1ST STRUCTURALLY CHARACTERIZED LINKAGE ISOMERS OF 2 THIOCYANATOCOPPER(II) COMPLEXES

Two linkage isomers of [Cu(aat)2(NCS)2] (aat = 3-acetylamino-1,2,4-triazole), one with S- and one with N-bonded thiocyanate, have been prepared and characterized by spectroscopy and X-ray crystallography. These compounds are the first structurally characterized linkage isomers of a copper(II) thiocyanate complex. In both cases the copper atoms exhibit an elongated octahedral geometry with two axial thiocyanates and, in equatorial positions, two chelating aat ligands. The N-bonded isomer presents one of the smallest Cu-N-C angles [118.1 (2)-degrees] ever reported for thiocyanates and a quite long Cu-N (NCS) distance [2.521(3) angstrom]. In the S-bonded isomer the Cu-S(NCS) distance is 2.864(2) angstrom. As both compounds can be obtained from the same batch, packing differences must account for the isolation of the two different isomers. The different intermolecular hydrogen bonding between the ligands and anions exhibited by both crystal lattices is compared. 'Ab-initio' molecular orbital calculations have also been performed to study the theoretical stabilities of the isomers.