Unusual coordination mode of thiosemicarbazone ligands. A search for the origin

Twelve mixed-ligand thiosemicarbazone complexes of ruthenium and osmium, ten of general formula [M(bpy)2(bztsc-R)]ClO4, (M = Ru, Os; bpy = 2,2'-bipyridine, Hbztsc-R = benzaldehyde thiosemicacbazone) and two of type [M(bpy)2(actsc)]ClO4 (Hactsc = acetonethiosemicarbazone), have been synthesized and characterized. All the complexes are diamagnetic (low-spin d6, S = 0) and in acetonitrile solution show several intense metal-to-ligand charge-transfer (MLCT) transitions in the visible region. Structures of Hbztsc-OMe, [Ru(bpy)2(bztsc-NO2)]ClO4 and [Ru(bpy)2(actsc)]ClO4 have been determined by X-ray crystallography. Benzaldehyde thiosemicarbazone exists in the thione form with the phenyl group trans to the hydrazinic nitrogen. The benzaldehyde thiosemicarbazone ligand coordinates to the metals through the hydrazinic nitrogen and sulfur with a bite angle of approximately 67 degrees, forming a four-membered chelate ring. However, the actsc ligand coordinates through the imine nitrogen and sulfur, forming a five-membered chelate ring with a bite angle of approximately 81 degrees. The difference in coordination modes of two types of thiosemicarbazone ligands, viz., bztsc-R and actsc, appears to result from the difference in steric bulk of the aryl and methyl group trans to the hydrazinic nitrogen. In acetronitrile solution they all show a reversible metal(II)-metal(III) oxidation in the range 0.18-0.58 V vs SCE followed by an irreversible oxidation in the range 1.11-1.60 V vs SCE. Two successive one-electron reductions of the coordinated bipyridine are also observed in the range -1.53 to -1.96 V vs SCE.     

Synthesis, crystal structures, electrochemical and spectroscopic properties of ruthenium(II) complexes containing diamino-1,3,5-triazine derivatives

Three Ru(II) complexes [Ru(bpy)₂(1-IQTNH)](ClO₄)₂ (1), [Ru(bpy)₂(2-QTNH)](ClO₄)₂ (2) and [Ru(bpy)₂(3-IQTNH)](ClO₄)₂ (3) (bpy = 2,2′-bipyridine, 1-IQTNH = 6-(isoquinolin-1-yl)-1,3,5-triazine- 2,4-diamine, 2-QTNH = 6-(quinolin-2-yl)-1,3,5-triazine- 2,4-diamine, 3-IQTNH = 6-(isoquinolin-3-yl)-1,3,5-triazine-2,4-diamine) have been synthesized and characterized by elemental analysis, ¹H NMR spectroscopy, electrospray ionization mass spectrometry and X-ray crystallography. The electrochemical and spectroscopic properties of the complexes differ from those of [Ru(bpy)₃]²⁺ owing to the structural differences between the ligands and their complexes.     

Chemistry of ruthenium in N2P2X2 (X = Cl, Br) coordination sphere: Synthesis, characterization and reactivities

Reaction of 2-(phenylazo)pyridine (pap) with [Ru(PPh₃)₃X₂] (X = Cl, Br) in dichloromethane solution affords [Ru(PPh₃)₂(pap)X₂]. These diamagnetic complexes exhibit a weakdd transition and two intense MLCT transitions in the visible region. In dichloromethane solution they display a one-electron reduction of pap near − 0.90 V vs SCE and a reversible ruthenium(II)-ruthenium(III) oxidation near 0.70 V vs SCE. The [Ru^III(PPh₃)₂(pap)Cl₂]⁺ complex cation, generated by coulometric oxidation of [Ru(PPh₃)₂(pap)Cl₂], shows two intense LMCT transitions in the visible region. It oxidizes N,N-dimethylaniline and [Ru^II(bpy)₂Cl₂] (bpy = 2,2′-bipyridine) to produce N,N,N′,N′-tetramethylbenzidine and [Ru^III(bpy)₂Cl₂]⁺ respectively. Reaction of [Ru(PPh₃)₂(pap)X₂] with Ag⁺ in ethanol produces [Ru(PPh₃)₂(pap)(EtOH)₂]²⁺ which upon further reaction with L (L = pap, bpy, acetylacetonate ion(acac⁻) and oxalate ion (ox²⁻)) gives complexes of type [Ru(PPh₃)₂(pap)(L)]ⁿ⁺ (n = 0, 1, 2). All these diamagnetic complexes show a weakdd transition and several intense MLCT transitions in the visible region. The ruthenium(II)-ruthenium(III) oxidation potential decreases in the order (of L): pap > bpy > acac⁻ > ox²⁻. Reductions of the coordinated pap and bpy are also observed.     

Chemistry of osmium in N2P2Br2 coordination sphere: Synthesis,structure and reactivities

A family of three mixed-ligand osmium complexes of type [Os(PPh₃)₂(N-N)Br₂], where N-N=2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (Me₂bpy) and 1,10-phenanthroline (phen), have been synthesized and characterized. The complexes are diamagnetic (low-spin d⁶, S=0) and in dichloromethane solution they show intense MLCT transitions in the visible region. The two bromide ligands have been replaced from the coordination sphere of [Os(PPh₃)₂(phen)Br₂] under mild conditions by a series of anionic ligands L (where L=quinolin-8-olate (q), picolinate (pic), oxalate (Hox) and 1-nitroso-2-naphtholate (nn)) to afford complexes of type [Os(PPh₃)₂(phen)(L)]⁺, which have been isolated and characterized as the perchlorate salt. The structure of the [Os(PPh₃)₂(phen)(pic)]ClO₄ complex has been determined by X-ray crystallography. The PPh₃ ligands occupy trans positions and the picolinate anion is coordinated to osmium as a bidentate N,O-donor forming a five-membered chelate ring. The [Os(PPh₃)₂(phen)(L)]⁺ complexes are diamagnetic and show multiple MLCT transitions in the visible region. The [Os(PPh₃)₂(N-N)Br₂] complexes show an osmium(II)–osmium(III) oxidation (−0.02 to 0.12 V vs. SCE) followed by an osmium(III)–osmium(IV) oxidation (1.31 to 1.43 V vs. SCE). The [Os(PPh₃)₂(phen)(L)]⁺ complexes display the osmium (II)–osmium (III) oxidation (0.26 to 0.84 V vs. SCE) and one reduction of phen (−1.50 to −1.79 V vs. SCE). The osmium (III)–osmium (IV) oxidation has been observed only for the L=q and L=Hox complexes at 1.38 V vs. SCE and 1.42 V vs. SCE respectively. The osmium(III) species, viz. [Os^III(PPh₃)₂(N-N)Br₂]⁺ and [Os^III(PPh₃)₂(phen)(L)]²⁺, have been generated both chemically and electrochemically and characterized in solution by electronic spectroscopy and cyclic voltammetry.     

1-(2′-Pyridylazo)-2-naphtholate complexes of ruthenium: Synthesis,characterization, and DNA binding properties

Reaction of 1-(2′-pyridylazo)-2-naphthol (Hpan) with [Ru(dmso)₄Cl₂] (dmso = dimethylsulfoxide), [Ru(trpy)Cl₃] (trpy = 2,2′,2″-terpyridine), [Ru(bpy)Cl₃] (bpy = 2,2′-bipyridine) and [Ru(PPh₃)₃Cl₂] in refluxing ethanol in the presence of a base (NEt₃) affords, respectively, the [Ru(pan)₂], [Ru(trpy)(pan)]⁺ (isolated as perchlorate salt), [Ru(bpy)(pan)Cl] and [Ru(PPh₃)₂(pan)Cl] complexes. Structures of these four complexes have been determined by X-ray crystallography. In each of these complexes, the pan ligand is coordinated to the metal center as a monoanionic tridentate N,N,O-donor. Reaction of the [Ru(bpy)(pan)Cl] complex with pyridine (py) and 4-picoline (pic) in the presence of silver ion has yielded the [Ru(bpy)(pan)(py)]⁺ and [Ru(bpy)(pan)(pic)]⁺ complexes (isolated as perchlorate salts), respectively. All the complexes are diamagnetic (low-spin d⁶, S = 0) and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a Ru(II)–Ru(III) oxidation on the positive side of SCE. Except in the [Ru(pan)₂] complex, a second oxidative response has been observed in the other five complexes. Reductions of the coordinated ligands have also been observed on the negative side of SCE. The [Ru(trpy)(pan)]ClO₄, [Ru(bpy)(pan)(py)]ClO₄ and [Ru(bpy)(pan)(pic)]ClO₄ complexes have been observed to bind to DNA, but they have not been able to cleave super-coiled DNA on UV irradiation.     

Spectral and electrochemical studies of ruthenium(II) complexes with N-methyl-4-nitrobenzaldehyde and N-methyl-4-nitrobenzophenone thiosemicarbazone: Potential anti-trypanosomal agents

N⁴-Methyl-4-nitrobenzaldehyde thiosemicarbazone (H4NO₂Fo4M), N⁴-methyl-4-nitrobenzophenone thiosemicarbazone (H4NO₂Bz4M) and their ruthenium(II) complexes [Ru(4NO₂Fo4M)₂(PPh₃)₂] (1), [Ru(4NO₂Bz4M)₂(PPh₃)₂] (2), [Ru(4NO₂Fo4M)₂(dppb)] (3) and [Ru(4NO₂Bz4M)₂(dppb)] (4) (dppb = 1,4-bis(diphenylphospine)butane) were obtained and characterized. The crystal structure of H4NO₂Fo4M has been determined. Electrochemical studies have shown that the nitro anion radical, one of the proposed intermediates in the mechanism of action of nitro-containing anti-trypanosomal drugs, is formed at approximately −1.00 V in the free thiosemicarbazones as well as in their corresponding ruthenium(II) complexes, suggesting their potential to act as antitrypanosomal drugs. The natural fluorescence of H4NO₂Fo4M, H4NO₂Bz4M and complexes (1)–(4) provides a way to identify and to monitor their concentration in biological systems.     

Reaction of alkenyl carbonyl ruthenium(II) complexes with t-butyl isocyanide. Synthesis of η1-acylruthenium(II) complexes by intramolecular CO insertion

Reaction of Ru(CO)Cl(CHCHR)(PPh₃)₂ or Ru(CO)Cl(CHCHR)(PPh₃)₂L (L = py, Me₂Hpz) with 1 equivalent of t-butyl isocyanide gives the alkenyl derivatives Ru(CO)Cl(CHCHR)(PPh₃)₂(t-BuNC). When an excess of isocyanide is used, further reaction results in intramolecular CO insertion to yield η¹-acyl complexes [Ru(COCHCHR) (t-BuNC)₃(PPh₃)₂]Cl. Related complexes were obtained from [Ru(CO)(CHCHR)(MeCN)₂(PPh₃)₂]PF₆ and an excess of isocyanide.     

Ruthenafuran Complexes Supported by the Bipyridine-Bis(diphenylphosphino)methane Ligand Set: Synthesis and Cytotoxicity Studies

Mononuclear and dinuclear Ru(II) complexes cis-[Ru(κ²-dppm)(bpy)Cl₂] (1), cis-[Ru(κ²-dppe)(bpy)Cl₂] (2) and [Ru₂(bpy)₂(μ-dpam)₂(μ-Cl)₂](Cl)₂ ([3](Cl)₂) were prepared from the reactions between cis(Cl), cis(S)-[Ru(bpy)(dmso-S)₂Cl₂] and diphosphine/diarsine ligands (bpy = 2,2′-bipyridine; dppm = 1,1-bis(diphenylphosphino)methane; dppe = 1,2-bis(diphenylphosphino)ethane; dpam = 1,1-bis(diphenylarsino)methane). While methoxy-substituted ruthenafuran [Ru(bpy)(κ²-dppe)(C^O)]⁺ ([7]⁺; C^O = anionic bidentate [C(OMe)CHC(Ph)O]⁻ chelate) was obtained as the only product in the reaction between 2 and phenyl ynone HC≡C(C=O)Ph in MeOH, replacing 2 with 1 led to the formation of both methoxy-substituted ruthenafuran [Ru(bpy)(κ²-dppm)(C^O)]⁺ ([4]⁺) and phosphonium-ring-fused bicyclic ruthenafuran [Ru(bpy)(P^C^O)Cl]⁺ ([5]⁺; P^C^O = neutral tridentate [(Ph)₂PCH₂P(Ph)₂CCHC(Ph)O] chelate). All of these aforementioned metallafuran complexes were derived from Ru(II)–vinylidene intermediates. The potential applications of these metallafuran complexes as anticancer agents were evaluated by in vitro cytotoxicity studies against cervical carcinoma (HeLa) cancer cell line. All the ruthenafuran complexes were found to be one order of magnitude more cytotoxic than cisplatin, which is one of the metal-based anticancer agents being widely used currently.     

Synthesis,characterization and anticancer activity of 3-aminopyrazine-2-carboxylic acid transition metal complexes

Synthetic procedures are described that allow access to the new complexes cis-[Mo₂O₅(apc)₂], cis-[WO₂(apc)₂], trans-[UO₂(apc)₂], [Ru(apc)₂(H₂O)₂], [Ru(PPh₃)₂(apc)₂], [Rh(apc)₃], [Rh(PPh₃)₂(apc)₂]ClO₄, [M(apc)₂], [M(PPh₃)₂(apc)]Cl, [M(bpy)(apc)]Cl (M(II) = Pd, Pt), [Pd(bpy)(apc)Cl], [Ag(apc)(H₂O)₂] and [Ir(bpy)(Hapc)₂]Cl₃, where Hapc, is 3-aminopyrazine-2-carboxylic acid. These complexes were characterized by physico-chemical and spectroscopic techniques. Both Hapc and several of its complexes display significant anticancer activity against Ehrlich ascites tumour cells (EAC) in albino mice.     

Activation of thiocyanogen and selenocyanogen by low oxidation state transition metal complexes

Thiocyanogen and selenocyanogen react with Ru(CO)₃(PPh₃)₂ to give respectively the complexes Ru(CO)₂(PPh₃)₂(NCS)₂ and Ru(CO)₂(PPh₃)₂(NCSe)₂. (M—NCS and M—SCN represent N- and S-thiocyanato groups, M—NCSe and M—SeCN represent N- and Se-selenocyanato groups respectively, while M—CNS indicates the bridging coordination mode of thiocyanate.) Only the thiocyanogen reacts with Ru₃(CO)₁₂ giving [Ru(CO)₂(CNS)₂]_n, which dissolves in hot coordinating solvents, such as pyridine, to form Ru(CO)₂(py)₂(NCS)₂. Selenocyanogen is less effective than thiocyanogen in the oxidative addition reactions with rhodium(I) and iridium(I) complexes; in fact selenocyanogen does not react with Rh(CO)(PPh₃)₂Cl while with Ir(CO)(PPh₃)₂Cl the former gives Ir(CO)(PPh₃)₂(SeCN)₂Cl by an equilibrium reaction. The coordination number of the metal and the charge on the complex do not change the bonding mode of the thiocyanate and selenocyanate groups in the iridium(III) complexes; in the Ir(PPh₃)₂ClX₂ and [Ir(Ph₂PC₂H₄PPh₂)₂X₂]⁺ (X = SCN and SeCN) complexes the pseudohalogens are S- and Se-bonded.The complexes trans-M(PPh₃)₂(SeCN)₂ (M = Pd, Pt) have been obtained by reacting M(PPh₃)₄ with selenocyanogen.     

Synthesis and characterization of transition metal complexes of a new bidentate ligand {2-(diphenylphosphino)ethyl}benzylamine

A new bidentate ligand {2-(diphenylphosphino)ethyl}benzylamine(DPEBA) was synthesized and characterized based on the IR, mass and ¹H, ¹³C and ³¹P NMR spectra. Various complexes of platinum group metal ions and Ni(II) and Co(II) ions with the ligand were synthesized. Reaction of RuCl₂(PPh₃)₃ or RuCl₂(Me₂SO)₄ with the ligand DPEBA, resulted in formation of a penta-coordinate, Ru(II) species of the composition [RuCl(DPEBA)₂]Cl. Carbonylation of [RuCl(DPEBA)₂]Cl gave an octahedral carbonyl complex of the type [RuCl(CO)(DPEBA)₂]Cl. The reaction of RuCl₃·3H₂O or RuCl₃(AsPh₃)₂MeOH with a twofold excess of the ligand gave an octahedral Ru(III) cationic species [Ru(DPEBA)₂Cl₂]Cl. Carbonylation of the Ru(III) complex gave rise to a carbonyl complex [RuCl(CO)(DPEBA)₂]Cl₂. The ligand DPEBA reacts with cobalt(II) chloride in methanol to give the 1 : 1 complex [Co(DPEBA)Cl₂]. A series of Rh(I) complexes [Rh(DPEBA)₂Cl], [ RhCl(CO)(DPEBA)] and [Rh(DPEBA)₂]Cl were synthesized by the reaction of DPEBA with RhCl(PPh₃)₃, RhCl(CO)(PPh₃)₂ and [Rh(COD)Cl]₂, respectively. Reaction of [Ir(COD)Cl]₂ and IrCl(CO)(PPh₃)₂ with the ligand DPEBA, gave the square-planar complexes [Ir(DPBA)₂]Cl and [Ir(DPEBA)(CO)Cl], respectively. Octahedral cationic complexes of the type [M(DPEBA)₂Cl₂]Cl (M = Rh(III), Ir(III)) were synthesized by the reaction of the ligand DPEBA and rhodium and iridium trichlorides. Reaction of NiCl₂·6H₂O with DPEBA in 1 : 2 molar equivalents, in boiling butanol gave an octahedral neutral complex [Ni(DPEBA)₂Cl₂] which readily rearranges to the square-planar complex [Ni(DPEBA)₂]Cl₂ in methanol. Reaction of Pd(II) and Pt(II) chlorides with DPEBA gave square-planar, cationic complexes of the type [M(DPEBA)₂Cl]Cl (M = Pd, Pt). All the complexes were characterized on the basis of their analytical and spectral data.     

Disproportionation of rhenium(V). Imidazolate coordination of pyridylbenzimidazole in a rhenium(III) complex

Reaction of trans-[ReOCl₃(PPh₃)₂] with 2-(2′-pyridyl)benzimidazole (pbiH) in methanol led to the isolation of the rhenium(III) compound [ReCl₂(pbi)(PPh₃)₂] (1). Complex 1 could also be prepared in better yield by the reduction of [ReO₄]^? with PPh₃ in the presence of pbiH and hydrochloric acid. An X-ray crystallographic study showed that pbi is coordinated as a bidentate monoanionic chelate, with deprotonation of the imidazolyl NH group. The PPh₃ ligands are trans to each other.     

Synthesis, structure, spectroscopic properties, electrochemistry, and DFT correlative studies of N-[(2-pyridyl)methyliden]-6-coumarin complexes of Cu(I) and Ag(I)

6-Aminocoumarin reacts with pyridine-2-carboxaldehyde and has synthesized N-[(2-pyridyl)methyliden]-6-coumarin (L). The ligand, L, reacts with [Cu(MeCN)₄]ClO₄/AgNO₃ to synthesize Cu(I) and Ag(I) complexes of formulae, [Cu(L)₂]ClO₄ and [Ag(L)₂]NO₃, respectively. While similar reaction in the presence of PPh₃ has isolated [Cu(L)(PPh₃)₂]ClO₄ and [Ag(L)(PPh₃)₂]NO₃. All these compounds are characterized by FTIR, UV-Vis and ¹H NMR spectroscopic data. In case of [Cu(L)(PPh₃)₂]ClO₄ and [Ag(L)(PPh₃)₂]NO₃, the structures have been confirmed by X-ray crystallography. The structure of the complexes are distorted tetrahedral in which L coordinates in a N,N′ bidentate fashion and other two coordination sites are occupied by PPh₃. The ligand and the complexes are fluorescent and the fluorescence quantum yields of [Cu(L)(PPh₃)₂]ClO₄ and [Ag(L)(PPh₃)₂]NO₃ are higher than [Cu(L)₂]ClO₄ and [Ag(L)₂]NO₃. Cu(I) complexes show Cu(II)/Cu(I) quasireversible redox couple while Ag(I) complexes exhibit deposition of Ag(0) on the electrode surface during cyclic voltammetric experiments. gaussian 03 computations of representative complexes have been used to determine the composition and energy of molecular levels. An attempt has been made to explain solution spectra and redox properties of the complexes.     

Thiosemicarbazonates of Ruthenium(II): Crystal Structures of [Bis(triphenylphosphine)][bis(N‐phenyl‐pyridine‐2‐carbaldehyde Thiosemicarbazonato)]ruthenium(II) and [Bis(diphenylphosphino)butane][bis(salicylaldehyde Thiosemicarbazonato)]ruthenium(II)

Reaction of RuCl₂(PPh₃)₃ with N‐Phenyl‐pyridine‐2‐carbaldehyde thiosemicarbazone (C₅H₄N–C²(H)=N³‐N²H–C¹(=S)N¹HC₆H₅, Hpytsc‐NPh) in presence of Et₃N base led to loss of ‐N²H‐proton and yielded the complex [Ru(pytsc‐NPh)₂(Ph₃P)₂] ( 1 ). Similar reactions of precursor RuCl₂[(p‐tolyl)₃P]₃ with a series of thiosemicarbazone ligands, viz. pyridine‐2‐carbaldehyde thiosemicarbazone (Hpytsc), salicylaldehyde thiosemicarbazone (H₂stsc), and benzaldehyde thiosemicarbazone (Hbtsc), have yielded the complexes, [Ru(pytsc)₂{(p‐tolyl)₃P}₂] ( 2 ), [Ru(Hstsc)₂{(p‐tolyl)₃P}]₂ ( 3 ), and [Ru(btsc)₂{(p‐tolyl)₃P}₂] ( 4 ), respectively. The reactions of precursor Ru₂Cl₄(dppb)₃ {dppb = Ph₂P–(CH₂)₄–PPh₂} with H₂stsc, Hbtsc, furan‐2‐carbaldehyde thiosemicarbazone (Hftsc) and thiophene‐2‐carbaldehyde thiosemicarbazone (Httsc) have formed complexes of the composition, [Ru(Hstsc)₂(dppb)] ( 5 ), [Ru(btsc)₂(dppb)] ( 6 ), [Ru(ftsc)₂(dppb)] ( 7 ), and [Ru(ttsc)₂(dppb)] ( 8 ). The complexes have been characterized by analytical data, IR, NMR (¹H, ³¹P) spectroscopy and X‐ray crystallography ( 1 and 5 ). The proton NMR confirmed loss of –N²H– proton in all the compounds, and ³¹P NMR spectra reveal the presence of equivalent phosphorus atoms in the complexes. In all the compounds, thiosemicarbazone ligands coordinate to the Ru^II atom via hydrazinic nitrogen (N²) and sulfur atoms. The arrangement around each metal atom is distorted octahedral with cis:cis:trans P, P:N, N:S, S dispositions of donor atoms.     

Energy-level tailoring in a series of redox-rich quinonoid-bridged diruthenium complexes containing tris2-pyridylmethyl)amine as a co-ligand

Reactions of [{Ru(tmpa)}₂(μ‐Cl)₂][ClO₄]₂, ( 2 [ClO₄]₂, tmpa=tris(2‐pyridylmethyl)amine) with 2,5‐dihydroxy‐1,4‐benzoquinone ( L¹ ), 2,5‐di‐[2,6‐(dimethyl)‐anilino]‐1,4‐benzoquinone ( L² ), or 2,5‐di‐[2,4,6‐(trimethyl)‐anilino)]‐1,4‐benzoquinone ( L³ ) in the presence of a base led to the formation of the dinuclear complexes [{Ru(tmpa)}₂(μ‐ L¹ _{?2 H})][ClO₄]₂ ( 3 [ClO₄]₂), [{Ru(tmpa)}₂(μ‐ L² _{?2 H})][ClO₄]₂ ( 4 [ClO₄]₂), and [{Ru(tmpa)}₂(μ‐ L³ _{?2 H})][ClO₄]₂ ( 5 [ClO₄]₂). Structural characterization of 5 [ClO₄]₂ showed the localization of the double bonds within the quinonoid ring and a twisting of the mesityl substituents with respect to the quinonoid plane. Cyclic voltammetry of the complexes show two reversible oxidation and quinonoid‐based reduction processes. Results obtained from UV/Vis/NIR and EPR spectroelectrochemistry are invoked to discuss ruthenium‐ versus quinonoid‐ligand‐centered redox activity. The complex 3 [ClO₄]₂ is compared to the reported complex [{Ru(bpy)}₂(μ‐ L¹ _{?2 H})]²⁺ ( 1²⁺ , bpy=2,2′‐bipyridine). The effects of substituting the bidentate and better π‐accepting bpy co‐ligands with tetradentate tmpa ligands [pure σ‐donating (amine) as well as σ‐donating and π‐accepting (pyridines)] on the redox and electronic properties of the complexes are discussed. Comparisons are also made between complexes containing the dianionic forms of the all‐oxygen‐donating L¹ ligand with the L² and L³ ligands containing an [O,N,O,N] donor set. The one‐electron oxidized forms of the complexes show absorption in the NIR region. The position as well as the intensity of this band can be tuned by the substituents on the quinonoid bridge. In addition, this band can be switched on and off by using tunable redox potentials, making such systems attractive candidates for NIR electrochromism.     

Spectral Properties of Ruthenium(II) Mixed-Ligands Complexes with 2,2'-Bipyridyl and Phosphines

Spectral-kinetic luminescence characteristics of the complexes cis-[Ru(bpy)(dppe)X2], cis- [Ru(bpy)2(PPh₃)X](BF₄) and cis-[Ru(bpy)₂X₂] [bpy = 2,2'-bipyridyl, dppe = 1,2-bis(diphenylphosphino)ethane, PPh₃ is triphenylphosphine, X = NO₂ ^- and CN^-] in the ethanol-methanol 4:1 mixtures and adsorbed on the oxide SiO₂ or porous polyacrylonitrile polymer surface were studied. Luminescence and luminescence exitation spectra were registered at 77 and 293 K in 230-750 nm range and the luminescence decay time was measured. Introduction of phosphine ligands to the ruthenium(II) bipyridyl complexes inner sphere leads to rise in singlet and triplet state energy at the charge transfer from Ru(II) to 2,2'-bipyridyl in the series [Ru(bpy)₂X₂] < Ru(bpy)₂(PPh₃)X](BF₄) < [Ru(bpy)(dppe)X₂]. The complex adsorption on SiO₂ or polyacrylonitrile surface affects noticeably the luminescence spectro-kinetic characteristics.     

Amino acid complexes of ruthenium: synthesis, characterization and cyclic voltammetric studies

Reaction of α-amino acids (HL) with [Ru(PPh₃)₃Cl₂] in the presence of a base afforded a family of complexes of type [Ru(PPh₃)₂(L)₂]. These complexes are diamagnetic (low-spin d⁶, S=0) and show ligand-field transitions in the visible region. ¹H and ³¹P NMR spectra of the complexes indicate the presence of C₂ symmetry. Cyclic voltammetry on the [Ru(PPh₃)₂(L)₂] complexes show a reversible ruthenium(II)–ruthenium(III) oxidation in the range 0.30–0.42 V vs. SCE. An irreversible ruthenium(III)–ruthenium(IV) oxidation is also displayed by two complexes near 1.5 V vs. SCE.     

Homo- und Hetero-Zweikernkomplexe des D2h-symmetrischen Bis(chelat)-Liganden 2,2′-Bipyrimidin mit den elektronenreichen Metallfragmenten Mo(CO)4, Re(CO)3Cl, [Cu(PPh3)2]+ und [Ru(bpy)2]2+

Homo- and Heterodinuclear Complexes of the D_2h-symmetric Bis(chelate) Ligand 2,2′-Bipyrimidine with Electron-Rich Metal Fragments Mo(CO)₄, Re(CO)₃Cl, [Cu(PPh₃)₂]⁺, and [Ru(bpy)₂]²⁺ All homo- and heterodinuclear complexes (L_nM)(μ-bpym)(ML_n)′, bpym = 2,2′-bipyrimidine, ML_n (ML_n)′ = Mo(CO)₄, Re(CO)₃Cl, [Cu(PPh₃)₂]⁺, [Ru(bpy)₂]²⁺, have been synthesized and studied by cyclic voltammetry, absorption spectroscopy, and by electron spin resonance of singly reduced forms. The individual capabilities of the low-valent metal fragments to undergo oxidation and to shift the reduction potential of the bpym π acceptor ligand on coordination combine to result in variable electrochemical potential differences. After consideration of different Franck-Condon factors, absorption intensities, additional low-lying unoccupied orbitals of the bridging acceptor ligand and solvatochromic effects, we have assigned the considerably varying metal-to-ligand charge transfer transitions in the visible.     

Monodentate imido and bidentate aminophenolate coordination of 2-aminophenol in rhenium(V) complexes

Reactions of trans-[ReOCl₃(PPh₃)₂] and trans-[ReO(OEt)I₂(PPh₃)₂] with 2-aminophenol (H₂ap) in acetonitrile led to the formation of cis-[ReOCl₂(Hap)(PPh₃)] (1) and trans-[Re(ap)(Hap)I(PPh₃)₂]I (2), respectively. The X-ray crystal structures show that Hap is coordinated as a bidentate chelate via the neutral amino nitrogen and deprotonated phenolate oxygen, and ap is coordinated as a monodentate through the imido nitrogen. The complexes have been characterized by IR spectroscopy, NMR spectrometry and X-ray crystallography. The bite angle of the Hap chelate is 76.9(1)° and 76.0(1)° in 1 and 2, respectively.     

Synthesis and characterization of Ru(III), Rh(III), Pt(IV) and Ir(III) thiosemicarbazone complexes

Ru(III), Rh(III), Pt(IV) and Ir(III) complexes of 2-furfural thiosemicarbazone as ligand have been synthesised. These complexes have the composition [M(ligand)₂X₂]X (M = Ru(III) Rh(III) and Ir(III) X = Cl and Br) and [Pt(ligand)₂ X₂] X₂ (X = Cl, Br and 1/2SO₄). The deprotonated ligand forms the complexes of the formulae M(ligand-H)₃ and Pt(ligand-H)₃Cl. All these complexes have been characterized by elemental analysis, magnetic measurements, electronic and infrared spectral studies. All the complexes are six-coordinate octahedral.