Alignment of acentric MoO3F3 anions in a polar material: (Ag3MoO3F3)(Ag3MoO4)Cl |
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Authors: | Paul A Maggard Charlotte L Stern |
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Institution: | a Department of Chemistry, 2620 Yarbrough Drive, North Carolina State University, Raleigh, NC 27695-8204, USAb Department of Chemistry, 2145 Sheridan Road, Northwestern University, Evanston, IL 60208-3113, USA |
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Abstract: | (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)Å, c=5.9190(7) Å). The transparent colorless crystals are comprised of chains of distorted fac-MoO3F33− octahedra and MoO42− tetrahedra anions, as suggested by the formulas Ag3MoO3F3 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 . 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-fluoride 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). |
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Keywords: | Polar compound Dipole moment calculation Metal oxyfluoride anions |
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