Rare azido-bridged manganese(II) systems: Syntheses, crystal structures, and magnetic properties

Two new polymeric azido-bridged manganese complexes of formulas [Mn(N-3)(2)(bpee)], (1) and {[Mn(N-3)(dpyo)Cl(H2O)(2)](H2O)}(n), (2) [bpee, trans- 1 2 -bis(4-pyridyl) ethylene; dpyo, 4,4'-dipyridyl N,N'-dioxide] have been synthesized and characterized by single-crystal X-ray diffraction analysis and low-temperature magnetic study. Both the complexes 1 and 2 crystallize in the triclinic system, space group P $(1) over bar $, with a = 8.877(3) angstrom, b 11.036(3) angstrom, c = 11.584(4) angstrom, alpha = 72.62(2)degrees, beta = 71.06(2)degrees, gamma = 87.98(3)degrees, and Z = 1 and a = 7.060(3) angstrom, b 10.345(3) angstrom, c = 11.697(4) angstrom, alpha. = 106.86(2)degrees, beta = 113.33(2)degrees, gamma = 96.39(3)degrees, and Z = 2, respectively. Complex 1 exhibits a 2D structure of [-Mn(N-3)(2)-](n) chains, connected by bpee ligands, whose pyridine rings undergo pi-pi and C-H-...pi interactions. This facilitates the rare arrangement of doubly bridged azide ligands with one end-on and two end-to-end (EO-EE-EE) sequence. Complex 2 is a neutral 1D polymer built up by [Mn(N-3)(dpyo)Cl( H2O)(2)] units and lattice water molecules. The metals are connected by single EE azide ligands, which are arranged in a cis position to the Mn(l I) center. The 1 D zipped chains are linked by H-bonds involving lattice water molecules and show pi-pi stacking of dpyo pyridine rings to form a supramolecular 2D layered structure. The magnetic studies were performed in 2-300 K temperature range, and the data were fitted by considering an alternating chain of exchange interactions with S = 5/2 (considered as classical spin) with the spin Hamiltonians H = -J(j)Sigma(S3iS3i+1 + S3i+1S3i+2) - J(2)Sigma S3i-1S3i and H = -J(i)Sigma S2j+1 - J(2)Sigma S2i+1S2i+2 for complexes 1 and 2, respectively. Complex 2 exhibits small antiferromagnetic coupling between the metal centers, whereas 1 exhibits a new case of topological ferrimagnetism, which is very unusual.