Synthesis, crystal structures and thermal behaviour of organic–inorganic hybrids incorporating a chiral diamine

A series of noncentrosymmetric metal sulfates [R-C5H14N2][MII(H2O)6](SO4)2 and [S-C5H14N2][MII(H2O)6](SO4)2 (MII = Mn (1, 2), Fe (3, 4), Co (5, 6) and Ni (7, 8)) have been synthesized by slow evaporation conditions through the use of enantiomorphically pure sources of either R-2-methylpiperazine (R)-C5H12N2 or S-2-methylpiperazine (S)-C5H12N2. These materials crystallize in the polar, noncentrosymmetric space group P21 (No. 4), crystal class 2 (C2). Isolated [MII(H2O)6]2+, [(R)-C5H14N2]2+ or [(S)-C5H14N2]2+ cations and (SO4)2− anions linked together via two types of hydrogen bonds, Ow–Hw⋯O and N–H⋯O, from which supramolecular structures are formed. The use of single enantiomer of either R-2-methylpiperazine or S-2-methylpiperazine precludes inversion symmetry within the crystal lattices and forces crystallization in noncentrosymmetric structures. Compounds 1–8 were characterized using single crystal X-ray diffraction, infrared spectroscopy and thermal analyses. The structural arrangements and the intermolecular interactions such as hydrogen-bonding are discussed.