Second-order Jahn-Teller Effect Research Articles

High-pressure synthesis, structure, phase relation of polar LiNbO3-type ZnTiO3

Ferroelectricity, piezoelectricity, pyroelectricity, and second-order nonlinear optical behavior are technologically important. Because these properties are attributable to the noncentrosymmetric (NCS) structure[1], the search for materials exhibiting such characteristics must begin with a search of NCS materials. Among them, LiNbO3-type (LN-type) compounds with a chemical formula of ABX3 exhibit NSC structures with hexagonal polar space group R3c whose BX6 octahedra three-dimensionally share their corners the same as perovskite-type compounds[2]. In LN-type compounds, the A cation - B cation repulsion directs the spontaneous polarization along c-axis(Fig. 1). Therefore, we might find attractive functional properties by the selection of constituent ions based on their having a naturally occurring polar LN-type structure attributable to the cation-cation repulsion. With the ideas mentioned above, we have investigated the high-pressure synthesis and characterization of novel LN-type oxides such as ZnSnO3, PbNiO3, CdPbO3 as well as known MnMO3 (M = Ti, Sn). Recently, we have successfully synthesized a polar LN-type titanate ZnTiO3 (LN-ZTO) under high pressure and high temperature [3]. The first principles calculation indicates that LN-ZTO is a meta-stable phase obtained by the transformation in the decompression process from the perovskite-type phase, which is stable at high pressure and high temperature. The Rietveld structural refinement reveals that LN-ZTO exhibits greater intra-distortion of the TiO6 in LN-ZTO than that of the SnO6 in LN-type ZnSnO3 (LN-ZSO). The estimated spontaneous polarization are greater than those of LN-ZSO, which is attributed to the great displacement of Ti along c-axis and the greater Born effective charge of Ti (+6.1) than that of Sn (+4.1). Furthermore, the spontaneous polarization of LN-ZTO is greater than that of LiNbO3, indicating that LN-ZTO, like LiNbO3, is a candidate ferroelectric material with high performance. The second harmonic generation (SHG) response of LN-ZTO is 24 times greater than that of LN-ZSO. The findings indicate that the intra-octahedral distortion, spontaneous polarization, and SHG response are caused by the stabilization of the polar LN-type structure and reinforced by the second-order Jahn-Teller effect attributable to the orbital interaction between oxygen ions and d0 ions such as Ti4+. We also discuss the relationship between the intra-distortion of BO6 and polarity in several LN-type oxides.

Extended x-ray absorption fine structure spectroscopy and first-principles study of SnWO4

The local atomic structure in α- and β-SnWO4 was studied by synchrotron radiation W L3-edge x-ray absorption spectroscopy at 10 and 300 K. Strongly distorted WO6 octahedra were found in α-SnWO4, whereas nearly regular WO4 tetrahedra were observed in β-SnWO4, confirming previous results. The structural results obtained were supported by the first-principles calculations, suggesting that the second-order Jahn–Teller effect is responsible for octahedral distortion.

Pure and Zn-doped Pt clusters go flat and upright on MgO(100).

Pure and doped sub-nanoclusters can exhibit superb catalytic activity, which, however, strongly depends on their size, shape, composition, and the nature of the support. This work is about surface-deposited sub-nano Pt-based clusters, which are promising catalysts for the reactions of dehydrogenation. Using density functional theory and ab initio calculations, and an ab initio genetic algorithm for finding the global minima of clusters, we found a peculiar effect that Pt5 and Pt4Zn clusters exhibit upon deposition on MgO(100). Both of them change shapes from the gas phase 3-D form to a planar form, and they stand upright on the support. Several reasons are responsible for this behaviour. In part, clusters go flat due to the electron transfer from the support. Indeed, the anionic Pt5(-) and Pt4Zn(-) species are flat also in the gas phase. Charging induces the second-order Jahn-Teller effect (or partial covalency) facilitated by the recruitment of the higher-energy 6p atomic orbitals on Pt into the valence manifold, and that is the reason for the planarization of the anions. Secondly, clusters maximize interactions with the surface O atoms (resulting in further favouring of 2-D structures over 3-D), and avoid contacts with surface Mg atoms (resulting in upright morphologies).

Why Is (SiO)4 Calculated To Be Tetrahedral, Whereas (CO)4 Is Square Planar? A Molecular Orbital Analysis

Qualitative molecular orbital (MO) theory predicts that square-planar tetrasilacyclobutanetetraone D4h-(SiO)4 should, like D4h-(CO)4, have a triplet ground state, and the results of the (U)CCSD(T)-F12b/cc-pVTZ-F12//(U)B3LYP/6-311+G(2df) calculations, reported here, confirm this expectation. Calculations at the same level of theory find that square-planar tetrasilacyclobutanetetrathione D4h-(SiS)4 also has a triplet ground state. However, these ab initio calculations predict that (SiO)4 and (SiS)4 both have a singlet state of much lower energy, with a tetrahedral (Td) equilibrium geometry and six, electron-deficient, Si-Si bonds. In contrast, the lowest singlet state of (CO)4 and of (CS)4 is calculated to prefer a D4h to a Td geometry. An analysis, based on the second-order Jahn-Teller effect, rationalizes the influence of the electronegativity difference between A and Y in (AY)4 on the energy difference between a D4h and Td geometry. This analysis predicts that (BF)4 and (BCl)4, which are isoelectronic with, respectively, (CO)4 and (CS)4, should both prefer a Td to a D4h equilibrium geometry. These qualitative predictions have been confirmed by our calculations, and (BCl)4 is known experimentally to have a Td equilibrium geometry.

High-Pressure Synthesis, Crystal Structure, and Phase Stability Relations of a LiNbO3-Type Polar Titanate ZnTiO3and Its Reinforced Polarity by the Second-Order Jahn–Teller Effect

A polar LiNbO3-type (LN-type) titanate ZnTiO3 has been successfully synthesized using ilmenite-type (IL-type) ZnTiO3 under high pressure and high temperature. The first principles calculation indicates that LN-type ZnTiO3 is a metastable phase obtained by the transformation in the decompression process from the perovskite-type phase, which is stable at high pressure and high temperature. The Rietveld structural refinement using synchrotron powder X-ray diffraction data reveals that LN-type ZnTiO3 crystallizes into a hexagonal structure with a polar space group R3c and exhibits greater intradistortion of the TiO6 octahedron in LN-type ZnTiO3 than that of the SnO6 octahedron in LN-type ZnSnO3. The estimated spontaneous polarization (75 μC/cm(2), 88 μC/cm(2)) using the nominal charge and the Born effective charge (BEC) derived from density functional perturbation theory, respectively, are greater than those of ZnSnO3 (59 μC/cm(2), 65 μC/cm(2)), which is strongly attributed to the great displacement of Ti from the centrosymmetric position along the c-axis and the fact that the BEC of Ti (+6.1) is greater than that of Sn (+4.1). Furthermore, the spontaneous polarization of LN-type ZnTiO3 is greater than that of LiNbO3 (62 μC/cm(2), 76 μC/cm(2)), indicating that LN-type ZnTiO3, like LiNbO3, is a candidate ferroelectric material with high performance. The second harmonic generation (SHG) response of LN-type ZnTiO3 is 24 times greater than that of LN-type ZnSnO3. The findings indicate that the intraoctahedral distortion, spontaneous polarization, and the accompanying SHG response are caused by the stabilization of the polar LiNbO3-type structure and reinforced by the second-order Jahn-Teller effect attributable to the orbital interaction between oxygen ions and d(0) ions such as Ti(4+).

Electronic structure effects in the vectorial bond-valence model

The vectorial bond-valence model (VBVM) describes the spatial distribution of bonds to each atom in a system in terms of the vector sum of the incident bond valences. It has been applied in the past to cations not subject to electronic structure effects (e.g., lone-pair or Jahn-Teller effects) in which case the expectation is that the vector sum will be approximately zero. Here we analyze 178 simpleoxide crystal structures and show that the vectorial bond-valence sum is a predictable function of the atomic valence (oxidation state) of each atom and the valence of the strongest bond to atoms for which second-order Jahn-Teller and lone-pair effects play a role in determining molecular geometry. Outliers are uniformly metastable or unstable under ambient conditions, suggesting that deviation from ideal vectorial bond-valence sums might be used as a proxy for some aspect of structural potential energy. These results are all strictly in harmony with the VSEPR model of molecular geometry, but may allow for more quantitative prediction.

Ab initio LCAO study of the atomic, electronic and magnetic structures and the lattice dynamics of triclinic CuWO4

The electronic, structural and phonon properties of antiferromagnetic triclinic CuWO4 have been studied using the first-principles spin-polarized linear combination of atomic orbital (LCAO) calculations based on the hybrid exchange–correlation density functional (DFT)/Hartree–Fock (HF) scheme. In addition, the local atomic structure around both Cu and W atoms has been probed using extended X-ray absorption fine structure (EXAFS) spectroscopy. We show that, by using the hybrid DFT–HF functional, one can accurately and simultaneously describe the atomic structure (the unit cell parameters and the atomic fractional coordinates), the band gap and the phonon frequencies. In agreement with our EXAFS results, the LCAO calculations reproduce a strong distortion of both the CuO6 and the WO6 octahedra, which occur due to the first-order and second-order Jahn–Teller effects, respectively. We found that the HF admixture of 13–16%, which is implemented in the PBE0–13% and WCGGA–PBE-16% functionals, produces the best result for CuWO4. The calculated properties agree well with the available experimental data provided by diffraction, optical, X-ray photoelectron and Raman spectroscopies.

Quantum chemical DFT study of two types of stable structures of Ni(II) high-spin binuclear carboxylate complexes

Quantum chemical calculations of the electronic structure of [Ni2(μ-O2CCH3)4(O-DMSO)2] complex were performed using the DFT B3LYP method in the 6-31G(d,p) basis. The calculations made it possible to detect the existence of two types of stable structures of Ni(II) high-spin binuclear carboxylate complexes with different terminal ligands, i.e. with a relatively symmetrical metal-carboxylate Ni2(μ-O2CR)4 framework and with its significant distortion caused by the second-order Jahn-Teller effect.

Dielectric properties of a polar ZnSnO3 with LiNbO3-type structure

The dielectric properties of a polar LiNbO3-type ZnSnO3 synthesized under high-pressure have been investigated with respect to the dielectric permittivity in the relative low frequency range of 10kHz to 1MHz and the SHG response at an optical frequency. The small temperature dependence of dielectric permittivity without anomaly was observed in the temperature range of 300K to 780K. LiNbO3-type ZnSnO3 exhibits the maximum SHG efficiency of approximately 50 times that of quartz. We then compare the structure and SHG response with those of iso-structural LiNbO3 and other known LiNbO3-type oxides. It was found that the magnitude of SHG response is correlated to the magnitude of intra-octahedral distortion, which is effectively brought by the second-order Jahn–Teller effect.

Asymmetrically distorted structures of monosilacyclobutane and disilacyclobutane radical cations studied by ab initio and density functional theories

The geometrical and electronic structures of a series of six monosilacyclobutane and 1,3-disilacyclobutane radical cations were systematically studied using ab initio and density functional theories. It was shown that all six radical cations possess an asymmetrically distorted structure in their ground electronic states. In the asymmetrically distorted C1 structure of monosilacyclobutane cations, one Si–C bond was elongated and the other was shortened. For the disilacyclobutane cations, two ring bonds were elongated and the other two contracted. The asymmetrical distortion was enhanced by exocyclic methyl substitutions and weakened by endocyclic Si substitution. The unpaired electron was localized mainly in the elongated σ(Si–C) ring bond(s) in all six cations. Studies of the excited electronic states of the cations provided strong support that the asymmetrical distortion in the four-membered-ring cations originates from the second-order Jahn–Teller effect. It was found that the puckered ring structures in the monosilacyclobutane molecules were maintained upon ionization, whereas 1,3-disilacyclobutane cations changed to a planar ring structure. Examination of the potential energy surfaces of all six cations showed that the Si–C ring bond elongation is the main contributor to the significant difference in the geometry change between monosilacyclobutane and disilacyclobutane species upon ionization.

PbMSeO6 (M = Mo and W): New quaternary mixed metal selenites with asymmetric cationic coordination environments

Two new isostructural mixed metal selenites, PbMSeO(6) (M = Mo(6+) or W(6+)), that are only composed of second-order Jahn-Teller (SOJT) distortive cations have been synthesized by standard solid-state reaction techniques using PbO, SeO(2), and MoO(3) (or WO(3)) as reagents. The structures of the reported materials were determined by single-crystal and powder X-ray diffraction. The materials show a three-dimensional framework structure consisting of chains of corner-shared MO(6) octahedra connected by SeO(3) and PbO(8) polyhedra. All of the constituent cations (M(6+), Se(4+), and Pb(2+)) are in distorted environments attributable to second-order Jahn-Teller (SOJT) effects. While the Mo(6+) cations undergo a C(2)-type intraoctahedral distortion toward an edge, the Se(4+) and Pb(2+) cations are in asymmetric coordination environments attributable to their lone pairs. The SeO(3) polyhedra strongly influence the direction of the Mo(6+) intraoctahedral distortion. Infrared spectroscopy, thermogravimetric analysis, the magnitudes of out-of-center distortions, and dipole moment calculations are also presented. Crystal data: PbMoSeO(6), triclinic, space group P-1 (No. 2), with a = 6.8944(6) Å, b = 7.2219(6) Å, c = 10.8294(9) Å, α = 99.751(2)°, β = 99.996(2)°, γ = 90.041(2)°, V = 523.09(8) Å(3), and Z = 2; PbWSeO(6), triclinic, space group P-1 (No. 2), with a = 6.8689(2) Å, b = 7.2398(2) Å, c = 10.9037(3) Å, α = 99.699(4)°, β = 100.348(3)°, γ = 90.139(4)°, V = 525.50(3) Å(3), and Z = 2.

ChemInform Abstract: Stereochemistry of Post‐Transition Metal Oxides: Revision of the Classical Lone Pair Model

AbstractReview: 60 refs.

Crystal structure evolution and local symmetry of perovskite solid solution Ba[(Fe1/2Nb1/2)1−xTix]O3 investigated by Raman spectra

The local crystal structure and phonon modes of Ba[(Fe1/2Nb1/2)1−xTix]O3 solid solutions (x = 0, 0.2, 0.4, 0.6, 0.8, 0.85, 0.9, 0.95) were investigated by Raman spectroscopy in the range of 100–1000 cm− 1 at room temperature. Typical tetragonal structure with C4v symmetry was determined for Ba[(Fe1/2Nb1/2)0.05Ti0.95]O3, which was in accordance with the X-ray diffraction (XRD) result. Similar Raman spectra with broader peaks were observed for x decreasing from 0.95 to 0.80, indicating weakening of the Ti4 + displacement. New features in low-, medium- and high-wavenumber regions were observed in Raman spectra of Ba[(Fe1/2Nb1/2)1−xTix]O3 system with x ≤ 0.6, which could be attributed to the heterogeneous distribution of multiple B-site ions. Most interestingly, two-mode-like behavior was observed in the high-wavenumber region in Raman spectra of Ba(Fe1/2Nb1/2)O3 and Ba[(Fe1/2Nb1/2)0.8Ti0.2]O3, which was probably caused by very local chemically heterogeneous zones of NbO6 and FeO6. As the existence of the local Nb rich region, slight distortion of octahedron could be expected due to the second-order Jahn-Teller (SOJT) effect of Nb5 + ion. The local composition fluctuation could play an important role in the unique relaxor-like dielectric characteristics of Ba(Fe1/2Nb1/2)O3.

Stereochemistry of post-transition metal oxides: revision of the classical lone pair model

The chemistry of post transition metals is dominated by the group oxidation state N and a lower N-2 oxidation state, which is associated with occupation of a metal s(2) lone pair, as found in compounds of Tl(I), Pb(II) and Bi(III). The preference of these cations for non-centrosymmetric coordination environments has previously been rationalised in terms of direct hybridisation of metal s and p valence orbitals, thus lowering the internal electronic energy of the N-2 ion. This explanation in terms of an on-site second-order Jahn-Teller effect remains the contemporary textbook explanation. In this tutorial review, we review recent progress in this area, based on quantum chemical calculations and X-ray spectroscopic measurements. This recent work has led to a revised model, which highlights the important role of covalent interaction with oxygen in mediating lone pair formation for metal oxides. The role of the anion p atomic orbital in chemical bonding is key to explaining why chalcogenides display a weaker preference for structural distortions in comparison to oxides and halides. The underlying chemical interactions are responsible for the unique physicochemical properties of oxides containing lone pairs and, in particular, to their application as photocatalysts (BiVO(4)), ferroelectrics (PbTiO(3)), multi-ferroics (BiFeO(3)) and p-type semiconductors (SnO). The exploration of lone pair systems remains a viable a venue for the design of functional multi-component oxide compounds.

Synthesis, Structure, and Theoretical Investigations of an Alkaline Earth Vanadate Oxide Compound (Ca4V4O14): Electronic, Optical, and Chemical Bond Properties

One novel purely inorganic d0 polyoxovanadate compound Ca4V4O14 (1) was obtained and characterized structurally. The chain-like [V4O14]8– anion, built up from distorted VO5 trigonal bipyramids and VO4 tetrahedras is rarely observed. The reason for structural distortions is ascribed to the second-order Jahn-Teller effect. The band structure, the density of states, linear optical response functions, the dielectric constants of the static case ϵ(0), and refractive indexes were calculated by the density functional theory method. The nature of the V–O and Ca–O bonds, and of the electronic absorption peak are discussed in detail.

Hydrated metal ions in aqueous solution: How regular are their structures?

The hydration reaction is defined as the transfer of an ion or neutral chemical species from the gaseous phase into water, Mn+(g) → Mn+(aq). In this process, water molecules bind to metal ions through ion-dipole bonds of mainly electrostatic character. The hydration reaction is always strongly exothermic with increasing heat of hydration with increasing charge density of the ion. The structures of the hydrated metal ions in aqueous solution display a variety of configurations depending on the size and electronic properties of the metal ion. The basic configurations of hydrated metal ions in aqueous solution are tetrahedral, octahedral, square antiprismatic, and tricapped trigonal prismatic. This paper gives an overview of the structures of hydrated metal ions in aqueous solution with special emphasis on those with a non-regular coordination figure. Metal ions without d-electrons in the valance shell form regular aqua complexes with a coordination figure, allowing a maximum number of water molecules to be clustered around the metal ion. This number is dependent on the ratio of the metal ion radius to the atomic radius of oxygen in a coordinated water molecule (1.34 Å). The lighter lanthanoid(III) ions have a regular tricapped trigonal prismatic configuration with the M–O distance to the capping water molecules somewhat longer than to the prismatic ones. However, with increasing atomic number of the lanthanoid(III) ions, an increasing distortion of the capping water molecules is observed, resulting in a partial loss of water molecules in the capping positions for the heaviest lanthanoids. Metal ions with d4 and d9 valance shell electron configuration, as chromium(II) and copper(II), respectively, have Jahn–Teller distorted aqua complexes. Metal ions with low charge and ability to form strong covalent bonds, as silver(I), mercury(II), palladium(II), and platinum(II), often display distorted coordination figures due to the second-order Jahn–Teller effect. Metal ions with d10s2 valence shell electron configuration may have a stereochemically active lone electron pair (hemi-directed complexes) or an inactive one (holo-directed). The hydrated tin(II), lead(II), and thallium(I) ions are hemi-directed in aqueous solution, while the hydrated bismuth(III) ion is holo-directed. The structures of the hydrated cationic oxo-metal ions are reported as well.

Polar Hexagonal Tungsten Bronze-Type Oxides: KNbW2O9, RbNbW2O9, and KTaW2O9

The synthesis, crystal structures, second-harmonic generation (SHG), piezoelectric, pyroelectric, and ferroelectric properties of three polar noncentrosymmetric (NCS) hexagonal tungsten bronze-type oxides are reported. The materials KNbW 2O 9, RbNbW 2O 9, and KTaW 2O 9 were synthesized by standard solid-state techniques and structurally characterized by laboratory powder X-ray diffraction. The compounds are isostructural, crystallizing in the polar NCS space group Cmm2. The materials exhibit a corner-shared MO 6 (M = Nb (5+)/W (6+) or Ta (5+)/W (6+)) octahedral framework, with K (+) or Rb (+) occupying the "hexagonal" tunnels. The d (0) transition metals, Nb (5+), Ta (5+), and W (6+), are displaced from the center of their oxide octahedra attributable to second-order Jahn-Teller effects. SHG measurements using 1064 nm radiation revealed frequency-doubling efficiencies ranging from 180 to 220 x alpha-SiO 2. Converse piezoelectric measurements resulted in d 33 values ranging from 10 to 41 pm V (-1). The total pyroelectric coefficient, p, at 50 degrees C ranged from -6.5 to -34.5 muC K (-1) m (-2). The reported materials are also ferroelectric, as demonstrated by hysteresis loops (polarization vs electric field). Spontaneous polarization values, P s, ranging from 2.1 to 8.4 muC cm (-2) were measured. The magnitudes of the SHG efficiency, piezoelectric response, pyroelectric coefficient, and ferroelectric polarization are strongly dependent on the out-of-center distortion of the d (0) transition metals. Structure-property relationships are discussed and explored. Crystal data: KNbW 2O 9, orthorhombic, space group Cmm2 (No. 35), a = 21.9554(2) A, b = 12.60725(15) A, c = 3.87748(3) A, V = 1073.273(13) A (3), and Z = 6; RbNbW 2O 9, orthorhombic, space group Cmm2 (No. 35), a = 22.00985(12) A, b = 12.66916(7) A, c = 3.8989(2) A, V = 1086.182(10) A (3), and Z = 6; KTaW 2O 9, orthorhombic, space group Cmm2 (No. 35), a = 22.0025(2) A, b = 12.68532(14) A, c = 3.84456(4) A, V = 1073.05(2) A (3), and Z = 6.

Probing the R Lines in Tris(acetylacetonato) Chromium(III) and Tris(3-bromo-acetylacetonato) Chromium(III) by Luminescence and Excitation Line Narrowing Spectroscopy

Site-selective and narrowed luminescence and excitation spectra in the region of the (2)E <-- (4)A 2 transitions are reported for single crystals of Al(acac) 3/Cr(III) and Al(3-Br-acac) 3/Cr(III) (where acac is acetylacetonate). The R 2 line is pronounced in the brominated system and displays a comparable oscillator strength as the R 1 line. The (2)E splitting is found to be 138 cm (-1), and the (4)A 2 ground-state splitting is 1.39 cm (-1). However, in the case of the Al(acac) 3/Cr(III) system the R 2 line is not a distinct feature. We propose that vibronic coupling via a second-order Jahn-Teller effect leads to a redistribution of R 2 intensity over several vibrational sidelines. An upper limit for the R 1 line width Gamma h = 15 MHz is deduced for the Al(acac) 3/Cr(III) 1% system at 1.5 K. This line width is limited by direct and indirect electron-spinelectron-spin interactions. Accurate zero-field splittings (1.20, 1.19, 1.17 cm (-1)) for the three sites in Al(acac) 3/Cr(III) are determined and compared with previously published electron paramagnetic resonance (EPR) data.

A Convergent Approach to the Synthesis of Multimetallic Dithiolene Complexes

Controlled base hydrolysis of one or both of the protected 1,2-dithiolene chelates of 1,3,5,7-tetrathia- s-indacene-2,6-dione (OCS 2C 6H 2S 2CO) enables the stepwise synthesis of di- and trimetallic complexes with 1,2,4,5-benzenetetrathiolate as the connector. Treatment of OCS 2C 6H 2S 2CO with MeO (-), followed by [NiBr 2(dcpe)] [dcpe = 1,2-bis(dicyclohexylphosphino)ethane], yields [(dcpe)Ni(S 2C 6H 2S 2CO)] ( 4). The reaction of 4 with EtO (-), followed by [MX 2(dcpe)] (X = halide), yields [(dcpe)Ni(S 2C 6H 2S 2)M(dcpe)] [M = Ni ( 5a), Pd ( 5b)]. Deprotection of the 1,3-dithiol-2-one group of 4, followed by introduction of (1)/ 2 equiv of MX 2 and then I 2, yields the neutral trimetallic compounds [(dcpe)Ni(S 2C 6H 2S 2)] 2M [M = Ni ( 6a), Pt ( 6b)]. Tetrahedralization at nickel is observed in 5a, which density functional theory calculations attribute to second-order Jahn-Teller effects, while 6a and 6b display an end-to-end folding of approximately 46 degrees . A color darkening is observed in moving from 4 to compounds 6 due to the increasing size of the conjugated metal-organic pi system. Intense, broad absorptions in the near-IR are observed for 6a and 6b.

Synthesis, Structure, Characterization, and Calculations of Two New Sn2+−W6+−oxides, Sn2WO5 and Sn3WO6

Two new Sn2+-W6+-oxides, Sn2WO5 and Sn3WO6, have been synthesized hydrothermally, and their structures have been determined by single-crystal X-ray diffraction methods. Both materials exhibit layered structural topologies consisting of two edge-shared WO6 octahedra connected to SnO3 and SnO4 polyhedra. Both the W6+ and Sn2+ cations are in locally asymmetric coordination environments attributable to second-order Jahn-Teller effects. Infrared and Raman spectroscopy, UV-vis diffuse reflectance spectroscopy, and thermogravimetric analysis were also performed on the reported materials. Theoretical calculations using the tight binding linear muffin tin orbital method agree with the observed electronic properties of these materials and indicate that the stereoactive lone pair on the Sn2+ is similar for both materials. Crystal data: Sn2WO5, monoclinic, space group P21/n (No. 14), a = 7.994(2) A, b = 13.712(4) A, c = 10.383(3) A, beta = 110.507(3) degrees , V = 1066.0(5) A3, and Z = 4; Sn3WO6, monoclinic, C2/c (No. 15), a = 12.758(3) A, b = 8.0838(16) A, c = 13.865(3) A, beta = 112.49(3) degrees , V = 1321.2(5) A3, and Z = 8.