mm divergence slit and 2.5 degree Soller slits on the incident beam side, LynxEye detector and Bruker DIFFRAC software.Diffraction data were measured from 2θ = 5° -40°; step size, 0.0101°.Freshly prepared crystalline powders of the samples were loaded into borosilicate capillaries with a 0.7 mm inside diameter and measured while spinning.

Magnetometry
Magnetic susceptibility data were collected on freshly prepared polycrystalline powders on a Quantum Design Dynacool PPMS equipped with a 9 T magnet in the temperature range 2 -300 K.The samples were added in Quantum Design VSM Powder Sample Holders (P125E) with eicosane present and then transferred to PPMS brass half-tube sample holders.Diamagnetic corrections from the holders and eicosane were applied.In addition, diamagnetic corrections were applied to the observed paramagnetic susceptibilities using Pascal's constants.
Low-temperature, high field magnetisation data were measured by the use of a conventional inductive probe in pulsed magnetic fields, where the temperature reached as low as 0.4 K.The maximum field reached was 32.5 T.
Polycrystalline samples with a typical mass of 10 mg were mounted in a capillary tube made of polyimide.The sample, which was not fixed within the sample tube, was aligned along the magnetic field direction.
Magnetisation curves were found to be identical after we applied the magnetic field several times due to the saturation of the orientation effect.

Heat Capacity
Heat capacity measurements were carried out using a Quantum Design PPMS in the temperature range 2 -50 K.
The polycrystalline samples were in the form of a thin pressed pellet (ca. 1 mg), thermalized by ca.0.2 mg of Apiezon N grease, whose contribution was subtracted by using a phenomenological expression.

Computational Details
We have used Density Functional Theory (DFT) in the Gaussian 09 suite [4] to compute the magnetic exchange coupling constants (J) for 1-2 on tri-and tetrametallic model complexes created from the crystal structures of 1 and 2. These are models 1M1-1M5 for 1 and models 2M1-2M2 for 2 (Figures S9-10).Models 1M1-1M4 and 2M1-2M2 are trimetallic models with terminal Ga III ions employed to maintain the same electronic environment.In model 1M5, four Fe III centres and two terminal Ga III ions are used.Noodleman's broken symmetry approach, [5] a reliable tool for estimating magnetic exchange coupling, has been employed to estimate the magnetic exchange interactions.For the trimetallic models (1M1-1M4 and 2M1-2M2) we have computed one high spin configuration with all three Fe III spins aligned parallel (S = 15/2) and three broken symmetry configurations with one of the Fe III spins aligned antiparallel to other two (S = 5/2).For 1M5 we have computed one high spin configuration with all four Fe III spins aligned parallel (S = 10), two broken symmetry configurations with one of the Fe III spins aligned antiparallel (S = 5), and three broken symmetry configurations with two of the Fe III spins aligned anti-parallel (S = 0).All spin configurations are summarised in Tables S7-S8.The errors associated with all the estimated magnetic exchange values are found to be less than 0.1%.We have employed the hybrid B3LYP functional [6] with the TZV basis set for Fe, the SVP basis set for Ga, Zn, O, N and the SV basis set for Cl, C and H. [7] Table S1

Figure S1 .
Figure S1.Powder X-ray diffraction pattern of 1. Experimental (red), predicted (grey).Crystals are stable outside the mother liquor and in vacuo.

Figure S2 .
Figure S2.Alternative views of the molecular structure of complex 1 in (a) ball and stick and (b) polyhedral formats.(c) The metal-oxygen magnetic core.(d) The metallic skeleton highlighting the non-planar arrangement of Fe III ions.Colour code: Fe = green, Zn = pale blue, O = red, N = blue, C = grey, Cl = yellow.H atoms omitted.The highlighted section in a) shows the Fe6-Fe7 unit containing the µ-OMe ligand and the non-bonded arm of the teaH ligand.

Figure S6 .
Figure S6.Alternative views of the molecular structure of complex 2 in (a) ball and stick, and (b) polyhedral formats.(c) The metal-oxygen magnetic core.(d) The metallic skeleton highlighting the bowl-or U-shaped arrangement of Fe III ions.Colour code: Fe = green, Zn = pale blue, O = red, N = blue, C = grey, Cl = yellow.H atoms omitted.

Figure S7 .Figure S8 .Figure S9 .
Figure S7.The packing of 2 in the extended structure as viewed down the a-, b-and c-axis, respectively.The clusters are shown in polyhedral format.Colour code: Fe = green, Zn = pale blue, O = red, N = blue, C = grey.H atoms omitted.d) Microscope image of the crystals of 2.

Figure S10 .
Figure S10.The model complexes 2M1-2M2 (dashed green circles) employed to calculate the magnetic exchange interactions in 2 (lower left).Colour Code: Fe, dark-green; Ga, black; Zn, cyan; Cl, yellow; O, red; N, blue; C, grey.H atoms omitted for clarity.The terminal Fe III centres in all model complexes have been replaced with Ga III ions in order to keep the electronic environment around the Fe III centres the same as in 2.

Figure S11 .
Figure S11.The metal-oxygen core of 1 with the tabulated JDFT values calculated for each bridge labelled.Colour Code: Fe, green; Zn, cyan; Cl, yellow; O, red; N, blue; C, grey.H atoms omitted for clarity.

Figure S12 .
Figure S12.The metal-oxygen core of 2 with the tabulated JDFT values calculated for each bridge labelled.Colour Code: Fe, green; Zn, cyan; Cl, yellow; O, red; N, blue; C, grey.H atoms omitted for clarity.

Figure S13 .
Figure S13.DFT computed spin density plots for models 1M1-1M5 indicating a strong spin-delocalization mechanism for the magnetic exchange.The isodensity surface for all the spin density plots are corresponding to 0.005 e bohr -3 .

Figure S14 .
Figure S14.DFT computed spin density plots for models 2M1-2M2 indicating a strong spin-delocalization mechanism for the magnetic exchange.The isodensity surface for all the spin density plots are corresponding to 0.005 e bohr -3 .

Table S2 .
Bond valence sum calculations for the metal ions in 1 and 2.