Stereochemical Activity Of Lone Pair Research Articles

Formation of monomeric Sn(ii) and Sn(iv) perfluoropinacolate complexes and their characterization by 119Sn Mössbauer and 119Sn NMR spectroscopies.

The synthesis and characterization of a series of Sn(ii) and Sn(iv) complexes supported by the highly electron-withdrawing dianionic perfluoropinacolate (pinF) ligand are reported herein. Three analogs of [SnIV(pinF)3]2- with NEt3H+ (1), K+ (2), and {K(18C6)}+ (3) counter cations and two analogs of [SnII(pinF)2]2- with K+ (4) and {K(15C5)2}+ (5) counter cations were prepared and characterized by standard analytical methods, single-crystal X-ray diffraction, and 119Sn Mössbauer and NMR spectroscopies. The six-coordinate SnIV(pinF) complexes display 119Sn NMR resonances and 119Sn Mössbauer spectra similar to SnO2 (cassiterite). In contrast, the four-coordinate SnII(pinF) complexes, featuring a stereochemically-active lone pair, possess low 119Sn NMR chemical shifts and relatively high quadrupolar splitting. Furthermore, the Sn(ii) complexes are unreactive towards both Lewis bases (pyridine, NEt3) and acids (BX3, Et3NH+). Calculations confirm that the Sn(ii) lone pair is localized within the 5s orbital and reveal that the Sn 5px LUMO is energetically inaccessible, which effectively abates reactivity.

A Design Strategy for Single-Stranded Helicates using Pyridine-Hydrazone Ligands and PbII.

The reactions of py-hz ligands (L1-L5) with Pb(CF3 SO3 )2 ⋅H2 O resulted in some rare examples of discrete single-stranded helical PbII complexes. L1 and L2 formed non-helical mononuclear complexes [PbL1(CF3 SO3 )2 ]⋅CHCl3 and PbL2(CF3 SO3 )2 ][PbL2CF3 SO3 ]CF3 SO3 ⋅CH3 CN, which reflected the high coordination number and effective saturation of PbII by the ligands. The reaction of L3 with PbII resulted in a dinuclear meso-helicate [Pb2 L3(CF3 SO3 )2 Br]CF3 SO3 ⋅CH3 CN with a stereochemically-active lone pair on PbII . L4 directed single-stranded helicates with PbII , including [Pb2 L4(CF3 SO3 )3 ]CF3 SO3 ⋅CH3 CN and [Pb2 L4CF3 SO3 (CH3 OH)2 ](CF3 SO3 )3 ⋅2 CH3 OH⋅2 H2 O. The acryloyl-modified py-hz ligand L5 formed helical and non-helical complexes with PbII , including a trinuclear PbII complex [Pb3 L5(CF3 SO3 )5 ]CF3 SO3 ⋅3CH3 CN⋅Et2 O. The high denticity of the long-stranded py-hz ligands L4 and L5 was essential to the formation of single-stranded helicates with PbII .

Lone pair effects on ternary infrared nonlinear optical materials.

First-principles studies of the crystal structures, electronic structures and optical properties of noncentrosymmetrical (NCS) K3AsS4, Li3AsS3, Pb9As4S15 and Ag3AsS3 have been performed by means of density functional theory. Via a theoretical method to compute the intensity of the lone pair stereochemical activity of an As-S group, the correlated mechanism among the crystal structures, the stereo-chemical activity of lone pairs on As and the second harmonic generation (SHG) response has been clarified. The results prove that the SHG response is not only attributed to the lone pair stereochemical activity of the As-S group but also related to the direction of the forming layers in the crystal structure arrangement. Besides, the quantitative method for the stereo-chemical activity of lone pairs is universal, which is valid for other lone pair systems like those containing Pb2+, Bi3+, Sn2+, etc. The findings facilitate the exploration of materials that may exhibit a relatively large second order NLO reaction and can be used in infrared applications.

Multifunctional property exploration: Bi4O5I2 with high visible light photocatalytic performance and a large nonlinear optical effect.

Exploration of the versatility of materials is very important for increasing the utilization of materials. Herein, we successfully prepared Bi4O5I2 powders via a facile solvothermal method. The Bi4O5I2 photocatalyst exhibited significantly higher photocatalytic activity as compared to the common BiOI photocatalyst in the degradation of methyl orange, methylene blue and rhodamine B under visible light irradiation. Especially, for the degradation of methyl orange, the photocatalytic activity of Bi4O5I2 is about 10 times that of BiOI. Moreover, Bi4O5I2 exhibits an extremely high second harmonic generation response of about 20 × KDP (the benchmark) estimated by the unbiased ab initio calculations. The coexisting multifunction of Bi4O5I2 is mainly because of the increased dipole moment due to the stereochemical activity of lone pairs that promotes separation and transfer of photogenerated carriers, then enhances the photocatalytic activity and results in a high second harmonic generation response. This indicates that Bi4O5I2 may have good potential applications in photocatalytic and nonlinear optical fields.

Structure of russellite (Bi2WO6): origin of ferroelectricity and the effect of the stereoactive lone electron pair on the structure.

The structure of the low-temperature polar (orthorhombic) phase of russellite (Bi2WO6) was examined on artificial specimens with precise single-crystal X-ray diffraction experiments. The final atomic arrangement thus obtained was identical to that reported by Knight [Miner. Mag. (1992), 56, 399-409] with powder neutron diffraction. The residual density attributable to a stereochemically-active lone pair of electrons of bismuth was prominent at approximately the centre of a larger cap of BiO8 square antiprisms, that is on the line from the Bi sites to an adjacent WO42- slab along the b-axis direction. Quite uneven Bi-O distances and the formation of a vacant coordination hemisphere (within 3 Å) should, therefore, be ascribed to the strong demand of bismuth to form shorter Bi-O bonds to use up its electrostatic charge within its coordination environment. The shift of bismuth along -c propagates via the correlated shift of the W site and these cooperative shifts cause ferroelectricity in the compound. This propagation was easily effected by the intrusion of molecules such as acetone into the structure.

A -cation control of magnetoelectric quadrupole order in A(TiO)Cu4(PO4)4(A=Ba,Sr,and Pb)

Ferroic magnetic quadrupole order exhibiting macroscopic magnetoelectric activity is discovered in the novel compound $A$(TiO)Cu$_4$(PO$_4$)$_4$ with $A$ = Pb, which is in contrast with antiferroic quadrupole order observed in the isostructural compounds with $A$ = Ba and Sr. Unlike the famous lone-pair stereochemical activity which often triggers ferroelectricity as in PbTiO$_3$, the Pb$^{2+}$ cation in Pb(TiO)Cu$_4$(PO$_4$)$_4$ is stereochemically inactive but dramatically alters specific magnetic interactions and consequently switches the quadrupole order from antiferroic to ferroic. Our first-principles calculations uncover a positive correlation between the degree of $A$-O bond covalency and a stability of the ferroic quadrupole order.

Pb8M(BO3)6 (M = Mg, Ca): Two new borates with large birefringence activated by the ∞[Pb8B6O18]2- double layers

Two new isostructural lead borates, Pb8Mg(BO3)6 and Pb8Ca(BO3)6, have been synthesized via high temperature solution method. The single crystal structures of title compounds contain ∞[Pb8B6O18]2- double layers composed of planar BO3 triangles, Pb(2)O9 and distorted Pb(1)O5 polyhedra, these layers condense in c-axis, and the MgO6 (or CaO6) polyhedra fill into the layers, forming a three-dimensional framework. The stereochemical activity of lone pair (SCALP) electrons were found in the Pb(1)O5 polyhedra, which combine with the BO3 units, generating strong optical anisotropy. The calculated birefringences of Pb8Mg(BO3)6 and Pb8Ca(BO3)6 using first-principles method are 0.15@1064 nm and 0.12@1064 nm, respectively, which are comparable to the commercial α-BaB2O4 (α-BBO) crystal and imply that they probably can be used as birefringent materials. The electronic structures, density of states of title compounds were calculated by density functional theory (DFT). Meanwhile, the TG-DSC curves, infrared spectral and UV–Vis–NIR diffuse reflectance spectral were measured.

Crystal Structure Evolution and Notable Thermal Expansion in Hybrid Perovskites Formamidinium Tin Iodide and Formamidinium Lead Bromide.

The temperature-dependent structure evolution of the hybrid halide perovskite compounds, formamidinium tin iodide (FASnI3, FA+ = CH[NH2]2+) and formamidinium lead bromide (FAPbBr3), has been monitored using high-resolution synchrotron X-ray powder diffraction between 300 and 100 K. The data are consistent with a transition from cubic Pm3m (No. 221) to tetragonal P4/mbm (No. 127) for both materials upon cooling; this occurs for FAPbBr3 between 275 and 250 K, and for FASnI3 between 250 and 225 K. Upon further cooling, between 150 and 125 K, both materials undergo a transition to an orthorhombic Pnma (No. 62) structure. The transitions are confirmed by calorimetry and dielectric measurements. In the tetragonal regime, the coefficients of volumetric thermal expansion of FASnI3 and FAPbBr3 are among the highest recorded for any extended inorganic crystalline solid, reaching 219 ppm K-1 for FASnI3 at 225 K. Atomic displacement parameters of all atoms for both materials suggest dynamic motion is occurring in the inorganic sublattice due to the flexibility of the inorganic network and dynamic lone pair stereochemical activity on the B-site. Unusual pseudocubic behavior is displayed in the tetragonal phase of the FAPbBr3, similar to that previously observed in FAPbI3.

First-principles study lone-pair effects of Sb (III)-S chromophore influence on SHG response in quaternary potassium containing silver antimony sulfides

First-principles studies of the geometric structures, electronic structures and optical properties of non-centrosymmetrical (NCS) KAg2SbS4, K2AgSbS4 and K2Ag3Sb3S7 and centrosymmetrical (CS) KAg2SbS3 and K3Ag9Sb4S12 have been performed by means of density functional theory. It is indicated that although they have similarity in their anionic groups and, the electronic structures, prominent features of the optical anisotropy or second-order nonlinear optical (NLO) susceptibilities are apparently different. The calculated birefringences are 0.0537, 0.0343, 0.1324, 0.2217 and 0.0604 which are attributed to the different anionic groups [SbS3] and triangles [AgS3]. Also, the calculated NLO responses are about 0.5×, 1.0× and 2.0× times than that commercial AgGaS2 (AGS, d36=11pm/V) for K2AgSbS4, KAg2SbS4 and K2Ag3Sb3S7, respectively. In comparison with the absolute magnitude of second harmonic generation (SHG) coefficients, the order K2Ag3Sb3S7>KAg2SbS4>K2AgSbS4 is clearly established in the SHG response. Further analysis based on the real-space atom-cutting method reveals that the main sources of the SHG properties of these compounds are from the Sb-S group, especially K2Ag3Sb3S7 is mainly attributed to the lone pair stereochemical activity of Sb (III)-S group.

The activity of lone pair contributing to SHG response in bismuth borates: a combination investigation from experiment and DFT calculation.

Second harmonic generation (SHG) response is one of the most essential properties of nonlinear optical (NLO) materials. To achieve relatively strong SHG response, a feasible strategy is to introduce stereochemically active lone pair (SCALP) cations, such as Bi3+. NLO materials with Bi3+ usually exhibit a huge difference in SHG response, the inner correlation between the activity of SCALP and SHG response still being unclear owing to the lack of quantization estimation of the intensity of SCALP. Based on the calculation results of density functional theory (DFT), we develop a theoretical method to compute the intensity of the Bi-6s SCALP, which could describe the stereochemical behavior and exert significantly influences on some apparent optical properties, such as SHG response. Using the method, we further analyze a series of bismuth borates which exhibit an apparent hierarchy in SHG response: BiB2O4F (12 × KDP), α-BiB3O6 (8.2 × KDP), Bi2ZnOB2O6 (4 × KDP), CaBi2B2O7 (2 × KDP), and Bi2B8O15 (1.2 × KDP). Combining the experimental measurements for the SHG responses, electronic structure analysis and the real-space atom cutting method, we explore the mechanism of the hierarchy in SHG response.

Dynamic Stereochemical Activity of the Sn(2+) Lone Pair in Perovskite CsSnBr3.

Stable s(2) lone pair electrons on heavy main-group elements in their lower oxidation states drive a range of important phenomena, such as the emergence of polar ground states in some ferroic materials. Here we study the perovskite halide CsSnBr3 as an embodiment of the broader materials class. We show that lone pair stereochemical activity due to the Sn(2+) s(2) lone pair causes a crystallographically hidden, locally distorted state to appear upon warming, a phenomenon previously referred to as emphanisis. The synchrotron X-ray pair distribution function acquired between 300 and 420 K reveals emerging asymmetry in the nearest-neighbor Sn-Br correlations, consistent with dynamic Sn(2+) off-centering, despite there being no evidence of any deviation from the average cubic structure. Computation based on density functional theory supports the finding of a lattice instability associated with dynamic off-centering of Sn(2+) in its coordination environment. Photoluminescence measurements reveal an unusual blue-shift with increasing temperature, closely linked to the structural evolution. At low temperatures, the structures reflect the influence of octahedral rotation. A continuous transition from an orthorhombic structure (Pnma, no. 62) to a tetragonal structure (P4/mbm, no. 127) is found around 250 K, with a final, first-order transformation at 286 K to the cubic structure (Pm3̅m, no. 221).

SHG Materials SnGa4Q7 (Q = S, Se) Appearing with Large Conversion Efficiencies, High Damage Thresholds, and Wide Transparencies in the Mid-Infrared Region

Two new ternary noncentrosymmetric (NCS) isostructural compounds, SnGa4S7 (1) and SnGa4Se7 (2), have been synthesized by a high-temperature solid-state reaction method. Both compounds crystallize in the monoclinic polar space group Pc (7), and their three-dimensional (3D) frameworks are assembled from [SnQ4] tetragonal pyramids and tetranuclear [Ga4Q11] units. The two crystals show large second harmonic generation (SHG) conversion efficiencies, high laser-induced damage thresholds (LIDTs), and wide transparent regions in the mid-infrared (MIR) zone. Compound 2 exhibits the largest SHG conversion efficiency among type-I phase-matchable chalcogenides of about 3.8 × AgGaS2 at 2.05 μm radiation and a high LIDT of 4.6 × AgGaS2. Theoretical studies elucidate that the stereochemically active lone-pair (SCALP) electrons of Sn2+ can significantly improve the polarity of the [SnQ4] unit. Large nonlinear optical (NLO) responses for 1 and 2 originate from the covalent interactions of Sn–Q and the cooperative effects ...

Lead(ii) chloride ionic liquids and organic/inorganic hybrid materials – a study of chloroplumbate(ii) speciation

A range of chloroplumbate(II) organic salts, based on the two cations, 1-ethyl-3-methylimidazolium and trihexyl(tetradecyl)phosphonium, was prepared by ionothermal synthesis. Depending on the structure of the organic cation and on the molar ratio of PbCl2 in the product, χPbCl2, the salts were room-temperature ionic liquids or crystalline organic/inorganic hybrid materials. The solids were studied using Raman spectroscopy; the crystal structure of [C2mim]{PbCl3} was determined and shown to contain 1D infinite chloroplumbate(II) strands formed by edge-sharing tetragonal pyramids of pentacoordinate (PbCl5) units. The liquids were analysed using (207)Pb NMR and Raman spectroscopies, as well as viscometry. Phase diagrams were constructed based on differential scanning calorimetry (DSC) measurements. Discrete anions: [PbCl4](2-) and [PbCl3](-), were detected in the liquid state. The trichloroplumbate(II) anion was shown to have a flexible structure due to the presence of a stereochemically-active lone pair. The relationship between the liquid phase anionic speciation and the structure of the corresponding crystalline products of ionothermal syntheses was discussed, and the data were compared with analogous tin(II) systems.

Novel 3D bismuth-based coordination polymers: Synthesis, structure, and second harmonic generation properties

Two new 3D bismuth containing coordination polymers are reported along with their single crystal structures and SHG properties. Compound 1: Bi2O2(pydc) (pydc=pyridine-2, 5-dicarboxylate), crystallizes in the monoclinic, polar space group, P21 (a=9.6479(9)Å, b=4.2349(4)Å, c=11.9615(11)Å, β=109.587(1)°), which contains Bi2O2 chains that are connected into a 3D structure via the pydc ligands. Compound 2: Bi4Na4(1R3S-cam)8(EtOH)3.1(H2O)3.4 (1R3S cam=1R3S-camphoric acid) crystallizes in the monoclinic, polar space group, P21 (a=19.0855(7)Å, b=13.7706(5)Å, c=19.2429(7)Å, β=90.701(1)°) and is a true 3D coordination polymer. These are two example of SHG compounds prepared using unsymmetric ligands (compound 1) or chiral ligands (compound 2), together with metals that often exhibit stereochemically-active lone pairs, such as Bi3+, a synthetic approach that resulted in polar, non-centrosymmetric, 3D metal-organic coordination polymer.

Magnetoelectric Ordering of BiFeO3 from the Perspective of Crystal Chemistry

In this paper we examine the role of crystal chemistry factors in creating conditions for formation of magnetoelectric ordering in BiFeO3. It is generally accepted that the main reason of the ferroelectric distortion in BiFeO3 is concerned with a stereochemical activity of the Bi lone pair. However, the lone pair is stereochemically active in the paraelectric orthorhombic beta-phase as well. We demonstrate that a crucial role in emerging of phase transitions of the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order types belongs to the change of the degree of the lone pair stereochemical activity - its consecutive increase with the temperature decrease. Using the structural data, we calculated the sign and strength of magnetic couplings in BiFeO3 in the range from 945 C down to 25 C and found the couplings, which undergo the antiferromagnetic-ferromagnetic transition with the temperature decrease and give rise to the antiferromagnetic ordering and its delay in regard to temperature, as compared to the ferroelectric ordering. We discuss the reasons of emerging of the spatially modulated spin structure and its suppression by doping with La3+.

Crystal Chemistry Search of Multiferroics with the Stereochemically Active Lone Pair

On the basis of our previous studies of magnetoelectric ordering of BiFeO3, TbMnO3, TbMn2O5 and BiMn2O5 we formulate the crystal chemistry criteria for the search of multiferroics and reveal potential multiferroics Pb2Cu(OH)4Cl2, Pb5Cr3F19, Mn(SeO3){\dot}H2O and BiPbSr2MnO6 each containing the ion with a lone pair.

The synthesis and reaction chemistry of new amino-functionalised tin(ii) alkoxides

Sn(ii) derivatives of the aminoalcohols (t)Bu(H)NC(Me)(H)CH(2)OH (Htbap, ), (R(1)R(2)NCH(2))(2)C(H)OH (R(1) = R(2) = Me, , Hbdmap; R(1) = (t)Bu, R(2) = H, , Hbtbap), (R(1)R(2)NCH(2))(3)COH (R(1) = R(2) = Me, , Htdmap; R(1) = (t)Bu, R(2) = H, , Httbap) have been synthesised by reaction of the alcohol with Sn[N(SiMe(3))(2)](2). The structures of the ligands , .H(2)O, along with Sn(ttbap)(2) have been determined; the latter is pseudo-trigonal bipyramidal with nitrogen atoms in axial sites and oxygen atoms and a stereochemically-active lone pair in the equatorial positions. Sn(ttbap)(2) reacts with Fe(2)(CO)(9) in 2 : 1 ratio (Sn : Fe = 1 : 1) to afford the donor-acceptor complex (ttbap)(2)Sn:-->Fe(CO)(4), while in 1 : 1 ratio (Sn : Fe = 1 : 2) the Sn(0) complex (Httbap)Sn[Fe(CO)(4)](2) is formed, in which Httbap is a neutral zwitterionic form of the ligand. The structures of both bimetallic species are reported. Thermal decomposition of (Httbap)Sn[Fe(CO)(4)](2) under low-pressure CVD conditions gives a film containing a mixture of cubic-Sn, cubic-Fe and the hexagonal intermetallic phase Fe(3)Sn.

Subtle Interplay of Weak Intermolecular Interactions. Crystal Structures of Lead(II) Complexes with 4,4′‐Dimethyl‐2,2′‐bipyridine

AbstractThree adducts of the N,N′‐bidentate aromatic base 4,4′‐dimethyl‐2,2′‐bipyridine (dmbpy) of lead(II) salts, [Pb(dmbpy)2(NO3)2] (1), [Pb(dmbpy)2(ClO4)2] (2) and [Pb(dmbpy)(NCS)2]n (3) have been synthesized and characterized by elemental analysis, IR, 1H‐NMR and 13C‐NMR spectroscopy and studied by thermal analysis as well as X‐ray crystallography. The single‐crystal structures of these complexes show that the 6s electrons of lead(II) constitute a stereochemically active lone pair (SALP). The coordination numbers of the PbII ions are eight and seven, respectively. The supramolecular features in these complexes are guided/controlled by weak directional intermolecular interactions.

Structural and Spectroscopic Impact of Tuning the Stereochemical Activity of the Lone Pair in Lead(II) Cyanoaurate Coordination Polymers via Ancillary Ligands

The reaction of Pb(ClO4)2 x xH2O, an ancillary ligand L, and two equivalents of Au(CN)2(-) gave a series of crystalline coordination polymers, which were structurally characterized. The ligands were chosen to represent a range of increasing basicity, to influence the stereochemical activity (i.e., p-orbital character) of the Pb(II) lone pair. The Pb(II) center in [Pb(1,10-phenanthroline)2][Au(CN)2]2 (1) is 8-coordinate, with a stereochemically inactive lone pair; all 8 Pb-N bonds are similar. The Au(CN)2(-) units propagate a 2-D brick-wall structure. In [Pb(2,2'-bipyridine)2][Au(CN)2]2 (2), the 8-coordinate Pb(II) center has asymmetric Pb-N bond lengths, indicating moderate lone pair stereochemical activity; the supramolecular structure forms a 1-D chain/ribbon motif. For [Pb(ethylenediamine)][Au(CN)2]2 (3), the Pb(II) is only 5-coordinate and extremely asymmetric, with Pb-N bond lengths from 2.123(7) to 3.035(9) A; a rare Pb-Au contact of 3.5494(5) A is also observed. The Au(CN)2(-) units connect the Pb(ethylenediamine) centers to form 1-D zigzag chains which stack via Au-Au interactions of 3.3221(5) A to yield a 2-D sheet. (207)Pb MAS NMR of the polymers indicates an increase in both the chemical shielding span and isotropic chemical shift with increasing Pb(II) coordination sphere anisotropy (from delta iso = -2970 and Omega = 740 for 1 to delta iso = -448 and Omega = 3980 for 3). The shielding anisotropy is positively correlated with Pb(II) p-character, and reflects a direct connection between the NMR parameters and lone-pair activity. Solid-state variable-temperature luminescence measurements indicate that the emission bands at 520 and 494 nm, for 1 and 2, respectively, can be attributed to Pb --> L transitions, by comparison with simple [Pb(L)2](ClO4)2 salts. In contrast, two emission bands for 3 at 408 and 440 nm are assignable to Au-Au and Pb-Au-based transitions, respectively, as supported by single-point density-functional theory calculations on models of 3.

1,4,6,9‐Tetraoxa‐5λ4‐selena‐spiro[4.4]nonane – A Combined Theoretical and Experimental Study

AbstractThe symmetric spiro‐selenurane derived from ethylene glycol, 1,4,6,9‐tetraoxa‐5λ4‐selena‐spiro[4.4]nonane, was prepared from selenium tetrachloride and ethylene glycol and its molecular structure was determined by single crystal X‐ray diffraction. NBO analyses for the title compound and a related compound were conducted to assess the role of the stereochemical active lone pair on the selenium atom on the structure.