Ligand Substitution Induced Single-Crystal-to-Single-Crystal Transformations in Two Ni(II) Coordination Compounds Displaying Consequential Changes in the Proton Conductivity
The discrete mononuclear [Ni(H2L)(bpyBr)2]•2H2O (1) and one-dimensional [Ni2(H2L)2(bpyBr)2(H2O)3]n (2) coordination compounds were obtained and characterized (H4L = 5,5’-(butane-1,4-diylbis(oxy)) diisophthalic acid; bpyBr = 4,4’-dibromo -2,2’-bipyridyl). The two compounds can SC-SC transform to each other, stimulated by excess H4L or bpyBr, involves coordination bonds cleavage and formation, which is a very rare case and should be defined as SN2 nucleophilic ligand substitution reaction of coordination compounds. Additionally, the proton conductivities of the Nafion membrane doped by compounds 1 and 2 have been studied. Compounds 1 and 2 can enhance the proton conductivity of the composite membrane about 51.80% and 20.94% higher than that of pure Nafion. It is speculated that the high proton density offered by the uncoordinated protonated carboxylate groups may endow the good conductivies of the two compounds. And the better hydrophility and stronger acidity of compound 1 deduced from the structure analyses and verified by the water uptakes tests and IR spectra lead to its higher conductivity.