Showing papers in "Polyhedron in 1987"

Abstract: Preparation of pure metal(II) 4,9,16,23-phthalocyanine tetraamine 2-hydrates of copper, cobalt, nickel and zinc are reported. Elemental analysis, electronic spectra, FT-IR spectra, powder X-ray diffraction, magnetic-susceptibility measurements, dynamic thermogravimetric MS and GC-MS spectral studies are carried out to check the purity, structural integrity, thermal stability and mode of fragmentation of these complexes. Magnetic-susceptibility measurements showed a variation in the magnetic moments of these complexes with magnetic field strength, indicating the presence of a co-operative intermolecular effect.

Abstract: The previously reported preparation of some Anderson-type molybdopolyanions containing divalent metal ions (Zn, Cu, Co or Mn) as a heteroatom has been reinvestigated. The molybdopolyanions of Zn(II) and Cu(II) were confirmed, although the Cu(II) polyanion was not stable and could not be recrystallized. On the other hand, the polyanions of Co(II) and Mn(II) could not be reproduced. Another type of heteropoly compound, [X(H2O)6-x(Mo7O24)]4− [X = Cu(II), Co(II) or Mn(II)], was isolated as solids, which are not stable thermally. The mixed-type Anderson polyanions, [Ni(II)Mo6-xWx,O24H6]4−, which have been questioned as mixtures of species with different x values, were also reinvestigated using IR, UV absorption and MCD spectra. They are single species, but not mixtures, although some positional isomers may be present for the compounds where x = 2-4. The possibility of oxidation of the heteroatom with the Anderson structure maintained was examined. The oxidation of [Ni(II)Mo6O24H6]4− by the S2O2−8 ion in aqueous solution gave the Waugh-type [Ni(IV)Mo9O32]6− polyanion, whereas the oxidation of [Ni(II)W6O24H6]4− gave no heteropoly compound.

Abstract: Attempts to extract estimates of the δ-bond strength of quadruply metal-metal-bonded molecules from their δ→δ* electronic transitions have been hindered in the past by limited understanding of the origins of the energies and intensities of these transitions. We show that the energies of the δ→δ* transitions of a wide variety of these molecules are adequately interpreted in terms of a simple zero-differential-overlap model that yields one-electron δ-δ* splittings of 5000–10,000 cm−1 and two-electron exchange terms [K(δ,δ*)] of 5000–8000 cm−1. Because of the magnitude of K, singlet-triplet δ→δ* splittings are very large, and configuration interaction is important for the correct description of the ground state. The intrinsic intensity of 1(δ→δ*) is estimated to be quite low. The considerable intensities observed in many cases do not correlate with δ-bond strength, but instead reflect intensity stealing from charge-transfer excited states as a result of δ,δ*-orbital mixing with ligand orbitals. The intrinsic δ-bond stabilization is estimated to be on the order of 10 kcal mol−1.

Abstract: The reactions of the MM triple bonds in compounds of type Cp 2 M 2 (CO) 4 (M = Cr, Mo or W) are reviewed. These reactions are grouped under the headings of synthesis and structures of Cp 2 M 2 (CO) 4 -type compounds, nucleophilic additions to the MM bonds, reactions with 1,3-dipoles, oxidative reactions with nonmetals, and cluster-building reactions. Literature coverage is until the end of 1985 with 102 references.

Abstract: A series of 20 complexes of general formula R3SnL (R = CH3, n-C3H7, n-C4H9, C6H5, c-C6H11 ; L = anion of thiophene 2-, thiophene 2-acetic, furoic 2- and pyrrole 2- carboxylic acids) has been prepared. All of these complexes are monomers except those of triphenyltin(IV) which are polymers and have been characterised by molecular weight determination, IR, 1H-NMR and 119mSn Mossbauer studies. Tetrahedral and trigonal bipyramidal structures have been assigned and it has been found that none of the ring hetero atoms bond to tin(IV).

Abstract: The syntheses, characterization, X-ray structure and magnetism of a number of dinuclear compounds, with general formula M2(μ-OH2)(μ-O2CR)2(O2CR)2(tmen)2 are described. In this formula M = Co(II), Ni(II), R = CH3, CH2Cl, CHCl2, and CCl3, and tmen stands for N,N,N′,N′-tetramethyl-1,2-diaminoethane. The X-ray structures of two examples, M = Co and R = CCl3(I) and M = Co, Ni and R = CH2Cl(II) are described in detail. Compound I crystallizes in space group P21/c, with a = 23.610(7), b = 10.439(2) and c = 17.920(4) A, β = 110.43(4)° and Z = 4. Using 5196 measured reflections collected on a diffractometer with graphite monochromatized Mo-Kα radiation, the structure was refined to R = 0.089. The dimeric units Co2(OH2)(O2CCl3)2 [Co … Co = 3.696(3) A, angle CoOCo = 116.1(6)°] resemble very much those of earlier reported structures with M = Ni, Co and other bridging carboxylato anions. Apart from the two bridging carboxylato anions, two monodentate CCl3CO−2 anions are present, in addition to the normal bidentate tmen ligands, completing the octahedral geometry for each metal ion. The dimeric structure, with the bridging water ligand, appears to be highly stabilized by intramolecular hydrogen bonding with one of the oxygens of the monodentate CCl3CO−2 ligands (O … O contacts of 2.56–2.60 A). This stabilization by hydrogen bonding appears to be very similar to the proposed hydrogen bonding in hemerythrine, in which the coordinated dioxygen seems to be hydrogen bonded with the bridging -OH group. Compound II has essentially the same basic structure; it crystallizes also in the space group P21/c, with a = 16.034(7), b = 13.114(7), c = 15.344(7), β = 91.20(4) and Z = 4. From 4701 measured reflections the structure was refined to R = 0.043. The dimeric units exhibit a Co-Ni distance of 3.596(1) A, with a Ni-O-Co angle of 116.5°. The slightly smaller distances around Ni(II) made distinction from Co(II) possible. The metal ions in these Co and Ni compounds are antiferromagnetically coupled, just as the Fe ions in hemerythrine. This antiferromagnetic interaction has been studied by low-temperature magnetic susceptibility measurements. The magnitude of the coupling appears to vary as a function of the metal, the M … M distance and the MOM angle.

Abstract: The biochemistry of zinc is now beginning to be understood. The background to this understanding is a deep knowledge of the chemistry of the element. In this article I shall show some of the ways in which evolution has searched for and found the outstanding potential of zinc in catalysts. As a background an analogy is drawn with man's efforts to evolve analytical methods of high selectivity for the estimation of zinc. The article also illustrates some of my own interests in zinc which started in Professor Irving's laboratory.

Abstract: Copper complexes of two heterocyclic thiosemicarbazones were synthesized and characterized by magnetic-moment measurement, and ESR and IR spectroscopy. Implications of the magnetic and spectral data in relation to the structures of the complexes are discussed.

Abstract: The formation of borate complexes of several mono-, di- and trisaccharides in aqueous solution [t = 25°C, I = 0.1 M (KCl)] was studied by the potentiometric method. Values of the stability constants β1 and β2 of the 1 : 1 and 1 : 2 species were calculated for all compounds, using an extended version of the Antikainen equation. Raffinose, melezitose, saccharose and other fructose-containing oligosaccharides gave complexes of low stability, whereas lactulose and fructose gave very stable complexes. It is concluded that fructose moieties in oligosaccharides complex the borate anion by their 2- and 3-OH groups, in agreement with recent work by 11B NMR.

Abstract: The charge-transfer (CT) absorption spectra in the UV region (30,000–50,000 cm−1) of most W(VI) and Mo(VI) polyoxoanions, attributed to the oxygen-to-metal transitions, are interpreted on the basis of structural considerations through edge- and/or corner-sharings of some octahedral units. Polyoxoanions studied here are classified into two groups according to a common fragment constituting their structures; one group contains an ‘M5O18’ fragment [M = W(VI) and Mo(VI)] such as Weakley-type [Ce(IV)(W5O18)2]8− anion, [W10O32]4− and [M′W5O19]n− [M′ = V(V), Nb(V), W(VI)] polyanions and the other contains an A-α-‘XM9O34’ fragment (X = heteroatom) such as Keggin-type [α-XM12O40]n− and Dawson-type [α-P2M18O62]6− heteropolyanions. The first- and second-lowest energy CT (LECT) bands of the respective group are qualitatively discussed from the CT interactions among some fragments.

Abstract: The goal of this article is to present a historical perspective to theoretical calculations of metal-metal multiple bonds, to explain why calculations on these systems are so difficult and to predict the direction of future research in this area.

Abstract: Two new quadridentate Schiff base ligands formed from 2,5-hexanedione and S-alkyldithiocarbazic acids and their nickel(II), zinc(II) and cadmium(II) complexes having the general formula [M(SNNS)] (SNNS 2− is the dinegatively charged ligands) have been synthesized and characterized by elemental analysis and magnetic and spectroscopic methods. The Ni(SNNS) complexes are diamagnetic and square-planar. The Zn(SNNS) complexes are assigned with polymeric structures with mercapto sulphur-bridging. The Cd(SNNS) complexes presumably have polymeric structures.

Abstract: The strength of multiple metal-metal bonds in the metal dimers M 2 (M = Cr, Mo or W) and binuclear complexes M 2 (OH) 6 (M = Cr, Mo or W), M 2 Cl 4 (PH 3 ) 4 M = V, Cr, Mn, Nb, Mo, Tc, Ta, W or Re) has been studied by a non-local density functional theory. The method employed here provides metal-metal bond energies [ D (M-M)] in good accord with experiments for Cr 2 and Mo 2 , and predicts that W 2 of the three dimers M 2 (M = Cr, Mo or W) has the strongest metal-metal bond with D (W-W) = 426 kJ mol −1 and R (W-W) = 2.03 A. Among the binuclear complexes studied here we find the 3 d elements to form relatively weak metal-metal bonds (40–100 kJ mol −1 ), compared to the 4 d and 5 d elements with bonding energies ranging from 250 to 450 kJ mol −1 . The metal-metal bond for a homologous series is calculated to be up to 100 kJ mol −1 stronger for the 5 d complex, than for the 4 d complex. An energy decomposition of D (M-M) revealed that the σ-bond is somewhat stronger than each of the π-bonds, and one order of magnitude stronger than the δ-bond. For the same transition metal we find D (M-M) to be larger for M 2 (PH 3 ) 4 Cl 4 (M = Cr, Mo or W) than for M 2 (OH) 6 (M = Cr, Mo or W), and attribute this to a stronger π-interaction in the former series. While many of the findings here are in agreement with previous HFS studies, the order of stability D (3 d -3 d ) « D (4 d -4 d ) D (5 d -5 d ) differs from the order D (3 d -3 d ) « D (5 d -5 d ) D (4 d -4 d ) obtained by the HFS method, and the present method provides in general more modest values for D (M-M) than the HFS scheme.

Abstract: Reaction of (1,10-diamino-4,7-diazadecane)copper(II) in basic methanol with formaldehyde and the carbon acid nitroethane leads to the facile and high-yielding synthesis of the (10-methyl-10-nitro-1,4,8,12-tetraazacyclopentadecane)copper(II) cation. The similar reaction with diethylmalonate, a weaker carbon acid, yields the (10,10-dicarboxyethyl-1,4,8,12-tetraazacyclopentadecane)copper(II) cation in only low yield.

Abstract: A series of early transition metal organometallic derivatives containing the ancillary ligand 2,6-diphenylphenoxide (OAr-2,6Ph 2 ) have been synthesized. Compounds of stoichiometry Ti(OAr-2,6Ph 2 ) 2 (R) 2 (R = CH 3 , CH 2 SiMe 3 , CH 2 Ph and Ph) and Ti(OAr-2,6Ph) 3 (R) (R = CH 3 , CH 2 SiMe 3 ) are obtained by treating the corresponding homoleptic alkyl, TiR 4 , with the required amount of phenol, HOAr-2,6Ph 2 . For the Group 5 metals Nb and Ta, the methyl derivatives M(OAr-2,6Ph 2 ) 2 (CH 3 ) 3 and M(OAr-2,6Ph 2 ) 3 (CH 3 ) 2 are obtained via methylation of the corresponding chloro-aryloxides. Besides routine spectroscopic characterization the diphenyl Ti(OAr-2,6Ph 2 ) 2 (Ph) 2 and mono-alkyl Ti(OAr-2,6Ph 2 ) 3 (CH 2 SiMe 3 ) have been structurally characterized by X-ray diffraction techniques. Both molecules contain a pseudo-tetrahedral environment about the titanium atom with short 1.794(3)–1.806(2) A, TiO distances and large, 153–179°, TiOAr angles. The TiC distances appear normal for these types of compounds.

Abstract: The new tropolonato (trop) complexes Os(trop) 3 , Ir(trop) 3 , [Pt(trop)(PPh 3 ) 2 ] BPh 4 , OsO 2 (trop) 2 , MoO 2 (trop) 2 and W 2 O 5 (trop) 2 are reported. The vibrational, 1 H and 13 C NMR spectra of the complexes have been measured and the X-ray crystal structure of MoO 2 trop 2 has been determined. The crystals are monoclinic with α = 15.485(3), b = 13.583(3), c = 14.211(3)A, β = 117.74(1)°, space group C 2/ c , Z = 8; and the structure has been refined to R = 0.033.

Abstract: Praseodymium(III) macrocyclic complexes of types [Pr(L)(H2O)2]Cl3, [Pr(mac1)]Cl3 and [Pr(mac2)(H2O)2]Cl3 (L = ligands derived by the condensation of diacetyl or benzil with semicarbazide or thiosemicarbazide; mac1 = macrocyclic ligands derived by the condensation of diacetyl or benzil with carbohydrazide; mac2 = macrocyclic ligands derived by the condensation of diacetyl or benzil with semicarbazide, thiosemicarbazide or thiocarbohydrazide) have been prepared and characterized by conductance magnetic moment, spectral data, thermal and elemental analyses.

Abstract: X-ray crystallographic studies on the lithium diphenylphosphide adducts (Me2NCH2CH2)2NMe2 · LiPPh2 ( 1) and Me2NCH2CH2NMe2 · LiPPh2 (2) are reported. 1 is monomeric, with a terminal PPh2 unit containing a pyramidally coordinated phosphorus atom attached to the four-coordinate metal atom by a Li-P bond of length 2.567(6) A. 2 crystallizes as dimers, (Me2NCH2CH2NMe2 · LiPPh2)2, with bridging PPh2 units containing (distorted) tetrahedrally coordinated phosphorus atoms: their planar (LiP)2 rings are roughly square-shaped (mean PLiP angle 91°, mean LiP distance 2.61 A). Discussion of features of these structures is facilitated by ab initio MO calculations on the model systems LiPH2 and (LiPH2)2. Cryoscopic molecular mass measurements and high-field 7Li/31P NMR spectroscopic studies on solutions of 1 and 2 indicate that both solid-state structures are retained in arene solution, though some dissociation of2 into monomers is apparent.

Abstract: Cyclometallated complexes derived from organic ligands where two initial metallation sites are present have been synthesized. The preferred palladation position is discussed on the basis of electronic and steric effects, and the regioselectivity of the cyclometallation is characterized by means of IR and 1 H NMR spectroscopy. The spectral studies show that the less favored position is not attached to the metal atom. Acetato- and halogeno-bridged dimers, as well as phosphine monomers derived from the latter, have been obtained and studied by spectroscopical methods.

Abstract: By reaction of MoCl3(THF)3 with NaSH in tetrahydrofuran, followed by addition of Me2PCH2CH2PMe2(dmpe), then chromatography on silica-gel, and finally addition of NH4PF6, the compound [Mo3S4Cl3(dmpe)3]PF6·CH3OH was prepared in moderate yield. X-ray crystallography showed the presence of a chiral cation based on a Mo3S4 core with chelating dmpe units arranged like the blades of a ship's screw. The three Cl atoms fill the remaining octahedral sites on each metal atom. The compound crystallizes in space group R3c with (hexagonal) cell dimensions of a = 15.310(7) A, c = 30.640(3) A and Z = 6. The [Mo3S4Cl3(dmpe)3]+ ion and the PF6− ion each have crystallographic C3 symmetry. The principal distances and theirs esds are: MoMo, 2.766(4) A; Mo(μ3-S), 2.360(9) A; Mo(μ2-S), 2.290(7) A, 2.336(7) A; MoP, 2.534(8) A, 2.605(8) A; MoCl, 2.473(7) A; PF, 1.56(2) A, 1.64(3) A. The correct enantiomer was obtained by refining both to convergence, which give R = 0.059 and R = 0.064.

Abstract: The reaction of [Bzo 2 Me 4 [14]hexaenato(2−)N 4 ]Ni(II) and [Bzo 2 Me 2 Ph 2 [14]hexaenato(2−)N 4 ]Ni(II) with glutaryl chloride leads to new γ,γ′-disubstituted derivatives having γ,δ-unsaturated-δ-lactonic rings as substituents. The demetalation of the new complexes by means of gaseous HCl is described. The new compounds were characterized by elemental analysis, IR, 1 H NMR and MS data.

Abstract: NaVO 3 Na 2 MoO 4 solutions acidified with HCl were studied at the atomic V/Mo ratios equal to 3 : 1, 1 : 1, 1 : 3, 1 : 6 and vanadium concentration [V] = 0.1, 0.04, 0.004 and 0.0004 M in the range pH 7-2. Their 51 V NMR spectra (measured at H ito = 7 T) were compared with those of VW solutions containing mixed metal complexes of known composition. The VMo 5 O 19 3− ( 51 V NMR chemical shift relative to VOCl 3 , δ, −502 ppm), V 2 Mo 4 O 19 4− (δ −494), V 2 Mo 4 O 19 3− δ −507), V 9 MoO 28 5− (δ −422, −492, −501, −512, −521.5) and HV 9 MoO 28 4− polyanions (p.a.) have been found to be dominant mixed species in Na-V-Mo solutions. Along with them the V itx MO 13-itx O −itx−3 40 p.a.( x ∼2–3) of the Keggin type (δ −496, −498, −516, −522) are supposed to be formed at pH 0.01 M). The V 2 Mo 6 O 26 6− p.a., isolated at pH ∼ 5 as the sodium salt (solid state δ −482), seem to be present in concentrated Na-V-Mo solutions only as minor species. On dissolving the salt the V 2 Mo 6 O 26 6− p.a. mainly disproportionates into the complexes mentioned. From solutions containing mainly the V 9 MoO 28 5− p.a. the sodium salt of V 10 O 28 6− is crystallized. The V 9 WO 28 6− p.a. are detected in VW solutions at V/W > 1. 17 O and 95 Mo NMR spectra of some mixed complexes are described. The distribution diagrams for VMo and V-W solutions at [V] = 0.004 M and V/Mo(W) = 1:3, derived from their 51 V NMR spectra, are given.

Abstract: W2(OR)6Ln compounds [R = But n = 0; R = Pri or Np (Np = neopentyl), L = py (py = pyridine) or HNMe2, n = 2] react with alkynes (R′C-CR′) under mild conditions (hexane solutions, room temperature or below) to yield a variety of products depending upon the nature of the alkoxide, the alkyne and the mole ratio of the reactants. The products include alkylidyne complexes Ln(RO)3W CR′ (n = 1 or 0) (Schrock et al., Organometallics 1985, 4, 74), alkyne adducts, W2(OR)6(py)n(μ-C2R′2), alkylidyne-capped tritungsten complexes, W3(μ3-CR′)(OR)9, and W2(OR)6(L)(μ-C4R′4) or W2(OR)6(μ-C4R′4) (μ2-C2R′2) compounds. Evidence for equilibria involving alkyne adducts and alkylidyne species is found for certain combinations of R and R′. (1) The alkylidyne complexes (ButO)3 WCMe and (py)2(PriO)3 W CNMe2 react with CO (1 atm 22°C, in hexane) to yield alkyne adducts W2(OBut)6(μ-C2Me2)(CO) and W2[(OPri)6(CO)2(η2-C2(NMe2)2], respectively. (2) The alkylidyne complexes [PriO)2(HNMe2)(R′C)W(μ-OPri)]2 react with alkynes R′CCR′ (> 2 equiv, hexane, 22°C) to give W2(OPri)6(μ-C4R′4)(η2-C2R′2) compound (R′ = Me or Et). (3) The alkyne adducts W2(ONp)6(py)n(μ-C2R′2) (R′ = Et or Ph, n = 1; R′ = Me, n = 2) react with W2(ONp)6(py)2 in a 1:2 mole ratio at 22°C in hexane to yield W3(μ3-CR′)(ONp)(9 compounds. In related reactions involving 1,2-bishydrocarbyl-tetraalkoxides, W2(CH2R″)2(OR)4, and alkynes (R′CCR′) (2 equiv), alkyne adducts of formula W2(CH2R″)2(η2-C2R′2)2(OPri)4 and W2(CH3)2(μ-C2R′2)(OBut)4(py), alkylidyne-bridged complexes HW2(μ-CR″)(μ-C4R′4)(OPri)4 and products of WW and CC metathesis have been isolated for various combinations of R, R′ and R″.

Abstract: A new series of amino acid Schiff base Ni(II) complexes of 2-hydroxy- 1 -naphthaldehyde with glycine, l -alanine, l -valine, l -leucine, dl -isoleucine, dl -norleucine, l -serine and l -aspartic acid has been prepared by constituent combination. The structure of the complexes is investigated by microanalysts, conductance, electronic and IR spectral measurements. It is concluded that the bivalent anions of the Schiff bases coordinated to Ni(II) as a tetradentate ligand (O N O O), in the case of the aspartic acid moiety, or as a tridentate ligand (O N O) in the case of the other amino acid moieties. The structure of the Ni(II) complexes is suggested to be square planar.