Synthesis and magnetic study of μ1,1-azido-bridged dinuclear manganese(II) complexes based on tripyridyl ligands

Three azido-bridged Mn-II complexes of formulas [Mn-2(N-3)(4)(ttp)(2)] (1), [Mn-2(N-3)(4)(ttp-N-3)(2)] (2) and [Mn-2(N-3)(4)(ttp-N-3)(2)](3)[Mn-III(ttp-N-3)(N-3)(3)](2) (3), where ttp and ttp-N-3 represent 4'-p-tolyl-2,2':6',2"-terpyridine and 4'-p-azidomethylphenyl-2,2':6',2"-terpyridine, were synthesized and characterized by single-crystal X-ray diffraction analysis and magnetic studies. The Mn ions in complexes I and 2 are coordinated by three N atoms of the ttp or ttp-N-3 ligands, and they are connected by double end-on (EO) azide ligands; this forms a dinuclear Mn-II system with Mn-N-Mn bridging angles of 103.5 and 103.1 degrees. The Br atoms of the -CH2Br ligands were replaced by azido groups during the formation of complexes 2 and 3. The structure of complex 3 comprises two structurally similar Mn-II dimers with double end-on bridging azide groups and one mononuclear Mn-III structure. The bridging Mn-N-Mn angles in 3 are 104.2, 105.1, and 106.73 degrees. Magnetic studies indicate the presence of intramolecular ferromagnetic superexchange. The strength of ferromagnetic coupling within the Mn-2 cores in 1-3 is dependent on the Mn-N-Mn bridging angles. The magnetic coupling constants for intermolecular exchange are 2.46(4), 2.25(2), and 1.92(4) cm(-1) for 1, 2, and 3, respectively, on the basis of Hamiltonian (H) over cap = -2J (S) over cap (1)(S) over cap (2). ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).