Synthesis, spectroscopic and redox properties of some ruthenium(II) thiosemicarbazone complexes: structural description of four of these complexes

Sixteen neutral mixed ligand thiosemicarbazone complexes of ruthenium having general formula [Ru(PPh3)(2)L-2], where LH = 1-(arylidine)4-aryl thiosemicarbazones, have been synthesized and characterized. All complexes are diamagnetic and hence ruthenium is in the +2 oxidation state (low-spin d(6), S = 0). The complexes show several intense peaks in the visible region due to allowed metal to ligand charge transfer transitions. The structures of four of the complexes have been determined by single-crystal X-ray diffraction and they show that thiosemicarbazone ligands coordinate to the ruthenium center through the hydrazinic nitrogen and sulfur forming four-membered chelate rings with ruthenium in N2S2P2 coordination environment. In dichloromethane solution, the complexes show two quasi-reversible oxidative responses corresponding to loss of electron from HOMO and HOMO - 1. The E-0 values of the above two oxidations shows good linear relationship with Hammett substituents constant (sigma) as well as with the HOMO energy of the molecules calculated by the EHMO method. A DFT calculation on one representative complex suggests that there is appreciable contribution of the sulfur p-orbitals to the HOMO and HOMO - 1. Thus, assignment of the oxidation state of the metal in such complexes must be made with caution. (c) 2005 Elsevier B.V. All rights reserved.

Synthesis, structure and solution chemistry of quaternary oxovanadium(V) complexes incorporating hydrazone ligands

[VIVO(acac)(2)] reacts with an equimolar amount of benzoyl hydrazone of 2-hydroxyacetophenone (H2L1) or 5-chloro-2-hydroxyacetophenone (H2L2) in the presence of excess pyridine (py) in methanol to produce the quaternary [(VO)-O-V(L-1)(OCH3)(py)] (1) and [(VO)-O-V(L-2)(OCH3)(py)] (2) complexes, respectively, while under similar condition, the benzoyl hydrazones of 2-hydroxy-5-methylacetophenone (H2L3) and 2-hydroxy-5-methoxyacetophenone (H2L4) afforded only the methoxy bridged dimeric [(VO)-O-V(L-3/L-4)(OCH3)](2) complexes. The X-ray structural analysis of 1 and 2 indicates that the geometry around the metal is distorted octahedral where the three equatorial positions are occupied by the phenolate-O, enolate-O and the imine-N of the fully deprotonated hydrazone ligand in its enolic form and the fourth one by a methoxide-O atom. An oxo-O and a pyridine-N atom occupy two axial positions. Quaternary complexes exhibit one quasi-reversible one-electron reduction peak near 0.25 V versus SCE in CH2Cl2 and they decompose appreciably to the corresponding methoxy bridged dimeric complex in CDCl3 solution as indicated by their H-1 NMR spectra. These quaternary VO3+ complexes are converted to the corresponding V2O34+-complexes simply on refluxing them in acetone and to the VO2+-complexes on reaction with KOH in methanol. An equimolar amount of 8-hydroxyquinoline (Hhq) converts these quaternary complexes to the ternary [(VO)-O-V(L)(hq)] complexes in CHCl3. (C) 2009 Elsevier B. V. All rights reserved.

Palladium(II) and platinum(II) complexes with tridentate iminophosphine ligands; synthesis and structural studies

The previously synthesised Schiff-base ligands 2-(2-Ph2PC6H4N = CH) - R' - C6H3OH (R' = 3-OCH3, HL1; 5-OCH3, HL2; 5-Br, HL3; 5-Cl, HL4) were prepared by a faster, more efficient route involving a microwave assisted co-condensation of 2-(diphenylphosphino) aniline with the appropriate substituted salicylaldehyde. HL1-4 react directly with (MCl2)-Cl-II (M = Pd, Pt) or (PtI2)-I-II(cod) affording neutral square-planar complexes of general formula [(MCl)-Cl-II(eta(3)-L1-4)] (M = Pd, Pt, 1 - 8) and [(PtI)-I-II(eta(3)-L1-4)] (M = Pd, Pt, 9 - 12). Reaction of complexes 1 - 4 with the triarylphosphines PR3 (R = Ph, p-tolyl) gave the novel ionic complexes [Pd-II(PR3)(eta(3)- L1-4)] ClO4 (13 - 20). Substituted platinum complexes of the type [Pt-II(PR3)(eta(3)- L1-4)] ClO4 (R = P(CH2CH2CN)(3) 21 - 24) and [Pt-II( P(p-tolyl)(3))(eta(3)-L-3,L-4)] ClO4 ( 25 and 26) were synthesised from the appropriate [(PtCl)-Cl-II(eta(3)-L1-4)] complex (5 - 8) and PR3. The complexes are characterised by microanalytical and spectroscopic techniques. The crystal structures of 3, 6, 10, 15, 20 and 26 were determined and revealed the metal to be in a square-planar four-coordinate environment containing a planar tridentate ligand with an O, N, P donor set together with one further atom which is trans to the central nitrogen atom.

Synthesis, crystal structure and reactivity of copper(II) complexes of tetradentate N2S2 donor ligands

Two new hexa-coordinated mononuclear copper(II) complexes of two ligands L-1 and L-2 containing NSSN donor sets formulated as [Cu(L)(H2O)(2)](NO3)(2) [1a, L = 1,2-bis(2-pyridylmethylthio)ethane (L-1), 1b L = 1,3-bis(2-pyridyl-methylthio)propane (L-2)] were synthesized and characterized by physico-chemical and spectroscopic methods. In 1a the single crystal X-ray crystallography analysis showed a distorted octahedral geometry about copper(II) ion. The crystal packing evidences pairs of complexes arranged about a center of symmetry and connected through a H-bond occurring between aquo ligands and nitrate anions. On reaction with chloride and pseudohalides (N-3(-) and SCN-), in acetonitrile at ambient temperature. complexes 1 changed to monocationic penta-coordinated mononuclear copper(H) species formulated as [Cu(L)(Cl)]NO3 (2), [Cu(L)(N-3)]NO3 (3). and [Cu(L)(SCN)]NO3 (4). These copper(II) complexes have been isolated in pure form from the reaction mixtures and characterized by physico-chemical and spectroscopic tools. The solid-state structure of 2a, established by X-ray crystallography, shows a trigonal bipyramidal geometry about the metal ion with a trigonality index (tau) of 0.561. (C) 2009 Elsevier B.V. All rights reserved.

Cyclam derivatives containing three acetate pendant arms: synthesis, acid-base, metal complexation and structural studies

The ligands 1,4,8,11-tetraazacyclotetradecane-1,4,8-triacetic-11-methylphosphonic acid (H(5)te3a1p) and 1,4,8,11-tetraazacyclotetradecane-1,4,8-triacetic acid (H(3)te3a) were synthesized, the former one for the first time. The syntheses of these ligands were achieved from reactions on 1,4,8,11-tetraazacyclotetradecane-1,4,8-tris( carbamoylmethyl) hydroiodide (te3am center dot HI), and compounds (Hte3am)(+), 1, and (H(7)te3a1p)(2+), 4, were characterized by X-ray diffraction. Structures of two other compounds resulting from side-reactions, (H(2)te2lac)(2+), 2, and (H(4)te2a2p(OEt2))(2+), 3, were also determined by X-ray diffraction. Potentiometric titrations of H(5)te3a1p and H(3)te3a were performed at 298.2 K and ionic strength 0.10 mol dm(-3) in NMe4NO3 to determine their protonation constants. H-1 and P-31 NMR titrations of H(5)te3a1p were carried out in order to determine the very high first protonation constant of this ligand and to elucidate the sequence of protonation. Potentiometric studies of the two ligands with Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ metal ions performed in the same experimental conditions showed that the complexes of H5te3a1p present very high thermodynamic stability while complexes of H(3)te3a, particularly Co2+ and Zn2+, are even more stable. P-31 NMR spectra of the cadmium(II) complex of H(5)te3a1p showed that the phosphonate moiety was coordinated to the metal ion. The UV-vis-NIR spectroscopic data and magnetic moment values of Co2+ and Ni2+ complexes of H(5)te3a1p and H(3)te3a together with the EPR of the corresponding Cu2+ complexes indicated that all these complexes adopt distorted octahedral coordination geometries in solution. This was confirmed by the single crystal structure of [Cu-2(Hte3a)(H2O)(3)Cl]Cl-0.5(ClO4)(0.5) center dot 2H(2)O that showed two distorted octahedral copper centres bridged by a N-acetate pendant arm with a Cu center dot center dot center dot Cu distance of 4.890(1) angstrom. The first one is encapsulated into the macrocyclic cavity surrounded by four nitrogen and two oxygen donors from the macrocycle, whereas the second one is on the periphery of the macrocycle and is coordinated to two oxygen atoms of one acetate pendant arm in chelating fashion, one chloride and three water molecules.

Diorganoruthenium complexes incorporating noninnocent [C6H2(CH2ER2)2-3,5]22-(E = N, P) Bis-Pincer bridging ligands: synthesis, spectroelectrochemistry, and DFT studies

The dinuclear complex [(tpy)Ru-II(PCP-PCP)Ru-II(tPY)]Cl-2 (bridging PCP-PCP = 3,3',5,5'-tetrakis(diphenylphosphinomethyl)biphenyl, [C6H2(CH2PPh2)(2)-3,5](2)(2-)) was prepared via a transcyclometalation reaction of the bis-pincer ligand [PC(H)P-PC(H)P] and the Ru(II) precursor [Ru(NCN)(tpy)]Cl (NCN = [C6H3(CH2NMe2)(2)-2,6](-)) followed by a reaction with 2,2':6',2 ''-terpyridine (tpy). Electrochemical and spectroscopic properties of [(tpy)Ru-II(PCP-PCP)Ru-II(tPY)]Cl-2 are compared with those of the closely related [(tpy)Ru-II(NCN-NCN)Ru-II(tpy)](PF6)(2) (NCN-NCN = [C6H2(CH2- NMe2)(2)-3,5](2)(2-)) obtained by two-electron reduction of [(tpy)Ru-III(NCN-NCN)Ru-III(tpy)](PF6)(4). The molecular structure of the latter complex has been determined by single-crystal X-ray structure determination. One-electron reduction of [(tpy)Ru-III(NCN-NCN)Ru-III(tpy)](PF6)(4) and one-electron oxidation of [(tpy)Ru-II(PCP-PCP)RUII(tpy)]Cl-2 yielded the mixed-valence species [(tpy)Ru-III(NCN-NCN)RUII(tpy)](3+) and [(tpy)Ru-III(PCP-PCP)RUII(tpy)](3+), respectively. The comproportionation equilibrium constants K-c (900 and 748 for [(tpy)Ru-III(NCN-NCN)Ru-III(tpy)](4+) and [(tpy)Ru-II(PCP-PCP)RUII(tpy)](2+), respectively) determined from cyclic voltammetric data reveal comparable stability of the [Ru-III-Ru-II] state of both complexes. Spectroelectrochemical measurements and near-infrared (NIR) spectroscopy were employed to further characterize the different redox states with special focus on the mixed-valence species and their NIR bands. Analysis of these bands in the framework of Hush theory indicates that the mixed-valence complexes [(tpy)Ru-III(PCP-PCP)RUII(tpy)](3+) and [(tpy)Ru-III(NCN-NCN)RUII(tpy)](3+) belong to strongly coupled borderline Class II/Class III and intrinsically coupled Class III systems, respectively. Preliminary DFT calculations suggest that extensive delocalization of the spin density over the metal centers and the bridging ligand exists. TD-DFT calculations then suggested a substantial MLCT character of the NIR electronic transitions. The results obtained in this study point to a decreased metal-metal electronic interaction accommodated by the double-cyclometalated bis-pincer bridge when strong sigma-donor NMe2 groups are replaced by weak sigma-donor, pi-acceptor PPh2 groups

The synthesis, structure, reactivity and electrochemical properties of ruthenium complexes featuring cyanoacetylide ligands

The complex [Ru(C&3bond; CC&3bond; N)(dppe)Cp*] (1) is readily obtained (ca. 70%) from the sequential reaction of [Ru(C=CH2)(dppe)Cp*]PF6 with (BuLi)-Bu-n and phenyl cyanate. The complex behaves as a typical transition metal acetylide upon reaction with tetracyanoethene, affording a metallated pentacyanobutadiene. Complex I is a useful metalloligand, and its reactions with [W(thf)(CO)5], [RuCl(PPh3)(2)Cp], [RuCl(dppe)Cp*] or cis-[RuCl2(dppe)(2)] all afforded products featuring the M-C&3bond; CC&3bond; N-M' motif, for which ground state structures indicate a degree of polarisation. Electrochemical and spectroelectrochemical studies reveal moderate interactions between the metal centres in the 35-electron dications [{Cp*(dppe)Ru}(mu-C&3bond; CC&3bond; N){RuL2Cp'}](2+) Ru(PPh3)(2)CP, Ru(dppe)Cp*).

Synthesis, photophysical, photochemical, and redox properties of nitrospiropyrans substituted with Ru or Os tris(bipyridine) complexes

Photochromic nitrospiropyrans substituted with 2,2'-bipyridine (bpy), [Ru(bpy)(3)](2+), and [Os(bpy)(3)](2+) groups were synthesized, and their photophysical, photochemical, and redox properties investigated. Substitution of the spiropyran with the metal complex moiety results in strongly decreased efficiency of the ring-opening process as a result of energy transfer from the excited spiropyran to the metal center. The lowest excited triplet state of the spiropyran in its open merocyanine form is lower in energy than the excited triplet MLCT level of the [Ru(bpy)(3)](2+) moiety but higher in energy than for [Os(bpy)(3)](2+), resulting in energy transfer from the excited ruthenium center to the spiropyran but inversely in the osmium case. The open merocyanine form reduces and oxidizes electrochemically more easily than the closed nitrospiropyran. Like photoexcitation, electrochemical activation also causes opening of the spiropyran ring by first reducing the closed form and subsequently reoxidizing the corresponding radical anion in two well-resolved anodic steps. Interestingly, the substitution of the spiropyran with a Ru or Os metal center does not affect the efficiency of this electrochemically induced ring-opening process, different from the photochemical path.

Coordination behavior of symmetrical hexadentate O2N2S2-donor Schiff bases toward zinc (II): synthesis, characterization, and crystal structure

Two series of zinc(II) complexes of two Schiff bases (H2L1 and H2L2) formulated as [Zn(HL1/HL2)]ClO4 (1a and 1b) and [Zn(L1/L2)] (2a and 2b), where H2L1 = 1,8-bis(salicylideneamino)-3,6-dithiaoctane and H2L2 = 1,9-bis(salicylideneamino)-3,7-dithianonane, have been prepared and isolated in pure form by changing the chemical environment. Elemental, spectral, and other physicochemical results characterize the complexes. A single crystal X-ray diffraction study confirms the structure of [Zn(HL1)]ClO4 (1a). In 1a, zinc(II) has a distorted octahedral environment with a ZnO2N2S2 chromophore.

Metal-directed assembly of large dinuclear copper(II) dithiocarbamate macrocyclic complexes

The synthesis of a range of dinuclear Cu(II) dithiocarbamate (dtc)-based macrocycles and their characterisation are described. By carefully tuning the size of the aromatic spacer, cavities of different dimensions can be designed. The length and flexibility of the chosen spacer group dictates the intermetallic distance and hence the degree of communication between the two metal centres as evidenced by electrochemical and EPR experiments. This is illustrated by crystallographic evidence that show the macrocycles can host guests (such as CH2Cl2) or can fold and form unexpected Cu(I) dtc clusters.

Synthesis, crystal structures, magnetic properties and catecholase activity of double phenoxido-bridged penta-coordinated dinuclear nickel(II) complexes derived from reduced Schiff-base ligands: mechanistic inference of catecholase activity

Three double phenoxido-bridged dinuclear nickel(II) complexes, namely [Ni-2(L-1)(2)(NCS)(2)] (1), [Ni-2(L-2)(2)(NCS)(2)] (2), and [Ni-2(L-3)(2)(NCS)(2)] (3) have been synthesized using the reduced tridentate Schiff-base ligands 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL1), 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL2), and 2-[1-(3-dimethylarnino-propylamino)-ethyl]-phenol (HL3), respectively. The coordination compounds have been characterized by X-ray structural analyses, magnetic-susceptibility measurements, and various spectroscopic methods. In all complexes, the nickel(II) ions are penta-coordinated in a square-pyramidal environment, which is severely distorted in the case of 1 (Addison parameter tau = 0.47) and 3 (tau = 0.29), while it is almost perfect for 2 (tau = 0.03). This arrangement leads to relatively strong antiferromagnetic interactions between the Ni(II) (S = 1) metal centers as mediated by double phenoxido bridges (with J values of -23.32 (1), -35.45 (2), and -34.02 (3) cm(3) K mol(-1), in the convention H = -2JS(1)S(2)). The catalytic activity of these Ni compounds has been investigated for the aerial oxidation of 3,5-di-tert-butylcatechol. Kinetic data analysis following Michaelis-Menten treatment reveals that the catecholase activity of the complexes is influenced by the flexibility of the ligand and also by the geometry around the metal ion. Electrospray ionization mass spectroscopy (ESI-MS) studies (in the positive mode) have been performed for all the coordination compounds in the presence of 3,5-DTBC to characterize potential complex-substrate intermediates. The mass-spectrometry data, corroborated by electron paramagnetic resonance (EPR) measurements, suggest that the metal centers are involved in the catecholase activity exhibited by the complexes.

Synthesis, crystal structures and magnetic properties of two bis(μ-phenoxido)dicopper(II) complexes derived from reduced Schiff base ligands

Two phenoxido bridged dinuclear Cu(II) complexes, [Cu-2(L-1)(2)(NCNCN)(2)] (1) and [Cu-2(L-2)(2)(NCNCN)(2)]center dot 2H(2)O (2) have been synthesized using the tridentate reduced Schiff-base ligands 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL1) and 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL2), respectively. The complexes have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Both the complexes present a diphenoxido bridging Cu2O2 core. The geometries around metal atoms are intermediate between trigonal bipyramid and square pyramid with the Addison parameters (tau) = 0.57 and 0.49 for 1 and 2, respectively. Within the core the Cu-O-Cu angles are 99.15 degrees and 103.51 degrees and average Cu-O bond distances are 2.036 and 1.978 angstrom for compounds 1 and 2, respectively. These differences have marked effect on the magnetic properties of two compounds. Although both are antiferromagnetically coupled, the coupling constants (J = -184.3 and -478.4 cm (1) for 1 and 2, respectively) differ appreciably.

Ruthenium mediated C–H activation of benzaldehyde thiosemicarbazones: Synthesis, structure and, spectral and electrochemical properties of the resulting complexes

Reaction of five 4R-benzaldehyde thiosemicarbazones (R = OCH3, CH3, H, Cl and NO2) with [ Ru(PPh3)(3)(-CO)(H) Cl] in refluxing methanol in the presence of a base (NEt3) affords complexes of two different types, viz. 1-R and 2-R. In the 1-R complexes the thiosemicarbazone is coordinated to ruthenium as a dianionic tridentate C,N,S-donor via C-H bond activation. Two triphenylphosphines and a carbonyl are also coordinated to ruthenium. The tricoordinated thiosemicarbazone ligand is sharing the same equatorial plane with ruthenium and the carbonyl, and the PPh3 ligands are mutually trans. In the 2-R complexes the thiosemicarbazone ligand is coordinated to ruthenium as a monoanionic bidentate N, S-donor forming a four-membered chelate ring with a bite angle of 63.91(11)degrees. Two triphenylphosphines, a carbonyl and a hydride are also coordinated to ruthenium. The coordinated thiosemicarbazone ligand, carbonyl and hydride constitute one equatorial plane with the metal at the center, where the carbonyl is trans to the coordinated nitrogen of the thiosemicarbazone and the hydride is trans to the sulfur. The two triphenylphosphines are trans. Structures of the 1-CH3 and 2-CH3 complexes have been determined by X-ray crystallography. All the complexes show intense transitions in the visible region, which are assigned, based on DFT calculations, to transitions within orbitals of the thiosemicarbazone ligand. Cyclic voltammetry on the complexes shows two oxidations of the coordinated thiosemicarbazone on the positive side of SCE and a reduction of the same ligand on the negative side.

Synthesis and crystal structures of μ-oxido- and μ-hydroxido-bridged dinuclear iron(III) complexes with an N2O donor ligand - a theoretical study on the influence of weak forces on the Fe-O-Fe bridging angle

The synthesis and crystal structures of three nonheme di-iron(III) complexes with a tridentate N,N,O Schiff-base ligand, 2-({[2-(dimethylamino) ethyl] imino} methyl) phenol (HL), are reported. Complexes [Fe2OL2(NCO)(2)] (1a) and [Fe2OL2(SAL)(2)]center dot H2O [SAL = o-(CHO)C6H4O-] (1b) are unsupported mu-oxido-bridged dimers, and [Fe-2(OH)L-2(HCOO)(2)-(Cl)] (2) is a mu-hydroxido-bridged dimer supported by a formato bridging ligand. All complexes have been characterized by X-ray crystallography and spectroscopic analysis. Complex 1b has been reported previously; however, it has been reinvestigated to confirm the presence of a crucial water molecule in the solid state. Structural analyses show that in 1a the iron atoms are pentacoordinate with a bent Fe-O-Fe angle [142.7(2)degrees], whereas in 2 the metal centers are hexacoordinate with a normal Fe-OH-Fe bridging angle [137.9(2)degrees]. The Fe-O-Fe angles in complexes 1a and 1b differ significantly to those usually shown by (mu-oxido) Fe-III complexes. A theoretical study has been performed in order to rationalize this deviation. Moreover, the influence of the water molecule observed in the solid-state structure of 1b on the Fe-O-Fe angle is also analyzed theoretically.

Synthesis and spectroscopic properties of cobalt(III) complexes of some aroyl hydrazones: x-ray crystal structures of one cobalt(III) complex and two aroyl hydrazone ligands

Cobalt(III) complexes of diacetyl monooxime benzoyl hydrazone (dmoBH(2)) and diacetyl monooxime isonicotinoyl hydrazone (dmoInH(2)) have been synthesized and characterized by elemental analyses and spectroscopic methods. The X-ray crystal structures of the two hydrazone ligands, as well as that of the cobalt(III) complex [Co(III)(dmoInH)(2)]Cl center dot 2H(2)O, are also reported. It is found that in the cobalt(III) complexes the Co(III) ion is hexa-coordinated, the hydrazone ligands behaving as mono-anionic tridentate O,N,N donors. In the [Co(III)(dmoInH) (2)]Cl center dot 2H(2)O complex, the amide and the oxime hydrogens are deprotonated for both the ligands, while the isonicotine nitrogens are protonated. In the [Co(III)(d-moBH)(2)] Cl complex, only the amide nitrogens are deprotonated. It is shown that the additional hydrogen bonding capability of the isonicotine nitrogen results in different conformation and supramolecular structure for dmoInH(2), compared to dmoBH(2), in the solid state. Comparing the structure of the [CoIII(dmoInH)(2)]Cl center dot 2H(2)O with that of the Zn(II) complex of the same ligand, reported earlier, it is seen that the metal ion has a profound influence on the supramolecular structure, due to change in geometrical dispositions of the chelate rings.