Transition Metal Chemistry of Quinuclidinone-Containing Ligands. III. Electronic and Structural Properties of Several Transition Metal Complexes Containing trans-2-(2\u27-Quinolyl)methylene-3-quinuclidinone

The complexes of the title ligand, Qnqn, with iron(II), cobalt(II), nickel(II), and copper(II) chloride and nickel(II) bromide have been prepared and characterized utilizing analytical, spectral, and magnetic techniques. In each case the compounds are found to be pseudotetrahedral in structure and to have M(Qnqn)X2 stoichiometry; the coordination sphere contains the two halide ions and the two Qnqn nitrogen donor atoms. Two isomeric complexes may be obtained with Qnqn and nickel(II) chloride. The yellow isomer is dimeric, [Ni(Qnqn)Cl2]2, with square-pyramidal coordination about the two nickel ions and the two bridging chloride ions between them. The violet isomer is pseudotetrahedral in structure. These two nickel isomers undergo a unique solid-state structural interconversion from the yellow isomer to the violet isomer at high temperature (ca. 230°) and from the violet isomer to the yellow isomer at low temperature (-78°)

The Transition-metal Chemistry of Quinuclidinone-containing Ligands. Part VI

A thermochemical determination of the relative solid-state stabilities of the yellow [Ni(qnqn)Cl22] and violet [Ni(qnqn)Cl2] isomers (where qnqn is trans-2-(2-quinolyl)methylenequinuclidin-3-one) has indicated that the violet isomer is the metastable isomer at room temperature. D.t.a.-t.g. measurements have been obtained for the iron, cobalt, nickel, and copper chloride and nickel bromide complexes of qnqn and reveal in the case of the nickel chloride isomers an endothermic structural transformation of the yellow dimer to the violet monomer at 230 °C. No related transformation is observed in the remaining complexes. The unusual inter-related thermal properties of the nickel chloride isomers are discussed in terms of the various properties of the two complexes