A novel one-dimensional nickel(II) alternating chain from discrete pyrazolate-based dinuclear complexes

Abstract

Hexadentate dinucleating ligands that are based on a bridging pyrazolate bearing chelating side arms [3,5-(R₂NCH₂)₂C₃N₂H₂; R₂N = Me₂N(CH₂)₃NMe (HL¹), Me₂N(CH₂)₂NMe (HL²)] reacted with NiCl₂·6H₂O to yield complexes ClNi(µ-Cl)(µ-L¹)NiCl 1 (Ni₂L¹Cl₃) and ClNi(µ-Cl)(µ-L²)NiCl 2 (Ni₂L²Cl₃), respectively. Depending on the side-arm chain length and the solvent used for crystallisation these complexes either crystallised as dicrete bimetallic units (1) or were assembled via di-µ-chloro linkages to form a tetranuclear compound [ClNi(µ-Cl)(µ-L²)Ni(µ-Cl)₂Ni(µ-Cl)(µ-L²)NiCl] 2a ([Ni₂L²Cl₃]₂) or a novel bridge-alternating one-dimensional chain [Ni(µ-Cl)(µ-L¹)Ni(µ-Cl)₂]_∞ 2b ([Ni₂L²Cl₃]_∞) in the solid state. Variable-temperature magnetic susceptibility measurements revealed antiferromagnetic coupling within the basic µ-chloro-µ-pyrazolato bridged bimetallic framework in all cases and also suggested antiferromagnetic superexchange propagated by the di-µ-chloro linkage in 2b. The latter result is rationalised on the basis of the specific geometric findings for this di-µ-chloro linkage, in particular the unusually large Ni–Cl–Ni angle [101.37(4)°].