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

A novel series of dinuclear copper(II) pyrazolenophanes of the formula [Cu-2(mu-4-Mepz)(2)(mu-ClO4)(ClO4)(bpm)(2)] (1), [Cu-2(mu-pz)(2)(mu-H2O)(ClO4)(4,7-Me(2)phen)(2)]ClO4 center dot H2O center dot CH3CN (2), [Cu-2(mu-pz)(2)(mu-H2O)(ClO4)(3/2)(H2O)(1/2)(phen)(2)](2)[Cu-2(mu-pz)(2)(mu-ClO4)(ClO4)(2)(phen)(2)]center dot 8H(2)O (3), and [Cu-2(mu-pz)(2)(CH3CN)(2)(3,4,7,8-Me(4)phen)(2)](ClO4)(2) (4) (Hpz = pyrazole, H-4-Mepz = 4-methylpyrazole, bpm = 2,2'-bipyrimidine, phen = 1,10-phenanthroline, 4,7-Me(2)phen = 4,7-dimethyl-1,10-phenanthroline, and 3,4,7,8-Me(4)phen = 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-Me(2)phen (2), phen (3), and 3,4,7,8-Me(4)phen (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) angstrom (3)], bis(pyrazolate)(aqua) [r = 3.383(1) (2) and 3.357(1) angstrom (3)], and bis(pyrazolate) bridges [r = 3.098(1) angstrom (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 = -JS(1).S-2 with S-1 = S-2 = S-Cu = 1/2).