Synthesis, structure and characterization of binuclear silver(I) complexes

Summary Two binuclear Ag^I complexes, [{Ag(dppp)}₂](NO₃)₂ (1) and [{Ag(dppb)}₂(NO₃)]₂ (2) (dppp = Ph₂P(CH₂)₃PPh₂, dppb = Ph₂P(CH₂)₄PPh₂], were synthesized and characterized by elemental analysis, t.g., i.r. and ³¹P-n.m.r. spectra. Single crystals of complex (2) were obtained from MeOH-CHCl₃. The X-ray crystal structure shows that the dppb ligand is bidentate, with two ligands bridging two metal ions to form a centrosymmetric dimer.     

Synthesis,structure and characterization of binuclear copper(I) complexes

Binuclear copper(I) complexes [Cu(dppm)(NO3)]2 (1), dppm=Ph2PCH2PPh2, [Cu(dppm)(2,9-Me2Phen)]2(NO3)2 (2), [Cu(dppm)(I)]2 (3) and [Cu(dppm)(py)]2(NO3)2 (4), (py=pyridine) have been synthesized by ligand reduction of cupric nitrate with dppm in EtOH and characterized by elemental analyses, molecular weight determination, t.g.a., 31P-n.m.r spectra; their electronic conductivities and c.v. waves have also been measured. The results show that dppm coordinates as a bridging bidentate ligand to the CuI atoms, and that NO3 behaves as a monodentate ligand or free ion in the newly prepared complexes.     

Synthesis, structure and characterization of binuclear copper(Ⅱ) complexes

At room temperature, dibenzoyl peroxide undergoes oxidative addition reaction with metallic copper powder and pyridine N-oxide (triphenylphosphine oxide or 2,9-dimethyl-4,7-diphenyl-1,10-phenanthrolin) which affords the last products as binuclear copper(II) complexes, [Cu(C5H5NO)-(C6H5COO)2]2(1), [Cu(OPPh3)(C6H5COO)2]2(2) and [Cu(C6H5COO)(C26H2oN2)](3, C26H2oN2 is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthrolin). The structure of the complexes were characterized by elemental analyses, IR spectra, TG-DTA and magnetic property. Crystals(1) are triclinic, space group P1,a=0.92617(36),b=1.06973(17), c=1.08813(29) nm, a=59.60(2)°, β=74.83(3)°,γ=72.80(2)°, V=0.880 nm3, Dc=1.520 g/cm3, Z=1, R=0.044, Rw=0.048, Mr=805.78, 3477 reflections with I > 3σ(I). Each copper(Ⅱ) ion is coordinated by two bridging bidentate benzoate ligands and one pyridine N-oxide or triphenylphosphine oxide to form dimeric binuclear molecules. The structure of the compound(1) shows a clear centre of symmetry.     

Syntheses and crystal structures of binuclear ruthenium complexes bearing 1,8′-bis(diphenylphosphinomethyl)naphthalene

Treatment of [RuCl₂(η⁶-C₆H₆)]_x with bidentate phosphine ligand BDNA [1,8-bis(diphenylphosphinomethyl)naphthalene] in methanol at room temperature gave η⁶-benzene-ruthenium complexes Ru₂Cl₄(η⁶-C₆H₆)₂(μ-BDNA) (1). Complex 1 further reacted with AgBF₄ to form complex [Ru₂Cl₂(μ-Cl)(η⁶-C₆H₆)₂(μ-BDNA)](BF₄) (2). [RuCl₂(η⁶-C₆H₆)]_x reacted with BDNA in refluxing methanol and then the reaction solution was treated with AgBF₄ to generate complex [Ru₂Cl₂(η⁶-C₆H₆)₂(μ-BDNA)₂](BF₄)₂ (3). Their compositions and structures had been determined by elemental analyses, NMR spectra and single crystal X-ray diffractions. X-ray diffraction showed that complex 1 belonged to monoclinic crystal system, P2₁/c space group with Z = 4, a = 12.810 Å, b = 21.507 Å, c = 18.471 Å, β = 107.95°; complex 2 belonged monoclinic crystal system, P2₁/n space group with Z = 4, a = 14.498 Å, b = 15.644 Å, c = 20.788 Å, β = 103.404°, and complex 3 belonged to monoclinic crystal system, P2₁/n space group with Z = 2, a = 13.732 Å, b = 14.351 Å, c = 19.733 Å, β = 94.82°.     

Orientational control of electronic coupling in mixed-valence, binuclear ruthenium(II)-bis(2,2':6',2' '-terpyridine) complexes

A series of binuclear ruthenium(II)-bis(2,2':6',2' '-terpyridine) complexes has been prepared around a central biphenylene unit equipped with a strap of variable length. Partial oxidation forms the mixed-valence complex that displays both ligand-to-metal, charge-transfer, and intervalence charge-transfer (IVCT) transitions in the near-IR region. On the basis of Hush theory, the electronic coupling matrix element for interaction between the metal centers decreases with increasing length of the tethering strap. This effect arises because the strap modulates the torsion angle between the phenyl rings and thereby controls the extent of through-bond electronic coupling. The coupling element favors a maximum for planar geometries and a minimum for orthogonal structures, but the full impact of the torsion angle is not realized due to thermal fluctuations.     

Hybrid DFT study of electronic structure on quasi-one-dimensional halogen-bridged binuclear metal complexes (MMX)

The electronic structure of quasi-one-dimensional halogen-bridged binuclear metal complex Ni₂(dta)₄I (dta=CH₃CS₂⁻) was investigated by hybrid density functional theory. UB3LYP was successfully applied to reproduce averaged-valence spin density wave state. The magnetic interactions between Ni dimers were estimated by calculating effective exchange integrals (J_ab) using Ni₂(dta)₄I dimer and tetramer models. Calculated J values were consistent with that of experimental results. The natural orbital analysis of the broken-symmetry UB3LYP solution were performed to elucidate symmetry-adapted molecular orbitals and their occupation numbers. Several chemical indices such as polyradical character and information entropy were introduced on the basis of the occupation numbers to discuss the bonding character of MMX chain. All these indices supports that Ni₂(dta)₄I was in the strongly correlating electron system.     

Electronic structure and FeNO conformation of nonheme iron-thiolate-NO complexes: an experimental and DFT study

Reactions of NO and CO with Fe(II) complexes of the tripodal trithiolate ligands NS3 and PS3* yield trigonal-bipyramidal (TBP) complexes with varying redox states and reactivity patterns with respect to dissociation of the diatomic ligand. The previously reported four-coordinate [Fe(II)(NS3)](-) complex reacts irreversibly with NO gas to yield the S = 3/2 {FeNO}(7) [Fe(NS3)(NO)](-) anion, isolated as the Me(4)N(+) salt. In contrast, the reaction of NO with the species generated by the reaction of FeCl(2) with Li(3)PS3* gives a high yield of the neutral, TBP, S = 1 complex, [Fe(PS3*)(NO)], the first example of a paramagnetic {FeNO}(6) complex. X-ray crystallographic analyses show that both [Fe(NS3)(NO)](-) and [Fe(PS3*)(NO)] feature short Fe-N(NO) distances, 1.756(6) and 1.676(3) A, respectively. However, whereas [Fe(NS3)(NO)]- exhibits a distinctly bent FeNO angle and a chiral pinwheel conformation of the NS3 ligand, [Fe(PS3*)(NO)] has nearly C(3v) local symmetry and a linear FeNO unit. The S = 1 [Fe(II)(PS3)L] complexes, where L = 1-MeIm, CN(-), CO, and NO(+), exhibit a pronounced lengthening of the Fe-P distances along the series, the values being 2.101(2), 2.142(1), 2.165(7), and 2.240(1) A, respectively. This order correlates with the pi-backbonding ability of the fifth ligand L. The cyclic voltammogram of the [Fe(NS3)(NO)](-) anion shows an irreversible oxidation at +0.394 V (vs SCE), apparently with loss of NO, when scanned anodically in DMF. In contrast, [Fe(PS3*)(NO)] exhibits a reversible {FeNO}(6)/{FeNO}(7) couple at a low potential of -0.127 V. Qualitatively consistent with these electrochemical findings, DFT (PW91/STO-TZP) calculations predict a substantially lower gas-phase adiabatic ionization potential for the [Fe(PS3)(NO)](-) anion (2.06 eV) than for [Fe(NS3)(NO)](-) (2.55 eV). The greater instability of the {FeNO}(7) state with the PS3* ligand results from a stronger antibonding interaction involving the metal d(z(2)) orbital and the phosphine lone pair than the analogous orbital interaction in the NS3 case. The antibonding interaction involving the NS3 amine lone pair affords a relatively "stereochemically active" dz2 electron, the z direction being roughly along the Fe-N(NO) vector. As a result, the {FeNO}(7) unit is substantially bent. By contrast, the lack of a trans ligand in [Fe(S(t)Bu)3(NO)](-), a rare example of a tetrahedral {FeNO}(7) complex, results in a "stereochemically inactive" d(z(2)) orbital and an essentially linear FeNO unit.     

Synthesis and characterization of several dicopper(I) complexes and a spin-delocalized dicopper(I,II) mixed-valence complex using a 1,8-naphthyridine-based dinucleating ligand

The synthesis of dicopper(I) complexes [Cu2(BBAN)(MeCN)2](OTf)2 (1), [Cu2(BBAN)(py)2](OTf)2 (2), [Cu2(BBAN)(1-Me-BzIm)2](OTf)2 (3), [Cu2(BBAN)(1-Me-Im)2](OTf)2 (4), and [Cu2(BBAN)(mu-O2CCPh3)](OTf) (5), where BBAN = 2,7-bis((dibenzylamino)methyl)-1,8-naphthyridine, py = pyridine, 1-Me-Im = 1-methylimidazole, and 1-Me-BzIm = 1-methylbenzimidazole, are described. Short copper-copper distances ranging from 2.6151(6) to 2.7325(5) A were observed in the solid-state structures of these complexes depending on the terminal ligands used. The cyclic voltammogram of compound 5 dissolved in THF exhibited a reversible redox wave at E1/2 = -25 mV vs Cp2Fe+/Cp2Fe. When complex 5 was treated with 1 equiv of silver(I) triflate, a mixed-valence dicopper(I,II) complex [Cu2(BBAN)(mu-O2CCPh3)(OTf)](OTf) (6) was prepared. A short copper-copper distance of 2.4493(14) A observed from the solid-state structure indicates the presence of a copper-copper interaction. Variable-temperature EPR studies showed that complex 6 has a fully delocalized electronic structure in frozen 2-methyltetrahydrofuran solution down to liquid helium temperature. The presence of anionic ligands seems to be an important factor to stabilize the mixed-valence dicopper(I,II) state. Compounds 1-4 with neutral nitrogen-donor terminal ligands cannot be oxidized to the mixed-valence analogues either chemically or electrochemically.     

Electronic structure and spectra of ruthenium binuclear complexes: Localized versus delocalized model

Calculations of spectral characteristics of Ru binuclear (II, II) and (III, III) complexes were performed by the restricted CI method. Both delocalized and localized basis sets were used and led to equivalent results. The post-Hartree–Fock nature of (III, III) compound wave functions were demonstrated. The advantage of a localized model in describing the properties of large molecular systems built from a number of clearly distinguished fragments is discussed. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65 : 183–193, 1997     

Rhodium(III) and iridium(III) complexes of thioarylazoimidazoles: Synthesis,structure, spectral characterization,electrochemistry and DFT calculation

[M(SRaaiNR′)Cl₃] (M = Rh(III), Ir(III) and SRaaiNR′ = 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole) complexes are described in this article. The single crystal X-ray structure of one of the complexes, [Rh(SMeaaiNEt)Cl₃] (3b), shows a tridentate chelation of SMeaaiNEt via N(imidazole), N(azo) and S(thioether) donor centres. Spectral characterization has been done by IR, UV–Vis and ¹H NMR data. The electronic structure, redox properties and spectra are well supported by DFT and TDDFT computation on the complexes.     

Synthesis,characterization, X-ray structure and DFT calculation of two Mo(VI) and Ni(II) Schiff-base complexes

In this study, the syntheses of two new Mo(VI) and Ni(II) complexes with H₂L tridentate (ONO) Schiff-base ligand have been described and fully characterized by means of elemental analysis, FT–IR, electronic, ¹H-NMR spectroscopy and single-crystal X-ray diffraction. In both complexes, the Schiff-base completely deprotonates and coordinates to the metal ion as a dianionic tridentate ligand via the donor oxygens and nitrogen atoms. The coordination numbers of Mo(VI) and Ni(II) are six and four, respectively. The DFT-B3LYP/6–31 + G (d,p) and PBEPBE/6–31 + G (d,p) calculations are carried out for the determination of the optimized structures. Frequency calculations and NBO analysis are also performed for characterization. According to the theoretical analysis of the complexes, ligand-to-metal donation is greater than back donation. NBO data revealed that the main contribution of the frontier orbitals belongs to L⁻².     

Synthesis,characterization and magnetic analysis of binuclear nickel(II) terephthalato complexes

Six new binuclear nickel (II) complexes have been synth-esized and characterized, namely: [Ni2(4X-TP-HA)(L)4](ClO4)2 [L = 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (NO2-phen) or 2,2-bipyridyl (bipy)], where 4X-TPHA is the tetrabromoterephthalate dianion (X = Br) or the tetraiodoterephthalate dianion (X = I). Based on i.r. spectra, elemental analyses and conductivity measurements, these complexes are proposed to have terephthalato-bridged structures containing two NiII ions, each in a distorted octahedral environment. The temperature dependences of the magnetic susceptibility for [Ni2(4Br-TPHA)(phen)4]- (ClO4)2·H2O (1) and [Ni2(4I-TPHA)(phen)4]-(ClO4)2·- 2H2O (4) were measured over the 4–300K range and the observed data indicate weak antiferromagnetic spin exchange interaction between the metal ions.     

Synthesis and characterization of neutral ligand-bridged binuclear dialkylcobalt(III) complexes

A series of neutral ligand-bridged binuclear dialkylcobalt(III) chelates has been prepared. Chelate systems based on monoanions of dimethylglyoxime (dm     

Electronic structure of adducts of Nd(III) carboxylate complexes determined by DFT and XPS methods

X-ray photoelectron spectroscopy and quantum chemistry methods are used to study Nd(tol)₃ and Nd(сor)₃ carboxylate complexes and their adducts with 1,10-phenanthroline (Nd(tol)₃Phen and Nd(сor)₃Phen₂). The electronic structure and specific features of the nature of chemical bonds are studied, as well as the effect of 1,10-phenanthroline on the electronic structure of the adduct. We propose the band assignment of the valence band of the XPS spectra of all compounds.     

Preparation,characterization and biological evaluation of two chiral binuclear copper(II) complexes

Two chiral Cu(II) complexes of [Cu₂(R‐L)₂](PF₆)₂·2C₂H₅OH ( 1 ) and [Cu₂(S‐L)₂](PF₆)₂·2C₂H₅OH ( 2 ) (HL = 2‐(Bis(quinolin‐2‐ylmethyl)amino)‐1‐propanol) were designed and synthesized to serve as chemical nucleases and anticancer drugs. X‐ray crystallography revealed that two complexes contain chiral binuclear cations and PF₆^? anions. The interaction of two complexes with CT‐DNA was researched via various spectroscopic techniques and viscosity measurement, indicating that the complexes were bound to CT‐DNA by a classical intercalation binding mode. In addition, the two complexes exhibited remarkable DNA cleavage activity with an optimal dosage of 10 μM in the absence of any exogenous oxidant agent. Both of the complexes showed excellent in vitro cytotoxicity on A549 cell lines with IC₅₀ values in the low micromolar range. Moreover, complex 2 could damage DNA of A549 cells into fragmentation and then induced cell apoptosis in a dose‐dependent manner, which was demonstrated by comet assay and Hoechst 33342 staining experiment. Further research showed that complex 2 could also induce G₂ and S phase cell cycle arrest.     

Structural characterization, solution studies, and DFT calculations on a series of binuclear gold(III) oxo complexes: relationships to biological properties

A series of structurally related oxo-bridged binuclear gold(III) compounds, [Au2(mu-O)2(N;N)2](PF6)2, where N;N is 2,2'-bipyridine or a substituted 2,2'-bipyridine, have recently been shown to exhibit appreciable stability under physiological-like conditions and to manifest important antiproliferative effects toward selected human tumor cell lines (J. Med. Chem. 2006, 49, 5524). The crystal structures of four members of this series, namely, [Au2(mu-O)2(bipy)2](PF6)2, cis-[Au2(mu-O)2(6-Mebipy)2](PF6)2, trans-[Au2(mu-O)2(6-oXylbipy)2](PF6)2, and [Au2(mu-O)2(6,6'-Me2bipy)2](PF6)2, have been solved here and the respective structural parameters comparatively analyzed. Remarkably, all of the compounds contain a common structural motif consisting of a Au2O2 "diamond core" linked to two bipyridine ligands in a roughly planar arrangement. Interestingly, introduction of different kinds of alkyl or aryl substituents on the 6 (and 6') position(s) of the bipyridine ligand leads to small structural changes that nonetheless greatly affect the reactivity of the metal centers. The chemical behavior of these compounds in solution has been studied in detail, focusing in particular on the electrochemical properties. Some initial correlations among the structural parameters, the chemical behavior in solution, and the known cytotoxic effects of these compounds are proposed. Notably, we have found that the 6,6'-dimethyl-2,2'-bipyridine derivative, which showed the largest structural deviations with respect to the model compound [Au2(mu-O)2(bipy)2](PF6)2, also had the highest oxidizing power, the least thermal stability, and the greatest cytotoxic activity. The positive correlation that exists between the oxidizing power and the antiproliferative effects seems to be of particular interest. Moreover, the electronic structures of these compounds were extensively analyzed using DFT methods, and the effects of the various substituents on reactivity were predicted; overall, very good agreement between theoretical expectations and experimental data was achieved. In turn, theoretical predictions offer interesting hints for the design of new, more active binuclear gold(III) compounds.     

Synthesis and structural investigation of N,N',N' '-trialkylguanidinato-supported zirconium(IV) complexes

The addition of 2 equiv of N,N',N' '-triisopropylguanidine (guanH(2)) to Zr(CH(2)Ph)(4) produced the bis(guanidinato)bis(benzyl)zirconium complex [((i)PrNH)C(N(i)Pr)(2)](2)Zr(CH(2)Ph)(2) (1). The mono(guanidinato) complex [((i)PrN)(2)C(NH(i)Pr)]ZrCl(3) (2) was accessible by the reaction of 2 equiv of guanH(2) with ZrCl(4). Guanidinium hydrochloride, [C(NH(i)Pr)(3)]Cl, is a byproduct of this reaction. When crystallized from THF, complex 2 was isolated as the THF adduct [((i)PrNH)C(N(i)Pr)(2)]ZrCl(3)(THF) (2-THF). The mixed cyclopentadienyl guanidinato complex [eta(5)-1,3-(Me(3)Si)(2)C(5)H(3)][((i)PrNH)C(N(i)Pr)(2)]ZrCl(2) (3) was prepared by treatment of [1,3-(Me(3)Si)(2)C(5)H(3)]ZrCl(3) with the in situ generated lithium triisopropylguanidinate salt. The reaction of guanH(2) with [1,3-(Me(3)Si)(2)C(5)H(3)]ZrMe(3) affords the dimethyl derivative [eta(5)-1,3-(Me(3)Si)(2)C(5)H(3)][((i)PrNH)C(N(i)Pr)(2)]ZrMe(2) (4). Definitive evidence for the molecular structures of these products is provided through single-crystal X-ray characterization of 1, 2-THF, and 3, which are presented. The extent of pi delocalization within the guanidinato ligand is discussed in the context of the metrical parameters obtained from these structural studies.     

Dinuclear Rh(I) complex with 2,7-bis(diphenylphosphino)-1,8-naphthyridine: Synthesis,structure, and dynamic property

Reaction of [RhCl(cod)]₂ with 2,7-bis(diphenylphosphino)-1,8-naphthyridine (dpnapy) and 2,6-xylyl isocyanide (XylNC) in the presence of NH₄PF₆ afforded the dirhodium(I) complex, [Rh₂(μ-dpnapy)₂(XylNC)₄](PF₆)₂ (5), and similar procedures using [MCl₂(cod)] (M = Pt, Pd) resulted in the formation of [Pt₂(μ-dpnapy)₂(XylNC)₄](PF₆)₄ (6) and [Pd₂Cl₂(μ-dpnapy)₂(XylNC)₂](PF₆)₂ (7). Complexes 5–7 were characterized by elemental analysis, IR, UV–Vis, ¹H and ³¹P{¹H} NMR, and ESI mass spectroscopic techniques, to involve a small and rigid d⁸ {M₂(μ-dpnapy)₂} metallomacrocycle. Complex 5 readily incorporated a silver(I) ion into the macrocycle to afford [Rh₂Ag(μ-dpnapy)₂(XylNC)₄](PF₆)₃ (8) which was characterized by X-ray crystallography. The Ag(I) ion is trapped by two trans N atoms of dpnapy ligands, resulting in an asymmetric Rh–Ag⋯Rh structure, determined as a disordered model in the crystal structure, and however, in a CH₂Cl₂ solution, a dynamic interconversion of the two Ag-trapped sites was observed with low-temperature NMR studies, which was further supported by DFT molecular orbital calculations. When an acetonitrile solution of complex 5 was treated over a droplet of mercury(0), the polymeric compound formulated as {[Rh(μ-dpnapy)(XylNC)₂](PF₆)}_n (9) was isolated as yellow single crystals, which were revealed by X-ray crystallography to consist of C₆ helical rods along c axis with a pitch of 33.5 Å (rise of unit = 5.6 Å) and a diameter of 20.64 Å.     

Crystal structure of N,N,N',N'-tetrakis(methyldiphenylphosphino)-bis(2'-phenoxy)-3,6-dioxaoctane.

The title molecule, [C70H68N2O4P4], is a polydentate podand consisting of four etheral oxygens, two tertiary amine nitrogens and four diphenylphosphin groups. It crystallizes in the triclinic space group P1, and there is only one half a molecule in the asymmetric unit. The coordinations around the N and P atoms are pyramidal. The conformations about C20-C21, O2-C21 and O2-C22 are gauche, anti and anti, respectively.