Hexacoordinate Complexes Research Articles

X-ray structural study on spirocyclic bis(ethane-1,2-dithiolato[2−]-S,S′)tin(IV) and its pyridine and 2-(2-pyridyl)ethylamine adducts

Spirocyclic bis(ethane-1,2-dithiolato[2−]-S,S′)tin(IV) forms hexacoordinate crystalline complexes with pyridine and 2-(2-pyridyl)ethylamine. The compounds have been prepared by conventional methods and the crystal structures have been determined by an X-ray diffraction study. In the parent compound the tin is tetracoordinate in a highly distorted tetrahedral structure, with a weak intermolecular Sn···S interaction. On the contrary, the adducts are essentially octahedral about the tin, with longer SnS bonds in the five-membered rings SnS2C2. The 2-(2- pyridyl)ethylamine ligand is bonded to the metal through the aminic nitrogen.

Reactions of alkenyl and alkynyl ruthenium(II) complexes with isocyanides: Synthesis of α, β-unsaturated η1-acylruthenium(II) complexes and X-ray structure of [Ru(CCPh)(CN+Bu)3(PPh3)2]PF6

Abstract Reaction of (E)-alkenyl complexes Ru(CO)Cl(CHCHR)(PPh3)2 and Ru(CO)Cl(CHCHR) (PPh3)2L (L  Me2Hpz, py) with an excess of an isocyanide R′NC (R′tBu or cyclohexyl (Cy)) gives (E)-α,β-unsaturated-η1-acyl complexes [Ru(COCHCHR)(CNR′)3(PPh3)2]Cl in good yield. The corresponding reactions with 1 equivalent of isocyanide give the hexacoordinate complexes Ru(CO)Cl(CHCHR)(CNR′)(PPh3)2. The reaction of [Ru(CO)(CHCHR)(NCMe)2(PPh3)2]PF6 with tBuNC also affords η1-acyl complexes [Ru(COCHCHR)(CNtBu)3(PPh3)2]PF6. On the other hand, treatment of alkynyl complexes [Ru(CO)(CCR)(py)2(PPh3)2]PF6 with an excess of tBuNC under forcing conditions promotes substitution of CO and pyridine ligands by the isocyanide, yielding alkynyl derivatives [Ru(CCR)CNtBu)3(PPh3)2]PF6. An X-ray diffraction study of one of the complexes (R  Ph) confirmed the proposed structure. Similarly, reaction of the alkynyl complexes with CO gives only the ligand-substitution products [Ru(CO)2(CCR)(py)(PPh3)2][PF6]. The reaction of (E)-alkenyl ruthenium(II) complexes with alkyl isocyanides proceeds under mild conditions to yield (E)-α,β-unsaturated-η1-acyl ruthenium(II) complexes. Although these complexes are obtained from intermediates with both CO and isocyanide ligands, exclusive migratory insertion of the alkenyl ligand into the RuCO bond is observed. The related alkynyl carbonyl ruthenium(II) complexes do not undergo insertion, reacting sluggishly with the isocyanides to yield new alkynyl ruthenium complexes in which the carbonyl ligand has been replaced by an isocyanide ligand. The corresponding reaction with CO leads to dicarbonyl alkynyl complexes by substitution of the pyridine trans to the alkynyl ligand.

Synthesis and Structural Investigation of Some Mixed-Ligand Cyanonitrosyl {CrNO}5Complexes of Monovalent Chromium with Some Drugs and Vitamin

Abstract The present communication describes the synthesis of some new mixed-ligand hexa-coordinated cyanonitrosyl complexes of chromium(I) of the composition [Cr(NO)(CN)2(L)2(H2O)] (where L = chlorpheniramine maleate, pheniramine maleate, mepyramine maleate, nikethamide or vitamin B6). These complexes were prepared by the interaction of potassium pentacyanonitrosylchromate(I) monohydrate, K3[Cr(NO)(CN)5].H2O with L, the said drugs and vitamin. The resulting compounds have been characterized by elemental analyses, magnetic measurements, electron spin resonance and infra-red spectral studies. All the complexes have a low-spin {CrNO}5 electron configuration. An octahedral structure has been proposed for all the complexes where CN is trans to CN and the ligands L are trans to each other in equatorial positions and where NO is trans to water in the axial position.

Multicomponent Polyanions. 45. A Multinuclear NMR Study of Vanadate(V)--Oxalate Complexes in Aqueous Solution.

The two complexes formed in the aqueous vanadooxalate system, V(Ox)- and V(Ox)2(3-), have been characterized using 51V, 13C and 17O NMR. For the V(Ox)2(3-) complex, two peaks are observed in 13C NMR and four in 17O NMR. This leads to the conclusion that each oxalate ligand has two different distances to the VO2 group. This fact, together with the peak integrals and the chemical shifts, indicates strongly that the hexacoordinate complex [VO2(C2O4)2]3- found in single-crystal X-ray structure determinations persists in aqueous solution. The dependence of the 13C NMR linewidths upon temperature reveals two types of dynamic processes: (1) a rearrangement in which the two different V-Oox switch places and (2) an exchange of the oxalate ligands in the [VO2(C2O4)2]3- complex with free oxalate, probably through a dissociative process. Rate constants and activation parameters for the two dynamic processes involving [VO2(C2O4)2]3- have been calculated from the shape of the 13C NMR signals. For the V(Ox)- complex, only one relatively narrow peak is obtained in 13C NMR and three peaks in 17O. This fact, as well as the relative positions of these peaks, is in accordance with a pentacoordinate complex [VO2(C2O4)H2O]-, where the two V-O distances to the oxalate ligand are equal. We also show that, in the pH range 0.8-6.6, there is no protonation of the studied complexes, in agreement with previous potentiometric results.

Multiple bonds between main-group elements and transition metals. 77. Condensation reactions of methyltrioxorhenium(VII) with catechols and aromatic thiols

The title compound methyltrioxorhenium (VII) reacts with catechols to yield complexes of the formula CH 3 Re(O) 2 (1,2-O 2 C 6 R 4 ) ( ) that are fully characterized as pyridine adducts 3. Conducting these reactions in the presence of nucleophiles, e.g; halides, gives the hexacoordinate anions [CH 3 Re(O) 2 (1,2-O 2 C 6 R 4 )(X)] - (X=Cl,Br,I). The rhenium (V) species «CH 3 ReO 2 », prepared in situ from 1 by reduction with (polymer bound) triphenylphosphane, reacts with phenanthrenequinone in the presence of pyridine to give the neutral hexacoordinate complex CH 3 Re(O) 2 (9,10,O 2 C 14 H 8 )(NC 5 H 5 ) (5). Reaction of 1 with thiophenol gives initially the rhenium (VII) complex CH 3 ReO(SC 6 H 5 ) 4 (6), which upon heating undergoes intramolecular elimination of diphenyl disulfide, C 6 H 5 SSC 6 H 5 , to give the dinuclear rhenium (V) complex [CH 3 ReO(μ-SC 6 H 5 )(SC 6 H 5 )] 2 (7;X-ray diffraction study). Condensation of 1 with benzene-1,2-dithiol gives the rhenium (VII) complex CH 3 ReO(1,2-S 2 C 6 H 4 ) 2 (8)

Arylamidoxime Complexes of Antimony(V)

Abstract Arylamidoximes (LH) react with SbCl5 to give adducts of the general formula SbCl5LH. Sodium arylamidoximates react with Ph3SbBr2 to give compounds of the general formula Ph3SbL2. These hexa-coordinated antimony complexes were characterized by elemental analyses, spectral data and conductivity measurements.

ESR Studies on [Cu(trien)(enMe4)](BØ4)2and [Cu(trien)(enEt2)](BØ4)2

ESR studies on [Cu(trien)(enMe 4 )](BO 4 ) 2 and [Cu(trien)(enEt 2 )](BO 4 ) 2 are carried out to understand the coordination behaviour, fluxional nature, N-alkylation effects on metal ligand bonds. It is found that the alkylated N-donor atoms are occupying axial positions in these hexacoordinate complexes having CuN 4 N 2 ′ moieties. It is also observed that in frozen pyridine solutions these complexes have undergone geometric transition from distorted elongated octahedral to distorted compressed tetrahedral symmetry.

The Raman Spectral Study on the Solution Structure of Iron(III)-edta Complexes

Abstract The Raman spectra of iron(III) complexes with ethylenediaminetetraacetate were observed for the purpose of elucidating the structure of the complexes in solution. In a Raman spectral study on the solid complexes, the spectra in the 300–600 cm−1 region were found to be diagnostic to coordination geometry. Namely, the coordination number can be determined on the basis of the wavenumber difference of the two major bands observed in the 450–600 cm−1 region; the wavenumber differences observed for heptacoordinate complexes lie between 32 and 42 cm−1, while that for the hexacoordinate complex is 62 cm−1. Complexes containing a sexidentate edta exhibit a single intense band around 470 cm−1 in the 450–500 cm−1 region, while complexes containing a quinquedentate edta exhibit two intense bands in this region. These Raman spectral criteria were then applied for the determination of the solution structure. The Raman spectral features observed for solutions of Fe(III)-edta complexes indicate that the any alkali metal salts and acid salts of FeIII(edta)− give sexidentate heptacoordinate complex ions in water. The dimeric complex which is formed in an alkaline solution was characterized as being a dinuclear complex consisting of two quinquedentate hexacoordinate iron(III) moieties with a Fe–O–Fe bridging unit.

Substitutionsreaktionen am Tetrafluorotantal-Komplex (η5-C5Me5)—TaF4 / Substitution Reactions at the Tetrafluorotantalum Complex (η5-C5Me5)—TaF4

Cp*TaF4 (1) (Cp* = η5-C5Me5) reacts with lithium salts of benzamidines or 1,3-diketones to form hexa-coordinated complexes of composition Cp*TaF3[(Me3SiN)2CPh] (2), Cp*TaF3[(Me3SiN)2C(p-CF3C6H4)] (3) and Cp*TaF3(O=CPhCH=CPhO) (4). The reactions proceed under elimination of LiF. The X-ray crystal structure of Cp*TaF3(O=CPhCH=CPhO) (4) has been determined shows tantalum to have a distorted octahedral environment, if the Cp* ligand is considered to occupy one coordination site.

Characterization of metal complexes of 1,10-phenanthroline, 2,2′-bipyridine, and their derivatives by fast atom bombardment mass spectrometry

A series of 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (5-NO2-phen), 2,9-dimethyl- 1,10-phenanthroline (dmp), 2,2′-bipyridine (bpy), and 4,4′-dimethy-2,2′-bipyridine (dmb) metal complexes has been characterized using fast atom bombardment mass spectrometry (FAB MS). Intact cations are observed in the positive ion FAB mass spectra of all tetracoordinated complexes, [Ag(L)2]NO3, [Cu(L)2]2 SO4•5H2O, [Cu(L)2]SO4, and [Tl(L)2](ClO4), where L=bpy, phen, or dmp. Structurally significant fragment ions (ML2+, ML+, M+, and (L+H)+, where M+=metal ion) are also observed. Species such as Ag[Ag(L)2]NO3+, where L=bpy or phen, and Tl[Tl(phen)2](ClO4)+ are also seen. The hexacoordinate complexes, [Co(phen)3]Cl2, [Ru(bpy)Cl2], [Fe(phen)2(CN)2], [Fe(L)3](ClO4), where L=5-NO2-phen, dmb, or bpy, and [Fe(L)3]SO4, where L=bpy or phen, show intact cations in the positive ion spectra; [Ni(bpy)3]X2, where X=Cl−,Br−, NO3−, ClO4−, SCN−, and tartrate2−, and [Co(bpy)3](ClO4) do not. Generally, fragment ions such as ML3+, ML2X+, ML2+, MLX+, and (L+H)+ are observed, where X=singly charged intact anion or HSO4−. Comparison of FAB results with those of laser mass spectrometry (LMS) show that they are comparable, through reduction processes are more important for FAB. LMS always gave the intact cation while FAB was not consistent. Keywords: FAB mass spectrometry, phenanthroline complexes, bipyridine complexes, laser desorption mass spectrometry.

ChemInform Abstract: In situ Nucleophilic Activation in the Propellane 5‐Chloro‐1‐aza‐5‐silatricyclo(3.3.3.01,5)undecane and Its Hydrolysis in Solution

The compound 5-chloro-1-aza-5-silatricyclo[3.3.3.01,5]undecane (C9H18NSiCl) combines with water to form an association complex with the formula C9H18NSiCl·H2O. Proton NMR studies at various temperatures, concentrations and magnetic fields indicate that this compound exists in solution as an equilibrium mixture of the initial chloride and its association complex with water, a structure for which is proposed. Evidence is provided against a rigid hexacoordinate complex. The equilibrium is shown to correspond to a reversible hydrolysis of C9H18NSiCl which is nucleophilically activated by the intramolecularly coordinating nitrogen present in situ. The reverse reaction is the decomposition of the association complex C9H18NSiCl·H2O to C9H18NSiCl and free water. As a consequence, this paper presents a reversible hydrolysis of a chlorosilane interconverting two directly observable pentacoordinate species without addition of an external nucleophile, and proceeding with retention of configuration at the silicon atom. We further argue that this reaction cannot proceed through a rigid hexacoordinate octahedral intermediate, but could proceed through two non-rigid species, the averaged dynamic behaviour of which is identical to a non-octahedral hexacoordinate transition state.

Ein weiteres Silicat-Anion: [Si(NCSe)6]2– / A Further Silicate Anion: [Si(NCSe)6]2–

Abstract Reaction of SiCl4 with NMe4NCSe or NEt4NCSe in cold acetonitrile leads to the corresponding crystalline salts of the new hexa-coordinate silicon complex anion [Si(NCSe)6]2- (1 ] ; . Their crystallographic data were determined: [NMe4]2[Si(NCSe)6]: rhombohedral. R3̄. a = 897 pm. a = 84.1°. Z = 1. [NEt4]2[Si(NCSe)6], tetragonal modification (from pure acetonitrile): P42/m, a = 1056 pm. c - 1580 pm. Z = 2. [NEt4]2[Si(NCSe)6]. orthorhombic modification (from acetonitrile containing NEt4Cl): a = 1704 pm. b = 1986 pm. c = 1028 pm. Z = 4. N-bonding of the NCSe groups in [Si(NCSe)6]2 is proved by the X-ray structure analysis of [NMe4]2[Si(NCSe)6] and by IR spectra. The concentration dependence of the molar conductance of an acetonitrile solution of [NMe4]2[Si(NCSe)6] was studied. At low concentrations partial dissociation of the hexa-isoselenocyanatosilicate ion is observed.

Spectral characterization of manganese peroxidase, an extracellular heme enzyme from the lignin-degrading basidiomycete, Phanerochaete chrysosporium.

Manganese peroxidase (MnP) is a component of the lignin degradation system of the basidiomycetous fungus, Phanerochaete chrysosporium. This novel MnII-dependent extracellular enzyme (Mr = 46,000) contains a single protoporphyrin IX prosthetic group and oxidizes phenolic lignin model compounds as well as a variety of other substrates. To elucidate the heme environment of this enzyme, we have studied its electron paramagnetic resonance and resonance Raman spectroscopic properties. These studies indicate that the native enzyme is predominantly in the high-spin ferric form and has a histidine as fifth ligand. The reduced enzyme has a high-spin, pentacoordinate ferrous heme. Fluoride and cyanide readily bind to the sixth coordination position of the heme iron in the native form, thereby changing MnP into a typical high-spin, hexacoordinate fluoro adduct or a low-spin, hexacoordinate cyano adduct, respectively. EPR spectra of 14NO- and 15NO-adducts of ferrous MnP were compared with those of horseradish peroxidase (HRP); the presence of a proximal histidine ligand was confirmed from the pattern of superhyperfine splittings of the NO signals centered at g approximately equal to 2.005. The appearance of the FeII-His stretch at approximately 240 cm-1 and its apparent lack of deuterium sensitivity suggest that the N delta proton of the proximal histidine of the enzyme is more strongly hydrogen bonded than that of oxygen carrier globins and that this imidazole ligand may be described as having a comparatively strong anionic character. Although resonance Raman frequencies for the spin- and coordination-state marker bands of native MnP, nu 3 (1487), nu 19 (1565), and nu 10 (1622 cm-1), do not fall into frequency regions expected for typical penta- or hexacoordinate high-spin ferric heme complexes, ligation of fluoride produces frequency shifts of these bands very similar to those observed for cytochrome c peroxidase and HRP. Hence, these data strongly suggest that the iron in native MnP is predominantly high-spin pentacoordinate. Analysis of the Raman frequencies indicates that the dx2-y2 orbital of the native enzyme is at higher energy than that of metmyoglobin. These features of the heme in MnP must be favorable for the peroxidase catalytic mechanism involving oxidation of the heme iron to FeIV. Consequently, it is most likely that the heme environment of MnP resembles those of HRP, cytochrome c peroxidase, and lignin peroxidase.

In situ nucleophilic activation in the propellane 5‐chloro‐1‐aza‐5‐silatricyclo[3.3.3.01,5]undecane and its hydrolysis in solution

AbstractThe compound 5‐chloro‐1‐aza‐5‐silatricyclo[3.3.3.01,5]undecane (C9H18NSiCl) combines with water to form an association complex with the formula C9H18NSiCl·H2O. Proton NMR studies at various temperatures, concentrations and magnetic fields indicate that this compound exists in solution as an equilibrium mixture of the initial chloride and its association complex with water, a structure for which is proposed. Evidence is provided against a rigid hexacoordinate complex. The equilibrium is shown to correspond to a reversible hydrolysis of C9H18NSiCl which is nucleophilically activated by the intramolecularly coordinating nitrogen present in situ. The reverse reaction is the decomposition of the association complex C9H18NSiCl·H2O to C9H18NSiCl and free water. As a consequence, this paper presents a reversible hydrolysis of a chlorosilane interconverting two directly observable pentacoordinate species without addition of an external nucleophile, and proceeding with retention of configuration at the silicon atom. We further argue that this reaction cannot proceed through a rigid hexacoordinate octahedral intermediate, but could proceed through two non‐rigid species, the averaged dynamic behaviour of which is identical to a non‐octahedral hexacoordinate transition state.

Synthesis and physico-chemical studies of some novel mixed-ligand cyanonitrosyl {CrNO}5 complexes of chromium with 2-3-pyrazoline-5-one derivatives

A new series of spin-paired hexa-coordinated mixed-ligand cyanonitrosyl complexes of chromium (having {CrNO}5 electron configuration(1)) of the type [Cr(NO)(CN)2(L)2(H2O)] (where L=4-methyl-2-pyrazoline-5-one(1), 2,3-dimethyl-1-phenyl-3-pyrazoline-5-one(2) or 4-dimethylamino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one(3) have been synthesized in the solid state by the interaction of potassium pentacyanonitrosylchromate(I) monohydrate, K3[Cr(NO)(CN)5]· H2O with L in aqueous acetic acid. The products, which have been characterized by elemental analyses, molar conductances, thermogravimetric analyses, magnetic measurements, electron spin resonance and infrared spectral studies, contain low-spin chromium(I). An octahedral structure has been suggested for the complexes.

Ligand recombination to the alpha and beta subunits of human hemoglobin.

The rebinding of CO, O2, NO, methyl, ethyl, n-propyl, and n-butyl isocyanide to isolated alpha and beta chains and intact hemoglobin at pH 7, 20 degrees C was examined both during and after a 30-ns dye laser pulse. The resultant absorbance changes were analyzed in terms of a linear three-step reaction scheme: Hb + X in equilibrium with C in equilibrium with B in equilibrium with A or HbX, where A is the final bound state, and C and B are geminate states. Rate constants were assigned for each of the transitions in this mechanism using fitting procedures described previously for analyzing ligand rebinding to sperm whale myoglobin at room temperature (Gibson, Q. H., Olson, J. S., McKinnie, R. E., and Rohlfs, R. J. (1986) J. Biol. Chem. 261, 10228-10239). Five major conclusions were obtained. First, initial geminate recombination phases for the NO and O2 complexes of hemoglobin and its isolated subunits exhibit half-times equal to approximately 12 and approximately 440 ps, respectively. These values are in excellent agreement with more direct, picosecond measurements of the geminate recombination of HbNO (Cornelius, P. A., Hochstrasser, R. M., and Steele, A. W. (1983) J. Mol. Biol. 163, 119-128) and HbO2 (Friedman, J. M., Scott, T. W., Fisanick, G. J., Simon, S. R., Findsen, E. W., Ondrias, M. R., and MacDonald, V. W. (1985) Science 229, 187-229) following extremely short laser pulses. Second, the correspondence between our nanosecond measurements and the published picosecond data suggests strongly that the intrinsic photochemical yield of all ferrous, hexacoordinate heme complexes approaches one. Third, the major differences between the isolated alpha and beta chains involve the rate of ligand migration to the solvent, kC----X and the extent of recombination from the second geminate state, C, as measured by the ratio kC----B/kC----X. Fourth, for both isolated chains and intact hemoglobin, the rate and equilibrium constants for the formation of the initial O2 geminate state starting from ligand in the solvent (i.e. kX----B and KX----B) are 5-10 times greater than the corresponding parameters for the formation of the first CO geminate state. Fifth, the rate-limiting step for NO, O2, and isonitrile binding to hemoglobin and its isolated subunits is ligand migration up to the initial geminate state (i.e. kX----B). In the case of CO binding, both migration to state B and iron-ligand bond formation (kB----A) affect the overall, bimolecular association rate constant.

Quantum-chemical simulation of the active center of vitamin B12

The electronic structure of porphin and corrin complexes of cobalt differing with respect to the oxidation state of the central ion has been investigated by the MO-LCAO-SCF-CNDO method with the Kai-Nishimoto parameters for transition metals. On the basis of an analysis of the distribution of the electron density and the structure of the energy spectrum, it has been shown that the oxidation-reduction processes of the complexes are accompanied by restructuring of the energy spectrum, and the differences between the electronic structures of porphin and corrin complexes have been discussed. It has been established that cobalt(I) porphin has stronger nucleophilic properties than does cobalt(I) corrin. The electronic structure of hexacoordinate complexes in which an imidazole molecule and a molecule of L′ (L = H2O, CH3+, CN−) are axially coordinated has been calculated. The mechanisms of the dissociation of cobalt alkyl complexes and the differences between the processes of the heterolytic dissociation of porphin and corrin complexes have been discussed. It has been shown that the elimination of a CH3+ cation, which plays an important role in biomethylation reactions, is more favorable in corrin complexes.

Synthesis of mixed sphere β-diketonate nickel(II) complexes

Complexes of the type [Ni(β-diketonate)(L L) 1,2] (LL = diphosphine, ( 2), en or dipy, ( 3)) have been synthesized from [Ni(β-diketonate) 2] ( 1) and the free ligand under stoichiometric conditions in ethanol. Complexes 2 are square-planar species, while compounds 3 are hexacoordinate complexes, all being quite stable toward ligand disproportionation. The ligand-set {P 2O 2 -} appears to be particularly stable in the nickel(II) coordination sphere and turns out to exert a fairly strong average ligand field.

EXAFS STUDY OF ACTIVE INTERMEDIATES : HEME ENZYMES AND MODEL COMPOUNDS

The iron coordination structures of the oxygenated cytochrome P-450-CAM and chloroperoxidase and of a number of penta- and hexa-coordinate ferrous porphyrin complexes containing biologically relevant, sulfur axial ligands have been investigatied by EXAFS spectroscopy. The two oxygenated enzymes have both been found to contain a sulfur atom located 2.37 A from the central heme iron. In the CO-ligated series of model complexes, two distinct categories of Fe-Sax distances have been observed that correlate with thiolate and non-thiolate ligation (~2.33 and ~2.41 A, respectively) . The data for these model ferrous-CO ccomplexes, together with previously reported Fe-S distance in oxygenated heme iron model complexes ; allows the sulfur atoms in oxygenated P-450-CAM and chloroperoxidase to be identified as a thiolate sulfur.

Theoretical study of the static Jahn-Teller effect—III. Type of vibronic coupling in hexahalo complexes

Three types of vibronic coupling in hexacoordinate complexes are compared: the T ig −( a 1 g + e g ) type in the group O h , the E g −(α 1 g + e g ) type in the group D 3 d , and the E g −(α 1 g + b 1 g ) type in the group D 4 h . It is shown that the group with the highest symmetry ( O h ) does not imply the best model of vibronic coupling. Numerical applications were obtained for 29 complexes of the MX q 6 type having a triply degenerate electronic state in an octahedral geometry on the CNDO-UHF level of the MO-LCAO-SCF method. Characteristics of these Jahn-Teller active systems are calculated and discussed.