Directed assembly and characterization of 1D polymers based on [MII(BMA)]2+ node (M = Cu, Mn, Ni and Zn; BMA = N,N-bis (benzimidazol-2-yl-methyl)amine) with linear bridging dicyanamide and terephthalate ligands

Abstract

The directed assembly of N,N-bis(benzimidazol-2-yl-methyl)amine (BMA) with Cu(II), Mn(II), Ni(II) and Zn(II) salts based on dicyanamide (mu(1,5)-dca) and terephthalate (mu-ta) linear bridging ligands, respectively, leads to four novel compounds: [Cu(BMA)(mu(1,5)-dca)(ClO(4))](n) (1), {[Mn(BMA)(mu(1,5)-dca)(CH(3)OH)] x ClO(4) x C(10)H(9)N(3)O x CH(3)OH}(n) (2), {[Ni(2)(BMA)(2)(mu-ta)(mu(1,5)-dca)] x ClO(4) x CH(3)OH x H(2)O}(n) (3), and {[Zn(2)(BMA)(2)(mu-ta)(mu(1,5)-dca)] x ClO(4) x CH(3)OH}(n) (4), which were characterized by single-crystal X-ray diffraction, elemental analysis, IR, fluorescence spectroscopy, and magnetic measurement. X-Ray analysis revealed that 1 and 2 are two infinite 1D coordination polymers, in which dca units serving as an end-to-end out-of-plane bridge bring about linear chains for 1 and zigzag chains for 2. Complexes 3 and 4 are similar, in which the metal atoms are bridged alternately by terephthalate and mu(1,5)-dicyanamide ligands into 1D zigzag chains. In all these complexes, each BMA ligand adopts a tridentate chelating mode to coordinate with a transition metal forming a [M(BMA)](2+) node. Different rigidity bridging ligands together with the stereochemistry and supramolecular effects of benzimidazol planes may result in the dramatic structural changes from 1D to multidimensional networks for all 1-4. Fluorescent measurements established that, in solution, complex 3 displays weak blue luminescence which originates from the BMA but is significantly red-shifted and has a much lower emission intensity, compared to the free BMA ligand. Complex 4 shows stronger luminescence than 3 and still reduces luminescence efficiency compared to the free BMA ligand. The variable-temperature magnetic susceptibility measurements (2-300 K) of 1 and 3 show the dominant weak ferromagnetic interactions between the copper(II) centers with J = 3.02 cm(-1), zJ' = -2.70 cm(-1) for 1, and the nickel(II) centers with J = 1.94 cm(-1), J'; = -0.38 cm(-1) for 3, while weak antiferromagnetic interactions between the Mn(II) centers for 2 with J = -0.27 cm(-1).