Correlation of electron density and spin-exchange interaction in dimeric copper(II) formates, acetates and silanecarboxylates

Abstract

The structures of six dimeric copper(II) formates and acetates with picoline as an axial ligand, (I)-(VI), have been determined at room temperature and electron density distributions in lithium acetate dihydrate, (VII), and copper(II) formate diurea dihydrate, (VIII), have been studied at 120K. (VI) show no important geometrical differences in the Cu2(COO)4 cage between the copper acetates and formates. The observed deformation-density distributions in the CH3COO-(VII) and HCOO-(VIII) ions are in accord with theoretical expectations. Mulliken population analysis of eight carboxylate ions using STO-6G basis sets indicates that the electron population of the carboxylate group of the bridging ligand correlates with the -2J values of the binuclear copper(II) carboxylates. The key point that determines the strength of the spin-exchange interaction is the 2px orbital population of the carboxylate C atom (x is parallel to the C--R bond axis in the RCOO-ion). The electron population on a carboxylate O atom is shown to exhibit a roughly linear correlation with the pKa value of the parent carboxylic acid. The conundrum of why formate and fluoroacetate are exceptions to the correlation of -2J with pKa value has been solved in this paper.

The local structure of molecular reaction intermediates at surfaces

“…This final structural conclusion, of course, means that the geometry of the formate-Cu surface bonding on both (100) and (110) surfaces that is actually very similar to that found in coordination chemistry, and is not some new type of bonding. Specifically, both the local metal-formate geometry and the associated Cu-O bondlengths are closely similar to those found in several copper formate complexes [19,20,21,22]. This re-interpretation of the adsorption geometry of formate on Cu(100) has also been supported by the results of cluster calculations [23].…”

Synthesis, structure, and urease inhibitory activities of three binuclear copper(II) complexes with protocatechuic acid derivative

“…There are two copper ions in each complex, linked by four (for 1 and 2) or three (for 3) bridging bidentate L 1 . The carboxylate bridged Cu…Cu distances of 1-3 are 2.6377(4), 2.5789(10), and 2.9069 (6) Å, respectively, comparable to those reported in similar binuclear carboxylate copper complexes[29][30][31][32]. 3.1.1.…”

Dimeric nickel(II) carboxylates and a silanecarboxylate: [Ni(Me3CCOO)2(2,5-lutidine)]2, [Ni(MePh2CCOO)2(quinoline)]2.2CHCl3, [Ni(Me2PhCCOO)2(quinoline)]2, [Ni(Me3CCOO)2(2-ethylpyridine)]2, [Ni(Me3CCOO)2(2-picoline)]2 and [Ni(MePh2SiCOO)2(Ph3P)]2

“…Dimeric Cu n carboxylates show antiferromagnetism as a result of spin superexchange between the two metal centers through the carboxylate bridges; the magnitude of the spin-exchange interaction depends on the electric structure of the carboxylate bridges (Yamanaka et al, 1991). The cryomagnetic behavior of the Ni II dimers resembles that of the corresponding Cu r~ dimers (Bencini, Benelli, Gatteschi & Zanchini, 1980;Hirashima et al, 1990) although the nature of the demagnetization has yet to be clarified.…”