M. Ramakrishna Udupa

Abstract: Cobalt(II) complexes of creatinine [Co(creat)2X2] (X = Cl, Br, I or NCS) and [Co(creat)2X2(H2O)2] (X = HCO2, HOCH2CO2 or CNCH2CO2) have been prepared. Their i.r. spectra show an increase in ν(NH) of the cyclic secondary amine group, compared to free ligand (3300 cm−1), indicating that cyclic nitrogen is involved in coordination. The thiocyanate group coordinates through nitrogen and carboxylates coordinate as univalent unidentate ligands. The electronic spectra and magnetic moments suggest a d7 configuration for cobalt: a tetrahedral geometry (4.4 B.M.) for halide and thiocyanate complexes, and an octahedral geometry (5.0 B.M.) for the carboxylate complexes. On heating, the ligand moiety is lost and the respective cobalt halide or cobalt carboxylate is formed, which is converted finally into Co3O4. There is a correlation between the high intensity electronic transitions and the polarographic half-wave potentials.

Abstract: The interaction of hard base chelating agents (LH) such as 8-quinolinol (oxH), salicylaldehyde (salH) andN-nitrosophenylhydroxylamine (NphaH) with ammonium tetrathiomolybdate(VI), (1), in aqueous solution yields disulphidomolybdenum(VI) complexes, [MoS2L2] The ir absorptions at 540 and 510 cm−1 are assigned tov(Mo-S), which indicate that the two sulphido-groups arecis to each other, The interaction of (1) with soft base chelating agents (SS), such as dithiocarbamates (dtc), dithiophosphate (dtp) and xanthates (xan) yields dimeric sulphido-bridged sulphidomolybdenum(V) complexes, [Mo2S4(SS)2] and with potassium ethylthioxanthate (KEttxan) yields a molybdenum(IV) complex, [Mo(Ettxan)4] The [Mo2S4(R2dtc)2] complexes were also obtained by the interaction of [MoO2(R2dtc)2] with phosphorus pentasulphide in xylene It was concluded that tetrathiomolybdate(VI) undergoes facile reduction when compared with tetraoxomolybdate(VI)

Abstract: The reactions of (diethyldithiocarbamato)halogenotellurium(II) with thiourea, benzimidazole-2-thiol, halides (Cl–, Br–, I–) and 1,10-phenanthroline (phen) have been studied. The products were principally characterized by elemental analyses, IR and 1H NMR spectroscopies. Novel anionic (diethyldithiocarbamato)dihalogenotellurate(II) complexes resulted from the reactions of Te(S2CNEt2)X (X = Br or I) with NEt4X (X = Br or I) and phen. The crystal structures of the complexes [NEt4][Te(S2CNEt2)I2], [H(phen)2][Te(S2CNEt2)I2] and [H(phen)2][Te(S2CNEt2)Br2] have been determined. In the anions tellurium is co-ordinated to two sulfur atoms of the dithiocarbamate in an almost isobidentate manner and to two halides in an overall planar trapezoidal geometry. In [NEt4][Te(S2CNEt2)I2] the two iodides are almost equidistant to tellurium with distances of 3.079(1) and 3.072(1)A, whereas in [H(phen)2][Te(S2CNEt2)I2] the two Te–I distances are 3.151(1) and 3.038(1)A and in [H(phen)2][Te(S2CNEt2)Br2] the two Te–Br distances are 2.911(1) and 2.986(1)A. In [H(phen)2]+ the proton is bound to one of the nitrogen atoms of a phenanthroline group and the two phen groups are held together by three hydrogen bonds, of which two are of the interesting type C–H ⋯ N.

Abstract: Molybdenum(V) complexes [MoOX(4-Morphdtc)2] (X=F, Cl, Br or I; 4-Morphdtc = 4-morpholinyldithiocarbamate) have been prepared from molybdenum trioxide using hydrazine hydrohalides as reducing agents. The magnetic moment values atca. 1.65 B.M. and e.p.r. studies indicated that the complexes are mononuclear and that molybdenum is in + 5 oxidation state. The i.r. spectral bands at 1500 and 960 cm−1 suggest that the dithiocarbamate acts as a univalent bidentate ligand and the bands at 930 cm−1 confirms the presence of a MoO3+ moiety in the complex. The low conductivity values for the complexes inN, N-dimethylformamide indicate that the complexes are non-ionic. The [MoOX(4-Morphdtc)2] complexes (X=F, Cl or Br) decompose in the first step by the loss of one dithiocarbamate group, whereas in [MoOI(4-Morphdtc)2] the iodine atom is lost in the first step. The second and third steps lead to the formation of MoS3 and MoO3, respectively. A six coordinate structure around Mo with an oxo, halo and two dithiocarbamate groups is proposed.

Abstract: A series of intramolecularly coordinated organochalcogen compounds incorporating the 8-(dimethylamino)-1-naphthyl and 2-[(dimethylamino)methyl]phenyl groups has been synthesized. All the compounds were synthesized using the ortholithiation methodology. Insertion of elemental selenium into the Li−C bond of RLi (6) (R = 8-(dimethylamino)-1-naphthyl) afforded the lithium areneselenolate RSeLi (7). Oxidative workup of 7 yielded the yellow diselenide 8 in good yield. Reaction of 8 with a stoichiometric amount of sulfuryl chloride gave the monochloro derivative (9). Controlled bromination of diselenide (8) with bromine in carbon tetrachloride gave the stable selenenyl bromide (10). Compound 8 underwent facile reaction with a stoichiometric amount of iodine to give the corresponding novel monoiodo compound (11) in which selenium is covalently bonded to iodine. Attempts to synthesize the chalcogenides, R2E, 12 (E = Se) and 13 (E = Te), by the reaction of 6 with Se(dtc)2 and Te(dtc)2 (dtc = diethyldithiacarbamate)...

Abstract: Presentation des travaux concernant la preparation, la structure moleculaire, la caracterisation spectrometrique et la reactivite de complexes de metaux de transition avec des coordinats carboxyliques, heterocycliques, polyamines ou aldimines

Abstract: The chemistry of these two industrially important metals bears a close general resemblance to that of niobium and tantalum. There is the same emphasis on the highest oxidation state, in this case six. Common to both pairs of metals are such important features as polymeric oxyanions, metal-metal bonding in lower halides, formation of bronzes, a certain paucity of classical co-ordination compounds with a resulting prominence of the binary halide chemistry, and lack of hydrated cations.

Abstract: A comprehensive review is made of the analytical methods available for the inorganic acids derived from sulphur.

Abstract: A survey of the crystallographic literature of tellurium(II)/(IV) 1,1-dithiolates (dithiocarbamate, xanthate, dithiophosphate, or dithiophosphinate) is presented. Coordination numbers range from a low of three in some organotellurium(II) 1,1-dithiolates to a high of eight in the binary tellurium(IV) dithiocarbamates. The coordination geometries are rich and varied due to the stereochemical influence exerted by up to two lone pairs of electrons and the penchant of tellurium to increase its coordination number by forming secondary Te⋯X interactions, where X = sulphur, halide, tellurium, oxygen, and, in one case, a π system defined by a four-membered TeS2C chelate. Stereochemical roles of the lone pairs of electrons are always evident in the tellurium(II) structures. By contrast, a stereochemical position is not always evident for the lone pair of electrons in the tellurium(IV) derivatives, in particular in circumstances where the tellurium centre has a high coordination number. Supramolecular aggregation mediated by Te⋯X secondary interactions often leads to the formation of dimeric aggregates but sometimes to supramolecular polymers, and rarely three-dimensional networks. Comparisons between closely related structures clearly indicate that the dithiocarbamate ligand is a more effective chelating ligand compared with the other 1,1-dithiolate ligands covered in this survey. This difference in coordinating ability is clearly correlated with the observation that non-dithiocarbamate structures are more likely to form high-dimensional supramolecular architectures.