Anisotropic exchange in transition-metal dinuclear complexes. 2. Crystal and molecular structure and EPR spectra of a dinuclear copper oxamidato complex

The compound (~-N,N'-bis(6-ethyl-3,6-diazaoctyl)oxamidato(2-)-~1,N3,N6,0:N",N3',N6',~~dicopper(bIIis)( tetraphenylborate)- 2-acetone, CU~L(BP~~)~.~(CH,w),aCs sOyn, thesized and its crystal structure solved at room temperature. It crystallizes in the monoclinic system, space group P2,/n,w ith 2 = 2. The lattice constants are a = 16.639 (7) h;, 6 = 18.305 (9) A, c = 11.089 (9) A, and p = 103.2 (2)'. Least-squares refinement of the structure led to a conventional R factor of 0.055. The structure consists of centrosymmetric dinuclear species Cu2L+, tetraphenylborate anions, and acetone solvent molecules. The single-crystal EPR spectra reveal that the zero-field splitting tensor is dominated by the magnetic dipolar contribution, although substantial magnetic exchange is operative between the two x2 - y2 ground magnetic orbitals. The small exchange contribution to the zero-field splitting is related to the exchange pathway between a ground x2 - y2 and an excited xy magnetic orbital, which is rather ineffective in the present case.