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

Article abstract of DOI:10.1016/j.poly.2016.05.019

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.