Showing papers in "Inorganic Chemistry in 1990"

Electrochemical parametrization of metal complex redox potentials, using the ruthenium(III)/ruthenium(II) couple to generate a ligand electrochemical series

Abstract: : A ligand electrochemical parameter, El (L), is described to generate a series which may be used to predict M(n)/M(n-1( redox potentials by assuming that all ligand contributions are additive. In this fashion it performs a similar purpose to the Dq parameter in electronic spectroscopy. The parameter is defined as 1/6 that of the Ru(III)/Ru(II) potential for species RuL6 in acetontrile. The El(L) values for over 200 ligands are presented and the model is tested over a wide range of coordination complexes and organometallic species. The redox potential of a M(n)/M(n-1) couple is defined to be equal to:- E(calc) = f Sigma EL (L) + c. The values of f and C, which are tabulated, depend upon the metal and redox couple, and upon spin state and stereochemistry, but, in organic solvents, are generally insensitive to the net charge of the species. Consideration is given to synergism, the potentials of isomeric species, and the situations where the ligand additivity model is expected to fail. In this initial study, the redox couples are restricted almost exclusively to those involving the loss or addition of an electron to the tzg (in Oh) sub-level.

Anion-exchange reactions of layered double hydroxides

Abstract: Layered double hydroxides are antitypes of 2/1 clay minerals. In spite of a high surface charge density, as in micas, they react easily with various types of organic anions. Short- and long-chain anions are rapidly exchanged for the inorganic interlayer anions, and high degrees of reaction are attained. The pronounced preference of primary long-chain compounds as typical of the more highly charged clay minerals is not observed. The small equivalent area forces the alkyl chain compounds (fatty acid anions, dicarboxylates, alkyl sulfates) to point away from the interlamellar surfaces and to form monomolecular films of high regularity

From semiconductor-semiconductor transition (42 K) to the highest-Tc organic superconductor, κ-(ET)2Cu[N(CN)2]Cl (Tc = 12.5 K)

Abstract: The discovery of an organic superconductor with the highest transition temperature (125 K) recorded following the suppression of a semiconductor-semiconductor transition (42 K) is reported. The reported compound is a kappa-phase superconductor, kappa-(ET){sub 2}Cu(N(CN){sub 2})Cl, which is isostructural with the recently prepared ambient-pressure superconductor kappa-(ET){sub 2}Cu(N(CN){sub 2})Br with a transition temperature of 11.5 K that has been previously reported. Band electronic structural calculations show the newly discovered compound to be a two-dimensional metal. 15 refs., 2 figs.

Luminescence studies of pyridine .alpha.-diimine rhenium(I) tricarbonyl complexes

Abstract: The room- and low-temperature luminescences of ReL(CO){sub 3}X where L = 2,2{prime}-bipyridine, 1,10-phenanthroline, or 5-phenyl-1,10-phenanthroline and X = substituted pyridine or quinoline were studied. Relatively small but useful variations in the state energies can be effected by altering the Hammett {sigma} values of substituents on the pyridines. All complexes exhibit metal to ligand charge-transfer (MLCT) phosphorescences at room temperature. However, by choice of suitable ligands, the emissions can be switched to ligand-localized phosphoresecence on cooling to 77 K. This behavior is explained on the basis of the proximity of the lowest MLCT and {pi}-{pi}{sup *} triplet states and the changes in energy of the MLCT state as a function of temperature. At room temperature the MLCT state can equilibrate to an energy that is lower than that of {sup 3}{pi}-{pi}{sup *} state and give MLCT luminescence. In rigid low-temperature media, however, the MLCT state cannot relax during the excited-state decay and emission is from the lower energy {sup 3}{pi}-{pi}{sup *} state. At room temperature, lifetimes are predominantly affected by alterations in the nonradiative rate constant, as described by the energy-gap law. From {sigma} values of the substituents, both state energies and lifetimes can be predicted before synthesis. The design ofmore » new luminescent complexes is discussed. 25 refs., 6 figs., 2 tabs.« less

Luminescent and redox-reactive building blocks for the design of photochemical molecular devices: mono-, di-, tri-, and tetranuclear ruthenium(II) polypyridine complexes

Abstract: The syntheses, characterization, absorption spectra, luminescence spectra, luminescence lifetimes, and electrochemical behavior of 16 mono-, di-, tri-, and tetrametallic ruthenium(II) polypyridine complexes have been investigated. The general formulas of the complexes studied are RuL 2 (BL) 2+ , L 2 Ru(μ-BL)RuL 2 4+ , LRu(μ-BL)RuL 2 ] 2 6+ , and Ru[(μ-BL)RuL 2 ] 3 8+ , where L=2,2'-bipyridine or 2,2'-biquinoline and BL=2,3- or 2,5-bis(2-pyridyl)pyrazine

New hexaaza macrocyclic binucleating ligands. Oxygen insertion with a dicopper(I) Schiff base macrocyclic complex

Abstract: Direct 2:2 condensation of isophthalaldehyde with diethylenetriamine produces a hexaaza 24-membered macrocyclic tetra Schiff base in good yield. The crystal structure of an isomeric form of the Schiff base is reported. The amber binuclear Cu(I) complex of the tetraaza macrocyclic Schiff base combines with a molar equivalent of dioxygen to form a green binuclear Cu(II) complex, wich contains a bridging hydroxide ion and, by oxygen insertion, a bridging phenolate donor

Alcohol adducts of alkoxides: intramolecular hydrogen bonding as a general structural feature

Abstract: Characterization of Zr{sub 2}(O{sup i}Pr){sub 8}({sup i}PrOH){sub 2} by {sup 1}H and {sup 13}C NMR spectroscopy, ir spectroscopy, and single-crystal x-ray diffraction ({minus}100{degree}C) is reported. The unit cell contains four half-dimers in the asymmetric unit, all of which differ only in the rotational conformation about Zr-O and O-C bonds. In each dimer, the edge-shared bioctahedron has two {mu}-O{sup i}Pr groups. On opposite sides of this Zr{sub 2}({mu}-OR){sub 2} plane, each dimer forms two hydrogen bonds, one each between a coordinated alcohol and a terminal alkoxide. The NMR spectra at 25{degree}C are so simple as to be structurally uninformative, a result of rapid fluxionality which includes, as one component, proton migration among all O{sup i}Pr units. At {minus}80{degree}C in toluene, the NMR spectra are now too complex to be accounted for by a single edge-shared bioctahedral structure. The hafnium analogue is isomorphous with the zirconium compound. Although Ce{sub 2}(O{sup i}Pr){sub 8}({sup i}PrOH){sub 2} is not isomorphous, it exhibits an analogous hydrogen-bonded structure in which the O{hor ellipsis}O distance is as short as it is in the Zr analogue, in spite of a metal-metal separation which is longer by 0.28 {angstrom}. The generality of hydrogen bonding between M-OR and M-O(H)R groups whenmore » they are aligned parallel in a metal cluster is reviewed. 44 refs., 2 figs., 4 tabs.« less

AM1 parameters for sulfur

Abstract: AM1 has been parametized for sulfur. Calculations are reported for a wide range of sulfur-containing molecules. The calculated heats of formation and other properties of organosulfur molecules are much superior to those from MNDO and superior overall to those from PM3. AM1 calculations for several reactions agree well which experimental values. The results for compounds of sulfur in its higher valence states are also satisfactory, except for SF 4 , where the error is probably due to the neglect of d AOs

Structures and Properties of Dibridged ( μ -Oxo)diiron(III) Complexes. Effects of the Fe-O-Fe Angle

Abstract: A series of (μ-oxo)diiron(III) complexes of tris(2-pyridylmethyl)amine (TPA), [Fe 2 (TPA) 2 O(L)](CIO 4 ) n , were synthesized and characterized where L represents the bridging ligands carbonate, hydrogen maleate, diphenyl phosphate, diphenylphosphinate, maleate, and phthalate. Together with the linear dichloride complex, this series of compounds provides a unique opportunity to systematically study the effects of the Fe-O-Fe angle on the electronic spectral and magnetic properties of the (μ-oxo)diiron(III) core

Linear-chain gadolinium(III) nitronyl nitroxide complexes with dominant next-nearest-neighbor magnetic interactions

Abstract: Gd(hfac) 3 NITiPr (hfac= hexafluoroacetylacetonate; NITiPr-2-isopropyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl3-oxide) crystallizes in the monoclinic space group P2 1 /n with cell parameters a=11.916 (1) A, b=17.625 (9) A, c=18.055 (1) A, β=96.98 (1) o , V=3763.82 A 3 , and Z=4. The structure refinement converged to R=0.086

Synthesis and characterization of a series of novel rhodium and iridium complexes containing polypyridyl bridging ligands: Potential uses in the development of multimetal catalysts for carbon dioxide reduction

Abstract: A series of bis chelate rhodium(III) and iridium(III) complexes containing polypyridyl bridging ligands have been prepared. Complexes of the type (Rh(L){sub 2}Bt{sub 2}){sup +} and (Ir(L){sub 2}Cl{sub 2}){sup +} (where L = 2,2{prime}-bipyrimidine (bpm), 2,3-bis(2-pyridyl)pyrazine (dpp), 2,3-bis(2-pyridyl)quinoxaline (dpq), or 2,3-bis(2-pyridyl)benzoquinoxaline (dpb)) have been prepared, and their syntheses and characterization are reported herein. The complex (Rh(dpq){sub 2}Br{sub 2})(PF{sub 6}){center dot}CH{sub 3}CN and the ligand 2,3-bis(2-pyridyl)quinoxaline have been crystallized and the crystal structures determined. The electrochemical and spectroscopic properties of these novel bridging ligand complexes differ considerably from those of the previously prepared (2,2{prime}-bipyridine)rhodium and iridium complexes. All of the bridging ligands used are easier to reduce than bipyridine. Thus, the complexes reported here are easier to reduce and exhibit electronic transitions at lower energy. A number of these new polypyridyl bridging ligand rhodium and iridium complexes catalyze the reduction of carbon dioxide to formate. Remote nitrogens on the polypyridyl bridging ligand rhodium and iridium complexes catalyze the reduction of carbon dioxide to formate. Remote nitrogens on the polypyridyl bridging ligands make these complexes ideal building blocks for the development of multimetal systems. 35 refs., 7 figs., 10 tabs.

Oxalato-bridged and related dinuclear copper(ii) complexes : theoretical analysis of their structures and magnetic coupling

Abstract: A theoretical analysis of the structural variations found for dinuclear Cu(II) complexes with oxalato and related polynuclear bridging ligands and their influence on the magnitude of the magnetic exchange interactions is presented in this paper. The family of compounds studied can be represented by the general formula [(AA)Cu(μ−C 2 O 4 )Cu(AA)] X n , where AA can be a chelating ligand like 2,2'-bipyridine (bpy) or tetramethylethylenediamine (tmen), and X is a counteranion or a solvent molecule. An evaluation of second-order Jahn-Teller distortions through the analysis of orbital topologies and atomic electronegativities is presented, which might be helpful in predicting how stable a distorted molecule is relative to the undistorted one, as well as the relative extent for such distortions in a series of related structures

Synthesis, characterization, and EPR studies of stable ruthenium(III) Schiff base chloro and carbonyl complexes

Abstract: These complexes are characterized by elemental analysis and IR, UV-visible, differential-pulse polarography, conductivity, magnetic susceptibility, and EPR techniques. The oxidation state of the metal ion in these complexes is confirmed to be +3 by electrochemical, magnetic susceptibility, and EPR measurements

A tetranuclear hydroxo-bridged copper(II) cluster of the cubane type. Preparation and structural and magnetic characterization of tetrakis[(2,2'-bipyridyl)hydroxocopper(II)] hexafluorophosphate

Abstract: The title compound, [Cu(bpy)(OH)] 4 (PF 6 ) 4 , has been synthesized, and its structure has been determined by X-ray crystallographic methods. Crystal data: monoclinic system, space group C2/c

Molecular topology exchange interaction: synthesis and magnetic properties of [Cu(II)3M(II)] (M = cadmium, nickel, manganese) tetranuclear species

Abstract: Three tetranuclear complexes of formulas [{Cu(oxpn)} 3 Cd](NO 3 ) 2 •2H 2 O, [Cu 3 Cd], [{Cu(oxpn)}Ni](ClO 4 ) 2 •2H 2 O, [Cu 3 Ni], and [{Cu(oxpn)} 3 Mn](ClO 4 ) 2 •2H 2 O, [Cu 3 Mn], where oxpn 2− is N,N'-bis(3-aminopropyl) oxamidato have been synthesized. Magnetic susceptibility and EPR measurements in the 4.2-3.00 K temperature range have been carried out for this series of complexes

Photochemical carbon dioxide reduction catalyzed by bis(2,2'-bipyridine)dicarbonylruthenium(2+) using triethanolamine and 1-benzyl-1,4-dihydronicotinamide as an electron donor

Abstract: Irradiation with visible light of a CO{sub 2}-saturated triethanolamine (TEOA)/N,N-dimethylformamide (DMF) solution (1:4 v/v) containing (Ru(bpy){sub 3}){sup 2+} and (Ru(bpy){sub 2}(CO){sub 2}){sup 2+} (bpy = 2,2{prime}-bipyridine) selectively produced HCOO{sup {minus}} with a maximum quantum yield of 14%. On the other hand, the photochemical CO{sub 2} reduction in CO{sub 2}-saturated H{sub 2}O/DMF (1:9 v/v) containing (Ru(bpy){sub 3}){sup 2+}, (Ru(bpy){sub 2}(CO){sub 2}){sup 2+}, and 1-benzyl-1,4-dihydronicotinamide (BNAH) gave not only CO but also HCOO{sup {minus}} with maximum quantum yields of 14.8 and 2.7%, respectively. In those photochemical CO{sub 2} reductions, the luminescent-state (Ru(bpy){sub 3}){sup 2+}* was quenched reductively by TEOA and BNAH, affording (Ru(bpy){sub 3}){sup +}, which functioned as a reductant of (Ru(bpy){sub 2}9co0{sub 2}){sup 2+}, and the change in the main product from HCOO{sup {minus}} in TEOA/DMF to CO in H{sub 2}O/DMF can be explained in terms of the acid-base equilibria among (Ru(bpy){sub 2}(CO){sub 2}){sup 2+}, (Ru(bpy){sub 2}(CO)(C(O)OH)){sup +}, and (Ru(bpy){sub 2}(CO)(COO{sup {minus}})){sup +}. 53 refs., 6 figs., 1 tab.

Uranium(IV) hydrolysis constants and solubility product of UO2.cntdot.xH2O(am)

Abstract: The solubility of UO{sub 2} {times} xH{sub 2}O was examined in dilute solutions at room temperature in the pH range from 2 to 12. Iron powder and Eu{sup 2+} were used to effectively eliminate O{sub 2} and to maintain the possibility of oxidation of U(IV) to U(VI) during the experiments. The UO{sub 2} {times} xH{sub 2}O was found to be amorphous to x-rays, and its solubility, especially at pH values > 4, was found to be 3-4 orders of magnitude lower than previously reported. Values of log K at zero ionic strength for the solubility reaction UO{sub 2} {times} xH{sub 2}O(am) + 3H{sup +} {r equilibrium} UOH{sup 3+} + (x+1)H{sub 2}, and recalculation of values of the first hydrolysis constant from spectrophotometric data reported in the literature were consistent with both the reliable solubility and spectrophotometric data and the thermodynamic properties of other actinides. 23 refs., 4 figs., 2 tabs.

pH dependence of relaxivities and hydration numbers of gadolinium(III) complexes of macrocyclic amino carboxylates

Abstract: In the authors' previous paper, they reported the pH dependence of T[sub 1] relaxivities (R[sub 1], the second-order rate constant that describes the catalytsis of T[sub 1] relaxation by a paramagnetic species) for Gd(III) complexes, and hydration numbers (q, the number of inner-sphere coordinated water molecules) for analogous Tb(III) complexes of the linear amino carboxylic acid ligands: EDTA, HEDTA, EGTA, DTPA, and TTHA. A plot of R[sub 1] vs q values for all the complexes of the linear amino carboxylic acids in monomeric forms gave a straight line with an intercept of 2.2[plus minus]0.1 (mM s)[sup [minus]1] and a slope of 1.6[plus minus]0.1 (mM s)[sup [minus]1] per coordinated water. It was concluded that the intercept represents the outer-sphere relaxivity for these Gd(III) complexes, and the slope represents the estimated contribution of each inner-sphere water to R[sub 1]. To further examine the effect of charge and ligand structure on the relaxation behavior, they have determined the relaxivities and inner-sphere hydration numbers of Gd(III) and Tb(III) complexes of three macrocyclic amino carboxylic acids, i.e., DO3A, HP-DO3A, and DOTA as a function of solution pH. An energy-transfer quenching experiment using Eu(III) and Tb(III) complexes was carried out to detect any marked tendency tomore » form oligomers in these macrocyclic complex solutions. 24 refs., 4 figs., 1 tab.« less