Linear correlations with positive slopes have been found for the zero-field splitting parameters (D) and the anisotropic exchange parameters (D ex) vs the singlet-triplet separations (-2J) for [Cu 2(O 2CR) 4(L) 2] (R = F 3C, FCH 2 Cl 3C, ClCH 2, CH 3, H, and C 6H 5CO) for a wide range of -2J values, ca. 240-650 cm -1. The values of D and D ex for benzoylformate were found to be the highest ever studied. The quality of the linear relations of -2J, D ex and D with the square of the coefficient of 2p x(C) of the symmetric HOMO of the bridging carboxylate ions, coeff, 2 were found to be in the order, -2J vs coeff 2 > D ex vs coeff 2 > D vs coeff 2. A roughly linear relationship with a negative slope was found for D vs -2J for a system, [Cu 2(O 2CCMe nPh 3-n) 4 (L) 2], in which the -2J values cover a relatively small range, ca. 320-370 cm -1.
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