Synthesis, structure, spectroscopy, and magnetism of unique propeller-typelinear trinuclear Cu-II complexes with in-situ prepared formamidine ligands

Three new copper(II) linear trinuclear compounds are reported, all of which were synthesized in-situ, with the general formula [Cu-3(L)(4)](CF3SO3)(2) (Y)(x), where L is the dehydronated ligand: N,N'-bis(pyridine-2-yl)formamid ine (abbreviated as Hpdf), N, N'-bis(pyrimidine-2-yl)form amidine (abbrevia ted as Hpmf) and N,N'-bis(5-methylpyridine-2-yl)formamidine (abbreviated as Hmpdf), Y = EtOH or H2O and x = 0.5-1.5. The compounds were characterized by X-ray diffraction, IR, LF, and EPR spectroscopy and by magnetic suscepti bility down to 4 K. The structure of the compound [Cu-3(pmf)(4)](CF3SO3](2) (H2O)(1/2) was determined by X-ray crystallography; it was found to crystal lise in the triclinic space group P-l with a: = 8.529(5), b = 15.760(5), c = 19.639(5) A, alpha = 101.793(5), beta = 101.263(5), gamma = 102.389(5)deg rees, Z = 2. The structure [Cu-Cu-Cu angle 174.96(11)degrees] consists of f our nearly Rat molecules of the ligand, which contribute to the propeller-t ype structure around the Cu-Cu-Cu axis. A strong antiferromagnetic interact ion between the Cu-II ions is observed with calculated J values, based on t he Hamiltonian H = -2J(S-1.S-2 + S-2.S-3)-2J'.S-1.S-3, of -174(1) cm(-1), - 120(1) cm(-1), and -167(1) cm(-1) for the compounds studied with L = pdf, p mf, and mpdf, respectively. These values are in agreement with an S = 1/2 g round state below temperatures of 120-160 K.