WZIRCONIUM BIS(MONOHYDROGEN ORTHOPHOSPHATE) MONOHYDRATE 43 1 strained by hydrogen bonding and packing requirements; however, this may be in part a reflection of absorption errors.The dihedral angles that completely specify the orientation of the thiourea groups relative to the planes defined by Ni and S atoms are given in Table 111.Three factors contribute to these orientations : (a) hydrogen bonding to the bromide ion, (b) steric requirements that restrict the thiourea groups, and (c) electrostatic interactions between electrons in the S-C p 7~ molecular orbitals and the metal d,,, dyr, d,, orbitals, all of which are filled. Obviously all three factors contribute to the specific orientation of a thiourea group and studies are currently underway in this laboratory to determine which factor(s) predominate(s). Preliminary photographic data indicate that N i ( t~)~B r~ and Ni(tu)& are isomorphous and a comparison of the specific orientations of thiourea groups in this series to the orientation of thiourea groups in Pt(t~)4C12,~O Pd(tu)4Clz,lg and the isomorphous series M n ( t~)~C l~, Fe(tu)Klz, Cd(tu)4Clz, and C O (~U )~C~Z~* -~~ is being made.The crystal structure of a-zirconium bis(monohydrogen orthophosphate) monohydrate, Zr(HPO&. HzO, has been determined from integrated precession data (568 nonzero reflections). The crystals are monoclinic, space group P21/c, with cell dimensions a = 9.076 f 0.003 A, b = 5.298 =k 0.006 A, c = 16.22 =k 0.02 A, and @ = 111.5 f 0.1'. The calculated density with Z = 4 is 2.76 g/cm3 compared to an observed density of 2.72 f 0.04 g/cms. The structure was refined to an R factor of 8.4% by least-squares methods. The structure is a layered one, each layer consisting of planes of zirconium atoms bridged through phosphate groups which alternate above and below the metal atom planes. Each phosphate group bonds to three different zirconium !toms producing octahedral coordination about the zirconium atoms. The Zr-0 bond distances range from 2.04 to 2.11 A. The fourth phosphate oxygen bears the hydrogen and points toward an adjacent layer. A water molecule resides in the center of each cavity and is hydrogen bonded to phosphate groups. The relation between structure and ionexchange properties of the crystals is discussed in this and a forthcoming paper.The layers are arranged relative to each other in such a way as to form zeolitic-type cavities.(1) Portions of this paper were taken from the Ph.D. thesis of G. D.
Smith presented toThe a phase (a-ZrP) has been shown to be zirconium bis(monohydrogen orthophosphate) monohydrate, Zr(HP04)2.Hz0, on the basis of its composition, dehydration, and ion-exchange b e h a~i o r .~ Crystals large enough for a single-crystal X-ray diffraction study were prepared from the microcrystals as described below. An attempt to solve the structure by twodimensional methods was only partially successful.6Severe overlap of several oxygen atom peaks in the Fourier projections prevented a complete solution of the structure. A three-dimensional study has now been carried...