On the solvatochromic properties of the oxalate-bridged complexes [(BuCO2)3M2]2(μ-O2C2O2) where M = Mo or W

The room temperature electronic absorption spectra of the oxalate bridged MM quadruply bonded complexes [(^tBuCO₂)₃M₂]₂(μ-O₂C₂O₂), where M = Mo or W have been recorded in H₂O, THF:H₂O mixtures, THF, CH₂Cl₂, toluene, DMSO, aniline, toluene saturated with N,N-dimethylaniline and ethanol. The strong absorptions in the visible region of the electronic absorption spectra assignable to the metal-to-ligand (bridge) charge transfer are shown to be highly solvent dependent. Those samples prepared in H₂O, CH₂Cl₂ and toluene are shown to comprise of a suspension of microcrystalline particles ranging in size from 100 nm to 5 μm. Individual particles were found by scanning electron microscopy to have an aspect ratio of ∼10:1, all being needle shaped. The spectra in THF, EtOH, aniline, DMSO and toluene-N,N-dimethylaniline all show similar vibronic progressions and are attributed to discrete solvated molecular species. The spectra recorded in aniline are notably red-shifted which is proposed to arise from a combination of hydrogen bonding and Lewis base stabilization of the photoexcited state.     

Oxidative nuclease activity of ferromagnetically coupled μ-hydroxo-μ-propionato copper(II) complexes [Cu3(L)2(μ-OH)2(μ-propionato)2] (L = N-(pyrid-2-ylmethyl)R-sulfonamidato, R = benzene, toluene, naphthalene)

Three doubly-bridged, trinuclear copper(II) compounds with hydroxo and carboxylato bridges, ^∞₁[Cu₃(L1)₂(μ-OH)₂(μ-propionato)₂](1), [Cu₃(L2)₂(μ-OH)₂(μ-propionato)₂(DMF)₂] (2) and ^∞₁{[Cu₃(L3)₂(μ-OH)₂(μ-propionato)₂]} [Cu₃(L3)₂(μ-OH)₂(μ-propionato)₂(DMF)₂]} (3) [HL1 = N-(pyrid-2-ylmethyl)benzenesulfonylamide, HL2 = N-(pyrid-2-ylmethyl)toluenesulfonylamide, HL3 = N-(pyrid-2-ylmethyl)naphthalenesulfonylamide], have been synthesized and characterized. 1 is built from [Cu₃(L1)₂(μ-OH)₂(μ-propionato)₂] clusters. Each unit contains three copper(II) with two different coordination environments: the terminal centers are square-base pyramidal whereas the central copper is square planar. 2 presents a similar square-base pyramidal geometry in the terminal centers, but the central copper is six-coordinate. 3 shows an unusual 1D coordination polymer comprised of two distinct building blocks: one similar to that found in 1 and the other similar to that found in 2. The magnetic susceptibility measurements (2-300 K) reveal a ferromagnetic interaction between the Cu(II) ions with J values of 76.0, 55.0, and 48.0 cm⁻¹ for 1, 2, and 3, respectively. Emission spectroscopy, thermal denaturation, viscosimetry and cyclic voltammetry show an interaction of the complexes with DNA through the sugar-phosphate backbone. All three Cu(II) complexes were found to be very efficient agents of plasmid DNA cleavage in the presence of ascorbato or mercaptopropionic acid. Both the kinetics and the mechanism of the cleavage reaction have also been examined.     

A one-dimensional copper (II) coordination polymer [Cu3(ampym)2(μ1,1-N3)4(μ1,3-N3)2(dmf)2]n (ampym = 2-aminopyrimidine) containing both end-on and end-to-end azido bridges

A new polynuclear copper (II) complex, derived from the azido-bridging ligand and 2-aminopyrimidine, has been synthesized and its 3-D structure has been determined by X-ray diffraction methods at two different temperatures. The compound crystallizes in the triclinic system space group, with the central copper atom lying on an inversion centre. The crystal structure is built up by trinuclear units (each of them contains two double end-on azido bridges) linked through two azide ions in an end-to-end (EE) fashion, to yield the polymer chain [Cu₃(ampym)₂(μ_1,1-N₃)₄(μ_1,3-N₃)₂(dmf)₂]_n. Magnetic susceptibility measurement shows a ferromagnetic interaction above 30 K, whereas a weak anti-ferromagnetic interaction prevails in the range of 30-2 K.     

Crystal and molecular structures of {Cu(μ-CCPh)(triphos)}2 [triphos = (PPh2CH2)3CMe]

The binuclear complex {Cu(μ-CCPh)(triphos)}₂ [triphos = (PPh₂CH₂)₃CMe] has been obtained from a reaction between {Cu(CCPh)}_n and triphos. The two copper atoms are bridged unsymmetrically by two CCPh groups, each attached through one carbon only [Cu-C, 2.016(4) Å], the separation between the two coppers being 2.4663(8) Å. Only two of the three phosphorus atoms in each ligand are coordinated to copper [Cu-P(1,2) 2.281, 2.273(1) Å]. The observed structure may be rationalised using a recent theoretical study [C. Mealli, S.S.M.C. Godinho, M.J. Calhorda, Organometallics 20 (2001) 1734] and differs from that assumed for the rationalisation of its luminescence properties [V. Pawlowski, G. Knör, C. Lennartz, A. Vogler, Eur. J. Inorg. Chem. (2005) 3167].     

Oxidative addition of thiols to (CO)3Mo(μ-dppm)2Ru(CO)3 with formation of hydrido, bridged-thiolate complexes (dppm = Ph2PCH2PPh2)

The room temperature reactions of RSH (R = Et, Ph) with (CO)₃Mo(μ-dppm)₂Ru(CO)₃ (1) in toluene yield (CO)₂Mo(μ-SR)(μ-CO)(μ-dppm)₂Ru(H)(CO) [R = Et (3); Ph (4)], which are characterized by elemental analysis, ¹H NMR and IR spectroscopies and, in the case of 3, by X-ray crystallography. The complexes contain a trans,trans-Mo(μ-dppm)₂Ru unit with a bridging thiolate, a terminal hydride at the Ru, three terminal CO ligands (two at the Mo, and one at the Ru), and one semi-bridged CO closer to the Mo.     

Thiotungstates containing the syn-[W2(O/S)2(μ-S)2] (E = O, S) and cuboidal [W2Cu2(μ3-S)4] cores

Reaction of [W^VIS₄]²⁻ with ethane-1,2-dithiol edtH₂ in the presence of the sulfide scavenger Cd²⁺ yielded the dinuclear tungstate syn-[{(edt)W^V(O/S)}₂(μ-S)₂]²⁻ (1), with the terminal S/O disordered over the two tungsten sites in the ratio 0.8:02. In the presence of thiocyanate, phosphine and CuI, the anionic cuboidal clusters of composition [{(SCN)₃W^V}₂{Cu^I(PPh₃)}₂(μ₃-S)₄]²⁻ (2) and (3, diphos = 1,2-bis(o-diphenylphosphinophenyl)ethane), and possibly via an intermediate [{(SCN)₃W^VS}₂(μ-S)₂]⁴⁻. The crystal and molecular structures of [Et₄N]₂1, [Et₄N]₂2 · H₂O and [Et₄N]₂3 · H₂O have been determined.     

Synthesis, protonation and electrochemical properties of trinuclear NiFe2 complexes Fe2(CO)6(μ3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, Ph) with an internal pendant nitrogen base as a proton relay

Two trinuclear NiFe₂ complexes Fe₂(CO)₆(μ₃-S)₂[Ni(Ph₂PCH₂)₂NR] (R = n-Bu, 1; Ph, 2) containing an internal base were prepared as biomimetic models for the active sites of FeFe and NiFe hydrogenases. Treatment of complex Fe₂(CO)₆(μ₃-S)₂[Ni(Ph₂PCH₂)₂N(n-Bu)] (1) with HOTf gave an N-protonated complex [Fe₂(CO)₆(μ₃-S)₂{Ni(Ph₂PCH₂)₂NH(n-Bu)}][OTf] ([1H][OTf]). The structures of complexes 1, 2 and [1H][OTf] were determined by X-ray crystallography, which shows that the proton held by the N atom of [1H][OTf] lies in an equatorial position. Cyclic voltammograms of complexes 1 and [1H][OTf] were studied and compared with that of Fe₂(CO)₆(μ₃-S)₂[Ni(dppe)].     

A novel tetranuclear hydrogenphosphate-bridged Cu(II) cluster. Synthesis, structure, spectroscopy and magnetism of [Cu4(dpyam)4(μ4,η-HPO4)2(μ-X)2]X2(H2O)6 (X = Cl, Br)

Two novel tetranuclear compounds with an unprecedented mode of a hydrogenphosphato bridge, [Cu₄(dpyam)₄(μ₄,η³-HPO₄)₂(μ-X)₂]²⁺ (in which dpyam = di-2-pyridylamine and X = Cl (1), Br (2)) have been synthesised and characterised structurally and magnetically. The Cu(II) ions in the structures each display a square-pyramidal geometry, with two tridentate hydrogenphosphato groups bridging four copper atoms in a μ₄,η³ coordination mode which is rarely found in hydrogenphosphate metal compounds. Each (different) pair of Cu(II) ions is additionally bridged by halide ions, with relatively long Cu-X distances (2.551(3)-2.604(3) Å for 1 and 2.707(1)-2.766(2) Å for 2) and subsequently also a small Cu-X-Cu angle (65.7(1)° and 65.1(1)° for 1 and 61.6(1)° and 62.4(1) for 2) and a large Cu-X-Cu angle (95.5(1)° and 96.5(1)° for 1 and 91.1(1)° and 92.6(1)° for 2). Cu?Cu distances in the tetranuclear units varies from 2.802(3) to 5.232(3) Å for 1 and from 2.834(1) to5.233(1) Å in 2. The lattice structures are stabilised by extensive intermolecular hydrogen bonds. The magnetic susceptibility measurements down to 5 K revealed a weak ferromagnetic interaction between the outer pairs of Cu(II) ions which vary from 22 to 46 cm⁻¹ in 1 and 12 to 33 cm⁻¹ in 2 and a moderately strong antiferromagnetic interaction between the inner Cu(II) ions of −79 cm⁻¹ in 1 and −83 cm⁻¹ in 2, via the Cu-O-P-O-Cu pathway.     

Hydrido-derivatives of [Ir4(CO)10(diphosphine)]: X-ray analyses of [Ir4H(CO)9(μ-Ph2PH(CH3)PPh2)] and [Ir4 H(CO)9(μ-Ph2P(CH2)nPPh2)] (n = 2, 3)

Some novel hydrido-anions of general formula [Ir₄H(CO)₉(μ-L-L)]⁻ (L-L = Ph₂PCH(CH₃)PPh₂, Ph₂P(CH₂)₂PPh₂, Ph₂P(CH₂)₃PPh₂ and Ph₂AsCH₂AsPh₂) have been obtained by the reaction of [Ir₄(CO)₁₀(μ-L-L)] with the base 1,8-diazabicyclo[5.4.0]undec-7-ene in wet dichloromethane. According to IR and ¹H, ³¹P and ¹³C NMR data at low temperature, these anionic derivatives display a single conformation in solution: three edge-bridging COs around the triangular basal face and both the hydride and the bidentate ligands located in axial positions relative to this face. The structures of four compounds were established by X-ray diffraction studies, which confirmed the configuration proposed on the basis of spectroscopic data.     

Dithiolate and diselenolate complexes [Pt2(μ-ECH2CHCHCH2E)(PPh3)4] (E = S, Se): Synthesis, characterisation and mass spectrometric formation of the dichalcogenide species [Pt2(μ-E2)(PPh3)4]

The reactions of [Pt₂(μ-E)₂(PPh₃)₄] (E = S, Se) with cis-1,4-dichlorobut-2-ene (cis-ClCH₂CHCHCH₂Cl) give the dichalcogenolate complexes [Pt₂(μ-ECH₂CHCHCH₂E)(PPh₃)₄]²⁺; an X-ray structure determination on the thiolate complex was carried out. The complexes give the expected dications in ESI mass spectra recorded at very low cone voltages, but at moderate cone voltages undergo facile fragmentation via a retro-Diels-Alder reaction and loss of 1,3-butadiene, giving the dichalcogenide species [Pt₂(μ-E₂)(PPh₃)₄]²⁺. Analogous species containing bidentate phosphine or arsine ligands have been previously generated electrochemically, and studied theoretically.     

Synthesis, crystal structures, and spectroscopic characterization of the neutral monomeric tetrahedral [M(Diap)2(OAc)2] · H2O complexes (M = Zn,Cd; Diap = 1,3-diazepane-2-thione; OAc = acetate) with N-H?O and O-H?O intra- and intermolecular hydrogen bonding interactions

The title complexes, [M(Diap)₂(OAc)₂] · H₂O (M = Zn,Cd; Diap = 1,3-diazepane-2-thione; OAc = acetate) with an MO₂S₂ configuration, have been characterized by X-ray crystallography as well as FT-IR, ¹H and ¹³C NMR spectroscopy. In these complexes, the metal atoms lie in a pseudo-tetrahedral environment and are coordinated by the thione sulfur atoms of two neutral 1,3-diazepane-2-thione ligands and one oxygen atom from each of two monodentate acetate anions. In both complexes, there are two intramolecular N-H?O hydrogen bonds, each being between one NH group of a Diap ligand and the uncoordinated O atom of an OAc ligand. The water molecule is also involved in hydrogen bonds, as an acceptor and as a donor twice, linking together three symmetry-related complexes. The Cd complex undergoes a structural phase transition from a monoclinic form at 150 K with Z′ = 2 to a smaller monoclinic cell at room temperature with Z′ = 1 without loss of crystallinity. The Zn complex does not exhibit an equivalent phase transition, and at 150 K is isostructural with the room-temperature form of the Cd complex. All three crystallographically independent molecules found for the Cd complex (two at low temperature and one at room temperature) have essentially the same structure except for small changes in the conformations of the ligands. Tetrahedral coordination with monodentate carboxylate ligands is common for Zn complexes of this kind, but is unusual for Cd complexes, and is the result of the bulky Diap ligands.     

Synthesis and electrochemical aspects of group 14 iron complexes of the type (η-C5H5)Fe(L)2ER3, L2 = (CO)2, (Ph2P)2CH2; E = C, Si, Ge, Sn

The dicarbonyl and diphosphine complexes of the type (η⁵-C₅H₅)Fe(L)₂ER₃ (L₂ = (CO)₂ (a), (Ph₂P)₂CH₂ (b); ER₃ = CH₃ (1a/b); SiMe₃ (2a/b), GeMe₃ (3a/b), SnMe₃ (4a/b)) were synthesized and studied electrochemically. Cyclic voltammetric studies on the dicarbonyl complexes 1a-4a revealed one electron irreversible oxidation processes whereas the same processes for the chelating phosphine series 1b-4b were reversible. The E_ox values found for the series 1a-4a were in the narrow range 1.3-1.5 V and in the order Si > Sn ≈ Ge > C; those for 1b-4b (involving replacement of the excellent retrodative π-accepting CO ligands by the superior σ-donor and poorer π-accepting phosphines) have much lower oxidation potentials in the sequence Sn > Si ≈ Ge > C. This latter oxidation potential pattern relates directly to the solution ³¹P NMR chemical shift data illustrating that stronger donation lowers the E_ox for the complexes; however, simple understanding of the trend must await the results of a current DFT analysis of the systems.     

First crystallographic determination of dichloro-bridged dinuclear rhodium Cp* complex with neutral Me2CO molecules. [Rh2(Cp*)2(μ-Cl)2(Me2CO)2](BF4)2 (Cp* = η-C5Me5)

The single crystals of dichloro-bridged dinuclear Rh-Cp* complex with neutral Me₂CO molecules, [Rh₂(Cp*)₂(μ-Cl)₂(Me₂CO)₂](BF₄)₂ (Cp* = η⁵-C₅Me₅), was isolated and the structure was in first determined crystallographically.     

A facile reaction of bibenzyl trisulfide with [(η-C5H5)Cr(CO)3]2: formation of a thiolato-bridged dichromium complex of [CpCr(CO)2(SBz)]2 (Bz = PhCH2-)

The reaction of [CpCr(CO)₃]₂ (Cp = η⁵-C₅H₅) (1) with an equivalent of Bz₂S₃ at ambient temperature gave [CpCr(CO)₂]₂S (3) [L.Y. Goh, T.W. Hambley, G.B. Robertson, Organometallics 6 (1987) 1051], novel complexes of [CpCr(CO)₂(SBz)]₂ (4) and together with [CpCr(SBz)]₂S (5) as main products. Thermolytic studies showed that 4 underwent complete decarbonylation to give [CpCr(SBz)]₂S (5). Final thermal decomposition of 3 and 5 eventually yielded Cp₄Cr₄S₄ (6) (Goh et al., 1987) after prolonged reaction at 100 °C. However, the reaction of [CpCr(CO)₂]₂ (CrCr) (2) with Bz₂S₃ was much slower at ambient temperature which required 72 h to complete eventually yielding 3 and 5. All the products have been characterized by elemental and spectral analyses. 4 has been structurally determined.     

The reaction between orthodiphenylphosphinobenzaldehyde and [(η-C5Me5)MCl(μ-Cl)]2 (M=Rh and Ir)

The benzaldehyde functionalized phosphine Ph₂PC₆H₄CHO-2 underwent reaction with [(η⁵-C₅Me₅)MCl(μ-Cl)]₂ (M=Rh, Ir) to form (η⁵-C₅Me₅)MCl₂(κP-Ph₂PC₆H₄CHO-2), which underwent activation of the aldehyde C-H bond to form (η⁵-C₅Me₅)MCl(κP,κC-Ph₂PC₆H₄CO-2). Formally the reaction involves oxidative addition of C-H across the metal and reductive elimination of HCl. The structure of (η⁵-C₅Me₅)RhCl(κP,κC-Ph₂PC₆H₄CO-2) has been determined by single-crystal X-ray diffraction.     

Syntheses and crystal structures of the first iridium complexes with m- and p-terphenyl (tp). {[Ir2(p-tp)(cod)2](BF4)2 · 2CH2Cl2}3 and [Ir(m-tp)(η-C5Me5)](BF4)2

Novel two iridium terphenyl complexes were prepared and their structures were characterized crystallographically. The reaction of [Ir(cod)₂]BF₄ with p-terphenyl (p-tp) in CH₂Cl₂ was carried out to afford dinuclear Ir(I) complex {[Ir₂(p-tp)(cod)₂](BF₄)₂ · 2CH₂Cl₂}₃ (cod=1,5-cyclooctadiene) (1 · 2CH₂Cl₂), whereas the reaction of the intermediate [Ir(η⁵-C₅Me₅)(Me₂CO)₃]³⁺ in Me₂CO with m-terphenyl (m-tp) was done to provide mononuclear Ir(III) complex [Ir(m-tp)(η⁵-C₅Me₅)](BF₄)₂ (2). In complex 1 · 2CH₂Cl₂, two Ir atoms are η⁶-coordinated to both sides of terminal benzene rings from the upper and lower sides in the p-tp ligand, while one Ir atom is η⁶-coordinated to one side of the terminal benzene ring in the m-tp ligand in complex 2. Each crystal structure describes the first coordination mode found in metal complexes with the m- and p-tp ligands.     

Succinate bridged dimeric Cu(II) system containing sandwiched non-coordinating succinate dianion: Crystal structure, spectroscopic and thermal studies of [(phen)2Cu(μ-L)Cu(phen)2]L · 12.5H2O (H2L = succinic acid; phen = 1,10-phenanthroline)

A mixed ligand and dimeric Cu^II complex [(phen)₂Cu(μ-L)Cu(phen)₂]L · 12.5H₂O (H₂L = succinic acid) containing bridging succinate moiety and also non-coordinated succinate dianion was prepared from polymeric Cu(II) succinate by nucleophilic reaction with o-phenanthroline (phen) followed by depolymerization. The dimeric product was characterized by crystallographic, spectroscopic and thermoanalytical studies. The complex crystallizes in triclinic crystal system and is composed of succinate bridged [(phen)₂Cu(μ-L)Cu(phen)₂]²⁺ complex cations, non-coordinated succinate anions and hydrogen bonded water molecules. Within the dimeric cationic unit, each of the Cu atoms is octahedrally coordinated by four N atoms of both phen ligands and both O atoms of a carboxylate moiety of the bridging succinate group in chelating form. Through intermolecular π-π stacking interactions, the complex cations form positively charged 2-D layers, between which the non-coordinating succinate anions and water molecules are sandwiched. Both the electronic and EPR studies indicate that the dimeric complex undergoes partial dissociation in solution state to exist in two structural forms. The kinetic and thermodynamic parameters involved in three stage thermal decompositions of the dimeric complex could also be evaluated using Coats-Redfern method.     

A versatile entry into aqueous niobium chemistry: isolation and structure of the intermediate Nb4(μ2-O)2(μ2-OC2H5)4Cl4(OC2H5)4(HOC2H5)4

The reduction of ethanolic solutions of niobium pentachloride with zinc, followed by treatment with aqueous acids serves as a versatile entry into the aqueous solution chemistry of niobium. From the zinc-reduced solution, the major intermediate, Nb₄(μ₂-O)₂(μ₂-OC₂H₅)₄Cl₄(OC₂H₅)₄(HOC₂H₅)₄, was isolated and the crystal structure determined by X-ray crystallography. The complex crystallizes in the orthorhombic space group Pccn, with Z=4, a=21.0105(9), b=11.0387(5), c=19.1389(8), V=4438.9(3) ų, M_r=1090.19,R₁=0.0327 and wR₂=0.0876. The structure revealed a centrosymmetric tetrameric Nb(IV) complex, consisting of a pair of edge-sharing bi-octahedral Nb₂(μ₂-OC₂H₅)₄Cl₂(OC₂H₅)₂(HOC₂H₅)₂ units that are joined by two axial oxo ligands. The Nb-Nb distance of 2.7458(3) Å is consistent with a single metal-metal bond.     

Synthesis and structural characterisation of the lead-platinum sulfido aggregates [Pt2(μ-S)2(PPh3)4PbX2] (X = Br, I); promotion of rare tetrahedral geometry for lead(II)

The reactions of [Pt₂(μ-S)₂(PPh₃)₄] with excess PbBr₂ or PbI₂ in methanolic suspension result in the formation of the neutral lead(II) halide adducts [Pt₂(μ-S)₂(PPh₃)₄PbX₂] (X = Br, I). The X-ray structure determination of the lead iodide adduct reveals an essentially tetrahedral lead(II) centre, which is a rare coordination geometry for lead(II), which almost invariably is hemidirected, with a stereochemically active lone pair. In contrast, the structure of the PbBr₂ adduct, although suffering from some disorder, shows a more typical, distorted arrangement of ligands; these results are discussed in terms of the tendency for soft, bulky ligands to promote symmetric, holodirected geometries. The ESI mass spectra of the adducts are reported, and yield [M−halide]⁺ ions.     

Thallium(III) complexes of the metalloligands [Pt2(μ-S)2(PPh3)4] and [Pt2(μ-Se)2(PPh3)4]

Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with the diarylthallium(III) bromides Ar₂TlBr [Ar = Ph and p-ClC₆H₄] in methanol gave good yields of the thallium(III) adducts [Pt₂(μ-S)₂(PPh₃)₄TlAr₂]⁺, isolated as their salts. The corresponding selenide complex [Pt₂(μ-Se)₂(PPh₃)₄TlPh₂]BPh₄ was similarly synthesised from [Pt₂(μ-Se)₂(PPh₃)₄], Ph₂TlBr and NaBPh₄. The reaction of [Pt₂(μ-S)₂(PPh₃)₄] with PhTlBr₂ gave [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]⁺, while reaction with TlBr₃ gave the dibromothallium(III) adduct [Pt₂(μ-S)₂(PPh₃)₄TlBr₂]⁺[TlBr₄]⁻. The latter complex is a rare example of a thallium(III) dihalide complex stabilised solely by sulfur donor ligands. X-ray crystal structure determinations on the complexes [Pt₂(μ-S)₂(PPh₃)₄TlPh₂]BPh₄, [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]BPh₄ and [Pt₂(μ-S)₂(PPh₃)₄TlBr₂][TlBr₄] reveal a greater interaction between the thallium(III) centre and the two sulfide ligands on stepwise replacement of Ph by Br, as indicated by shorter Tl-S and Pt?Tl distances, and an increasing S-Tl-S bond angle. Investigations of the ESI MS fragmentation behaviour of the thallium(III) complexes are reported.