A Plausible Formation Mechanism of Polyoxoperoxomolybdates With Variable Structures

Metal oxyhalides: an emerging family of nonlinear optical materials

“…Materials containing central metals of [MO m X n ] belonging to the d 0 /d 10 transition metals or heavy post-transition metals manifesting second-order Jahn–Teller (SOJT) distortions are of particular interest. 27 The SOJT distortions of [MO m X n ] groups can induce large local asymmetry, which would be superimposed to large macroscopic asymmetry when the [MO m X n ] groups are well-aligned. Therefore, the formed metal–oxyhalide polyhedra can be preferable FBBs for the design and discovery of novel NLO materials, owing to their asymmetric characteristics that have natural advantages in producing NCS structures, strong SHG effects, as well as large optical anisotropies (birefringences).…”

Order and Disorder: Toward the Thermodynamically Stable α-BaMoO2F4 from the Metastable Polymorph

“…17−27 Especially, the second-order Jahn−Teller (SOJT) distortive cation, Mo 6+ , has been identified as one of the strongest distorters. 28,29 Thus, molybdenum oxyfluorides have been expected to exhibit diverse asymmetric structural features. 30,31 A few representative molybdenum oxyfluorides include peculiar helical chains containing periodical tendril perversion [A 2 MoO 2 F 3 (A = Rb, NH 4 , and Tl)], 32 perovskites exhibiting unique features of atomic ordering and octahedral tilting [Na 2 MoO 2 F 4 and α-A 3 MoO 3 F 3 (A = K and Rb)], 33,34 luminescence materials with high thermal stability [CsMoO 2 F 3 , K 3 MoOF 7 , and K 2 MoO 2 F 4 • H 2 O], 35−37 and large birefringence materials [K 6 Mo 4 O 8 F 10 and Na 3 Cs(MoO 2 F 4 ) 2 ].…”

Sr2Nb6O13F8·4H2O and Sr3Nb2O2F12·2H2O: A Variant of Three-Dimensional Tungsten Bronze and a Polar Molecular Oxide Fluoride

“…Different types of interstitial channels also exist in which various cations with distinct size and concentration reside. On the basis of their structures, tungsten bronzes can be further classified to perovskite-type, tetragonal, hexagonal, and intergrowth tungsten bronzes. − The tungsten bronze family has also been exhibiting many fascinating characteristics including magnetic, electric, optical, and electrochromic properties. − Especially, tungsten bronzes with noncentrosymmetric (NCS) structures constructed by alignment of the distorted octahedra have revealed very interesting characteristics such as piezoelectricity, second-harmonic generation (SHG), and ferroelectricity. − The structure-related properties, mainly originating from the out-of-center distortion of second-order Jahn–Teller distortive cations, might be widely applied to operations in transducers, frequency conversions, medical lasers, optical communications, and memories. − We have been very interested in exploring tungsten bronze materials containing Nb 5+ , with the d 0 transition-metal cation exhibiting large octahedral distortion and F – being the most electronegative anion that can generate a wide transparency. , Thus far, several tungsten bronze-type niobium oxyfluorides such as NaNb 2 O 5 F, SrK 2 Nb 5 O 14 F, K 1– x Nb 3 O 9– x F x (0 ≤ x < 1), K 3 (Nb 3 Ti 2 )­O 11 F 4 , KNb 2 O 5 F, etc., have been known. In this paper, we report two new hydrothermally synthesized strontium niobium oxyfluorides, Sr 2 Nb 6 O 13 F 8 ·4H 2 O and Sr 3 Nb 2 O 2 F 12 ·2H 2 O.…”