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

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]- -kappa 1O)([NO3]- -kappa 2O,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 center dot- . 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 sigma-dimerized dianion (TCNQ-TCNQ)2- has been obtained. The influence of NO3- , TCNQ center dot- 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.

Automated summary

This study presents a series of complexes with the cation [Ni(neoc)2(NO3)]+ and different counterions, including NO3-, TCNQ-, and (TCNQ-TCNQ)2-. By comparing the crystal structures of these complexes with analogous Mn, Fe, and Co compounds, a correlation between the coordination geometry of the nitrato ligand and the covalent radius of the central metal atom is revealed. The influence of different counterions on the crystal structure of the cation [Ni(neoc)2(NO3)]+ is also studied, showing that all complexes have supramolecular structures governed by hydrogen bonding systems, enhancing their stability.