Syntheses, crystal structures and magnetic properties of complexes based on [Ni(L-L)3]2+ complex cations with dimethylderivatives of 2,2′-bipyridine and TCNQ

Abstract

From the aqueous-methanolic systems Ni(NO3)2 – LiTCNQ – 5,5′-dmbpy and Ni(NO3)2 – LiTCNQ – 4,4′-dmbpy three novel complexes [Ni(5,5′-dmbpy)3](TCNQ)2 (1), [Ni(4,4′-dmbpy)3](TCNQ)2 (2) and [Ni(4,4′-dmbpy)3]2(TCNQ-TCNQ)(TCNQ)2∙0.60H2O (3), were isolated in single crystal form. The new compounds were identified using chemical analyses and IR spectroscopy. Single crystal studies of all samples corroborated their compositions and have shown that their ionic structures contain the complex cations [Ni(5,5′-dmbpy)]2+ (1) or [Ni(4,4′-dmbpy)]2+ (2 and 3). The anionic parts of the respective crystal structures 1–3 are formed by TCNQ⋅- anion-radicals and in 3 also by a σ-dimerized dianion (TCNQ-TCNQ)2- with a C-C distance of 1.663(5) Å. The supramolecular structures are governed by weak hydrogen bonding interactions. The variable-temperature (2–300 K) magnetic studies of 1 and 3 confirmed the presence of magnetically active Ni(II) atoms with S = 1 and TCNQ⋅- anion-radicals with S = 1/2 while the (TCNQ-TCNQ)2- dianion is magnetically silent. The magnetic behavior was described by a complex magnetic model assuming strong antiferromagnetic interactions between some TCNQ⋅- anion-radicals.