Synthesis and magnetic properties of new nickel(II)-copper(II)-nickel(II) trinuclear complexes with irregular spin-state structure

Summary Four novel heterotrinuclear complexes were prepared, namely {[Ni(L)₂]₂[Cu(pba)]}(ClO₄)₂, where pba = pro-pylene-1,3-bis(oxamato) and L = 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (NO₂-phen), 2,2-bipyridyl (bpy), 4,4-dimethyl-2,2-bipyridyl (Me₂bpy). Based on i.r., elemental analyses, conductivity measurements and electronic spectra oxamato-bridged structures are proposed for these complexes, consisting of two nickel(II) ions, each in a distorted octahedral environment, and a copper(II) ion in a square planar environment, respectively. The temperature dependence of the magnetic susceptibility of {[Ni(phen)₂]₂[Cu(pba)]}(ClO₄)₂·H₂O was studied in the 4–300 K range, giving the exchange integral J = - 106 cm^–1. TheX _scm T versusT plot exhibited a minimum at ca. 98 K, characteristic of this kind of coupled polymetallic complex with an irregular spin-state structure. E.s.r. spectra of these complexes clearly indicated a strong rhombicity withg ₁ = 5.20,g ₂ = 2.29 andg ₃ = 2.02 (approximately), which agrees with an anisotropicS = ±1/2 Kramer doublet in the ground state.     

Ruthenium(II) complexes of 2-phenylimidazo[4,5-f] [1,10]phenanthroline. Synthesis,characterization and third order nonlinear optical properties

Three Ru^II complexes [Ru(bpy)₂(PIP)]²⁺, [Ru(PIP)₂(bpy)]²⁺ and [Ru(PIP)₃]²⁺ (PIP = 2-phenylimidazo[4,5-f][1,10]phenanthroline, bpy = 2,2-bipyridine) were prepared and characterized by electrospray mass spectrometry, ¹H-n.m.r, u.v.–vis. and electrochemistry. The nonlinear optical properties (NLO) of the Ru^II complexes were investigated by Z-scan techniques with 12 ns laser pulses at 540 nm, and all of them exhibit both NLO absorption and self-defocusing effects. The corresponding effective NLO susceptibility |³| of the complexes is in the (4.15 – 4.86) × 10^–12 e.s.u. range.     

Synthesis and studies of spectroscopic and electrochemical properties of dinuclear ruthenium(<Emphasis Type="SmallCaps">II</Emphasis>) and manganese(<Emphasis Type="SmallCaps">II</Emphasis>) complexes

New dinuclear ruthenium manganese complexes of general composition (bpy)₂Ru(L)MnCl_x(H₂O)₂ (L is 1,10-phenanthroline-5,6-dione, 3,3′-dicarboxy-2,2′-bipyridyl, or bis(pyrazolyl); x = 2 or 4) were synthesized by the reaction of (bpy)₂Ru(L) with MnCl₂ · 4H₂O. These compounds and the starting mononuclear ruthenium complexes were studied by spectrophotometric and electrochemical methods in MeCN. The position of the charge-transfer band Ru^II → L in the spectra depends on the donor-acceptor characteristics of the ligand L. For the dinuclear complex under study, the formal potentials of reversible one-electron oxidation of Ru^II are in the range of 0.9–1.2 V (vs. the standard hydrogen electrode), whereas oxidation of Mn^II occurs at more positive (by 0.1–0.2 V) potentials. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2281–2285, October, 2005.     

Synthesis,spectroscopic, photophysical and electrochemical behaviour of ruthenium(II) and copper(I) isocyano-bridged complexes with polypyridine ligands: 2,2′-bipyridine and 1,10-phenanthroline

New binuclear complexes with [Cu(PPh₃)₃]⁺ and [Cu(PPh₃)(N—N)]⁺ (N—N – 2,2-bipyridine, 1,10-phenanthroline) moieties connected via the isocyanide group to [Ru(bpy)₂(py)]⁺ and [Ru(phen)₂(py)]⁺ have been prepared and isolated as PF₆ ^– salts. In addition, new trinuclear complexes, [{(PPh₃)₃Cu(-NC)}₂Ru(bpy)₂](PF₆)₂ and [{(N—N)-(PPh₃)Cu(-NC)}₂Ru(bpy)₂](PF₆)₂, have been synthesized using [Ru(bpy)₂(CN)₂]. The complexes have been characterized by elemental analyses, i.r., n.m.r., u.v.–vis., FAB mass spectra and by conductivity measurements. The i.r. spectra reveal an increase in v;(CN) in the isocyano-bridged complexes compared to the mononuclear parent complexes. The complexes are luminescent with emission wavelengths in the 458–550 and 600–636 nm ranges. The half wave reduction potentials in MeCN are always more positive than those of the parent complexes. It is observed that the isocyano-bridged complexes are more powerful excited state reductants than the cyano-bridged, Cu^(I)(-CN)Ru^(II) complexes.     

Xanthate complexes of nickel with nitrogen donor ligands. Part V

Nickel(II) xanthate complexes of general formula, [Ni(Rxa)₂(L)] [R = i-Pr, i-Am, xa = OCS^– ₂, L = 4,7-diphenyl-1,10-phenanthroline(baphen), 4,4-dimethyl-2,2-bipyridyl (me₂bpy), 2-9-dimethyl-1,10-phenanthroline(neo) or trans-1,2-diaminocyclohexane (dch)] and [Ni(Rxa)(cyclam)](Rxa) (= 1,4,8,11-tetraazacyclotetradecane) have been synthesized and characterized by elemental analyses, i.r. and electronic spectroscopy, magnetic and conductivity measurements. The complexes with cyclam were studied by cyclic voltammetry. Values of magnetic moments at room temperature lie within the 3.25–3.51 B.M. range and thus indicate the presence of two unpaired electrons, except for the complexes with cyclam, where the anomalous values of 1.76 and 1.74 B.M. were obtained in respect to the nickel(II) complexes. Magnetic susceptibility data for [Ni(i-Prxa)(cyclam)](i-Prxa) were measured over the 79–298 K range and indicate no exchange interaction between paramagnetic nickel(II) centres.     

Preparations and properties of vanadium(III) complexes of bidentate and terdentate nitrogen-donor ligands

Summary Vanadium(III) chloride reacts with 1,10-phenanthroline and 2,2-bipyridyl, and with substituted derivatives of each ligand (B), in ethanol or in acetonitrile as solvent (L), to yield two different series of complexes. These are (a) the neutral species VCl₃BL, where B = 1,10-phenanthroline, 5-chloro-1,10-phenanthroline, 5-methyl-1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline, 2,2-bipyridyl, 4,4-dimethyl-2,2-bipyridyl, L = ethanol. The complexes in which B = 1,10-phenanthroline or 2,2-bipyridyl were also obtained with L = acetonitrile, (b) [VCl₂B₂]⁺[VCl₄B]^– where B is the same series of ligands listed above. Vanadium(III) chloride yields VCl₃ (terpy) with 2,2,2 -terpyridyl. All the complexes have been characterised by elemental analyses, conductance measurements, electronic- and i.r. spectral measurements, and by their temperature-range (297–77 K) magnetic moments; ring substituents have little influence on any chemical or physical properties of these complexes.     

A new class of organometallic compound

Summary Organometallic compounds of general formula (SCN)₂M(NCSeHgR)₂ (M=Co^II, Ni^II, R=n-C₅H₁₁,i-C₅H₁₁) have been prepared. They behave as Lewis acids, forming complexes with pyridine and 2,2-bipyridyl, characterized by elemental analysis, molecular weight, molar conductance, i.r. spectral (4000–200 cm^–1), electronic spectral and magnetic susceptibility measurements. The Lewis acids are monomeric with bridging thiocyanate, or selenocyanate between M²⁺ and Hg²⁺. Cobalt and nickel acquire tetrahedral and octahedral configurations respectively through axial bridging, whereas mercury retains its linearity. Pyridine links to the metal in the Lewis acid and forms L₂(SCN)₂M(NCSeHgR)₂ complexes. Bipyridyl ruptures the NCX bridge and forms cationic-anionic [M(bipy)₃][(NCS)(NCSe)HgR]₂ complexes.     

Chemistry of Ruthenium Polypyridine Complexes: V. Electronic Structure of Ruthenium(II) Bipyridine-Diphosphine Mixed-Ligand Complexes

Comparative analysis of the donor-acceptor capacities of diphosphine ligands in two series of complexes: cis-[Ru(bpy)2(LL)]^{q +} [LL = 2,2'-bipyridine (bpy), o-benzoquinonediimine (bqdi), cis-1,2-bis(diphenylphosphino)ethane, cis-1,2-bis(diphenylphosphino)ethylene (dppen), (NH3)2, and (CO)2] and [Ru(NH₃)₄. (LL)]^{2 +} (LL = bpy, dppen, and bqdi), was performed. Diphosphines are the strongest donors; they compare in -acceptor capacity which is associated with phosphorus d orbitals with 2,2'-bipyridine and fall far short of o-benzoquinonediimine and carbonyl.     

Synthesis,spectral and magnetic studies on mixed-ligand complexes M(DIAFO)2(NCS)2 and M(DIAFH)2X2 (M = FeII,CoII, NiII). The crystal structure of Co(DIAFO)2(NCS)2

Summary A series of mixed-ligand complexes of group VIII metals, M(DIAFO)₂(NCS)₂ and M(DIAFH)₂X₂ (M = Fe^II, Co^II, Ni^II, X = NCS^–, Cl^–) with the 3,3-bridged derivative of 2,2-bipyridyl (bipy) (1) were prepared, where DIAFO (2) and DIAFH (3) are 4,5-diazafluoren-9-one and 4,5-diazafluoren-9-hydrazone, respectively. These complexes were investigated by i.r., u.v.-vis-near i.r. spectroscopy and by variable-temperature magnetic susceptibility measurements. The electronic spectra show that the two ligands exert a field strength far removed from the Fe^II cross-over value. All the complexes are paramagnetic, following the Curie-Weiss law in the 77–300 K range. A typical crystal structure of Co(DIAFO)₂(NCS)₂ for these compounds was determined with orthorhombic, space group Pcan, a = 10.377(5) Å, b = 13.289(6) Å, c= 16.629(7) Å, V = 2293(2) ų, D _c = 1.563 g cm^–3, F(000) = 1091.74, Z = 4, R = 0.043, R = 0.047. Steric effects are thought to be operative in both ligands studied, but are weaker than those of the typical bidentate diimine ligand bipy.Author to whom all correspondence should be directed.     

Synthesis,Characterization, Electrochemical and Spectroscopic Properties of [Ru(dppt)(bpy)Cl]+ and [Ru(pta)(bpy)Cl]+

Two novel Ru^II complexes [Ru(dppt)(bpy)Cl]ClO₄ (1) and [Ru(pta)(bpy)Cl]ClO₄ (2)[dppt, pta and bpy = 3-(1,10-phenanthrolin-2-yl)-5,6-diphenyl-as-triazine, 3-(1,10-phenanthrolin-2-yl)-as-triazino[5,6-f]acenaphthylene and 2,2-bipyridine, respectively] were synthesized and characterized by elemental analysis and electrospray mass spectrometry, ¹H-n.m.r., and u.v.–vis spectroscopy. The redox properties of the complexes were examined using cyclic voltammetry. Due to the strong -accepting character of asymmetric ligands, the MLCT bands of (1) and (2) are shifted significantly to lower energies by comparison with [Ru(tpy)(bpy)Cl]⁺.     

Oligothiophene-2-yl-vinyl bridged mono- and binuclear ruthenium(II) tris-bipyridine complexes: Synthesis, photophysics, electrochemistry and electrogenerated chemiluminescence

A series of mono- and binuclear ruthenium(II) tris-bipyridine complexes tethered to oligothienylenevinylenes have been synthesized and characterized by ¹H NMR, ¹³C NMR and TOF-MS spectrometry. Photophysics, electrochemistry and electrogenerated chemiluminescence (ECL) properties of these complexes are investigated. The electronic absorption spectra of the mononuclear ruthenium complexes show a significant red shift both at MLCT (metal-to-ligand charge transfer) and π-π^∗ transitions of oligothienylenevinylenes with increase in the number of thiophenyl-2-yl-vinyl unit. For the binuclear complexes these two absorption bands are overlapped. All the metal complexes have very weak emission compared to that of the reference complex Ru(bpy)²⁺₃. The first reduction potentials of all mononuclear ruthenium complexes are less negative than that of Ru(bpy)²⁺₃, due to the moderate electron-withdrawing effect of oligothienylenevinylenes. For binuclear ruthenium complexes, only one Ru(II/III) oxidation peak (E_1/2 = 0.96 V vs. Ag/Ag⁺) was observed, suggesting a weak interaction between two metal centers. Three successive reduction processes of bipyridine ligands are similar among all ruthenium complexes except for RuTRu, which has a very sharp peak owing to the accumulation of neutral product on the electrode surface. All these ruthenium complexes exhibited different ECL property in CH₃CN solution without any additional reductant or oxidant. For three mononuclear ruthenium complexes, the ECL intensity strengthens with increase in the number of thiophene-2-yl-vinyl unit. However, the ECL efficiency dramatically decreased in the binuclear ruthenium complexes. The ECL efficiencies of all the reported complexes do not exceed that of Ru(bpy)²⁺₃, where the ECL efficiency decreases in the order of RuTRu > Ru3T > Ru2T > RuT > Ru2TRu (RuT,bis-2,2′-bipyridyl-(4-methyl-4′-(2-thienylethenyl)-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru2T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru3T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}}-2,2′-bipyridine) ruthenium dihexafluorophosphate; RuTRu, bis-2,2′-bipyridyl-ruthenium-bis-[2-((E)-4′-methyl-2, 2′-bipyridinyl-4)-ethenyl]-thienyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate; Ru2TRu, bis-2,2′-bipyridyl-ruthenium-(E)-1,2-bis-{2-[2-((E)-4′-methyl-2,2′-bipyridinyl-4)-ethenyl]-thienyl}-ethenyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate).     

Kinetics and mechanism of ethylenediaminetetraacetic acid-, 2,2′-bipyridyl-, and 1,10-phenanthroline-assisted chromium(VI) oxidation of 2-propanol

Complexing agents ethylenediaminetetraacetic acid (EDTA), 2,2-bipyridyl (bpy), and 1,10-phenanthroline (phen) influence the rate of chromic acid oxidation of 2-propanol in aqueous HClO₄ solutions. EDTA and bpy catalyse the oxidation rate, whereas phen has no effect, but at higher concentration it acts as an inhibitor. Dependent on conditions, the reactions follow differing order kinetics. In the presence of EDTA and bpy, at the end of the reaction, chromium(III) is present as the EDTA–Cr^III and bpy–Cr^III complexes. Probable mechanisms are proposed involving a negatively charged termolecular intermediate complex formed from chromic acid, complexing agent, and 2-propanol.     

A mechanistic study of the ethylenediaminetetraacetic acid-, 2,2′-bipyridyl-, and manganese(II)-assisted one-step two- and three-electron oxidation of lactic acid by chromium(VI)

The kinetic results of the oxidation of lactic acid by Cr^VI in the absence and presence of ethylenediaminetetraacetic acid (EDTA), 2,2-bipyridyl (bpy), Mn^II and Ce^IV are presented. EDTA, bpy and Mn^II catalyse the reaction, whereas Ce^IV acts as an inhibitor. Irrespective of the conditions, the order with respect to [lactic acid] was found to lie between one and two, and one in [Cr^VI]. In the EDTA, bpy and Mn^II-catalysed paths, Cr^VI–EDTA, Cr^VI–bpy and lactic acid–Mn^II complexes have respectively been suggested as the active oxidant and reductant. The kinetic and cerium(IV) effect studies are consistent with a one-step two-electron transfer mechanism in the absence/presence of EDTA and bpy where a chromate–ester mechanism experiences a redox decomposition (C—H cleavage) in the rate-determining step. On the other hand, the catalytic effect of Mn^II is described as a one-step three-electron redox decomposition (C—C cleavage) mechanism. Mechanisms in accordance with the experimental data have been proposed for the reactions. Activation parameters have also been evaluated and discussed.     

Coordination compounds of nickel with trithiocyanuric acid. Part IV. Structure of [Ni(pmdien)(ttcH)] (pmdien = N,N,N′,N′,N′′-pentamethyldiethylenetriamine,ttcH3 = trithiocyanuric acid)

Ni^II mixed-ligand complexes of compositions [Ni(pmdien)(ttcH)] (1), [Ni(baphen)₂(ttcH)] · 4H₂O (2), [Ni-(dpa)(ttcH)(H₂O)] (3), [Ni(cyclam)(ttcH)] · 2H₂O (4), [Ni(hexaa)](ttcH) (5) and [Ni(hexab)(ttcH)] · 2H₂O (6), (baphen = 4,7-diphenyl-1,10-phenanthroline, dpa = 2,2-dipyridylamine, cyclam = 1,4,8,11-tetraazacyclotetradecane, hexaa = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.1^6,9]-octadecane, hexab = 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane) have been prepared and characterized by means of i.r., u.v.–vis. spectroscopies and magnetochemical measurements. The redox properties of the complexes were studied by cyclic voltammetry. The crystal and molecular structure of [Ni(pmdien)(ttcH)] was determined. The nickel atom is penta-coordinated by three N atoms of pmdien, and by S and N atoms of trithiocyanurate(2–) anion.     

Synthesis,characterization and DNA-binding properties of mixed porphyrin–polypyridyl ruthenium(II) complexes

Two mixed porphyrin–polypyridyl Ru^II complexes [Ru(bpy)₂(MPyTPP)Cl]Cl (1) and [Ru(phen)₂(MPyTPP)Cl]Cl ( 2 ) (bpy=2,2-bipyridine; phen=1,10-phenanthroline; MPyTPP=5-monopyridyl-10,15,20–triphenylporphyrin) have been synthesized and characterized by elementary analysis, e.s.–m.s., cyclic voltammetry and u.v.–vis. spectroscopy. The DNA-binding properties of these complexes were investigated by electronic spectra, c.d. spectra and viscosity experiments. The results suggested that both complexes (1) and (2) bind to DNA in an outside binding mode. At the same time, theoretical calculations applying the ab initio and the density functional theory (DFT) methods were also performed, and the results showed that there is no good planarity on the main ligand MPyTPP of these complexes, and there are rather great distortion angles (dihedral angles ca. 72°) between the porphrin ring and each of the 10-, 15-, 20-phenyl groups. This may be the reason why the complexes bind to DNA in an outside mode, instead of an intercalative mode.     

Kinetic study of the reaction between protonatedtrans-dioxotetracyanomolybdate(IV) and 2,2′-bipyridyl

Summary The kinetics of the reaction between the protonated forms of [MoO₂(CN)₄]^4– and 2,2-bipyridyl (bpy) have been studied in the 8.5–11.7 pH range. This study showed that the diprotonated form, [MoO(OH₂)(CN)₄]^2– is the only reactive species. The rate-limiting step is the substitution of the aqua ligand. This is followed by fast closure of the chelate ring, accompanied by the substitution of a cyanide ligand. With excess bpy the relatively slow formation of an adduct occurs. The nature of this adduct is discussed.     

Characterization of the Excited State Properties of Some New Photosensitizers of the Ruthenium (Polypyridine) Family

The photophysical and electron transfer properties of the lowest excited state of nine ruthenium (polypyridine) complexes have been characterized. The complexes studied are Ru (bpy)_3-n (LL)²⁺_n, where n varies from 0 to 3, and LL is 4, 4′-di-t-butyl-2,2′-bipyridine (DTB-bpy), 3, 3′-dimethyl-2, 2′-bipyridine (DM-bpy), or a 2, 2′-diquinolyl derivative (DMCH). The results obtained show that the Ru (bpy)₂(DMCH)²⁺ complex is expected to be a more efficient mediator than Ru (bpy)²⁺₃ in the water-splitting reaction by solar energy.     

Synthesis,structure, redox property and ligand replacement reaction of ruthenium(II) complexes containing a terpyridyl ligand with a redox active moiety

Ruthenium(II) complexes bearing a redox-active tridentate ligand 4′-(2,5-dimethoxyphenyl)-2,2′:6′,2′′-terpyridine (tpyOMe), analogous to terpyridine, and 2,2′-bipyridine (bpy) were synthesized by the sequential replacement of Cl by CH₃CN and CO on the complex. The new ruthenium complexes were characterized by various methods including IR and NMR. The molecular structures of [Ru(tpyOMe)(bpy)(CH₃CN)]²⁺ and two kinds of [Ru(tpyOMe)(bpy)(CO)]²⁺ were determined by X-ray crystallography. The incorporation of monodentate ligands (Cl, CH₃CN and CO) regulated the energy levels of the MLCT transitions and the metal-centered redox potentials of the complexes. The kinetic data observed in this study indicates that the ligand replacement reaction of [Ru(tpyOMe)(bpy)Cl]⁺ to [Ru(tpyOMe)(bpy)(CH₃CN)]²⁺ proceeds by a solvent-assisted dissociation process.     

Improved syntheses of Ru(CO)2 (O3SCF3)2 (bidentate) complexes and their conversion into new [Ru(CO)2 (bidentate)2]2+ complexes

Reaction of the complexes Ru(CO)₂Cl₂L [L = 2,2′-bipyridyl (bpy) or 1,10-phenanthroline (phen)] with trifluoromethanesulphonic acid under carefully controlled conditions yields Ru[cis-(CO)₂] [cis-(O₃SCF₃)₂] (bidentate complexes. From reactions of the trifluoromethanesulphonates with the appropriate bidentate ligands, the new complexes [cis-Ru(CO)₂-L(L′)]²⁺ (L as above; L′ = 4,4′-dimethyl-2,2′-bipyridyl or 4,4′-diisopropyl-2,2′-bipyridyl) as well as the known [_cis-Ru(CO)₂L₂]²⁺ and [cis-Ru(CO)₂bpy(phen)]²⁺ have been prepared.     

The effect of complexing agents on the DMF–chromium(VI) reaction. A kinetic study

The kinetics of the reduction of chromium(VI) by dimethylformamide (DMF) in the presence of ethylenediaminetetraacetic acid (EDTA) and 2,2-bipyridyl (bpy) was investigated in aqueous HClO₄ acid solutions spectrophotometrically. The experimental findings, that the reaction has an induction period followed by autoacceleration, is explained. After the reduction, chromium(III) is present as the EDTA- and bpy-complexes, although such complexes form very slowly under the same experimental conditions from chromium(III) and the EDTA and bpy, respectively. Increases in the reaction rate with increasing [EDTA] were observed, while added bpy had negligible effect on the reaction rate. The reaction is first-order each in [Cr^VI] and [H⁺]. The first-order kinetics with respect to EDTA at low concentrations shift to zero-order at higher concentrations. The reaction is considered to proceed through the formation of a very stable chromium(VI)–DMF–EDTA complex. The suggested mechanism refers only to the induction period of the reaction. The net rate of oxidation of DMF, as measured by the consumption of chromium (VI), is given by: –d[Cr^VI]/dt = kK ₁ K _b[H⁺][DMF]_T[EDTA][Cr^VI]_T/(1 + K ₁[EDTA])(1 + K _b[H⁺])