K. Venkatasubramanian

An unexpected cleavage of the boronnitrogen bond in the coordinated dihydrobis(1-pyrazolyl)borate: synthesis and crystal structure of [RuII(pz)2(pzH)3(DMSO)] and synthesis of [RuIICl2(pzH)2(DMSO)2]

Abstract The reaction of cis-RuCl2(DMSO)4 with K[H2B(pz)2] in acetonitrile leads to a cleavage of the BN bond followed by the formation of [Ru(pz)2(pzH)3(DMSO)] (1). The crystal structure analysis of 1 (triclinic, space group P 1 , a=8.559(1), b=15.431(2), c=9.155(1) A, α=90.1(1), β=115.3(1), γ=92.95(2)°, Z=2, final conventional R=0.059) has revealed that two out of the five coordinated pyrazole groups are deprotonated (pyrazolyl anion) to satisfy the charge requirement of the central Ru2+ ion. There is a considerable difference in the two RuN(pz) distances which may be attributed to the trans effect of the coordinated DMSO molecule. The individual pyrazole rings are planar within 0.01 A. The disposition of the rings are interpreted in terms of the torsion angles between these planes. The molecular structure is held in three dimensional space by an extensive network of intramolecular hydrogen bonding. Under similar reaction conditions, cis-RuCl2(DMSO)4 reacts with free pyrazole (pzH) to give [RuIICl2(pzH)2(DMSO)2] (2).

Metal α, ω dicarboxylate complexes. 4. Effect of N-donor substitutions on the polymeric network in cobalt(II) hexanedioate complexes: synthesis and single crystal X-ray investigations

Abstract Three cobalt (II)hexanedioate complexes [Co(H2O)4(H2L)]n 1 (H2L=hexanedioic acid), Co(imidazole)4 (H2L)]n 2 and [Co(pyridine)2 (H2O)4][H2L] 3 are synthesized and structurally characterized to study the effect of N-donor substituents coordinated to the metal center on the polymeric network. Complex 1 is an extended linear polymer; Co(H2O)4 units are linked by the monodendate carboxylate from either end of the extended deprotonated hexanedioic acid. There are intra- and interchain H-bonding interactions between the coordinated water molecules and the end carboxylate O atoms, the uncoordinated O atom creates two dimensional hydrogen bonding pattern. Complex 2 also is a linear polymer; Co(imidazole)4 units are linked by monodentate dibasic acid at the either end but with S shaped conformation of the hexanedioic acid, not as fully extended as in 1. The effect of bulkier N-donor substitution is seen in the distortion of the octahedral coordination polyhedron of Co(II). The noncordinated carboxylate oxygen makes one intra and one interchain H-bonding interaction with the imidazole N–H group making a two-dimensional H-bonded network as in 1. In 3 with the two strong N-donor pyridines coordinated to the metal center, the hexanedioate is out of the coordination sphere and acts as a counter ion. The Co(pyridine)2(H2O)4 units are linked by H-bonding in both the dimensions by extensively folded adipate dianion forming a sheet structure parallel to ab plane. According to our knowledge this is the first example showing a strong H-bonding network in which a tetraaquaCo(II) center forms an eight-membered ring with bidendate H-bonding interactions. None of the coordination polymeric structures form any channels in their molecular packing, even to include a small entity as a water molecule.

Kinetics and mechanism of ligand substitution reactions of propylenediamine tetracetato complex of ruthenium(III) in aqueous solution and the X-ray crystal structure of [Ru(PDTA-H)(H2O)] ·H2O

Abstract The X-ray crystal structure of [Ru(PDTA-H)(H2O)]·H2O (1) was determined using single crystal X-ray diffraction techniques. The coordination of ruthenium in the complex is distorted octahedral with pentadentate PDTA-H and one of the four carboxylate arms uncomplexed. Ring E occurs as an envelope, while ring R1 is planar. Rings R2 and G also occur as envelopes. The structure is held in space by an elaborate network of hydrogen bonds. The kinetics of substitution reactions of H2O in complex 1 with thiourea and SCN− were studied as a function of pH (2–9), concentration of 1 and temperature. An attempt has been made to explain the lability of the complex towards substitution.

Synthesis, characterization and X-ray crystal structure studies of ruthenium(II) pyrazole complexes and their interaction with small molecules

Abstract Six-coordinate complexes of ruthenium(II) of the type [Ru(X) 2 (L)(Y) 3 ] ( 1 ) and [Ru(X) 2 (L) 2 (Y) 2 ] ( 2 ) (where X = Cl − , L = pyrazole and Y = DMSO) were synthesized and characterized by elemental analysis, IR, UV-vis, 1 H and 13 C NMR spectroscopy and differential pulse polarography. An X-ray crystallographic structural determination of complexes 1 and 2 shows that the complexes have a distorted octahedral geometry around the central metal ion. Chlorines are cis to one another in 1 and trans to one another in 2 . Pyrazole binds as a monodentate in both 1 and 2 and the remaining positions of the coordination polyhedron are occupied by the DMSO moieties through the RuS bond. The reactions of complexes 1 and 2 with small molecules such as CO, PPh 3 , NO + , H − and BH 4 − were studied by the isolation of the products, which were characterized by elemental analysis, IR, UV-vis, 1 H, 31 P and 11 B[ 1 H] NMR spectroscopy and conductance measurements.

Complexes of Ru(III) with aminopolycarboxylic acids and their interaction with molecular oxygen to form Ru(IV)-μ-peroxo complexes

The interaction of Ru(III) with IMDA, HEDTA, EDTA, PDTA, CDTA and DTPA was studied by potentiometric and spectrophotometric methods at 25°C and 0.10 M ionic strength. Experiments were carried out under nitrogen and oxygen atmospheres. Evidence for the formation of dioxygen complexes in these systems is presented. Stability constants for the different species existing in each of the systems were calculated using a computer programme. Ru(III) forms very strong complexes with aminopolycarboxylic acids, which then interact with molecular oxygen to form a series of μ-peroxo and μ-hydroxo-μ-peroxo complexes.

Characterization of an unusual reaction product of TIN(II) chloride with sodium N,N-diethyldithiocarbamate

Abstract The reaction of sodium N,N-diethyldithiocarbamate trihydrate with tin(II) chloride under aerobic conditions yields the unexpectedcis-dichlorobis(N,N-diethyl-dithiocarbamato)tin(IV) which has been characterized by X-ray crystallography. This illustrates the tin to be in a distorted octahedral configuration; the coordination valencies being provided by the two chlorines incis positions and two dithiocarbamates incis-orientations. The119Sn NMR of the complex is consistent with the presence of six coordinated tin(IV). The formation of the complex is explainedvia the intermediate product, tetrahethylthiuram disulphide.

Synthesis and structural characterization of [α,α'-bis{bis(2-diphenylphosphino)ethyl)amino}ethane]bis(tetrahydroborato)dicopper(I). Hydrogen bridge attachment of the tetrahydroborate group

Abstract The synthesis and structural characterization of [α,α′-bis{bis(2-(diphenylphosphino)ethyl)amino}ethane]bis(tetrahydroborato)dicopper(I) complex is reported. Crystal structure analysis shows that each copper atom possesses a distorted tetrahedral geometry with ligation to two phosphorus atoms of the ligand and two hydrogen atoms of BH4−. 1H, 13C, 31P and 11B NMR and IR data are also presented.

Crystal and molecular structure of chloroglycyl-dl-methioninatopalladium(II) monohydrate and its interaction with guanosine, cytidine and cytosine

Abstract The crystal and molecular structure of the parent complex, chloroglycol- dl -methionatopalladium(II) monohydrate has been determined by X-ray diffraction analysis. Palladium has a square planar disposition in the complex and the deprotonated peptide moiety acts as a terdentate ligand and binds through N, O and S. The fourth coordination position on the metal ion is occupied by the chloride ion. The structure involves an extensive network of hydrogen bonds. Mixed ligand complexes of chloroglycyl- dl -methionato-palladium(II) monohydrate with guanosine, cytosine and cytidine were synthesized and characterized by elemental analysis, conductivity measurements, IR and 1H NMR spectral studies. In the case of guanosine, the metal coordinating site is N(7) whereas in cytosine and cytidine it is N(3).

Metal α,ω dicar☐ylate complexes—3. Synthesis, characterization and single crystal X-ray investigation of [tetrakis(2-methylimidazolo) (μ-diadipato)dicobalt(II)] monohydrate

Abstract Interaction of 2-methyl imidazole with tetraaquoadipatocobalt(II) polymer in water-ethanol mixture yielded dimeric cobalt(II) complex [Co(COO-(CH2)4-COO) (C4N2H6)2·H2O. The complex has been characterized by elemental analysis. IR spectroscopy and single crystal X-ray diffraction techniques. The crystal structure contains a dimer consisting of two Co(cis-2 Melm) units joined by two molecules of a folded dibasic acid forming an 18 membered ring. The metal center possesses a highly distorted octahedral geometry comprising two N-atoms from two 2-methylimidazoles and four O-atoms form two adipate anions forming strained four membered chelate rings. The molecule has a center of symmetry and forms a through channel with the maximum and minimum dimensions of 8.25(7)Aand 5.27(2)Arespectively. The hexagonally close packed dimeric units along a-axis includes a water molecule in the exterior channel.

Nitrosyl ethylenediaminetetraacetato ruthemium(III) — an efficient oxygen atom transfer agent for the oxidation of olefins by molecular O2 and PhIO through ligand-mediated nitrosyl/nitro couple

The complexes [RuIII(EDTA—H)NO]BF4 1 and [RuIII(EDTA)(NO)] 1a were synthesized and characterised by elemental analysis, IR and UV—Vis spectroscopy, conductivity, magnetic susceptibility, EPR and electrochemical studies. Complex 1a catalyses the oxidation by molecular oxygen of 1-hexene to 2-hexanone and cyclohexene to cyclohexene oxide through the ligand-mediated RuIII—EDTA—NO 1a/Ruv—EDTA—NO2 2 oxygen atom transfer. The oxidation reactions were studied in 7:3 ethanol—water medium in the temperature range 30–45 °C (μ=0.1 M KCl). The oxidation of 1-hexene and cyclohexene proceeds with a turnover number of 50 and 44 moles product per mole catalyst per hour. The rate of oxidation is first order with respect to catalyst concentration and one-half order with respect to molecular oxygen concentration. At higher substrate concentrations, the reaction rate was found to be independent of substrate concentration. 18O2 studies indicate that the source of O atom transferred to the substrate is from molecular O2. The formation of an organometallic metallocyclic intermediate is proposed for the reaction. The rate of oxygenation of cyclohexene by iodosyl benzene catalyzed by 1a was found to be identical with that obtained with O2 as oxidant. The rate of oxygenation of 1a to 2 was studied independently by an O atom transfer from iodosyl benzene.