Samaresh Bhattacharya

Synthesis, structure, spectroscopic properties and cytotoxic effect of some thiosemicarbazone complexes of palladium

Reaction of salicylaldehyde thiosemicarbazone (H2L1), 2-hydroxyacetophenone thiosemicarbazone (H2L2) and 2-hydroxynaphthaldehyde thiosemicarbazone (H2L3) (general abbreviation H2L, where H2 stands for the two dissociable protons, one phenolic proton and one hydrazinic proton) with Na2[PdCl4] affords a family of polymeric complexes of type [{Pd(L)}n]. Reaction of the polymeric species with two monodentate ligands (D), viz. triphenylphosphine (PPh3) and 4-picoline (pic), has yielded complexes of type [Pd(L)(D)]. These mixed-ligand complexes have also been obtained from reaction of the thiosemicarbazones with [Pd(PPh3)2Cl2] and [Pd(pic)2Cl2]. Crystal structures of [Pd(L1)(PPh3)] and [Pd(L2)(pic)] have been determined. The [Pd(L)(D)] complexes show characteristic 1H NMR spectra and intense absorptions in the visible and ultraviolet region. They also fluoresce in the visible region at ambient temperature. In vitro cytotoxicity screenings of the complexes along with four human clinical drugsviz.cisplatin, BCNU, 5-fluorouracil (5-FU) and hydroxyurea have been carried out in two human tumor cell lines, namely promyelocytic leukemia HL-60 and histiocytic lymphoma U-937. [Pd(L2)(PPh3)] shows the lowest IC50 value and is found to be much more cytotoxic than the reference anticancer drugs in both the cell lines. An apoptosis study in HL-60 with [Pd(L2)(PPh3)] confirms that at 10 µM concentration it induces apoptosis to a greater extent than cisplatin and camptothecin.

8-Quinolinolate complexes of ruthenium(ii). Synthesis, characterization and electron transfer properties

Abstract Two stable 8-quinolinolate complexes of ruthenium(II), [Ru(bpy)(Q)]ClO 4 and [Ru(tap) 2 (Q)]ClO 4 [bpy = 2,2′-bipyridine, Q=8-quinolinolate anion, tap = 2-( m -tolylazo) pyridine] have been synthesized. The complexes are diamagnetic and show strong absorption near 1100 cm −1 in the IR spectra due to the presence of ClO − 4 . In acetonitrile solution they behave as 1:1 electrolytes. The complexes display intense absorption bands in the visible region (400–700 nm) which are assigned to MLCT transitions. The formal potential ( E 0 298 ), determined cyclic voltammetrically for the ruthenium(II)-ruthenium(III) oxidation, is 0.48 V vs SCE for [Ru(bpy) 2 (Q)] + . The same oxidation takes place irreversibly at 1.00 V vs SCE ( E pa value) in the case of [Ru(tap) 2 (Q)] + . Reductions of the bound bpy and tap ligands are also observed.

Synthesis, characterization, electron-transfer properties and reactivities of a group of ruthenium(II) complexes with RuN2P2X2 (X = Cl, Br) coordination spheres

Abstract Four dihaloruthenium(II) complexes of general formula Ru(PPh 3 ) 2 (L)X 2 [L = 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen); X = Cl, Br] have been synthesized by the reaction of L with Ru(PPh 3 ) 3 X 2 in dichloromethane. The complexes are diamagnetic and show intense absorptions in the visible region which are assigned to the MLCT transitions. In dichloromethane solution they show a reversible ruthenium(II)-ruthenium-(III) oxidation near 0.4 vs SCE. Two [Ru III (PPh 3 ) 2 (L)(Cl 2 )] + ions have been generated in solution by electrochemical oxidation of Ru II (PPh 3 ) 2 (L)Cl 2 . Solutions of the oxidized complexes show LMCT transitions in the visible region and at 77 K show rhombic EPR spectra. The distortions from octahedral symmetry have been quantified, in these species, with the help of EPR data analysis. The axial distortion is much larger than the rhombic one. The two X − ligands are easily displaced from Ru(PPh 3 ) 2 (L)X 2 by its reaction with Ag + in ethanol producing [Ru(PPh 3 ) 2 (L)(EtOH) 2 ] 2+ , which upon reacting with L′ [L′ = bpy, phen, acetylacetonate ion (acac−), oxalate ion (ox 2− )] affords complexes of type [Ru)PPh 3 ) 2 (L)(L′) n + ( n = 0, 1, 2). Five such complexes have been synthesized and characterized. They all are diamagnetic and show intense MLCT transitions in the visible region. The ruthenium(II)-ruthenium(III) oxidation is very sensitive to the nature of L′. The potential decreases in the order (of L′); bpy (or phen) > acac − > ox 2− . Reductions of the coordinated bpy and phen are also observed.

Synthesis, structure and redox properties of some thiosemicarbazone complexes of rhodium

Reaction of salicylaldehyde thiosemicarbazone (H2L1), 2-hydroxyacetophenone thiosemicarbazone (H2L2) and 2-hydroxynaphthaldehyde thiosemicarbazone (H2L3) (general abbreviation H2L, where H2 stands for the two dissociable protons, one phenolic proton and one hydrazinic proton) with [Rh(PPh3)3Cl] afforded a family of rhodium(III) complexes of the type [Rh(PPh3)2(L)Cl]. The crystal structure of [Rh(PPh3)2(L2)Cl] has been determined by X-ray diffraction. The thiosemicarbazone ligands are coordinated, via dissociation of the two protons, as dianionic tridentate O,N,S-donor ligands forming one six-membered and one five-membered chelate rings. The complexes are diamagnetic (low-spin d6, S=0) and their 1H NMR spectra are in excellent agreement with their compositions. All three [Rh(PPh3)2(L)Cl] complexes display intense absorptions in the visible and ultraviolet regions. They also show strong emission in the visible region at ambient temperature. Cyclic voltammetry on all the complexes shows two irreversible oxidations, the first one is observed within 0.77 to 0.85 V vs. SCE and the second one within 1.13 to 1.23 V vs. SCE, and one irreversible reduction within −1.05 to −1.14 V vs. SCE.

Thiosemicarbazone complexes of the platinum metals. A story of variable coordination modes

Salicylaldehyde thiosemicarbazone (H2saltsc) reacts with [M(PPh3)3X2] (M = Ru, Os; X = Cl, Br) to afford complexes of type [M(PPh3)2(Hsaltsc)2], in which the salicylaldehyde thiosemicarbazone ligand is coordinated to the metal as a bidentate N,S-donor forming a four-membered chelate ring. Reaction of benzaldehyde thiosemicarbazones (Hbztsc-R) with [M(PPh3)3X2] also affords complexes of similar type, viz. [M(PPh3)2(bztsc-R)2], in which the benzaldehyde thiosemicarbazones have also been found to coordinate the metal as a bidentate N,S-donor forming a four-membered chelate ring as before. Reaction of the Hbztsc-R ligands has also been carried out with [M(bpy)2X2] (M = Ru, Os; X = Cl, Br), which has afforded complexes of type [M(bpy)2(bztsc-R)]+, which have been isolated as perchlorate salts. Coordination mode of bztsc-R has been found to be the same as before. Structure of the Hbztsc-OMe ligand has been determined and some molecular modelling studies have been carried out determine the reason for the observed mode of coordination. Reaction of acetone thiosemicarbazone (Hactsc) has then been carried out with [M(bpy)2X2] to afford the [M(bpy)2(actsc)]ClO4 complexes, in which the actsc ligand coordinates the metal as a bidentate N,S-donorformingafive-membered chelate ring. Reaction of H2saltsc has been carried out with [Ru(bpy)2Cl2] to prepare the [Ru(bpy)2(Hsaltsc)]ClO4 complex, which has then been reacted with one equivalent of nickel perchlorate to afford an octanuclear complex of type [Ru(bpy)2(saltsc-H)4Ni4](ClO4)4.

Chemistry of [Ru(tpy)(pap)(L′)n+ (tpy = 2,2′,6′,2″-terpyridine; pap = 2-(phenylazo)pyridine; L′ = Cl−, H2O, CH3CN, 4-picoline, N3−; n = 1,2). X-ray crystal structure of [Ru(tpy)(pap)(CH3CN)](ClO4)2 and catalytic oxidation of water to dioxygen by [Ru(tpy)(pap)(H2O)]2+

Abstract The reaction of [Ru(tpy)Cl3] with pap has afforded [Ru(tpy)(pap)Cl]+ which has been isolated and characterized as the perchlorate salt. Treatment of [Ru(tpy)(pap)Cl]+ with Ag+ in aqueous solution gives [Ru(tpy)(pap)(H2O)]2+. This aquo-complex has been reacted with three monodentate ligands (L′ = CH3CN, 4-picoline and N3− to afford complexes of type [Ru(tpy)(pap)(L′)]n+. Structure determination of [Ru(tpy)(pap) (CH3CN)](ClO4)2 by X-ray crystallography shows that tpy is coordinated to ruthenium in the usual meridional fashion and the pap ligand is bound to ruthenium with the azo-nitrogen trans to CH3CN. All these complexes except [Ru(tpy)(pap)H2O)]2+ show a Ru(II)–Ru(III) oxidation in the range 1.11–1.50 V vs SCE and three ligand(pap)/(tpy)-based reductions on the negative side of SCE. The aquo-complex shows a RuIIOH2/RuIVO couple in aqueous solution (pH = 1–4), the E° of this oxidation is estimated to be 0.82 V vs SCE. Attempt to chemically oxidize the aquo-complex by Ce4+ in aqueous solution (1 M HClO4) results in the catalytic oxidation of water to dioxygen.

Chemistry of ruthenium with some phenolic ligands: synthesis, structure and redox properties

Abstract Reaction of three phenolate ligands, viz. salicylaldehyde (HL 1 ), 2-hydroxyacetophenone (HL 2 ) and 2-hydroxynaphthylaldehyde (HL 3 ), (abbreviated in general as HL, where H stands for the phenolic proton) with [Ru(PPh 3 ) 3 Cl 2 ] in 1:1 mole ratio gives complexes of the type [Ru(PPh 3 ) 2 (L)Cl 2 ]. The structure of the [Ru(PPh 3 ) 2 (L 2 )Cl 2 ] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is O 2 P 2 Cl 2 with a cis – trans – cis geometry, respectively. The [Ru(PPh 3 ) 2 (L)Cl 2 ] complexes are one-electron paramagnetic (low-spin d 5 , S =1/2) and show rhombic ESR spectra in 1:1 dichloromethane–toluene solution at 77 K. In dichloromethane solution the [Ru(PPh 3 ) 2 (L)Cl 2 ] complexes show several intense LMCT transitions in the visible region. Reaction between the phenolic ligands and [Ru(PPh 3 ) 3 Cl 2 ] in 2:1 mole ratio in the presence of a base affords the [Ru(PPh 3 ) 2 (L) 2 ] complexes in two isomeric forms. 1 H NMR spectra of one isomer shows that it does not have any C 2 symmetry and has the cis – cis – cis disposition of the three sets of donor atoms. 1 H NMR spectra of the other isomer shows that it has C 2 symmetry. The structure of the isomer of the [Ru(PPh 3 ) 2 (L 1 ) 2 ] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is O 4 P 2 with a cis – trans – cis disposition of the carbonylic oxygens, phenolate oxygens and phosphorus atoms, respectively. The [Ru(PPh 3 ) 2 (L) 2 ] complexes are diamagnetic (low-spin d 6 , S =O) and show intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ru(PPh 3 ) 2 (L)Cl 2 ] complexes shows a ruthenium(III)ruthenium(II) reduction near −0.3 V versus SCE and a ruthenium(III)ruthenium(IV) oxidation in the range 1.08–1.24 V versus SCE. Cyclic voltammetry on both isomers of the [Ru(PPh 3 ) 2 (L) 2 ] complexes shows a ruthenium(II)ruthenium(III) oxidation within 0.09–0.41 V versus SCE, followed by a ruthenium(III)-ruthenium(IV) oxidation within 1.31–1.52 V versus SCE.

CHEMISTRY OF 2-(ARYLAZO)PHENOLATE COMPLEXES OF RUTHENIUM. SYNTHESIS, STRUCTURE AND REACTIVITIES

Abstract A group of six ruthenium(III) complexes of type [Ru(acac)(L)2]where acac=acetylacetonate anion and L=2-(arylazo)-4-methylphenolate anion or 1-(phenylazo)-2-naphtholate anion have been synthesized and characterized Structural characterization of a representative complex where L=1-(phenylazo)-2-naphtholate anionshows that the azophenolate ligands are coordinated as NO-donor ligands forming six-membered chelate rings The complexes are paramagnetic (low-spin d5S=1/2) and show rhombic ESR spectra in 1:1 dichloromethane–toluene solution at 77 K In carbon tetrachloride solution these complexes show intense LMCT transitions in the visible region together with weak ligand-field transitions in the near-IR region All the complexes display two cyclic voltammetric responses a ruthenium(III)–ruthenium(IV) oxidation in the range of 083 to 103 V vs SCE and a ruthenium(III)–ruthenium(II) reduction in the range of −024 to −052 V vs SCE Formal potentials of both the couples correlate linearly with the Hammett constant of the para substituent in the arylazo fragment of the 2-(arylazo)-4-methylphenolate ligand The ruthenimn(IV) and ruthenium(II) congeners of the [RuIII(acac)(L)2] complexes have been generated by chemical or electrochemical methods and they have been characterized by electronic spectroscopy and cyclic voltammetry.

Synthesis, characterization and reactivity of a ruthenium-quinone complex

Abstract A mixed ligand ruthenium-quinone complex, Ru(trpy)(DBQ)Cl [trpy = 2,2′: 6′,2″-terpyridine, DBQ = 3,5-di-tert-butylquinone] has been synthesized. The complex is paramagnetic (1 upe) and shows a sharp EPR signal at g ≈ 2. A Ru II -DBSQ [DBSQ = semiquinonate form of DBQ] charge distribution is therefore assigned to this complex. It shows intense absorption bands in the visible and near-infrared regions which are assigned to allowed charge-transfer transitions. In dichloromethane solution it shows three reversible cyclic voltammetric responses, one ruthenium(II)-ruthenium(III) oxidation and the reductions of DBSQ and trpy ligands. The chloride ligand in Ru(trpy)(DBSQ)Cl can be replaced in aqueous medium by reacting it with Ag + to afford the [Ru(trpy)(DBSQ)(H 2 O] + ioin, which has been isolated and characterized as the perchlorate salt. This aquo complex is easily converted back to the parent chloro complex by reaction with the chloride ion.

Chemistry of ruthenium with some dioxime ligands. Syntheses, structures and reactivities

Abstract Reaction of two dioxime ligands, viz. dimethylglyoxime (H2dmg) and diphenylglyoxime (H2dpg), (abbreviated in general as H2L, where H stands for the oxime protons) with [Ru(PPh3)3Cl2] in 1:1 mole ratio affords complexes of type [Ru(PPh3)2(H2L)Cl2]. Structure of the [Ru(PPh3)2(H2dpg)Cl2] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is N2P2Cl2 with the two PPh3 ligands in trans and the two chlorides in cis positions. Reaction of the dioxime ligands with [Ru(PPh3)3Cl2] in 2:1 mole ratio in the presence of a base affords complexes of type [Ru(PPh3)2(HL)2]. Structure of the [Ru(PPh3)2(Hdmg)2] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is N4P2 with the two PPh3 ligands in trans positions. Reaction of the [Ru(PPh3)2(H2dpg)Cl2] complex with a group of bidentate acidic ligands, viz. picolinic acid (Hpic), quinolin-8-ol (Hq) and 1-nitroso-2-naphthol (Hnn), (abbreviated in general as HL′, where H stands for the acidic proton) in the presence of a base affords complexes of type [Ru(PPh3)2(H2dpg)(L′)]+ isolated as perchlorate salts. All the complexes are diamagnetic (low-spin d6, S=0) and in dichloromethane solution show several intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a reversible ruthenium(II)–ruthenium(III) oxidation within 0.36–0.98 V versus SCE followed by a quasi-reversible ruthenium(III)–ruthenium(IV) oxidation within 0.94–1.60 V versus SCE.