Characterization and crystal structure of cadmium(II) halide complexes with amino acids and their derivatives VI. The comparison of crystal structures of cadmium(II) halide complexes with three kinds of piperidine carboxylic acids

Six cadmium(II) halide complexes with dl-piperidine-2-carboxylic acid (DL-Hpipe-2), dl-piperidine-3-carboxylic acid (DL-Hpipe-3), and piperidine-4-carboxylic acid (Hpipe-4), have been prepared and characterized by means of IR and Raman spectra and thermal analysis. The crystal structures of CdCl2(DL-Hpipe-2)(H2O)], CdBr2(DL-Hpipe-3)], and CdCl2(Hpipe-4)] have been determined by X-ray diffraction. These three complexes have one-dimensional polymer structures bridged by halide atoms. The crystal of CdCl2(DL-Hpipe-2)(H2O)] is orthorhombic with the space group Pca2(1). The cadmium atom is in an octahedral geometry, ligated by a carboxyl oxygen atom, two bridging chlorine atoms, a terminal chlorine atom, a water molecule and a carboxyl oxygen atom of a neighboring molecule. The carboxyl oxygen atoms of DL-Hpipe-2 are coordinated to two cadmium atoms. The unit cell consists of two types of one-dimensional polymer structures: CdCl2(D-Hpipe-2)(H2O)] and CdCl2(L-Hpipe-2)(H2O)]. Therefore, it is better to write CdCl2(DL-Hpipe-2)(H2O)] as CdCl2(D-Hpipe-2)(H2O)]CdCl2(L-Hpipe-2)(H2O)]. The crystal structure of CdBr2(DL-Hpipe-3)] is monoclinic with space group P2(1). The cadmium atom is in a distorted octahedral geometry ligated by two carboxyl oxygen atoms and four bridging bromine atoms. This complex consists of either D-Hpipe-3 or L-Hpipe-3. Therefore CdBr2(DL-Hpipe-3)] is written as CdBr2(D or L-Hpipe-3)]. The crystal of CdCl2(Hpipe-4)] is monoclinic with space group P2(1)/n. The structure is similar to that of CdBr2(D or L-Hpipe-3)].