SYNTHESIS, STRUCTURE, AND PHYSICAL-PROPERTIES OF (MU-OXO)(MU-CARBOXYLATO)BIS((TRIS(2-PYRIDYLMETHYL)AMINE)CHROMIUM(III)) COMPLEXES

Three μ-oxo-μ-carboxylato-bridged complexes of the form [(tmpa)Cr(O)(RCO2)Cr(tmpa)]3+(R = H, CH3, C6H5; tmpa = tris(2-pyridylmethyl)amine) have been prepared and characterized through measurements of electronic and infrared spectra, ionization constants of conjugate hydroxy-bridged acids, magnetic susceptibility temperature dependences, and cyclic voltammograms. A perchlorate salt of the methyl derivative, [(tmpa)Cr(O)(CH3CO2)Cr(tmpa)](C1O4)3(Cr2Cl3O15N8C38H390.7H2O), crystallizes in the monoclinic system (space group P21/c (No. 14)), with a = 10.509 (5) Å, b = 21.040 (16) Å, c = 20.724 (7) Å, β = 98.46 (4°), and V = 4532 (4) Å3; Z = 4. The Cr-O-Cr core is characterized by nonequivalent Cr-O bond distances of 1.789 (9) and 1.853 (9) Å, a bond angle of 131.9° and trans influences toward Cr-N bonds of 0.054 and 0.034 Å, respectively. Linear correlations of free carboxylic acid pKavalues with both the pKa's of [(tmpa)Cr(OH)(RCO2)Cr(tmpa)]4+species and the antiferromagnetic coupling constants of [(tmpa)Cr(O)(RCO2)Cr(tmpa)]3+dimers demonstrate that enhanced Cr-O(carboxylate) bond strengths, linked to increasing RC02-nucleophilicity, occur at the expense of π-bonding within the CrOCr bridging unit. Electronic spectra and one-electron oxidation waves of the μ-oxo-μ-carboxylato dimers are consistent with expectations when a linear (D4h) CrOCr complex is bent to pseudo-C2vsymmetry with some retention of π-bonding. © 1990, American Chemical Society. All rights reserved.