Showing papers in "Journal of The Chemical Society-dalton Transactions in 1990"

Synthesis and study of a mixed-ligand ruthenium(II) complex in its ground and excited states: bis(2,2′-bipyridine)(dipyrido[3,2-a : 2′,3′-c]phenazine-N4N5)ruthenium(II)

Abstract: The ruthenium (II) complex [Ru(bipy)2(dppz)]2+(bipy = 2,2′-bipyridine, dppz = dipyrido[3,2-a : 2′,3′-c]phenazine) was synthesized, characterized, and studied. Its oxidation and first reduction potentials are respectively 1.24 and –1.02 V (vs. saturated calomel electrode). The maxima of the metal-to-ligand charge-transfer absorption and emission occur respectively at 448 and 610 nm. These data suggest that [Ru(bipy)2(dppz)]2+ is made up of two electronically independent units, one behaving as a [Ru(bipy)3]2+-like chromophore, the other as a phenazine-like electron acceptor. Excited-state absorption spectra were obtained for [Ru(bipy)2(dppz)]2+ and its parent complex [Ru(bipy)3]2+. Above 500 nm the latter shows only one maximum (at 510 nm), and the former shows two maxima (around 526 and 557 nm), whereas radical anions of both bipyridine and phenazine or dipyridophenazine show two maxima (at 512 and 552 nm for phenazine). In the case of [Ru(bipy)2(dppz)]2+ these results can be interpreted in terms of a light-induced directed charge transfer from the ruthenium to the phenazine part of the dipyridophenazine ligand, and its localization on this ligand moiety. Photochemical properties of [Ru(bipy)2(dppz)]2+ were studied in ethanol. The excited state of the complex is quenched both by an electron acceptor (methylviologen, kq= 1.37 × 109 dm3 mol–1 s–1) and an electron donor (triethanolamine, kq= 4.40 × 107 dm3 mol–1s–1).

Synthesis and co-ordination behaviour of 6′,6″-bis(2-pyridyl)-2,2′ : 4,4″ : 2″,2″′-quaterpyridine; ‘back-to-back’ 2,2′ : 6′,2″-terpyridine

Abstract: The oligopyridine 6′,6″-bis(2-pyridyl)2,2′ : 4,4″ : 2″,2″′-quaterpyridine (L) has been prepared. It may be regarded as a ‘back-to-back’ analogue of the well known 2,2′ : 6′2″-terpyridine (terpy). Complexes with ruthenium(II) and palladium(II) have been characterised. The diruthenium(II) complex cation [(terpy)RuLRu(terpy)]4+ has been shown to exhibit no Ru–Ru interactions, and behaves as two non-interacting Ru(terpy)2 units.

Spectroscopy and redox properties of the luminescent excited state of [Au2(dppm)2]2+ (dppm = Ph2PCH2PPh2)

Abstract: The electronic absorption spectrum of [Au2(dppm)2]2+[dppm = bis(diphenylphosphino)methane] in acetonitrile exhibits an absorption band at 290 nm, attributable to a pσâ†�dσ* transition. A much weaker band in the region 300–370 nm is assigned to a pσâ†�dδ* transition. Excitation of [Au2(dppm)2]2+ in degassed acetonitrile at 310–390 nm at room temperature results in phosphorescence centred at 575 nm, which is most likely to be derived from the 3B1u[(dδ*)1(pσ)1] state. The phosphorescence of [Au2(dppm)2]2+* is found to be quenched by a number of electron acceptors and donors, as well as energy-transfer acceptors. The powerful reducing nature of [Au2(dppm)2]2+* is revealed by its excited-state redox potential E°[Au2(dppm)23+/2+*] of –1.6(1) V vs. a saturated sodium chloride calomel electrode (s.s.c.e.) which was determined through studies of quenching by a series of pyridinium acceptors.

Cyclometallation reactions of 6-phenyl-2,2′-bipyridine; a potential C,N,N-donor analogue of 2,2′: 6′,2″-terpyridine. Crystal and molecular structure of dichlorobis(6-phenyl-2,2′-bipyridine)ruthenium(II)

Abstract: Metallated and non-metallated complexes of the ligand 6-phenyl-2,2′-bipyridine (HL) with ruthenium(II), rhodium(II), platinum(II), palladium(II), and gold(III) have been prepared. The crystal and molecular structure of the complex [Ru(HL)2Cl2][triclinic, a= 8.671(1), b= 10.360(2), c= 16.139(3)A, α= 89.18(2), β= 81.26(1), γ= 67.11 (1)°, direct methods, least-squares refinement and Fourier difference synthesis, R= 0.0310, R′= 0.0359] indicates that it contains two N-bonded ligands and a cis arrangement of the chlorides.

Novel luminescent polynuclear gold(I) phosphine complexes. Synthesis, spectroscopy, and X-ray crystal structure of [Au3(dmmp)2]3+[dmmp = bis(dimethylphosphinomethyl)methylphosphine]

Abstract: Reaction of K[AuCl4] with bis(dimethylphosphinomethyl)methylphosphine (dmmp) in the presence of thiodiglycol (2,2′-thiodiethanol) in methanol yielded [Au3(dmmp)2]3+, which was isolated as its perchlorate salt. The X-ray crystal structure of [Au3(dmmp)2][ClO4]3 has been determined: monoclinic, space group P21/n, a= 1 2.880(3), b= 14.210(1), c= 21.208(2)A, β= 106.25(1)°, Z= 4, R= 0.047 for 2 927 observed Mo-Kα data. The Au–Au–Au bond angle of 136.26(4)° is greatly distorted from rectilinear geometry, with intramolecular Au ⋯ Au distances of 2.981 (1) and 2.962(1)A. Excitation of a degassed acetonitrile solution of [Au3(dmmp)2]3+ at 300–370 nm resulted in dual phosphorescence (λ= 467 nm, τ0= 1.6 ± 0.2 µs; λ= 580 nm, τ0= 7.0 ± 0.5 µs). A comparison between the electronic absorption and emission spectra of [Au3(dmmp)2]3+ and [Au2(dmpm)2]2+[[dmpm = bis(dimethylphosphino)methane] has been made. The assignment of the lowest electronic excited state in the (P2Au)n system has been suggested to be 3[(dδ*)(pσ)]. The excited-state redox potentials of [Au3(dmmp)2]3+* and [Au2(dmpm)2]2+* have been determined through oxidative quenching experiments with a series of pyridinium acceptors of variable reduction potential.

Concept of the H(δ+)⋯ H(δ–) interaction. A low-temperature neutron diffraction study of cis-[IrH(OH)(PMe3)4]PF6

Abstract: The structure of the rare hydridohydroxy complex cis-[IrH(OH)(PMe3)4]PF6 has been analyzed at 20 K by single-crystal neutron diffraction. The results confirm the geometry derived from an earlier X-ray analysis. Perhaps the most significant result concerns the bending of the O–H group towards the hydride ligand, with a smaller-than-usual Ir–O–H angle of 104.4(7)°, suggestive of an attractive interaction between the electron-deficient H atom of the hydroxy group and the electronegative hydride ligand.

Oxidation reaction of [{Cu(Hpz)2Cl}2](Hpz = pyrazole): synthesis of the trinuclear copper(II) hydroxo complexes [Cu3(OH)(pz)3(Hpz)2Cl2]·solv (solv = H2O or tetrahydrofuran). Formation, magnetic properties, and X-ray crystal structure of [Cu3(OH)(pz)3(py)2Cl2]·py (py = pyridine)

Abstract: The trinuclear copper(II) complexes [Cu3(OH)(pz)3(Hpz)2Cl2]·solv (Hpz = pyrazole, pz = pyrazolate anion, solv = H2O or tetrahydrofuran) have been obtained by oxidation reactions of [{Cu(Hpz)2Cl}2]. When treated with pyridine(py), both CuII derivatives gave the related compound [Cu3(OH)(pz)3-(py)2Cl2]·py, which has been characterized by a single-crystal X-ray structure analysis. Crystals are orthorhombic, space group Pnma(no. 62), a= 19.883(3), b= 15.063(3), c= 9.495(2)A, Z= 4, R= 0.035 and R′= 0.041 for 1 472 absorption corrected reflections having I > 3σ(I).

Crystallographic characterization of the polyoxotungstate [Eu3(H2O)3(SbW9O33)(W5O18)3]18– and energy transfer in its crystalline lattices

Abstract: The potassium salt of the new mixed-polyoxotungstate anion [Eu3(H2O)3(SbW9O33)(W5O18)3]18–(1) has been prepared from WO3, Sb2O3, Eu(NO3)3·6H2O, and KOH in water and isolated in crystalline form as K15H3[Eu3(H2O)3(SbW9O33)(W5O18)3]·25.5 H2O. It crystallizes in the monoclinic space group C2/m, with a= 30.250(7), b= 18.568(5), c= 22.101 (6)A, β= 109.19(8)°, and Z= 4. A central Eu3(H2O)3 core is co-ordinated by a B-type α-SbW9O33 unit and three W5O18 units with tetrahedral conformation. Each Eu3+ in the core exhibits eight-co-ordination by oxygen atoms belonging to H2O, SbW9O33, and W5O18 units. The intramolecular energy transfer from the O→W charge-transfer levels for the polyoxotungstate crystalline lattices to the emitting 5D0 level of Eu3+ takes place efficiently at least over 6.9 A which is the largest distance between W and Eu atoms in the anion. A comparison of the lifetime and quantum yield of the emission among (1), [Eu(W5O18)2]9–, and [Eu(SiW11O39)2]13– indicates that the hopping of a d1 electron between WO6 octahedra is the predominant deactivation channel of the O→W charge-transfer levels, which reduces drastically the communication with the excited levels of Eu3+.

Ligand effects of ruthenium 2,2′-bipyridine and 1,10-phenanthroline complexes on the electrochemical reduction of CO2

Abstract: Electrochemical reduction of CO2catalysed by [RuL1(L2)(CO)2]2+[L1,L2=(bipy)2, (bipy)(dmbipy), (dmbipy)2, or (phen)2], [Ru(phen)2(CO)Cl]+(phen = 1,10-phenanthroline), and [RuL(CO)2Cl2][L = 2,2′-bipyridine (bipy) or 4,4′-dimethyl-2,2′-bipyridine (dmbipy)] were carried out by controlled-potential electrolysis at –1.30 V vs. saturated calomel electrode in acetonitrile–water (4 : 1, v/v), MeOH, or MeCN–MeOH (4 : 1, v/v). In acetonitrile–water (4 : 1, v/v) no difference in activities between the catalysts was observed, however in MeOH the amounts of carbon monoxide produced became larger than those of HCO2– upon introduction of the dmbipy ligand. This is attributed to the equilibrium constants among the reaction intermediates [RuL1(L2)(CO)2]2+, [RuL1(L2)(CO)-{C(O)OH}]+, and [RuL1(L2)(CO)(C02–)]+ which become smaller on substitution of bipy by dmbipy, because of the donor property of the CH3 group.

Crystal structure and electronic properties of dibromo- and dichloro-tetrakis[µ3-bis(2-pyridyl)amido]tricopper(II) hydrate

Abstract: The crystal structures of [Cu3(bipyam–H)4Cl2]·H2O (1) and [Cu3(bipyam–H)4Br2]·H2O (2) where bipyam–H = bis(2-pyridyl)amide, have been determined by X-ray analysis, in the orthorhrombic space group Pnn2: (1), a= 14.092(3), b= 12.895(3), (c)= 11.190(2)A, Z= 2, and R= 0.032 for 2 453 observed and 2 029 unique reflections; (2), a= 14.186(3), b= 13.040(3), c= 11.313(2)A, Z= 2, and R= 0.043 for 1 574 observed and 1 465 unique reflections. The two structures are isomorphous with near isostructural [Cu3(bipyam–H)4X2] units in special positions of two-fold symmetry and a non-co-ordinated water molecule. The Cu3N12X2 chromophores involve nearly linear Cu3 units, Cu–Cu–Cu 178.4°(mean), terminated by the two halide anions. The four separate bipyam–H ligands act as tridentate ligands, involving co-ordination to the three separate copper(II) ions, with Cu–Cu distances of 2.471(1) and 2.468(1)A, for (1) and (2), respectively. If the Cu–Cu separations are ignored, the central Cu atom in both structures involves a four-co-ordinate rhombic coplanar CuN4 chromophore generated by the central amido nitrogens of the four bipyam–H ligands. The two terminal Cu atoms involve a square-based pyramidal CuN4X chromophore, generated by the terminal pyridine nitrogens of the four bipyam–H ligands and an axial halide anion. An average dihedral angle of 48° is involved between the planes of the pyridine rings of the individual bipyam–H ligands, which results in a spiral configuration of the [Cu3(bipyam–H)4X2] units. The spin-only magnetic moment of complex (1) is ca. 1.40 B.M. per Cu atom, consistent with antiferromagnetic coupling between the copper(II) atoms of the trimer. Both complexes are e.s.r. silent, again consistent with strong antiferromagnetic coupling. The electronic spectra of (1) and (2) have a band maximum at 15 500 cm–1, with a high-energy shoulder at 19 230 cm–1, consistent with the two different stereochemistries present.

Synthesis and crystal structure of hexanuclear copper(I) complexes of µ3-pyridine-2-thionate

Abstract: 1H-Pyridine-2-thione (C2H4NSH) reacts with [Cu(MeCN)4]PF6 in acetone to give an orange compound [Cu6(C5H4NS)6], which crystallized in the monoclinic space group P21/n, a= 12.257(2), b= 16.029(2), c= 9.581 (1)A, β= 108.859(9)°, and Z= 2. The single-crystal X-ray structure of the complex shows a distorted octahedral core of six copper atoms, with metal–metal distances ranging from 2.795(1) to 3.160(1)A. Each copper has a trigonal geometry constituted by the two thiolate sulphur and one pyridine nitrogen atoms, as distinct from the common copper–thione sulphur co-ordination in other copper(I)–C5H4NSH complexes. The copper atom deviates highly from the S2N co-ordination plane. The reaction solution was examined by 1H n.m.r. spectroscopy, which reveals the formation of several low-molecular-weight species in the early stages of the reaction.

Gold complexes with heterocyclic thiones as ligands. X-Ray structure determination of [Au(C5H5NS)2]ClO4

Abstract: Displacement of the weakly co-ordinating tetrahydrothiophene (tht) ligand in [AuX(tht)], [Au(tht)2]ClO4, or [Au(PPh3)(tht)]ClO4(X = Cl or C6F5) by heterocyclic thiones HL (HL = C3H5NS2, C4H4N2S, C5H5NS, C7H5NS2, or C7H6N2S), leads to the formation of neutral or cationic complexes of the types [AuX(HL)], [Au(HL)2]ClO4, or [Au(PPh3)(HL)]ClO4. For gold(III) complexes the tht ligand cannot be displaced but [Au(C6F5)3(OEt2)] reacts with HL to give neutral complexes [AuR3(HL)]. Deprotonation of the NH unit in the cationic complexes leads to neutral monomeric complexes and since the deprotonated N atom is now a donor, binuclear complexes can be prepared by displacement of a weakly co-ordinating ligand from other suitable complexes. The structure of [Au(HL)2]ClO4(HL = C5H5NS) has been established by X-ray crystallography [space group P, a= 9.609(3), b= 15.024(6), c= 16.712(7)A, α= 97.52(4), β= 104.17(2), γ= 104.76(2)°, and R′= 0.045 for 5 499 unique observed reflections]. The cations are arranged in a way that is unprecedented for gold(I) compounds. Five of the six cations in the cell are linked by short Au ⋯ Au contacts (3.3 A) and the sixth cation is monomeric.

Polynuclear platinum-silver, -copper, and -gold acetylide complexes. Molecular structure of [Pt2Ag4(C≡CBut)8]

Abstract: Hexanuclear complexes [Pt2Ag4(CCR)8] [R = Ph (1) or But (2)] have been obtained by treating [PtCl2(tht)2] (tht = tetrahydrothiophene) with [Ag(CCR)]n(Pt/Ag 1 : 4). The complexes [Pt2M4(CCR)8] [M = Cu, R = Ph (3) or But (4); M = Au, R = But (5)] were obtained from [Pt2Ag4(CCR)8] with CuCl or [AuCl(tht)] respectively. Alternatively, the reactions between [NBu4]2[Pt(CCR)4] and AgClO4, CuCl–NaClO4, or [AuCl(tht)]–NaClO4 yield respectively complexes (1)–(5). The molecular structure of [Pt2Ag4(CCBut)8] has been determined by an X-ray diffraction study: monoclinic, space group C2 with a = 37.062(7), b = 12.0223(16), c = 20.459(3) A, β = 107.485(15)°, Z = 6, R 0.0416, R′ 0.0465 for 5 613 reflections with F > 6σ(F). The six metal atoms are arranged in a slightly irregular octahedron with the platinum atoms mutually trans and the silver atoms in the equatorial plane, with Pt ⋯ Ag and Ag ⋯ Ag distances longer than 3.0 A. Each platinum atom is in an almost square-planar environment formed by four CCBut ligands. Each acetylenic fragment also forms an asymmetric π interaction with one silver atom of the equatorial positions so that each silver atom is bonded to two acetylenic fragments, of two different Pt(CCBut), moieties. These moieties of each [Pt2Ag4(CCBut)8] unit are staggered.

Synthesis of intermediates in the C–H activation of acetone with 2-phenylazophenylgold(III) complexes and in the C–C coupling of aryl groups from diarylgold(III) complexes. Crystal and molecular structures of [Au{C6H3(NNC6H4Me-4′)-2-Me-5}(acac-C)Cl](acac = acetylacetonate), cis-[Au(C6H4NNPh-2)Cl2(PPh3)], and [Au(C6H4CH2NMe2-2)(C6F5)Cl]

Abstract: The complex [[graphic omitted]Ph-2)Cl2] reacts with [HgR2](R = C6H4NO2-2 or C6F5) and NMe4Cl (2 : 1 : 2) to give [[graphic omitted]Ph-2)(R)Cl][R = C6H4NO2-2, (1); or C6F5(2)]. Similarly, [[graphic omitted])Cl2](3)[C–N = C6H3(NNC6H4Me-4′)-2-Me-5], prepared by the reaction of [AuCl3(tht)](tht = tetrahydrothiophene) with [Hg(C–N)Cl] and NMe4Cl (1 : 1 : 1), reacts with Tl(acac)(Hacac =acetylacetone)(1 : 1) to give [[graphic omitted])(acac-C)Cl](4). Reaction of (2) with PPh3(1 : 1) leads to [[graphic omitted]Ph-2)(C6F5)Cl(PPh3)](5), which upon standing in dichloromethane solution decomposes to give a mixture of [Au(C6F5)(PPh3)], C6H4C6F5-1 -NNPh-2, and [Au(C6H4NNPh-2)Cl2(PPh3)](6). Crystal structures were determined for complexes (4), (6), and [[graphic omitted]Me2-2)(C6F5)Cl](7)[(4), space group P, a= 9.475(4), b= 9.923(4), c= 10.913(4)A, α= 63.75(3), β= 84.92(3), γ= 89.41 (3)°, Z= 2, R= 0.020 for 3 057 reflections at –95 °C; (6), space group P21/n, a= 10.361(3), b= 28.194(8), c= 10.724(4)A, β= 116.26(2)°, Z= 4, R= 0.038 for 3 734 reflections at 20 °C; (7), space group Pbca, a= 11.996(4), b= 14.484(4), c= 18.310(7)A, Z= 8, R= 0.045 for 1 909 reflections at 20 °C]. The three structures reveal neutral molecules with square-planar geometry around the gold atom. In complexes (4) and (7) the aryl groups act as chelating ligands, forming a five-membered ring [(4), Au–C 2.026(4), Au–N 2.158(3)A; (7), Au–C 2.022(10), Au–N 2.128(10), Au–C6F5 2.012(11)A] while in complex (6) the aryl group acts as a monodentate ligand [Au–C 2.033(5)A]. The chloro ligand in complex (4) is trans to the carbon atom of the aryl ligand [Au–Cl 2.349(2)A], and the acac ligand is C-bonded to the gold atom [Au–C 2.083(4)A]. This is one of the few isolated acetylacetonatogold(III) complexes and the first structurally characterized. In complex (6), chloro atoms are mutually cis[Au–Cl (trans to C) 2.377(2), (trans to N) 2.325(2)A]. The chloro ligand in complex (7) is trans to the aryl group of the chelating ligand [Au–Cl 2.347(3)A]. The isolation of complexes (1) and (2) and the observed geometry of (4) support the pathway suggested for the C–H activation of acetone with 2-phenylazophenylgold(III) complexes.

Detection of a new polymeric species formed through the hydrolysis of gallium(III) salt solutions

Abstract: A previously unreported gallium species has been detected which is formed by the hydrolysis of aqueous gallium(III) solutions. N.m.r. studies have shown that this species has a tetrahedrally co-ordinated gallium nucleus whose chemical shift suggests that it is structurally analogous to the central tetrahedral aluminium occurring in the [AlO4Al12(OH)24(H2O)12]7+ cation. The size of the polymeric gallium species was estimated by measuring the increase in the basal (d001) spacing of a montmorillonite upon intercalation. The hydrated height of the gallium polymer in its orientation relative to the phyllosilicate sheets was found to be approximately 9.4 A, which is about 5.6% larger than the size of the Al13 cationic unit, measured by the same method. This compares well with geometric calculations which show that a Ga13 cationic species would be expected to be about 5.7% larger than the analogous aluminium species. These results suggest strongly that a [GaO4Ga12(OH)24(H2O)12]7+ cation forms during the hydrolysis of gallium(III) solutions at a pH range of approximately 3–4. The reason why this species has not been previously reported may be related to the fact that it appears to be much less stable in solution than the analogous aluminium species, as revealed by n.m.r. evidence.

Weak charge-transfer polyoxoanion salts: the reaction of quinolin-8-ol (Hquin) with phosphotungstic acid and the crystal and molecular structure of [H2quin]3[PW12O40]·4EtOH·2H2O

Abstract: Different solvated charge-transfer salts between quinolin-8-ol (Hquin) and phosphotungstic acid have been synthesized and characterized. Spectroscopic data support the presence of a sizeable electronic interaction between electron-rich aromatic organics and the inorganic acid, both in the solid state and in solution, provided that a large excess of the organic is present. This interaction is responsible for the formation of photosensitive compounds and provides a rationale for the subsequent facile photo-oxidation of the organic substrate. The crystal and molecular structure of [H2quin]3[PW12O40]·4EtOH·2H2O has been solved by the heavy-atom method and refined to a final R= 0.083, for 4 902 reflections with I 3σ(I): triclinic space group P; with a= 11.721(3), b= 12.818(3), c= 12.878(3)A, α= 89.20(2), β= 104.10(2), γ= 117.30(2)°, and Z= 1. The anion structure consists of an α-Keggin-type molecule in two-fold disorder. The 8-hydroxyquinolinium moieties (three per [PW12O40]3–) are stacked approximately along the x direction, with alternative interplanar spacings of 3.25 and 3.57 A. The crystal structure determination reveals the absence of any substantial, direct interaction between the organic cations and the phosphototungstate anions. Therefore no clear structural basis for the electronic interaction noted above can be given.

Isolation, characterization, and kinetics of formation of the cis and trans isomers of bis(acetonitrile)dichloroplatinum(II)

Abstract: The bis(acetonitrile)dichloroplatinum(II) obtained by the standard procedure has been shown to be a mixture of the cis and trans isomers the composition of which depends upon the experimental conditions used. The pure isomers have been characterized by i.r. and 1H n.m.r. spectroscopy and the conditions for the preferential obtainment of each isomer have been explored. Kinetic measurements have shown that the formation of the cis isomer is kinetically favoured in the reaction of [PtCl3(NCMe)]– with a second molecule of acetonitrile, indicating that the chlorine ligand exerts a trans-labilizing effect greater than that of acetonitrile.

Comparison of the hydrolyses of gallium(III) and aluminium(III) solutions by nuclear magnetic resonance spectroscopy

Abstract: A quantitative 71Ga n.m.r. study of the base hydrolysis of gallium(III) salt solutions has been undertaken. The resulting spectra were very similar to the 27Al n.m.r. spectra obtained for aluminium solutions hydrolysed under analogous conditions. No evidence was observed of any species different from those seen for aluminium, despite the fact that the eventual outcomes of the hydrolyses are different, i.e. precipitation of an oxyhydroxide of diaspore structure in the case of gallium, and the eventual formation of a gibbsite hydroxide phase in the case of aluminium. For aluminium, the formation of the [AlO4Al12(OH)24(H2O)12]7+ tridecamer is well known, and the formation of an analogous species for gallium has also been proposed. Although the 71Ga n.m.r. studies undertaken herein appear to show that much less of the gallium polyoxycation is formed than is the case for aluminium, clay mineral pillaring studies have suggested that this apparent difference is not real. Through consideration of both the extremely broad nature of the tetrahedral gallium peak and the high quadrupole moment of the 71Ga nucleus, it is proposed that the gallium tridecamer is much more distorted than the aluminium species, and that the integrated area of the n.m.r. peak assigned to this species does not accurately represent the amount actually present in solution.

Linear co-ordinative bonding at oxygen: a spectroscopic and structural study of phosphine oxide-Group 13 Lewis acid adducts

Abstract: A number of adducts composed of phosphine oxides and Group 13 Lewis acids R3PO·EX3(R = Ph, NMe2, or PhO; E = B, Al, or Ga; X = F, Cl, or Br) have been spectroscopically characterised by multinuclear n.m.r. spectroscopy. Three isostructural derivatives have been structurally characterised by X-ray crystallography. Crystal data (all hexagonal, space group 3, Z= 6): Ph3PO·AlCl3, a= 13.663(2), c= 18.258(2)A, R= 0.062; Ph3PO·AlBr3, a= 14.021 (6), c= 18.387(3)A, R= 0.041; Ph3PO·GaCl3, a= 13.753(6), c= 18.345(6)A, R= 0.079. The structures show a uniquely linear or almost linear P–O–E backbone, which lies on the three-fold axis, in contrast to the bent structures observed for the corresponding BF3 adducts and other related systems. Short Al–O bonds [X = Cl, 1.733(4); Br, 1.736(7)A] are observed in both aluminium derivatives (E = Al). These compounds have narrow lines in the solution 27Al n.m.r. spectra, indicative of a highly symmetric environment for the aluminium centre, and consistent with a linear geometry in solution. The results provide experimental evidence for axially symmetric dative bonding by oxygen, support the triple-bond model for the phosphine oxide unit, and imply the possibility of a delocalised π interaction over the P–O–E framework.

A study of the comparative donor properties to CuII of the terminal amino and imidazole nitrogens in peptides

Abstract: The synthesis of the tetrapeptides Ala-Gly-Gly-His, Boc-Ala-Gly-Gly-His (Boc = t-butoxycarbonyl), Ala-Gly-Gly-His(π-bom)(π-bom =Nπ-benzoxymethyl), Ala-Gly-Gly-His-OMe, and Ala-Gly-Pro-His is reported, together with the results of a pH-metric and spectroscopic (absorption, c.d., and e.s.r.) study of their complexes with H+ and CuII. The work was designed to study the initial site of binding to CuII in peptides containing both a terminal amino nitrogen and a histidyl residue. Results show that the π-N of the imidazole ring of the histidyl residue is the primary anchoring site for copper(II) co-ordination, and that the next nitrogen to bond can be the terminal amino N, forming a macrocyclic chelate ring.

A convenient preparation of 2,2′:6′,2″:6″,2‴-quaterpyridine; the crystal and molecular structures of 2,2′:6′,2″:6″,2‴-quaterpyridine and bis(acetonitrile)-(2,2′:6′,2″:6″,2‴-quaterpyridine)nickel(II) hexafluorophosphate–acetonitrile(1/1)

Abstract: 2,2′:6′,2″:6″,2‴-Quaterpyridine has been prepared in 40–45% yield by the nickel(0) coupling of a 6-halogeno-2,2′-bipyridine. The reaction initially yields a nickel(II) complex of 2,2′:6′, 2′:6″,2‴-quaterpyridine which may be demetallated by treatment with NaCN. The crystal and molecular structures of 2,2′:6′,2″:6″,2‴-quaterpyridine [monoclinic, a= 6.348(1), b= 8.179(2), c= 14.894(3)A, β= 100.15(1)°, space group P21/n, Z= 2] and bis(acetonitrile)-(2,2′:6′,2″:6″,2‴-quaterpyridine)nickel(II) hexafluorophosphate-acetonitrile (1/1)[monoclinic, a= 22.348(9), b= 11.504(5), c= 15.636(6)A, β= 128.41 (2)°, space group C2/c, Z= 4] have been determined. The free ligand is essentially planar with transoid arrangements of the pyridyl rings as observed in 2,2′-bipyridine. The nickel complex is approximately octahedral with the 2,2′:6′,2″:6″,2‴-quaterpyridine occupying the equatorial sites; the Ni–N distances to the terminal pyridine rings are longer than those to the inner rings.

cis- and trans-Dichloro-derivatives of six- and seven-co-ordinate zirconium and hafnium bonded to quadridentate Schiff-base ligands. Crystal structures of [Zr(acen)Cl2(thf)], [M(salphen)Cl2(thf)]·0.5thf, [M(acen)Cl2], (M = Zr or Hf), and [Zr(msal)Cl2][acen =N,N′-ethylenebis(acetylacetoneiminate), salphen =N,N′-o-phenylenebis(salicylideneiminate), msal =N-methylsalicylideneiminate, and thf = tetrahydrofuran]

Abstract: The reaction of MCl4·2thf (thf = tetrahydrofuran) with the sodium salt of quadridentate Schiff bases [L =N,N′-ethylenebis(acetylacetoneiminate)(acen), N,N′-ethylenebis(salicylideneiminate)(salen), N,N′-ethylenebis(α-methylsalicylideneiminate)(dmsalen), or N,N′-o-phenylenebis(salicylideneiminate)(salphen)] yields the complexes [MLCl2(thf)]. X-Ray analyses showed for all of them that the metal ion is seven-co-ordinate with a pseudo-pentagonal bipyramidal geometry. Details of the structures of [Zr(acen)Cl2(thf)](5), [Zr(salphen)Cl2(thf)]·0.5thf (10), and of the corresponding isostructural hafnium complex [Hf(salphen) Cl2(thf)]·0.5thf (11) are reported. The equatorial plane of the bipyramid is defined by the N2O2 donor atoms and by the oxygen atom from thf, while the two chlorine atoms are trans to each other [Cl–Zr–Cl 169.1 (1), (5); 165.2(1), (10); Cl–Hf–Cl 166.3(1)°, (11)]. Recrystallization of the seven-co-ordinate complexes from toluene removed the thf leading to six-co-ordinate complexes. The structural determination of the isostructural [Zr(acen)Cl2](12) and [Hf(acen)Cl2](13) showed the six-co-ordination of the metal with the two chlorines assuming a cis arrangement [Cl–Zr–Cl 87.2(1), (12); Cl–Hf–Cl 87.4(1)°, (13)]. Bond lengths within the co-ordination sphere are significantly shorter in the six-co-ordinate complexes. The cis and trans isomers do not interconvert in solutions of non-co-ordinating solvents, i.e. C6H6 or CH2Cl2, as shown by their distinctive 1H n.m.r. spectra. In the absence of geometrical constraints zirconium(IV) prefers six-co-ordination and a cis arrangement of the chloride ligands. This was confirmed by synthesizing [Zr(msal)2Cl2](15)(msal =N-methylsalicylideneiminate), [Cl–Zr–Cl 97.9(1)°] containing a bidentate Schiff-base ligand. Its crystallization from thf gave the unsolvated six-co-ordinated form. Crystallographic details: complex (5), space group P, a= 8.401 (1), b= 15.987 (2), c= 7.805(1)A, α= 98.41 (1), β= 90.32(1), γ= 76.65(1)°, Z= 2, and R 0.042 for 3 713 observed reflections; (10), space group P, a= 12.759(2), b= 13.332(2), c= 7.587(1)A, α= 91.60(2), β= 98.45(1), γ= 85.30(1)°, Z= 2, and R 0.033 for 3 813 observed reflections; (11), space group P, a= 12.737(7), b= 13.269(7), c= 7.564(4)A, α= 91.48(1), β= 98.56(1), γ= 85.26(1)°Z= 2, and R 0.027 for 4 227 observed reflections; (12), space group P21/n, a= 24.150(5), b= 9.160(2), c= 7.282(1)A, β= 90.90(1)°, Z= 4, and R 0.034 for 1 894 observed reflections; (13), space group P21/n, a= 24.096(10), b= 9.161 (4), c= 7.262(3)A, β= 90.87(1)°, Z= 4, and R 0.024 for 2 124 observed reflections; (15), space group P, a= 13.024(3), b= 14.522(3), c= 9.797(2)A, α= 90.10(1), β= 93.14(1), γ= 96.09(1)°, Z= 4, and R 0.044 for 3 294 observed reflections.

Crystal structures and physical properties of bis(ethylenedithio)-tetrathiafulvalene charge-transfer salts with FeX4–(X = Cl or Br) anions

Abstract: Two new charge-transfer salts [bettf]2[FeCl4](1) and [bettf][FeBr4](2) have been prepared and crystallised electrochemically [bettf = bis(ethylenedithio)tetrathiafulvalene]. The crystal structures of both salts have been refined in the P space group, the unit-cell parameters being: (1), a= 6.626(2), b= 15.025(2), c= 17.805(2), α= 82.80(2), β= 89.53(2), γ= 88.15(2), Z= 2, R= 0.044; (2), a= 8.634(2), b= 10.980(2), c= 11.773(2), A, α= 91.91(2), β= 102.84(2), γ= 93.73(2), Z= 2, R= 0.054. The structure of (1) consists of stacks of dimerised bettf molecules with short ⋯ contacts, forming layers separated by sheets of FeCl4–. In (2) there are no stacks of bettf molecules: the structure consists of discrete dimers separated by FeBr4–. Compound (1) shows semi-conducting behaviour from 160 to 300 K with Iµa= 0.21 eV and σ≈ 10–2 S cm–1 at 300 K while (2) is a quasi-insulator at room temperature with σ≈ 10–6 S cm–1. The magnetic susceptibility of both salts from 5 to 300 K is dominated by the S=5//2 Fe3+ with small Weiss constants [–6(1) for (1) and –5(1 )K for (2)].

Synthesis of the WW triply bonded dimers [W2(η-C5H4R)2X4](X = Cl, R = Me or Pri; X = Br, R = Pri) and X-ray crystal structures of [W(η-C5H4Pri)Cl4] and [W2(η-C5H4Pri)2Cl4]

Abstract: The syntheses of the WW triply bonded species [W2(η-C5H4R)2X4](X = Cl, R = Me or Pri; X = Br, R = Pri) and of their singly bonded congeners [Mo2(η-C5H4R)2(µ-X)4](X = Cl, R = Me or Pri; X = Br, R = Me) are reported along with X-ray crystal-structure determinations of [W(η-C5H4Pri)Cl4] and [W2(η-C5H4Pri)2Cl4]. The molecular structure of [W2(η-C5H4Pri)2Cl4] consists of two mutually trans W(η-C5H4Pri)Cl2 units linked by an unsupported WW triple bond [WW 2.367 8(6)A].

Manganese(II) and iron(III) complexes of the tridentate ligands bis(benzimidazol-2-ylmethyl)-amine (L1) and -methylamine (L2). Crystal structures of [MnL1(CH3CO2)2], [FeL2Cl3], and [Fe2L12(µ-O){µ-(CH3)3CCO2}2][ClO4]2

Abstract: The preparation and characterisation of [MnL1(CH3CO2)2](1), [Mn6(µ4-O)2(C6H5CO2)10(H2O)4](9), [FeL1Cl3](10), [FeL2Cl3](2), and [Fe2L12(µ-O){µ-(CH3)3CCO2}2][ClO4]2(3) are reported where L1 and L2 are bis(benzimidazol-2-ylmethyl)amine and bis(benzimidazol-2-ylmethyl)methylamine. The molecular structures of (1), (2), and (3) were determined by X-ray diffraction. Complex (1) exists as a discrete, neutral, mononuclear species in the solid state. The manganese(II) ion is five-co-ordinate with the tridentate ligand bound in a meridional manner. Both acetates are monodentate with Mn–O distances of 2.076(5) and 2.158(5)A. Complex (9) contains a [Mn6(µ-O)2]10+ core, formally 4MnII :2MnIII. Complex (2) is neutral, mononuclear, distorted octahedral. The ligand co-ordinates in a similar manner to that seen in (1) and the chlorides occupy the three remaining meridional sites, with Fe–Cl(equatorial) 2.318(5)A and Fe–Cl(axial) 2.322(5) and 2.433(5)A. The Mossbauer spectrum of (10) at room temperature comprises a quadrupole doublet: δ= 0.40(1), ΔEQ= 0.33(2) mm s–1. Complex (3) is a dinuclear iron(III) species containing the triply bridged [Fe2(µ-O)(µ-RCO2)2]2+ core. The Fe ⋯ Fe distance is 3.075(5)A and the Fe–O(oxo)–Fe angle is 117.0(6)°. The high-spin iron(III) centres are antiferromagnetically coupled with J=–116 cm–1. The Mossbauer spectra of (3) at room temperature and 70 K consist of doublets with δ= 0.44(1), ΔEQ= 1.37(2), and δ= 0.55(1), ΔEQ= 1.30(2) mm s–1 respectively.

Polyhedral metallacarbaborane chemistry: preparation, molecular structure, and nuclear magnetic resonance investigation of [3-(η5-C5Me5)-closo-3,1,2-MC2B9H11] (M = Rh or Ir)

Abstract: Reaction between Cs[nido-7,8-C2B9H11] and [{M(η5-C5Me5)Cl2}2] (M = Rh or Ir) yielded orange-yellow, air-stable crystals of [3-(η5-C5Me5)-closo-3,1,2-RhC2B9H11] [compound (2), 34%] or [3-(η5-C5Me5)-closo-3,1,2-IrC2B9H11] [compound (3), 96%] both of which were characterized by their assigned 11B and 1H n.m.r. spectra and by single-crystal X-ray diffraction analyses. Crystals of (2) were orthorhombic, space group P212121, with a = 1 081.0(2), b = 1 278.2(1), c = 1 278.4(2) pm, and Z = 4; R = 0.0197, R′ = 0.0204 for 1 756 observed reflections [I > 2.0σ(I)]. Crystals of (3) were also orthorhombic, space group P212121, with a = 1 076.3(1), b = 1 282.9(1), c = 1 292.8(2) pm, and Z = 4; R = 0.0286, R′ = 0.0307, for 1 712 observed reflections [I > 2.0σ(I)]. The n.m.r. properties of the C2B9H11 fragments of (2) and (3) are compared with the 11B and hitherto unreported 1H n.m.r. characteristics of the corresponding fragments of [3-(η5-C5H5)-closo-3,1,2-CoC2B9H11] (4), closo-1,2-C2B10H12, nido-7,8-C2B9H13, and [nido-7,8-C2B9H12]−, in order to assess any n.m.r. shielding patterns that might reveal bonding trends. The unique endo/bridging open-face hydrogen atom in [nido-7,8-C2B9H12]− is discussed in the light of its n.m.r. properties.

Manganese(III) complexes of 1,2-bis(2-pyridinecarboxamido)benzene: synthesis, spectra, and electrochemistry

Abstract: The synthesis and solution properties of the high-spin (µeff.= 4.78–4.86 at 298 K) manganese(III) complexes [Mn(bpb)X][X = Cl–, N3–, or SCN–; H2bpb = 1,2-bis(2-pyridinecarboxamido)benzene], are described. The brown crystalline complexes display ligand-to-metal charge-transfer transitions at ca. 430 nm, while in the near-infrared region crystal-field transitions are observed. In N,N-dimethylformamide solution the complexes exhibit a quasi-reversible MnIII–MnII couple [E298°–0.03 to + 0.03 V vs. saturated calomel electrode (s.c.e.)]. The complexes [Mn(bpb)Cl] and [Mn(bpb)(N3)] display an additional quasi-reversible MnIV–MnIII couple [E298°+0.87 (Cl–); + 0.49 V (N3–)vs. s.c.e.].

Macrocyclic complexes with lanthanoid salts part 38. Synthesis and luminescence study of homo- and hetero-binuclear complexes of lanthanides with a new cyclic compartmental Schiff base

Abstract: Homo- and hetero-binuclear lanthanide(III) complexes with the macrocyclic ligand H2L1 derived from the condensation of 4-chloro-2,6-diformylphenol and the polyamine NH2(CH2)2O(CH2)2O(CH2)2NH2 have been synthesized: [Ln2L1(NO3)4]·nH2O (Ln = La, Pr, Sm, Eu, Gd, Tb, or Dy; n= 1 or 2) and [LnxLn′2 –xL1(NO3)4]·nH2O (Ln,Ln′= La,Sm; La,Gd; La,Dy; La,Eu; Dy,Gd; Dy,Eu; Gd,Eu; Gd,Tb; Eu,Tb; or La,Tb; n= 1 or 2). Their possible structure and the interaction between the metal ions are discussed on the basis of spectroscopic, mass spectrometric, and magnetic data together with scanning electron microprobe analyses. Electron microscopy with X-ray fluorescence analysis as well as magnetic susceptibility measurements suggest that the complexes containing two different lanthanide ions may be truly heterobinuclear, with the two metal centres lying at a long distance from each other and not connected by any bridging heteroatoms. Laser-excited luminescence spectra and lifetimes also point to the presence of heterobinuclear species. The yield of the TbIII to EuIII energy transfer was quantified and the intermetallic distance evaluated.

Synthesis, structure, and spectral and magnetic properties of trinuclear copper(II) complexes bridged by glyoximate groups

Abstract: Copper(II) complexes of composition Cu3L2L′2(ClO4)2 or Cu3L2L′2(CH3OH)2(NO3)2 were obtained where L = dimethylglyoximate (dmg), diphenylglyoximate (dpg), or o-benzoquinone dioximate (bqd) dianion, L′= 2,2′-bipyridyl (bipy) or 1,10-phenanthroline (phen). The crystal structures of Cu3(dmg)2(bipy)2(CH3OH)2(NO3)2 and Cu3(dpg)2(bipy)2(CH3OH)2(NO3)2 were solved by the single-crystal X-ray method. Both have an essentially similar trinuclear structure where the [CuL2]2– dianion functions as a bridge between two copper(II) ions through its deprotonated oximate oxygens. The configuration around the central copper (with two L2– ions) is an elongated octahedron with two NO3– ions above and below the [CuL2]2–. The configuration around the terminal copper is a square pyramid with two nitrogens of bipy and two oxygens of oximate groups in the basal plane and the methanol oxygen at the apical site. Cryomagnetic investigations (80–300 K) revealed the operation of a very strong antiferromagnetic spin exchange through the oximate bridges, causing complete or nearly complete spin coupling even at room temperature. Exchange integrals (–J) larger than 300 cm–1 were evaluated for all the complexes. Based on e.s.r. spectra in methanol, it is suggested that the unpaired electron is localized on the terminal copper atom. The complexes dimerized in dimethylformamide, especially at a low temperature, and their frozen solutions each showed an e.s.r. spectrum typical of the spin-triplet state.

Copper(II) complexes with anti-inflammatory drugs as ligands. Molecular and crystal structures of bis(dimethyl sulphoxide)tetrakis(6-methoxy-α-methyl-2-naphthaleneacetato)dicopper(II) and bis(dimethyl sulphoxide)tetrakis[1-methyl-5-(p-toluoyl)-1H-pyrrole-2-acetato]dicopper(II)

Abstract: The copper complexes of tolmetin [1-methyl-5-(p-toluoyl)-1H-pyrrole-2-acetic acid (HL1)], ibuprofen [α-methyl-4-(isopropylmethyl)benzeneacetic acid (HL2)], and naproxen [6-methoxy-α-methyl-2-naphthaleneacetic acid (HL3)], common anti-inflammatory drugs were prepared and characterized. The available evidence supports a dimeric structure for the dimethyl sulphoxide (dmso) adducts and monomeric for the pyridine analogues. The e.s.r. spectra of the powdered solids are consistent with spin S= 1 and g values for dimers, g∥= 2.38 and g⊥= 2.07. The crystal structures of [Cu2L14(dmso)2] and [Cu2L34(dmso)2] have been determined and refined by least-squares methods using three-dimensional Mo-Kα data. The complex [Cu2L14(dmso)2] crystallizes in space group P in a cell of dimensions a= 9.008(2), b= 12.902(4), c= 14.446(4)A, α= 97.98(2), β= 81.52(2), and γ= 108.94(2)°. The Cu ⋯ Cu separation was 2.662(1)A. The complex [Cu2L34(dmso)2] crystallizes in space group P21 in a cell of dimensions a= 17.166(2), b= 10.518(2), c= 18.184(3)A, and β= 118.69(1)°. The Cu ⋯ Cu separation was 2.629 (1)A.