Cyanide-bridged one-dimensional bimetallic complexes based on a tridentate copper(II) building block: synthesis,crystal structures and magnetic properties

The reactions of [M^III(CN)₆]^3? (M = Cr or Co) with Cu^II complexes of a tridentate schiff base [Cu(aemp)Cl] or [Cu(aemp)Ac]₂ (Haemp = 2-[(2-amino-ethylimino)-methyl]-phenol) give rise to 1D cyanide-bridged bimetallic coordination polymers [Cu₄(aemp)₄(H₂O)₂][Cr(CN)₆]Cl (1) and [Cu₃(aemp)₃(H₂O)][Co(CN)₆]·2H₂O·MeOH (2). In complex 1, the six cyanide ligands of the [Cr(CN)₆]^3? moiety are involved in bridging, while in complex 2 only five cyanide ligands act as bridges to give a neutral chain. Magnetic studies reveal that complex 1 exhibits intermetallic ferromagnetic coupling, with J = 8.2 cm^?1.     

One-dimensional octacyanomolybdate-based Cu(II)--Mo(V) bimetallic assembly with a novel rope-ladder chain structure

A new type of one-dimensional cyanide-bridged Cu(II)--Mo(V) bimetallic assembly, [Cu(cyclam)](3)[Mo(CN)(8)](2)x5H(2)O (cyclam = 1,4,8,11-tetraazacyclotetradecane), was prepared by self-assembling Mo(CN)(8)(3)(-) and Cu(cyclam)(2+) ions in a 2:3 stoichiometric ratio. The overall molecular view is delineated as a novel rope-ladder chain structure. It displays a dominant ferromagnetic behavior within a pentanuclear Cu(3)Mo(2) unit (J(p) = 3.88 cm(-)(1)). Interunit ferromagnetic interactions (J(c) = -0.03 cm(-)(1)) through a longer magnetic pathway of Cu--Mo and weak antiferromagnetic couplings (zJ' = -0.46 cm(-)(1)) resulting from interchain interactions are obtained.     

A novel heteroditopic terpyridine-pincer ligand as building block for mono- and heterometallic Pd(II) and Ru(II) complexes

A palladium-catalyzed Stille coupling reaction was employed as a versatile method for the synthesis of a novel terpyridine-pincer (3, TPBr) bridging ligand, 4'-{4-BrC6H2(CH2NMe2)2-3,5}-2,2':6',2' '-terpyridine. Mononuclear species [PdX(TP)] (X = Br, Cl), [Ru(TPBr)(tpy)](PF6)2, and [Ru(TPBr)2](PF6)2, synthesized by selective metalation of the NCNBr-pincer moiety or complexation of the terpyridine of the bifunctional ligand TPBr, were used as building blocks for the preparation of heterodi- and trimetallic complexes [Ru(TPPdCl)(tpy)](PF6)2 (7) and [Ru(TPPdCl)2](PF6)2 (8). The molecular structures in the solid state of [PdBr(TP)] (4a) and [Ru(TPBr)2](PF6)2 (6) have been determined by single-crystal X-ray analysis. Electrochemical behavior and photophysical properties of the mono- and heterometallic complexes are described. All the above di- and trimetallic Ru complexes exhibit absorption bands attributable to (1)MLCT (Ru --> tpy) transitions. For the heteroleptic complexes, the transitions involving the unsubstituted tpy ligand are at a lower energy than the tpy moiety of the TPBr ligand. The absorption bands observed in the electronic spectra for TPBr and [PdCl(TP)] have been assigned with the aid of TD-DFT calculations. All complexes display weak emission both at room temperature and in a butyronitrile glass at 77 K. The considerable red shift of the emission maxima relative to the signal of the reference compound [Ru(tpy)2]2+ indicates stabilization of the luminescent 3MLCT state. For the mono- and heterometallic complexes, electrochemical and spectroscopic studies (electronic absorption and emission spectra and luminescence lifetimes recorded at room temperature and 77 K in nitrile solvents), together with the information gained from IR spectroelectrochemical studies of the dimetallic complex [Ru(TPPdSCN)(tpy)](PF6)2, are indicative of charge redistribution through the bridging ligand TPBr. The results are in line with a weak coupling between the {Ru(tpy)2} chromophoric unit and the (non)metalated NCN-pincer moiety.     

Oxalato complexes of Pd(II) with Co(II) and Ni(II) as single-source precursors for bimetallic nanoalloys

Journal of Thermal Analysis and Calorimetry - The explanation of abnormal enhancement of transported energy in colloidal nanoparticles in a liquid has sparked much interest in recent years. The...     

Bis(3-cyano-pentane-2,4-dionato) Co(II) as a linear building block for coordination polymers: combinations with two polypyridines

Two types of bis(β-diketonato) Co(II) complexes, [Co(CNacac)₂] (CNacac?=?3-cyano-pentane-2,4-dionato), and [Co(dbm)₂] (dbm?=?dibenzoylmethanato or 1,3-diphenyl-propane-1,3-dionato) were examined as linear building blocks for the construction of coordination polymers in combination with two oligopyridines, 1,4-bis(4,2’:6’,4”-terpyridin-4’-yl)benzene (L1) and 1,3-bis(3,2’:6’,3”-terpyridin-4’-yl)benzene) (L2). From combinations of [Co(CNacac)₂] with L1 and L2, 2-D coordination polymers, [Co(CNacac)₂]₂(L1)·(CHCl₃)·(CH₃OH) (CoCN-1) and [Co(CNacac)₂](L2)_1/2·(tetrachloroethane)_3/2 (CoCN-2), are obtained. Both CoCN-1 and CoCN-2 have 2D (4,4) net structures, in which L1 and L2 are tetradentate. In contrast, combination of [Co(dbm)₂] with L2 affords a 1-D coordination polymer, [Co(dbm)₂](L2)·4(CH₃OH) (Codbm-1), in which L2 is bidentate. L2 as a tetradentate ligand was inhibited by bulky phenyl rings in [Co(dbm)₂]. These results indicate that [Co(CNacac)₂] with a relatively simplified structure is useful as a linear building block in combinations with bulky oligopyridines.     

Synthesis, resolution, and applications of 1,16-dihydroxytetraphenylene as a novel building block in molecular recognition and assembly

This paper concerns the synthesis of 1,16-dihydroxytetraphenylene (DHTP) (2) by employing a novel NBS bromination route. (+/-)-DHTP 2 was successfully resolved into its optical antipodes and converted to (+/-)-1,16-bis(diphenylphosphino)tetraphenylene (BPTP) (26), whose platinum complex BPTP-PtCl(2) (27) was also obtained. As a hydrogen bond donor, racemic and optically active DHTP 2 was allowed to assemble with 4,4'-bipyridine to form single crystals of good quality. X-ray Diffraction studies of these crystals revealed that the crystallographic packing of the hydrogen bonded complex between (+/-)-2 and 4,4'-bipyridine was different from the one formed from (S)-2 and 4,4'-bipyridine. It was found that an infinite zigzag chain with alternate chirality was formed in the assembly of (+/-)-2 and 4,4'-bipyridine, while (S)-2 and 4,4'-bipyridine failed to show the same assembly pattern. The reason (+/-)-2 formed an alternate and zigzag chain with 4,4'-bipyridine was most likely due to the inherent stability of this supramolecular assembly. The chiral recognition between 2 and optically active BINAP under the direction of platinum(II) has also been examined. (1)H and (31)P NMR spectroscopic studies demonstrated that there was an obvious discrimination of 2 between the enantiomers of BINAP-PtCO(3).     

An unusual 3D entangled Co(II) coordination polymer directed by ferromagnetic molecular building block

A fascinating 3D entangled metal-organic framework, namely, {[Co(2)(bcp)(2)]·3H(2)O}(n) (1), was obtained through the solvothermal generation of flexible and long dicarboxylate (bcp) and metal salt. The crystal structure contains a 1D metal chain with bcp ligands wrapped around it in a wavy line and features an unusual entangled topological net. Furthermore, the magnetic behavior of 1 was also studied and indicated the existence of ferromagnetic interaction and long-range ordering character.     

Tetraphosphinitoresorcinarene complexes: cationic silver(I) and copper(I) halide complexes as mercurate(II) anion receptors

The reactions of mercury(II) halides with the tetraphosphinitoresorcinarene complexes [P4M5X5], where M=Cu or Ag, X=Cl, Br, or I, and P4=(PhCH2CH2CHC6H2)4(O2CR)4(OPPh2)4 with R=C6H11, 4-C6H4Me, C4H3S, OCH2CCH, or OCH2Ph, have been studied. The reactions of the complexes with HgX2 when M=Ag and X=Cl or Br occur with elimination of silver(I) halide and formation of [P4Ag2X(HgX3)], but when M=Ag and X=I, the complexes [P4Ag4I5(HgI)] are formed. When M=Cu and X=I, the products were the remarkable capsule complexes [(P4Cu2I)2(Hg2X6)]. When M=Ag and X=I, the reaction with both CuI and HgI2 gave the complexes [P4Cu2I(Hg2I5)]. Many of these complexes are structurally characterized as containing mercurate anions weakly bonded to cationic tetraphosphinitoresorcinarene complexes of copper(I) or silver(I) in an unusual form of host-guest interaction. In contrast, the complex [P4Ag4I5(HgI)] is considered to be derived from an anionic silver cluster with an iodomercury(II) cation. Fluxionality of the complexes in solution is interpreted in terms of easy, reversible making and breaking of secondary bonds between the copper(I) or silver(I) cations and the mercurate anions.     

Synthesis,crystal structure,and magnetism properties of coordination polymer: Co(2-mpac)2(H2O)2 as molecular building block

Utilizing Co(2-mpac)₂(H₂O)₂ as molecular building block, a coordination polymer, [Co₂(2-mpac)₄(4,4′-bpy) · 2H₂O] _n (1) (2-mpac = 5-methyl-2-pyrazinecarboxylic acid; 4,4′-bpy = 4,4′-bipyridine), was synthesized and structurally characterized by X-ray single crystal diffraction. Elemental analysis, infrared, and magnetism are presented. Variable temperature magnetic susceptibility measurements exhibit weak antiferromagnetic interaction between Co centers in 1.     

Construction of molecular wires based on a gold(I) bis-sigma-acetylide building block incorporated into ruthenium(II) polypyridyl complexes

An Ru(II)-Au(I)-Ru(II) triad has been synthesized from [Ru(bpy)2(3-ethynylphenanthroline)]2+ with Au(tht)Cl and characterized by spectroscopic means such as NMR and ESI-MS; the Ru(II)-Au(I)-Ru(II) triad shows an intense emission at 620 nm upon excitation at 360 nm, which suggests an efficient energy transfer from the Au site to Ru sites via extended pi-conjugation through the ethynyl units.     

Bicarbonate as a proton donor in catalysis by Zn(II)- and Co(II)-containing carbonic anhydrases.

Catalysis of (18)O exchange between CO(2) and water catalyzed by a Co(II)-substituted mutant of human carbonic anhydrase II is analyzed to show the rate of release of H(2)(18)O from the active site. This rate, measured by mass spectrometry, is dependent on proton transfer to the metal-bound (18)O-labeled hydroxide, and was observed in a site-specific mutant of carbonic anhydrase II in which a prominent proton shuttle residue His64 was replaced by alanine, which does not support proton transport. Upon increasing the concentration of bicarbonate, the rate of release of H(2)(18)O increased in a saturable manner to a maximum of 4 x 10(5) s(-)(1), consistent with proton transfer from bicarbonate to the Co(II)-bound hydroxide. The same mutant of carbonic anhydrase containing Zn(II) had the rate of release of H(2)(18)O smaller by 10-fold, but rate of interconversion of CO(2) and HCO(3)(-) about the same as the Co(II)-containing enzyme. These data as well as solvent hydrogen isotope effects suggest that the bicarbonate transferring the proton is bound to the cobalt in the enzyme. The enhancement of (18)O exchange caused by increasing bicarbonate concentration during catalysis by the Zn(II)-containing carbonic anhydrase from the archaeon Methanosarcina thermophila suggests that a very similar mechanism for proton donation by bicarbonate occurs with this wild-type enzyme.     

The thiolate anion as a nucleophile Part XII. Reactions of Lead(II) Benzenethiolate

The reactions of various fluoroaromatics, C₆F_6?xH_x, and C₆F₅X (X = C₆F₆, Cl, Me, NO₂, CF₃, COCl, CH₂Br, OMe, and NH₂) with lead(II) benzenethiolate in DMF have been examined. Lead thiolate acted as an excellent source of benzenethiolate anions and displacement of fluorine, chlorine or the nitro group was observed. The new products have been characterized by elemental analysis, and NMR (H?1 and F?19), infrared and mass spectroscopy.     

Synthesis,crystal structure and magnetic behavior of a two-dimensional copper(II) complex with mellitic anion as bridging ligand

A two-dimensional complex Cu₃[C₆(COO)₆](H₂O)₁₀ · 2H₂O has been prepared and its crystal structure determined by X-ray crystallography. In the complex each mellitic anion provides four carboxylate groups as coordinate groups and, according to the coordination, the four carboxylate groups are classified as two types according to its coordinate modes. The first is that a carboxylate group coordinates a copper(II) ion via its one oxygen atom, and the second one is that a carboxylate group, as a two-dentate ligand, coordinates to two copper(II) ions. The copper(II) ions also are classified as being of two types according to their coordinate modes. The configuration around each copper(II) ion is a distorted pyramid. The variable-temperature magnetic susceptibility of the complex was measured in the 4–300 K range and the magnetic data indicate that the magnetic interaction between bridging copper(II) ions displays an antiferromagnetic coupling below 42 K, while above 42 K a ferromagnetic interaction appears.     

Development of homogeneous and heterogenized rhodium(I) and palladium(II) complexes with ligands based on a chiral proton sponge building block and their application as catalysts

Chiral compounds prepared from proton sponge building block 8-((2R,5R)-2,5-dimethylpyrrolidin-1-yl)naphthalen-1-amine were found to be effective chiral ligands for obtaining complexes of rhodium(I) and palladium(II) by reaction with [RhCl(cod)](2), PdCl(2)(cod) or Pd(OAc)(2). The complexes bearing triethoxysilane groups were immobilized on mesoporous MCM-41 in order to obtain new heterogeneous catalysts. Both materials are active in the hydrogenation of alkenes and could be recycled without loss of activity or enantioselectivity.     

Synthesis of a novel copper(II) complex and its crystal structure

One novel chiral copper(II) complex was successfully synthesized from the reaction of chiral 1,3-thiazolidine-2-thione ligand with CuCl₂ in dichloromethane in the presence of Et₃N and DMAP at room temperature. Its unique crystal structure was unambiguously disclosed by X-ray analysis. The crystal is tetragonal, space group I4(1), space group a=15.0875(11), b=15.0875(11), c=19.362(3) Å, =90, β=90, γ=90°, V=4407.4(8) ų, Z=8, ρ_calc=1.639 mg cm⁻³.     

Spin-crossover behavior in cyanide-bridged iron(II)-silver(I) bimetallic 2D Hofmann-like metal-organic frameworks

Two new series of compounds formulated {Fe(3-Xpyridine)2[Ag(CN)2]2} (X = F (1), Cl (2), Br (3), I (4)) and {Fe(3-Xpyridine)2[Ag(CN)2][Ag(3-Xpyridine)(CN)2]}.3-Xpy (X = Br (5), I (6)) have been synthesized and characterized. The six compounds are made up of stacking of slightly corrugated two-dimensional coordination polymers defined by sharing {Fe4[Ag(CN)2]4}n motifs. The stacking is different for the two families. In compounds 1-4 the layers are organized by pairs displaying argentophilic interactions; the Ag...Ag distance was found to be in the interval 3.0-3.3 A, while the Ag...Ag separation between two consecutive layers belonging to different pairs was found to be around 6 A. Compounds 5 and 6 are isostructural with a crystal packing defined by an almost homogeneous distribution of layers separated by around 8.3 A (referred to the Fe...Fe interlayer distance). Between the layers an uncoordinated 3-Xpyridine molecule is included. Another 3-Xpyridine molecule, which remains in the plane defined by the {Fe4[Ag(CN)2]4}n windows, coordinates one silver atom. Both series display quite different properties; at 300 K, 1-4 are pale-yellow and display similar distorted [FeN6] octahedron cores characteristic of the iron(II) ion in the high-spin state. 1 and 2 undergo a two-step (T(1)1/2 = 96 K and T(2)1/2 = 162 K) and a 50% spin transition (T1/2 = 106 K), respectively. Compounds 3 and 4 are high-spin compounds at ambient pressure. 5 and 6 are deep red in color at 300 K and undergo spin-crossover behavior at significantly higher temperatures T1/2 = 306 and 261 K, respectively.     

Spin-crossover behavior in cyanide-bridged iron(II)-gold(I) bimetallic 2D Hofmann-like metal-organic frameworks

The synthesis and characterization of new two-dimensional (2D) cyanide-bridged iron(II)-gold(I) bimetallic coordination polymers formulated, {Fe(3-Xpy)2[Au(CN)2]2} (py = pyridine; X = F (1), Cl (2), Br (3), and I (4)) and the clathrate derivative {Fe(3-Ipy)2[Au(CN)2]2}.1/2(3-Ipy) (5), are reported. The iron(II) ion lies in pseudoctahedral [FeN6] sites defined by four [Au(CN)2](-) bridging ligands and two 3-Xpy ligands occupying the equatorial and axial positions, respectively. Although only compounds 2 and 4 can be considered strictly isostructurals, all of the components of this family are made up of parallel stacks of corrugated {Fe[Au(CN)2]2}n grids. The grids are formed by edge sharing of {Fe4[Au(CN)2]4} pseudosquare moieties. The stacks are constituted of double layers sustained by short aurophilic contacts ranging from 3.016(2) to 3.1580(8) A. The Au...Au distances between consecutive double layers are in the range of 5.9562(9)-8.790(2) A. Compound 5, considered a clathrate derivative of 4, includes one-half of a 3-Ipy molecule per iron(II) atom between the double layers. Compound 1 undergoes a half-spin transition with critical temperatures Tc downward arrow = 140 K and Tc upward arrow = 145 K. The corresponding thermodynamic parameters derived from differential scanning calorimetry (DSC) are Delta H = 9.8 +/- 0.4 kJ mol(-1) and Delta S = 68.2 +/- 3 J K mol(-1). This spin transition is accompanied by a crystallographic phase transition from the monoclinic P2(1)/c space group to the triclinic P1 space group. At high temperatures, where 1 is 100% high-spin, there is only one crystallographically independent iron(II) site. In contrast, the low temperature structural analysis shows the occurrence of two crystallographically independent iron(II) sites with equal population, one high-spin and the other low-spin. Furthermore, 1 undergoes a complete two-step spin transition at pressures as high as 0.26 GPa. Compounds 2- 4 are high-spin iron(II) complexes according to their magnetic and [FeN6] structural characteristics. Compound 5, characterized for having two different iron(II) sites, displays a two-step spin transition with critical temperatures of Tc(1) = 155 K, Tc(2) downward arrow = 97 K, and Tc(2) upward arrow = 110 K. This change of spin state takes place in both sites simultaneously. All of these results are compared and discussed in the context of other {Fe(L) x [M(I)(CN)2]} coordination polymers, particularly those belonging to the homologous compounds {Fe(3-Xpy)2[Ag(CN)2]2} and their corresponding clathrate derivatives.