Rupam Dinda

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.

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.