Bridging Chloride Research Articles

Structural Design Parameters for Highly Birefringent Coordination Polymers.

A series of coordination polymer materials incorporating the highly anisotropic 2-(2-pyridyl)-1,10-phenanthroline (phenpy) building block have been synthesized and structurally characterized. M(phenpy)[Au(CN)2]2 (M = Cd, Mn) are isostructural and form a 1-D chain through bridging [Au(CN)2](-) units and extend into a 2-D sheet through aurophilic interactions. M(phenpy)(H2O)[Au(CN)2]2·2H2O (M = Cd, Mn, and Zn) are also isostructural but differ from the first set via the inclusion of a water molecule into the coordination sphere, resulting in a 1-D topology through aurophilic interactions. In(phenpy)(Cl)2[Au(CN)2]·0.5H2O forms a dimer through bridging chlorides and contains a free [Au(CN)2](-) unit. In the plane of the primary crystal growth direction, the birefringence values (Δn) of 0.37(2) (Cd(phenpy)[Au(CN)2]2), 0.50(3) (In(phenpy)(Cl)2[Au(CN)2]·0.5H2O), 0.56(3) and 0.59(6) (M(phenpy)(H2O)[Au(CN)2]2·2H2O M = Cd and Zn, respectively) were determined. β, a structural parameter defined by phenpy units rotated in the A-C plane relative to the light propagation (C) direction, was found to correlate to Δn magnitudes. The addition of a carbon-carbon double bond to terpy has increased the molecular polarizability anisotropy of the building block, and all structures have reduced deviation from planarity in comparison to terpy and terpy derivative structures, leading to these higher Δn values, which are among the highest reported for crystalline solids.

Crystal structure of a mixed-ligand dinuclear Ba-Zn complex with 2-meth-oxy-ethanol having tri-phenyl-acetate and chloride bridges.

The dinuclear barium-zinc complex, μ-chlorido-1:2κ(2) Cl:Cl-chlorido-2κCl-bis-(2-meth-oxy-ethanol-1κO)bis-(2-meth-oxy-ethanol-1κ(2) O,O')bis-(μ-tri-phenyl-acetato-1:2κ(2) O:O')bariumzinc, [BaZn(C20H15O2)2Cl2(C3H8O2)4], has been synthesized by the reaction of barium tri-phenyl-acetate, anhydrous zinc chloride and 2-meth-oxy-ethanol in the presence of toluene. The barium and zinc metal cations in the dinuclear complex are linked via one chloride anion and carboxyl-ate O atoms of the tri-phenyl-acetate ligands, giving a Ba⋯Zn separation of 3.9335 (11) Å. The irregular nine-coordinate BaO8Cl coordination centres comprise eight O-atom donors, six of them from 2-meth-oxy-ethanol ligands (four from two bidentate O,O'-chelate inter-actions and two from monodentate inter-actions), two from bridging tri-phenyl-acetate ligands and one from a bridging Cl donor. The distorted tetra-hedral coordination sphere of zinc comprises two O-atom donors from the tri-phenyl-acetate ligands and two Cl donors (one bridging and one terminal). In the crystal, O-H⋯Cl, O-H⋯O and C-H⋯Cl inter-molecular inter-actions form a layered structure, lying parallel to (001).

Crystal structure of bis-[μ-bis-(di-phenyl-phosphan-yl)methane-κ(2) P:P']-μ-chlorido-chlorido-1κCl-(1-phenyl-thio-urea-2κS)disilver aceto-nitrile hemisolvate.

In the dinuclear title complex, [Ag2Cl2(C7H8N2S)(C25H22P2)2]·0.5CH3CN, each AgI ion displays a distorted tetra­hedral coordination geometry with two P atoms from two bis­(di­phenyl­phosphan­yl)methane (dppm) ligands, one bridging chloride ion, one terminal chloride ion and one terminal S atom from the N,N′-phenyl­thio­urea (ptu) ligand. The dppm ligands and the bridging chloride ion force the two Ag atoms into close proximity, with a short Ag⋯Ag separation of 3.2064 (2) Å. In the crystal, complex mol­ecules are linked by N—H⋯Cl hydrogen bonds forming a dimer. The dimers are linked via weak C— H⋯Cl hydrogen bonds forming a two-dimensional supra­molecular architecture in the yz plane. In addition, an intra­molecular N—H⋯Cl hydrogen bond is observed.

Synthesis, characterization and molecular structures of copper(II) and nickel(II) complexes derived from diacetylmonooxime thiosemicarbazone and diacetylmonooxime S-benzyl dithiocarbazonate

The dinuclear Cu(II) and Ni(II) complexes, [{M(Oxsbz)}2], [{M(Oxtsc)}2] (M = Cu or Ni), [{Cu(HOxsbz)}2](NO3)2, and [{Cu(HOxsbz)Cl}2], as well as the mononuclear [Ni(Oxtsc)HIm] and [Ni(Oxtsc)HPyr], where H2Oxsbz and H2Oxtsc refer, respectively, to diacetylmonooxime S-benzyldithiocarbazonate and diacetylmonooxime thiosemicarbazone, have been prepared and characterized by IR, UV–vis and 1H NMR spectral measurements as well as ESI mass spectra. The magnetic properties of [{Cu(Oxsbz)}2], [{Cu(Oxtsc)}2], [{Cu(HOxsbz)}2](NO3)2, and [{Cu(HOxsbz)Cl}2] have also been studied. The single-crystal diffraction studies indicated that in [{Cu(HOsbz)Cl}2], each Cu(II) is in a distorted square pyramidal environment and the Cu(II) centers are connected by chloride bridges. In both [Ni(Oxtsc)HIm] and [Ni(Oxtsc)HPyr], HIm = imidazole and HPyr = pyrazole, Ni(II) is in a distorted square planar environment, bound to the Oxtsc dianion via deprotonated oxime nitrogen, imine nitrogen, and deprotonated thiol sulfur; the fourth coordination site is occupied by the heterocyclic nitrogen.

Phenylpyrazole‐Based Hypervalent Phosphorus Compounds: From Positional Isomerism to Stacking Interactions

AbstractThe lithium salt of 3,5‐dimethyl‐1‐phenyl‐1H‐pyrazole (PyrC6H4Li) reacts with (Et2N)2PCl to give the precursor [PyrC6H4P(NEt2)2] (2), which, after reaction with PCl3, affords PyrC6H4PCl2 (3) in 79 % yield. The phosphorus atom in 3 has four‐coordinate disphenoidal geometry with an axial arrangement of Cl atoms. The length of the hypervalent N–P bond in this compound [1.775(1) Å] is comparable to that of common single bonds. The structure of 3 is better described by canonical formulae containing charges on the N, P, and Cl atoms. The 1H NMR spectrum of 3 in CDCl3 shows five pairs of nonequivalent Me groups, which correspond to the positional isomers that exist in the equilibrium mixture. Compound 3 easily exchanges chlorine with methyl iodide to form the diiodo derivative 4 (PyrC6H4PI2) with nonequivalent P–I bonds. The reduction of 3 with aluminium foil or [GeCl2(diox)] gave cationic diphosphines [(PyrC6H4P)2(μ‐Cl)][AlCl4] (8) and [(PyrC6H4P)2(μ‐Cl)][GeCl3] (9), respectively, with a chloride bridge between the phosphorus atoms. Compounds 4, 8 and 9 show a disphenoidal arrangement around the hypervalent phosphorus atoms. The dichloro and diiodo derivatives 3 and 4 are destroyed on heating in pyridine to give diphosphines [(PyrC6H4PCl)2] (10) and [(PyrC6H4P)2(μ‐I)]+[I] (12), respectively, containing hypervalent (trivalent four‐coordinate) phosphorus. The crystal structure of 10 shows multiple C···C, C···Cl, H···H, and C···H short contacts between the adjacent molecules. Compound 3 exchanges chlorine for oxygen atoms on heating in dimethylformamide to give the dioxide PyrC6H4PO2 (13) with an N–PV distance [1.808(1) Å] even longer than that in 3.

Unexpected proline coordination in the copper chain polymer [Cu(μ-Cl)₂(μ-DL-proline-κ²O:O')]¹∞.

In catena-poly[copper(II)-di-μ-chlorido-μ-proline-κ(2)O:O'], [CuCl2(C5H9NO2)]n, two symmetry-independent metal cations adopt distorted octahedral coordination, typical for d(9) Jahn-Teller systems. Each chloride bridge is involved in both a short and a very long interaction with a Cu(II) centre. The centrosymmetric crystal structure contains homochiral chains of opposite handedness which extend along the shortest lattice parameter (i.e. a). The O:O'-bridging coordination mode of proline, although a common motif for such complexes in general, is remarkable for Cu(II); the vast majority of amino acid derivatives of this cation are characterized by N,O-chelation.

Synthesis, structure, and properties of rare earth chloride complexes {[Ap´Y(THF)](μ2-Cl)2(μ3-Cl)Li(THF)}2, {[Ap9MeLn(THF)](μ2-Cl)3Li(THF)2}2 (Ln = Y, Nd, Sm), and {[Ap*Ln(THF)](μ2-Cl)3Li(THF)2}2 (Ln = Nd, Sm) containing amidopyridinate ligands

New amidopyridinate chloride complexes {[Ap´Y(THF)](μ2-Cl)2(μ3-Cl)Li(THF)}2, {[Ap9MeLn(THF)](μ2-Cl)3Li(THF)2}2 (Ln = Y, Nd, Sm), and {[Ap*Ln(THF)](μ2-Cl)3Li(THF)2}2 (Ln = Nd, Sm) were synthesized by the exchange reactions of lithium amidopyridinates ApLi(OEt2) (Ap´ is N-(2,6-diisopropylphenyl)-6-(2,6-dimethylphenyl)pyridine-2-amine; Ap9Me is N-mesityl-6-(2,4,6-triisopropylphenyl)pyridine-2-amine; Ap* is N-(2,6-diisopropylphenyl)-6-(2,4,6-triisopropylphenyl)pyridine-2-amine) with anhydrous rare earth chlorides. The X-ray diffraction study showed that the amidopyridinate chloride derivatives are heterobimetallic ate-complexes, in which two rare earth metal atoms are linked by bridging chloride ligands and bridging Cl—Li—Cl groups. The three-component system {[Ap*Nd(THF)](μ2-Cl)3Li(THF)2}2—AlBui 3—[Ph3C][B(C6F5)4] (1: 10: 1 molar ratio) catalyzes the isoprene polymerization.

Coordination of metronidazole to Cu(II): Structural characterization of a mononuclear square-planar compound

The reaction between metronidazole [1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole, MET] and CuCl2⋅2H2O in methanol solution has allowed isolation of blue crystals of composition Cu(MET)2Cl2⋅MeOH. These crystals have been shown by X-ray diffraction to consist of mononuclear square-planar trans-Cu(MET)2Cl2 molecules in which the metronidazole ligands are trans to each other, as are the Cl ligands. The structure of this compound is very different from other compounds that have been obtained from the reaction between CuCl2⋅2H2O and metronidazole, namely [Cu(MET)2(μ-Cl)Cl]2 and [Cu(MET)2(μ-Cl)(OH2)]2[Cl]2, which are dimers featuring bridging chloride ligands.

Ferromagnetic copper(II)–copper(II) interaction in a single chlorido and dicyanamido bridged mixed–valence copper(I/II) 2-D polymer generated by in situ partial reduction of copper(II)

A mixed-valence 2-D Cu(I/II) complex, [{Cu(II)(dmen)(μ-Cl)(μ1,5-dca)}{Cu(I)(μ1,5-dca)}]n (1) (dmen = N,N-dimethylethylenediamine, dca = dicyanamide = [N(CN)2]−), has been synthesized by in situ partial reduction of Cu(II) to Cu(I) using benzoin (2-hydroxy-1,2-di(phenyl)ethanone) as reductant. Complex 1 was characterized by spectroscopic techniques, single crystal X-ray diffraction, and low temperature magnetic measurements. Structural investigation reveals that 1 represents a mixed-valence 2-D coordination polymer formed by parallel 1-D [Cu(II)(dmen)(Cl)Cu(I)(μ1,5-dca)2]n chains running along the b axis, where chloride bridges Cu(II) ions of adjacent polymers through long connections (2.8401(1) Å) to form a 2-D network. The metal centers have two different geometrical environments (distorted square pyramidal and distorted trigonal planar geometries for Cu(II) and Cu(I), respectively). The Cu(II) ions in [Cu(II)(dmen)(μ-Cl)(dca)]n are interconnected through single chloride bridges while within the [Cu(I)(μ1,5-dca)]n units, the dca connects adjacent Cu(I) ions through μ1,5-dca bridges. Magnetic susceptibility measurements reveal weak ferromagnetic interactions (J = +0.3 cm−1) within the chlorido-bridged Cu(II) regular chain present in 1. Simultaneous presence of μ1,5-dca and single chlorido bridges with ferromagnetic coupling is believed to be unique in mixed-valence Cu(I)/Cu(II) complexes.

Redox inactive metal ion triggered N-dealkylation by an iron catalyst with dioxygen activation: a lesson from lipoxygenases.

Utilization of dioxygen as the terminal oxidant at ambient temperature is always a challenge in redox chemistry, because it is hard to oxidize a stable redox metal ion like iron(III) to its high oxidation state to initialize the catalytic cycle. Inspired by the dioxygenation and co-oxidase activity of lipoxygenases, herein, we introduce an alternative protocol to activate the sluggish iron(III) species with non-redox metal ions, which can promote its oxidizing power to facilitate substrate oxidation with dioxygen, thus initializing the catalytic cycle. In oxidations of N,N-dimethylaniline and its analogues, adding Zn(OTf)2 to the [Fe(TPA)Cl2]Cl catalyst can trigger the amine oxidation with dioxygen, whereas [Fe(TPA)Cl2]Cl alone is very sluggish. In stoichiometric oxidations, it has also been confirmed that the presence of Zn(OTf)2 can apparently improve the electron transfer capability of the [Fe(TPA)Cl2]Cl complex. Experiments using different types of substrates as trapping reagents disclosed that the iron(IV) species does not occur in the catalytic cycle, suggesting that oxidation of amines is initialized by electron transfer rather than hydrogen abstraction. Combined experiments from UV-Vis, high resolution mass spectrometry, electrochemistry, EPR and oxidation kinetics support that the improved electron transfer ability of iron(III) species originates from its interaction with added Lewis acids like Zn(2+) through a plausible chloride or OTf(-) bridge, which has promoted the redox potential of iron(III) species. The amine oxidation mechanism was also discussed based on the available data, which resembles the co-oxidase activity of lipoxygenases in oxidative dealkylation of xenobiotic metabolisms where an external electron donor is not essential for dioxygen activation.

Cobalt(II), nickel(II), and copper(II) complexes of 14-membered hexaazamacrocycles: synthesis and characterization

Cobalt(II), nickel(II), and copper(II) complexes containing 5,12-di(4-bromophenyl)-7,14-dimethyl-1,2,4,8,9,11-hexaazacyclotetradeca-7,14-diene-3,10-dione (H2L1) and 5,12-diphenyl-7,14-dimethyl-1,2,4,8,9,11-hexaazacyclotetradeca-7,14-diene-3,10-dione (H2L2) have been synthesized. All complexes were characterized by elemental analysis, MALDI TOF-MS spectrometry, and electronic absorption spectroscopy. The crystal structures of two compounds, [Cu2(H2L1)Cl4]n and [NiL2], were determined by X-ray powder diffraction. In the polymeric [Cu2(H2L1)Cl4]n, the Cu2Cl4 units and H2L1 molecules are situated on inversion centers. Each Cu(II) has a distorted trigonal-bipyramidal coordination environment formed by N and O from H2L1 [Cu–N 2.340(14) Å, Cu–O 1.952(11) Å], two bridging chlorides [Cu–Cl 2.332(5), 2.279(5) Å] and one terminal chloride [Cu–Cl 2.320(6) Å]. In the [NiL2] complex, the Ni(II) situated on inversion center has a distorted square-planar coordination environment formed by four nitrogens from L2 [Ni–N 1.860(11), 1.900(11) Å].

Synthesis, crystal structure, and electronic structure of a copper(II) chloride complex with 9(E)-phenanthrene-9,10-dione[(1Z)-3,3-dimethyl-3,4-dihydroisoquinolin-1(2H)-ylidene]hydrazone [Cu2(L-H)2Cl2

The [Cu2(L-H)2Cl2] compound (I) has been obtained by the reaction of 9(E)-phenanthrene-9,10-dione[(1Z)-3,3-dimethyl-3,4-dihydroisoquinolin-1(2H)-ylidene]hydrazone with copper(II) chloride. The crystal and molecular structure of I has been determined by X-ray crystallography. The L-H anion acts as a tridentate chelating ligand and is coordinated to the Cu atom through the O(1) atoms of the phenanthrenequinone moiety, the N(1) atom of the dihydroisoquinoline moiety, and the N(3) atom of the azo group to form two five-membered chelate rings. Complex I is a dimer with a double chloride bridge. The coordination polyhedron of the Cu atom is completed to a distorted pyramid by two chlorine atoms. The molecular and electronic structures of the L molecule and the model [Cu(L-H)Cl] complex have been determined by the density functional theory method. Spectroscopic characteristics of I have been determined.

Bridging phenyl ligands. Unsaturated mercury-triosmium carbonyl cluster complexes containing bridging phenyl ligands

The gold phosphine group in the complex Os3(CO)10(μ-η1-Ph)(μ-AuPPh3), 1 can be replaced by mercury halide groups by reactions with mercury halides. The reaction of 1 with HgI2 yielded the new compound [Os3(CO)10(μ-η1-Ph)(μ-HgI)]4, 2 in 19% yield. The reaction of 1 with HgCl2 yielded the new compound Os4(CO)13(μ-η1-Ph)(μ-Cl)3, 3 in 18% yield. When heated to reflux in cyclohexane solvent, compound 2 was converted into the compound [Os3(CO)9(μ3-C6H4)(μ-H)(μ3-Hg)]2Os(CO)4, 4 in 11% yield. All new compounds were characterized by single-crystal X-ray diffraction analyses. Compound 2 is a tetramer of the unit “Os3(CO)10(μ-η1-Ph)(μ-HgI)” that is held together by a cubane-like Hg4I4 core having D2 symmetry. Each triosmium cluster is formally electronically unsaturated and contains one edge-bridging phenyl ligand. Compound 3 contains a Os3(CO)10(μ-η1-Ph)(μ-Hg) cluster, but in this case the Hg atom bridges to an additional Os(CO)3 group via three bridging chloride ligands. Compound 4 contains two Os3(CO)9(μ3-C6H4)(μ-H)(μ3-Hg) clusters that are linked by a bridging Os(CO)4 group. Each Os3 cluster in 4 contains a triply bridging C6H4 benzyne ligand and one bridging hydrido ligand.

Supramolecular architecture of PGM-arene-amino acid complexes

Arene complexes of Platinum Group Metals (PGM) show various biological effects and there are several promising anticancer drug candidates in this class of compounds. Synergism of biological activity is foreseen when anciliary ligands such as amino acid derivatives or other bioligands are incorporated into the complexes. A series of Ru(II), Os(II), Rh(III) and Ir(III) complexes were studied and interesting kinetic/equilibrium/structural properties could be revealed [1-3]. According to our latest results presented here the N-acetylcysteine complex of the [(η6-Ar)Ru]2+ core (Ar = p-cymene) is a dimer showing bridging thiolate and chloride cordination (Figure 1, a) while a monomeric complex was formed with [S, COO–,NH2] coordination for S-methyl-cysteine when the counter ion is nitrate (Figure 1, b). With methionine an analogous compound was formed (Figure 1, c). Supramolecular analysis of the complexes indicates competing steric/Coulombic/van der Waals interactions and hydrogen bonds. X-ray diffraction and spectroscopic analysis revealed the structure of the complexes both in solution and in the solid state and also support kinetic/equilibrium findings. Acknowledgement: The research was supported by the EU and co-financed by the European Social Fund under the project ENVIKUT (TÁMOP-4.2.2.A-11/1/KONV-2012-0043). The work was supported by the Hungarian Scientific Research Fund (OTKA K76142), too. P.B. thanks members of the EU COST Action CM1105 for motivating discussions. G.B. acknowledges the support of the Bolyai János Scholarship of the Hungarian Academy of Sciences.

Synthesis, characterization, interactions with DNA and bovine serum albumin (BSA), and antibacterial activity of cyclometalated iridium(III) complexes containing dithiocarbamate derivatives

Three mononuclear cyclometalated iridium(III) complexes having dithiocarbamate ligands, [IrIII(2-C6H4py)2(L)] (where 2-C6H4py = 2-phenylpyridine; and L1H = 4-MePipzcdtH, L2H = MorphcdtH, and L3H = 4-BzPipercdtH for 1, 2, and 3, respectively), were synthesized from [Ir(2-C6H4py)2Cl]2·1/4CH2Cl2 by displacing the two bridging chlorides with one dithiocarbamate ligand. The complexes were characterized using physicochemical and spectroscopic tools along with structural analysis of [Ir(2-C6H4py)2(L2)] (2) by single crystal X-ray diffraction. Structural analysis of 2 showed a distorted octahedron in which the nitrogen donor of one 2-phenylpyridine and the carbon donor of another 2-phenylpyridine are in axial positions, trans to one another. Electrochemical analysis by cyclic voltammetry showed the irreversible two-electron equivalent reduction voltammograms of 1, 2, and 3 attributable to Ir(III) to Ir(I). Electronic characterizations of these complexes are consistent with significant delocalization of the sulfur electron density onto the empty metal d-orbital. The intercalative interaction of the complexes with calf thymus DNA was evaluated using absorption, fluorescence quenching, and viscosity measurements. The binding affinities of these complexes with bovine serum albumin were estimated in terms of quenching constants using the Stern–Volmer equation. Study of antibacterial activities of the complexes by agar disk diffusion against some species of pathogenic bacteria was also performed.

Copper(II)-catalyzed disulfide scission--stepwise aerobic oxidative cleavage to sulfinate and sulfonate and reductive anaerobic cleavage to thiols.

The Cu(II)-catalyzed oxidative and reductive cleavage of the disulfide bond of N-(2-(2-(2-picolinamido)phenyl)disulfanyl)phenyl)picolinamide, L, is reported for the first time. Aerobic oxidation with Cu(II) gives complete oxidation of S-S bond to sulfonates, whereas Ag(I) gives only partial oxidation up to sulfinates, in the absence of any other oxidizing agent, in tetrahydrofuran/water solution. The in situ generated sulfonate product forms a thermally stable, two-dimensional H-bonded polymeric complex with Cu(II) ions in two polymorphic forms. L in the presence of Cu(II), in an inert atmosphere, results in a reductive cleavage of the disulfide bond and an in situ formation of a new C-S bond. The latter forms a unique tetranuclear complex with Cu(II) employing deprotonated amide groups and bridging thiol and chloride atoms. The disulfide precursor and the products were characterized by X-ray crystallography and spectroscopic techniques.

Hexa-μ2-chlorido-μ4-oxido-tetra-kis[(morpholine-κN)copper(II)] methanol disolvate.

In the title solvate, [Cu4(μ2-Cl)6(μ4-O)(C4H9NO)4]·2CH3OH, each Cu2+ ion in the tetra­nuclear complex has a trigonal–bipyramidal coordination arising from three bridging chloride ions in equatorial positions and the central μ4-O2− ion and morpholine N atom in axial positions. The morpholine rings adopt chair conformations, with the N—Cu bonds in equatorial orientations. In the crystal, the components are linked by N—H⋯O and O—H⋯O and O—H⋯Cl hydrogen bonds, which generate a three-dimensional network. One methanol mol­ecule is disordered over two sets of sites in a 0.642 (9):0.358 (9) ratio.

Di-μ-chlorido-bis-(chlorido-{N'-[phen-yl(pyridin-2-yl-κN)methyl-idene]pyridine-2-carbohydrazide-κ(2) N',O}cadmium).

The title compound, [Cd2Cl4(C18H14N4O)2], was obtained from the reaction of Cd(NO3)2·4H2O with 2-phenyl­pyridine­keton picolinoyl hydrazone and sodium chloride. Each Cd2+ cation is coordinated by two N atoms and one O atom of the tridentate ligand and three chloride anions, forming a distorted CdNOCl3 octahedron. Each pair of adjacent metal cations is linked by two bridging chloride ligands, resulting in a dinuclear complex unit. The mol­ecular conformation is stabilized by intra­molecular N—H⋯N and C—H⋯O hydrogen bonds. In the crystal, mol­ecules are linked by nonclassical C—H⋯O and C—H⋯Cl hydrogen bonds into a three-dimensional network. In addition, π–π stacking inter­actions [centroid–centroid distances = 3.777 (2) and 3.631 (2) Å] contribute to the stabilization of the crystal packing.

Reversible switching of the coordination modes of a pyridine-functionalized quinonoid zwitterion; its di- and tetranuclear palladium complexes.

The coordination chemistry of a new functional quinonoid zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(μ-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(μ-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in loss of one of the two dmba ligands and formation of an unusual tetranuclear Pd(II) complex, [{Pd(dmba)}(μ-L)Pd]2(OTf)2 (5), in which two dinuclear entities have dimerized, one pyridine donor group from each dimer forming a bridge with the other dinuclear entity. This results in a N2, O2, NPy, NPy hexadentate behavior for the ligand L. Complexes 3 and 4 constitute an unprecedented reversible, switchable system where deprotonation or protonation promotes the reversible migration of the [Pd(dmba)](+) moieties, from the NPy sites in 3, to the N,O donor sites of the quinonoid core in 4, respectively. This switch modifies the extent of π-delocalization involving the potentially antiaromatic quinonoid moiety and is accompanied by a significant color change, from red in 3 to green in 4. The presence of uncoordinated pyridine donor groups in 4 allowed the use of this complex for the preparation of the neutral tetranuclear complex [{Pd(dmba)}2(μ-L){PdCl(dmba)}2] (6) in which 4 acts as a NPy,NPy-bidentate metalloligand toward two PdCl(dmba) moieties. Halide abstraction from 6 afforded the monocationic, tetranuclear complex [{Pd(dmba)}2(μ-L){Pd(dmba)}2(μ-Cl)]PF6 (7) in which the two Pd(dmba) moieties are connected by ligand L and a bridging chloride. By Cl/PF6 anion metathesis, it was possible to switch quantitatively from complex 6 to 7 and vice versa. All new compounds were unambiguously characterized by IR, NMR, and mass spectroscopy. Single-crystal X-ray diffraction is also available for molecules 2-5 and 7.

1,2-Bis(di-cyclo-hexyl-phosphan-yl)-1,2-dicarba-closo-dodeca-borane-2κ(2) P,P']di-μ-chlorido-1:2κ(4) Cl:Cl-di-chlorido-1κ(2) Cl-dimercury(II).

The title compound, [Hg2Cl4(C26H54B10P2)], was synthesized by the reaction of 1,2-bis­(di­cyclo­hexyl­phosphan­yl)-1,2-dicarba-closo-dodeca­borane with HgCl2. Both HgII atoms show a distorted tetra­hedral coordination geometry, provided by the two bridging chloride anions and the P atoms of the diphosphanyl ligand for one metal atom, and by two bridging and two terminal chloride anions for the other. The five-membered HgP2C2 chelate ring assumes an envelope conformation, with the HgII atom displaced by 0.1650 (5) Å from the mean plane of the other four atoms (r.m.s. deviation = 0.002 Å). In the crystal, B—H⋯Cl interactions link the molecules, forming a supramolecular chain along the a-axis direction.