Evidence for Nonpolar Alignment of [NbOF₅]^2- Anions in Cd(pyridine)₄NbOF₅ Chains

Abstract

A new phase of Cd(py) 4 NbOF 5 (py) pyridine) (A) is a rare example of a mixed metal oxide fluoride in an ordered linear chain structure. This phase is of particular interest because it is a polymorph of a previously reported Cd(py) 4 NbOF 5 phase (B) that crystallizes in disordered linear chains. The ordered polymorph A contains two distinct Cd 2+ sites: one which is coordinated to the oxide ligands from two [NbOF 5 ] 2units, and another that is coordinated to two trans fluoride ligands. As a result, the structure of polymorph A features nonpolar linear chains with locally ordered [NbOF 5 ] 2anions. This ordering is explained in terms of the inherent electronic differences between oxide and fluoride ligands. The stabilization provided by π-stacking interactions between pyridine ligands on neighboring chains, as well as the effects of reactant stoichiometry on the general structure of the products in the CdO‚1/2Nb 2 O 5 /(HF) x ‚py/H 2 O system, is also discussed. Crystal data for the ordered Cd(py) 4 NbOF 5 polymorph: monoclinic space group P2 1 /c (No. 14) with a) 14.097(1) Å, b) 16.353(1) Å, c) 10.4380(9) Å,) 95.569(2)°, and Z) 4.

Molecular structure and DFT study of hydrothermally synthesized niobium oxide fluoride

“…An asymmetrically distorted anion is indicated by an atomic valence on niobium that is significantly less than 5 as shown in Table 2. Similar lower values are commonly found in niobium oxyfluorides such as [Cd(py) 4 NbOF 5 ] and [pyH] 2 [Cd(-py) 4 (NbOF 5 ) 2 ] [4,5].…”

“…They are potential candidates for use in pyroelectricity, piezoelectricity, second-order nonlinear optical activity, and ferroelectricity [1][2][3]. Octahedral coordinated early d 0 transition metals with the general formula [MO x F 6Àx ] 2À (x = 1, M = V, Nb, Ta; and x = 2, M = Mo, W) are also of interest because of their distorted octahedral environment [4]. To date, most of reported are out-of-center distortions of NbOF 5 octahedron but is also found in NbO 6 and NbF 6 octahedra and can be explained by the second-order Jahn-Teller theorem [5][6][7], such as (NH 4 ) 2 NbOF 5 and [pyH] 2 [Cu(py) 4 (NbOF 5 ) 2 ] [8,9].…”

Making an order: the concerted alignment of [MOF5]2− (M = Nb and Ta) dipolar anions in one-dimensional coordination chains sustained by tris(3,4,5-trimethyl-1H-pyrazole)copper(II)

“…x -(M V = Nb or Ta; M II = late transition metal cation; L = organic coligand) grant a collinear disposition of the polar axes within an infinite array and they are perfectly suited as a basic structural motif for polar crystals (Guillory et al, 2006;Gautier et al, 2012). However, implementation of this attractive strategy still presents a challenge.…”

catena-Poly[bis(μ-2,2′-bipyridin-6-olato)-κ3N,N′:O;O:N,N′-dicopper(I,II) [[tetrafluoridoniobium(V)]-μ-oxido]]

“…Up to now, several niobium oxyfluorides based on the [NbOF 5 ] 2À anion have been synthesized and reported, e.g. [H 2 N(C 2 H 4 ) 2 NH 2 ][NbOF 5 ] (Feng et al, 2010), (HNC 6 H 6 -OH) 2 [Cu(py) 4 (NbOF 5 ) 2 ] (py is pyridine; Welk et al, 2002), (pyH) 2 [Cu(py) 4 (NbOF 5 ) 2 ] (Halasyamani et al, 1996), Cd-(py) 4 NbOF 5 (Guillory et al, 2006), (4-apyH) 2 [Cu(4-apy) 4 -(NbOF 5 ) 2 ] (4-apy is pyridin-4-amine; Izumi et al, 2005), and Cd(3-apy) 4 NbOF 5 and Cu(3-apy) 4 NbOF 5 (3-apy is pyridin-3amine; Izumi et al, 2005). However, in comparison with such well characterized niobium oxyfluorides based on the [NbOF 5 ] 2À anion, investigations of the [NbOF 4 ] À anion are relatively rare, examples being (Hphen)[NbOF 4 ]ÁH 2 O (Hphen is 1,10-phenanthrolinium; Zhao et al, 2009), and NH 4 NbOF 4 , Ag(pyz)NbOF 4 (pyz is pyrazine) and Cu(bpy)NbOF 4 Á2H 2 O (bpy = bipyridine) (Lin & Maggard, 2010).…”