Structural Effect of Adding Paired and Unpaired Electrons to Otherwise Identical Transition Metal Systems
Relation between the magnetic and structural properties in iron(III) complexes
The crystal and molecular structures of the title complexes were solved by single-crystal x-ray diffraction using computer techniques. Crystal data: Cr(S2CNC4H8O)3·(C 6H6)2, C2/c, Z = 4, a = 19.314 (5) Å, b = 18.046 (4) Å, c = 12.307 (2) Å, β = 53.48 (2)°, U = 3448 Å3, R = 3.2%, 1674 reflections; Fe(S2CNC4H8O)3·(C 6H6)2, C2/c, Z = 4, a = 19.22 (1) Å, b = 17.916 (4) Å, c = 12.275 (4) Å, β = 53.41 (3)°, U = 3394 Å3, R = 4.7%, 3026 reflections; Co(S2CNC4H8O)3·(C 6H6)2, C2/c, Z = 4, a = 19.094 (3) Å, b = 17.874 (2) Å, c = 12.283 (2) Å, β = 53.15 (1)°, U = 3354 Å3, R = 3.6%, 2378 reflections; Rh(S2CNC4H8O)3·(C 6H6)2, C2/c, Z = 4, a = 19.327 (6) Å, b = 18.036 (5) Å, c = 12.286 (5) Å, β = 52.43 (6)°, U = 3395 Å3, R = 5.4%, 1875 reflections; Ir(S2CNC4H8O)3·(C 6H6)2, C2/c, Z = 4, a = 19.390 (9) Å, b = 18.108 (8) Å, c 12.256 (9) Å, β = 52.09 (5)°, U= 3395 Å3, R = 5.0%, 1961 reflections. The complex molecules are reasonably well separated from one another and from the solvating benzene molecules. In each case the metal atom and one ligand atom lie along a twofold axis. The average metal-ligand bond length, 〈M-L〉, increases as the number of unpaired d electrons increases, especially in the t2 subshell: 〈Co-S〉 = 2.273 (1) Å (t26), 〈Fe-S〉 = 2.317 (1) Å (mainly t25, some t23e2), 〈Cr-S〉 = 2.396 (3) Å (t23). 〈M-L〉 increases vertically downwards from the first to the second or third transition series: 2.273 (1) in 3d6, 2.365 (4) and 2.372 (3) Å in 4d6 and 5d6. The temperature dependence of the magnetic moment of the ferric complex differs dramatically from that of the analogous complex solvated by dichloromthane and that of the unsolvated complex, though each of the three forms exhibits a spin state equilibrium. This equilibrium is displaced towards the low and high spin sides in the C6H6 solvate and the unsolvated complexes, respectively. However, in the dichloromethane solvate, the equilibrium is between a new intermediate quartet (S = 3/2) state and the high spin (S = 5/2) state, and this difference in the magnetic properties is reflected in an 〈M-L〉 difference of more than 0.1 Å between the benzene and dichloromethane solvated complexes. An even greater 〈M-L〉 difference is therefore implied for a transition from pure low spin to pure high spin species. The M-L stretching frequencies are compatible with but inconclusive about a spin-state equilibrium in the iron complexes rather than a single mixed spin state.
R. J. Butcher and E. Sinn, "Structural Effect of Adding Paired and Unpaired Electrons to Otherwise Identical Transition Metal Systems," Journal of the American Chemical Society, American Chemical Society (ACS), Jan 1976.
The definitive version is available at http://dx.doi.org/10.1021/ja00425a010
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© 1976 American Chemical Society (ACS), All rights reserved.