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

Abstract

In this work, we present the synthesis of three novel 3D Cd(II) coordination polymers, {[Cd(IN)₂]·H₂O}_n (1), [Cd₂(IN)₂(SO₄)(DMF)₂]_n (2) and {[Cd₃(IN)_5.5]·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 Schläfli symbol (4·6²)₂ (4²·6¹⁰·8³) constructed from mononuclear [CdO₄N₂] clusters with the help of HIN. 2 is defined as a 6-connected pcu net with the Schläfli symbol {4¹²·6³} which is built from binuclear [Cd₂(SO₂)₂] clusters and HIN linkers. 3 can be regarded as a 9-connected ncd net with the Schläfli symbol {3⁶·4²²·5⁸}, which consists of paddlewheel trinuclear [Cd₃(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.