Alignment of acentric MoO3F3-3 anions in a polar material:: (Ag3MoOT3F3(Ag3MoO4)Cl

(Ag3MoO3F3)(Ag3MoO4)Cl was synthesized by hydro(solvato)thermal methods and characterized by single-crystal X-ray diffraction (P3m1, No. 156, Z = 1, a = 7.4488(6) Angstrom, c = 5.9190(7) Angstrom). The transparent colorless crystals are comprised of chains of distorted fac-MoO3F33- octahedra and MoO42- tetrahedra anions, as suggested by the formulas (AgMoO3F3)-Mo-3 and Ag3MoO4+, and are connected through Ag+ cations in a polar alignment along the c-axis. One Cl- anion per formula unit serves as a charge balance and connects the two types of chains in a staggered fashion, offset by similar to1/2 x c. In MoO42- the Mo atom displaces towards a single oxide vertex, and in MoO3F33- the Mo displaces towards the three oxide ligands. The ordered oxide-flouride ligands on the MoO3F33- anion is important to prevent local inversion centers, while the polar organization is directed by the Cl- anion and interchain dipole-dipole interactions. The dipole moments of MoO3F33- and MoO42- align in the negative c-axis direction. to give a polar structure with no cancellation of the individual moments. The direction and magnitude of the dipole moments for MoO3F33- and MoO42- were calculated from bond valence analyses and are 6.1 and 1.9 debye (10(-18)esu cm) respectively, compared to 4.4 debye for polar NbO6 octahedra in LiNbO3, and 4.5 debye for polar TiO6 octahedra in KTiOPO4 (KTP). (C) 2003 Elsevier Science (USA). All rights reserved.