Employing mixed-ligand strategy to construct a series of luminescent Cd(II) compounds with structural diversities

Eight new cadmium compounds, namely, {Cd-2(ox)(2)(bib)(1.5)}(n) (1), {Cd(mal)(bib)(0.5)}(n) (2), {Cd(fum)(bib)(H2O)}(n) (3), {Cd-2(suc)(bib)(NO3)(2)(H2O)}(n) (4), {Cd-2(glu)(2)(bib)}(n) (5), {Cd(adp)(bib)}(n) (6), {[Cd(sub)(bib)]center dot(H2O)(3)}(n) (7) and {[Cd(aze)(bib)(1.5)]center dot(H2O)(5)}(n) (8) (bib=1,4-bis(N-imidazolyl) butane, H(2)ox = oxalic acid, H(2)mal = malonic acid, H(2)fum = fumaric acid, H(2)suc = succinic acid, H(2)glu = glutaric acid, H(2)adp = adipic acid, H(2)sub = suberic acid, and H(2)aze = azelaic acid) were constructed from flexible bis(imidazole) ligands incorporating a variety of aliphatic dicarboxylic acids. They were characterized using elemental analysis, IR, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. Compound 1 exhibits a 3D self-penetrating framework with a novel {4(4).5(4).6(2).7(4).8}{5(3).6(2).7}(2) topology that can interestingly be regarded as a cross-link of two interpenetrating pcu networks. Compound 2 displays a six-connected self-penetrating pillared-layer framework with a roa topology. The structure of 3 is an unprecedented 2D -> 3D polycatenation based on a (4(2).6(4)) bilayer. If hydrogen bonding interactions are taken into account, the resulting structure displays a 3-fold interpenetrated 3D rob network. Compound 4 is comprised of 2D (4,4) networks, and the adjacent sheets are extended into a 3D interdigitated framework via hydrogen-bonding interactions. Compounds 5 and 6 are based upon 3D pillared-layer frameworks constructed from [Cd(glu)](n)/[Cd(adp)](n) layers and the bib pillars. Both 7 and 8 are 3D frameworks with the same dia topology except that the former shows an abnormal 4-fold [2 + 2] interpenetrating mode and the latter is a single dia network without interpenetration. A comparison of compounds 1-8 demonstrates that the structure diversities may be greatly induced by increasing the spacer lengths and coordination modes of aliphatic dicarboxylic acids. Moreover, the photoluminescent properties of 1-8 are also discussed.