Rare Azido-Bridged Manganese(II) Systems:  Syntheses, Crystal Structures, and Magnetic Properties

Two new polymeric azido-bridged manganese complexes of formulas [Mn(N3)2(bpee)] n (1) and {[Mn(N3)(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 P1̄, with a = 8.877(3) Å, b = 11.036(3) Å, c = 11.584(4) Å, α = 72.62(2)°, β = 71.06(2)°, γ = 87.98(3)°, and Z = 1 and a = 7.060(3) Å, b = 10.345(3) Å, c = 11.697(4) Å, α = 106.86(2)°, β = 113.33(2)°, γ = 96.39(3)°, and Z = 2, respectively. Complex 1 exhibits a 2D structure of [−Mn(N3)2−] n chains, connected by bpee ligands, whose pyridine rings undergo π−π and C−H···π 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(N3)(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(II) center. The 1D zipped chains are linked by H-bonds involving lattice water molecules and show π−π 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 i Σ(S 3 i S 3 i +1 + S 3 i +1 S 3 i +2) − J 2ΣS 3 i - 1 S 3 i and H = −J i ΣS 2 i S 2 i +1 − J 2ΣS 2 i +1 S 2 i +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.