Parbati Sengupta

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.

Ruthenium(II) complexes of NSO donor ligands in the form of ring-substituted 4-phenyl-thiosemicarbazones of salicylaldehyde and o-hydroxyacetophenone

This work describes the preparation and characterisation of ruthenium(II) complexes of several ONS donor ligands in the form of ring-substituted 4-phenylthiosemicarbazones of salicylaldehyde and o-hydroxyacetophenone. Reactions of these thiosemicarbazone ligands with [Ru(PPh3)3]Cl2 in refluxing MeOH furnished ruthenium(II) complexes of general formula [Ru(PPh3)2(LH)Cl] where the ligands acted as monoanionic tridentate ONS donors attached to the ruthenium(II) acceptor centre through the deprotonated phenolic oxygen, thione sulphur and azomethine nitrogen.

A family of mononuclear molybdenum-(VI), and -(IV) oxo complexes with a tridentate (ONO) ligand

The salicylhydrazone of anthranilhydrazide (H2L) reacted with MoO2(acac)2 in refluxing alcohols to yield compounds of the general formula MoO2L(ROH) (where R = CH3, C2H5, n-C3H7, n-C4H9). The complex MoO2L(C2H5OH) is found to undergo facile reaction with heterocyclic bases to form MoO2L(Q)-type complexes where Q = pyridine, 4-picoline, imidazole and substituted imidazoles. Single crystal X-ray structural studies on the ligand H2L (1) and the complexes MoO2L(C2H5OH) (2) and MoO2L(Imz) (3) indicate that the free ligand exists in its keto form, but in the two complexes 2 and 3 the ligand coordinates to the MoO22+ core through the enolate oxygen, the phenolate oxygen and the azomethine nitrogen. Reaction of MoO2L(C2H5OH) with PPh3 in CH3CN under dry dinitrogen, in the absence and presence of bipy, produced MoIVOL (2a) (brown) and MoIVOL(bipy) (2b) (green) respectively along with Ph3PO. This reaction is reminiscent of the oxotransfer reaction from the MoO2+2 core of a molybdoenzyme to the substrate PPh3. Complexes 2 and 3 crystallized in the P21/n and P21/c space groups respectively and for both of them Z = 4. The structures clearly show that 2 and 3 have distorted octahedral coordination environments in which the Mo–O(ethanol) bond of 2 and the Mo–N (imidazole) bond of 3 are significantly longer than is usually observed. This is indicative of the weak bonding of ethanol and imidazole to the MoO22+ core and points to the inherent weakness of the sixth coordination position of the coordination polyhedron of the MoO22+ core in MoO2L(C2H5OH) and MoO2L(Imz).

The reactivity of a ruthenium(III) ammine complex, [Ru(NH3)5Cl]Cl2, towards α-N-heterocyclic mono- and di-carboxylic acids. The synthesis and characterisation of biologically active mixed ligand ruthenium(III) complexes

Ruthenium(III) complexes containing one, two or three α-N-heterocyclic mono- and di-carboxylic acid groups were prepared from the ammine complex, [Ru(NH3)5Cl]Cl2 by judicious interplay of controlling factors such as the metal:ligand ratio, reflux time etc. All the complexes were characterised by elemental analyses, spectroscopic (u.v.-vis., i.r., e.p.r.) techniques, magnetic measurements (at room temperature) and conductance measurements in solution. The electrochemical behaviour of the soluble complexes was studied by cyclic voltammetry. Their biological activity, in terms of the growth inhibition of Escherichia coli 10536, has been examined.

AN UNUSUAL RUTHENIUM(II) COMPLEX OF 2-(2-PYRIDYL)BENZOTHIAZOLE

Abstract The ligand 2-(2-pyridyl)benzothiazole (L) can act both as an N-N and an N-S chelating donor. The latter coordination mode is expected to be preferred when it is involved in coordination to Ru(II) which is a soft acceptor centre However, in the title compound, chlorobis(acetonitrile)triphenylphosphino-2-(2-pyridyl)benzothiazole-N,N-ruthenium(II) chlride, [Ru(L)(PPh3(CH3CN)2Cl]Cl, the ligand acts in N,N-bidentate manner and the Ru(II) ion is found to be present in an N4PCl coordination environment. PPh3 and Cl are trans to each other and the two CH3CN ligands occupy cis positions facing the NN donor atoms of ligand L.

Cobalt(III) and Low Spin Cobalt(II) Complexes of the Two Highly Flexible Hexadentate Ligands 1,3-di(o-salicylaldiminophenylthio)propane and 1,2-di(o-salicylaldiminophenylthio)xylene

The hexadentate dibasic Schiff base ligands 1,3-di(o-salicylaldiminophenylthio)propane (H2DSAL PTP) and 1,2-di(o-salicylaldiminophenylthio)xylene (H2DSAL PTX), with N2S2O2 donor atoms, reacted with Co(II) salts, Co X2 ·6H2O (X=Cl, ClO4), to give the complexes [Co(DSAL PTP)]2[CoCl4] (1), [Co(DSAL PTX)(NH3)2] (2) [Co(DSAL PTP)]ClO4 (3) and [Co(DSAL PTX)]ClO4 (4). H2DSAL PTP reacted with CoCl2 to provide a mixed valency complex containing Co(II) and Co(III) acceptor centres (1). The Co(III) centre in (1) is coordinated to the hexadentate ligand and the tetrachloro cobalt(II) ion is present as the counter anion. From the molecular structure of (1) it is observed that [CoCl}4]2- remains in channels in the crystal lattice. An interesting structural features in that the anions and cations are linked in the crystal via hydrogen bonds. H2DSAL PTX reacted with CoCl2 in presence of NH3 to give low-spin, Co(II) complex (2) in which two NH3 ligands are directly attached to the central metal ion. Co(ClO4)2 on the other hand, reacted smoothly with the ligands in absence of NH3 and furnished the diamagnetic Co(III) complexes (3) and (4). Magnetic susceptibility measurements were carried out at 300 K. Cyclic voltammetric studies of all the complexes in DMF exhibit Co(II)/Co(III) redox couples at room temperature.