title: Polar alignment of Λ-shaped basic building units within transition metal oxide fluoride materials.
abstract: A series of pseudosymmetrical structures of formula K10(M2OnF11-n)3X (M = V and Nb, n = 2, X = (F2Cl)1/3, Br, Br4/2,I4/2; M = Mo, n = 4, X = Cl, Br4/2, I4/2) illustrates generation of polar structures with the use of Λ-shaped basic building units (BBUs). For a compound to belong to a polar space group, dipole moments of individual species must be partially aligned. Incorporation of d(0) early transition metal polyhedral BBUs into structures is a common method to create polar structures, owing to the second-order Jahn-Teller distortion these polyhedra contain. Less attention has been spent examining how to align the polar moments of BBUs. To address alignment, we present a study on previously reported bimetallic BBUs and synthesized compounds K10(M2OnF11-n)3X. These materials differ in their (non)centrosymmetry despite chemical and structural similarities. The vanadium compounds are centrosymmetric (space groups P3m1 or C2/m) while the niobium and molybdenum heterotypes are noncentrosymmetric (Pmn21). The difference in symmetry occurs owing to the presence of linear, bimetallic BBUs or Λ-shaped bimetallic BBUs and related packing effects. These Λ-shaped BBUs form as a consequence of the coordination environment around the bridging anion of the metal oxide fluoride BBUs.
authors: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60628-3113, United States.
authors: Michael
authors: M
authors: Holland
authors: Martin D
authors: MD
authors: Donakowski
authors: Eric A
authors: EA
authors: Pozzi
authors: Andrew M
authors: AM
authors: Rasmussen
authors: Thanh Thao
authors: TT
authors: Tran
authors: Shannon E
authors: SE
authors: Pease-Dodson
authors: P Shiv
authors: PS
authors: Halasyamani
authors: Tamar
authors: T
authors: Seideman
authors: Richard P
authors: RP
authors: Van Duyne
authors: Kenneth R
authors: KR
authors: Poeppelmeier