Neutral Tetranuclear Complex Research Articles

Tri- and Tetranuclear Metal-String Complexes with Metallophilic d10 -d10 Interactions.

The reaction of 2,6‐F2C6H3SiMe3 with Ph2PLi provided 2,6‐(Ph2P)2C6H3SiMe3 (1), which can be regarded as precursor for the novel anionic tridentate ligand [2,6‐(Ph2P)2C6H3]− (PCP)−. The reaction of 1 with [AuCl(tht)] (tht=tetrahydrothiophene) afforded 2,6‐(Ph2PAuCl)2C6H3SiMe3 (2). The subsequent reaction of 2 with CsF proceeded with elimination of Me3SiF and yielded the neutral tetranuclear complex linear‐[Au4Cl2(PCP)2] (3) comprising a string‐like arrangement of four Au atoms. Upon chloride abstraction from 3 with NaBArF 4 (ArF=3,5‐(CF3)2C6H3) in the presence of tht, the formation of the dicationic tetranuclear complex linear‐[Au4(PCP)2(tht)2](BArF 4)2 (4) was observed, in which the string‐like structural motif is retained. Irradiation of 4 with UV light triggered a facile rearrangement in solution giving rise to the dicationic tetranuclear complex cyclo‐[Au4(PCP)2(tht)2](BArF 4) (5), which comprises a rhomboidal motif of four Au atoms. In 3–5, the Au atoms are associated by a number of significant aurophilic interactions. The atom‐economic and selective reaction of 3 with HgCl2 yielded the neutral trinuclear bimetallic complex [HgAu2Cl3(PCP)] (6) comprising significant metallophilic interactions between the Au and Hg atoms. Therefore, 6 may be also regarded as a metallopincer complex [ClHg(AuCAu)] between HgII and the anionic tridentate ligand [2,6‐(Ph2PAuCl)2C6H3]− (AuCAu)− containing a central carbanionic binding site and two “gold‐arms” contributing pincer‐type chelation trough metallophilic interactions. Compounds 1–6 were characterized experimentally by multinuclear NMR spectroscopy and X‐ray crystallography and computationally using a set of real‐space bond indicators (RSBIs) derived from electron density (ED) methods including Atoms In Molecules (AIM), the Electron Localizability Indicator (ELI‐D) as well as the Non‐Covalent Interaction (NCI) Index.

Silver(I)‐Based Complexes Used as High‐Performance Photocatalysts for the Degradation of Organic Dyes in Water

Coordination compounds have been used as efficient photocatalysts for the degradation of pollutive organic dyes due to their semiconductive nature and diverse structures that may be adjusted by the central metals and ligands. Herein we prepared N′,N′‐2,2‐tetrakis(diphenylphosphanylmethyl)thiocarbohydrazide (tpptch) and utilized it to react with AgX (X = Br, I, CN) in different solvent systems. These reactions afforded two dicationic tetranuclear complexes {[Ag4X2(tpptch)2]X2 (1: X = Br; 2: X = I)}, one 1D coordination polymer [Ag2I2(tpptch)]n (3) and one neutral tetranuclear complex [Ag4(CN)2(dptpptch)2] (4, dptpptch is the anion of deprotonated tpptch after an enolization). In 1–4, the S atom of the C=S group binds at one AgI atom in 1 or 2, or remains uncoordinated in 3, or connects with two AgI atoms after transforming into the C–S– end in 4. The catalytic activities of these compounds toward the photodegradation of nine organic dyes under UV irradiation were examined, among which 3 showed the best performance. Their anodic photocurrent responses and HOMO–LUMO energy gaps derived from density functional theory (DFT) calculations correlated well with the photocatalytic activities. The different bindings of the S end of tpptch and dptpptch ligands with AgI centers in 2–4 may be contributed to the discrepancy in their catalytic activities. The results provide a ready route to design and prepare highly stable and efficient photocatalysts for treating dye‐polluted water.

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.

Cyclo-Tetrakis(μ2-D-penicillaminato-κ4N,S:O,S)tetrapalladium(II) 9.75-hydrate

The asymmetric unit of the title compound, [Pd4(C5H9NO2S)4]·9.75H2O, contains two neutral tetranuclear complex molecules with similar conformations and 19.5 solvent water mol­ecules. Of the 21 independent water molecules, three exhibit an occupancy of one-half. In each tetranuclear complex molecule, the four PdII atoms have a square-planar coordination environment and are spanned by four d-penicillaminate ligands in a κ4 N,S:S,O coordination mode, forming an eight-membered Pd4S4 metallacycle. In the crystal, two tetra­nuclear mol­ecules are connected to each other through eight N—H⋯O hydrogen bonds between amine and carboxyl­ate groups, constructing a cylindrical dimer. The dimers are further hydrogen-bonded with the solvent water mol­ecules, completing a three-dimensional network.

Zinc(II), Copper(II), and Nickel(II) Complexes of Bis(tripodal) Diamide Ligands – Reversible Switching of the Amide Coordination Mode upon Deprotonation

AbstractA series of dinuclear Zn(II), Cu(II) and Ni(II) complexes of two new bis‐tripodal ligands with aromatic (H2‐4a) and aliphatic (H2‐4b) diamide spacers has been synthesized and structurally characterized. Each of the two tripodal entities of the neutral dinucleating ligands coordinates to one metal ion via three amine functions and a carbonyl oxygen atom of the amide groups. Either trifluoroacetate counterions or solvent molecules complete the trigonal‐bipyramidal (Zn, 5a), square‐pyramidal (Cu, 6a and 6b), and octahedral (Ni, 7a and 7b) coordination environment at the metal centers. Complexes 5a, 6a, and 7a with the phenylene‐bridged diamide ligand are readily deprotonated by potassium tert‐butoxide effecting a rearrangement of the dinuclear complexes. In the resulting zinc and copper complexes 8 and 9, one of the metal centers is coordinated by three amine functions of a tripodal subunit and the two amidate nitrogen atoms of the deprotonated ligand 4a2– while the coordination geometry of the second metal atom remains unchanged. The analogous nickel compound crystallizes as neutral tetranuclear complex (10)2 with intermolecular coordination of two amide carbonyl oxygen atoms to the nickel atoms of an adjacent dinuclear complex. The resulting coordination mode with binding of all four donor functions of the diamide spacer to three discrete metal centers is to date unprecedented for ortho‐phenylene‐bridged acetamides. The rearrangement upon deprotonation has been shown to be fully reversible and the starting complexes can be retrieved upon protonation of the two amidate functions. Synthesis of the trinuclear zinc complex 11 with coordination of the two amidate nitrogen atoms to a third metal center was achieved via deprotonation of (H6‐4a)(CF3CO2)4 by three equivalents of diethylzinc. In protic solvents 11 rapidly rearranges to give the entropically favored dinuclear complex 8 with elimination of one equivalent of zinc trifluoroacetate.

Synthesis, structures and magnetic properties of four new oxamidato-bridged heterobimetallic complexes

Four new heterobimetallic coordination polymers, namely, {[Cu(aeoe)M(H 2O) 3 · 2H 2O] 2} n (M = Mn(II) ( 1), Co(II) ( 2), Ni(II) ( 3)) and [Cu(aeoe)Ni(H 2O) 3] 2 ( 4) (H 4aeoe = N′-(2-aminoterephthalic acid)- N′′-(ethylenediamine)oxamidato) have been synthesized and characterized structurally. Complexes 1– 3 are allomerism and feature 1-D ladder-like chain structure constructed from neutral tetranuclear complex units through the syn– anti carboxylate bridges, whereas complex 4 is a cyclic neutral tetranuclear complex unit. Their magnetic properties are also investigated based on their structures.

Tetra‐ and Decanuclear Iron(II) Complexes of Thiacalixarene Macrocycles: Synthesis, Structure, Mössbauer Spectroscopy and Magnetic Properties

AbstractTwo iron(II) complexes, namely [Fe4(L)2]·H2O (1) and [Fe10(L)4Cl4]·2H2O (2), have been synthesised under solvothermal conditions by treating p‐tert‐butylthiacalix[4]arene (LH4) with FeCl2 in methanol. Compound 1 crystallises in the orthorhombic system (space group Immm) with the unit‐cell parameters a = 17.8308(4), b = 19.1372(3), c = 28.8391(6) Å and V = 9840.8(3) Å3 (Z = 2). Compound 2 crystallises in the triclinic system (space group P$\bar {1}$) with the unit‐cell parameters a = 13.8036(4), b = 18.8373(4), c = 20.1978(6) Å, α = 65.772(2)°, β = 74.120(1)°, γ = 71.922(1)° and V = 4487.6(2) Å3 (Z = 1). Compound 1 is a neutral tetranuclear complex and is best described as an iron(II) square sandwiched between two thiacalixarene macrocycles. Each iron centre is six‐coordinate in a trigonal‐prismatic geometry made up of four phenoxy oxygen atoms plus two sulfur atoms. Compound 2 is a neutral centrosymmetric decanuclear complex and may be viewed as a dimer of double chloro‐bridged pentanuclear complexes. Mössbauer spectra of compounds 1 and 2 have been recorded at different temperatures between 80 and 298 K. Each sub‐spectrum can be characterised by a quadrupolar doublet corresponding to different iron environments where all iron ions are in high‐spin state (S = 2). The hyperfine parameters (quadrupole splitting, isomer shift and line width) as well as the Mössbauer spectra area‐ratios are in good agreement with the crystallographic data. The two compounds exhibit magnetic behaviours indicating that antiferromagnetic interactions occur between the iron(II) centres. The simulation of the magnetic susceptibility was done in the case of compound 1 with a single exchange coupling constant (J = –4 cm–1 and g = 2.02) between the iron(II) ions[H = –J(S1S2 + S2S3 + S3S4 + S1S4)]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Heteronuclear rhodium, palladium, platinum, and gold organoimido complexes from dinuclear organoamido rhodium precursors.

Treatment of the organoamido complexes [Rh(2)(mu-4-HNC(6)H(4)Me)(2)(L(2))(2)] (L(2) = 1,5-cyclooctadiene (cod), L = CO) with nBuLi gave solutions of the organoimido species [Li(2)Rh(2)(mu-4-NC(6)H(4)Me)(2)(L(2))(2)]. Further reaction of [Li(2)Rh(2)(mu-4-NC(6)H(4)Me)(2)(cod)(2)] with [Rh(2)(mu-Cl)(2)(cod)(2)] afforded the neutral tetranuclear complex [Rh(4)(mu-4-NC(6)H(4)Me)(2)(cod)(4)] (2), which rationalizes the direct syntheses of 2 from [Rh(2)(mu-Cl)(2)(cod)(2)] and Li(2)NC(6)H(4)Me. Reactions of [Li(2)Rh(2)(mu-4-NC(6)H(4)Me)(2)(CO)(4)] with chloro complexes such as [Rh(2)(mu-Cl)(2)(CO)(4)], [MCl(2)(cod)] (M = Pd, Pt), and [Ru(2)(mu-Cl)(2)Cl(2)(p-cymene)(2)] afforded the homo- and heterotrinuclear complexes PPN[Rh(3)(mu-4-NC(6)H(4)Me)(2)(CO)(6)] (5; PPN=bis(triphenylphosphine)iminium), [(CO)(4)Rh(2)(mu-4-NC(6)H(4)Me)(2)M(cod)] (M = Pd (6), Pt(7)) and [(CO)(4)Rh(2)(mu-4-NC(6)H(4)Me)(2)Ru(p-cymene)] (8), while the reaction with [AuCl(PPh(3))] gave the tetranuclear compound [(CO)(4)Rh(2)(mu--4-NC(6)H(4)Me)(2)[Au(PPh(3))](2)] (9). The structures of complexes 6, 8, and 9 were determined by X-ray diffraction studies. The anion of 5 reacts with [AuCl(PPh(3))] to give the butterfly cluster [[Rh(3)(mu-4-NC(6)H(4)Me)(2)(CO)(6)]Au(PPh(3))] (10), in which the Au atom is bonded to two rhodium atoms. Reaction of the anion of 5 with [Rh(cod)(NCMe)(2)](BF(4)) gave the tetranuclear complex [Rh(4)(mu-4-NC(6)H(4)Me)(2)(CO)(6)(cod)] (11) in which the Rh(cod) fragment is pi-bonded to one of the arene rings, while the reaction of the anion of 5 with [PdCl(2)(cod)] afforded the heterotrinuclear complex 6 through a metal exchange process.

The synthesis and structure of a neutral tetranuclear zinc(II) complex [Zn4(L)4] [LH2 = N,N-bis(2-mercaptoethyl)benzylamine

The reaction of benzylamine with ethylene sulfide yields the monoamine–dithiol N,N-bis(2-mercaptoethyl)benzylamine, LH2. Reaction of Na2L with Zn(BF4)2 affords the neutral tetranuclear complex [Zn4L4], which shows an unusual Zn4S4 metallacyclic structure.

Hydrogen Bonding and Isomerism Arising from the Coordination Modes of Bridging Benzimidazole-2-thiolate Ligands in Tetranuclear Rhodium Complexes

Reaction of the dinuclear complex [Rh(2)(&mgr;-HBzimt)(2)(cod)(2)] with [Rh(2)(&mgr;-Cl)(2)(cod)(2)] (cod = 1,5-cyclooctadiene) gives the neutral tetranuclear complex [Rh(4)(&mgr;-HBzimt)(2)Cl(2)(cod)(4)] (2) in dichloromethane and the trinuclear cationic complex [Rh(3)(&mgr;-HBzimt)(2)(cod)(3)]Cl (3) in methanol, respectively. The ionization ability of the solvent seems to be the driving force to give 3, while the ability to coordinate a further RhCl(cod) fragment leads to 2 in poorer ionizing media. The complexes [M(4)(&mgr;-HBzimt)(2)Cl(2)(diolefin)(4)] (M = Rh, diolefin = tetrafluorobenzobarrelene (tfbb) (5); M = Ir, diolefin = cod (6)), formally analogous to 2, were isolated from the reactions of the appropriate complexes [MCl(H(2)Bzimt)(diolefin)] and [M(acac)(diolefin)] in acetone. A X-ray diffraction study on 2 shows the HBzimt(-) ligands to bridge two rhodium atoms through the sulfurs, forming a basic four-membered Rh(2)(&mgr;-(1:2kappaS)-HBzimt)(2) ring along with two RhCl(cod) moieties bonded to the nitrogen atoms. Two intramolecular hydrogen bonds between the chloro ligands and the acidic NH protons should stabilize the syn-endo disposition of the thiolate type bridging ligands. Replacement of the olefin in 2 by carbon monoxide gives [Rh(4)(&mgr;-HBzimt)(2)Cl(2)(cod)(CO)(6)] and [Rh(4)(&mgr;-HBzimt)(2)Cl(2)(CO)(8)] (7) depending on the reaction conditions. The X-ray structure of 7 shows the HBzimt(-) ligands in a HT-Rh(2)(&mgr;-(1kappaN,2kappaS)-HBzimt)(2) disposition with two RhCl(CO)(2) fragments coordinated to the sulfur atoms. In addition, two tetranuclear units 7 are associated in a dimer through four intermolecular hydrogen bonds. This association occurs even in solution, where the two species are observed. The equilibrium constant for the dissociation fits a linear plot of ln K(eq) versus 1/T, which gives DeltaH = 43.3 kJ mol(-)(1) and DeltaS = 114.7 J K(-)(1) mol(-)(1). Deprotonation of 7 with [Rh(2)(&mgr;-OMe)(2)(cod)(2)] gives the hexanuclear complex [Rh(6)(&mgr;-Bzimt)(2)(&mgr;-Cl)(2)(cod)(2)(CO)(8)] (10). Complexes 7 and 10 show identical conformations of the eight-membered HT-Rh(2)(&mgr;-(1kappaN,2kappaS)-Bzimt)(2) metallacycle and identical configurations of the sulfur atoms.

Reactivity of (NBu4)[Pt(C6F5)2(acac)] toward Electrophilic Metal Centers: Metal−Metal vs Metal−Cγ(acac) Bond Formation. Crystal Structure of [PtAg(C6F5)2(acac)(CH2Cl2)]2, a Complex Containing a μ2-acac-O,O‘ Bridging Ligand and a Coordinated Dichloromethane

The reaction between (NBu4)[Pt(C6F5)2(acac)] and AgClO4 (1:1 molar ratio) in CH2Cl2 at room temperature gives the neutral tetranuclear complex [PtAg(C6F5)2(acac)]2 (1) in a good yield. The structure, which has been determined by single-crystal X-ray diffraction methods, shows two anionic fragments [Pt(C6F5)2(acac)]- linked by two Ag+ atoms, each silver center being bonded to a Pt atom of one fragment and to an oxygen atom of the acac ligand of the other fragment. Noteworthy structural features are the O-acac coordination of the silver atom (instead of the more usual Cγ coordination) and the unexpected presence of a dichloromethane molecule coordinated to the silver center. The reaction of 1 with tht (tht = SC4H8, tetrahydrothiophene) or PPh3 gives the dinuclear complexes [PtAg(C6F5)2(acac)(L)] (L = tht (2), PPh3 (3)) by cleavage of the O−Ag bond; alternatively, complexes 2 and 3 can be one-pot synthesized by reaction of (NBu4)[Pt(C6F5)2(acac)] and O3ClOAgL (L = tht, PPh3). Their structural characterizatio...