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Publisher Summary The multi-metallic coordination of organic molecules at clusters facilitates substrate transformations not readily achievable at mononuclear complexes. The aggregation of metal atoms within a metal cluster core can afford molecules with a large number of accessible oxidation states which may have the potential to function as electron reservoirs. A significant number of mixed-metal clusters contain metals from the same group or adjacent groups, but far fewer mixed-metal clusters incorporating disparate metals have been reported. The presence of differing metals introduces the possibility of metallo-selectivity into ligand substitution. This selectivity should be enhanced upon accentuating the disparity between the metals. The introduction of differing metals into a cluster core also reduces the effective symmetry over that of related homo-metallic clusters, rendering coordination sites for incoming ligands inequivalent and affording the prospect of site- as well as metallo-selectivity.

Publisher Summary The multi-metallic coordination of organic molecules at clusters facilitates substrate transformations not readily achievable at mononuclear complexes. The aggregation of metal atoms within a metal cluster core can afford molecules with a large number of accessible oxidation states which may have the potential to function as electron reservoirs. A significant number of mixed-metal clusters contain metals from the same group or adjacent groups, but far fewer mixed-metal clusters incorporating disparate metals have been reported. The presence of differing metals introduces the possibility of metallo-selectivity into ligand substitution. This selectivity should be enhanced upon accentuating the disparity between the metals. The introduction of differing metals into a cluster core also reduces the effective symmetry over that of related homo-metallic clusters, rendering coordination sites for incoming ligands inequivalent and affording the prospect of site- as well as metallo-selectivity.

The quadrupolar ruthenium alkynyl cruciform complex is reversibly converted to tetravinylidene complex or tetraruthenium(III) tetracationic complex forms by protonation or oxidation, respectively; linear and nonlinear proto- and electrochromism studies reveal independent switching of NLO properties by the protic and electrochemical stimuli, respectively, aspects of which have been rationalized by theoretical studies.

The title compound, [Ru(C12H7Br2N2)2(CO)2], possesses a distorted octa­hedral environment about the Ru atom, with two cyclo­metallated 4,4′-dibromo­azobenzene ligands and two mutually cis carbonyl ligands. The donor atoms are arranged such that the N atoms are respectively trans to a carbonyl ligand and an aryl C atom.

The title compound, [Ru(C12H7Br2N2)2(CO)2], possesses a distorted octa­hedral environment about the Ru atom, with two cyclo­metallated 4,4′-dibromo­azobenzene ligands and two mutually cis carbonyl ligands. The donor atoms are arranged such that the N atoms are mutually trans and the aryl C atoms are trans to carbonyl ligands.

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Hyper-Rayleigh scattering is used to investigate the nonlinear optical properties of novel organometallic compounds. For a series of ruthenium and gold y-arylacetylides, including some bimetallic complexes, the influence of the organometallic donor group, chain length and type of acceptor on the quadratic hyperpolarizability is studied. The hyperpolanzabiities found are among the highest (1027 esu) known for organometallic compounds. Moreover, electric-field induced second-harmonic generation confirms these values and indicates that only one major tensor component is present. Keywords: hyper-Rayleigh scattering, nonlinear optics, second-harmonic generation, organometallic compounds

The dispersion of cubic nonlinearity in the organometallic dendrimer 1,3,5-(3,5-{trans-[(dppe)2(4-O2NC6H4CC)RuCC]}2C6H3CCC6H4-4-CC)3C6H3 can be understood in terms of an interplay of two-photon absorption and absorption saturation. Simple dispersion relations reproduce the behavior of both the real and imaginary components of the hyperpolarizability.

The title compound, [RuCl(C25H22P2)2(H2O)]PF6·1.73CH4O, contains a pseudo-octahedral ruthenium complex cation with two bidentate diphosphine ligands and cis-disposed chloro and aqua ligands, together with a disordered hexa­fluoro­phosphate anion and disordered methanol solvent mol­ecules. Identification as an aqua­ruthenium(II) complex rather than a hydroxo­ruthenium(III) complex was confirmed by cyclic voltammetry.

Seed-catalyzed, heteroepitaxial growth of high aspect-ratio, uniform ZnSe nanowires is reported, in which Ag2Se nanoparticles serve as heterogeneous seeds and as epitaxial substrates. Due to the difference in solubility product constants (Ksp: Ag2Se ≪ ZnSe), Ag2Se is precipitated before ZnSe and in situ seeds and catalyzes the nanowire growth in a one-pot solution synthesis. The lattice match between metastable tetragonal Ag2Se{212} and cubic ZnSe{220} planes facilitates the heteroepitaxial growth of ZnSe nanowires. Conversion of small, uniform Ag particles, which are produced from the reduction of Ag+ ions by reductants/surfactants such as polyvinyl pyrrolidone (PVP) and oleylamine (OA), into Ag2Se with small size and high uniformity is shown to be an effective strategy to control the diameter size and distribution of ZnSe nanowires. The third-order nonlinear optical behavior of the as-prepared nanowires has been evaluated by Z-scan measurements.

The alkynes HC≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2 (4) and HC≡CC6H4-4-C≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2 (6) and gold alkynyl complexes Au{C≡CC6H2-2,5-(OEt)2-4-C≡CC6H4-4-NO2}(PPh3) (7), Au(C≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2)(PPh3) (8), and Au(C≡CC6H4-4-C≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2)(PPh3) (9) have been synthesized. The linear optical properties and quadratic optical non-linearities of 7–9 have been measured, the latter by hyper-Rayleigh scattering at 1064 nm, and compared with data for the previously reported complexes Au(C≡CC6H4-4-NO2)(PPh3) (10) and Au(C≡CC6H4-4-C≡CC6H4-4-NO2)(PPh3) (11). The optical absorption maximum red-shifts and the first hyperpolarizabilities increase on π-system lengthening and on introduction of electron-releasing substituents on the π-bridge ring adjacent to the metal centre. The cubic non-linear optical properties of 1,4-{(PCy3)Au(C≡C)}2C6H4 (12) and {(PCy3)Au(C≡C-4-C6H4C≡C)}6C6 (13) have been assessed by wide spectroscopic range femtosecond Z-scan studies; the maximal values of the imaginary component and the effective two-photon absorption cross-section increase markedly on proceeding from linear complex 12 to 6-fold-symmetric complex 13, an increase that is maintained when data are scaled by relative molecular weight.

Reactions of hexamethylenetetramine (hmt) and AgSCN in different solvents generated three distinct [AgSCN]n-based coordination polymers (CPs): [Ag(1,3-μ2-SCN)(μ2-hmt)]n (1), {[Ag(1,1,3-μ3-SCN)]2(μ2-hmt)}n (2) and [Ag(1,1,3-μ3-SCN)(μ4-hmt)0.5]n (3). The identities of the coordination polymers (CPs) 1–3 have been unambiguously established by elemental analysis, IR, UV-vis spectra and single-crystal X-ray diffraction studies. Interestingly, 1 displays a two-dimensional (2D) (4,4) network involving one-dimensional (1D) zigzag [Ag(1,3-μ2-SCN)]n chains bridged by μ2-hmt linkers. 2 and 3 are novel 2D and three-dimensional (3D) supramolecular isomers: 2 presents an unusual 2D threaded-loop type (3,4)-connected {(3·4·5)(52·7)}{(3·4·53·63·72)(3·54·63·72)} network containing puckered [Ag(1,1,3-μ3-SCN)]n networks linked by μ2-hmt bridges, while 3 exhibits a unique 3D pillared-layer (3,4,6)-connected (4·62)(66)2(42·610·83) framework in which the undulating [Ag(1,1,3-μ3-SCN)]n layers are supported by μ4-hmt pillars. 1–3 all possess good third-order nonlinear optical (NLO) properties. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations have afforded insight into the electronic transitions and spectral characterization of these functionalized NLO molecular materials.

The cubic hyperpolarizabilities of 1,3,5-(trans-[RuCl(dppe)2(C≡CC6H4-4-C≡C)])3C6H3 (1), 1,3,5-(trans-[Ru(C≡CPh)(dppe)2(C≡CC6H4-4-C≡C)])3C6H3 (2), 1,3,5-(trans-[Ru(C≡CC6H4-4-NO2)(dppe)2(C≡CC6H4-4-C≡C)])3C6H3 (3), 1,3,5-{trans-[Ru(C≡C-3,5-(trans-[Ru(C≡CPh)(dppe)2(C≡CC6H4-4-C≡C)])2C6H3)(dppe)2(C≡CC6H4-4-C≡C)]}3C6H3 (4), and 1,3,5-{trans-[Ru(C≡C-3,5-(trans-[Ru(C≡CC6H4-4-NO2)(dppe)2(C≡CC6H4-4-C≡C)])2C6H3)(dppe)2(C≡CC6H4-4-C≡C)]}3C6H3 (5) have been assessed over the spectral range 520–1600 nm using the Z-scan technique and ~150 fs pulses. All complexes exhibit negative values of γreal (corresponding to self-defocusing behaviour) and significant positive values of γimag (corresponding to two-photon absorption) at short wavelengths (up to 1000 nm). The maximal values of γreal and γimag increase in magnitude on dendrimer generation increase (proceeding from 2 to 4 or 3 to 5). The open-aperture Z-scan results have been used to confirm and contrast the two-photon (2PA) and three-photon absorption (3PA) behaviour of 1–5, the data being consistent with the existence of 2PA at the short wavelength range, but with significant 3PA at longer wavelengths for 1–3 and 5, a record 3PA coefficient for an inorganic complex for 5 at 1180 nm, and appreciable 3PA at the telecommunications wavelength of 1300 nm.

The title compound, deca­carbonyl-1κ2C,2κ2C,3κ3C,4κ3C-bis­[1,2(η5)-methyl­cyclo­pentadienyl]-tetrahedro-ditungsten­diirid­ium, [W2Ir2(C6H7)2(CO)10], is a mixed-metal cluster with tetrahedral metal-core geometry. The W atoms are each ligated by a η5-methyl­cyclo­penta­dienyl ligand and two carbonyl ligands, and the Ir atoms are each ligated by three carbonyl ligands.

The title compound, octa­carbonyl-μ-di­phenyl­acetyl­ene-bis(η5-methyl­cyclo­penta­dienyl)­diiridium­ditungsten, W2Ir2(μ4-η2-C2Ph2)(μ-CO)4(CO)4(η-C5H4Me)2 or [W2Ir2(C6H7)2(C14H10)(CO)8], is a mixed-metal cluster with a butterfly metal core geometry, W atoms at the wing-tip sites and Ir atoms at the hinge positions. A di­phenyl­acetyl­ene ligand is μ4-η2-coordinated with the C—C bond parallel to the Ir—Ir vector, completing a pseudo-octahedral W2Ir2C2 unit. The W atoms are each ligated by a methyl­cyclo­penta­dienyl ligand, and the Ir atoms are each ligated by two terminal carbonyls, with the coordination completed by four bridging carbonyls, each of which lies across a W—Ir linkage.

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In the cation of the title complex, cis,cis,cis-[Ru(η2-O2CMe)(dppe)2]PF6·2MeOH [dppe is 1,2-bis­(di­phenyl­phosphino)­ethane, C26H24P2], the Ru atom is in a pseudo-octahedral coordination environment with two chelating dppe ligands and one chelating acetate ligand. Intra-phosphine and intra-acetate bond lengths and angles are unexceptional. Deviations from idealized octahedral coordination angles at ruthenium [O—Ru—O 59.43 (8)° and P—Ru—P 103.19 (2)°] presumably derive from constraints imposed by the chelate rings. The Ru—P distances for the mutually trans P-donor atoms [2.3785 (6) A] are significantly longer than those for the Ru—P linkages trans to the acetate ligand [2.3074 (6) A]. The Ru1, C1 and C2 atoms lie on a twofold axis, and atom P3 of the anion lies on an inversion centre.

Department of Chemistry, Australian National UniVersityCanberra, ACT 0200, AustraliaPhotonics CooperatiVe Research Centre, Laser Physics CentreResearch School of Physical Sciences and EngineeringAustralian National UniVersityCanberra, ACT 0200, AustraliaFrontier Research ProgramThe Institute of Physical and Chemical Research (RIKEN)Hirosawa 2-1, Wako-shiSaitama 351-01, JapanCentre for Research on Molecular Electronics and PhotonicsLaboratory of Chemical and Biological DynamicsUniVersity of LeuVen, Celestijnenlaan 200DB-3001 LeuVen, BelgiumReceiVed August 18, 1998There has been considerable interest recently in the quadraticnonlinear optical (NLO) properties of molecules that possessoctopolar symmetry.

This experiment describes the isolation and characterization of complexes containing examples of two important monohapto ligands, namely vinylidene and alkynyl ligands. The former is a tautomer of acetylene that has minimal (10-10 s) existence as an uncomplexed molecule, providing an interesting example of the stabilization of reactive organic species at transition metals--an important motif in organometallic chemistry. The latter ligand affords complexes that have attracted a great deal of interest recently for their potentially useful electronic or optical properties, illustrating a major focus of contemporary organometallic chemistry, the search for useful materials. The particular strength of this experiment is in demonstrating the utility of a range of spectroscopic and analytical techniques in inorganic complex identification. The students observe unusual chemical shifts in the 13C NMR (vinylidene metal-bound carbon), meet heteronuclear NMR (31P), assign intense metal-to-ligand charge transfer (MLCT) bands in the UV-visible spectra, observe the utility of mass spectra in characterizing complexes of poly-isotopic transition metals, and are introduced to redox potentials (cyclic voltammetry).

The complexes [Au(4-CA≡CC6F4OMe)(L)] [L = PMe3 (1), PPh3 (2)],trans-[Ru(4-C=CHC6F4OMe)Cl(dppm)2]PF6(3) and trans-[Ru(4-CA≡CC6F4OMe)Cl(dppm)2](4) have been prepared and the identity of (2) was confirmed by a structural study. Electrochemical data for (3) and (4) suggest that the 4-C6F4OMe group lies midway between Ph and 4-C6H4NO2in electron-withdrawing strength. Quadratic non-linearities at 1064 nm, determined by the hyper-Rayleigh scattering technique, increase for co-ligand variation, in the order PPh3 < PMe3, in proceeding from (2) to (1), whereas data for the vinylidene/alkynyl complexes (3) and (4) are experimentally indistinguishable. The quadratic non-linear optical data for (1) and (2) are comparable to those of their 4-nitrophenylalkynyl analogues, however, (1) and (2) are more optically transparent.

This experiment involves interconversions of carbene and alkenyl ligands, important monohapto ligands which are often met in an advanced undergraduate organometallic chemistry course. References are provided to extend the experiment to include alkynyl and vinylidene ligands.

Efficient syntheses of the cis and trans isomers of [OsCl2(Me2SO)4] are reported. While a structural study of thetrans isomer confirms the spectroscopically assigned all-S-bound Me2SO configuration, a crystallographic determination of the cis isomer reveals a previously unheralded all-S-bound Me2SO geometry, in contrast to the spectroscopically inferred configuration predominant in solution which has one O-bound ligand. Fortrans-[OsCl2(Me2SO)4], crystals are tetragonal, space group I 4/m, with a 9·092(2), c 11·212(3) Å, Z 2, 566 unique reflections (34 parameters), converging at R 0·026 and Rw 0·032. For cis-[OsCl2(Me2SO)4], crystals are triclinic, space group P-1, with a 8·193(2), b 8·941(3), c 13·837(3) Å, α 79·77(2), β 79·91(2), γ 65·03(2)°, Z 2, 4152 unique reflections (173 parameters), converging at R 0·021 and Rw 0·018.

The structures of Ni(C≡CR)(PPh3)(η-C5H5) (R = Ph (1), C6H4-4-NO2 (2), 4-C6H4C6H4-4′-NO2 (3), (E)-4-C6H4CH=CHC6H4-4′-NO2 (4), 4-C6H4C≡CC6H4-4′-NO2 (5), 4-C6H4N=CHC6H4-4′-NO2 (6)) have been determined by single-crystal X-ray diffraction studies, refining by full-matrix least-squares analysis. For (1), crystals are triclinic, space group P-1, with a 10·094(2), b13·429(3), c 18·835(5) Å,α 103·24(2), β 91·50(2), γ 90·10(2)°, Z 4, 5844 unique reflections (595 parameters), converging at R 0·033 and Rw 0·024. For (2), crystals are orthorhombic, space group Pna21, with a 16·799(2), b 8·681(2), c 17·485(2) Å, Z 4, 1774 unique reflections (325 parameters), converging at R 0·031 and Rw 0·029. For (3), crystals are monoclinic, space group P 21/c, with a 11·140(3), b 18·282(4), c 15·296(2) Å, β 105·18(2)°, Z 4, 3132 unique reflections (397 parameters), converging at R 0·039 and Rw 0·024. For (4), crystals are monoclinic, space group P 21/n, with a 12·929(7), b 16·953(8), c 15·601(7) Å, β 112·55(3), Z 4, 3023 unique reflections (397 parameters), converging at R 0·039 and Rw 0·025. For (5), crystals are monoclinic, space group P 21/n, with a 12·710(5), b 16·882(3), c 15·693(4) Å, β 111·37(3)°, Z 4, 3216 unique reflections (397 parameters), converging at R 0·035 and Rw 0·030. For (6), crystals are monoclinic, space group P 21/n, with a 12·594(1), b 16·936(2), c 15·611(1) Å, β 112·476(5)°, Z 4, 3564 unique reflections (397 parameters), converging at R 0·038 and Rw 0·041. For structurally characterized 18-electron (cyclopentadienyl)nickel(II) acetylide complexes, statistically insignificant decreases in the average Ni-C(1) distance and trans influence and an increase in the average C(1)-C(2) parameter are observed on introduction of an acceptor substituent at the alkynyl ligand.

The structures of Au(4-C≡CC6H4XYC6H4-4′-NO2)(PPh3) (XY = (E )-CH=CH (1), (Z)-CH=CH (2), C≡C (3), N=CH (4)) have been determined by single-crystal X-ray diffraction analyses, refining by full-matrix least-squares analysis. For (1), crystals are triclinic, space group P-1, with a8·847(1), b 17·870(4), c 19·705(3) Å, α116·25(1), β 93·33(1), γ 92·64(2)˚, Z 4, 6747 unique reflections (703 parameters), converging at R 0·025 and Rw 0·029. For (2), crystals are monoclinic, space group P 21/a, with a 10·718(6), b 19·398(5), c14·469(3) Å, β 108·96(2)˚, Z 4, 3295 unique reflections (352 parameters), converging atR 0·040 and Rw 0·034. For (3), crystals are triclinic, space group P-1, with a 10·671(4), b 17·599(7), c 18·220(8) Å, α 116·31(3), β 105·00(4), γ 95·08(4)˚, Z 4, 4828 unique reflections (703 parameters), converging at R 0·043 and Rw 0·030. For (4), crystals are triclinic, space group P-1, with a 8·8314(6), b 17·834(2), c 20·001(2) Å, α 115·249(7), β 90·930(7), γ 94·082(7)˚, Z 4, 4724 unique reflections (703 parameters), converging at R 0·035 and Rw 0·034. Despite the [ligated metal donor]-bridge-[nitro acceptor] composition of these complexes, Au–C and C≡C distances are normal and consistent with minimal allenylidene contribution to the ground-state geometry. Within the 3σ confidence limits, the structural data do not provide evidence for π*-back-bonding in these complexes

The authors present an experiment illustrating some diverse principles of metal cluster chemistry, employing the relatively cheap metal cobalt.