Transition metal compounds of 1,2-bis(2-pyridyl)ethyne. Synthesis, spectroscopic characterization and X-ray structures of dinuclear [Cu 2(1,2-bis(2-pyridyl)ethyne) 3(NO 3) 4] and polynuclear [Co(1,2-bis(2-pyridyl)ethyne)(NO 3) 2] n

Abstract

Five new compounds of the ligand 1,2-bis(2-pyridyl)ethyne ( 1), viz. [M(1,2-bis(2-pyridyl)ethyne)(NO 3) 2)] n (M = Co, Ni, Cu), [Zn(1,2-bis(2-pyridyl)ethyne)Cl 2] n and [Cu 2(1,2-bis(2-pyridyl)ethyne) 3(NO 3) 4] are described. The first four compounds, prepared from the ligand and the metal salts in ethanol, acetone or tetrahydrofuran (thf) are infinite chain compounds in the solid state, with the ligand serving to bridge the metal centers solely through the pyridine nitrogen atoms. A crystal structure of [Co(1,2-bis(2-pyridyl)-ethyne)(NO 3) 2)] n , space group Pbc2 1 shows that the coordination polymers are linear and parallel to the b-axis. The donor nitrogen atoms are coordinated to the cobalt ion in a cis arrangement with CoN distances of 2.073(6) and 2.076(6) Å. Each cobalt is further coordinated by two nitrate ions in an asymmetric chelating fashion with short cobalt to oxygen distances of 2.020(10) and 2.011(9) Å and two longer contacts at 2.473(13) and 2.458(12) Å. Reaction of ligand 1 with Cu(NO 3) 2 in ethanol gave a complex in which, in the solid state, two molecules of the ligand act in a monodentate manner toward copper, and a single ligand acts as a didentate ligand. The compound [Cu 2(bis(2-pyridyl)acetylene) 3(NO 3) 4] crystallizes in the P-1 space group. The Cu(II) ions within the dinuclear molecule are at a distance of 6.909(8) Å, while the Cu(II)Cu(II) distance in neighboring molecules is 6.845(8) Å. Each copper ion is coordinated by two pyridyl nitrogens, each at a distance of 1.995(3) Å, in a trans fashion, by two nitrate ions in an asymmetric chelating fashion with the short Cu(II) to oxygen distances of 2.001(3) and 2.002(3) Å, and by two additional nitrate oxygens at 2.560(4) and 2.448(4) Å, completing a distorted octahedron. Substantial differences in the IR spectra of the nitrate complexes between samples prepared in KBr and fluorinated mineral oil (KelF) can be explained in terms of displacement of part of the nitrate ions by bromide under moderate pressure, a phenomenon observed earlier by some of us in complexes of substituted pyrazoles.