New nickel(ii) thiocyanato coordination compounds: synthetic aspects, polymorphism, thermal reactivity and magnetic properties

Abstract

Reaction of Ni(NCS)₂ with bis(3-aminopropyl)amine (dpt) and pyridine (pyr) in water and molar ratios leads to the formation of the new polymorphic modifications [Ni(NCS)₂(dpt)(pyr)] (1a and 1b). Slight variation of the reaction conditions results in the formation of the new nickel(II) thiocyanato coordination compounds {[Ni(dpt)₂]²⁺·[(NCS)₂]²⁻} (2), {[Ni(SCN)₃(dpt)]⁻·[Ni(dpt)₂·(NCS)]⁺·H₂O} (3), {[Ni(μ-1,3-NCS)(dpt)(NCS)]₂·[Ni(NCS)₂(dpt)(H₂O)]₂·(H₂O)₄} (4) and [Ni(μ-1,3-NCS)(dpt)(NCS)]₂ (5). All compounds were structurally characterized and investigated for their thermal, spectroscopic and magnetic properties. The polymorphic modifications 1a and 1b were additionally investigated by solvent mediated conversion experiments and DSC measurements for their thermodynamic stability, which show that form 1a represents the thermodynamically most stable over the whole temperature range. Investigations on the thermal degradation behavior of compounds 1a–4 show that only for compounds 1a and 4 ligand-deficient intermediates can be found whereas for all other compounds only complete decomposition is observed. Compound 4 decomposes to the literature known ligand-deficient compound {[Ni(μ-1,3-NCS)(dpt)(NCS)]₂·[Ni(μ-1,3-NCS)(dpt)(NCS)]₄} (Refcode MUYRAZ), whereas the intermediate of compound 1a could not be structurally characterized. On the basis of IR and Raman spectroscopic investigations it could be shown that in the intermediate of 1a bridging anions could be found and a tetrameric structure can be assumed. Magnetic measurements of compounds 1a–4 reveal only Curie and Curie-Weiss paramagnetism.