Self-assembly, binding ability and magnetic properties of dicopper(ii) pyrazolenophanes

Abstract

A novel series of dinuclear copper(II) pyrazolenophanes of the formula [Cu₂(μ-4-Mepz)₂(μ-ClO₄)(ClO₄)(bpm)₂] (1), [Cu₂(μ-pz)₂(μ-H₂O)(ClO₄)(4,7-Me₂phen)₂]ClO₄·H₂O·CH₃CN (2), [Cu₂(μ-pz)₂(μ-H₂O)(ClO₄)_3/2(H₂O)_1/2(phen)₂]₂[Cu₂(μ-pz)₂(μ-ClO₄)(ClO₄)₂(phen)₂]·8H₂O (3), and [Cu₂(μ-pz)₂(CH₃CN)₂(3,4,7,8-Me₄phen)₂](ClO₄)₂ (4) (Hpz = pyrazole, H-4-Mepz = 4-methylpyrazole, bpm = 2,2'-bipyrimidine, phen = 1,10-phenanthroline, 4,7-Me₂phen = 4,7-dimethyl-1,10-phenanthroline, and 3,4,7,8-Me₄phen = 3,4,7,8-tetramethyl-1,10-phenanthroline) have been synthesized and magneto-structurally investigated. The crystal structures of 1–4 contain bis(pyrazolate)(perchlorate)- (1 and 3), bis(pyrazolate)(aqua)- (2 and 3), or bis(pyrazolate)-bridged (4) dicopper(II) entities of the metallacyclophane-type with bpm (1), 4,7-Me₂phen (2), phen (3), and 3,4,7,8-Me₄phen (4) as blocking bidentate ligands. All of them exhibit a saddle conformation with an overall not planar but bent, six-membered Cu–(N–N′)₂–Cu metallacyclic core with relatively short intermetallic distances across the bis(pyrazolate)(perchlorate) [r = 3.3076(5) (1) and 3.382(1) Å (3)], bis(pyrazolate)(aqua) [r = 3.383(1) (2) and 3.357(1) Å (3)], and bis(pyrazolate) bridges [r = 3.098(1) Å (4)]. The analyses of the variable-temperature magnetic susceptibility of 1–4 reveal the occurrence of a moderately strong antiferromagnetic coupling across the bis(pyrazolate)(perchlorate) [−J = 228 (1) and 193 cm⁻¹ (3)], bis(pyrazolate)(aqua) [−J = 189 (2) and 221 cm⁻¹ (3)], and bis(pyrazolate) bridges [−J = 197 cm⁻¹ (4)] (the spin Hamiltonian being defined as H = −JS₁·S₂ with S₁ = S₂ = S_Cu = ½).