X-ray crystal structure and spectroscopy of a pseudo-square pyramidal Cu(II) complex, trans-dinitratotetrakis (trans-4-styrylpyridine)copper(II)

Single crystals of the title Cu(II) complex, [Cu(stpy)(4)(ONO2)(ONO2)'] [st py = trans-4-styrylpyridine] have been prepared and characterized by elemen tal and thermal analyses, IR, electronic and EPR spectral measurements, and X-ray crystal structure determination. The complex crystallizes in the mon oclinic space group P2(1)/c with unit-cell parameters, a = 12.985(2), b = 2 2.865(8), c = 17.024(10) Angstrom, beta = 112.29(3)degrees, and Z = 4. The structure consists of discrete monomeric units of [Cu(stpy)(4)(ONO2)(ONO2)' ]. The equatorial positions of the Cu(II) polyhedron are occupied by nitrog en atoms of the four stpy ligands and the axial positions by the oxygens of two unidentate nitrate anions. One of these oxygens is at rather longer di stance [2.609(3) Angstrom] and may be considered to be semicoordinated. If this semibond is ignored, the coordination geometry lies closer to an ideal ized square pyramid than to the trigonal bipyramid geometry. IR spectra rev eal nitrogen coordination from stpy and asymmetry in the monodentate oxygen binding of the two nitrate ligands. The optical reflectance band at 600 nm suggests pseudo-square-based pyramidal geometry around Cu(II). Well-resolv ed Cu(II) hyperfine features in the EPR spectra reveal the absence of excha nge interactions between adjacent copper centers. Optical and EPR spectra o f a methanolic solution of the complex indicate solvent interactions. Therm ogravimetric analysis shows the complex to be stable up to 175 degrees C.