Syntheses, structures and properties of nickel(II) and manganese(II) coordination polymers based on V-shaped bis-imidazole and aromatic carboxylate ligands

Abstract

Using V-shaped mixed ligands bis-imidazole and aromatic carboxylic acids, five new coordination polymers namely, {[Ni(B-im)(Br-a)Cl]·H2O}n (1), {[Ni(B-im)(I-a)(H2O)2]·0.5H2O}n (2), [Ni(B-im)(I-a)(H2O)2]n (3), [Ni(B-im)(M-a)(H2O)2]n (4) and {[Mn2(B-im)2(I-a)2]·2H2O}n (5) [B-im=1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole), Br-a=5-bromonicotinic acid, I-a=isophthalic acid and M-a=5-methylisophthalic acid] were solvothermally synthesized and fully characterized by IR spectra, element analyses, X-ray powder and single-crystal diffractions, and thermogravimetric analyses. Complexes 1 and 2 feature polymeric macrocyclic chain structures containing interesting nanotubular channels, which are constructed by bridging 30-membered macrocyclic [Ni3(B-im)3] subunits with Br-a ligands and by bridging folded 20-membered macrocyclic [Ni2(B-im)2] subunits with I-a ligands, respectively. Isomorphic complexes 3 and 4 represent double-chain structures containing folded 18-membered macrocyclic [Ni2(B-im)(I-a)] subunits and [Ni2(B-im)(M-a)] subunits, respectively. Complex 5 is a 2D porous coordination polymer containing novel chiral four-stranded Mn(II) chains consisting of two (B-im)-bridged aspiral chiral chains and two (I-a)-bridged heterochiral coaxial 21-helical chains. The results of thermal gravimetric analyses suggest that the dehydrated frameworks of 1–5 are stable up to 320°C. Additionally, the magnetism of complexes 3 and 5 were also investigated.