Intermolecular Hydrogen Bonds of 5-Benzylidene-2,4-thiazolidinedione Derivatives and Related Compounds in Crystalline State

Abstract

Abstract From the viewpoint of noncentrosymmetric molecular arrangement design in crystalline state, which is indispensable to second order nonlinear optical materials, intermolecular hydrogen bond formation of eight 5-benzylidene-2,4-thiazolidinedione derivatives and related compounds were investigated by X-ray crystallography. 5-Benzylidene-2,4-thiazolidinedione (1) itself forms centrosymmetric head-to-head (or tail-to-tail) intermolecular hydrogen bonds and takes a centrosymmetric molecular arrangement in crystalline state. Introduction of 4-methoxy group into the phenyl moiety of 1 was the only useful means for head-to-tail type intermolecular hydrogen bond formation. 5-(4-Methoxybenzylidene)-2,4-thiazolidinedione shows head-to-tail type intermolecular hydrogen bonds and noncentrosymmetric molecular arrangement in crystalline state. Similarities in both hydrogen bond formation and molecular arrangement in crystalline state are obtained by conversion of 2,4-thiazolidinedione to 2-thioxo-4-oxazolidinone, but in the case of conversion to 2,4-oxazolidinedione only hydrogen bond formation is shown in a similar manner. In the case of conversion to rhodanine, no similarity in either hydrogen bond formation or molecular arrangement in crystalline state was shown. Such behaviors were considered from viewpoints of pKa and hydrogen bond energy.