SYNTHESIS, CRYSTAL-STRUCTURES, AND PROTON CONDUCTIVITY OF 2 LINEAR-CHAIN URANYL PHENYLPHOSPHONATES

Two uranyl phenylphosphonates, [UO2(HO3PC6H5)(2)(H2O)](2) . 8H(2)O (1) and UO2(HO3PC6H5)(2) . 2CH(3)CH(2)OH (2), have been synthesized and t heir structures solved by single-crystal methods. Both compounds cryst allize in the triclinic space group <P(1)over bar>. Unit cell paramete rs are a=11.724(4) Angstrom, b=16.676(8) Angstrom, c=11.375(2) Angstro m, alpha=101.61(5)degrees, beta=106.76(3)degrees, gamma=102.57(4)degre es, and Z=2 for compound 1 and a=9.332(6) Angstrom, b=11.48(1) Angstro m, c=5.672(2) Angstrom, alpha=98.98(6)degrees, beta=92.78(5)degrees, g amma=108.54(5)degrees, and Z=1 for compound 2. In both compounds the m etal to phosphonate ratio is 1:2, and they both form linear chains. Ea ch metal atom in these structures is surrounded by four oxygens of fou r different phosphonate groups which take up the metal's equatorial po sitions. However, in compound 1 an additional oxygen of a water molecu le binds to the uranium atom in the equatorial plane. This leads to a distorted pentagonal bipyramidal geometry of uranium in compound 1 and to a distorted octahedral geometry of uranium in compound 2. Adjacent uranium atoms are bridged by two phosphonates, and every phosphonate group uses only two of its oxygens for this purpose. The third oxygen is not involved in metal coordination, and it is protonated. In compou nd 1, all phenyl rings of each uranyl phosphonate chain point into one general direction, perpendicularly to the chain, and the adjacent cha ins orient their ''phenyl sides'' almost toward each other to form pla nes of alternating hydrophobic and hydrophilic regions. The hydrophili c regions are filled with solvent water molecules. In compound 2, the phenyl rings also point perpendicularly to the chains, but in opposite directions, and the chains are stacked in a ''staircase'' fashion wit hout forming regions of different natures as in compound 1. Compound 1 also exhibits a reasonably high proton conductivity sigma(25 degrees C)=3.25 x 10(-3) Omega(-1) cm(-1) at 85% humidity due to the Bronsted acidity of its phosphonate OH groups. Both compounds are unstable in a ir mainly due to the loss of their solvent molecules.