The synthesis and characterisation of some MnLnX2 complexes (n = 1, L = pyridine, 4-pyrrolidinopyridine,X = Cl,Br, I,NCS; n = 1, L = EtOH,X = Cl,Br; n = 2, L = EtOH,X = I,NCS)

Mono-ligand complexes MnLX₂ (L = pyridine, 4-pyrrolidinopyridine, X = Cl, Br, I, NCS) have been prepared. The pyridine complexes contain only bridging halide and pseudohalide groups, whereas the 4-py complexes contain both bridging and terminal bound anions. Ethanol is coordinated in Mn(EtOH)X₂ (X=C1, Br) and Mn(EtOH)₂X₂ (X=I, NCS). Although the MnLX₂ complexes have the same stoichiometry as the Mn(PR₃)X₂complexes none show any activity towaxds binding dioxygen either in the solid state or in solution.     

Diphosphines as bridging ligands in polymeric and dimeric thione-S-ligated Ag(I) nitrate complexes

Reactions of silver(I) nitrate with equimolar amounts of the diphos ligands 1,4-bis(diphenylphosphino)butane (dppb) or 1,2-bis(diphenylphosphino)ethane (dppe) and some heterocyclic thiones (L) in acetonitrile/methanol solvent afforded mixed-ligand complexes, the nature of which was found to be strongly influenced by the backbone length of the diphosphine ligand. The longer chained diphos ligand formed a series of dinuclear complexes of the type [Ag(dppb)(L)]₂(NO₃)₂ with both the diphosphine and thione ligands acting as bridging ligands between the two four-coordinate pseudo-tetrahedrally coordinated metal centers. In the unique case of L=4-methyl-5-trifluoromethyl-4H-1,2,4-triazoline-3(2H)-thione (mftztH), the reaction proceeded under exclusion of the thione ligand from the coordination sphere and coordination of the nitrate anions instead, leading to the diphosphine-doubly bridged dimeric compound [Ag(dppb)(NO₃)]₂. On the other hand, the complexes produced when using the short bite 1,2-bis(diphenylphosphino)ethane (dppe) turned out to be diphosphine-bridged cationic polymers of the type [Ag(dppe)(L)₂]_n(NO₃)_n. The structures of one representative for each of the two aforementioned series of complex compounds, namely [Ag(dppb)(py2SH)]₂(NO₃)₂ · 2H₂O and [Ag(dppe)(pymtH)₂]_n(NO₃)_n, have been established by single-crystal X-ray diffraction.     

Structural comparison of (CuICH3CN4·dibenzo-18-crown-6 (I) and (CuICH3CN)x (II) fluorescent copper(I) materials

The single crystal X-ray structures of (CuICH₃CN₄·dibenzo-18-crown-6 (I) and (CuICH₃CN) (II) have been determined at room temperature [(I) C₂₈H₃₆Cu₄I₄N₄o₆, monoclinic space group P2₁/n, a = 10.116(4), b = 18.092(8), c = 22.211(9) Å, β = 98.66(3)°, Z = 4; (II) C₂H₃CuIN, orthorhombic pBN2₁, a = 13.618(8), b =8.742(2), c = 4.298(2), Z = 4]. (I) exists as a distorted cube with copper and iodine at alternate corners, the fourth coordination site copper occupied by an acetonitrile molecule coordinated through nitrogen. The cluster contains no crystallographic symmetry element and CuCu distances average 2.770(5) Å. The dibenzo-18-crown-6 displays only second sphere type interactions with cluster. (II) displays a pleated double chain type structure with distorted rectangles of alternating Cu and I atoms sharing opposite edges in infinite array. Copper displays tetrahedral geometry by coordination to three iodine atoms and a nitrogen bound acetonitrile molecule.     

Hydrothermal syntheses, structural characterizations and magnetic properties of cobalt(II) and manganese(II) coordination polymeric complexes containing pyrazinecarboxylate ligand

Two novel coordination polymeric complexes [Co(pzca)₂(H₂O)]_n (1) and [Mn(pzca)₂]_n (2) (pzca=2-pyrazinecarboxylate) have been synthesized by hydrothermal reaction of M(CH₃COO)₂·4H₂O (M=Co, Mn) and 2-pyrazinecarboxylic acid. The complex 1 displays an infinite zigzag chain structure in which each cobalt(II) center was coordinated by three nitrogen and three oxygen atoms to generate a CoN₃O₃ octahedral geometry. The existence of hydrogen bond leads to the formation of the interpenetrating stacking structure. Complex 2 indicates a two-dimensional layer structure through the linkage of bridging oxygen atom of pzca ligand. Each Mn(II) center exhibits a distorted octahedral coordination environment with four oxygen atoms and two nitrogen atoms. The distances of adjacent Mn(II) atoms are 3.503 and 5.654 Å, respectively. The magnetic property analyses reveal that both complexes show weak antiferromagnetic exchange interactions between the metal centers.     

Homogeneous oxidative coupling catalysts: stoichiometry and characterization of the first stable oxotetranuclear solids [(Pip)nCuX]4O2 (n=1 or 2, Pip=piperidine, X=Cl, Br, I)

Copper(I) halides react quantitatively with piperidine (Pip) in dioxygen-free methylene chloride or nitrobenzene to form tetranuclear copper(I) complexes [(Pip)_nCuX]₄; n=1 or 2, X=Cl, Br or I. These complexes are very soluble and completely reduce dioxygen to dioxo bridging ligand, with stoichiometry, Δ[Cu(I)]/Δ[O₂]=4.0. The stable oxo solids [(Pip)_nCuX]₄O₂ mimic tyrosinase copper protein. They act as a homogeneous oxidative coupling catalysts for phenols. Electronic transition spectra in the near infrared with high molecular absorptivity are diagnostic for tetranuclear “Cu₄X₄” core structure. The electronic transitions are more likely due to charge transfer between a minimum of three halo ligands and copper(II) center. The room temperature EPR spectra of [(Pip)_nCuX]₄O₂ in methylene chloride are isotropic with four hyperfine lines. The room temperature solid-state EPR spectra of [PipCuX]₄O₂ show an axial spectra with d_x²−y² ground state, suggesting square pyramidal arrangement of the five coordinated ligands around copper(II) centers. Cyclic voltammetry measurements show that they are more likely irreversible in character and show slight quasi-reversability when X=Br or I. Constant potential electrolysis indicate that the number of electrons consumed are equal to four electrons which will be due to the reduction of four copper(II) to copper(I).     

Synthesis, crystal structures and in vitro anti-fungal activities of two silver(I) coordination polymers with fluconazole

Two new polymeric silver(I)-fluconazole complexes: [Ag(HFlu)(NO₃)]_n (1) and {[Ag(HFlu)₂](ClO₄)}_n (2), have been synthesized and structurally characterized. The crystal structure of 1 consists of infinite 1D single strand helical coordination arrays with alternative …PMPM… arrangements, which are interlinked through hydrogen bonding interactions to generate a 3D network. The shortest intrachain Ag?Ag distance bridged by HFlu ligand is 8.287(1) Å. In 2, each Ag(I) ion is coordinated by four triazole N atoms from four HFlu ligands to form a 2D coordination layer, which has a helical arrangement along the [1 0 0] direction. The results of anti-fungal studies demonstrate that both silver(I) complexes are more active in comparison to the fluconazole drug.     

Poly(1,2,3-benzotriazolyl)borate complexes with copper(I) and tri-organophosphane: an unprecedented κ-coordination of [H2B(btz)2] (btz=1,2,3-benzotriazolyl) in the X-ray crystal structure of [Cu(PBn3)2{(btz)BH2(btz)}]

New copper(I) triorganophosphane derivatives [Cu(PR₃)_n{H₂B(btz)₂}] and [Cu(PR₃)_n{HB(btz)₃}] (n=1 or 2) have been synthesized from the reaction of CuCl with PR₃ (R=phenyl, cyclohexyl, benzyl, o-, m-, or p-tolyl) or PMePh₂ and potassium dihydrobis(1,2,3-benzotriazolyl)borate K[H₂B(btz)₂] or potassium hydrotris(1,2,3-benzotriazolyl)borate K[HB(btz)₃]. The complexes obtained have been characterized by elemental analyses and FT-IR in the solid state and by NMR (¹H and ³¹P{¹H}) spectroscopy and conductivity measurements in solution. Solution data are consistent with partial dissociation of complexes occurring throughout breaking of the CuP bond. Single crystal structural characterizations were undertaken for two of them. The structurally authenticated arrays are, (a) [Cu(PBn₃)₂{(btz)BH₂(btz)}] with a three coordinate P₂Cu(N) coordination sphere and the donor [H₂B(btz)₂] coordinated throughout only one N3 atom. (b) [Cu(P-m-tolyl₃)_n{(btz)₃BH}] with a four coordinate PCuN₃ coordination sphere with the tris(benzotriazolyl)borate acting as tripodal donor throughout all its N2 atoms.     

Syntheses and characterizations of six hydrogen-bonded silver(I) complexes from assembly of silver(I) nitrate and aminobenzoic acid

Six hydrogen-bonded silver(I) complexes, Ag(4-abaH)₂(NO₃) (1), [Ag(4-abaH)₂(NO₃)]_n (2), {[Ag(4-aba)(4-abaH)] · H₂O}_n (3), {[Ag(4,4^′-bipy)(H₂O)](4-aba)_0.5(NO₃)_0.5 · (H₂O)_0.5}_n (4), [Ag[(3-abaH_0.5)₂] (5), and {[Ag(3-aba)] · H₂O}_n (6) (4-abaH=4-aminobenzoic acid, 3-abaH=3-aminobenzoic acid), have been synthesized and characterized by single-crystal X-ray diffraction analyses. In 1, 4-abaH serves as a monodentate ligand coordinating to Ag(I) through its nitrogen atom, while uncoordinated carboxylic group links (4-abaH)-Ag-(4-abaH) into a one-dimensional metallic carboxylic synthon. 2 may be regarded as an extension of 1 into a two-dimensional carboxylic synthon through NO₃ ⁻ bridging two adjacent Ag(I) centers. In 3, 4-abaH in a monodentate mode and 4-aba in a μ-N,O bridging mode link three-coordinated Ag(I) to form a one-dimensional swallow-like chain, which is further extended into a two-dimensional layer structure through inter-chain hydrogen bonding interactions. The alternating Ag(I) and 4,4^′-bipy in 4 give rise to a slightly distorted linear chain, which is further extended into a two-dimensional layer through the completely overlapping and off-set stacking interactions. The hydrogen bonds involving in weakly coordinated aqueous molecules and 4-aba further extend it into a three-dimensional framework. In 5, the inter-molecular hydrogen bonding and π-π stacking interactions extend Ag[(3-abaH_0.5)₂] into a two-dimensional supramolecular architecture. In 6, 3-aba in a μ₃-N,O,O^′ coordination mode links three three-coordinated Ag(I) into a two-dimensional network. Uncoordinated aqueous molecules and the adjacent 3-aba oxygen atoms form intermolecular hydrogen bonds.     

Studies on dithio-o-toluate copper(I) complexes with bis(diphenylphosphino)methane. Crystal structures of {di-μ3-dithio-o-toluato-S,S′,S′-bis[μ-bis(diphenylphosphino)methane-μ-dithio-o-toluato-S,S′]} tetracopper(I) and {di[μ-bis(diphenylphosphino)methane]bis(dithio-o-toluato-S,S′)} dicopper(I)

The structures of [(CuS₂CT)₂dppm]₂ (I) (T = o-tolyl; dppm = bis(diphenylphosphino)methane) and [CuS₂CTdppm]₂ (II) have been determined by X-ray methods. Crystals of I are monoclinic, space group P2₁/n, with a = 15.163(4), b = 18.691(5), c = 13.478(4) Å, β = 96.81(3)°, Z = 2; crystals of II are orthorhombic. space group Pccn, with a = 23.267(4), b = 13.016(3), c = 20.731(5) Å, Z = 4. The structures of I and II have been solved by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.082 for I and 0.092 for II. The structure of I consists of centrosymmetric tetranuclear complexes in which two pairs of Cu atoms are triply bridged by a dppm ligand and two dithiocarboxylate groups from the dithio-o-toluate ligands. These last behave differently: one of them through a sulphur atom is also bonded to a Cu atom of the other pair so forming a tetranuclear complex. The Cu atoms of each pair show different coordination: Cu(1) displays a distorted trigonal and Cu(2) a distorted trigonal pyramidal geometry. The structure of II consists of dimers, in which each copper atom, doubly bridged by two dppm ligands, completes a distorted trigonal pyramidal coordination through two sulphur atoms from dithio-o-toluate anions acting as chelating ligands. In both compounds the phenyl group of the dithio-o-toluate anions is orthogonal to the corresponding CS₂ group. Both complexes give methyldithio-o-toluate in high yields by reaction with methyl iodide.     

Imidazole-containing ternary complexes of N-benzyloxycarbonyl-aminoacids. Crystal and molecular structure of bis(N-benzyloxycarbonyl-alaninato)bis-(N-methylimidazole)copper(II) ethanol solvate

Mixed ligand complexes of the type Cu(Z-aminoacidato)₂(B₂) (Z = benzyloxycarbonyl group, Z-aminoacidate = Z-glycinate (Zgly), Z-alaninate (Zala); Z-valinate (Zval), Z-leucinate (Zleu) ion, B = imidazole (Im), N-methylimidazole (MeIm)) were synthesized and characterized by means of electronic, infrared and EPR spectroscopies. For one of them, bis(Z-alaninato)bis(N-methylimidazole)copper(II) ethanol solvate, the crystal and molecular structure was also determined by the single crystal X-ray diffraction method. The complex crystallizes in the monoclinic space group P2₁/c, with cell dimensions a = 11.1119(6), b = 18.8398(7), c = 8.9652(5) Å, β = 105.380(2)° and Z = 2. The structure was solved by conventional Patterson and Fourier methods and refined by full-matrix least-squares to an R value of 0.045. The complex has square-planar coordination via two centrosymmetric carboxylic oxygens and two N-methylimidazole nitrogens. The second carboxylate oxygen is 2.731(5) Å from the copper atom in an ‘out of plane’ position. Packing is mainly determined by hydrogen bondings between amide nitrogen and amide carboxyl oxygen. Electronic, infrared and EPR spectra are consistent with this type of coordination geometry for anhydrous complexes, while for hydrate complexes are suggestive of tetragonal bipyramidal geometry.     

Mononuclear rhodium(I) complexes of 4-Amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole. Crystal structure of [Rh(CO)2(NH2bpt)]ClO4

Reaction of 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole (NH₂bpt) or its potassium salt (KNHbpt) with several rhodium(I) compounds, produces new neutral and cationic complexes of Rh(I). One of the complexes [Rh(CO)₂(NH₂bpt)]ClO₄ has been characterized by single-crystal X-ray diffraction. The crystals are monoclinic, space group P2₁/n, with a = 17.6130(6), b = 11.3072(2), c = 9.0013(2) Å, β = 101.536(2)° and Z = 4. The structure has been refined to R = 0.049.     

Mono- and bimetallic gold(I) and silver(I) pentafluoropropionates and related compounds

A series of eight new carboxylate complexes of the general type (L)_nMOC(O)R (L=PMe₃; n=1; M=Ag, Au; R=C₂F₅. L=PPh₃; n=1-3; M=Ag; R=C₂F₅, t-Bu) have been prepared in high yields. Crystal and molecular structures have been determined for three representative examples. The crystal structure of (Ph₃P)AgOC(O)C₂F₅ contains dimers in which the silver atoms are bridged by the carboxylate oxygen atoms. This bridging resembles the structural motif found in silver carboxylates without ligand support. Usage of the smaller phosphine PMe₃ leads to the formation of a polymeric chain structure in (Me₃P)AgOC(O)C₂F₅ with bridging carboxylate anions and short Ag-Ag contacts holding the monomers together. The reaction of (4-Me₂N-C₆H₄)Ph₂ PAuCl with two equivalents of C₂F₅CO₂Ag leads to the formation of a mixed metal product containing both gold and silver. The crystal structure analysis of this compound revealed a tetranuclear complex containing a central dimeric silver pentafluoropropionate unit which is chelated by the (triarylphosphine)gold(I) pentafluoropropionate molecules via Ag-Au metallophilic contacts and Ag-O donor/acceptor interactions.     

X-ray structures of dinuclear copper(I) and polynuclear copper(II) complexes with the 2,4-bis(cyanamido)cyclobutane-1,3-dione dianion

From the 2,4-bis(cyanamido)cyclobutane-1,3-dione dianion (2,4-NCNsq²⁻), two copper complexes [Cu₂(PPh₃)₄(PhCN)₂(μ-2,4-NCNsq)] · PhCN (1) and [Cu(dien)(μ-2,4-NCNsq) · H₂O]_n (2) have been synthesized and characterized by IR and electronic absorption spectroscopies. Their structures have been determined by X-ray crystallography. Complex 1 is a dinuclear copper(I) compound with a 2,4-NCNsq²⁻ ligand bridging two copper atoms through the nitrile nitrogen atoms. Complex 2 appears as a 3D network constituted of copper(II) atoms bridged by 2,4-NCNsq²⁻ dianions. This complex presents an unexpected coordination mode of the bis(cyanamido) ligands which are both coordinated via the nitrile functions and via the amido nitrogen atoms of the NCN groups.     

Microsolvation effect and hydrogen-bonding pattern of taurine-water TA-(H2O)n (n = 1-3) complexes

The microsolvation of taurine (TA) with one, two or three water molecules was investigated by a density functional theory (DFT) approach. Quantum theory of atoms in molecules (QTAIM) analyses were employed to elucidate the hydrogen bond (H-bond) interaction characteristics in TA-(H₂O)_n (n = 1–3) complexes. The results showed that the intramolecular H-bond formed between the hydroxyl and the N atom of TA are retained in most TA-(H₂O)_n (n = 1–3) complexes, and are strengthened via cooperative effects among multiple H-bonds from n = 1–3. A trend of proton transformation exists from the hydroxyl to the N atom, which finally results in the cleavage of the origin intramolecular H-bond and the formation of a new intramolecular H-bond between the amino and the O atom of TA. Therefore, the most stable TA-(H₂O)₃ complex becomes a zwitterionic complex rather than a neutral type. A many-body interaction analysis showed that the major contributors to the binding energies for complexes are the two-body energies, while three-body energies and relaxation energies make significant contributions to the binding energies for some complexes, whereas the four-body energies are too small to be significant.     

Platinum(II) complexes of pyrimidine-derived ligands

A series of new Pt(II) complexes of hydrazinouracils were synthesized and studied. The complexes have the general formula [Pt₂L2^?Cl₂]nH₂O, where L^? is a deprotonated molecule of a ligand, n = 1?3 and there are two bridging chloride ions. The ligands are bonded through the amino group of the hydrazine residue and the nitrogen atom of the pyrimidine cycle. From ¹H NMR data it is concluded that the preferred type of coordination is Pt- N(3), hydrazine chelation, which is characteristic for solid complexes. Although the participation of the N(1) atom in formation on the polynuclear complexes is possible, it may be that N(1) coordination occurs only in solutions.     

The unrestricted local properties: application in nanoelectronics and for predicting radicals reactivity

I have performed quantum chemical calculations for the CF₃X (X = Cl, Br) ???Au_n (n?=?2, 3, and 4) complexes at M05-2X/aug-cc-pVDZ(PP) level. Two types of optimized structures were obtained. Type I complexes are stabilized by the coordination force between the negative electrostatic potential of halogen atom and the gold atom, and type II complexes contain halogen bonds formed between the σ-hole of the halogen atoms and the negative electrostatic potential of Au_n. Results of the interaction energy indicate that type I complexes are more stable than type II complexes. AIM analysis reveals that type II complexes are a closed shell interaction and there is a partially covalent nature for type I complexes.     

Copper-thioarylazoimidazole complexes: Structures, photochromism and redox interconversion between Cu(II) ↔ Cu(I) and correlation with DFT calculation

Reaction of Cu(ClO₄)₂·6H₂O, SRaaiNR′ (1-alkyl-2-[(o-thioalkyl)phenylazo]imidazole) and NH₄SCN (1:1:2 mol ratio) affords distorted square pyramidal, [Cu^II(SRaaiNR′)(SCN)₂] (3) compound while identical reaction with [Cu(MeCN)₄](ClO₄) yields -SCN- bridged coordination polymer, [Cu^I(SRaaiNR′)(SCN)]_n (4). These two redox states [Cu^II and Cu^I] are interconvertible; reduction of [Cu^II(SRaaiNR′)(SCN)₂] by ascorbic acid yields [Cu^I(SRaaiNR′)(SCN)]_n while the oxidation of [Cu^I(SRaaiNR′)(SCN)]_n by H₂O₂ in presence of excess NH₄SCN affords [Cu^II(SRaaiNR′)(SCN)₂]. They are structurally confirmed by single crystal X-ray diffraction study. Cyclic voltammogram of the complexes show Cu(II)/Cu(I) redox couple at ∼0.4 V and azo reductions at negative to SCE. UV light irradiation in MeCN solution of [Cu^I(SRaaiNR′)(SCN)]_n (4) show trans-to-cis isomerisation of coordinated azoimidazole. The reverse transformation, cis-to-trans, is very slow with visible light irradiation while the process is thermally accessible. Quantum yields (?_t→c) of trans-to-cis isomerisation are calculated and free ligands show higher ? than their Cu(I) complexes. The activation energy (E_a) of cis-to-trans isomerisation is calculated by controlled temperature experiment. Copper(II) complexes, 3, do not show photochromism. DFT and TDDFT calculation of representative complexes have been used to determine the composition and energy of molecular levels and results have been used to explain the solution spectra, photochromism and redox properties of the complexes.     

Thermodynamics of base interaction in (A)n and (A.U)n

Using precision scanning microcalorimetry we studied (A)_n and (A·U)_n melting in highly diluted solutions (0.3 to 5.0 mm) with different Na⁺ activity. This permitted us to determine directly the thermodynamic functions of stacking interaction in (A)_n and base-pairing in (A·U)_n. For (A-A) stacking at (A)_n melting temperature we obtained ΔH^(A)n_m = 12.6 kJ mol^?1; ΔS^(A)n_m = 41 J K^?1 mol^?1. For A·U base-pairing at a standard temperature of 298 K and 0.1 m-Na⁺ we have: ΔH^(A·U) = 34 kJ mol^?1; ΔS^(A·U) = 102 J K^?1 mol^?1ΔG^(A·U) = ?3.5 kJ mol^?1.     

A pyridine bridged dicarbene ligand and its silver(I) and palladium(II) complexes: synthesis, structures, and catalytic applications

The potentially tridentate ligand 2,6-bis[(3-methylimidazolium-1-yl)methyl]pyridine dibromide reacts readily with silver(I) oxide in dichloromethane or dimethylsulfoxide to give a dinuclear silver(I)-carbene complex that was isolated as the tetrafluoroborate salt. Single crystal X-ray crystallography shows that each silver(I) ion is bridged by two ligands bonding through the carbene donors. Treatment of the silver(I) complex with suitable palladium(II) precursors gave the complexes PdCl[(CNC)]BF₄ and [PdMe(CNC)]BF₄ (CNC=2,6-bis[(3-methylimidazolin-2-yliden-1-yl)methyl]pyridine), in which the pyridyl and both carbene moieties are coordinated to a single palladium(II). The palladium(II) complexes have been fully characterised, including X-ray crystallography, and exhibit good activities in the Heck coupling reaction of 4-bromoacetophenone and n-butyl acrylate.     

Comparative studies on copper(I) complexes: synthesis, X-ray crystallography and electrochemical properties of [Cu(dafone)nX] complexes (dafone=4,5-diaza-fluoren-9-one, X=Br, I, SCN)

The synthesis, X-ray structures and electrochemical properties of stable five-coordinate, trigonal-bipyramidal Cu^I complexes of dafone (4,5-diaza-fluoren-9-one) [Cu(dafone)₂X] with X=Br (1) or I (2) as ancillary ligands are discussed. The thiocyanate-bridged polymeric Cu^I complex of dafone, [Cu(dafone)(SCN)]_n (3), forms two-dimensional sheets in the crystal, held together by weak interactions involving the dafone ketone group, while the phenanthroline complex, [Cu(phen)(SCN)]_n (4), a zigzag arrangement of the phen ligands leads to interchain π-stacking within the lattice. The electrochemical studies reveal that dafone stabilizes the Cu^I oxidation state more efficiently than phen due to its better π-acceptor ability as indicated by more positive redox potentials for the Cu^I/Cu^II couple.