Graham A. Heath

Organometallic complexes for nonlinear optics. X. Molecular quadratic and cubic hyperpolarizabilities of systematically varied (cyclopentadienyl)bis(phosphine) ruthenium σ-arylacetylides: X-ray crystal structure of Ru((E)-4,4′-C CC6H4CHC6H4NO2)(PPh3)2(η-C5H5) ☆

Abstract The complexes Ru(4,4′-C  CC6H4C6H4NO2)(PPh3)2(η-C5H5) and Ru(4,4′-C  CC6H4C  CC6H4NO2)(PPh3)2(η-C5H5) have been prepared and the latter structurally characterized; they belong to a series of organometallic donor-bridge-acceptor compounds containing (cyclopentadienyl)bis(phosphine)ruthenium(II) centres as donors, conjugated arylacetylide bridges, and nitro acceptor groups. Electrochemical data for the series of complexes Ru(C  CR)(PR′3)2(η-C5H5) (R  Ph, 4-C6H4NO2, R′  Ph, Me; R = 4,4′-C6H4C6H4NO2, (E)-4,4′-C6H4CH  CHC6H4NO2, 4,4′-C6H4C  CC6H4NO2, 4,4′-C6H4N  CHC6H4NO2, R′  Ph) are consistent with an RuII/III couple whose oxidation potentials vary strongly with chain-lengthening from one-ring to two-ring acetylide ligand, but show little variation with changes at the bridging unit of the two-ring acetylide ligand. The molecular quadratic and cubic optical nonlinearities of the series of complexes have been determined by hyper-Rayleigh scattering (HRS) and Z-scan techniques, respectively. Molecular first hyperpolarizabilities by HRS at 1064 nm are dispersively enhanced; experimental and two-level corrected data suggest an increase in nonlinearity on chain-lengthening of the bridge, in proceeding from C6H4 to C6H4C6H4 and then C6H4C  CC6H4 and C6H4CH  CHC6H4, a general trend that is reproduced by semiempirical ZINDO computations. Cubic hyperpolarizabilities by Z-scan at 800 nm are negative for complexes with nitro acceptor groups, probably a result of two-photon dispersion, with absolute values (up to 850 × 10−36 esu) large for small organometallic complexes; as with quadratic nonlinearities, cubic nonlinearities increase substantially on bridge lengthening, with little variation on phosphine substitution.

The use of differential pulse polarography for the determination of stability constants

An equation is derived which enables the determination of stability constants of complex ions by differential pulse polarography. Values obtained by this method for the cadmium (II) chloride system are in excellent agreement with those determined by potentiometry using a cadmium amalgam electrode. Some of the particular advantages of the method are discussed.

Organometallic complexes for nonlinear optics. 15. Molecular quadratic hyperpolarizabilities of trans-bis{bis(diphenylphosphino)methane}ruthenium σ-aryl- and σ-pyridyl-acetylides: X-ray crystal structure of trans-[Ru(2-CCC5H3N-5-NO2)Cl(dppm)2]

The complexes trans -[Ru(2-CCC 5 H 3 N-5-R)Cl(dppm) 2 ] [R=H ( 6 ), NO 2 ( 7 )] have been prepared and 7 has been structurally characterized; comparison with the structural study of trans -[Ru(4-CCC 6 H 4 NO 2 )Cl(dppm) 2 ] ( 3 ) reveals a decrease in Ru–C(1) distance and increase in Ru–Cl(1) distance, consistent with stronger σ -bonding by the nitropyridylalkynyl ligand in 7 compared to the nitrophenylalkynyl ligand in 3 . Electrochemical data for 3 , 6 , 7 , precursor dichloro complexes [RuCl 2 (dppm) 2 ] [ cis ( 1a ), trans ( 1b )], and related alkynyl complexes trans -[Ru(4-CCC 6 H 4 R)Cl(dppm) 2 ] [R=H ( 2 ), 4-C 6 H 4 NO 2 ( 4 ), ( E )-4-CHCHC 6 H 4 NO 2 ( 5 )] have been determined by cyclic voltammetry. Introduction of nitro substituent in progressing from 2 to 3 or 6 to 7 leads to a substantial increase in E o Ru II/III , most of which is lost on chain-lengthening the alkynyl ligand in progressing from 3 to 4 or 5 . Replacement of phenyl by pyridyl in progressing from 2 to 6 or 3 to 7 results in a 0.1 V increase in E o Ru II/III . The optical spectra of representative complexes have been examined. Introduction of a nitro substituent onto the phenylalkynyl ligand, in progressing from 2 to 3 , results in a substantial (ca. 11 000 cm −1 ) red-shift in the intense MLCT band of the Ru II –CC–Ar–NO 2 moiety. Complexes 3 , 4 and 5 exhibit sizable solvatochromic shifts, suggestive of significant optical nonlinearities. Quadratic hyperpolarizabilities for 2 – 7 were determined by hyper-Rayleigh scattering (HRS) at 1064 nm; measurements are consistent with an increase in β HRS upon incorporation of nitro substituent (progressing from 2 to 3 or 6 to 7 ), chain-lengthening the alkynyl ligand (progressing from 3 to 4 and then to 5 ) and replacing phenyl by pyridyl in progressing from 2 to 6 , general trends that are maintained with the two-level-corrected data, and which parallel shifts in λ max to low energy. The observed and two-level-corrected β HRS values for 7 are lower than expected; it is perhaps significant that λ max for 7 is close to the second-harmonic.

Organometallic complexes for nonlinear optics. Part 31. Cubic hyperpolarizabilities of ferrocenyl-linked gold and ruthenium complexes

Abstract The complexes [Fe{η-C5H4(E)CHCH4-C6H4CCX}2] [X=SiMe3 (1), H (2), Au(PCy3) (3), Au(PPh3) (4), Au(PMe3) (5), RuCl(dppm)2 (7), RuCl(dppe)2 (8)] and [Fe{η-C5H4(E)CHCH4-C6H4CHCRuCl(dppm)2}2](PF6)2 (6) have been prepared and the identities of 1 and 7 confirmed by single-crystal X-ray structural studies. Complexes 1–8 exhibit reversible oxidation waves in their cyclic voltammograms attributed to the FeII/III couple of the ferrocenyl groups, 6–8 also showing reversible (7, 8) or non-reversible (6) processes attributed to Ru-centered oxidation. Cubic nonlinearities at 800 nm by the Z-scan method are low for 1–5; in contrast, complexes 6 and 7 exhibit large negative γreal and large γimag values. A factor of 4 difference in ∣γ∣ and two-photon absorption cross-section σ2 values for 6 and 7 suggest that they have potential as protically switchable NLO materials.

Porphyrin dimers linked by conjugated butadiyne bridges: preparations, spectra, voltammetry and reductive spectroelectrochemistry of {[M(OEP)](m-C4)[M(OEP)]} (M2 H4, Co2, Ni2, Cu2, Zn2, Pd2, Pt2, Co/Ni, Ni/Cu, Ni/Zn)

A series of derivatives M2P2 (M2 ≡ H4, Co2, Ni2, Cu2, Zn2, Pd2, Pt2, Co/Ni, Ni/Cu, Ni/Zn) of the ligand meso,meso′-bis(octaethylporphyrinyl)butadiyne has been prepared and characterized by 1H NMR, FT Raman and visible absorption spectroscopies as well as by cyclic and a.c. voltammetry in CH2Cl2 solution at 20 and −40 °C. The electronic spectra exhibit multiple Soret bands and the voltammetry reveals successive one-electron reductions indicating the accessibility of ‘mixed valence’ π-radical anions and π-dianions. Using in situ thin layer spectroelectrochemistry, the UV to near-IR spectra of [M2P2]1− and [M2P2]2− (M as above) were recorded at ≤ −40 °C. Apart from the Co complexes (reduced at the metal ion), the bis(porphyrin) anions have spectra which include sharp, intense near-IR bands (e = 50 000–200 000 M−1cm−1) at c. 4500 and 11 500 cm−1([M2P2]1−) and 9500 cm−1([M2P2]2−). An empirically constructed semiquantitative frontier orbital model explains the observed electronic absorption bands. Inter-porphyr...

The electronic absorption spectrum and structure of the emitting state of the tris(2,2′-bipyridyl)ruthenium(II) complex ion

The directly determined absorption spectrum (250–650 nm) of the optically excited species *[Ru(bipy)3]2+(bipy = 2,2′-bipyridyl) is presented and assigned. The promoted (metal to ligand charge transfer) electron is localised on one of the three bipy ligands, as in the formulation [RuIII(bipy)2(bipy–)]2+, while the known emission photoselection data imply that the promoted electron resides on the same ligand throughout.

Electrochemical and Spectroscopic Investigation of the Reduction of Dimethylglyoxime at Mercury Electrodes in the Presence of Cobalt and Nickel

Voltammograms (polarograms) obtained from solutions of cobalt and nickel containing dimethylglyoxime (dmgH(2)) are widely used for the trace determination of these metals. Detailed electrochemical and spectroscopic studies on the reduction process observed in the analytically important ammonia buffer media at mercury dropping, hanging, and pool electrodes are all consistent with an overall 10-electron reduction process, in which both the dmgH(2) ligand and cobalt ions are reduced in the adsorbed state:  Co(II) + 2dmgH(2) ⇌ (solution) [Co(II)(dmgH)(2)] + 2H(+); [Co(II)(dmgH)(2)] + Hg ⇌ (electrode) [Co(II)(dmgH)(2)](ads)Hg; and [Co(II)(dmgH)(2)](ads)Hg + 10e(-) + 10H(+) → Co(Hg) + 2[2,3-bis(hydroxylamino)butane]. The limited solubility of the nickel complex in aqueous media restricts the range of studies that can be undertaken with this system, but an analogous mechanism is believed to occur. Low-temperature voltammetric studies in dichloromethane at a frozen hanging mercury drop electrode and in situ electron spin resonance electrochemical measurements on more soluble analogues of the dimethylglyoxime complexes are consistent with an initial one-electron reduction step being available in the absence of water. Deliberate addition of water to acetone solutions enables the influence of the aqueous environment on voltammograms and polarograms to be examined. The results of the present study are compared with the wide range of mechanisms proposed in other studies.

Diazene-N-(di-imide) and hydrazido-(2–)N-(aminoimido) complexes: the addition of acids to dinitrogen complexes

The protonation and reduction of dinitrogen in a mononuclear complex are described. The diazene compounds [MX2(N2H2)(dpe)2](I; M = W, X = Cl or Br; M = MO, X = Br; dpe = Ph2PCH2CH2PPh2), and hydrazido (2–)N complex salts, [Mo(N2H2)(depe)2]X (X = Cl or Br; depe = Et2PCH2CH2PEt2) and trans-[WCl(N2H2)(PMe2Ph)4]Cl were prepared by the reaction of trans-[M(N2)2(diphos)2](M = MO or W; diphos = dpe or depe) or cis-[W(N2)2(PMe2Ph)4] with an excess of the appropriate hydrogen halide. Compounds (I) contain labile halogen and are converted into the hydrazido-(2–)N complex salts [MX(N2H2)(dpe)2]Y (Y = BPh4, ClO4, or PF6, M = W; Y = BF4, M = MO) by treatment with NaBPh4, LiClO4, NaPF6, or [NEt4]BF4 as appropriate. The structural implications of the i.r., 1H and 31P n.m.r. spectroscopic properties of the N2H2 compounds and of their 15N analogues are discussed.With only 2 mol equiv. of HCl, trans-[W(N2)2(dpe)2] gives the hydride [WH(N2)2(dpe)2]HCl2 and trans-[Mo(N2)2(dpe)2] gives the dihydride [MoH2Cl2(dpe)2]. [WH(N2)2(dpe)2]HCl2 is converted into [WH2Cl2(dpe)2] in refluxing methanol and [WCl2(N2H2)(dpe)2] gives [WCl2{N2H(COCH3)}(dpe)2] with acetyl chloride or acetic anhydride.This work provides the first chemical evidence that dinitrogen is as likely to be reduced at a mono- as at a bi-metal site in nitrogenase.

High-field NMR spectroelectrochemistry of spinning solutions: simultaneous in situ detection of electrogenerated species in a standard probe under potentiostatic control

Abstract This report summarizes the design and performance of the first practicable in situ electrogenerative high-field solution-NMR cell, designed for simultaneous NMR spectroelectrochemistry in a conventional 10- or 16-mm 300 MHz probe. The axially symmetric three-electrode assembly is stationary and self-aligning. It dips into a standard spinning 10-mm sample tube and is adapted for convenient operation in any commercial high-field, multi-nuclear, variable-temperature FT NMR spectrometer. The tubular, rf-transparent working electrode (presently consisting of a gold film, coated on glass) completely spans the detection region; the recommended coating thickness is ≤0.01 δ , where δ is the rf-absorbing conductor skin depth. With careful shimming, very narrow 1 H signals (∼1 Hz) can be obtained. The performance of the in situ NMR-electrochemical cell is illustrated by monitoring the progressive reduction of ‘ p -quinone’ (1,4-benzoquinone) to its dihydro-form by controlled-potential electrolysis in an acidic medium.

Organometallic complexes for nonlinear optics. Part 32: Synthesis, optical spectroscopy and theoretical studies of some osmium alkynyl complexes

Abstract The complexes trans -[Os(CCPh)Cl(dppe) 2 ] ( 1 ), trans -[Os(4-CCC 6 H 4 CCPh)Cl(dppe) 2 ] ( 2 ), and 1,3,5-{ trans -[OsCl(dppe) 2 (4-CCC 6 H 4 CC)]} 3 C 6 H 3 ( 3 ) have been prepared. Cyclic voltammetric studies reveal a quasi-reversible oxidation process for each complex at 0.36–0.39 V (with respect to the ferrocene/ferrocenium couple at 0.56 V), assigned to the Os II/III couple. In situ oxidation of 1 – 3 using an optically transparent thin-layer electrochemical (OTTLE) cell affords the UV–Vis–NIR spectra of the corresponding cationic complexes 1 + – 3 + ; a low-energy band is observed in the near-IR region (11 000–14 000 cm −1 ) in each case, in contrast to the neutral complexes 1 – 3 which are optically transparent below 20 000 cm −1 . Density functional theory calculations on the model compounds trans -[Os(CCPh)Cl(PH 3 ) 4 ] and trans -[Os(4-CCC 6 H 4 CCPh)Cl(PH 3 ) 4 ] have been used to rationalize the observed optical spectra and suggest that the low-energy bands in the spectra of the cationic complexes can be assigned to transitions involving orbitals delocalized over the metal, chloro and alkynyl ligands. These intense bands have potential utility in switching nonlinear optical response, of interest in optical technology.