Saktiprosad Ghosh

A new route for the synthesis of bis(pyridine dicarboxylato)bis(triphenylphosphine) complexes of ruthenium(II) and X-ray structural characterisation of the biologically active trans-[Ru(PPh3)2(L1H)2] (L1H2=pyridine 2,3-dicarboxylic acid)

Abstract Ruthenium(II) complexes of the general formula Ru(LH)2(PPh3)2, (LH2=pyridine 2,3-; 2,4-; 2,5- and 2,6-dicarboxylic acid) are synthesised by a new method. All the pyridine dicarboxylic acids are found to behave as bidentate, monobasic chelating donors, with one carboxyl group remaining idle. The electrochemical behaviour of the compounds is explored with the help of cyclic voltammetry. The antibacterial activities of these compounds were examined against Escherichia coli in nutrient broth in order to check their potential for antitumour activity. Single-crystal X-ray analysis of the complex involving pyridine 2,3-dicarboxylic acid (L1H2) revealed that the coordination environment consists of a centrosymmetric, axially elongated N2P2O2 octahedron with a pair of coordinated L1H ligands occupying the equatorial plane.

Synthesis, characterisation and crystal structure of cis-dioxomolybdenum(VI) complexes of some potentially pentadentate but functionally tridentate (ONS) donor ligands

Abstract Neutral cis-dioxomolybdenum(VI) complexes with potentially pentadentate ONSNO donor Schiff bases of thiocarbodihydrazone of salicylaldehyde (H3L1), 5-bromo (H3L2), 5-nitro salicylaldehyde (H3L3) and 2-hydroxyacetophenone (H3L4) acting as tridentate ONS donor ligands have been synthesised. The complexes are found to be of the form MoO2LH(ROH) (R=CH3) where, LH=LIH, L2H, L3H and L4H. The complexes were characterised by elemental analyses, UV, IR, and 1H NMR spectroscopy, magnetic susceptibility measurement, molar conductivities in solution and by cyclic voltammetry. Two of the complexes [MoO2(L2H)(MeOH)] and [MoO2(L4H)(MeOH)] were crystallographically characterised. The structures reveal that the molybdenum acceptor centre is present in a distorted octahedral NO4S donor environment. The presence of a substituent either on the aromatic ring of the salicylaldehyde moiety or on the carbon atom of its carbonyl group is found to exhibit little effect on the corresponding metal ligand bond distances and angles. The sixth coordination site of the complexes harboring the weakly coordinated ROH moiety is found to act as the binding site for various neutral monodentate Lewis bases.

Synthesis and characterization of some biologically active ruthenium(II) complexes of thiosemicarbazones of pyridine 2-aldehyde and thiophene 2-aldehyde involving some ring substituted 4-phenylthiosemicarbazides and 4-cyclohexylthiosemicarbazide. Crystal structure of cis-[Ru(PPh3)2(L6H)2](ClO4)2·2H2O [L6H=4-(cyclohexyl) thiosemicarbazone of pyridine 2-aldehyde]

Abstract A series of ruthenium(II) complexes of potentially NNS tridentate but functionally NS bidentate chelating ligands in the form of 4-substituted 4-phenyl and 4-cyclohexyl thiosemicarbazones of pyridine 2-aldehyde and thiophene 2-aldehyde (LH) have been synthesized using Ru(PPh3)3Cl2 as the starting material. The complexes are of the general formula [Ru(PPh3)2(LH)2]X2, [L1H, L2H, L3H, L4H, L5H and L6H are 4-(p-fluorophenyl), 4-(p-chlorophenyl) 4-(p-iodophenyl), 4-(p-hydroxyphenyl), 4-(p-methylphenyl) and 4-(p-cyclohexyl) thiosemicarbazones of pyridine 2-aldehyde and L7H is the 4-cyclohexyl thiosemicarbazone of thiophene 2-aldehyde (Figure 1) and X=ClO4, PF6]. A complex [Ru(bipy)(L6H)2](ClO4)2, has also been synthesized. All the complexes were characterized by elemental analyses, measurement of conductance in solution, magnetic susceptibility at room temperature and by spectroscopic techniques. Electrochemical behavior of the complexes has been examined by cyclic voltammetry. Structure of one of the complexes cis-[Ru(PPh3)2(L6H)2](ClO4)2·2H2O, has been solved by single crystal X-ray diffraction technique. All the ligands are found to be chelated to the ruthenium(II) center in its thione form through its imine nitrogen and the thione sulfur. The pyridine ring nitrogen remained uncoordinated. The two PPh3 molecules are situated cis to each other. All the complexes are found to exhibit biological activity in terms of Escherichia coli growth-inhibition capacity and two of them hold the possibility of displaying antitumor activity.

Solution Study of a Structurally Characterized Monoalkoxo-Bound Monooxo-Vanadium(V) Complex: Spontaneous Generation of the Corresponding Oxobridged Divanadium(V,V) Complex and its Electroreduction to a Mixed-Valence Species in Solution

An interesting transformation of a structurally characterized monooxoalkoxovanadium(V) complex [VO(OEt)L] (LH 2 = a dibasic tridentate ONO donor ligand) in solution leading to the formation of the corresponding monooxobridged divanadium(V,V) complex (VOL) 2O is reported. This binuclear species in solution is adequately characterized by elemental analysis, measurement of conductance (in solution), various spectroscopic (UV-vis, IR, NMR, and mass spectrometry) techiniques and by cyclic voltammetry. The corresponding mixed-valence vanadium(IV,V) species has been generated in CH 3CN solution by controlled potential electrolysis of (VOL) 2O. This mixed-valence species is identified and studied by EPR technique (at room temperature and at liquid nitrogen temperature) and also by UV-vis spectroscopy. This study may be regarded as a general method of obtaining monooxo-bridged binuclear vanadium(V,V) species from the corresponding mononuclear monooxoalkoxovanadium(V) complexes of some selected dibasic tridentate ONO chelating ligands, which can be utilized as the precursor of monooxobridged divanadium(IV,V) mixed-valence species in solution obtainable by controlled potential electrolysis.

Synthesis and characterisation of some ruthenium(II) complexes of α-N heterocyclic carboxylic acids: X-ray structures of cis-[Ru(PPh3)2(L1)2].2CH3OH and cis-[Ru(PPh3)2(L3H)2] (L1H = pyridine 2-carboxylic acid and L3H2 = imidazole 4,5-dicarboxylic acid)

Abstract Synthesis and characterisation of ruthenium(II) complexes of several α-N heterocyclic carboxylic acids of the general formula [Ru(PPh3)2(L)2] are reported [LH=pyridine 2-carboxylic acid (L1H), pyrazine 2-carboxylic acid (L2H), imidazole 4,5-dicarboxylic acid (L3H2) and pyrazine 2,3-dicarboxylic acid (L4H2)]. All the acids behaved as bidentate N–O chelating donors, the second carboxyl group of the dicarboxylic acids remaining free. Electrochemical behaviour of the complexes was explored by cyclic voltammetry. Single-crystal X-ray analysis of the two complexes cis-[Ru(PPh3)2(L1)2]·2CH3OH and cis-[Ru(PPh3)2(L3H)2] led to the elucidation of the structures and showed that in both the complexes the two bulky PPh3 groups were cis to each other.

A study of ruthenium complexes of some selected N—S donors Part II. Ligational behaviour of 2-formylpyridine(4-phenyl) thiosemicarbazone towards ruthenium

Ru(II) and Ru(III) complexes of the biologically active tridentate NNS donors 2-formylpyridine(4- phenyl) thiosemicarbazone (L1H) and 2-formylpyridine thiosemicarbazone (LH) have been synthesized and characterized by elemental analysis, conductance and magnetic susceptibility measurements, as well as by spectroscopic techniques such as UV—Vis, IR and NMR. A series of mononuclear bis chelates of the formulae [Ru(L1H)2](SCN)2, [Ru(L1H)(L1)] Cl, [Ru(L1)2], [Ru(L)(LH)]ClO4·2H2O and mononuclear mixed ligand complexes such as [Ru(L1H)Cl2(CH3OH)], [Ru(L1H)(imz)Cl2], [Ru(L1H)(2-pico)(imz)]ClO4, [Ru(L1H)(TTSC)]Cl·12(C2H5)2O, [Ru(L1H)(imz)(thiosal)]Cl·CH3OH, [Ru(L1H)(bipy)Cl]Cl2·CH2Cl2 have been isolated and characterized. Binuclear complexes [Ru2(L1)2(OH)2], [Ru2(L1)2Cl4]·4H2O, [Ru2(L1)2(SCN)4]·H2O, [Ru2(L1)(imz)Cl4]·3CH3OH, [Ru2(L1)(H2O)Cl4] have also been synthesized and characterized. From the analysis of spectroscopic and magnetic data the donor sites of the ligands have been located and the geometries of the donor environment around the Ru(II)/Ru(III) acceptor centre have been proposed.

Synthesis and reactivity of the oxovanadium(IV) complexes of two NO donors and potentiation of the antituberculosis activity of one of them on chelation to metal ions: Part IV☆

A new series of oxovanadium(IV) complexes of two aromatic acidhydrazides (BH and AH) have been reported. Of these two donors, AH is known to possess considerable in vitro antitubercular activity. At pH 2-4, oxometal complexes of the type [VO(BH/AH)2SO4].nH2O (n = 1, 0) and [VO(BH/AH)(C2O4)H2O].H2O (BH = C6H5CONHNH2 and AH = (2-NH2)C6H4.CO.NHNH2) were obtained. Reactions of [VO(BH/AH)(C2O4)H2O].H2O with a monodentate Lewis base lead to the isolation of metal-ligand complexes [VO(BH/AH)(C2O4)L].nH2O (L = NH3, n = 1, L = py, n = 2). Disposition of the bonding sites of donor molecules around the oxometal acceptor center and status of the metal-oxygen multiple bond have been established. A monomeric and distorted octahedral donor environment for the oxovanadium(IV) ion has been proposed on the basis of the electron paramagnetic resonance (EPR) spectra and magnetic susceptibility measurements. Antitubercular activities, in vitro, of the oxovanadium(IV) complexes of AH have also been evaluated towards tuberculosis mycobacteria such as Mycobacterium flae, Mycobacterium smegmatis and Mycobacterium H37Rv.

A study of Ru(II) complexes of some selected NS donors

A number of Ru(II) complexes of six monoacid bidentate NS donors in the form of ring substituted 4-phenylthiosemicarbazides have been synthesized and characterized by elemental analysis, conductance and magnetic susceptibility measurements as well as by various spectroscopic techniques such as UV-Vis, IR and NMR spectroscopy. All the complexes have the general formula [Ru(LH)2X2]·nH2O where LH = a substituted thiosemicarbazide and X = Cl and I. From IR study the trans disposition of these two coordinated X− ions has been established. In all the complexes the ligand binds itself to the Ru(II) ion in its keto form through its thiocarbonyl sulphur atom and the nitrogen atom of the terminal −NH2 group of the thiosemicarbazide moiety. Reactivity of these [Ru(LH)2X2]·nH2O complexes towards various types of reagents like pyridine, DMF, NH4SCN, NaHSO3, C6H5CN and PPh3 has been examined and the products have been characterized. In all these reactions ruthenium is found to retain its +2 oxidation state. Antibacterial activity of some of the Ru(LH)2X2·nH2O complexes have been examined against E. coli and the corresponding minimum inhibitory concentration (MIC) values are reported.

A structural and electrochemical study of some oxovanadium(IV) heterochelate complexes

Abstract Physicochemical studies on two oxovanadium(IV) heterochelates involving the biologically active ONO donor ligand, dipicolinic acid (DPA) is reported. Structure of the complex [VO(DPA)(ophen)] · 3H2O has been determined and this led to the understanding of the geometry of the donor sites around the oxovanadium(IV) centre of other related complexes. Electrochemical behavior of the complexes were explored by cyclic voltammetry.

Ligational behavior of two biologically active N-S donors toward oxovanadium(IV) ion and potentiation of their antibacterial activities by chelation to

Chelating behavior of two biologically active ligands, pyridine-2-carboxaldehyde thiosemicarbazone (PT) and pyridine-2-carboxaldehyde-(4-phenyl)thiosemicarbazone (PPT), toward oxovanadium(IV) ion has been studied. The ligands are found to react in the thioketo form (pH 2-4), yielding the complexes [VO(PT)X2](X = Cl-, Br-, ClO4-), [VO(PT)(SO4)H2O], [VO(PPT)2X]X (X = Cl-, Br-, ClO4-) and [VO(PPT)2SO4]. Reactions of [VO(PT)(SO4)H2O] and [VO(PPT)2X]X (X = Cl-, Br-, ClO4-) with a monodenate Lewis base (B) like pyridine lead to the formation of [VO(PT)(SO4)Py]H2O and [VO(PPT)2py]X2 respectively. Bonding sites of the donor molecules around the oxometal cation have been located. Nature of the EPR spectra and magnetic moment values point to the monomeric character of the complexes and suggest a distorted octahedral donor environment for the oxovanadium(IV) ion. Status of the metal-oxygen multiple bond in all the complexes has been computed in terms of the V-O(1) stretching force constant. The ligands themselves and most of their oxovanadium(IV) complexes are found to exert powerful in vitro antibacterial activities towards E. coli.