| Available from UMI in association with The British Library. Requires signed TDF.; This thesis reports the exploratory synthesis and characterisation of some phosphates of the metals manganese, iron and cobalt, using the techniques of hydrothermal synthesis, single crystal X-ray diffraction, and X-ray and neutron powder diffraction.; In a study of the system M{dollar}sb7{dollar}(PO{dollar}sb4)sb6{dollar}H{dollar}sb{lcub}rm x{rcub}{dollar} (M = Mn, Fe, Co; x = 0-4), two new compounds, M{dollar}sb7{dollar}(PO{dollar}sb4)sb2{dollar}(HPO{dollar}sb4)sb4{dollar} (M = Mn or Co) have been synthesized. Their structures are shown to be related to that of the mixed-valence iron phosphate Fe{dollar}sb7{dollar}(PO{dollar}sb4)sb6{dollar} (P1, a = 6.314, b = 9.358, c = 7.967A, {dollar}alpha{dollar} = 105.61, {dollar}beta{dollar} = 101.15, {dollar}gamma{dollar} = 107.90{dollar}spcirc{dollar}). A partially reduced iron phase has been prepared, from which the existence of a solid solution Fe{dollar}sb7{dollar}(PO{dollar}sb4)sb6{dollar} - Fe{dollar}sb7{dollar}(PO{dollar}sb4)sb2{dollar}(HPO{dollar}sb4)sb4{dollar} has been inferred. Cation distributions in the two solid solutions (Mn,Fe){dollar}sb7{dollar}(PO{dollar}sb4)sb6{dollar} and (Co,Fe){dollar}sb7{dollar}(PO{dollar}sb4)sb6{dollar} have been studied by powder neutron diffraction. Iron exists in the trivalent state in these systems, and preferentially occupies two of the four available cation sites. This ordering is rationalized in terms of Coulombic and ligand field effects.; The structure of MnPO{dollar}sb4{dollar}.H{dollar}sb2{dollar}O, previously and erroneously reported as MnPO{dollar}sb4{dollar}.1.5H{dollar}sb2{dollar}O, has been determined by using high-resolution synchrotron X-ray powder diffraction data. The compound crystallises in the space group C2/c, a = 6.912(1), b = 7.470(1), c = 7.351(1)A, {dollar}beta{dollar} = 112.3(1){dollar}spcirc{dollar}, with a structure related to those of the divalent sulphates MSO{dollar}sb4{dollar}.H{dollar}sb2{dollar}O.; Two novel Mn{dollar}sp{lcub}3+{rcub}{dollar} phosphates have been synthesized, and characterised by single crystal X-ray techniques. Both structures contain edge-sharing chains of MnO{dollar}sb6{dollar} octahedra, of a type previously unobserved in phosphates. The condensed KMn{dollar}sb2{dollar}O(PO{dollar}sb4{dollar})(HPO{dollar}sb4{dollar}) (P2{dollar}sb1{dollar}/m, a = 6.226(1), b = 6.890(2), c = 8.809(1)A, {dollar}beta{dollar} = 107.67(1){dollar}spcirc{dollar}) is produced at 3kbar and 400{dollar}spcirc{dollar}C, whilst the more open NH{dollar}sb4{dollar}Mn{dollar}sb2{dollar}O(PO{dollar}sb4{dollar})(HPO{dollar}sb4{dollar}).H{dollar}sb2{dollar}O (P2{dollar}sb1{dollar}2{dollar}sb1{dollar}2{dollar}sb1{dollar}, a = 6.879(2), b = 7.741(2), c = 16.244(3)A) is produced under milder conditions at 200{dollar}spcirc{dollar}C and 30bar.; A novel layered pyrophosphate, K{dollar}sb2{dollar}Co{dollar}sb3{dollar}(P{dollar}sb2{dollar}O{dollar}sb7{dollar}){dollar}sb2{dollar}.2H{dollar}sb2{dollar}O (P2{dollar}sb1{dollar}/a, a = 9.229(2), b = 8.110(1), c = 9.122(4)A, {dollar}beta{dollar} = 99.31(4){dollar}spcirc{dollar}), has been prepared, and its structure determined by single crystal X-ray methods. The ammonium analogue of this compound has also been synthesized. A rather unusual mixed-valence phase, K{dollar}sb3{dollar}Fe{dollar}sb4{dollar}H(PO{dollar}sb4{dollar}){dollar}sb3{dollar}(C{dollar}sb2{dollar}O{dollar}sb4{dollar}){dollar}sb2{dollar} (P2{dollar}sb1{dollar}/a, a = 10.338(6), b = 11.811(3), c = 16.419(3)A, {dollar}beta{dollar} = 104.62(3){dollar}spcirc{dollar}), has also been prepared and characterised. A layer-like structure is adopted, with Fe{dollar}sp{lcub}3+{rcub}{dollar} preferentially occupying a five-coordinate site. |
