High-dimensional manganese(II) compounds with noncovalent and/or covalent bonds derived from flexible ligands: Self-assembly and structural transformation

A hydrogen- and covalent-bonded 3D array, [Mn(bpe)(H2O)(4)](n)(ClO4)(2n)(bpe)(4n)(H2O)(2n) (2) [bpe = 1,2-bis(4-pyridyl)ethane], a covalent-bonded 3D network, [Mn(bpe)(1.5)(H2O)(tp)](n)(H2O), (3) [tp = terephthalate], and a covalent-bonded 2D sheet, [Mn(bpe)(N-3)(2)](n) (4), have been synthesized and characterized by spectroscopic data and single-crystal X-ray diffraction studies. Complex 2 contains two types of packing bpe molecules: One type of bpe molecules (=N31-bpe and symmetry-related bpe) run along the chain direction, and the other type of bpe molecules (=N11-bpe and N21-bpe) are slanted to the chain linked by bridging bpe (=N1-bpe). The chain is coupled with hydrogen bonds via N31-bpe, while hydrogen bonds through packing bpe molecules of N11- and N21-bpe sew the chains, leading to a 3D interlocking network structure. The bpe ligands in 3 have an anti conformation for the bridging bpe and a gauche conformation for the capping bpe with a dihedral angle between the two pyridyl rings of 44.5 degrees. The tp ligand acts as a linker of three metal ions through the unidentate and bridging modes, leading to the formation of a 2D layer. The final molecular dimensionality in 3 is determined from adding bpe ligands to the 2D sheet connected by tp ligands, resulting in a covalent-bonded 3D array where the bridging bpe ligands link the tp-bridged layers. The manganese(II) center in 4 consists of four equatorial azido nitrogen atoms and two axial bpe nitrogen atoms. The one-dimensional chains formed by two azido bridging ligands are interconnected by bpe ligands, each of which has two pyridyl rings with a dihedral angle of 67 degrees, leading to a two-dimensional sheet. Variable-temperature magnetic susceptibility data of 2 and 4 have been fitted to the infinite-chain model (H = -J Sigma S-Ai.SAi+1) derived by Fisher under the molecular field approximation (J '). Obtained exchange parameters are J = -0.083 cm(-1), g = 2.0 for 2 and J = -12.5 cm(-1), g = 2.0, J' = 1.3 cm(-1) for 4. In the case of 3, the magnetic nature was interpreted by the dimer model (H = -JS(1).S-2), affording parameters J = -0.96 cm(-1), g 1.99, J' = -0.005 cm(-1). MO calculations on a hypothetical dimeric unit (NH3)(5)Mn-bpe-Mn(NH3)(5) are discussed to evaluate the magnetic nature for the bpe-bridged system 4.