Apical Coordination Site Research Articles

Complexes of Triamidoamines with the Early Actinides. Synthetic Routes to Monomeric Compounds of Tetravalent Uranium and Thorium Containing Halide and Amide Ligands.

The reaction of the lithiated triamidoamine [Li(3)(NN'(3))(THF)(3)] [NN'(3) = N(CH(2)CH(2)NSiMe(2)Bu(t))(3)] with AnCl(4) (An = U, Th) followed by sublimation gives monomeric [An(NN'(3))Cl]. Reaction of these complexes with SiMe(3)X (X = Br, I) gives [An(NN'(3))X]. The amido derivatives [An(NN'(3))(NEt(2))] are prepared from H(3)(NN'(3)) and [U(NEt(2))(4)] and from [Th(NN'(3))Cl] and [Li(NEt(2))]. In each case, the complexes [U(NN'(3))X] (X = Cl, Br, I, NEt(2)) are shown by X-ray crystallography to contain a triamidoamine ligand disposed with 3-fold symmetry about the metal center. The structures are distorted from trigonal bipyramidal by displacement of the uranium atoms out of the equatorial plane of the three amido nitrogen atoms by ca. 0.8 Å. The ligand backbone is distorted in such a manner as to cause the tert-butyldimethylsilyl groups to encircle the equatorial plane of the metal atom rather than surround the apical coordination site as is observed in the transition metal complexes of this type. Variation of the auxiliary ligand has little effect on the orientation, bond lengths, and angles within the (triamidoamine)uranium fragment. The tert-butydimethysilyl-substituted triamidoamine ligand is thus ideally suited for coordination to large metals since it stabilizes the formation of 3-fold symmetric structures while also allowing reactivity at the fifth coordination site.

Enantioselective Ti(IV) Sulfoxidation Catalysts Bearing C3-Symmetric Trialkanolamine Ligands: Solution Speciation by 1H NMR and ESI-MS Analysis

Sulfoxidation catalysts generated from titanium(IV) isopropoxide and enantiopure trialkanolamine ligands promote the enantioselective oxidation of aryl alkyl sulfides to the corresponding sulfoxides even at low (1−2%) catalyst loadings. Electrospray ionization mass spectrometry (ESI-MS), in combination with conventional low-temperature NMR techniques, provides a powerful tool for understanding the unique nature of these catalysts. Tetradentate ligation of the titanium atom by the trialkanolamine ligand provides a highly robust titanatrane core which is retained even in hydroxylic solvents and/or under acidic conditions. In contrast, the remaining apical coordination site is shown to be substitutionally labile. Previously ill-defined species formed when the catalyst is generated in situ with a slight excess of trialkanolamine are shown to consist of discrete 2:1, 3:2, and 4:3 oligomers in which the excess trialkanolamine bridges multiple titanatrane units. In the presence of excess tert-butyl hydroperoxide, all of the precatalyst species are cleanly converted to a mononuclear titanium(IV) peroxo complex which serves as the active sulfoxidation catalyst. Ab initio molecular orbital calculations were used to probe the structure and position of protonation of the catalytic species. Other ionization techniques (fast ion bombardment or electron impact) proved less useful than ESI-MS due to high levels of fragmentation during the ionization process.

Synthesis and spectroscopic characterisation of copper(II) complexes with 5-methyl-1-(2′-pyridyl) pyrazole-3-carboxamide (MP yP zCA): X-ray crystal structure of [Cu(MP yP zCA) 2(H 2O)](ClO 4) 2

The coordination mode of the title ligand, MP y P z CA (synthesised for the first time and characterised by elemental analyses, mass, IR and PMR spectral parameters), is reported by solid state isolation and physicochemical identification of copper(II) complexes, Cu(MP y P z CA) 2X 2.H 2O (X=Cl/Br/NO 3/ClO 4). Magnetic and electronic spectral features classify the reported complexes as six coordinate distorted octahedral ones. IR spectra (4000–200 cm −1) of MP y P z CA and its complexes indicate different denticity of the two ligand moities namely neutral bidentate function through pyrazolyl 2N and pyridyl 1′N of one ligand (A) and the neutral tridentate behaviour through pyrazolyl 2N, pyridyl 1′N and the amidic oxygen of the second ligand system (B). The sixth apical coordination site is occupied by a water molecule in the perchlorate complex (as evident by X-ray data) or by the counter ion, X (X=Cl/Br/NO 3). The electrochemical studies demonstrate easy oxidative nature of Cu(II) in the reported species. X-ray crystallographic studies of the perchlorate complex, [Cu(MP y P z CA) 2(H 2O)](ClO 4) 2, (Pna2 1, orthorhombic), has substantiated the conjecture that the geometry is distorted octahedral. The Cu-N (pyrazolyl) and Cu-N (pyridyl) bond lengths are 2.001(3) and 1.969(3) Å and 2.020(4) and 2.206(4) Å in the ligand systems, A and B. respectively; Cu-O (amidic oxygen) for ligand system B and Cu-O (water) bond lengths are 2.783(3) and 2.010(3) Å, respectively. The crystal structure is highly stabilised through extensive hydrogen bonding.

Synthesis and Characterization of Cs(5)Sb(8)S(18)(HCO(3)): A New Layered Phase Containing Interstitial Cations and Anions.

A new pseudoternary phase, Cs(5)Sb(8)S(18)(HCO(3)), was prepared from supercritical ammonia at 160 degrees C over 4 days using stoichiometric quantities of Cs(2)CO(3), Sb(2)S(3), and S(8). Red parallelepipeds of the title phase crystallize in the centrosymmetric monoclinic space group C2/c, with a = 27.064(3) Å, b = 11.634(4) Å, c = 12.642(3) Å, beta = 97.45(2) degrees, and Z = 4. The compound has a layered structure, with the layers formed from ribbons of condensed psi-SbS(4) trigonal bipyramids linked via S(3)(2)(-) chains, and both Cs(+) and HCO(3)(-) ions between the layers, giving rise to the formula Cs(5)Sb(8)S(12)(S(3))(2)(HCO(3)). Each layer is approximately 10 Å thick, with two layers per unit cell. The condensation of the group 15/16 building blocks into ribbons is the result of a combination of edge- and vertex-shared antimony(III) sulfide pseudo trigonal bipyramids. In this phase, the S(3) chains always link adjacent ribbons via apical coordination sites on the antimony atoms. The open cavities created by the linking trisulfide dianions between neighboring ribbons accommodate the antimony lone pairs and two unique cesium cations. A third cesium cation is located between layers. Unique to this compound, the anionic antimony sulfide layers are separated not only by cesium cations but also by bicarbonate anions. Results derived from infrared spectroscopy, diffuse reflectance, bond valence sums, and magnetic susceptibility measurements support the formulation of this compound as an electron-precise, wide-bandgap material. Thermal stability studies of Cs(5)Sb(8)S(18)(HCO(3)) are also discussed.

(Acetonitrile)[N,N-bis(3-aminopropyl)-1,3-propanediamine-N,N',N'',N''']copper(II) Diperchlorate

The structure of the title compound, [Cu(C 2 H 3 N)(C 9 H 24 N 4 )](ClO 4 ) 2 , consists of (acetonitrile)[tris(3-amino-n-propyl)amine-N,N',N,N']copper(II) cations and perchlorate anions linked by an extensive network of weak N-H...O and C-H...O hydrogen bonds. The Cu II atom has a coordination geometry intermediate between tetragonal pyramidal (with one of the three primary amine N atoms occupying the apical coordination site) and trigonal bipyramidal (with the tertiary amine and acetonitrile N atoms in the axial positions). Main dimensions include Cu-N(amine) 2.035(8)-2.121(8)A and Cu-N(acetonitrile) 2.099(7)A.

Pt(PMe3)2(dppm)]Cl2.2H2O [dppm = Bis(diphenylphosphino)methane

The crystal structure of [bis(diphenylphosphino)methane]bis(trimethylphosphine)platinum(II) chloride dihydrate, [Pt(C3H9P)2(C25H22P2)]Cl2.2H2O, contains [Pt(PMe3)2(dppm)]2+ cations with the PtII ion bound to a distorted square-planar arrangement of one chelating dppm ligand and two PMe3 ligands [Pt—P(dppm) 2.317 (6), 2.352 (7) A; Pt—P(PMe3) 2.331 (7), 2.345 (7) A]. A weakly inter­acting Cl− ion occupies an apical coordination site [Pt⋯Cl 3.175 (7) A] and a discrete Cl− anion is present to balance the charges. Two H2O molecules are also present in the asymmetric unit.

Synthesis, Structure, and Reactivity of Three-Coordinate Vanadium(III) Chalcogenolates and Vanadium(V) Chalcogenide Chalcogenolates

Reaction between [(Me3Si)2N]2V(Br)(THF) and (THF)2LiER (E = Se,Te; R = Si(SiMe3)3, SiPh3) afforded the three-coordinate [(Me3Si)2N]2VER complexes in 60−80% yield. The −SeSi(SiMe3)3 complex and both of the −TeR derivatives were characterized crystallographically, and their X-ray structures are presented for comparative purposes. The structures feature a three-coordinate vanadium center with agostic interactions between two C−H groups of the amido trimethylsilyl ligands at the vacant apical coordination sites of vanadium. Reaction of [(Me3Si)2N]2V(Br)(THF) with (DME)LiSeC(SiMe3)3 (DME = 1,2-dimethoxyethane) afforded the vanadium(IV) dimer {[(Me3Si)2N]2V(μ-Se)}2 in moderate yield. X-ray crystallography confirmed a dimeric structure in the solid state with a long V−V distance of 3.044(1) Å. The three-coordinate compounds were oxidized by styrene oxide, propylene sulfide, and Ph3PSe or Se to yield the oxo−, sulfide−, and selenide−vanadium(V) complexes, respectively; these derivatives were characterized by 1H, 13C{1H}, and 51V NMR spectroscopy. [(Me3Si)2N]2V(E‘)[SeSi(SiMe3)3] (E‘ = O, S, Se) and [(Me3Si)2N]2V(O)[TeSi(SiMe3)3] were isolated as deeply colored, crystalline solids and [(Me3Si)2N]2V(Se)[SeSi(SiMe3)3] was characterized crystallographically. Styrene oxide also reacted with [(Me3Si)2N]2V(Br)(THF) affording [(Me3Si)2N]2V(O)(Br) as orange crystals in 70% yield. In general, the vanadium(V) selenolates are more stable than the tellurolates, the latter being susceptible to reduction. For example, [(Me3Si)2N]2V(E)[TeSi(SiMe3)3] (E = S, Se) cleanly decomposes in solution affording Te2[Si(SiMe3)3]2 and {[(Me3Si)2N]2V(μ-E)}2. The compounds [(Me3Si)2N]2V(O)(X) (X = Br, SeSi(SiMe3)3) thermally rearrange to the siloxide−imido species, [(Me3Si)2N](Me3SiN)V(OSiMe3)(X). The isomerization occurs more readily when X = Br, where kinetic data demonstrated the reaction to be first order in starting material, implicating an intramolecular 1,3-trimethylsilyl migration from N to O. Activation parameters (ΔH⧧= 26 ± 1 kcal mol-1 and ΔS⧧= −0.60 ± 2 eu) are in the range of those determined for the related thermal rearrangement of β-ketosilanes to siloxyalkenes.

A dinuclear copper(II) complex [Cu2L2](ClO4)2 derived from 2,6-bis(aminomethyl)-4-methylphenol (HL)

The dinuclear copper(II) complex of 2,6-bis(aminomethyl)-4-methylphenol (HL), bis[μ-2,6-bis(aminomethyl)-4-methylphenolato-1κN,1:2κ 2 O,2κN']dicopper(II) diperchlorate, [Cu 2 (C 9 H 13 N 2 O) 2 ](ClO 4 ) 2 , has been synthesized and its structure determined. The title complex is crystallographically centrosymmetric about the midpoint of the Cu...Cu separation [3.013 (1) A] and consists of two distorted square-pyramidal copper(II) centres bridged via phenoxide O atoms. Each Cu atom is coordinated (type 4+1) by two bridging O atoms, two secondary amine N atoms and, weakly, by one O atom of a symmetry-related perchlorate ion occupying the apical coordination site

Influence of 3-methyl substitution on the ability of 2-pyrrolidone to form heterometallic polymeric structures; synthesis and X-ray crystal structure of [HgCu(C5H8NO)2(CH3O)(NO3)]2, where C5H8NO is the anion of 3-methyl-2-pyrrolidone

Abstract Reaction of Hg(C5H8NO)2 (where C5H8NO is the anion of 3-methyl-2-pyrrolidone) with copper(II) nitrate in methanol yields [HgCu(C5H8NO)2(CH3O)(NO3)]2 which has been characterized by X-ray diffraction. The crystals are triclinic, P 1 , a = 7.041(3), b = 11.343(4), c = 11.427(4) A, α = 69.13(3), β = 76.08(3), γ = 84.17(3)°, V = 828 A3, Z = 1. The structure was refined on 1338 reflections to R = 0.074. The compound has pairs of copper atoms bridged by two methoxide ions. Each copper atom has a square pyramidal coordination geometry formed by five oxygen atoms, two from methoxide ions, one from NO3−, and one from each of two different Hg(C5H8NO)2 units. These last two provide additional bridges between the basal and apical coordination sites of the bridged copper atoms and, in so doing, form 10-membered macrocyclic rings. Adjacent dimers are linked by pairs of Hg⋯O(nitrate) interactions, forming a loosely bound polymeric structure.

Molecular Structure of a Catalytically Active Chiral Ruthenium(II) Complex. Chlorohydridobis[(R)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl]ruthenium(II)

Abstract Molecular structure of the title complex was determined by the single crystal X-ray diffraction method. The complex has a typical octahedral structure and takes the trans configuration as a whole, where the Cl− and H− occupy the apical coordination sites. The configuration of the seven-membered chelate ring of the phosphine ligand is λ-skew(v).

Cobalt(II) tetrasulfophthalocyanine on titanium dioxide: A new efficient electron relay for the photocatalytic formation and depletion of hydrogen peroxide in aqueous suspensions

A novel synthesis for the covalent linkage of cobalt(II) tetrasulfophthalocyanine (Co^(II)TSP) to the surface of titanium dioxide (TiO_2) particles (d ≤ 0.5 µm) is described. Upon irradiation with light that exceeds the bandgap energy (E_g) of TiO_2 (i.e., ⋋ 5 380 nm), Co^(II)TSP is reduced to Co^ITSP under anoxic conditions both as a dry powder and in aqueous suspension. The photochemical reduction is shown to be fully reversible in the presence of molecular oxygen (O_2). Hydrogen peroxide (H_2O_2) is produced upon irradiation of an aerated aqueous suspension of the 'hybrid catalyst, TiO__2-Co^(II)TSP. Formation kinetics are followed in situ with a polarographic detector (detection limit ≃ 10^(7-) M H_2O_2); quantum yields, ϕ_(H_2O_2) between 0.16 and 0.49 have been determined. The reactive photocatalytic center appears to be generated by the attachment of molecular oxygen in the open apical coordination site of the hybrid Co^(II)TSP complex. Formation of Co^(II)TSP-O_2^(•-) is enhanced by the binding of TiO^- surface groups in the opposite apical position. Hydrogen peroxide is produced in a two-step electron transfer from the conduction band via the Co(III) center. The involvement of free radical intermediates in this mechanism appears to be highly unlikely. On the basis of its observed chemical and photochemical stability and the high quantum yields for O_2 reduction, the newly developed hybrid material is proposed to be applicable as a potent and stable oxidation catalyst.

Studies on metal complexes of isocytosine derivative: The crystal structure of zinc(II) complex of 2-hydrazino-4-hydroxy-6-methylpyrimidine.

The crystal structure of the copper (II) complex of 2-hydrazino-4-hydroxy-6-methylpyrimidine (LH) has been determined from three-dimensional X-ray diffractometer data by heavy atom Fourier methods. Crystals of [Cu (LH)2 (H2O)] Cl2·2H2O are triclinic with unit cell dimensions a=10.020 (2), b=14.384 (2), c=7.205 (1) A, α=104.63 (2)°, β=111.04 (1)°, γ=84.93 (2)°, space group P 1, and Z=2. Block-diagonal least-squares refinement using 3126 independent reflections yielded an R value of 0.062. There are two mirror-image complex molecules in a unit cell. Each copper (II) complex has five coordinated bonds and assumes a distorted square pyramid structure. The two ligand molecules, (LH)2 are trans coordinated to the copper (II) ion through nitrogen atoms N3 of the pyrimidine rings and also through the amino nitrogen atoms of the hydrazino groups. In each copper (II) complex, the one apical coordination site is occupied by the water oxygen atom. The hydroxyl group at C4 of the pyrimidine ring takes the keto form, since the hydrogen atom of the hydroxyl group transfers to N1 of the ring. The chloride ions are not directly hydrogen bonded to the N1 atoms of the pyrimidine bases, but are bound to the apical water oxygen atoms. The pyrimidine rings in the crystals are not stacked in parallel but are inclined at an angle of 18.9 or 18.8°.