Homologous series of redox-active, dinuclear cations [M(2)(O(2)CCH(3))(2)(pynp)(2)](2+) (M = Mo, Ru, Rh) with the bridging ligand 2-(2-pyridyl)-1,8-naphthyridine (pynp)

A homologous series of dinuclear compounds with the bridging ligand 2-(2-pyridyl)-1,8-naphthyridine (pynp) has been prepared and characterized by X-ray crystallographic and spectroscopic methods. [Mo(2)(O(2)CCH(3))(2)(pynp)(2)][BF(4)](2) x 3CH(3)CN (1) crystallizes in the monoclinic space group P2(1)/c with a = 15.134(5) A, b = 14.301(6) A, c = 19.990(6) A, beta = 108.06(2) degrees, V = 4113(3) A(3), and Z = 4. [Ru(2)(O(2)CCH(3))(2)(pynp)(2)][PF(6)](2) x 2CH(3)OH (2) crystallizes in the monoclinic space group C2/c with a = 14.2228(7) A, b = 20.3204(9) A, c = 14.1022(7) A, beta = 95.144(1) degrees, V = 4059.3(3) A(3), and Z = 4. [Rh(2)(O(2)CCH(3))(2)(pynp)(2)][BF(4)](2) x C(7)H(8) (3) crystallizes in the monoclinic space group C2/c with a = 13.409(2) A, b = 21.670(3) A, c = 13.726(2) A, beta = 94.865(2) degrees, V = 3973.9(8) A(3), and Z = 4. A minor product, [Rh(2)(O(2)CCH(3))(2)(pynp)(2)(CH(3)CN)(2)][BF(4)][PF(6)] x 2CH(3)CN (4), was isolated from the mother liquor after crystals of 3 had been harvested; this compound crystallizes in the triclinic space group, P1 with a = 12.535(3) A, b = 13.116(3) A, c = 13.785(3) A, alpha = 82.52(3) degrees, beta = 77.70(3) degrees, gamma = 85.76(3) degrees, V = 2193.0(8) A(3), and Z = 2. Compounds 1-3 constitute a convenient series for probing the influence of the electronic configuration on the extent of mixing of the M-M orbitals with the pi system of the pynp ligand. Single point energy calculations performed on 1-3 at the B3LYP level of theory lend insight into the bonding in these compounds and allow for correlations to be made with electronic spectral data. Although purely qualitative in nature, the values for normalized change in orbital energies (NCOE) of the frontier orbitals before and after reduction are in agreement with the observed differences in reduction potentials as determined by cyclic voltammetry.     

Photoluminescent dinuclear lanthanide complexes with tris(2-pyridyl)carbinol acting as a new tetradentate bridging ligand

A tripodal ligand, tris(2-pyridyl)carbinol, affords a novel tetradentate coordination mode in homodinuclear lanthanide complexes, which exhibit remarkably short distances between metal ions. The strong luminescences of Eu(III) and Tb(III) complexes with the ligand demonstrate that the ligand has a suitable excited state for energy transfer from the ligand to the Eu(III) and Tb(III) centers, respectively.     

Annelated derivatives of 2-phenylquinoline, 2-(2′-pyridyl)quinoline and 2-phenyl-1,8-naphthyridine

Annelated derivatives of 2-phenylquinoline, 2-(2′-pyridyl)quinoline, and 2-phenyl-1,8-naphthyridine have been prepared where the bridging unit contains from one to four methylene units. The conformational properties of these molecules have been analyzed by ¹H nmr and uv spectroscopy as well as by pK_a determinations.     

Synthesis, crystal structure, spectroscopy and magnetic properties of a dinuclear Cu complex with 3,5-bis(2-pyridyl)pyrazole bridging ligand

A dinuclear Cu^II complex [Cu₂(bpp)₂(H₂O)₂](ClO₄)₂ (1) with 3,5-bis(2-pyridyl)pyrazole (Hbpp), has been synthesized and characterized by elemental analyses, thermal analysis, conductance, UV-vis and IR spectra. The crystal structure of 1, determined by X-ray diffraction technique, reveals that two centrosymmetric Cu^II centers are bridged by a pair of tetradentate anionic bpp ligands, adopting a square-pyramidal environment with the water ligand occupying the axial site. An interesting feature of this structure is the formation of a two-dimensional supramolecular network through O-H?O hydrogen bonds between the water moieties of the cationic [Cu₂(bpp)₂(H₂O)₂]²⁺ subunits and perchlorate anions. The magnetic properties of 1 have been investigated by variable-temperature magnetic susceptibility and EPR measurements. Very strong antiferromagnetic interaction between the Cu^II centers (with H=−JS₁S₂, J=−368.3 cm⁻¹) has been observed, and the magneto-structural correlations was analyzed.     

Influence of the bridging azine ligand on the rate of ligand substitution in a series of dinuclear platinum(II) complexes

A series of azine‐bridged dinuclear platinum(II) complexes of the type [{trans‐Pt(NH₃)₂(OH₂)}₂(μ‐azn)](ClO₄)₄ (where azn = pyrazine (pzn, Pt1 ), 2,3‐dimethylpyrazine (2,3‐pzn, Pt2 ), and 2,5‐dimethylpyrazine (2,5‐pzn, Pt3 )) were synthesized to investigate the influence of the bridging azine ligand on the reactivity of the platinum(II) centers. The pK_a values of the complexes were determined via acid–base titration, and the rate of substitution of the aqua moiety by a series of neutral nucleophiles, viz. thiourea (TU), 1,3‐dimethyl‐2‐thiourea (DMTU), and 1,1,3,3‐tetramethyl‐2‐thiourea (TMTU), was determined under pseudo‐first‐order conditions as a function of concentration and temperature using standard spectrophotometric techniques. The introduction of the methyl groups to the bridging azine linker in Pt2 and Pt3 leads to a moderate increase in the pK_a values obtained for the first and second deprotonation steps, respectively, as a result of the increased σ‐donor capacity of the bridging azine ligand trans to the aqua moiety. A comparison of the rate constants, k₁ and k₂, at 298 K, obtained for the substitution of the aqua moieties from Pt1 , Pt2 , and Pt3 by TU, shows that the introduction of the σ‐donating methyl groups on the bridging azine ligand in Pt2 and Pt3 results in a corresponding decrease in the reactivity, by ca. five times for the first substitution step and ca. 10 times for the second substitution step. Density functional theory calculations at the B3LYP/LACVP** level of theory for the complexes demonstrate that the introduction of electron‐donating methyl groups results in (i) increased steric hindrance over the metal centers and (ii) decreased the positive charge on the metal center and increases energy separation of the frontier molecular orbitals (E_HOMO – E_LUMO) of the ground‐state platinum(II) complexes, leading to a less‐reactive metal center. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 161–174, 2011     

Stereospecific synthesis and redox properties of ruthenium(II) carbonyl complexes bearing a redox-active 1,8-naphthyridine unit

Two stereoisomers of cis-[Ru(bpy)(pynp)(CO)Cl]PF₆ (bpy = 2,2′-bipyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine) were selectively prepared. The pyridyl rings of the pynp ligand in [Ru(bpy)(pynp)(CO)Cl]⁺ are situated trans and cis, respectively, to the CO ligand. The corresponding CH₃CN complex ([Ru(bpy)(pynp)(CO)(CH₃CN)]²⁺) was also prepared by replacement reactions of the chlorido ligand in CH₃CN. Using these complexes, ligand-centered redox behavior was studied by electrochemical and spectroelectrochemical techniques. The molecular structures of pynp-containing complexes (two stereoisomers of [Ru(bpy)(pynp)(CO)Cl]PF₆ and [Ru(pynp)₂(CO)Cl]PF₆) were determined by X-ray structure analyses.     

Complexes of 1,8-bis(2-pyridyl)-3,6-dithiaoctane with cobalt(II) halides

Summary Several cobalt(II) halide complexes derived from 1,8-bis(2-pyridyl)-3,6-dithiaoctane (bpdto) are described. Chemical analysis suggests their formulae to be: Co(bpdto)X₂ (X=Cl^–, Br^–, or I^–). Electrolytic conductivities in acetonitrile, magnetic moments at different temperatures, solid state i.r. and u.v.-visible spectra support a tetrahedral stereochemistry around the cobalt(II). The ligand is bidentate andN-bonded in all cases.This work was presented in the Fifth Annual Meeting of the Portuguese Chemical Society, Porto (Portugal), March 1982.     

Asymmetric dinuclear copper(I) complexes of bis-(2-(2-pyridyl)ethyl)-2-(N-toluenesulfonylamino)ethylamine with short copper-copper distances

Addition of two equivalents of CuCl to deprotonated bis-(2-(2-pyridyl)ethyl)-2-(N-toluenesulfonylamino)ethylamine (PETAEA) and its derivatives yielded new types of dinuclear Cu(I) complexes, Cu(mu-PETAEA)CuCl, Cu(mu-PEMAEA)CuCl, and Cu(mu-PENAEA)CuCl (PEMAEA is the 4-methoxyphenyl derivative of PETAEA and PENAEA is the 4-nitrophenyl derivative), exhibiting a four coordinate N(4)Cu center, a two coordinate NCuCl center, and a metal-metal distance within the range of 2.6572(8) to 2.6903(3) A. Analysis of the covalent radii for four coordinate and two coordinate copper(I), the acute copper-nitrogen-copper angles, and density functional theory (DFT) calculations suggest a weak attraction between the two copper atoms. The complexes apparently formed in a two-step process with the formation of the tetracoordinate mononuclear complex preceding the coordination of a second equivalent of CuCl to the lone pair of the sulfonamidate ligand.     

Metal-metal interactions in dinuclear ruthenium complexes containing bridging 4,5-di(2-pyridyl)imidazolates and related ligands

The dinuclear bis(2,2'-bipyridine)ruthenium complex of 4,5-di(2-pyridyl)imidazolate has been prepared and separated into its (meso and rac) diastereoisomers. The 2-phenyl substituted analogue forms the meso isomer selectively. All three complexes have been characterised by 1H NMR and X-ray crystallography. Electrochemical measurements and spectroelectrochemistry of the mixed-valence states reveal strong metal-metal interactions and IVCT bands that are highly dependent on the electrolyte.     

A 2-D nickel coordination polymer with an unsymmetric ligand, 5-(3-pyridyl)-1,3,4-oxadiazole-2-thione

A new nickel coordination polymer was obtained from an unsymmetric building block 5-(3-pyridyl)-1,3,4-oxadiazole-2-thione (HL6) and Ni(NO₃)₂ · 6H₂O-afforded [Ni(L6)₂(H₂O)₂] _n (1) with a (4,4) network. Complex 1 exhibits moderate antimicrobial activity against Bacillus subtilis ATCC 6633 and Candida albicans ATCC 90028. Thermogravimetric data and magnetic moments for 1 have been investigated.     

2-(芘-1-基)-1,8-萘啶的合成、理论计算及超快三阶非线性光学响应

合成了一个供体-受体(D-A)型含芘萘啶衍生物2-(芘-1-基)-1,8-萘啶(PN)。 通过核磁共振波谱(NMR)、傅里叶变换红外光谱(FTIR)、液-质联用仪(LC-MS)表征了其结构。 通过电子光谱和Z-扫描技术方法分别研究了化合物PN的线性光学性质和三阶非线性光学吸收,采用综合热分析方法测定了它的热稳定性。 结果表明,在532 nm、180 fs条件下,PN的三阶非线性吸收行为为反饱和吸收,其吸收系数为β=9.0×10^-14 m/W,显示出超快三阶非线性光学响应。 运用密度泛函理论方法计算了分子轨道能量、极化率和超极化率,结果表明电子转移能够在分子内部进行。 2-(芘-1-基)-1,8-萘啶的紫外光谱在450 nm以上无吸收,在非线性光学吸收、激光防护、吸收型光开关或双稳器件等方面可作备选材料。     

2,5-Diphenyl-3,4-bis(2-pyridyl)cyclopenta-2,4-dien-1-one as a redox-active chelating ligand

2,5-Diphenyl-3,4-bis(2-pyridyl)cyclopenta-2,4-dien-1-one (1), a close relative of tetraphenylcyclopentadienone, is a new ligand platform for use in redox switches and sensors. Compound 1 acts as a molecular electrochemical sensor towards a range of divalent metal ions and exhibits favourable two-wave behaviour. It forms chelates of the type [(1)MX2], whose stability is enhanced by five orders of magnitude upon one-electron reduction. The bite angle of 1 is close to 90 degrees in these complexes. The attachment of the 14-valence-electron Cp*Co fragment to the cyclopentadienone pi system reduces the bite angle and thus modulates the binding characteristics of 1.     

Synthesis and luminescent properties of iridium(III) ionic binuclear complexes with 1,4-bis[2-(2-pyridyl)benzimidazolato]butane as a bridging ligand

New ionic binuclear complexes of iridium(III) containing 1,4-bis[2-(2-pyridyl)benzimidazolato]butane as a bridging ligand were synthesized. These compounds exhibit intensive photo- and electroluminescence of yellow-green, green-yellow, and pink colors. The maximal electroluminescence brightness was 4565 cd/m².     

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.     

Hydrothermal preparation of novel Cd(II) coordination polymers employing 5-(4-pyridyl)tetrazolate as a bridging ligand

The reaction of 4-cyanopyridine with NaN(3) in the presence of H(2)O and a Lewis acid (CdCl(2)) affords a novel 3D pillared-layered fluorescent and phosphorescent coordination polymer Cd(3)(OH)(2)Cl(2)(4-PTZ)(2) (4-PTZ = 5-(4-pyridyl)tetrazolate) (1) while the direct reaction of CdCl(2) with H-PTZ gives the simpler species Cd(4-PTZ)(2)(H(2)O)(2). The solid-state structure and nature of 1 provide an indication of the type of materials that may be formed as intermediates in the Sharpless-Demko reaction for the generation of 5-substituted 1H-tetrazoles.     

Synthesis, structure, and reactivity of dinuclear nickel amino-thiophenolate complexes bearing bridging VO2(OH)2- and VO2(OR)2- coligands

A series of novel mixed ligand dinickel complexes of the type [Ni(II)(2)L(μ-L')](+), where L' is a tetrahedral oxo-alkoxo vanadate (L' = [O(2)V(V)(OR)(2)](-), R = H or alkyl) and L a macrocyclic N(6)S(2) supporting ligand, have been prepared, and their esterification reactivity has been studied. The orthovanadate complex [Ni(2)L(μ-O(2)V(OH)(2))](+) (2), prepared by reaction between [Ni(2)L(μ-Cl)]ClO(4) with Na(3)VO(4) and a phase transfer reagent in CH(3)CN, reacts smoothly with MeOH and EtOH forming the vanadate diesters [Ni(2)L(μ-O(2)V(OMe)(2))](+) (3) and [Ni(2)L(μ-O(2)V(OEt)(2))](+) (4). The dialkyl orthovanadate esters in 3 and 4 are readily transesterified with mono- and difunctional alcohols. Complex 3 can also be generated from 4 by transesterification with MeOH. Complexes 3 and 4 react with diols (ethylene glycol, propylene glycol and diethylene glycol) as well to afford the complexes [Ni(2)L(μ-O(2)V(OH)(OCH(2)CH(2)OH))](+) (5), [Ni(2)L(μ-O(2)V(OCH(2))(2)CH(2))](+) (6), and [Ni(2)L(μ-O(2)V(OCH(2)CH(2))(2)O)] (7). The crystal structures of the tetraphenylborate salts of complexes 3-7 reveal in each case four-coordinate O(2)V(V)(OR)(2)(-) groups bonded in a μ(1,3)-bridging mode to generate trinuclear complexes with a central N(3)Ni(μ-S)(2)(μ(1,3)-O(2)V(OR)(2))NiN(3) core. The stabilization of the four-coordinate V(V)O(2)(OR)(2)(-) moieties is a consequence of both the two-point coordinative fixation to and the steric protection of the bowl-shape binding pocket of the [Ni(2)L](2+) fragment. Cyclic voltammetry experiments reveal that the encapsulated vanadate esters are not reduced in a potential window of -2.0 to +2.5 V vs SCE. The spins of the nickel(II) (S(i) = 1 ions) in 3 are weakly ferromagnetically coupled (J = +23 cm(-1), (H = -2JS(1)S(2))) to produce an S = 2 ground state.     

Synthesis and molecular structures of dinuclear complexes with 1,2-dihydro-1,2-diphenyl-naphtho[1,8-c,d]1,2-diphosphole as a bridging ligand

A bisphosphine in which a PhP-PPh bond bridges 1,8-positions of naphthalene, 1,2-dihydro-1,2-diphenyl-naphtho[1,8-cd]-1,2-diphosphole (1), was used as a bridging ligand for the preparation of dinuclear group 6 metal complexes. Free trans-1, a more stable isomer having two phenyl groups on phosphorus centers mutually trans with respect to a naphthalene plane, was allowed to react with two equivalents of M(CO)₅(thf) (M = W, Mo, Cr) at room temperature to give dinuclear complexes (OC)₅M(μ-trans-1)M(CO)₅ (M = W (2a), Mo (2b), Cr (2c)). The preparation of the corresponding dinuclear complexes bridged by the cis isomer of 1 was also carried out starting from the free trans-1 in the following way. Mono-nuclear complexes M(trans-1)(CO)₅ (M = W (3a), Mo (3b), Cr (3c)) which had been prepared by a reaction of trans-1 with one equivalent of the corresponding M(CO)₅(thf) (M = W, Mo, Cr) complex, were heated in toluene, wherein a part of the trans-3a-c was converted to their respective cis isomer M(cis-1)(CO)₅. Each cis trans mixture of the mono-nuclear complexes 3a-c was treated with the corresponding M(CO)₅(thf) to give a cis trans mixture of the respective dinuclear complexes 2a-c. The cis isomer of the ditungsten complex 2a was isolated, and its molecular structure was confirmed by X-ray analysis, showing a shorter W?W distance of 5.1661(3) Å than that of 5.8317(2) Å in trans-2a.