Quaternary phosphates of divalent 3d-metals – synthesis, crystal structures and spectroscopic characterization of quaternary chromium(II) phosphates and isotypic compounds including a detailed study of the colour of nickel(II) oxo-compound
Abstract
In this thesis preparative, crystallographic and spectroscopic explorations into quaternary phosphates of transition metals have been made. The first part reports on synthesis and crystal structures of chromium(II) phosphates. In the second part these results were compared to other 3d-metal phosphates. The crystal chemistry of mixed diphosphates A2P2O7 - M2P2O7 (A = Mg – Ba, M = Cr – Zn) is reviewed. In the third part the correlation of colour and crystal structure of nickel(II) oxo-compounds was examined.
In systems A / Cr / P / O (A = Mg – Ba) the new orthophosphates Mg3Cr3(PO4)4 (P21/n, R1 = 0,035) and Mg3.75Cr2.25(PO4)4 (P21/a, R1 = 0.032) with cation disorder on each metal position and Ca2Cr4(PO4)4 (C2/c, R1 = 0.034) with ordered cation distribution were synthesized and characterized. The existence of the solid solution Mg2P2O7 - Cr2P2O7 (0,01 £ X(Cr) £ 0,94) was shown. It is isotypic to b -Mg2P2O7 and b -Cr2P2O7. Three non isotypic diphosphates (CaCrP2O7 (P-1, R1 = 0.041), SrCrP2O7 (P21/c, R1 = 0,027), BaCrP2O7 (P-1, R1 = 0.085)) each with only one crystallographic position for Cr2+ were synthesized and characterized for the first time.
In systems A / M / P / O (A = Mg – Ba, M = Cr – Zn) eight compounds and three solid solutions were synthesized for the first time: CaFeP2O7, CaZnP2O7, SrCaP2O7, SrMnP2O7, BaFeP2O7; Mg1-xMnxP2O7, Mg1-xFexP2O7 and BaZn1-xCuxP2O7. Lattice parameters for the solid solutions were determined from powder data. The crystal structures of SrNiP2O7 (P21/c, R1 = 0.027), SrNi3(P2O7)2 (P21/c, R1 = 0.027), and SrMn2(PO4)2 (P-1, R1 = 0.046) were refined from single crystal data.
Colours of 14 nickel(II) oxo-compounds were investigated by powder reflectance measurements and modelling (program: CAMMAG) of the spectra within the angular overlap model (AOM). Remarkable good correlation of the geometry of the chromophors [NiOn] and observed electronic spectra were found by using only two independent parameters (B, es,max) to describe interactions of Ni2+ and O2-. Additional consideration of anisotropic p-interactions in terms of "second-sphere-ligand-field effect" led to interaction parameters es,norm, which can be transferred to other nickel(II) oxo-compounds.
