Neocuproine/nitrato complexes of Ni(II). Neutral and cationic species including salts with TCNQ: Preparation, chemical and spectroscopic properties and comparative structural chemistry

Abstract

The cationic complex [Ni(neoc)2(NO3)]+ with NO3− (1), TCNQ− (3), or (TCNQ-TCNQ)2− (4) as counterions, and the neutral complex [Ni(neoc)([NO3]−-κ1O)([NO3]−-κ2O,O´)(H2O)] (2) can be obtained from different reactions involving Ni(II), neoc, NO3− and TCNQ. The molecular and extended crystal structure of compound 2, which displays two different coordination modes for NO3−, are compared to those of the analogous Mn, Fe and Co compounds, revealing a correlation between the coordination geometry of the nominally monodentate nitrato ligand and the covalent radius of the central metal atom. Despite the differences in molecular geometry, the extended structures of the Ni (2) and Mn compounds are similar to each other but different from those of the Fe and Co complexes, which are similar to each other. Complex 1 was further used in the preparation of a new heterospin compound [Ni(neoc)2(NO3)](TCNQ) (3), having an ionic structure with the same complex cation present in 1, accompanied by centrosymmetric anion-radicals (ARs) TCNQ•−. Through a different preparation process, complex 4, with the formula [Ni(neoc)2(NO3)]2(TCNQ-TCNQ), containing the same complex cation as in complexes 1 and 3, but now with the centrosymmetric σ-dimerized dianion (TCNQ-TCNQ)2− has been obtained. The influence of NO3−, TCNQ•− and TCNQ-TCNQ2− anions on the crystal structure of the cation [Ni(neoc)2(NO3)]+ in the compounds has been studied. All of the complexes reported here have supramolecular structures governed by hydrogen bonding systems, adding to their stability.