Dibromo Complex Research Articles

Triazine-based mononuclear copper(ii) cis-dichloro and dibromo complexes as functional biomimetic model systems for phenoxazinone synthase and catecholase activities

Two new mononuclear Cu(ii) complexes were synthesized and thoroughly characterised. Molecular integrities were determined by SCXRD analysis and their catalytic activities and kinetics for the oxidation of o-aminophenol and catechol were examined.

Synthesis and reactivity in ethylene oligomerization by heteroscorpionate dibromonickel(II) complexes

Novel heteroscorpionate ligands were synthesized by a Peterson rearrangement during the reaction of 2-pyridinecarboxaldehyde (or 2-quinolinecarboxaldehyde) and 1,1-carbonyl-bis(pyrazoles). Nickel(II) dibromide reacts with these ligands in THF to give the heteroscorpionate dibromo complexes of general formula LNiBr2. Crystal structures of two full-sandwich heteroscorpionate Ni(II) complexes were determined. Preliminary studies of catalytic activity in ethylene oligomerization using different organoaluminum cocatalysts were performed. The addition of one equivalent of triphenylphosphine resulted in increased catalytic activity for most examples. The catalyst system of (2-[bis(3,5-dimethylpyrazol-1-yl)methyl]pyridine nickel(II) dibromide/Et2AlCl/PPh3 dimerized ethylene with an activity of 650g oligomer mol−1Nih−1 while the share of 1-butene in the mixture has reached 75%. Tris(3,5-dimethylpyrazol-1-yl)methyl nickel(II) dibromide, activated by Et2AlCl/PPh3 produced isobutylene (75% of the butene fraction).

Nickel Complexes with Two Types of Noninnocent Ligands: α-Diimine and Phenazine

The α-diimine nickel dibromo complex LNiBr2 (L = [(2,6-iPr2C6H3)NC(Me)]2) reacts with various amounts of potassium metal and phenazine (Phz) to afford the complexes [LNi(η4-C4-Phz)] (1) and [K(DME)]2[(LNi)2(μ-η1:η1-N,N-Phz)] (2), in which the Phz molecule adopts significantly different coordination modes with different oxidation states of Phz, Ni, and L.

Hydrogen-bonded 1D nanotubes and 2D layers of group 12 metal complexes with a pyridylurea ligand

A series of group 12 metal complexes, [ZnCl2L2]·H2O (1), [ZnBr2L2]·0.75EtOH (2a), [ZnBr2L2]·0.8H2O (2b), [ZnI2L2] (3), [HgCl2L2] (4), [HgBr2L2] (5), and [HgI2L] (6), have been synthesized from a naphthyl-substituted pyridylurea ligand N-(1-naphthyl)-N′-(3-pyridyl)urea (L) and zinc(II) or mercury(II) halides. In the zinc(II) dichloro complex, 1, the chloride ions participate not only in metal coordination but also in N–H⋯Cl hydrogen bonding with the urea NH groups, giving an overall layered structure. In contrast, the coordinated bromide and iodide anions in 2 and 3 are not involved in hydrogen bonding; instead, the urea groups undergo self-association to form nano-tubular structures with various pore sizes stacked by the semi-macrocyclic [ZnX2L2] synthons. Most interestingly, although different solvent molecules [EtOH (2a) and H2O (2b)] can be encapsulated in the nano-tubular zinc dibromo complexes, a competitive experiment conducted in the EtOH/H2O mixed solvents showed that the nanotube can selectively capture the EtOH molecule, as confirmed by X-ray single-crystal diffraction and solid-state fluorescence studies. With the tetrahedral mercury(II) ion, complexes 4 and 5 are isomorphous 2D sheet structures held by N–H⋯O hydrogen bonds and π–π stacking interactions. The 2D sheets are further linked by C–H⋯Cl/Br weak interactions into a hydrogen-bonded 3D framework. Notably, compound 6 contains an uncommon trigonal-planar HgII center and forms a 1D chain structure via the typical urea⋯urea hydrogen bonding and π–π stacking interactions of L, which further aggregates to a 2D parallelogram grid framework through C–H⋯I weak interactions. The solid-state fluorescent properties of L and the complexes 1–6 have also been investigated at room temperature.

Nickel complexes of a bis(benzimidazolin-2-ylidene)pyridine pincer ligand with four- and five-coordinate geometries

The four- and five-coordinate complexes [(CNC)NiX(2)] (X = Cl, Br, I), [(CNC)NiX]PF(6) (X = Cl, Br) and [(CNC)NiCl]Cl·H(2)O have been isolated, where CNC is the bis(N-butylbenzimidazolin-2-ylidene)-2,6-pyridine pincer ligand. A five-coordinate geometry is rare for this class of complex. Where amenable, the complexes have been structurally characterised by single crystal X-ray diffraction studies and in solution by NMR, UV-vis and MS studies. The five-coordinate dibromo complex [(CNC)NiBr(2)] is readily prepared on the gram-scale from the benzimidazolium salt precursor and Ni(OAc)(2)·4H(2)O in DMSO without the exclusion of air. Halide exchange and salt metathesis reactions using [(CNC)NiBr(2)] afford the other four- and five-coordinate complexes. [(CNC)NiBr(2)] displays very low solubility, and upon dissolution affords solutions of the four-coordinate [(CNC)NiBr](+). Factors that influence the formation of four- or five-coordinate complexes with this ligand class are discussed.

Asymmetric synthesis of a chiral hetero-bidentate As–P ligand containing both As and P-stereogenic centres

The organopalladium complex containing ortho-metalated ( S)-[1-(dimethylamino)ethyl]naphthalene as the chiral auxiliary has been used as the chiral template to promote the asymmetric cycloaddition reaction between phenyldivinylphosphine and 3,4-dimethyl-1-phenylarsole. The reaction was completed in 1 h at room temperature, with the formation of two isomeric cycloadducts in the ratio 1:3. The major phenylvinylphosphino-substituted asymmetrical hetero-bidentate arsanorbornene ligand with chirality residing on both As and P centers was obtained stereoselectively on the chiral palladium template in moderate yield. The chiral heterobidentate ligand was isolated in its enantiomerically pure form by removal of the chiral auxiliary using concentrated hydrochloric acid and subsequent cleavage from the neutral complex [(As–P)PdCl 2] by using potassium cyanide. Similar to the earlier reported analogous diphenylphosphino-substituted asymmetrical heterobidentate arsanorbornene (As–P) ligand, an arsenic elimination process was also found in the dichloro and dibromo palladium complex whereas the diiodo species did not show similar reactivity, but the corresponding η 2 diiodo complex could be obtained from the η 2 dibromo complex by treatment with sodium iodide.

Novel Stereochemistry, Reactivity, and Stability of an Arsenic Heterocycle in a Metal-Promoted Asymmetric Cycloaddition Reaction

The organopalladium complex containing ortho-metalated (S)-[1-(dimethylamino)ethyl]phenylene as the chiral auxiliary has been used as the chiral template to promote the asymmetric cycloaddition reaction between diphenylvinylphosphine and 3,4-dimethyl-1-phenylarsole. A diphenylphosphino-substituted asymmetrical heterobidentate arsanorbornene (As-P) ligand was obtained stereoselectively on the chiral palladium template in moderate yield. The chiral benzylamine auxiliary could be removed chemoselectively from the template by treatment with HCl to produce the neutral complex [(As-P)PdCl2]. In contrast to their reported P-P analogue, the arsenic donor in the dichloro complex could be eliminated stereospecifically under mild reaction conditions to generate the corresponding 1-(diphenylphosphino)-3,4-dimethyl-2,4-cyclohexadiene, which remained as a bidentate ligand at the PdCl2 unit via phosphorus and the eta2-C4-C5 double bond. The arsenic-elimination process was found to be influenced by the halo ligand in [(As-P)PdX2]. A similar process was observed with the analogous dibromo complex, but the corresponding diiodo species did not show similar reactivity. All of the novel As-Pd complexes have been characterized by X-ray crystallography.

Preparation and catalytic studies of bis(halogeno)dioxomolybdenum(VI)-diimine complexes

Dioxomolybdenum(VI) complexes of the type MoO 2X 2L containing ethylenediimine ligands were prepared in good yield by reaction of MoO 2X 2(THF) 2 (X = Cl, Br) with the bidentate ligands Ph 2C NCH 2CH 2N CPh 2 (PBED) or PhCH NCH 2CH 2N CHPh (BED). The crystal structure of MoO 2Br 2(BED) was determined by X-ray diffraction. The dichloro complexes were active as catalysts for the reaction of cyclooctene with tert-butyl hydroperoxide (TBHP) at 55 °C yielding epoxycyclooctane as the only product up to 7 h after the start of the reaction. The highest initial activity was obtained with MoO 2Cl 2(BED) (63 mol mol Mo −1 h −1). Other olefins were also tested, and activities decreased in the order cyclooctene > cyclododecene > ( R)-(+)-limonene > cyclohexene > trans-2-octene > 1-octene. The dibromo complexes exhibited much lower activities than the dichloro complexes for the epoxidation of cyclooctene.

Subsequent Hydride Substitution in (Arene)trihydridodiruthenium Complexes: Synthesis and Structure of Thiolato‐Bridged Diruthenium Cations of the Type [H2(arene)2Ru2(p‐X−C6H4−S)]+ and [H(arene)2Ru2(p‐X−C6H4−S)2]+

AbstractThe cationic complexes [HRu2(η6‐arene)2{μ2‐(p‐X−C6H4)−S}2]+ and [H2Ru2(η6‐arene)2{μ2‐(p‐X−C6H4)−S}]+ (arene = 1,2,4,5‐Me4C6H2 or C6Me6; X = Br and Me) are accessible in good yields from p‐X−C6H4−SH with [H3Ru2(1,2,4,5‐Me4C6H2)2][BF4] and [H3Ru2(C6Me6)2][BF4], respectively. The dibromo derivative [HRu2(C6Me6)2(p‐Br−C6H4−S)2]+ is found to undergo double Suzuki coupling reactions with 3‐thiophene boronic acid to give [HRu2(C6Me6)2(p‐C4H3S−C6H4−S)2]+. This dibromo complex is a potential precursor for the insertion of dinuclear hydrido organometallic entities in the main chain of conjugated molecules. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Molecular structure-activity relationships for the oxidation of organic compounds using mesoporous silica catalysts derivatised with bis(halogeno)dioxomolybdenum(VI) complexes.

Mo K-edge XAFS spectra have been measured for ordered mesoporous silica MCM-41 grafted with the complexes [MoO2X2(thf)2] (X=Cl, Br). For grafting reactions in the absence of triethylamine, materials with 1 wt. % Mo are obtained; the Mo K-edge EXAFS results indicate the co-existence of isolated surface-fixed monomeric species [MoO2[(-O)3SiO]2(thf)(n)] and [MoO2[(-O)3SiO]X(thf)(n)]. When Et3N is used in the grafting reactions, materials with 4 wt. % Mo are obtained. The EXAFS data for the material prepared using [MoO2Cl2(thf)2] and Et3N indicate the presence of dinuclear species with two Mo(VI) centres, each with two Mo=O groups and each linked by one or two oxo bridges (Mo...Mo 3.27 A). The molybdenum centres in the material prepared using the dibromo complex comprise mainly isolated four-coordinate dioxomolybdenum(VI) and trioxomolybdenum(VI) monomeric species, with a small contribution from dimeric species. All materials were further characterised in the solid state by powder X-ray diffraction, N2 adsorption analysis, MAS NMR (13C, 29Si) and FTIR spectroscopy. The derivatised MCMs perform differently as catalysts in the liquid-phase oxidation of various olefins and alcohols with tert-butyl hydroperoxide. The highest alkene epoxidation activity was recorded for the catalysts with low metal loading, whereas the material containing oxo-bridged dimers had the highest activity for oxidation of alcohols. The recyclability of all the catalysts was tested: the catalytic activity of the derivatised materials tended to stabilize with ageing.

Mechanisms of the Axial Ligand Substitution Reactions of Dinuclear, Head‐to‐Head α‐Pyrrolidonato‐ and Pivalamidato‐Bridged cis‐Diammineplatinum(III) Complexes with Halide Ions

AbstractThe acid dissociation constant of the axial aqua ligand in the Head‐to‐Head (HH) dinuclear pivalamidato‐bridged cis‐diammineplatinum(III) complex ([(H2O)Pt(NH3)2(μ‐C5H10NO)2Pt(NH3)2(H2O)]4+) and the formation constants of the successive substitution reactions on the axial sites of the HH α‐pyrrolidonato‐bridged cis‐diammineplatinum(III) dinuclear complex and the HH pivalamidato‐bridged cis‐diammineplatinum(III) dinuclear complex with halide ions X− (X− = Cl− and Br−) to give monohalo and dihalo complexes were determined spectrophotometrically at 25 °C and I = 2.0 M. A kinetic study was also performed for the monohalo and dihalo complex formations. The effect of the bridging ligand upon the axial site reactivity was compared and discussed. The ligand substitution behavior of the monohalo complex was affected by the axial ligand on the opposite Pt site and also by the bridging ligand. For both the α‐pyrrolidonato‐ and the pivalamidato‐bridged complexes, the formation of dichloro complexes proceeds only through the simple substitution path (k2 path), whereas the formation of dibromo complexes proceeds through the two parallel reaction paths: the k2 and k3 paths for the former and the k2 and k2# paths for the latter. The difference of the reaction paths is reasonably explained by the different trans effect of the halide ion on the opposite axial site for the former complex, but for the latter complex, the reaction paths are not easy to explain. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Novel Non-Symmetric Nickel-Diimine Complexes for the Homopolymerization of Ethene: Control of Branching by Catalyst Design

Non-symmetric diimine ligands (Ar-N=C(CH3)-(CH3)C=NAr*; Ar: 2,6-diisopropyl-phenyl; Ar*: 2,6-di(4-tert-butyl-phenyl)phenyl (4b), 2,6-di(4-OCH3)-phenyl)phenyl (4c)) were synthesized and converted in-situ into the corresponding nickel dibromo complexes (5b, c) by reaction with (DME)NiBr2. The complexes were activated for ethene polymerization by treatment with MAOat ambient temperature. The resulting highmolecular weight polymer products (MW > 4.0 x 106 g mol-1) have a branched microstructure (predominantly methyl groups), as indicated by 13C NMR spectroscopy. The degree of branching can be controlled by a proper choice of the 2,6-diphenyl modified aniline moieties resulting in melting transitions ranging from 92 - 130 °C.

Chelate Complexes of Functionalized Cycloheptatrienyl Ligands: 17- and 18-Electron Molybdenum Complexes with Linked Cycloheptatrienyl−Phosphane Ligands and Their Use in Transition Metal Catalysis

The synthesis of P-functionalized molybdenum chelate complexes incorporating the linked cycloheptatrienyl− phosphane ligand [2-(diphenylphosphanyl)phenyl]cycloheptatrienyl, o-Ph2P−C6H4−C7H6, is described. The air-stable ligand precursor [2-(cyclohepta-2,4,6-trienyl)phenyl]diphenylphosphane (2) can be obtained in large quantities by addition of lithiated 2-BrC6H4PPh2 (1) to the tropylium cation C7H7+. Hydride abstraction employing the trityl cation, Ph3C+, results in the formation of the tricyclic phosphonium salt 3. The P-functionalized cycloheptatriene 2 acts as an eight-electron ligand on reaction with Mo(CO)6 to afford the cycloheptatriene−phosphane complex [(o-Ph2PC6H4-η6-C7H7)Mo(CO)2(P−Mo)] (4) as a single, chiral regioisomer, which undergoes clean hydride abstraction on treatment with (Ph3C)BF4. The resulting cationic cycloheptatrienyl−phosphane complex 5 reacts with sodium bromide to yield the uncharged “chiral-at-metal” complex [(o-Ph2PC6H4-η7-C7H6)Mo(CO)Br(P−Mo)] (6). This 18-electron complex can be oxidized with 0.5 equiv. of Br2 to give the paramagnetic dibromo complex 7, which is a versatile starting material for the preparation of the 17-electron mono- and dialkyl complexes [(o-Ph2PC6H4-η7-C7H6)Mo(CH2SiMe3)X(P−Mo)] (X = Br, 8; X = CH2SiMe3, 9). In combination with Me3SiCH2MgCl, complexes 7 and 9 prove to be active catalysts for the ring-opening metathesis polymerization of norbornene. In addition, the X-ray crystal structures of 2, 4, 5·CH2Cl2, 7·CHCl3, 8, and 9·C6H14 are reported.

SYNTHESIS AND CHARACTERIZATION OF A NEW DIOXIME AND ITS COBALT(III) COMPLEXES AS VITAMIN B12 MODELS

A new dioxime ligand abbreviated as H2L, 2′,3′,3,8-tetramethyl-5,6-benzo-4,7-diazadeca-3,7-diene-2,9-dione dioxime, has been synthesized by the condensation reaction of 4,5dimethyl-2,3-diaminobenzene with diacetyl monoxime. The ligand provides a deep cleft within which axial ligands such as pseudo-halogens and Lewis base coordinate. The dibromo complex of this ligand [Co(HL)Br2] (3) has been prepared by the reaction of H2L with cobalt(II) bromide hexahydrate. This complex has been employed as a starting material for further substitution reactions. Octahedral cobalt (III) complexes containing a benzyl group as axial ligand have also been prepared by reacting (3) with benzyl chloride and pyridine or substituted pyridine. The structures of the dioxime and its complexes are proposed on the basis of elemental analyses, 1H and 13C NMR, IR and MS spectral data.

Dipyridylamine Ligands − Synthesis, Coordination Chemistry of the Group 10 Metals and Application of Nickel Complexes in Ethylene Oligomerization

A great variety of 2,2′-bipyridylamines can be synthesized starting from primary amines or 2-aminopyridines (for instance, symmetrically and unsymmetrically substituted as well as chiral ligands) by palladium-catalyzed aryl amination. The reaction of such ligands with [PdCl2(COD)] or [NiBr2(DME)] (COD = cycloocta-1,5-diene; DME = 1,2-dimethoxyethane) led to the corresponding dichloro or dibromo complexes. The results of X-ray crystal structure analyses of selected compounds show that the ligands coordinate through the two pyridine N-atoms. Their palladium complexes have a slightly distorted planar coordination (in the case of nickel a distorted tetrahedral coordination), with N−M−N angles of 96.0(2)° (M = Ni) and 85.7° (averaged, M = Pd). The nickel complexes are highly active ethylene oligomerization catalysts if activated with Et3Al2Cl3.

NewC2v- and ChiralC2-Symmetric Olefin Polymerization Catalysts Based on Nickel(II) and Palladium(II) Diimine Complexes Bearing 2,6-Diphenyl Aniline Moieties: Synthesis, Structural Characterization, and First Insight into Polymerization Properties

Four new 1,4-diaza-2,3-dimethylbutadiene ligands (Ar−NC(CH3)−(H3C)CNAr; Ar: 3a = 2,6-diphenylphenyl; 3b = 2,6-di(4-OCH3-phenyl)phenyl; 3c = 2,6-di(4-tert-butyl-phenyl)phenyl; 3d = 2,6-di(3,5-dimethylphenyl)phenyl) as well as the palladium dichloride complexes 4a−c and methyl monochloride derivatives 5a−c were prepared, and their polymerization behavior was investigated. The corresponding nickel species 6a−c were tested for the insertion polymerization of ethene by in situ reactions of 3a−c with (DME)NiBr2. The ligands are accessible by a three-step procedure. Aryl boronic acids were prepared by Grignard reactions of substituted aryl bromides and were coupled with 2,6-dibromo aniline according to a Suzuki cross-coupling protocol to give the corresponding terphenyl anilines 2a−d. Condensation of 2,3-butanedione with the corresponding aniline afforded the formation of the diimines 3a−d. The corresponding palladium dichloride complexes 4a−c are accessible by reaction with (PhCN)2PdCl2. The structures of 4a−c could be determined by X-ray analysis. While the terphenyl complex 4a adopts a C2v-symmetry, 4c exists in a chiral C2-symmetric coordination geometry, due to the repulsive interactions of the sterically demanding tert-butylphenyl substituents of the aniline moieties. All palladium and nickel complexes are catalysts for the polymerization of ethene. However, the chiral Ni(II) complex 6c shows by far the highest polymerization activity up to 2 × 104 kg(PE) [mol (Ni) h]-1. The polyethenes obtained with the palladium methyl monochloro catalysts activated with Na[(3,5-(CF3)2C6H3)4B] and the nickel dibromo complexes activated with MAO are linear and show in the case of the Ni(II) derivatives molecular weights up to 4.5 × 106 g mol-1 (Mw/Mn ≈ 2), which can be controlled by addition of hydrogen.

Syntheses and structures of six and seven-coordinate diene complexes of molybdenum and tungsten(II). The crystal and molecular structures of [WBr2(CO)2(PMePh2)(norbornadiene)] and [WBr2(CO)(NCCHCH2)(norbornadiene)

Abstract Reactions of [WI2(CO)3(NCMe)2] with norbornadiene (NBD) and 1,5-cycloctadiene (COD) give six-coordinate dicarbonyls [WI2(CO)2(NBD)] and [WI2(CO)2(COD)], respectively. The related dibromo complex [WBr2(CO)2(NBD)] reacts with tertiary phosphines L to give unstable seven-coordinate adducts [WBr2(CO)2(L)(NBD)] (L=PPh3, PMePh2, PEt3), which in the case of L=PMePh2 was shown to undergo CO loss to give the six-coordinate derivative [WBr2(CO)(PMePh2)(NBD)]. X-ray diffraction studies of [WBr2(CO)2(PMePh2)(NBD)] reveal a seven-coordinate structure (distorted pentagonal bipyramid) with the diene CC bonds on the pentagonal plane lying approximately parallel to the WCO axes. Reactions of [WBr2(CO)2(NBD)] with organonitriles NCR at room temperature afford CO substitution products (R=Me, Pri, Ph, C6H4Me-4, CHCH2) directly with no evidence for seven-coordinate intermediates. [WBr2(CO)2(COD)] and acetonitrile similarly give [WBr2(CO)(NCMe)(COD)]. X-ray diffraction studies of [WBr2(CO)(NCCHCH2)(NBD)] confirmed a distorted octahedral structure where the carbonyl lies trans to the acrylonitrile ligand.

Norbornadiene(bipyridyl)molybdenum(II) Complexes: Synthesis, Structure and Reactivity of [Mo(CO)(C7H8)(C10H6R2N2)X2] (X = I, Br)

AbstractThe reaction of [Mo(CO)4(C7H8)] (1) with I2 gave the norbornadienemolybdenum(II) complex [Mo(CO)2(C7H8)I2]n≥1 (2), which existed in an equilibrium of two isomeric forms. In acetonitrile, 2 reversibly formed the adduct [Mo(CO)2‐(C7H8)(NCCH3)I2] (3), whereas on treatment with 2,2′‐bipyridine or 4,4′‐di‐2,2′‐tBu‐bipyridine, it gave stable 7‐coordinated molybdenum(II) complexes, [Mo(CO)(C7H8)‐(C10H8N2)I2] (4) and [Mo(CO)(C7H8)(C10H6tBu2N2)I2] (5), in good yield. In similar reactions, the related dibromomolybdenum compounds [Mo(CO)(C7H8)(C10H8N2)Br2] (6) and [Mo‐(CO)(C7H8)(C10H6tBu2N2)Br2] (7) were prepared by oxidation of 1 with two equivalents of CuBr2. The X‐ray structural analysis of 6 reveals that the geometry around the molybdenum atom is nearly perfectly pentagonal bipyramidal, with the CO and one of the bipyridyl rings perpendicular to the plane formed by the other ligands. The compounds 5 and 6 react with AgSbF6 by halogen abstraction to give cationic complexes, {[Mo(CO)(C7H8)(C10H8N2)Br]SbF6}n≥1 (8) and {[Mo(CO)(C7H8)(C10H6tBu2N2)I]SbF6}n≥1 (9): In acetone, 8 and 9 reversibly formed the adducts [Mo(CO)(C7H8)(C10H8N2)(acetone)Br]SbF6 (8′) and [Mo(CO)(C7H8)(C10H6tBu2N2)(acetone)I]SbF6 (9′); while on treatment with PMe3, the stable monomeric complexes, [Mo(CO)(C7H8)(C10H8N2)(PMe3)Br]SbF6 (10) and [Mo(CO)(C7H8)(C10H6tBu2N2)(PMe3)I]SbF6 (11), were isolated in almost quantitative yield. In the presence of KBr, compound 8′ reverted to the dibromo complex 6, whereas 9′ reacted to produce a 1:1:2 mixture of 5, 7 and the bromo(iodo) complex [Mo(CO)(C7H8)(C10H6tBu2N2)BrI] (12). The same mixture is available from the reaction of 5 with one equivalent of 7.

Dichloro- and dibromo[N-(2-pyridylmethylidene)-2-thienylmethylamine-N,N']copper(II) complexes, [CuCl2(C11H10N2S)] and [CuBr2(C11H10N2S)

The crystal strutures of dichloro- (2) and dibromo[N-(2-pyridyl(ethylidene)-2-thienylmethylamine-N,N']copper(II) (1) have been determined to investigate the coordination of the metal centre. In both cases, the two N atoms and two halogen anions are coordinated to the copper(II) and the S atom is free. For the dibromo complex, the structure is monomeric, while the dichloro complex forms dimers (di-μ-chloro-bis{chloro[N(2-pyridylmethylidene)-2-thienylmethylamine-N,N']copper(II)})

Gold bromide complexes in acidic aqueous solutions from 25� to 300�C. A laser raman spectroscopic study

Raman spectra of gold bromide complexes in acidic solutions (pH=−0.3–3) have been recorded at 25° to 300°C and at pressures on the liquid vapor curve for the system. At 25°C, only the square planar Au(III) bromide complex, AuBr 4 − , is present in solution with bands at approximately 105, 197 and 215 cm−1. However, in these acidic solutions, when the temperature is 50°C or higher, the square planar Au(III) bromide complex is partially transformed into the linear Au(I) bromide complex, AuBr 2 − , with a single band near 208 cm−1. The transformation of the Au(III) square planar tetrabromo complex into the Au(I) linear dibromo complex is also favored by a reduction of the oxygen fugacity and an increase in pH.