Anisotropic exchange in transition-metal dinuclear complexes. 4. (.mu.-Benzotriazolato-N1,N3)bis[[tris(N1-methylbenzimidazol-2-ylmethyl)amine-N,N3,N3',N3'']copper(II)]trinitrate

Single-crystal EPR spectra of the title compound, [C~,(tmbma),(bta)](NO~h)a~v,e been recorded at room temperature at both X- and Q-band frequencies. The triplet spectra have been fit with parallel g and D tensors, whose principal values are g,, = 2.063 (l), gyy = 2.190 (2), g,, = 2.130 ( I ) , D,, = -45 (4). X lo4 cm-I, Dyy = 413 (3) X lo4 cm-I, and D, = -368 (5) X lo4 cm-'. The D values have been compared with those calculated for magnetic dipolar interactions between two S = spins centered on the two copper ions, which are 5.563 8, apart. The presence of a substantial exchange contribution to the zero-field splitting has thus been recognized, and a possible mechanism for justification is suggested.