Magnetic properties and crystal structures of bis(µ-pyrazolato)-bridged dicopper(II,II) complexes with 1,10-phenanthroline or 2,2′-bipyridine

Abstract

Novel bis(µ-pyrazolato)-bridged binuclear copper(II) complexes with 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy), Cu₂(NO₃)₂(L)₂(L′)₂·n(H₂O or MeOH), where L = pyrazolate (pz), 4-methylpyrazolate (4-Mepz), 4-chloropyrazolate (4-Clpz), or 4-bromopyrazolate (4-Brpz) anions and L′ = phen or bpy, were prepared and characterized by electronic spectra, magnetic susceptibilities and X-ray structure analyses. The crystal structures of [Cu₂(NO₃)(pz)₂(H₂O)(phen)₂]NO₃ 1, [Cu₂(NO₃)₂(pz)₂(phen)₂] 2, [Cu₂(NO₃)₂(4-Clpz)₂(phen)₂]·2MeOH 3·2MeOH, [Cu₂(NO₃)₂(4-Brpz)₂(phen)₂]·2MeOH 4·2MeOH, [Cu₂(4-Mepz)₂(H₂O)₂(bpy)₂][NO₃]₂ 5 and [Cu₂(4-Mepz)₂(H₂O)₂(phen)₂][NO₃]₂ 6 were determined by X-ray crystallography. All of the complexes consist of a discrete binuclear molecule with bis(µ-pyrazolato)-bridges. Complexes 1, 2, 3·2MeOH and 4·2MeOH have a distorted trigonal-bipyramidal configuration around each copper(II) ion. On the other hand, complexes 5 and 6 have a distorted square-bipyramidal geometry, and reside on a mirror plane so that one half of the molecule is crystallographically unique. The bending angles (δ_pz-bend) of the pyrazolato-bridges in 1–6, which represent dihedral angles of the least-squares plane of pz relative to the Cu–N(pz)–N(pz)–Cu plane, are in the 1.4–9.7° range. The angular structural parameters (τ) for 1–6, which are applicable to five-coordinate structures as an index of the degree of trigonality, are in the 0.10–0.76 range. The magnetic susceptibility data for 1–6 conform to the usual dimer equation with –2J values of 143–268 cm^–1, indicating the existence of an antiferromagnetic interaction. The strength of the antiferromagnetic interaction for 1–6 is correlated with δ_pz-bend and τ values. The τ value is a leading factor in determining the –2J value, and the bending angle (δ_pz-bend) plays an important supporting part.