Structural characterizations of some adducts of silver(I) nitrate and perchlorate with some cyclic di- (or tri-) ene organic ligands

Single crystal X-ray structural characterizations of some adducts of silver(I) nitrate and perchlorate with assorted organic poly-ene ligands (nbd = norbornadiene, bicyclo[2.2.1]hepta-2,5-diene; cod = 1,5-cyclooctadiene; cdt ≡ trans,trans,cis-cyclododeca-1,5,9-triene) are reported, all being polymeric in form (with the exception of mononuclear ionic AgClO₄:cod (1:2)), with chains comprised of alternating silver and nitrate/perchlorate components substituted or linked by unsaturated donors which complete the coordination spheres of the silver atoms. In AgNO₃:nbd (2:1) (a redetermination), pairs of silver/nitrate strands are linked in a one-dimensional polymer by the nbd ligands. In AgNO₃:nbd (1:1)_∞, meandering silver/nitrate strands containing pairs of independent silver and nitrate units in a crystallographic mirror plane are linked to either side with parallel planes by nbd ligands. In AgNO₃:cod (1:1)_∞, the cod ligands ‘chelate’ to the silver atoms in a silver/nitrate chain. In AgNO₃:cdt (1:2)_∞, pairs of ‘unidentate’ cdt ligands are pendant from a silver/nitrate chain, while in the (1:1)_∞ adduct, the cdt ligands bridge pairs of silver atoms from an adjacent chain forming a two-dimensional web. A common form of the bridging nitrate group in the above is as an O,O′-NO₃-O′,O″ bis-chelate, the pair of the bis-oxygen chelates having a common oxygen atom.     

Synthesis, characterization, crystal structure and luminescence properties of phosphinic silver(I) complexes with thiourea derivatives

Reaction of phenylisothiocyanate with different aromatic amines allowed the synthesis of compounds containing the thiourea moiety. By reacting silver bis(triphenylphosphine)nitrate with suitable ligands belonging to this family of sulphurated compounds, three new complexes have been afforded. Ligands and complexes were characterized also by X-ray diffraction. The structures reveal remarkable differences in the silver coordination geometry in function of the nature and size of the ligand. The emission properties of all compounds were characterized at 10 and at 298 K.     

A new family of lanthanide terpyridine nitrate complexes: Solvothermal syntheses, crystal structures and luminescent properties of [Ln(pytpy)(NO3)2(μ-OCH3)]2

The complexes [Ln(pytpy)(NO₃)₂(μ-OCH₃)]₂ (Ln = Eu(III), Tb(III), Dy(III), pytpy=4′-(n-pyridyl)-2,2′:6′,2″-terpyridine, n = 2, 3) were synthesized and characterized by IR, elemental analyses, UV–Vis and luminescent spectroscopy. Three complexes crystallized in monoclinic system, P2₁/n space group. Lanthanide ions are nine-coordinated by three nitrogen atoms from tridentate pytpy ligands, four oxygen atoms from two bidentate nitrate groups and two oxygen atoms from two methoxo groups, forming distorted tricapped trigonal prismatic geometries. The dimethoxo-bridges connect two metal ions in asymmetric fashion into dimeric structures with short LnLn distances of 3.767(1), 3.740(1) and 3.720(1) Å for Eu(III), Tb(III) and Dy(III) complexes, respectively. Photoluminescence measurement indicates that 1 and 3 emit the characteristic luminescence of Tb(III) and Eu(III) ions in the solid state, respectively. The luminescent spectrum of Eu(III) complex in solvents was also investigated.     

Preparation and structural characterization of group 1 metal complexes containing a chelating biphenolato phosphine ligand

The coordination chemistry of a potentially tridentate, dianionic biphenolato phosphine ligand with respect to group 1 metals is described. Deprotonation of bis-(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphine (H₂[OPO]) with two equivalents of n-BuLi, NaH, or KH in dimethoxyethane (DME) solutions produces the corresponding dinuclear alkali metal complexes [OPO]M₂(DME)₂ (M = Li, Na, K). The X-ray structure of [OPO]Li₂(DME)₂ reveals that the two lithium atoms are bridged by both phenolato oxygen donors with only one lithium being coordinated to the phosphorus donor. Consistently, variable-temperature ³¹P{¹H} and ⁷Li{¹H} NMR spectroscopic studies elucidate the coordination of the phosphorus donor in [OPO]Li₂(DME)₂ to one of the lithium atoms in solution. Interestingly, an X-ray diffraction study of the potassium complex indicates a dimeric structure with S₂ symmetry for this species in which the four potassium atoms are bridged by both phosphorus and oxygen donors of the biphenolato phosphine ligands. These alkali metal complexes are active initiators for catalytic ring-opening polymerization of ε-caprolactone.     

Nickel and palladium complexes bearing ortho-phenoxy modified anilido-imine ligands: Drastic steric effect on coordinated geometry, and catalytic property toward olefin polymerization

A series of new nickel complexes and palladium complexes bearing ortho-phenoxy modified anilido-imine ligands have been synthesized and characterized. X-ray diffraction analyses of the single crystal structures reveal that there are no direct metal-O interactions in all of the complexes. The steric hindrance of complexes has an importance influence on their coordinated geometries. The bulky complexes with 2,6-diisopropylphenyl substituent exist as a dimers with bromine-bridged structure while those with 2,6-dimethylphenyl or phenyl substituents adopt a distorted tetrahedral geometry with four nitrogen atoms of two anilido-imine ligands. The nickel complexes exhibited high activity up to 7.33 × 10⁶ g/(mol of Ni · h) and palladium complexes showed very high activity up to 2.63 × 10⁸ g/(mol of Pd · h) for norbornene polymerization with methylaluminoxane as cocatalyst. The nickel catalysts were attempted to polymerize ethylene at atmosphere pressure, however, only oligomers were produced.     

Syntheses, structures and photoluminescent properties of silver(I) complexes with in situ generated hexahydropyrimidine derivatives

Two new linear and V-shaped tetradentate ligands, namely 1,4-bis(2-hexahydropyrimidyl)benzene (L) and 1,3-bis(2-hexahydropyrimidyl)benzene (L^′), and their silver(I) complexes, [Ag₂L(μ-ONO₂)](NO₃) · 2H₂O (1), [Ag₂L(μ-pn)](NO₃)₂ (2), [Ag₂L(μ-pn)](ClO₄)₂ (3) and [Ag₄L^′₂(H₂O)](NO₃)₄ · 5H₂O (4) (pn=1,3-diaminopropane) have been synthesized in situ and structurally characterized by single-crystal X-ray diffraction. 1 and 2 were obtained from the same reaction solution but different crystallization conditions. 1 is an one-dimensional chain featuring cuboid tetranuclear silver(I) units interconnected through monoatomic nitrate bridges. Both 2 and 3 are ribbon-like helical compounds in which each L ligand acts in a tetradentate bridging mode to interconnect four metal atoms, and each pn ligand functions in a bidentate bridging mode to link a pair of metal atoms. 4 shows a truncated square-pyramidal tetranuclear motif arose by the V-shaped L^′ ligand. Close Ag?Ag separations (2.901-2.939 Å) assisted by bis(hexahydropyrimidine) bridges were observed in 1 and 4, indicating metal-metal interactions. Photoluminescence of 1-4 has also been observed in the solid state and solution at room temperature and low temperature, respectively.     

Synthesis of novel chiral Cu or Ag/S,N cluster complexes and absolute stereostructures as determined by x-ray crystallography

Novel chiral copper(I) and silver(I) metal complexes were synthesized from the reaction of chiral 1,3-thiazolidine-2-thione ligand with CuCl and AgOAc in dichloromethane in the presence of Et(3)N and DMAP at room temperature. Their unique crystal structures were determined by X-ray analysis. Four Cu(I) atoms and four 1,3-thiazolidine-2-thione ligands form a butterfly-type metal cluster. Six Ag(I) atoms and six 1,3-thiazolidine-2-thione ligands form another butterfly-type cluster.     

Silver coordination complexes of 2-(diphenylphosphinomethyl)pyridine and their bipyridine derivatives

Reaction of 2-(diphenylphosphinomethyl)pyridine (PMP-21) with the silver(I) salts of tetrafluoroborate , triflate (Otf⁻), and trifluoroacetate (tfa⁻) affords dinuclear complexes (2-4), where the ligand bridges the two silver centers, and the anions interact with the metal centers to varying degrees. Further reaction of AgBF₄ and AgOtf with reaction solutions containing PMP-21 and either the bidentate 5,5′-dimethyl-2,2′-bipyridine or 4,4′-bipyridine ligands produce dimeric and bridged structural motifs. The ability of 5,5′-dimethyl-2,2′-bipyridine to chelate and the 4,4′-bipyridine to serve as a connector between metal centers, allows the construction of coordinative structures where the effect of ligand ratio and either interacting or non interacting anions influence the silver coordination environment, allowing it to take on several geometries including trigonal bipyramidal, 5, both T-shaped and tetrahedral in a single structure, 6 and 8, trigonal pyramidal, 7, and trigonal planar, 9. Structures 2, 3, and 4 display comparable Ag-Ag contacts ranging from 2.7979(10) to 3.0538(4) Å, with a corresponding weakening of the metallophilic interaction when a bipyridine ligand is coordinated. Low-temperature luminescence spectra were collected for all compounds and are compared.     

Ru2(CO)4(OOCR)2(PPh3)2 sawhorse-type complexes containing μ2-η-carboxylato ligands derived from biologically active acids

The thermal reaction of Ru₃(CO)₁₂ with the biologically active acids acetyl salicylic acid (Aspirin), α-methyl-4-(isobutyl)phenylacetic acid (Ibuprofen) and 3α,7α,12α-trihydroxy-5β-cholanic acid (cholic acid) in refluxing tetrahydrofuran, followed by addition of triphenylphosphine, gives the dinuclear complexes Ru₂(CO)₄(OOCR)₂(PPh₃)₂ (1: R = C₆H₄-2-OCOMe, 2: R = CHMe-C₆H₄-4-Buⁱ, 3: C₂₃H₃₉O₃). The single-crystal structural analysis of 1 and 2 reveals a dinuclear Ru₂(CO)₄ sawhorse structure, the diruthenium backbone being bridged by the carboxylato ligands, while the two phosphine ligands occupy the axial positions at the ruthenium atoms. However, chiral carbon atoms in the carboxylic acid undergo racemisation during the thermal reaction.     

Synthesis and X-ray crystal structures of two transition metal complexes based on functionalised 1,5-anhydro-2-deoxy-D-galactitol and methyl 2-deoxy-alpha-D-galactopyranoside

Two new ligands of transition metal cations based on galactose-derived scaffolds were synthesised: 1,5-anhydro-2-deoxy-3,4,6-tri-O-(2-picolyl)-D-galactitol and methyl 2-deoxy-3,4,6-tri-O-(2-picolyl)-alpha-D-galactopyranoside. These ligands permitted the isolation as single crystals of a Co(II) and a Ni(II) complex, respectively. The structures of both complexes were determined by X-ray crystallography showing a coordination sphere including sugar-bound oxygen atoms. The sugar-derived ligands were found to be in both cases in high energy conformations in the crystal structures of the complexes. These conformations contain an arrangement of sugar-bound oxygen atoms similar to those observed in polyol-metal and carbohydrate-metal complexes.     

Coordination chemistry of di-2-pyridylamine-based bridging heterocyclic ligands: A structural study of coordination polymers and discrete dinuclear complexes

Four new bridging ligands containing two di-2-pyridylamine subunits have been synthesised. The coordination chemistry of these, along with one previously reported ligand, has been investigated through reactions with various silver(I), copper(II) and palladium(II) reactants. Typically, reaction of these ligands with silver(I) salts gave 1-D coordination polymers, within which the ligands act as divergent bridging units, while reaction with copper(II) and palladium(II) precursors provided discrete dinuclear complexes with chelating bidentate subunits. The complexes were characterised by a combination of elemental analysis, NMR spectroscopy and X-ray crystallography. The silver coordination polymers displayed interesting variations in supramolecular architecture, attributed to weak secondary interactions, such as Ag?π-bonding.     

Synthesis and properties of electrochemiluminescent dinuclear Ru(II) complexes assembled with ester-bridged bis(bipyridine) ligands

New bridging ligands, such as bpy-(COOCH₂)-bpy (BL1), mbpy-(CH₂)₃COOCH₂-bpy (BL2), bpy-COO(CH₂)₆OOC-bpy (BL3), and bpy-COOCH₂PhPhCH₂OOC-bpy (BL4), have been synthesized and coordinated to [RuL₂(acetone)₂](PF₆)₂ for various [Ru(L)₂(BL)Ru(L)₂](PF₆)₄-type dinuclear ruthenium complexes (where BL = BL1, BL2, BL3, BL4, and L = bpy, o-phen, DTDP). Their electrochemical redox potentials, spectroscopic properties and relative electrochemiluminescence were investigated in detail. All dinuclear Ru complexes exhibit MLCT (metal-to-ligand charge transfer) absorption and luminescence bands in the visible region. ECL intensities of dinuclear ruthenium(II) complexes were affected not only by the kind of the ligand, but also by the nature of the bridging ligand. Among the synthesized dinuclear Ru complexes, [(DTDP)₂Ru(mbpy)-(CH₂)₃COOCH₂-(bpy)Ru(DTDP)₂](PF₆)₄ exhibited enhanced ECL intensities as high as 2.9 times greater than that of the reference, [Ru(o-phen)₃](PF₆)₂.     

Syntheses, structures and vibrational spectroscopy of some 1:1 and 1:2 adducts of silver(I) oxyanion salts with 2,2′-bis(pyridine) chelates

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for a number of adducts of 1:1 stoichiometry of silver(I) oxyanion salts (perchlorate, nitrate, trifluoroacetate (‘tfa’) (increasing basicity)) with 2,2′-bis(pyridine) ligands (2,2′-bipyridyl, ‘bpy’; 2,2′-biquinolyl, ‘bq’; 2,2′-dipyridylketone, ‘dpk’; 2,9-dimethylphenanthroline, ‘dmp’). The adducts take two forms: (a) neutral mononuclear molecules, in which the 2,2′-bis(pyridine) ligand behaves as a chelate, with the silver coordination number dependent on the denticity of the anion; these are Agtfa:bpy (1:1) and AgClO₄:bq (1:1) (and various (ionic) acetonitrile or pyridine solvates AgClO₄:bq/dmp:MeCN/py (1:1:1), in which the solvent molecules are coordinated); and (b) one-dimensional polymers. The latter are diverse: in AgClO₄:bpy, dpk (1:1), the anion is discrete, the polymer made up of an array of two-coordinate silver atoms linked by bpy ligands twisted about their central connecting element. In AgNO₃:bpy, bq (1:1), the bpy ligands are chelating with the oxyanions bridging, cf. previously reported AgNO₃:dpk (1:1), in which the nitrate chelates the metal, with the dpk bridging, chelating N,O to one silver, while the other nitrogen bridges to the next. With Agtfa, a novel binuclear adduct has been isolated in conjunction with the hydrated ligand, Agtfa:dpk:(dpk · H₂O) (1:1:2). The far-IR spectra of several of these complexes show bands that can be assigned to the ν(AgN) modes, the positions of these bands correlating well with the relative Ag-N bond lengths.Syntheses and single-crystal X-ray structural characterizations are also reported for various adducts of silver(I) perchlorate, nitrate and trifluoromethanesulfonate with bpy, bq, ‘phen’ (= 1,10-phenanthroline), and ‘dmp’, of stoichiometry AgX:L (1:2). In each case the complex is ionic [AgL₂]X; the silver atom is four-coordinate, but diverse and remarkable variations in stereochemistries associated with changes in the interligand N-Ag-N angles, presumably influenced by the different packing arrangements, are observed.     

Synthesis and crystal structures of mono- and dinuclear silver(I) complexes bearing 1,8-naphthyridine ligand

Mononuclear and dinuclear silver(I) complexes bearing 1,8-naphthyridine (napy) were prepared. The crystal structures of [Ag(napy-κN)₂](PF₆) (1) and [Ag₂(μ-napy)₂](PF₆)₂ · 3CH₃CN (2 · 3CH₃CN) were determined by X-ray diffraction studies. In complex 1, intermolecular π-π interaction of napy ligands between neighboring molecules forms left-handed hexagonal columns in the solid state. On the other hand, two napy ligands bridging two Ag ions in the dinuclear complex 2 shape a face-to-face π-π stacking with those of the neighboring molecule to form the dimeric unit. Besides, two of four napy ligands, which are located in a diagonal position in the dimeric unit, build intermolecular back-to-back π-π stackings with those of the adjacent dimeric unit, and a ladder-like stairway structure is generated in the solid state. Irrespective of such characteristic structures of 1 and 2 in the solid state, both complexes show very rapid dynamic behavior in solutions. No conversion between 1 and 2 took place even in the presence of excess amounts of Ag⁺ or napy in solutions.     

Lone pair ··· π interactions between water oxygens and aromatic residues: Quantum chemical studies based on high‐resolution protein structures and model compounds

The π electron cloud of aromatic centers is known to be involved in several noncovalent interactions such as C—H···π, O—H···π, and π···π interactions in biomolecules. Lone-pair (lp) ··· π interactions have gained attention recently and their role in biomolecular structures is being recognized. In this article, we have carried out systematic analysis of high-resolution protein structures and identified more than 400 examples in which water oxygen atoms are in close contact (distance < 3.5 Å) with the aromatic centers of aromatic residues. Three different methods were used to build hydrogen atoms and we used a consensus approach to find out potential candidates for lp···π interactions between water oxygen and aromatic residues. Quantum mechanical calculations at MP2/6-311++G(d,p) level on model systems based on protein structures indicate that majority of the identified examples have energetically favorable interactions. The influence of water hydrogen atoms was investigated by sampling water orientations as a function of two parameters: distance from the aromatic center and the angle between the aromatic plane and the plane formed by the three water atoms. Intermolecular potential surfaces were constructed using six model compounds representing the four aromatic amino acids and 510 different water orientations for each model compound. Ab initio molecular orbital calculations at MP2/6-311++G(d,p) level show that the interaction energy is favorable even when hydrogen atoms are farthest from the aromatic plane while water oxygen is pointing toward the aromatic center. The strength of such interaction depends upon the distance of water hydrogen atoms from the aromatic substituents. Our calculations clearly show that the lp···π interactions due to the close approach of water oxygen and aromatic center are influenced by the positions of water hydrogen atoms and the aromatic substituents.     

Synthesis, characterization and antimicrobial activity of a series of substituted coumarin-3-carboxylatosilver(I) complexes

A series of new coumarin-derived carboxylate ligands and their silver(I) complexes have been synthesized, characterized and screened for their in vitro antibacterial activity against a range of Gram-positive and Gram-negative bacteria as well as for their antifungal activity against a clinical isolate of Candida albicans. The ligands were synthesised by either acid or base hydrolysis of their corresponding esters, which in turn were synthesised via the Knoevenegal reaction. The reaction of silver(I) nitrate with the coumarin carboxylate ligands in either aqueous or aqueous/ethanol solutions allowed the isolation of a series of novel Ag(I) carboxylate complexes. Whilst none of the ligands showed any antimicrobial activity, a number of the Ag(I) complexes exhibited potent activity. In particular, Ag(I) complexes of hydroxy-substituted coumarin carboxylates demonstrated potent activity against the clinically important methicillin-resistant Staphylococcus aureus (MRSA) bacterium (MIC₈₀ = 0.63 μM).     

Synthesis and characterization of new dinuclear complexes of molybdenum(V) with β′-hydroxy-β-enaminones

New dinuclear molybdenum(V) complexes have been obtained by the reaction of [Mo₂O₃(acac)₄] (acac=acetilacetonate ion) with the polydentate ligands, β′-hydroxy-β-enaminones. All prepared complexes consist of Mo₂O₄ ²⁺ core coordinated by two ligands as in the β-diketonates only through two donor oxygen atoms. Such bonding gives the opportunity for the sixth coordination place around molybdenum to be completed by the monodentate solvent molecule D. All compounds have been characterized by means of elemental analyses, one- and two-dimensional NMR spectroscopy, IR spectroscopy as well as by thermal analyses. The molecular and crystal structures of the molybdenum(V) complexes 1a and 1b coordinated by two different isomeric ligands as well as of the isomer a itself have been determined by a single crystal X-ray diffraction method.     

Ionic liquid based synthesis of the dinuclear complex Ag2I2(DPEphos)2 with Ag-Ag interaction

The reaction of equimolar amounts of AgI and the ligand bis(2-(diphenylphosphino)phenyl)ether (DPEphos) in the ionic liquid [NMe(n-Bu)₃]₂[N(Tf)₂] yields the dinuclear complex Ag₂I₂(DPEphos)₂. Herein, each silver atom is coordinated by two iodide anions and two DPEphos ligands, resulting in a distorted tetrahedral coordination. Moreover, Ag-Ag interaction (293.7 pm) is observed and represents the shortest bonding observed for dinuclear silver phosphine complexes.     

Uranyl nitrate complexes of some Schiff bases of 4-aminoantipyrine and certain carbonyl compounds

A series of nine complexes of uranyl nitrate with some Schiff bases derived from 4-aminoantipyrine and certain carbonyl compounds, such as benzaldehyde, 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 4- methylbenzaldehyde, 4-N,N-dimethylaminobenzaldehyde, 2-hydroxybenzaldehyde, 2-hydroxy-1-naphthaldehyde, acetylacetone and benzoylacetone have been synthesized. These complexes have been characterized by elemental analysis, molecular weight determination and IR spectral, conductance and magnetic studies. From these studies they can be formulated as [UO₂L₂(NO₃)₂], in which the first five ligands (in the order given above) and nitrate ions are coordinated bidentately, while the last four ligands (which have either a phenolic hydroxyl group or a side-chain carbonyl group as an additional site) act as terdentate ligands, and nitrate ions are coordinated monodentately. Hence the proposed general formula for the complexes suggests that the uranyl ion has a coordination number of eight in addition to the two oxygen atoms which have already been bonded to the U(VI) species.     

Synthesis and structural characterization of five-, six-, and seven-coordinate mononuclear manganese(II) complexes with N-tridentate ligands

A series of four mononuclear manganese (II) complexes with the N-tridentate neutral ligands 2,2^′:6,2^′′-terpyridine (terpy) and N,N-bis(2-pyridylmethyl)ethylamine (bpea) have been synthesized and crystallographically characterized. The complexes have five- to seven-coordinate manganese(II) ions depending on the additional ligands used. The [Mn(bpea)(Br)₂] complex (1) has a five-coordinated manganese atom with a bipyramidal trigonal geometry, while [Mn(terpy)₂](I)₂ (2) is hexa-coordinated with a distorted octahedral geometry. Otherwise, the reactions of Mn(NO₃)₂ · 4H₂O with terpy or bpea afforded novel seven-coordinate complexes [Mn(terpy)(NO₃)₂(H₂O)] (3) and [Mn(bpea)(NO₃)₂] (4), respectively. 3 has a coordination polyhedron best described as a distorted pentagonal bipyramid geometry with one nitrate acting as a bidentate chelating ligand and the other nitrate as a monodentate one. 4 possesses a highly distorted polyhedron geometry with two bidentate chelating nitrate ligands. These complexes represent unusual examples of structurally characterized complexes with a coordination number seven for the Mn(II) ion and join a small family of nitrate complexes.