Effects of solvents and temperature on the luminescence properties of Cd-isonicotinic acid frameworks based on mono-, bi-, and trinuclear cluster units

In this work, we present the synthesis of three novel 3D Cd(II) coordination polymers, {[Cd(IN)(2)]center dot H2O}(n) (1), [Cd-2(IN)(2)(SO4)(DMF)(2)](n) (2) and {[Cd-3(IN)(5.5)]center dot 0.5OH(-)}(n) (3) (HIN = isonicotinic acid). Coordination polymers 1 and 2 were obtained via solvothermal reactions. The synthesis of coordination polymer 3 was realized by a simple temperature induced single crystal to single crystal transition from 1. Single-crystal X-ray diffraction analyses revealed that 1-3 exhibit three different structural types: 1 displays a (6,3)-connected rtl net with the Schlafli symbol (4.6(2))(2)(4(2).6(10).8(3)) constructed from mononuclear [CdO4N2] clusters with the help of HIN. 2 is defined as a 6-connected pcu net with the Schlafli symbol {4(12).6(3)} which is built from binuclear [Cd-2(SO2)(2)] clusters and HIN linkers. 3 can be regarded as a 9-connected ncd net with the Schlafli symbol {3(6).4(22).5(8)}, which consists of paddlewheel trinuclear [Cd-3(O2C)(5)] clusters and a bridging HIN. Coordination polymers 1-3 display luminescence with emission maxima containing deep blue, blue, light blue and green at 298 K or 77 K both in solvents (polarity: DMF > CH3OH > CH2Cl2) and in the solid state. The lifetime of all the molecules is in microsecond scale.