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

The crystal structure of piperazinium(2+) selenate monohydrate has been resolved; this substance crystallizes in the monoclinic space group P2(1)/n, a = 6.4586(8), b = 11.8335(7), c = 11.8065(7) Angstrom, beta = 100.990(8)degrees; V = 885.80(13) Angstrom(5), Z = 4, R = 0.0446 for 1556 observed reflections. A similar compound, N,N'-dimethylpiperazinium(2+) selenate dihydrate, crystallizes in a triclinic system with space group P1 and lattice parameters a = 6.7370(8), b = 7.9845(9), c = 12.3802(12) Angstrom, alpha = 92.435(9)degrees, beta = 100.219(9)degrees, gamma = 114.699(10)degrees; V = 590.34(11) Angstrom(3), Z = 2, R = 0.0311 for 2071 observed reflections. While, in the former structure, the cations of piperazinium(2+) in the chair conformation are arranged roughly plane-parallel above one another, in the second substance, the N,N'-dimethylpiperazinium (2+) ions lie approximately perpendicularly above one another. The FTIR and FT Raman spectra of both test substances have been measured and studied. The thermoanalytical properties were studied using TG, DTG, and DTA methods in the temperature range 293-533 K. DSC measurements were carried out in the temperature range 95-343 K. No phase transition was found in this temperature region for either of the compounds. (C) 2000 Academic Press.