CATION DISTRIBUTION AND COORDINATION CHEMISTRY OF CU(II) IN ZN(II) HYDROXIDE NITRATE SOLID-SOLUTIONS - A STRUCTURAL AND SPECTROSCOPIC STUDY

The X-ray powder diffraction analysis of the appearing phases in hydro xide nitrate compounds (ZnxCu1-x) (OH)(2-y)(NO3H)(y) . zH(2)O is repor ted. Single-phase solid solutions are detected only for 0 < x < 0.30 ( structural type Cu-2(OH)(2)NO3, phase I) and for 0.50 < x < 0.65 (stru ctural type Zn-3(OH)(4)(NO3)(2), phase I'). In the interval 0.3 < x < 0.5 the structurally closely related phases I and I' coexist. For 0.65 < x less than or equal to 1.0 a second two-phase region with I' and a third structure type Zn-5(OH)(8)(NO3)(2) . 2H(2)O (phase Pi-b) was ob served. From the intensities of the X-ray reflections and the dependen ce of the lattice parameter b' on x it was deduced that only a small f raction of Cu2+ enters phase Pi-b. Using the structural data and the E PR spectra together with calculations within the angular overlap model (AOM) the observed EPR signals could be correlated with the occupatio n of the various Zn2+ sites by Cu2+ in the three phases. It was also p ossible to derive the changes of the Zn2+ host site geometries induced by substituting Cu2+ ions due to vibronic coupling. The nicely resolv ed EPR spectra at high x values originate from small amounts of Cu2+ i n phase Pi-b. They display patterns of tetragonally elongated and-in t he dynamical average-compressed Cu(OH)(6) octahedra at higher temperat ures, which are assigned to the Zn(2) and Zn(1) sites, respectively. A t 5 K the latter polyhedron freezes into a geometry with a strong orth orhombic distortion component due to vibronic Jahn-Teller coupling. Th e EPR spectra further indicate that the bulk of Cu2+ enters phases I a nd I'. Powder reflectance spectra at 5 K are in support of these concl usions. The bonding parameters of Cu2+ in phase Pi-b have been determi ned from the well-resolved hyperfine structure in the EPR spectra. (C) 1995 Academic Press, Inc.