Variation Of Coordination Number Research Articles

Variable co-ordination numbers in 1∶1 adducts of silver(I) tetrakis(pyrazolyl)borates with tertiary phosphines

Silver(I) derivatives containing tertiary phosphines and anionic tetrakis(pyrazol-1-yl)borates were prepared from AgO3SCF3, PR3 (R = phenyl, benzyl, cyclohexyl, 2,4,6-Me3C6H2, o-, m- or p-tolyl) or PPh2R′ (R′ = methyl or ethyl) and K[B(pz)4] or K[B(mpz)4] (Hpz = pyrazole, Hmpz = 3-methylpyrazole) and characterized through analytical and spectral (IR, 1H, 13C and 31P NMR) measurements. These compounds are stable, soluble in chlorinated solvents, and non-electrolytes in CH2Cl2 and acetone. Room-temperature single-crystal structural characterizations were made for several of them. The pyrazolyl ligand is potentially maximally tridentate, and the maximally four-co-ordinate array about the silver potentially of threefold symmetry (excepting the fourth pz moiety) where the symmetry of the phosphine permits. The variation in the silver(I) co-ordination number and environment in various combinations of various degrees of steric interaction among the above entities has been explored. The reactivity of [{AgB(pz)4}{P(C6H4Me-m)3}] and [{AgB(pz)4}{P(C6H4Me-o)3}] towards unidentate N-, S- and P-donors was also investigated.

Strong and weak solvation steric effects on lanthanoid(III) ions in N,N-dimethylformamide–N,N-dimethylacetamide mixtures

Structural parameters of solvated neodymium(III), gadolinium(III), thulium(III) and ytterbium(III) ions in N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA) and their mixtures have been obtained by an extended X-ray absorption fine structure (EXAFS) method. It revealed that the metal–oxygen bond length is shortened and the coordination number is thus decreased with increasing DMA content in the mixture. Interestingly, the decrease in the coordination number takes place evidently at a lower DMA content for the thulium(III) ion than the neodymium(III) ion, i.e., the geometry change is more favorable for the metal ion with a smaller ionic radius. 89Y NMR chemical shifts also demonstrate that the coordination number decreases with increasing DMA content in the mixture, and the profile of varying coordination number is similar to that for the thulium(III) ion. This indicates that the strong solvation steric effect operates with both thulium(III) and yttrium(III) ions in the DMF–DMA mixture. Variations of metal–oxygen bond length for other metal systems in the mixture indicate that, relative to the thulium(III) ion, the gadolinium(III) ion experiences a less strong solvation steric effect, and the neodymium(III) ion even less. Structural parameters have also been determined for a series of lanthanoid(III) ions in both DMF and DMA. The LnIII–O bond length in DMA is generally shorter than that in DMF, and the difference is smallest for the lanthanum(III) ion, and largest for the lutetium(III) ion. The difference is thus larger for a metal ion with a smaller ionic radius, implying that the solvation steric hindrance is enhanced with decreasing ionic radius.

Crystal Structure of N,N-Dimethylthioformamide Solvates of the Divalent Group 12 Ions with Linear Coordination Geometry for Mercury(II), Tetrahedral for Zinc(II), and Octahedral for Cadmium(II).

The crystalline solvates of the divalent group 12 metal ions with the soft sulfur donor N,N-dimethylthioformamide display an unusual variation in coordination number and geometry with two, four, and six ligands attached to the mercury(II), zinc(II), and cadmium(II), ions, respectively. Bis(N,N-dimethylthioformamide)mercury(II) perchlorate precipitates from acetonitrile solution when adding less than 2 equiv of N,N-dimethylthioformamide, while the zinc and cadmium solvates crystallize from saturated N,N-dimethylthioformamide solutions. The disolvate [Hg(SCHN(CH(3))(2))(2)](ClO(4))(2) crystallizes in the monoclinic space group P2(1)/n (No. 14) with a = 6.208(1) Å, b = 15.239(7) Å, c = 8.681(2) Å, beta = 99.30(3) degrees, and Z = 2. Centrosymmetric mercury(II) complexes with strong collinear bonds to two N,N-dimethylthioformamide molecules, Hg-S 2.350(2) Å, are joined by double bridges of perchlorate ions in chains along the a-axis by four weak interactions between the mercury and the perchlorate oxygen atoms, mean Hg-O distance 2.84 Å. Tetrakis(N,N-dimethylthioformamide)zinc trifluoromethanesulfonate, [Zn(SCHN(CH(3))(2))(4)](CF(3)SO(3))(2), crystallizes in the triclinic space group P&onemacr; (No. 2) with a = 10.487(3) Å, b = 12.910(3) Å, c = 13.489(5) Å, alpha = 68.800(4) degrees, beta = 69.260(4) degrees, gamma = 74.06(1) degrees, and Z = 2, with the zinc ions tetrahedrally surrounded by four N,N-dimethylthioformamide ligands, mean Zn-S distance 2.34 Å. Also the cadmium solvate of corresponding composition, [Cd(SCHN(CH(3))(2))(4)(CF(3)SO(3))(2)], crystallizes in the space group P&onemacr;, with a = 8.670(1) Å, b = 9.529(1) Å, c = 10.685(1) Å, alpha = 75.20(1) degrees, beta = 66.97(1) degrees, gamma = 65.31(1) degrees, and Z = 1, although the structure comprises centrosymmetric tetrakis(N,N-dimethylthioformamide)bis(trifluoromethanesulfonato)cadmium(II) complexes in which four Cd-S bonds (mean 2.65 Å) and two weaker Cd-O bonds at 2.470(2) Å to the trifluoromethanesulfonate ions give rise to a pseudo-octahedral coordination around the cadmium ion. When using perchlorate instead as counterion, hexakis(N,N-dimethylthioformamide)cadmium perchlorate, [Cd(SCHN(CH(3))(2))(6)](ClO(4))(2), crystallizes in the space group P2(1)/n with a = 12.757(1) Å, b = 7.4681(6) Å, c = 19.732(2) Å, beta = 96.31(1) degrees, and Z = 2. The mean Cd-S bond distance increases to 2.715 Å in the fully solvated cadmium ion with almost regular octahedral coordination geometry to its six centrosymmetrically related ligands. The effect of the weak internal hydrogen bonding occuring between the hydrogen atom of a -CHS group and the sulfur atom of neighboring N,N-dimethylthioformamide ligands is discussed.

The Biological and Medicinal Chemistry of Bismuth

AbstractBismuth compounds have been widely used in medicine for more than 200 years, and new bismuth‐containing drugs are now being developed. However the biological chemistry of bismuth is poorly understood. We review here methods for the study of bismuth compounds, and use of Bi(III) in antiulcer, antibacterial, anti‐HIV and radiotherapeutic agents is described. The chemistry of Bi(III) carboxylates and aminocarboxylates is dominated by intermolecular interactions which lead to polymeric structures. Bi(III) exhibits a highly variable coordination number and coordination geometry, and alkoxide ligands can induce a strong stereochemical “lone‐pair effect”. Bi(III) can bind to both Zn(II) sites (e.g. metallothionein) and Fe(III) sites (e.g. transferrin) in proteins. Further work is needed to understand the relationship between the structures and dynamics of bismuth compounds and their bioactivity.

X-ray absorption study of Ti-bearing silicate glasses

Ti K-edge XANES spectra have been collected on a series of Ti-bearing silicate glasses with metasilicate and tetrasilicate compositions. The intensity of the preedge feature in these spectra has been found to change with glass composition and varies from 29 to 58% (normalized intensity) suggesting a variation in structural environent around the absorbing atom. The pre-edge peak intensity increases for the alkali titanium tetrasilicate glasses from 35% to 58% in the order Li < Na < K < Rb, Cs whereas for the metasilicate compositions there is a maximum for the K-bearing glass. The pre-edge peak intensity remains constant for the alkaline earth titanium metasilicate glasses, Ca and Sr (34%) but increases slightly for Ba (41%). As the intensity of this feature is inversely correlated with coordination number, a comparison of the pre-edge intensity data for the investigated glasses with those of materials of known coordination number leads us to establish a regression equation and to infer that the average coordination number of Ti in these glasses ranges from 4.8 to 5.8. Large alkali cations appear to stabilize a relatively low average coordination number for Ti in silicate melts. The Ti structural environment results appear also to vary as a function of SiO2 content within the K2O-TiO2-SiO2 system. A number of physical properties of the melts from which these glasses were quenched and of other Ti-bearing silicate melts, have been determined in recent years. Clear evidence of a variable coordination number of Ti, consistent with the interpretation of the present XANES data is available from density measurements. These and other property determinations are compared with the present spectroscopic observations in an attempt to relate structure and properties in these melts which contain a major component with variable coordination number.

Solvation Structures of Manganese(II), Iron(II), Cobalt(II), Nickel(II), Copper(II), Zinc(II), Cadmium(II), and Indium(III) Ions in 1,1,3,3-Tetramethylurea As Studied by EXAFS and Electronic Spectroscopy. Variation of Coordination Number

The structures of solvated complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and In(III) ions in 1,1,3,3-tetramethylurea (TMU) have been determined by means of EXAFS (extended X-ray absorption fine structure) and electronic spectroscopy. The solvation structures in TMU are square pyramidal for the Mn(II) and Ni(II) ions, distorted tetrahedral for the Co(II) and Cu(II) ions, tetrahedral for the Zn(II) ion, and octahedral for the Cd(II) and In(III) ions, while in water all these metal ions are six-coordinated octahedrons. The solvation structure of Fe(II) ion is square pyramidal or trigonal bipyramidal. In the bulky TMU solvent, the coordination number should be reduced for relaxation of the sterically repulsive interaction around the solvated metal ions

Potassium triphenylsiloxide “-ate” compounds of tin(II): Molecular and separated ion forms and variable potassium coordination numbers

Neutral bis-silyloxidetin(II) dimers [Sn(OSiPh 3)(μ-OSiPh 3)] 2 ( 1) and [Sn{OSi( tBu)Me 2}{μ-OSi( tBu)Me 2}] 2 ( 2) were synthesized in one step from [Sm{N(SiMe 3) 2} 2] and 2 equiv. of silanol. Complexes 1 and 2 were characterized by IR, NMR ( 1H, 13C and 119Sn) and combustion analysis. The bis-triphenylsilyloxidetin(II) dimer [Sn(OSiPh 3 (μ-OSiPh 3)] 2 ( 1) reacted with 2 equiv. of [K(THF) n (OSiPh 3)], followed by crystallization from dimethoxyethane (DME) to afford [K(DME) 2Sn(μ-OSiPh 3) 3] ( 3). 1H NMR studies on [K(DME) 2Sn(μ-OSiPh 3) 3] demonstrated that this complex was kinetically labile on the NMR time-scale with respect to exchange with free, added DME. Single crystal X-ray diffraction studies revealed that [K(DME) 2Sn(μ-OSiPh 3) 3] exists in two crystalline states which formed under apparently identical conditions. Structure determinations showed Sn(μ-OSi Ph 3) 3K units with K + further coordinated by two bidentate DME ligands (monoclinic form) or by one bidentate and one monodentate DME (triclinic form). Crystal data : Monoclinic (at −135°C): a = 13.904(3), b = 22.431(5), c = 19.200(4) Å, β = 102.23(1)°, with Z = 4 in space group P2 1/ n. Triclinic (−154°C): a = 21.250(4), b = 22.258(5), c = 13.271(3) Å, α = 93.26 (1)°, β = 104.44(1)°, γ = 75.79(1)° with Z = 4 in space group P 1 . Reaction of [Sn(OSiPh 3)(μ-OSiPh 3)] 2 with 2 equiv. of [K(18-crown-6)(OSiPh 3)] in toluene gave [K(18-crown-6)(η 2-toluene) 2][K(18-crown-6){Sn(OSiPh 3) 3} 2] ( 4) in high yields. An X-ray diffraction study revealed a salt-like formulation [(η 2-toluene) 2K + (18-crown-6)][{(Ph 3SiO) 3Sn} 2K(18-crown-6) −]. Crystal data (at −155°C): a = 13.850(4), b = 18.510(5), c = 27.475(7) Å, β = 102.47(1)° with Z = 2 (asymmetric units) in space group P2 1/ c. Similarly, [Sn{OSi( tBu)Me 2}{μ-OSi( tBu)Me 2}] 2 ( 2) reacted with 2 equiv. of [K(OSiMe 2 tBu)] n, in toluene to give [KSn(μ-OSiMe 2 tBu) 3] ( 5) as a crystalline solid in good yields. The electronic structure, geometry and nucleophilicity of the model anion, Sn(OH) 3 −, have been probed using Fenske-Hall methods.

Copper(I) hemocyanin models: variable coordination number and distorted geometries in benzimidazole chelates

Dinuclear copper (I) complexes derived from three benzimidazole-containing binucleating ligands are described within the context of synthetic models for deoxyhemocyanin and carbon monoxyhemocyanin. The neutral, potentially septadentate ligand HL-Et, which contains bis((1-ethyl-2-benzimidazolyl) methyl) moieties at both ends of a 2-hydroxypropylenediamine spacer, forms the CO complex [Cu 2 (HL-Et)(CO) 2 ][CF 3 SO 3 ] 2 (1) and the acetonitrile complex [Cu 2 (HL-Et)(MeCN) 2 ] [CF 3 SO 3 ] 2 (2). The related tetrakis (1-methylbenzimidazole)-containing ligand HCAB-Me, having a 2,6-disubstituted cresol spacer, forms the acetonitrile complex [Cu 2 (HCAB-Me)(MeCN) 2 ][CF 3 SO 3 ] 2 (3). The unalkylated benzimidazole analogue of HL-Et, HL-H, forms the acetonitrile complex [Cu 2 (HL-H)(MeCN) 2 ][ClO 4 ] 2 1 / 3 Et 2 O (4) and the CO complex [Cu 2 (HL-H)(CO) 2 ][BF 4 ] 2 (5). Complexes 1-4 have been characterized by X-ray crystallography. Crystal data: 1, C 47 H 50 N 10 O 9 Cu 2 F 6 S 2 , triclinic, P1, a = 16.616 (8) A, b = 11.884 (5) A, c = 15.131 (4) A, α = 106.69 (3)˚, β = 83.25 (3)˚, γ = 110.75 (4)˚, Z = 2; 2, C 49 H 56 N 12 O 7 Cu 2 F 6 S 2 , orthorhombic, Pbcn, a = 15.473 (5) A, b = 16.369 (9) A, c = 44.178 (17) A, Z = 8; 3, C 51 H 51 O 7 Cu 2 F 6 S 2 , triclinic, P1, a = 14.20 (1) A, b = 13.39 (1) A, c = 15.31 (1) A, α = 104.52 (6)˚, β = 76.08 (7)˚, γ = 90.71 (8)˚, Z = 2; 4, C 39 H 40 N 12 O 9 Cu 2 Cl 2 1 / 3 C 4 H 10 O, monoclinic C2/c, a = 28.710 (9) A, b = 7.600 (2) A, c = 21.857 (9) A, β = 114.23 (3)˚

Structure of alkali borate glasses based on the chemical equilibrium concept

The structure of alkali borate glass has been simulated based on a chemical equilibrium concept among possible structural units. The structural units assumed include boroxol ring, diborate, triborate, di-triborate, metaborate, pyroborate, orthoborate units, “loose” BO 3 triangles, and “loose” BO 4 tetrahedra. As a first step, only one equation was used, and then the number of equations was increased so as to be able to obtain a best fit to the experimental data. It was found that equilibrium constants were almost unanimously determined by a trial and error technique. Assuming ten equilibrium equations and equilibrium constants, it was shown that the variation of coordination number of boron atoms and that of bridging and non-bridging oxygens in the glass as a function of alkali concentration can be reproduced in good agreement with the NMR data and Raman spectra.

Etude par RMN de la conductivite ionique dans Li 3ThF 7: comparaison entre materiau cristallise et amorphe

A 7Li and 19F NMR study allowed comparison over the temperature range 273-400K of the ionic conductivity of the two materials: crystalline Li 3ThF 7 and the Li 0.75Th 0.25F 1.75 glass which have the same LiF/ThF 4 ratio. Fluorine diffusion is not observed in the crystalline sample while the flourine mobility in the glass can be explained by the variable coordination number of thorium (8.5 to 9.5) and by the numerous breaks in the |ThF 9| polyhedra layers. The lithiums are mobile in the two phases, this phenomenon occuring about 35°C higher in Li 3ThF 7. Discussion of the diffusion process is based on knowledge of the Li 3ThF 7 structure.

Optical Absorption Spectra of Ni&lt;sup&gt;2+&lt;/sup&gt; Ions and IR Spectra in (100-&lt;i&gt;x&lt;/i&gt;) (PbO⋅GeO&lt;sub&gt;2&lt;/sub&gt;)⋅&lt;i&gt;x&lt;/i&gt;RO (R=Mg, Ca, Sr, Ba) Glasses

Optical absorption spectra of Ni2+ ion (100-x) (PbO⋅GeO2)⋅xRO⋅0.2wt% NiO glasses are measured, and the results are obtained as follows.The value of 10Dq which represents the intensity of the ligand field shifts toward higher wave number with increasing alkaline earth metal content. The increasing intensity of the ligand field is considered to be the formation of GeO68-, where the glass network was destroyed by alkaline earth metals. In this study, the ν4 peak appears only at 20mol% BaO, which represents a Ni2+ ion with 4-coordination. In other systems the ν4 peak does not appear clearly. It is considered that the Ni2+ ion does not become 4-coordination.According to the measurements of infrared spectra, most of this system consists of Ge6 groups, and the variation of coordination number of Ge with the alkaline earth metal contents hardly appear.

Vibrational Characteristics and Structure of Heavy Metal Fluoride Glasses Containing Thorium and Zirconium

This paper reports a vibrational spectroscopic study of a series of glasses composed of Li-Ba-Th-Zr-fluoride in which Th/sup 4 +/ is progressively replaced by Zr/sup 4 +/. In these glasses, Zr/sup 4 +/ shows a more pronounced variation in coordination number than previously observed. Distinct infrared reflectance and polarized Raman bonds due to Th/sup 4 +/ polyhedra are present only in the glasses containing less than 10 mole% ZrF/sub 4/. In the glasses containing 10 or more mole% ZrF/sub 4/, Raman and infrared bands due to Zr/sup 4 +/ polyhedra dominate the vibrational spectra, even in glasses where the ThF/sub 4/ concentration is greater than the ZrF/sub 4/ concentration. The difference in structural behavior or the Th/sup 4 +/ polyhedra as compared to the Zr/sup 4 +/ polyhedra is believed to be due to the smaller electric field intensity of the Th/sup 4 +/ and to the relatively restricted ability of Th/sup 4 +/ to vary its coordination number in response to the availability of F/sup 1 -/.

Ammonium uranyl carbonates - Complex compounds with variable coordination number?

A series of ammonium uranyl carbonate (AUC) solid samples were prepared. Their chemical composition varied systematically and corresponded to the formula (NH4)x[UO2(CO3)y] with molar coefficients from x = 4.0 and y = 3.0 to 1.1 and 1.3, resp. The first samples of this series, with x in the range 4.0-2.7 and y in the range 3.0-2.3, revealed identical IR spectra as well as X-ray patterns, in contrast to the other ones. A reliable explanation of this fact is not at hand, one of the possibilities being the variable coordination number of the uranyl central ion. IR spectra of AUC and its sodium analogue were confronted, too, with the conclusion that architecture of both complexes is the same but with distinct quantitative differences.

Structure and bonding in the metal complexes of ethylenediaminetetra-acetic acid

The metal-ion complexes of ethylenediaminetetra-acetic acid (EDTA) find widespread use not only in analysis, but also in foodstuffs, pharmacy, and medicine. A review of the structures of the solid complexes illustrates the considerable variation in co-ordination number of the metal-ion, and the possible denticities of EDTA. These data are relevant to the solid-state properties and also to the structures of the complexes in solution, which cannot be directly determined.

Electronic structure of disordered binary alloys

Presents an extension of the cluster-Bethe-lattice method to study the electronic properties of binary alloys with varying coordination numbers. Expressions for transfer functions which account for neighbour correlations are obtained. The method is applied to study effects of short-range order in the CsAu liquid alloy and in a hypothetical solid with one s-state per atom, and the coordination properties of the Si-O system.

Some interesting aspects of the extraction of zinc

Abstract

On Coordination Number "Eight" and the Variable Coordination Number, by Alfred Werner

Research Article| January 01 1967 On Coordination Number "Eight" and the Variable Coordination Number, by Alfred Werner George B. Kauffman George B. Kauffman Search for other works by this author on: This Site PubMed Google Scholar Chymia (1967) 12: 221–232. https://doi.org/10.2307/27757284 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation George B. Kauffman; On Coordination Number "Eight" and the Variable Coordination Number, by Alfred Werner. Chymia 1 January 1967; 12 221–232. doi: https://doi.org/10.2307/27757284 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentHistorical Studies in the Natural Sciences Search This content is only available via PDF. Copyright 1967 Trustees of the University of Pennsylvania Article PDF first page preview Close Modal You do not currently have access to this content.