Isothiocyanate copper(II) tetraaza-iminooxime macrocyclic complex: An example of linkage isomerism. Part I - Synthesis, infrared spectroscopy and crystal structure

The isothiocyanate complex [Cu(DOHPN)(NCS)] (DOHPN = 3,3'-trimethylenedinit rilobis(2-butanone oxime)) has been prepared and characterized by infrared spectroscopy and X-ray crystallography as the isomer of the thiocyanate com plex whose crystal structure is found in the literature. The formula unit o f the title compound, is [Cu(DOHPN)(NCS)](2)[Cu(DOHPN)(H2O)](ClO4) correspo nding to C35H59ClCu3N14O11S2. The crystal is triclinic, space group P-1, Z = 2, and has the following lattice constants: a = 7.460(1) Angstrom, b = 11 ,541(2) Angstrom, c = 29.149(6) Angstrom, alpha = 97.44(3)degrees, beta = 9 1.32(3)degrees, gamma = 96.68(3)degrees. In each of the three complexes whi ch compose the formula unit, the copper(II) lies in a square pyramidal envi ronment made of an axial ligand and four nitrogen atoms of the tetraaza lig and. The stronger the interaction between copper(II) and the axial ligand, the m ore the DOHPN bends resulting in a "butterfly-like" geometry. Formation of the thiocyanate isomer is kinetically favored over the thermodynamically mo re stable isothiocyanate isomer. This system is one of the very few example s of structurally characterized copper(II) thiocyanate-isothiocyanate linka ge isomers. Its study should contribute to understanding of the isomerizati on phenomena.