Cobalt complexes thiosemicarbazones

Preparations of heterocyclic thiosemicarbazone complexes with cobalt(II) salts of weakly coordinating anions (e.g., perchlorate and tetrafluoroborate) often result in cobalt(III) complexes due to air oxidation. The first 2-acetylpyridine thiosemicarbazone cobalt(III) complex was the diamagnetic [Co(15b-H)2]C104... 

Formylthiophene thiosemicarbazone, 26, forms [Co(26)2A2]A and [Co(26)A3(H20)] (A = Cl, Br, I, NO3, and OAc), by varying the preparative hgand to cobalt(II) salt mole ratio in hot ethanol [201]. Addition of sodium hydroxide allows isolation of [Co(29-H)3]. All complexes are weakly paramagnetic indicating spin paired complexes. Spectroscopic studies showed bonding via the azomethine nitrogen and thiol sulfur, but not the thiophene sulfur. 

Ethanol-dimethoxypropane solutions of either 1-formylisoquinoline or 2-formylquinoline thiosemicarbazone and cobalt(II) salts yield [Co(L)A2] complexes where A = Cl, Br, I, NO3, NCS, or NCSe [147]. All are non-electrolytes, have magnetic moments of 4.30-4.70 B.M. and are five coordinate with approximate trigonal bipyramidal stereochemistry involving NNS coordination based on electronic and infrared spectra. [Co(21-H)2] 2H2O was isolated from a cold methanolic solution of cobalt(II) chloride and 1-formylisoquinoline thiosemicarbazone [187]. Infrared spectral studies show NNS coordination the electronic spectral bands fit a distorted octahedral symmetry, and the magnetic moment is 4.48 B.M. 

Methyl-5-amino-l-formylisoquinoline thiosemicarbazone, 22, also yields cobalt(II) complexes from unheated methanol solution [202]. However, due to this ligand s added steric requirements, a complex, [Co(22)Cl2], with one ligand per metal ion center is formed. This brown solid has a magnetic moment of 4.42 B.M., is a non-electrolyte, has coordination of a neutral NNS ligand, and the electronic spectrum indicates approximate trigonal bipyramidal stereochemistry. 

Cobalt(II) complexes of 4-(2-thiazolyl)-l-(2-acetylfuran) thiosemicarbazone, 44, were isolated having stoichiometries of [Co(44)2Cl2] and [Co(44-H)2] [194]. The former complex is isolated from neutral solution and is octahedral with each 44 bonding NS. The latter complex is formed in basic media, involves a tetrahedral cobalt(II) center and has NS bonding based on infrared studies. 

Nickelfll) complexes of p-anisaldehyde thiosemicarbazone, [Ni(HL)2X2] with X = Cl [212], Br [213], showed greater activity than the corresponding ironfll), manganesefll) and cobalt(II) complexes against Alternaria (Sp.), Paecil-omyces (Sp.) and Pestalotia (Sp.). All complexes were more active than the uncomplexed thiosemicarbazone. 

Introduction of an organometallic moiety has been achieved by coupling ferrocenecarbaldehyde with thiosemicarbazide, with the resulting thiosemicarbazone (fctsc) forming the presumably octahedral cobalt(II) complex Co(fctsc)2Cl2,491 which showed antibacterial activity. Acetylferro-cene thiosemicarbazone complexes of Co were reported earlier,492 including a species of the same form as that given above. 

Thiosemicarbazone (RNH-CS-NH-N=CR/R//, tsc) complexes of cobalt(III) have been extensively studied since the early 1980s and continue to attract attention, gaining particularly from an interest in their biological activity and potential cytotoxicity. A truly extensive range of tsc compounds has now been reported, although structural definition of their complexes widely relied on basic analytical and spectroscopic techniques up to the late 1980s, when X-ray crystal structural studies of tsc compounds became more common. A review of thiosemicarbazone and S-alkyldithiocarbazate complexes has appeared.1053... 

Parallel to the behavior previously described for the corresponding cobalt, nickel, copper, and zinc complexes, the thiosemicarbazonate complex C5H4CHN(N) = C(S)NH2)]2Cd also undergoes a reversible, ferrocenyl-centered, two-electron oxidation E° = -t-0.46 V) in acetonitrile [120],... 

The synthesis of iron, cobalt and nickel complexes of 2-formylpyridine thiosemicarbazone has been reported [59]. The a-(AO-heterocyclic carboxaldehyde thlosemicarbazones strongly complex transition metals through their N -N -S ... 

Atomic absorption spectrometry (AAS) has been used to determine cationic and anionic surfactants indirectly. Two methods have been put forward based on the formation of the ion pair between surfactant and hexanitrocobaltate (for cationic compounds) or bis(benzoyl)pyridine thiosemicarbazone cobalt (III) (for anionic compounds). In the former case, the complex is extracted with 1,3-dicloroethane and in the latter with an isopentylacetate and isopentyl alcohol mixture. Concentration of cobalt is determined in the organic phase using electrothermal atomic absorption spectroscopy (ETAAS), while for anionic surfactants, flame atomic absorption spectroscopy (FAAS) can also be used. Interferences like metal ions, anions and organic compounds do not have a great relevance. The two methods were applied to determine dodecyltrimethylammonium bromide in shampoos (Chattaraj and Das, 1992) and sodium lauryl sulfate (SDS) in toothpastes (Chattaraj and Das, 1994). 

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