Vibrational behavior of SO42- guest ions included in K2Me(CrO4)(2)center dot 2H(2)O (Me = Co, Ni) and crystal structures of K2Me(CrO4)(2)center dot 2H(2)O (Me = Co, Ni)

摘要

Crystal structures of the isotypic compounds K2Co(CrO4)(2)center dot 2H(2)O and K2Ni(CrO4)(2)center dot 2H(2)O were refined from X-ray powder diffraction data (triclinic, space group P (1) over bar, Z = 1, a = 6.432(1)/6.425(1), b = 7.396(1)/7.355(1), c = 5.643(1)/5.619(1) angstrom, alpha = 96.61(1)/96.78(2), beta = 106.64(1)/106.60(1), gamma = 109.75(1)/ 109.84(1)degrees, V = 235.3/232.4 angstrom(3), R-wp = 8.22/9.27% for the Co/Ni-compound). The structures are composed of Me2+O4(H2O)(2) octahedra and CrO4 groups forming krohnkite-type octahedral-tetrahedral infinite chains which are linked by the potassium ions to layers and further to a three-dimensional framework. The proposed hydrogen-bonding scheme provides further linkage within the chains as well as between neighboring layers. The structures belong to 'type A' of the large group of compounds containing krohnkite-type chains. Vibrational spectra (infrared and Raman) of K2Me(CrO4)(2)center dot 2H(2)O(Me = Co, Ni) as well as infrared spectra of mixed crystals K2Me(CrO4)(2-x)(SO4)(x)center dot 2H(2)O (where x are approximately 0.05, 0.1 and 0.2 for the cobalt matrix, and 0.02, 0.1 and 0.15 for the nickel one) are presented and discussed with respect to the normal vibrations of the tetrahedral ions and the hydrogen bond system. The spectroscopic experiments reveal that v(1) of the CrO42- ions appear at higher frequencies thin two of the three components of v(3), i.e. v(1) > v(3b) (v(3a), v(3b) and v(3c) are site-group components of v(3), v(3c) being the lowest wavenumbered component).