Preparation and crystal structures of formato complexes of the [MIV3O4]4+ and [MIV3S4]4+ (M = Mo,W) clusters. Convenient precursors to the corresponding aqua complexes

In the aqueous chemistry of molybdenum(IV) and tungsten(IV), trinuclear, incomplete cubane-like, oxo and sulfido clusters of the type [M3E4]4+ (M = Mo, W; E = O, S) play a central role. We here describe how formato complexes of all these cluster cores can be prepared in high yields by crystallization from methanol-water or ethanol-water mixtures. Since potassium and ammonium formate are very soluble in these alcohol-water mixtures, high formate concentrations could be accomplished in the solutions from which the corresponding salts of cluster formato complexes crystallized. The [Mo3O4]4+ compounds could be synthesized without requiring the use of noncomplexing acids in the process. Some [M3E4]4+ compounds were characterized by single-crystal structure determinations. [NH4]3.20[K]0.80[H3O][Mo3O4(HCO2)8][HCO2].H2O was triclinic, space group P1 (No. 2) with a = 11.011(2) A, b = 13.310(2) A, c = 9.993(1) A, alpha = 106.817(7) degrees, beta = 91.651(9) degrees, gamma = 88.340(9) degrees, and two formula units per cell. [K]6[W3S4(HCO2)9][HCO2].2.27H2O.0.73CH3OH was monoclinic, space group C2/m (No. 12) with a = 19.605(6) A, b = 14.458(7) A, c = 13.627(5) A, beta = 118.94(2) degrees, and four formula units per cell. Generally, the nine coordination sites of [M3E4]4+ were occupied either by a mixture of monodentate and mu 2-bridging formato ligands or by monodentate formato ligands only. By dissolution in noncomplexing strong acid, all the formato complexes immediately hydrolyzed to form [M3E4(H2O)9]4+ aqua complexes. This allows, for example, high concentrations of [Mo3S4(H2O)9]4+ in CF3SO3H to be obtained and these solutions to be used for the synthesis of bimetallic clusters containing the cubane-like motif Mo3M'S4.     

(iPr3P)6Rh6H12]2+: a high-hydride content octahedron that bridges the gap between late and early transition metal clusters

Treatment of [(iPr3P)2Rh(nbd)][Y] {nbd = norbornadiene, Y = B{3,5-(CF3)2C6H3}4- [B(ArF)4] or 1-H-closo-CB11Me11-} with H2 (ca. 4 atm) results in the isolation, in moderate yield, of the octahedral cluster complex [(iPr3P)6Rh6H12][Y]2 1. The cluster (for both anions) has been characterized by NMR, mass spectroscopy, and X-ray crystallography. These show 1 to have 12 edge-bridging hydrogen atoms, and the structure bears more resemblance to clusters of the early transition metals with pi-donor ligands than those of the late transition metals with pi-acceptor ligands. Intermediate complexes on the route to 1, namely, the nonclassical dihydrogen complexes [(iPr3P)2Rh(H)2(eta2-H2)x][B(ArF)4] (x = 1 or 2), have been observed spectroscopically. The high hydride content of 1 makes it a possible model for nanocluster colloidal Rh(0) catalysts that are used in olefin and arene hydrogenation.     

Synthesis and structure of nickel-containing cuboidal clusters derived from [W3Se4(H2O)9]4+. Site-differentiated substitution at the nickel site in the series [W3NiQ4(H2O)10]4+ (Q = S, Se)

New Ni-containing heterometallic cuboidal cluster aqua complex [W3(NiCl)Se4(H2O)9]3+, the missing link in the family of the M3NiQ4 clusters (M = Mo, W; Q = S, Se), has been prepared by the reaction of [W3Se4(H2O)9]4+ with Ni in 2 M HCl. Single crystals of edge-linked double-cuboidal cluster [{W3NiSe4(H2O)9}2](pts)8.18H2O (pts = p-toluenesulfonate) were grown from the solution of the aqua complex in 3 M Hpts, and their structures were determined. The Ni site in the clusters [W3(NiCl)Q4(H2O)9]3+ selectively coordinates typical pi-acceptor ligands such as CO, olefins, acetylenes, phosphines, arsines, or SnCl3-. This allows stabilization by coordination of such elusive species as HP(OH)2 and As(OH)3. The stability constants for coordination of HP(OH)2, As(OH)3, and SnCl3- were determined. The Se for S substitution increases the stability by 1-2 orders of magnitude. Supramolecular adducts with cucurbit[6]uril (Cuc), [W3(Ni(HP(OH)2))Q4(H2O)9]Cl4.Cuc.11H2O and [W3(NiAs(OH)3)S4(H2O)8Cl]Cl3.Cuc.13H2O, were isolated and structurally characterized.     

Methylcyclopentadienyl-substituted tungsten(IV) sulfido cluster [(eta5-Cp')3W3S4]+ and its heterobimetallic derivative [(eta5-Cp')3W3S4Ni(PPh3)]+

The aqueous cluster salt [(H2O)9W3S4][pts]4.9H2O (pts = p-toluenesulfonate) was converted to the methylcyclopentadienyl (Cp') substituted cluster [(eta5-Cp')3W3S4][pts] ([1][pts]) from which the cubane-like cluster [(eta5-Cp')3W3S4Ni(PPh3)][pts] ([2][pts]) was obtained by reaction with Ni(cod)2 and PPh3. [2][pts] was characterized by X-ray crystal structure analysis.     

Computational modeling of di-transition-metal-substituted gamma-keggin polyoxometalate anions. Structural refinement of the protonated divacant lacunary silicodecatungstate

The B3LYP density functional method has been validated for the di-Mn-substituted gamma-Keggin polyoxometalate (POM) anion, [(SiO4)MnIII2(OH)2W10O32]4-, and for the divacant lacunary silicodecatungastate, gamma-[(SiO4)W10O32]8-. This approach was shown to adequately describe the geometries of [(SiO4)MnIII2(OH)2W10O32]4- and gamma-[(SiO4)W10O32]8. Three different geometrical models, "full", "medium", and "small", for Mn2-gamma-Keggin have also been validated. It was shown that the medium [(SiO4)MnIII2(OH)2W6O24H8]4- model, as well as small [(SiO4)MnIII2(OH)2W4O18H10]2- model, preserves structural features of the full system, [(SiO4)MnIII2(OH)2W10O32]4-. However, the small model distorts the charge distribution at the "active site" of the system and should be used with caution. The same computational approach was employed to elucidate the structure of the di-Fe-substituted gamma-Keggin POM. The structure of the acidic (tetra-protonated form) of lacunary POM, gamma-[(SiO4)W10O32H4]4-, was shown to be gamma-[(SiO4)W10O28(OH)4]4- with four terminal hydroxo ligands, rather than gamma-[(SiO4)W10O30(H2O)2]4- with two aqua and two oxo(terminal) ligands as reported by Mizuno and co-workers (Science 2003, 300, 964). The observed and calculated asymmetry in the W-O(terminal) bond distances of gamma-[(SiO4)W10O32H4]4- is explained in terms of the existence of O1H1...O2H2 and O4H4...O3H3 hydrogen-bonding patterns in the gamma-[(SiO4)W10O28(OH)4]4- structure.     

Study of the ligand substitution reactions of cis,cis-[(bpy)(2)(L)RuORu(L')(bpy)(2)](n+) (L,L' = H(2)O,OH(-), NH(3)) using electrospray ionization mass spectrometry and (1)H NMR

We have successfully applied electrospray ionization mass spectrometry (ESI-MS) and (1)H NMR analyses to study ligand substitution reactions of mu-oxo ruthenium bipyridine dimers cis,cis-[(bpy)(2)(L)RuORu(L')(bpy)(2)](n+) (bpy = 2,2'-bipyridine; L and L' = NH(3), H(2)O, and HO(-)) with solvent molecules, that is, acetonitrile, methanol, and acetone. The results clearly show that the ammine ligand is very stable and was not substituted by any solvents, while the aqua ligand was rapidly substituted by all the solvents. In acetonitrile and acetone solutions, the substitution reaction of the aqua ligand(s) competed with a deprotonation reaction from the ligand. The hydroxyl ligand was not substituted by acetonitrile or acetone, but it exchanged slowly with CH(3)O(-) in methanol. The substitution reaction of the aqua ligands in [(bpy)(2)(H(2)O)Ru(III)ORu(III)(H(2)O)(bpy)(2)](4+) was more rapid than that of the hydroxyl ligand in [(bpy)(2)(H(2)O)Ru(III)ORu(IV)(OH)(bpy)(2)](4+). In methanol, slow reduction of Ru(III) to Ru(II) was observed in all the mu-oxo dimers, and the Ru-O-Ru bridge was then cleaved to give mononuclear Ru(II) complexes.     

Triangular oxalate clusters [W(3)(mu(3)-S)(mu(2)-S(2))(3)(C(2)O(4))(3)](2)(-) as building blocks for coordination polymers and nanosized complexes

The reaction of aqueous [W3S7(C2O4)3](2-) with Ln(3+) and Th(4+) in a 1:1 molar ratio leads to oxalate-bridged heteropolynuclear molecular complexes and coordination polymers. La(3+) and Ce(3+) give a layered structure with big (about 1.8 nm) honeycomb pores which are filled with water molecules and lanthanide ions, in {[Ln(H2O)6]3[W3S7(C2O4)3]4}Br x xH2O (Ia and Ib). The smaller Pr(3+), Nd(3+), Sm(3+), Eu(3+), and Gd(3+) ions give discrete nanomolecules [(W3S7(C2O4)3Ln(H2O)5)2(mu-C2O4)] (with a separation of about 3.2 nm between the most distant parts of the molecule), which are further united into zigzag chains by specific S2...Br- contacts to achieve the overall stoichiometry K[(W3S7(C2O4)3Ln(H2O)5)2(mu-C2O4)]Br.xH2O (IIa-IId). Th(4+) gives K2[(W3S7(C2O4)3)4Th2(OH)2(H2O)10] x 14.33H2O (III) with a nanosized discrete anion (with a separation of about 2.7 nm between the most distant parts of the molecule), in which two thorium atoms are bound via two hydroxide groups into the Th2(OH)2(6+) unit, and each Th is further coordinated by five water molecules and two monodentate [W3S7(C2O4)](2-) cluster ligands. All compounds were characterized by X-ray structure analysis and IR spectroscopy. Magnetic susceptibility measurements in the temperature range of 2-300 K show weak antiferromagnetic interactions between two lanthanides atoms for compounds IIa, IIb, and IId. The thermal decomposition of Ia, Ib, and IIb was studied by thermogravimetry.     

Solid state structure of thorium(IV) complexes with common aminopolycarboxylate ligands

The crystal structures of the complexes formed by reaction of thorium(IV) nitrate with iminodiacetic acid (H(2)IDA), nitrilotriacetic acid (H(3)NTA), and ethylenediaminetetraacetic acid (H(4)EDTA) under hydrothermal conditions are reported. In [Th(HIDA)(2)(C(2)O(4))]·H(2)O (1), the metal atom is chelated by two carboxylate groups from two HIDA(-) anions and by two oxalate ligands formed in situ; two additional oxygen atoms from two more HIDA(-) anions complete the ten-coordinate environment of bicapped square antiprismatic geometry. The uncoordinated nitrogen atom is protonated and involved in hydrogen bonding. Two different ligands are present in [Th(NTA)(H(2)NTA)(H(2)O)]·H(2)O (2), one of them being a O(3),N-chelating trianion which acts also as a bridge toward two neighboring metal ions, and the other being a bis-monodentate bridging species with an uncoordinated carboxylic arm and a central ammonium group. An aqua ligand completes the nine-coordinated, capped square antiprismatic metal environment. The EDTA(4-) anion in [Th(EDTA)(H(2)O)]·2H(2)O (3) is chelating through one oxygen atom from each carboxylate group and the two nitrogen atoms, as in a previously reported molecular complex. Two carboxylate groups are bridging, which, with the addition of an aqua ligand, gives a capped square antiprismatic coordination polyhedron. Aminopolycarboxylate ligands have been much investigated in relation with actinide decorporation and nuclear wastes management studies, and the present results add to the structural information available on their complexes with thorium(IV), which has mainly been obtained up to now by extended X-ray absorption fine structure (EXAFS) spectroscopy. In particular, the bridging (non-chelating) coordination mode of H(2)NTA(-) is a novel feature in this context. All three complexes crystallize as two-dimensional assemblies and are thus novel examples of thorium-organic coordination polymers.     

Syntheses, crystal structures and properties of novel copper(II) complexes obtained by reactions of copper(II) sulfate pentahydrate with tripodal ligands

Three novel metal-organic frameworks (MOFs), [Cu(1)SO4].H2O (4), [Cu2(2)2(SO4)2].4H2O (5) and [Cu(3)(H2O)]SO4.5.5H2O (6), were obtained by hydrothermal reactions of CuSO4.5H2O with the corresponding ligands, which have different flexibility. The structures of the synthesized complexes were determined by single-crystal X-ray diffraction analyses. Complex 4 has a 2D network structure with two types of metallacycles. Complex 5 also has a 2D network structure in which each independent 2D sheet contains two sub-layers bridged by oxygen atoms of the sulfate anions. Complex 6 has a 2D puckered structure in which the sulfate anions serve as counter anions, which are different from those in complexes 4 (terminators) and 5 (bridges). The different structures of complexes 4, 5 and 6 indicate that the nature of organic ligands affected the structures of the assemblies greatly. The magnetic behavior of complex 5 and anion-exchange properties of complex 6 were investigated.     

Isomeric molecular rectangles resulting from self-assembly of dicopper complexes of macrocyclic ligands

Dinuclear copper complexes containing hexaazacyclophane macrocyclic ligands react with the disodium salt of terephthalic acid resulting in the self-assembly of rectangular molecules with the general formula [(Cu2L)2(p-(O2CC6H4CO2)2)]X4, where X = CF3SO3 and ClO4 (3X4, L = Me2p and 4X4, L = Me2m). Tetranuclear complexes 3(CF3SO3)4 (as polymorphs 3a and 3b) and 4(ClO4)4 have been characterized by single-crystal X-ray diffraction analysis providing definitive proof of their structure as well as their metrical parameters. 3a contains, in its unit cell, two isomeric cationic units (3asyn and 3aanti) that differ in the relative position of the two O carboxylate atoms which bind to the Cu atoms of the different macrocyclic complexes, leading to boxes with different metrical parameters. ESI-MS analyses of solutions of the tetranuclear complexes 3(CF3SO3)4 and 4(CF3SO3)4 exhibit cluster ions which match the solid state formulation, thus demonstrating that the cages are retained in solution.     

Construction of 3d-4f mixed-metal complexes based on a binuclear oxovanadium unit: synthesis, crystal structure, EPR, and magnetic properties

The oxovanadium(IV)-lanthanide(III) heteronuclear complexes, [[Ce(H2O)7(VO)(TTHA)0.5][(VO)2(TTHA)]].8H2O (2), [Pr(H2O)7(VO)3(TTHA)1.5].10H2O (3), and [Nd(H2O)7(VO)3(TTHA)(1.5)].10H2O (4) (H6TTHA = triethylenetetraaminehexaacetic acid), were prepared based on a binuclear building block of [(VO)2(TTHA)]2- in [VO(H2O)5][(VO)2TTHA].4H2O (1). The X-ray crystallographic studies show that 1 is an ion-pair complex, containing the [(VO)2(TTHA)]2- unit as a useful building block. Adding the light Ln3+ ions to this synthesis system, three new 3d-4f mixed-metal-based complexes were obtained. Although the light lanthanide ions always exhibit similar chemical behavior, the structures of 2-4 are not homologous. 2 is exhibited as a one-dimensional coordination polymer, comprising an unusual Ce2V2 heterometallic lattice in the chain structure, which is the second report of a oxovanadium(IV)-lanthanide(III) coordination polymer. 3 and 4 are isomorphic, every two of the Ln3+ cations linked three [(VO)2(TTHA)]2- anions, forming an interesting linear octanuclear structure. This kind of heteronuclear linear complex is rather rare, which expands the realm of 3d-4f complexes. Further investigations such as IR spectra, UV-vis spectra, magnetic properties, and EPR spectra were studied, and a detailed discussion is given for this system.     

Synthesis and Structural Characterization of a New Polyoxovanadium Borate: (H_3NCH_2CH_2NH_3)_4[(VO)_6(B_(10)O_(22))_2]·(H_3O)_7

1 INTRODUCTION Transition metal oxide clusters and their deriva- tives offer an unmatched variety of structural motifs and wide ranging applications in several areas, such as analytical chemistry, materials science and cataly- sis, nanotechnology, chemical sensing, environmental decontamination, biochemical and geochemical pro- cesses, and medicine[1～3]. Polyoxovanadates or vana- dium oxide clusters constitute an important subclass of polyoxometalates and have been studied exten- sively.…     

Tuning facial-meridional isomerisation in monometallic nine-co-ordinate lanthanide complexes with unsymmetrical tridentate ligands

The unsymmetrical tridentate benzimidazole-pyridine-carboxamide units in ligands L1-L4 react with trivalent lanthanides, Ln(III), to give the nine-co-ordinate triple-helical complexes [Ln(Li)3]3+ (i = 1-4) existing as mixtures of C3-symmetrical facial and C1-symmetrical meridional isomers. Although the beta13 formation constants are 3-4 orders of magnitude smaller for these complexes than those found for the D3-symmetrical analogues [Ln(Li)3]3+ (i = 5-6) with symmetrical ligands, their formation at the millimolar scale is quantitative and the emission quantum yield of [Eu(L2)3]3+ is significantly larger. The fac-[Ln(Li)3]3+ <--> mer-[Ln(Li)3]3+ (i = 1-4) isomerisation process in acetonitrile is slow enough for Ln = Lu(III) to be quantified by 1H NMR below room temperature. The separation of enthalpic and entropic contributions shows that the distribution of the facial and meridional isomers can be tuned by the judicious peripheral substitution of the ligands affecting the interstrand interactions. Molecular mechanics (MM) calculations suggest that one supplementary interstrand pi-stacking interaction stabilises the meridional isomers, while the facial isomers benefit from more favourable electrostatic contributions. As a result of the mixture of facial and meridional isomers in solution, we were unable to obtain single crystals of 1:3 complexes, but the X-ray crystal structures of their nine-co-ordinate precursors [Eu(L1)2(CF3SO3)2(H2O)](CF3SO3)(C3H5N)2(H2O) (6, C45H54EuF9N10O13S3, monoclinic, P2(1)/c, Z = 4) and [Eu(L4)2(CF3SO3)2(H2O)](CF3SO3)(C4H4O)(1.5) (7, C51H66EuF9N8O(15.5)S3, triclinic, P1, Z = 2) provide crucial structural information on the binding mode of the unsymmetrical tridentate ligands.     

Structural, electrochemical, and spectroscopic characterization of a redox pair of sulfite-based polyoxotungstates: alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5-

The synthesis, isolation, and structural characterization of the fully oxidized sulfite-based polyoxotungstate cluster (Pr4N)4{alpha-[W18O54(SO3)2]}.2CH3CN and the one-electron reduced form (Pr4N)5{alpha-[W18O54(SO3)2]}.2CH3CN has been achieved. alpha-[W18O54(SO3)2]5- was obtained as a Pr4N+ salt by reducing the "Trojan Horse" [W18O56(SO3)2(H2O)2]8- cluster via a template orientation transformation. Acetonitrile solutions of pure alpha-[W18O54(SO3)2]5- also were prepared electrochemically by one-electron bulk reductive electrolysis of alpha-[W18O54(SO3)2]4-. Cyclic voltammetry of alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5- in CH3CN (0.1 M Hx4NClO4) produces evidence for an extensive series of reversible one-electron redox processes, that are associated with the tungsten-oxo framework of the polyoxometalate cluster. Hydrodynamic voltammograms in CH3CN exhibit the expected sign and magnitude of the steady-state limiting current values for the alpha-[W18O54(SO3)2]4-/5-/6- series and confirm the existence of a stable one-electron reduced species, alpha-[W18O54(SO3)2]5-. Employment of the Randles-Sevcik (cyclic voltammetry) and Levich (rotating disk electrode) equations at a glassy carbon electrode (d=3 mm) enable diffusion coefficient values of 3.7 and 3.8x10(-6) cm2 s-1 to be obtained for alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5-, respectively. The tungsten polyoxometalates are highly photoactive, since measurable photocurrents and color changes are detected for both species upon irradiation with white light. EPR spectra obtained from both acetonitrile solution and solid samples, down to temperatures as low as 2.3 K, of the chemically and electrochemically prepared one-electron reduced species provided evidence that the unpaired electron in alpha-[W18O54(SO3)2]5- is delocalized over a number of atoms in the polyoxometalate structure, even at very low temperatures.     

Pentamethylcyclopentadienyl-iridium(III) complexes with pyridylamino ligands: synthesis and applications as asymmetric catalysts for Diels-Alder reactions

Reaction of the dimer [(Cp*IrCl)2(P-Cl)2] with chiral pyridylamino ligands (pyam, L1-L5) in the presence of NaSbF6 gave complexes [Cp*IrCl(pyam)][SbF6] 1-5 as diastereomeric mixtures, which have been fully characterised, including the X-ray molecular structure determination of the complexes (S(Ir),R(N),R(C))-[Cp*IrClL1][SbF6] 1a and (R(Ir),S(N),S(C))-[Cp*IrClL5][SbF6] 5a. Treatment of these cations with AgSbF6 affords the corresponding aqua species [Cp*Ir(pyam)(H2O)][SbF6]2 6-10 which have been also fully characterised. The molecular structure of the complex (S(Ir),R(N),R(C))-[Cp*IrL,(H2O)][SbF6]2 6 has been determined by X-ray diffractometric methods. The aqua complexes [Cp*Ir(pyam)(H2O)][SbF6]2 (6, pyam = L2 (7), L3 (8)) evolve to the cyclometallated species [Cp*Ir{kappa3(N,N',C)-(R)-(C6H4)CH(CH3)NHCH2C5NH4}][SbF6] (11), [Cp*Ir{kappa3(N,N',C)-(R)-(C10H6)CH(CH3)-NHCH2C5NH4)}][SbF6] (12), and [Cp*Ir{kappa3(N,N',C)-(R)-(C10H6)CH(CH3)NHCH2C9NH6)}][SbF6] (13) respectively, via intramolecular activation of an ortho C-H aryl bond. Complexes 6-10 are enantioselective catalysts for the Diels-Alder reaction between methacrolein and cyclopentadiene. Reaction occurs rapidly at room temperature with good exo : endo selectivity (from 81 : 19 to 98 : 2) and moderate enantioselectivity (up to 72%). The involved intermediate Lewis acid-dienophile compounds [Cp*Ir(pyam)(methacrolein)][SbF]2 (pyam = L4 (14), L5 (15)) have been isolated and characterised.     

A novel series of vanadium-sulfite polyoxometalates: synthesis, structural, and physical studies

Reaction of NH4VO3 with sulfur dioxide affords the hexanuclear cluster (NH4)2(Et4N)[(V(IV)O)6(mu4-O)2(mu3-OH)2(mu3-SO3)4(H2O)2]Cl x H2O (1), and the decapentanuclear host-guest compound (Et4N)5{Cl subset [(VO)15(mu3-O)18(mu-O)3]} x 3 H2O (2). Sequential addition of magnesium oxide to an acidic aqueous solution of NH4VO3 (pH approximately 0) followed by (NH4)2SO3 resulted in the formation of either the non-oxo polymeric vanadium(IV) compound trans-(NH4)2[V(IV)(OH)2(mu-SO3)2] (3) or the polymeric oxovanadium(IV) sulfite (NH4)[V(IV)O(SO3)1.5(H2O)] x 2.5 H2O (4) at pH values of 6 and 4, respectively. The decameric vanadium(V) compound {Na4(mu-H2O)8(H2O)6}[Mg(H2O)6][V(V)10(O)8(mu6-O)2(mu3-O)14] x 3 H2O (5) was synthesised by treating an acidic aqueous solution of NH4VO3 with MgO and addition of NaOH to pH approximately 6. All the compounds were characterised by single-crystal X-ray structure analysis. The crystal structure of compound 1 revealed an unprecedented structural motif of a cubane unit [M4(mu4-O)2(mu3-OH)2] connected to two other metal atoms. Compound 3 comprises a rare example of a non-oxo vanadium(IV) species isolated from aqueous solution and in the presence of the reducing agent SO3(2-), while compound 4 represents a rare example of an open-framework species isolated at room temperature (20 degrees C). In addition to the synthesis and crystallographic studies, we report the IR and magnetic properties (for 1, 2 and 3) of these vanadium clusters as well as theoretical studies on compound 3.     

Synthesis, crystal structures, and properties of oxovanadium(IV)-lanthanide(III) heteronuclear complexes

A new series of oxovanadium(IV)-lanthanide(III) heteronuclear complexes [Yb(H2O)8]2[(VO)2(TTHA)](3)21 H2O (1), {[Ho(H2O)7(VO)2(TTHA)][(VO)2(TTHA)](0.5)} 8.5 H2O (2), {[Gd(H2O)7(VO)2(TTHA)][(VO)2(TTHA)](0.5)}8.5 H2O (3), {[Eu(H2O)7][(VO)2(TTHA)](1.5)} 10.5 H2O (4), and [Pr2(H2O)6(SO4)2][(VO)2(TTHA)] (5) (H6TTHA=triethylenetetraaminehexaacetic acid) were prepared by using the bulky flexible organic acid H(6)TTHA as structure-directing agent. X-ray crystallographic studies reveal that they contain the same [(VO)2(TTHA)]2- unit as building block, but the Ln3+ ion lies in different coordination environments. Although the lanthanide ions always exhibit similar chemical behavior, the structures of the complexes are not homologous. Compound 1 is composed of a [Yb(H2O)8]3+ ion and a [(VO)2(TTHA)]2- ion. Compounds 2 and 3 are isomorphous; both contain a trinuclear [Ln(H2O)7(VO)2(TTHA)]+ (Ln=Ho for 2 and Gd for 3) ion and a [(VO)2(TTHA)]2- ion. Compound 4 is an extended one-dimensional chain, in which each Eu3+ ion links two [(VO)2(TTHA)]2- ions. For 5, the structure is further assembled into a three-dimensional network with an interesting framework topology comprising V2Pr2 and V4Pr2 heterometallic lattices. Moreover, 4 and 5 are the first oxovanadium(IV)-lanthanide(III) coordination polymers and thus enlarge the realm of 3d-4f complexes. The IR, UV/Vis, and EPR spectra and the magnetic properties of the heterometallic complexes were studied. Notably, 2 shows unusual ferromagnetic interactions between the VO2+ and Ho3+ ions.     

Reaction systems related to dissimilatory nitrate reductase: nitrate reduction mediated by bis(dithiolene)tungsten complexes

Kinetics of the oxygen atom transfer reactions [M(IV)(QC6H2-2,4,6-Pr(i)3)(S2C2Me2)2]1- + XO --> [M(VI)O(QC6H2-2,4,6-Pr(i)3)(S2C2Me2)2]1- + X in acetonitrile with substrates XO = NO3- and (CH2)4SO have been determined. The reactants are bis(dithiolene) complexes with M = Mo, W and sterically encumbered axial ligands with Q = O, S to stabilize mononuclear square pyramidal structures. The complex [MoIV(SC6H2-2,4,6-Pr(i)3)(S2C2Me2)2]1- is an analogue of the active site of dissimilatory nitrate reductase which in the reduced state contains a molybdenum atom bound by two pyranopterindithiolene ligands and a cysteinate residue. Nitrate reduction was studied with tungsten complexes because of unfavorable stability properties of the molybdenum complexes. Product nitrite was detected by a colorimetric method. All reactions with both substrates are second-order with associative transition states (deltaS approximately -20 eu). Variation of atoms M and Q, together with data from prior work, allows certain kinetics comparisons to be made. Among them, k2W/k2Mo = 25 for (CH2)4SO reduction (Q = S), an expression of the kinetic metal effect. Further, k2S/k2O = 28 and approximately 10(4) for nitrate and (CH2)4SO reduction, respectively, effects attributed to relatively more steric congestion in achieving the transition state with hindered phenolate vs thiolate ligands. The effect is more pronounced with the larger substrate. These results demonstrate the feasibility of tungsten-mediated nitrate reduction by direct atom transfer using molecules with both axial thiolate and phenolate ligands. Complexes of the type [M(IV)(OR)(S2C2Me2)2] are capable of reducing biological N-oxide, S-oxide, and nitrate substrates and thus constitute functional analogue reaction systems of enzymic transformations.     

Anion selectivity in zwitterionic amide-functionalised metal salt extractants

Amide-functionalised salen ligands capable of extracting metal salts have been synthesised and characterised. Single-crystal X-ray structure determinations of complexes of NiSO4, [Ni(L)(SO4)], confirm that the ionophores are in a zwitterionic form with Ni(II) bound in the deprotonated salen moiety and the SO4(2-) ion associated with protonated pendant N'-amidopiperazine groups. Treatment of [Ni(L)(SO4)] with base removes the protons from the pendant amido-amine group resulting in loss of the SO4(2-) ion and formation of metal-only complexes of type [Ni(L-2H)], which have been characterized by single-crystal X-ray diffraction. Three of the ligands with solubilities suitable for solvent extraction studies show loading and stripping pH-profiles that are suitable for the recovery of CuSO4 or CuCl2 from industrial leach solutions. The copper-only complexes, [Cu(L-2H)], are selective for Cl- over SO4(2-) in both solvent extraction and bulk liquid membrane transport experiments and were found to bind Cl- in two steps via the formation of a 1:1:1 [Cu(L-H)Cl] assembly, followed by a 1:1:2 [Cu(L)Cl2] assembly as the pH of the aqueous phase is lowered. The anion transport selectivity was evaluated for a number of other mono-charged anions and interestingly the ligands were found to display a preference for the Br- ion. To probe the influence of the Hofmeister bias on the selectivity of anion complexation, single-phase potentiometric titration experiments were employed to investigate the binding of SO4(2-) and Cl- by one of the copper only complexes, [Cu(L-2H)] in 95 %/5 % MeOH/water. Under these conditions selectivity was reversed (SO4(2-)>Cl-) confirming that the Hofmeister bias, which reflects the relative hydration energies of the anions, dominates the selectivity of anion extraction from aqueous media into CHCl3.     

Synthesis and characterization of silver(I) coordination networks bearing flexible thioethers: anion versus ligand dominated structures

This report describes the synthesis and X-ray characterization of a series of L(n)AgX complexes wherein Ln = PhS(CH2)nSPh (n = 2, 4, 6, 10) and X = CF3SO3-, CF3COO-, CF3CF2COO-, CF3CF2CF2COO-, NO3-, and ClO4-. This study was undertaken in order to rationalize the structure of the coordination networks formed as a function of the anion coordinating strength and the ligand structure. The following complexes were examined: with L(2), CF3SO3- (1), CF3COO- (2), ClO4- (3); L4, CF3SO3- (4), CF3COO- (5), CF3CF2COO- (6), CF3CF2CF2COO- (7); L6, CF3COO-.H2O (8), CF3CF2COO- (9), CF3CF2CF2COO- (10); and L10, NO3- (11). The anions selected are classified in three groups of increasing coordinating strength: perchlorates, fluorosulfonates, and perfluorocarboxylates. Except in two cases, all complexes form 2D-coordination networks. The 2D-network in 1 (L2, CF3SO3-) is made up of Ag(I) and L2, while the anion is only a terminal co-ligand that completes the trigonal coordination around Ag(I). In 4 (L4, CF3SO3-), a 1D-coordination polymer, [Ag-L4-]infinity, is observed where the anions are coordinated to Ag(I) in a trigonal fashion. The perfluorocarboxylates form tetrameric units in a zigzag shape, but only with the L4 ligand. In these (6 and 7), the silver-silver distances are very short, especially those of the central bond, indicating the presence of weak Ag-Ag interactions. Dimers, with short silver-silver distances, are observed with ligands L2 and L6 and perfluorocarboxylates. In 8 (L6, CF3COO-.H2O), a 3D channel-like structure is built through water molecules that connect adjacent layers. An unusual stoichiometry is noted in 3 (L2, ClO4-, acetone); Ag:L is 4:2.5. In 11 (L10 and NO3-), the nitrate acts as a bidentate ligand and an [Ag-NO3-]infinity chain is formed. Adjacent chains are linked by the L10 ligands into a 2D-coordination network.