Synthesis, X-ray crystal structure and spectroscopy of a Warner-type host Co(II) complex, trans-bisisothiocyanatotetrakis (trans-4-styrylpyridine)cobalt(II)

Single crystals of the title Co(II) complex, [Co(stpy)(4)(NCS)(2)] [stpy = trans-4-styrylpyridine] are prepared and characterized by elemental analysi s, IR, and UV-visible spectroscopy and X-ray crystal structure determinatio n. The complex crystallizes in the orthorhombic space group Pna2(1) with un it-cell parameters, a = 32.058(3), b = 15.362(5), c = 9.818(5) Angstrom, an d Z = 4. The structure consists of discrete monomeric units of [Co(stpy)(4) (NCS)(2)]. The equatorial positions of the Co(II) polyhedron are occupied b y nitrogen atoms of the four stpy ligands and the axial positions are occup ied by the nitrogen atoms of the two thiocyanate ions. The unit cell packin g reveals interpenetration of styryl groups owing to conformational flexibi lity of phenyl and pyridyl rings in stpy ligands. Thus, it leads to efficie nt packing of the crystal lattice leaving no space available for guest incl usion. IR spectra reveal nitrogen coordination from stpy and terminal -NCS coordination of the thiocyanate group. The optical reflectance bands 475, 5 40 (shoulder) and 1022 nm suggest octahedral geometry in accordance with th e X-ray data. However, the optical spectrum of acetonitrile solution shows an intense band at 615 nm and a weak shoulder at 570 nm suggesting particip ation of the solvent molecules in the coordination sphere. These bands indi cate the presence of both tetrahedral and octahedral species in solution. ( C) 2000 Elsevier Science B.V. All rights reserved.