Showing papers in "Inorganic Chemistry in 1996"
TL;DR: New, hydrophobic ionic liquids with low melting points (<−30 °C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophilic anions and thus water-soluble.
Abstract: New, hydrophobic ionic liquids with low melting points (<−30 °C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also described. The molten salts were characterized by NMR and elemental analysis. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1, 2, 3, and 4(5)-positions on these properties was scrutinized. Viscosities as low as 35 cP (for 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide). The hydrophobi...
4,089 citations
TL;DR: All members of the M(II) = Mn series have magnetic susceptibilities showing broad maxima at 55 K characteristic of two-dimensional antiferromagnetism, but the magnetization of several of the salts increases sharply below 27 K due to the onset of spin canting.
Abstract: The synthesis and structural and magnetic characterization of 16 compounds AMIIFeIII(C2O4)3 (A = N(n-C3H7)4, N(n-C4H9)4, N(n-C5H11)4, P(n-C4H9)4, P(C6H5)4, N(n-C4H9)3(C6H5CH2), (C6H5)3PNP(C6H5)3, As(C6H5)4; MII = Mn, Fe) are reported. X-ray powder diffraction profiles are indexed in R3c or its subgroup P6522 or P6/mmm to derive unit cell constants. The structures of all the compounds consist of two-dimensional honeycomb networks [MIIFeIII(C2O4)3-]∞. The MII = Fe compounds behave as ferrimagnets with Tc between 33 and 48 K, but five exhibit a crossover from positive to negative magnetization near 30 K when cooled in a field of 10 mT. The compounds exhibiting this unusual magnetic behavior are those that have the highest Tc. Within the set N(n-CnH2n+1)4FeIIFeIII(C2O4)3 (n = 3−5), Tc increases with interlayer separation and the low-temperature magnetization changes from positive (n = 3) to negative (n = 4, 5). In the M = MnII compounds, the in-plane cell parameter a0 is ∼0.03 A greater than in the correspond...
494 citations
TL;DR: Macrocyclic dicopper(II) complexes derived from 2,6-di(R)formylphenols and various linking diamines are surveyed and their magnetic and structural properties assessed.
Abstract: Macrocyclic dicopper(II) complexes derived from 2,6-di(R)formylphenols and various linking diamines are surveyed and their magnetic and structural properties assessed. For those systems with "flat" dinuclear centers and no electronic perturbations associated with electron-withdrawing ligands or ligand groups, the complexes exhibit a "straight-line" relationship between exchange integral and phenoxide bridge angle. Within the angle range 98.8-104.7 degrees, 11 complexes are included with -2J in the range 689-902 cm(-)(1). When electron-withdrawing species are present, either as ligands or as groups bound to the macrocycle itself, considerable suppression of the antiferromagnetic exchange component is observed. Single-crystal X-ray diffraction studies are reported for three complexes. [Cu(2)(L1)(H(2)O)(2)]F(2)(CH(3)OH)(2) (1) crystallized in the triclinic system, space group Po, with a = 8.1878(5) A, b = 9.0346(7) A, c = 10.4048(7) A, alpha = 103.672(6) degrees, beta = 101.163(5) degrees, gamma = 104.017(5) degrees, and Z = 1. [Cu(2)(L2)Cl(2)] [Cu(2)(L2) (H(2)O)(2)]Cl(ClO(4)).5.5H(2)O (2) crystallized in the monoclinic system, space group P2(1)/n, with a = 14.4305(5) A, b = 24.3149(8) A, c = 18.6584(8) A, beta = 111.282(3) degrees, and Z = 4. [Cu(2)(L3)(H(2)O)(2)](BF(4))(2) (3) crystallized in the triclinic system, space group Po, with a = 8.6127(4) A, b = 8.6321(7) A, c = 10.8430(10) A, a = 74.390(10) degrees, beta = 86.050(10) degrees, gamma = 76.350(10) degrees, and Z = 2. Square pyramidal copper ion stereochemistries are observed in all cases, with axially coordinated halogens or water molecules. Strong antiferromagnetic exchange is observed for all complexes (-2J = 784(8) cm(-)(1), Cu-O-Cu 103.65(10) degrees (1); -2J = 801(11) cm(-)(1), Cu-O-Cu 102.4(3), 107.5(3), 102.9(3), 106.1(3) degrees (2); -2J = 689(3) cm(-)(1), Cu-O-Cu 98.8(4) degrees (3)). The presence of electron-withdrawing CN groups on the periphery of the macrocyclic ligand leads to substantially reduced antiferromagnetic exchange.
356 citations
TL;DR: In this article, the monometallic complexes (bpy 2Ru(tpphz)Ru(NH3)4]4] 4+ (6) and bpy 2 Ru(Tpphz)-TppH 2+ (5) were obtained by reaction of 5,6-diamino-1,10-phenanthroline with [(bpy)2M(phendione)]2+ (M = RuII or OsII), where tpphz is the poorly soluble fully aromatic tetrapyrido.
Abstract: The monometallic complexes [(bpy)2Ru(tpphz)]2+ (4) and [(bpy)2Os(tpphz)]2+ (5), where tpphz is the poorly soluble fully aromatic tetrapyrido[3,2-a:2‘,3‘-c:3‘‘,2‘‘-h:2‘‘‘,3‘‘‘-j]phenazine, have been obtained by reaction of 5,6-diamino-1,10-phenanthroline with [(bpy)2M(phendione)]2+ (M = RuII or OsII). Reaction of 4 and 5 with metallic precursors yielded the homo- and heterobimetallic complexes [(bpy)2Ru(tpphz)Ru(NH3)4]4+ (6), [(bpy)2Ru(tpphz)Ru(bpy)2]4+ (7), [(bpy)2Os(tpphz)Os(bpy)2]4+ (8), and [(bpy)2Ru(tpphz)Os(bpy)2]4+ (9). The mononuclear 4 and 5 aggregate in solution, probably by π−π stacking of the tpphz part as shown from proton NMR. The complexes show one reversible metal-centered oxidation and several reversible (except 6) reductions which add one electron on the tpphz ligand, one electron on one bpy of each metallic end, a second electron on one bpy of each metallic end, and then a second electron on the tpphz ligand. The complexes (except 8) are luminescent in acetonitrile. Quenching of the lumi...
329 citations
TL;DR: In this article, the optical and redox properties of coordination compounds of the general type Ru(dmb)2(LL)(PF6)2 were reported for the attachment to semiconductor metal oxide surfaces.
Abstract: Coordination compounds of the general type Ru(dmb)2(LL)(PF6)2, where dmb is 4,4‘-(CH3)2-2,2‘-bipyridine and LL is 4-(CH3)-4‘-(COOH)-2,2‘-bipyridine, or 4-(CH3)-4‘-((CH2)3COOH)-2,2‘-bipyridine, or 4-(CH3)-4‘-((CH2)3COCH2COOC2H5)-2,2‘-bipyridine were prepared for the attachment to semiconductor metal oxide surfaces. The optical and redox properties of these compounds in dichloromethane solution are reported. Binding to porous nanostructured TiO2 films was analyzed with the Langmuir adsorption isotherm model. Photoelectrochemical measurements of the modified TiO2 electrodes in regenerative solar cells are reported. The results indicate that intimate electronic coupling between the surface link and the chromophoric ligand is not a strict requirement in the design of sensitizers for photovoltaic applications. Interfacial kinetics for recombination of the electron in the solid with the oxidized form of the sensitizer were quantitated by excited state absorption spectroscopy.
304 citations
TL;DR: The structure of the red form of Pt(bpy)Cl_2 (bpy = 2,2‘-bipyridine) has been studied by variable-temperature X-ray crystallography as discussed by the authors.
Abstract: The structure of the red form of Pt(bpy)Cl_2 (bpy = 2,2‘-bipyridine) has been studied by variable-temperature X-ray crystallography. The stack of square-planar Pt(bpy)Cl_2 units in the linear-chain material contracts with decreasing temperature; in the interval between 294 and 20 K, the platinum−platinum distance shortens from 3.449(1) to 3.370(2) A. Both absorption and emission spectra of the red compound depend strikingly on temperature; as previously found for tetracyanoplatinate salts, the emission maximum red-shifts as the temperature drops (613 nm at 300 K; 651 nm at 10 K), with the peak energy decreasing linearly with the inverse cube of the metal−metal separation.
264 citations
TL;DR: It was found that with increasing surfactant-to-metal ratios, new hexagonal P63/mmc and layered and layered Nb-TMS4 phases could be formed, while increasing the Surfactant chain length led to a new cubic phase (Nb- TMS3).
Abstract: A systematic study of the factors governing the formation of Nb-TMS1, a niobium-based mesoporous hexagonally-packed transition metal oxide molecular sieve, is reported. The synthesis of this material was achieved through a novel ligand-assisted liquid crystal templating mechanism in which a discrete covalent bond is used to direct the templating interaction between the organic and inorganic phases. In general, the synthesis of Nb-TMS1 is more strongly affected by starting conditions such as temperature, surfactant-to-metal ratio, pH, and solvent than by temperature and time of aging after the initial hydrolysis step. The results also show that Nb-TMS1 can be synthesized under conditions which strongly disfavor the formation of micelles. This suggests that Nb-TMS1 is formed via a mechanism involving self-assembly with concomitant condensation. It was found that with increasing surfactant-to-metal ratios, new hexagonal P63/mmc (Nb-TMS2) and layered (Nb-TMS4) phases could be formed, while increasing the surfactant chain length led to a new cubic phase (Nb-TMS3). Crystals of Nb-TMS1 of up to several mm in dimensions were also grown. These crystals are larger than the biggest mesoporous crystals reported by a factor of 3 orders of magnitude. These crystals retain their structure on micelle removal by acid treatment and are thus of great interest as hosts for quantum wires.
252 citations
TL;DR: The LCuGd(NO3)3·Me2CO complex crystallizes in the monoclinic space group P21/c (No. 14) in a cell having the dimensions a, b, c, and β and the magnetic behavior is characteristic of a ferromagnetic interaction between the Gd3+ and Cu2+ ions.
Abstract: The LCuGd(NO3)3·Me2CO complex crystallizes in the monoclinic space group P21/c (No. 14) in a cell having the dimensions a = 9.799(1) A, b = 18.926(3) A, c = 16.012(1) A, β = 96.530(8)°, Z = 4. The ...
239 citations
TL;DR: In this article, a model for the purple form of the DOPA-containing Mytilus edulis adhesive protein (Mefp1) involving bis(catecholato) coordination of ferric ions with most of the iron(III) complexed as EPR-silent μ-oxo- or μ-hydroxo-bridged binuclear clusters is suggested.
Abstract: Iron(III) binding to the DOPA-containing Mytilus edulis adhesive protein (Mefp1) has been studied by spectrophotometric titrations, electron paramagnetic resonance (EPR), and resonance Raman spectroscopies. At pH 7.0, two different forms of the iron−protein complex exist: one purple (λmax = 548 nm) and one pink (λmax = 500 nm). The pink form is favored at high DOPA:Fe ratios and the purple at low DOPA:Fe ratios. Resonance Raman spectroscopy of both forms demonstrates that the chromophores are ferric catecholate complexes. EPR spectra of both forms of the protein measured at the same iron concentration reveal a g ≈ 4.3 resonance of approximately 4 times the intensity in the spectrum of the pink complex compared with that of the purple form. On the basis of the collective evidence obtained here, a model for the purple form of the ferric Mefp1 involving bis(catecholato) coordination of ferric ions with most of the iron(III) complexed as EPR-silent μ-oxo- or μ-hydroxo-bridged binuclear clusters is suggested....
237 citations
TL;DR: A brief survey of the literature suggests that effects exist and have their origin in the extent of delocalization of the excited electron in the ligand pi framework and on acceptor ligand rigidity.
Abstract: In its most simple form, the energy gap law for excited-state nonradiative decay predicts a linear dependence of ln knr on the ground- to excited-state energy gap, where knr is the rate constant for nonradiative decay. At this level of approximation, the energy gap law has been successfully applied to nonradiative decay in a wide array of MLCT excited states of polypyridyl complexes of ReI, RuII, and OsII. This relationship also predicts a dependence of knr on the structural characteristics of the acceptor ligand. We report here a brief survey of the literature which suggests that such effects exist and have their origin in the extent of delocalization of the excited electron in the ligand π* framework and on acceptor ligand rigidity.
230 citations
TL;DR: The increment scheme also provides estimates of the strain energies of polynitrogen compounds, e.g., tetraazatetrahedrane, octaazacubane, and N(20) (27, 294.6 kcal/mol), and is useful in searching for new high-energy-high-density materials.
Abstract: Polynitrogen molecules have been studied systematically at high levels of ab initio and density functional theory (DFT). Besides N2, the thermodynamically most stable Nn molecules, located with the help of a newly developed energy increment system, are all based on pentazole units. The geometric, energetic, and magnetic criteria establish pentazole (2) and its anion (3) to be as aromatic as their isoelectronic analogues, e.g., furan, pyrrole, and the cyclopentadienyl anion. The bond lengths in 2 and 3 are equalized; both have large aromatic stabilization energies (ASE) and also substantial magnetic susceptibility exaltations (Λ). The Cs symmetric azidopentazole (14), a candidate for experimental investigation, is the lowest energy N8 isomer but is still 196.7 kcal/mol higher in energy than four N2 molecules. Octaazapentalene (12) with 10 π electrons also is aromatic. The D2d symmetric bispentazole (21) is the lowest energy N10 minimum but is 260 kcal/mol higher in energy than five N2 molecules. For strain...
TL;DR: In this article, the authors combined density functional and continuum dielectric theories to calculate molecular properties such as hydration enthalpies, redox potentials, and absolute pKa values of transition metal cations in solution.
Abstract: Density functional and continuum dielectric theories have been combined to calculate molecular properties such as hydration enthalpies, redox potentials, and absolute pKa values of transition metal cations in solution. The discrete cluster model, which is treated explicitly by density functional theory, includes six waters in the first hydration shell and another twelve waters in the second shell. The solvent reaction field is obtained from a finite-difference solution to the Poisson−Boltzmann equation and is coupled to the nonlocal density functional calculation in a self-consistent way. The calculated hydration enthalpies are 409, 1073, 431, and 1046 kcal/mol for Mn2+, Mn3+, Fe2+, and Fe3+, respectively, comparing fairly well to the experimental measurements of 440, 1087, 465, and 1060 kcal/mol. The calculated redox potentials for the Mn2+/Mn3+ and Fe2+/Fe3+ pairs are 1.59 and 1.06 V, respectively, in good agreement with the experimental values of 1.56 and 0.77 V. The computed absolute pKa values, 14.0,...
TL;DR: The corrected spectra of the mixed valence species have been deconvoluted to extract the parameters (position, intensity, width) of the intervalence bands, which allowed the determination of the metal-metal coupling (V(ab)) through the bridging unit using Hush's formula.
Abstract: A series of diferrocenylpolyenes of general formula Fc(CHCH)nFc with n = 1−6 (Fc = ferrocenyl group) has been prepared and studied from the point of view of intervalence transitions in the mixed valence state. Well-resolved intervalence transitions are observed in dichloromethane upon partial electrolytic oxidation. Comproportionation constants have been determined from redox titration data and in some cases from electrochemical wave splitting. The corrected spectra of the mixed valence species have been deconvoluted to extract the parameters (position, intensity, width) of the intervalence bands, which allowed the determination of the metal−metal coupling (Vab) through the bridging unit using Hush's formula. The decay of Vab with distance is close to an exponential law with an exponent of 0.087 A-1, constituting one of the smallest attenuations reported so far. A small deviation to the exponential law is detected.
TL;DR: The new chiral manganese complexes have been evaluated in the oxygenation of prochiral olefins and sulfides using sodium hypochlorite, hydrogen peroxide, or N-methylmorpholine N-oxide/m-chloroperbenzoic acid as oxidant.
Abstract: New chiral Schiff base complexes have been obtained by condensation of 2,2‘-diamino-1,1‘-binaphthalene or 1,2-diaminocyclohexane and various salicylaldehydes and by subsequent metalation with manganese, iron, cobalt, nickel, copper, or zinc. The complete 1H and 13C NMR characterization of the ligands is reported, as are the X-ray crystal structures of (1R,2R)-(−)-N,N‘-bis[3-(N,N-dimethylamino)salicylidene]-trans-1,2-cyclohexanediimine and [(1R,2R)-(−)-N,N‘-bis(salicylidene)-trans-1,2-cyclohexanediiminato]copper(II). The new chiral manganese complexes have been evaluated in the oxygenation of prochiral olefins and sulfides using sodium hypochlorite, hydrogen peroxide, or N-methylmorpholine N-oxide/m-chloroperbenzoic acid as oxidant.
TL;DR: Ambient-temperature photophysical studies reveal that two of the squares (4,4‘-bipyridine- and pyrazine-bridged species) readily luminesce in solution from relatively long-lived charge-transfer excited states.
Abstract: A new family of molecular squares containing ReI polypyridyl and polypyrazyl centers has been synthesized at quantitative yields via a self-assembly method. Ambient-temperature photophysical studies reveal that two of the squares (4,4‘-bipyridine- and pyrazine-bridged species) readily luminesce in solution from relatively long-lived charge-transfer excited states. These squares expand the growing field of inorganic cyclophane self-assembly chemistry to the octahedral metal systems.
TL;DR: The Cat-N-SQ radical ligand is obtained as the Cu(py)2(Cat-N -SQ) complex as mentioned in this paper, which has a S = 1 molecular spin state at temperatures up to 300 K.
Abstract: Stoichiometric quantities of 3,5-di-tert-butylcatechol and aqueous ammonia react in pyridine solution to form 2-amino-4,6-di-tert-butylphenol. Under an atmosphere of dioxygen the aminophenol is oxidized to either the corresponding iminosemiquinone or iminobenzoquinone. In the presence of Cu(II) iminosemiquinone condensation with the aminophenol gives the Cat-N-SQ radical ligand obtained as the Cu(py)2(Cat-N-SQ) complex. Metal and ligand magnetic orbitals are orthogonal and couple ferromagnetically to give a S = 1 molecular spin state at temperatures up to 300 K. In nonpolar solvents the complex undergoes ligand oxidation and disproportionation to give Cu(Cat-N-BQ)2. Crystallographic characterization on crystals obtained as the i-propanol solvate [orthorhombic, C2221, a = 19.548(3) A, b = 24.536(5) A, c = 23.655(5) A, V = 11346(4) A3, Z = 8, R = 0.068] show that the expected Jahn−Teller distortion appears in the trans Cu−O lengths of the equatorial plane rather than for the axial Cu−N lengths. Reactions ca...
TL;DR: An elaborate structure of cationic and anionic species within a polymeric anionic network is realized and the compound [Ni(II)(phen)(3)][NaCo(III)(dto)(3)].
Abstract: In analogy to the [M(II)(bpy)(3)](2+) cations, where M(II) is a divalent transition-metal and bpy is 2,2'-bipyridine, the tris-chelated [M(III)(bpy)(3)](3+) cations, where M(III) is Cr(III) or Co(III), induce the crystallization of chiral, anionic three-dimensional (3D) coordination polymers of oxalate-bridged (m-ox) metal complexes with stoichiometries [M(II)(2)(ox)(3)](n)()(2)(n)()(-) or [M(I)M(III)(ox)(3)](n)()(2)(n)()(-). The tripositive charge is partially compensated by inclusion of additional complex anions like ClO(4)(-), BF(4)(-), or PF(6)(-) which are encapsulated in cubic shaped cavities formed by the bipyridine ligands of the cations. Thus, an elaborate structure of cationic and anionic species within a polymeric anionic network is realized. The compounds isolated and structurally characterized include [Cr(III)(bpy)(3)][ClO(4)] [NaCr(III)(ox)(3)] (1), [Cr(III)(bpy)(3)][ClO(4)][Mn(II)(2)(ox)(3)] (2), [Cr(III)(bpy)(3)][BF(4)] [Mn(II)(2)(ox)(3)] (3), [Co(III)(bpy)(3)][PF(6)][NaCr(III)(ox)(3)] (4). Crystal data: 1, cubic, P2(1)3, a = 15.523(4) A, Z = 4; 2, cubic, P4(1)32, a = 15.564(3) A, Z = 4; 3, cubic, P4(1)32, a = 15.553(3) A, Z = 4; 4, cubic, P2(1)3, a = 15.515(3) A, Z = 4. Furthermore, it seemed likely that 1,2-dithiooxalate (dto) could act as an alternative to the oxalate bridging ligand, and as a result the compound [Ni(II)(phen)(3)][NaCo(III)(dto)(3)].C(3)H(6)O (5) has successfully been isolated and structurally characterized. Crystal data: 5, orthorhombic, P2(1)2(1)2(1), a = 16.238(4) A, b = 16.225(4) A, c = 18.371(5) A, Z = 4. In addition, the photophysical properties of compound 1 have been investigated in detail. In single crystal absorption spectra of [Cr(III)(bpy)(3)][ClO(4)][NaCr(III)(ox)(3)] (1), the spin-flip transitions of both the [Cr(bpy)(3)](3+) and the [Cr(ox)(3)](3)(-) chromophores are observed and can be clearly distinguished. Irradiating into the spin-allowed (4)A(2) --> (4)T(2) absorption band of [Cr(ox)(3)](3)(-) results in intense luminescence from the (2)E state of [Cr(bpy)(3)](3+) as a result of rapid energy transfer processes.
TL;DR: In this article, a variable-temperature solution-phase laser photolysis study of the 5T2 → 1A1 intersystem crossing in a series of related complexes is presented.
Abstract: Results are presented from a variable-temperature solution-phase laser photolysis study of the 5T2 → 1A1 intersystem crossing in a series of related complexes: [Fe(tpen)](ClO4)2, [Fe(tppn)](ClO4)2, [Fe(tptn)](ClO4)2, [Fe(t-tpchxn)](ClO4)2, and [Fe(dpa)2](ClO4)2. The hexadentate ligands are formed with four 2-pyridylmethyl arms attached to ethylenediamine (tpen), 1,2-diaminopropylene (tppn), 1,3-diaminopropylene (tptn), or trans-1,2-diaminocyclohexane (t-tpchxn). The dpa ligand is a tridentate analogue of these ligands, namely, bis(2-pyridylmethyl)amine. The complex [Fe(mtpen)](ClO4)2·2/3H2O, where mtpen is the same as tpen except one of the pyridyl rings has a 6-methyl substituent, crystallizes in the space group C2/c, which at 173 K has a unit cell with a = 41.390(13) A, b = 9.5239(16) A, c = 24.016(6) A, β = 108.24(3)°, and Z = 12. Refinement with 2844 observed [F > 5.0σ(F)] reflections gave R = 0.075 and Rw = 0.076. The complex [Fe(tppn)](ClO4)2·2/3H2O crystallizes in the space group P21/n, which at 2...
TL;DR: It is concluded that the principal role of the metal complexes is to aid in the initiation step for the free radical autoxidation of the aldehyde and that acylperoxy radicals generated in the Autoxidation reaction (or metal complexes formed by complexation of the acyl peroxy radicals) are the active epoxidizing agents.
Abstract: Mechanistic studies of the oxidation of olefins by dioxygen plus aldehyde in the presence of metal complexes such as metalloporphyrins and metal cyclam complexes have been carried out. Epoxides were the predominant products, with trace amounts of allylic oxidation products. cis-Stilbene was oxidized to a mixture of cis- and trans-stilbene oxides. It is concluded from this study that the principal role of the metal complexes is to aid in the initiation step for the free radical autoxidation of the aldehyde and that acylperoxy radicals generated in the autoxidation reaction (or metal complexes formed by complexation of the acylperoxy radicals) are the active epoxidizing agents.
TL;DR: Two novel tridentate dinucleating ligands containing benzimidazole were prepared and the interpretation of these data, including multiple scattering calculations, together with UV-vis titrations, shows that the complexes have the same structure in the crystalline state as well as in methanolic solution.
Abstract: Two novel tridentate dinucleating ligands containing benzimidazole were prepared, 1,3-bis(2-benzimidazolyl)-2-propanol (Hbbp, 1) and 1,5-bis(2-benzimidazolyl)-3-pentanol (Hbbpen, 2). Their complexing properties toward copper were studied in order to obtain structural and functional models for catechol oxidases. Syntheses and crystal structures of dinuclear Cu(II) complexes derived from these ligands are reported. [Cu2bbp2](ClO4)2·2MeOH, 3, crystallizes in the triclinic space group P1 with the following unit cell parameters: a = 7.702(3) A, b = 10.973(6) A, c = 12.396(6) A, α = 100.59(4)°, β = 99.02(4)°, γ = 98.90(4)°, V = 998.7(8) A3, and Z = 1. [Cu2bbpen2](ClO4)2·3MeOH, 4, crystallizes in the orthorhombic space group Pccn, with the following unit cell parameters: a = 17.478(9) A, b = 18.795(8) A, c = 13.888(6) A, V = 4562.2(4) A3, and Z = 4. Magnetic susceptibility measurements in the temperature ranges 4.6−459 K (3) and 4.6−425 K (4) indicate an antiferromagnetic coupling between the Cu(II) centers o...
TL;DR: In this article, it was shown that the mixed-valence dimer of [Pt(tpy)Cl] can be reduced in 0.1 M TBAH/DMF with a constant of 8(1) × 10 and 10(4] × 10 M^(-1), respectively.
Abstract: [Pt(tpy)Cl]^+ (tpy is 2,2‘:6‘,2‘‘-terpyridine) undergoes reversible one-electron reductions in 0.1 M TBAH/DMF (TBAH is tetrabutylammonium hexafluorophosphate) at E° ‘_(+/0) = −0.74 V and E° ‘_(0/-) = −1.30 V (vs AgCl (1.0 M KCl)/Ag). The first reduction couple is substantially positive of those observed for other M(II)−tpy complexes (for example, E° ‘_(0/-) = −1.36 V for [Zn(tpy)Cl_2]), a finding that suggests there is coupling between the empty 6p_z orbital of square planar Pt(II) and the π* orbital of tpy, stabilizing the (π*)^1 radical state. The dimerization constants of both [Pt(tpy)Cl]^+ and [Pt(tpy)Cl] in 0.1 M TBAH/DMF were determined spectroelectrochemically and found to be 8(1) × 10 and 10(4) × 10 M^(-1), respectively. On the basis of variable-concentration studies, a species observed at an intermediate level of reduction is formulated as the mixed-valence dimer [(Pt(tpy)Cl)_2]^+, with K_(mix) = [(Pt(tpy)Cl)_2^+]/([Pt(tpy)Cl^+][Pt(tpy)Cl]) = 18(4) × 10 M^(-1). Analysis of variable-temperature EPR spectra indicates that the first reduction is ligand-centered (^2B_2) with substantial contributions from Pt(II) 5d_(yz) (4−6%) and 6p_z (3−4%). The second reduction is tentatively assigned as metal-centered; 5d_(x^2 - y^2) is the likely acceptor orbital.
TL;DR: In this article, the Lewis acidic redox-active and photoactive ruthenium(II) bipyridyl moiety in combination with amide (CO−NH) groups was incorporated into acyclic, macrocyclic, and lower rim calix[4]arene structural frameworks to produce a new class of anion receptor with the dual capability of sensing anionic guest species via electrochemical and optical methodologies.
Abstract: The Lewis acidic redox-active and photoactive ruthenium(II) bipyridyl moiety in combination with amide (CO−NH) groups has been incorporated into acyclic, macrocyclic, and lower rim calix[4]arene structural frameworks to produce a new class of anion receptor with the dual capability of sensing anionic guest species via electrochemical and optical methodologies. Single-crystal X-ray structures of (1)Cl and (11)H2PO4 reveal the importance of hydrogen bonding to the overall anion complexation process. In the former complex, six hydrogen bonds (two amide and four C−H groups) stabilize the Cl- anion and three hydrogen bonds (two amide and one calix[4]arene hydroxyl) effect H2PO4- complexation with 11. Proton NMR titration investigations in deuterated DMSO solutions reveal these receptors form strong and, in the case of the macrocyclic 5 and calix[4]arene-containing receptor 11, highly selective complexes with H2PO4-. Cyclic and square-wave voltammetric studies have demonstrated these receptors to electrochemica...
TL;DR: The observed value of -J in the investigated oxalato-bridged nickel(II) complexes, which can vary from 22 to 39 cm(-)(1), is strongly dependent on the nature of the donor atoms from the peripheral ligands.
Abstract: Two nickel(II) complexes of formula (H3dien)2[Ni2(ox)5]·12H2O (1) and [Ni2(dien)2(H2O)2(ox)]Cl2 (2) (dien = diethylenetriamine and ox = oxalate dianion) have been synthesized and characterized by single-crystal X-ray diffraction. 1 crystallizes in the orthorhombic system, space group Abnn, with a = 15.386(4) A, b = 15.710(4) A, c = 17.071(4) A, and Z = 4. 2 crystallizes in the monoclinic system, space group P21/c, with a = 10.579(1) A, b = 7.258(1) A, c = 13.326(1) A, β = 93.52(3)°, and Z = 2. The structures of 1 and 2 consist of dinuclear oxalato-bridged nickel(II) units which contain bidentate oxalate (1) and tridentate dien in the fac-conformation (2) as terminal ligands. Both features, oxalato as a peripheral ligand and dien in the fac-conformation (instead of its usual mer-conformation), are unprecedented in the coordination chemistry of nickel(II). The nickel atom is six-coordinated in both compounds, the chromophores being NiO6 (1) and NiN3O3 (2). The Ni−O(ox) bond distances at the bridge (2.072(4)...
TL;DR: Surprisingly, very stable ring-opened species are formed such as cis-[Pt(CBDCA-O)(NH(3))(2)(L-HMet-S)] which has a half-life for Met-S,N ring-closure of 28 h at 310 K.
Abstract: Reactions of the anticancer drug carboplatin ("Paraplatin") with a variety of sulfur-containing amino acids have been investigated by (1)H and (15)N NMR spectroscopy and by HPLC. Thiols react very slowly and sulfur-bridged species containing four-membered Pt(2)S(2) rings are the predominant products. In contrast, reactions with thioether ligands are much more rapid, and kinetics for the initial stages of the reaction with L-methionine have been determined (k = 2.7 x 10(-)(3) M(-)(1) s(-)(1)). Surprisingly, very stable ring-opened species are formed such as cis-[Pt(CBDCA-O)(NH(3))(2)(L-HMet-S)] which has a half-life for Met-S,N ring-closure of 28 h at 310 K. A study of the formation of the analogous product for N-acetyl-L-methionine and its subsequent ring closure is reported. Reactions such as these may play a role in the biological activity of carboplatin.
TL;DR: In this paper, the synthesis and properties of several complexes of Ru(II) containing 4,4,dicarboxy-2,2,bipyridine (dcbpyH2), 2,6-bis(1-methylbenzimidazol-2-yl)pyridine, and monodentate ligands (X- = Cl-, I-, NCS-, NCSe-, CN-) are reported.
Abstract: The synthesis and properties of several complexes of Ru(II) containing 4,4‘-dicarboxy-2,2‘-bipyridine (dcbpyH2), 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (bmipy), or 2,6-bis(1-methylbenzimidazol-2-yl)-4-phenylpyridine (ph-bmipy), and monodentate ligands (X- = Cl-, I-, NCS-, NCSe-, CN-) are reported. The introduction of the ambident ligands X- = NCS-, NCSe-, and CN- into the coordination sphere of [Ru(bmipy)(dcbpy)I]- and cis-Ru(dcbpyH2)2Cl2 has been studied in situ via 1H and 13C NMR spectroscopy using 13C-enriched ligands X-. Introduction of thiocyanate and selenocyanate initially yields the two possible linkage isomers in comparable amounts; prolonged reaction time converts the S-bound isomer and the Se-bound isomer to the N-bound isomers. The isoselenocyanate complex decomposes rapidly, yielding the cyano complex under loss of Se. The N-bound isothiocyanato complex K[Ru(bmipy)(dcbpy)(NCS)] was found to be an efficient sensitizer for nanocrystalline TiO2; the incident monochromatic photon-to-current e...
TL;DR: A series of copper(II) complexes with tripodal polypyridylmethylamine ligands, such as tris(2-pyrIDylmethyl)amine (tpa), ((6-methyl-2- pyridolmethyl)methyl)bis(1)tpa) , bis(6- methyl- 2-piridyl)methyl(2)tPA), and bis(3)tpas, have been synthesized and characterized by
Abstract: A series of copper(II) complexes with tripodal polypyridylmethylamine ligands, such as tris(2-pyridylmethyl)amine (tpa), ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine (Me1tpa), bis((6-methyl-2-pyridyl)methyl)(2-pyridylmethyl)amine (Me2tpa), and tris((6-methyl-2-pyridyl)methyl)amine (Me3tpa), have been synthesized and characterized by X-ray crystallography. [Cu(H2O)(tpa)](ClO4)2 (1) crystallized in the monoclinic system, space group P21/a, with a = 15.029(7) A, b = 9.268(2) A, c = 17.948(5) A, β = 113.80(3)°, and Z = 4 (R = 0.061, Rw = 0.059). [CuCl(Me1tpa)]ClO4 (2) crystallized in the triclinic system, space group P1, with a = 13.617(4) A, b = 14.532(4) A, c = 12.357(4) A, α = 106.01(3)°, β = 111.96(2)°, γ = 71.61(2)°, and Z = 4 (R = 0.054, Rw = 0.037). [CuCl(Me2tpa)]ClO4 (3) crystallized in the monoclinic system, space group P21/n, with a = 19.650(4) A, b = 13.528(4) A, c = 8.55(1) A, β = 101.51(5)°, and Z = 4 (R = 0.071, Rw = 0.050). [CuCl(Me3tpa)][CuCl2(Me3tpa)]ClO4 (4) crystallized in the mon...
TL;DR: 1H and (113)Cd NMR studies are used to investigate the Cd(2+) binding sites on serum albumin in competition with other metal ions and show that the same two His residues of human serumalbumin are perturbed by Zn( 2+) and C d(2%) binding alike.
Abstract: 1H and 113Cd NMR studies are used to investigate the Cd2+ binding sites on serum albumin (67 kDa) in competition with other metal ions. A wide range of mammalian serum albumins possess two similar ...
TL;DR: Results of absorption titration, thermal denaturation, and differential pulse voltammetric experiments suggest that [Co(phen)2DPPZ]3+ and [Ni(phen]2+ are both avid binders of calf thymus DNA.
Abstract: Results of absorption titration, thermal denaturation, and differential pulse voltammetric experiments suggest that [Co(phen)2DPPZ]3+ and [Ni(phen)2DPPZ]2+ (phen = 1, 10-phenanthroline and DPPZ = dipyrido[3,2-a:2‘,3‘-c]phenazine) are both avid binders of calf thymus DNA. On the other hand, while the cobalt(III) complex has been found to effect the photocleavage of the supercoiled pBR 322 DNA, the nickel(II) complex is ineffective under similar experimental conditions.
TL;DR: A theoretical framework is presented for analysis of all three "multiline" EPR spectra (MLS) arising from the tetramanganese (Mn(4) cluster in the S(2) oxidation state of the photosynthetic water oxidizing complex (WOC).
Abstract: A theoretical framework is presented for analysis of all three "multiline" EPR spectra (MLS) arising from the tetramanganese (Mn(4)) cluster in the S(2) oxidation state of the photosynthetic water oxidizing complex (WOC). Accurate simulations are presented which include anisotropy of the g and (four) (55)Mn hyperfine tensors, chosen according to a database of (55)Mn(III) and (55)Mn(IV) hyperfine tensors obtained previously using unbiased least-squares spectral fitting routines. In view of the large (30%) anisotropy common to Mn(III) hyperfine tensors in all complexes, previous MLS simulations which have assumed isotropic hyperfine constants have required physically unrealistic parameters. A simple model is found which offers good simulations of both the native "19-21-line" MLS and the "26-line" NH(3)-bound form of the MLS. Both a dimer-of-dimers and distorted-trigonal magnetic models are examined to describe the symmetry of the Heisenberg exchange interactions within the Mn(4) cluster and thus define the initial electronic basis states of the cluster. The effect of rhombic symmetry distortions is explicitly considered. Both magnetic models correspond to one of several possible structural models for the Mn(4) cluster proposed independently from Mn EXAFS studies. Simulated MLS were constructed for each of the eight (or seven) doublet states of the Mn(4) cluster in the WOC for the two viable oxidation models (3Mn(III)-1Mn(IV) or 3Mn(IV)-1Mn(III)), and using a wide range of axial Mn hyperfine tensors, with either coaxial or orthogonal tensor alignments. We find accurate simulations using the 3Mn(III)-1Mn(IV) oxidation model. In the dimer-of-dimers coupling model, the spin state conversion between two doublet states |S(12),S(34),S(T)|(7)/(2),4,(1)/(2)> and |(7)/(2),3,(1)/(2)> is found to explain the large (25%) contraction in the hyperfine splitting observed upon conversion from the native MLS to the NH(3)-bound MLS. Stabilization of this excited state as the new ground state is caused by change in the intermanganese exchange coupling, without appreciable change in the intrinsic hyperfine tensors. The lack of good simulations of the Ca(2+)-depleted MLS suggests that Ca(2+)-depletion changes both Mn ligation and intermanganese exchange coupling. The 3Mn(IV)-1Mn(III) oxidation model is disfavored because only approximate simulations could be found for the native MLS and no agreement with the NH(3)-bound MLS was obtained. The scalar part of the hyperfine tensors for both Mn(III) and Mn(IV) ions were found to approximate (+/-5%) the values for the dimanganese(III,IV) catalase enzyme, suggesting similar overall ligand types. However, the large (30%) anisotropic part of the Mn(III) hyperfine interaction is opposite in sign to that found in all tetragonally extended six-coordinate Mn(III) ions (i.e., the usual Jahn-Teller splitting). The distribution of spin density from the high-spin d(4) electron configuration of each Mn(III) ion corresponds to a flattened (oblate) ellipsoid. This electronic distribution is favored in five-coordinate ligand fields having trigonally compressed bipyramidal geometry, but it could also arise, in principle, in strained six-coordinate ligand fields having tetragonally compressed geometry, i.e. [Mn(2)(m-O)](4+) (reverse Jahn-Teller distortion). The resulting valence electronic configurations are described as e'(2)e"(2) and (d(pi))(3)(d(x)()()2(-)(y)()()2)(1), respectively, in contrast to the (d(pi))(3)(d(z)()()2)(1) configuration common to unstrained six-coordinate tetragonally-extended Mn(III) ions, such as found in the [Mn(2)(m-O)(2)](3+) core in several synthetic dimers and catalase. Both of the former geometries predict strongly oxidizing Mn(III) ions, thereby suggesting a structural basis for the oxidative reactivity of the Mn(4) cluster in the WOC. The magnetic model needed to explain the MLS is not readily reconciled with the simplest structural and electronic models deduced from EXAFS studies of the WOC.
TL;DR: In this article, the temperature and pressure-driven solid state valence tautomeric transformations of [CoII(3,5DTBSQ)2(phen)]·C6H5CH) and nonsolvated [Co II(3.5 DTBSQ2phen)2 (phen)] have been studied by EXAFS and XANES.
Abstract: The temperature- and pressure-driven solid state valence tautomeric transformations of [CoII(3,5DTBSQ)2(phen)]·C6H5CH) and nonsolvated [CoII(3,5DTBSQ)2(phen)] have been studied by EXAFS and XANES. When the toluene solvate sample is cooled it converts in the 270−215 K region (Tc = 240 K) from a high-spin CoII complex at higher-temperatues to a low-spin CoIII complex at temperatures below ∼215 K. EXAFS data indicate that the HS-CoII tautomer has bond lengths of Co−O = 2.08 ± 0.02 A and Co−N = 2.13 ± 0.02 A, whereas the LS-CoIII tautomeric complex is smaller with Co−O = 1.91 ± 0.02 A and Co−N = 1.93 ± 0.02 A. The XANES spectra obtained in the 270−215 K interconversion region were simulated to obtain a plot of the fraction of HS-CoII complexes, n(HS-CoII), vs temperature. This plot of n vs T agrees with that obtained from magnetic susceptibility data for the toluene solvate. In the XANES spectral region transitions characteristic of either a HS-CoII or a LS-CoIII complex could also be used to monitor the vale...