The crystal structure, vibrational spectra, and thermal behavior of dilithium piperazinium(2+) selenate tetrahydrate and dilithium N,N′-dimethylpiperazinium(2+) selenate tetrahydrate

The crystal structure of dilithium piperazinium(2+) selenate tetrahydrate has been solved; this substance crystallizes in the triclinic space group P1̄, a=7.931(2)Å, b=7.974(2)Å, c=7.991(2)Å, α=106.99(2)°, β=101.83(2)°, γ=119.28(2)° Z=1, R=0.0280 for 1489 observed reflections. A similar compound, dilithium N,N′-dimethylpiperazinium(2+) selenate tetrahydrate crystallizes in a monoclinic system with space group P21/c and lattice parameters a=7.338(1)Å, b=8.792(2)Å, c=12.856(1)Å, β=92.04(2)°, Z=2, R=0.0334 for 1462 observed reflections. Both structures are centrosymmetric with center of symmetry in the center of eight membered ring formed with two SeO4 tetrahedra and two LiO4 tetrahedra connected through tops. The two remaining oxygens on each Li atom come from water molecules. The FTIR and FT Raman spectra of both natural and N,O-deuterated substances have been measured and studied. The thermoanalytical properties were studied using TG, DTG and DTA methods in the temperature range 293–873K for piperazinium derivative and in the range 293–523K for dimethylpiperazinium derivative. DSC measurements were carried out in the temperature range 95–343K. No phase transition was found in this temperature region for either of the compounds.