Synthesis of 2-(nitromethyl)ornithine from ornithine mediated by cobalt(III)

Rac.-p-(tris(2-aminoethyl)amine-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d) was obtained by a simple three-step procedure from ornithine using cobalt template chemistry. p-(Tris(2-aminoethyl)amine-ornithine)cobalt(III) trichloride (2a) was obtained from tris(2-aminoethyl)amine (tren) and (S)-ornithine in the presence of cobalt(II), which was oxidised to cobalt(III) during the reaction. Complex 2a was selectively oxidised with thionyl chloride-dimethyl formamide to p-(tris(2-aminoethyl)amine-dehydro-ornithine)cobalt(III) trichloride 2b. Complex 2c, in which reaction of thionyl chloride-dimethyl formamide has also occurred at the δ-amine of ornithine, was obtained at longer reaction times. Complex 2b reacted with nitromethane anion to give rac.-p-(tris(2-aminoethyl)amino-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d). The amino acid rac.-2-(nitromethyl)ornithine (1b) was released by reducing complex 2d with aqueous ammonium sulfide. Complex 2d was expected to release 2-(nitromethyl)ornithine (1b) in hypoxic cells, where the amino acid could act as an inhibitor of ornithine decarboxylase. Preliminary data indicated that complex 2d was weakly cytotoxic in one cell type studied.     

Synthesis and high ranked NLT properties of new sulfonamide-substituted indium phthalocyanines

The synthesis and characterization of three new indium phthalocyanines bearing eight N-alkyl- or N-arylsulfonamide groups is described. The new compounds are {2,3,9,10,16,17,23,24-octakis[4-(4-methoxyphenylaminosulfonyl]phenoxy]phthalocyaninato}indium(III) chloride (7), {2,3,9,10,16,17,23,24-octakis[4-diethylaminosulfonyl)phenoxy]phthalocyaninato}indium(III) chloride (8) and {2,3,9,10,16,17,23,24-octakis[4-didodecylaminosulfonyl)phenoxy]phthalocyaninato}indium(III) chloride (9), and were obtained in 23-49% yields. The precursors of phthalocyanines 7-9 are sulfonamide-substituted phthalonitriles that can be prepared by reacting 4,5-bis(4-chlorosulfonylphenoxy)phthalonitrile (3) with amines. The nonlinear transmission (NLT) of complexes 7-9 was determined at 532 nm using ns pulses. All three phthalocyanines behave as reverse saturable absorbers with increasing efficiency of optical limiting in the order 7 < 8 < 9. A comparative analysis of the NLT results is attempted in terms of the structural differences in 7-9.     

New monoterpene glycosides and phenolic compounds from Distylium racemosum and their inhibitory activity against ribonuclease H

Two new monoterpene glycosides, distyloside A-B (1-2), and a new megastigmane glucoside, iso-dihydrodendranthemoside A (3) were isolated from twigs and leaves of Distylium racemosum, along with five known phenolic compounds (4-8). The structures were established via spectroscopic techniques and chemical transformations, and the absolute stereochemistry of 3 was determined by Mosher’s esterification. A homogeneous fluorescence resonance energy transfer (FRET) quenching assay was used to determine the inhibitory activity of isolates (1-8) on the ribonuclease H enzymes from HIV-1, 2, human, and Escherichia coli. Among them, 6″-O-galloylsalidroside (6) showed potent inhibitory effects with an IC₅₀ value of 3.5 μM on HIV-2, and 1.7 μM on human RNase H, respectively.     

Synthesis, structures and properties of new cyclometalated iridium(III) complexes of 3-methoxy-6-methyl-2-(naphthalen-2-yl)pyridine

The reaction between 3-methoxy-6-methyl-2-(naphthalen-2-yl)pyridine 1 and IrCl₃ was performed in an attempt to synthesize a cyclometalated Ir(III) Cl-bridged dimer 2. An unexpected Ir(III) complex 3 was isolated, which was a five-coordinate bis-cyclometalated Ir(III) complex. The complexes 2 and 3 were converted to the same mononuclear complex 4 upon reacting with acetylacetonate (acac), respectively. All of the new compounds have been fully characterized by elemental analysis, IR, ¹H, ¹³C{¹H} NMR and ESI-MS. Additionally, the crystal structures and properties of these Ir(III) complexes are investigated. The most striking common features of the structures of 2 and 3 is intramolecular C-H···Cl hydrogen bonds. The complex 4 shows yellow phosphorescence with structureless emission peaks at about 556 nm.     

NL MIND-BEST: a web server for ligands and proteins discovery--theoretic-experimental study of proteins of Giardia lamblia and new compounds active against Plasmodium falciparum

There are many protein ligands and/or drugs described with very different affinity to a large number of target proteins or receptors. In this work, we selected Ligands or Drug-target pairs (DTPs/nDTPs) of drugs with high affinity/non-affinity for different targets. Quantitative Structure-Activity Relationships (QSAR) models become a very useful tool in this context to substantially reduce time and resources consuming experiments. Unfortunately most QSAR models predict activity against only one protein target and/or have not been implemented in the form of public web server freely accessible online to the scientific community. To solve this problem, we developed here a multi-target QSAR (mt-QSAR) classifier using the MARCH-INSIDE technique to calculate structural parameters of drug and target plus one Artificial Neuronal Network (ANN) to seek the model. The best ANN model found is a Multi-Layer Perceptron (MLP) with profile MLP 20:20-15-1:1. This MLP classifies correctly 611 out of 678 DTPs (sensitivity=90.12%) and 3083 out of 3408 nDTPs (specificity=90.46%), corresponding to training accuracy=90.41%. The validation of the model was carried out by means of external predicting series. The model classifies correctly 310 out of 338 DTPs (sensitivity=91.72%) and 1527 out of 1674 nDTP (specificity=91.22%) in validation series, corresponding to total accuracy=91.30% for validation series (predictability). This model favorably compares with other ANN models developed in this work and Machine Learning classifiers published before to address the same problem in different aspects. We implemented the present model at web portal Bio-AIMS in the form of an online server called: Non-Linear MARCH-INSIDE Nested Drug-Bank Exploration & Screening Tool (NL MIND-BEST), which is located at URL: http://miaja.tic.udc.es/Bio-AIMS/NL-MIND-BEST.php. This online tool is based on PHP/HTML/Python and MARCH-INSIDE routines. Finally we illustrated two practical uses of this server with two different experiments. In experiment 1, we report by first time Quantum QSAR study, synthesis, characterization, and experimental assay of antiplasmodial and cytotoxic activities of oxoisoaporphine alkaloids derivatives as well as NL MIND-BEST prediction of potential target proteins. In experiment 2, we report sampling, parasite culture, sample preparation, 2-DE, MALDI-TOF, and -TOF/TOF MS, MASCOT search, MM/MD 3D structure modeling, and NL MIND-BEST prediction for different peptides a new protein of the found in the proteome of the human parasite Giardia lamblia, which is promising for anti-parasite drug-targets discovery.     

Organogallium(III) complexes as apoptosis promoting anticancer agents for head and neck squamous cell carcinoma (HNSCC) cell lines

Organogallium(III) dinuclear (1-9) and tetranuclear (10) complexes present potential therapeutic agents for the treatment of various types of cancer. The antiproliferative activity of 1-10 was evaluated with cell lines of head and neck squamous cell carcinomas, e.g. HN (soft palate), Cal27, Cal33 (tongue) and FaDu (hypopharynx) cell lines. The activity of compound 8 is comparable with that of cisplatin on cell line Cal27 (IC₅₀ 4.6 μM for both compounds). The mode of cell death induced, caspase activity and cell cycle analysis were evaluated for potential hit compounds 3, 5 and 8 Potential hit compounds 3, 5 and 8 were further evaluated for the mode of cell death, caspase activity and cell cycle analysis. Apoptosis induced by compounds 3, 5 and 8 on Cal27 and FaDu cells was confirmed by DNA laddering , as well as acridine orange (AO) and ethidium bromide (EB) double staining. These compounds (3, 5 and 8) induced caspase-independent apoptosis (within 4 h of action) in cell line Cal27. Extrinsic-mediated apoptosis associated with caspase 8 and 3 activation is the main mode of cytotoxicity induced on FaDu cells by compounds 3, 5 and 8. Cell cycle perturbations caused by these compounds are also observed. Our data suggest that compounds 3, 5 and 8 should be studied further for the treatment of head and neck cancer.     

Restriction of apical coordination in the square-planar nickel(II) complexes of meso-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane with axially oriented C-methyl groups

Crystal structures of nickel(II) complexes coordinated with cyclam-type macrocyclic tetraamine, meso-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane (L) in two complex salts 1 and 2 have been determined by single-crystal X-ray crystallographic analysis. Complexes in both salts adopted trans-III structure, but the C-methyl groups of L adopted equatorial configuration in 1, while axial in 2. Complex 2 is the first example of complex of cyclam-type tetraamine with only axially oriented C-methyl groups. Complex in 1 adopted six-coordinated octahedral geometry with two water molecules occupying two apical sites, while in 2, apical sites were vacant resulting in four-coordinated square-planar geometry. UV-Vis spectra in various solutions also revealed the formation of octahedral six-coordinated complex for 1 but not for 2. Network of hydrogen bonds involving chloride ion, water, and N-H of L was present in crystals of both 1 and 2. Convenient synthetic paths for 1 and 2 are also presented.     

A series of mononuclear Co(III) complexes using tridentate N,O-donor ligands: chemical properties and cytotoxicity activity

Continuing our interest in tridentate ligands to develop new prototypes of cobalt-based metallodrugs for combating cancer, modifications in the backbone of HL1, [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine) were proposed in order to modulate the redox potential of new Co(III) complexes. Three ligands with electron withdrawing groups were synthesized: HL2: [(2-hydroxy-5-nitrobenzyl)(2-(pyridil-2-yl)ethyl]amine); HL3: [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]imine) and HL4: [(2-hydroxy-5-nitrobenzyl)(2-(pyridil-2-yl)ethyl]imine). They were used to obtain the respective mononuclear complexes 2, 3 and 4, which are discussed compared to the previous reported complex 1 (obtained from HL1). The new complexes were characterized and studied by several techniques including X-ray crystallography, elemental and conductimetric analysis, IR, UV-vis and ¹H NMR spectroscopies, and electrochemistry. The substitutions of the group in the para position of the phenol (HL1 and HL2) and the imine instead of the amine (HL3 and HL4), promote anodic shifts in the complexes reduction potentials. The influence of these substitutions in the biological activities of the Co(III) complexes against the murine melanoma cell line (B16F10) was also evaluated. Little effect was observed on cellular viability decrease for all free ligands, however the coordination to Co(III) enhances their activities in the following range: 1 > 4 ≈ 2 > 3. The data suggest that no straight correlation can be addressed between the reduction potential of the Co(III) center and the cell viability.     

Mononuclear single helices of lanthanum(III) and europium(III). Metal dependent diastereomeric excess

Using the 1:2 condensate of benzildihydrazone and 2-acetylpyridine as a tetradentate N donor ligand L, LaL(NO₃)₃ (1) and EuL(NO₃)₃ (2), which are pale yellow in colour, are synthesized. While single crystals of 1 could not be obtained, 2 crystallises as a monodichloromethane solvate, 2·CH₂Cl₂ in the space group Cc with a = 11.7099(5) Å, b = 16.4872(5) Å, c = 17.9224(6) Å and β = 104.048(4)°. From the X-ray crystal structure, 2 is found to be a rare example of monohelical complex of Eu(III). Complex 1 is diamagnetic. The magnetic moment of 2 at room temperature is 3.32 BM. Comparing the FT-IR spectra of 1 and 2, it is concluded that 1 also is a mononuclear single helix. ¹H NMR reveals that both 1 and 2 are mixtures of two diastereomers. In the case of the La(III) complex (1), the diastereomeric excess is only 10% but in the Eu(III) complex 2 it is 80%. The occurrence of diastereomerism is explained by the chiralities of the helical motif and the type of pentakis chelates present in 1 and 2.     

A series of thiolato-bridged di- and trinuclear complexes derived from [Tp∗Rh(SPh)2(MeCN)] (Tp∗ = hydrotris(3,5-dimethylpyrazol-1-yl)borate)

Treatment of the Rh(III) complex [Tp∗Rh(SPh)₂(MeCN)] (1) with a series of late transition metal complexes resulted in the formations of thiolate-bridged di- and trinuclear complexes, which include the Rh(III)-Rh(I) complexes, [Tp∗RhCl(μ-SPh)₂Rh(cod)] (2) and [Tp∗RhCl(μ-SPh)₂Rh(PPh₃)₂], the Rh(III)-Pd(II) complexes, [Tp∗RhCl(μ-SPh)₂Pd(η³-C₃H₅)] (4), [{Tp∗Rh(MeCN)}(μ-SPh)₂PdCl₂] (5), and [{Tp∗RhCl(μ-SPh)₂}₂Pd] (6), and the Rh(III)-Pt(II) complex [{Tp∗RhCl(μ-SPh)₂}₂Pt] (7). Early-late transition metal complexes containing the Rh(III)-Re(I) and Rh(III)-Mo(0) metal centers, [Tp∗RhCl(μ-SPh)₂Re(CO)₄] and [{Tp∗Rh(CO)}(μ-SPh)₂Mo(CO)₄] were also prepared from 1. The X-ray analysis has been carried out to confirm the structures for 2, 4, 5, 6, and 7.     

Synthesis and characterization of three mononuclear Fe(III) complexes containing bipodal and tripodal ligands: X-ray molecular structure of the dichloro[N-propanamide-N,N-bis-(2-pyridylmethyl)amine]iron(III) perchlorate

In this work, we present the synthesis and characterization of three mononuclear iron(III) complexes: dichloro[N-propanamide-N,N-bis-(2-pyridylmethyl)amine]iron(III) perchlorate (1), trichloro[N-methylpropanoate-N,N-bis-(2-pyridylmethyl)amine]iron(III) (2) and trichloro[bis-(2-pyridylmethyl)amine]iron(III) (3). The complexes were characterized by cyclic voltammetry, conductivimetry, elemental analyses, and by electronic, infrared and Mössbauer spectroscopies. Complex 1 was also characterized by X-ray structural analysis, which showed an iron center coordinated to one amide, one tertiary amine, two pyridine groups and two chloride ions. While for 1 the X-ray molecular structure and the infrared spectrum confirm the coordination of the amide group by the oxygen atom, the infrared spectrum of 2 indicates that the ester group present in the ligand is not coordinated, resulting in a N₃Cl₃ donor set, similar to the one present in 3. However, in 3 there is a secondary amine while in 2 a tertiary amine exists. These structural differences result in distinguishable variations in the Lewis acidity of the iron center, which could be evaluated by the analysis of the redox potential of the complexes, as well as by Mössbauer parameters. Thus, the Lewis acidity decreases in the following order: 1 > 2 > 3. It is important to notice that 1 has the amide group coordinated to the iron center, a feature present in metalloenzymes as lipoxygenase and isopenicillin N synthase, and in a small number of mononuclear iron(III) complexes.     

8-Quinolinolato complexes of ruthenium(II) and (III)

Reduction of RuQ₃ (1a, Q = 8-quinolinolato) with Zn/Hg in the presence of various π-acceptor ligands in ethanol affords RuQ₂L₂ (L₂ = (dimethylsulfoxide)₂ (2); (4-picoline)₂ (3); N,N′-dimethyl-1,4-diazabuta-1,3-diene, dab (4); cyclooctadiene, COD (5); norborna-2,5-diene, nbd (6)). Compound 6 is isolated as an equimolar mixture of cis,trans (6a) and trans,cis (6b) isomers, which can be separated by column chromatography. DFT calculations have been performed on 6a and 6b. Oxidation of 3 and 6b affords the corresponding ruthenium(III) species 7 and 8, respectively. The structures of 2, 3, 4 and 6 have been determined by X-ray crystallography.     

Diamagnetic 8-amidoquinoline and 8-(trialkylsilylamido)quinoline complexes of divalent nickel and zinc

Transamination of Zn[N(SiMe₃)₂]₂ with 8-(triisopropylsilylamino) (1a) and 8-(tert-butyldimethylsilylamino)quinoline (1b) yields monomeric heteroleptic bis(trimethylsilyl)amido zinc 8-(trialkylsilylamido)quinoline (2a, 2b). The reaction of Zn[N(SiMe₃)₂]₂ with 8-aminoquinoline leads to the formation of heteroleptic dimeric 8-amidoquinoline zinc bis(trimethylsilyl)amide (3). This compound shows fluxionality on the NMR time scale due to a transannular trans-cis isomerization process and also a strong temperature dependency of the ratio of these two isomers. Variation of the stoichiometry allows the synthesis and isolation of homoleptic zinc bis(8-amidoquinoline) (4) with the zinc atoms in a distorted tetrahedral environment. The metallation of 8-aminoquinoline with (tmeda)NiMe₂ yields diamagnetic nickel bis(8-amidoquinoline) (5) with a nickel center showing a distorted square planar coordination sphere. Dinuclear zinc complexes are accessible employing tetra-dentate di(8-aminoquinolyl)diphenylsilane (6). The metallation of 6 with dimethylzinc yields dimeric zinc di(8-amidoquinolyl)diphenylsilane (7) with tetrahedrally coordinated zinc atoms. A comparison of the molecular structures of 1a, 2b, 3, 4, 5, 6, and 7 shows nearly no dependency of the structural data of the quinolyl unit on the substitution pattern of the amino function. The metal-nitrogen bond lengths depend on the coordination numbers of the metal and the nitrogen atoms (terminal or bridging position) as well as the electrostatic attraction between the metal cations and the amino bases.     

Synthesis and characterization of monomer and dimer complexes of porphyrin iron(III) with bridging phenylcyanamide ligands

Several new mono and dinuclear complexes of [(P)Fe^III(L)], in which P is the dianion of tetraphenylporphyrin(TPP) and tetramesitylporphyrin(TMP) and L is the monoanion of 4-azo(phenylcyanamido)benzene (apc) (1) and (2) or dianion 1,4-di cyanamidobenzene (dicyd) (3), (4), (7), (8) and 4,4′-azo-diphenylcyanamide (adpc) (5), (6), (9), (10) have been prepared by the reaction of [(P)Fe^IIICl] with appropriate thallium salts of phenylcyanamide derivatives. Each of the complexes has been characterized by FT-IR, UV-Vis, ¹H NMR, MALDI-TOF and EPR spectroscopic data. In non-coordinating solvents (such as toluene or chloroform) these complexes exhibit ¹H NMR spectra that are characteristic of high-spin (S = 5/2) species. The cyanamide group (NCN) of the bridging ligand is coordinated to Fe(III) ions through the nitrile-nitrogen. The iron(III) phenylcyanamide complexes are not reactive toward dioxygen, they convert into [TPPFe^IIICl] when treated with HCl. EPR and NMR have shown that in dinuclear complexes weak magnetic interactions take place between two iron(III) paramagnetic centers.     

Effects of tethered ligands and of metal oxidation state on the interactions of cobalt complexes with the 26S proteasome

In this paper we report on the synthesis and characterization of three cobalt complexes described as [Co^II(L¹)₂] (1), [Co^II(L²)] (2), and [Co^III(L¹)₂]ClO₄(3). These complexes contain the deprotonated forms of the [NN′O] tridentate ligand HL¹ and its newly synthesized [N₂N′₂O₂] hexadentate counterpart H₂L², namely, 2,4-diiodo-6-((pyridine-2-ylmethylamino)methyl)phenol and 6,6′-((ethane-1,2-diylbis((pyridin-2-ylmethyl) azanediyl))bis(methylene))bis(2,4-diiodophenol). Characterizations for 1-3 include electrospray ionization (ESI) spectrometry, infrared, and UV-visible spectroscopies, and elemental analyses. A detailed ¹H-NMR study was conducted for 3 and X-ray structural data was obtained for 2. The viability of this series as potential agents for proteasome inhibition and cell apoptotic induction involving PC-3 cancer cells is presented comparing the behavior of the untethered [NN′O]₂ six-coordinate 1 and 3 and the tethered counterpart 2 with a 1:1 metal-to-ligand ratio. It is observed that the tethering in 2 decreases inhibition activity. When 1 and 3 are compared, the most inert, but redox-active, cobalt(III) species shows the highest chymotrypsin-like activity inhibition on purified proteasome and PC-3 cancer cells. A hypothesis based on the role of oxidation states for proteasome inhibition is offered.     

Probing the active site of rat porphobilinogen synthase using newly developed inhibitors

The structurally related tetrapyrrolic pigments are a group of natural products that participate in many of the fundamental biosynthetic and catabolic processes of living organisms. Porphobilinogen synthase catalyzes a rate-limiting step for the biosyntheses of tetrapyrrolic natural products. In the present study, a variety of new substrate analogs and reaction intermediate analogs were synthesized, which were used as probes for studying the active site of rat porphobilinogen synthase. The compounds 1, 3, 6, 9, 14, 16, and 28 were found to be competitive inhibitors of rat porphobilinogen synthase with inhibition constants ranging from 0.96 to 73.04 mM. Compounds 7, 10, 12, 13, 15, 17, 18, and 26 were found to be irreversible enzyme inhibitors. For irreversible inhibitors, loose-binding inhibitors were found to give stronger inactivation. The amino group and carboxyl group of the analogs were found to be important for their binding to the enzyme. This study increased our understanding of the active site of porphobilinogen synthase.     

Syntheses, structures, thermal behavior and solution studies of two types of Hg(II) complexes with [1,3-di(2-methoxy)benzene]triazene

The reaction of [1,3-di(2-methoxy)benzene]triazene, [HL], with Hg(CH₃COO)₂ and Hg(SCN)₂ in methanol as solvent, resulted in the formation of [HgL₂] (1) and [HgL(SCN)] (2), respectively. These compounds were characterized by means of X-ray diffraction, FT-IR spectroscopy, CHN and TGA-DTA analysis. In the lattice of the compound 1, the mono-nuclear complexes were connected to dimer structure by intermolecular non-classical C-H···O hydrogen bonds. Also, weak Hg-η²-arene π-interactions link the dimers into 1D supramolecular chains. The compound 2 is a 2D coordination polymer induced by C-H···π stacking interactions between 1D chains produced by weak Hg-η³-η³-arene π-interactions. The results of studies of the stoichiometry and formation of complexes of 1 and 2 in methanol solution were found to be in support of their solid state stoichiometry.     

Osteogenic activity of diphenyl ether-type cyclic diarylheptanoids derived from Acer nikoense

Osteogenic activity of six diarylheptanoids, acerogenin A (1), (R)-acerogenin B (2), aceroside I (3), aceroside B₁ (4), aceroside III (5) and (−)-centrolobol (6) and two phenolic compounds; (+)-rhododendrol (7) and (+)-cathechin (8), isolated from the stem bark of Acer nikoense (Nikko maple) was evaluated using alkaline phosphatase (ALP) activity as a marker for early osteoblast differentiation. We found that the diphenyl ether-type cyclic diarylheptanoids 1-5 promoted ALP activity in mouse preosteoblastic MC3T3-E1 cells without affecting cell proliferation, but linear-type diarylheptanoid 6 and phenolic compounds 7 and 8 did not. Diphenyl ether-type cyclic diarylheptanoids 1-4 also increased protein production of osteocalcin, a late stage maker for osteoblast differentiation, and induced osteoblastic mineralization. Structure-activity relationships of these compounds demonstrated that the stimulative efficacy of aglycones was higher than that of its glycosides. Taken together, diphenyl ether-type cyclic diarylheptanoids promote early- and late-stage osteoblastogenesis, which may open the possibility for the development of novel osteogenic agents.     

Synthesis and structural characterization of dinuclear complexes of trivalent aluminum, gallium, indium and chromium derived from pyrazole-2-ethanol

The reaction of 1-(2-hydroxyethyl)-3,5-dimethylpyrazole (HL) with anhydrous metal(III) halides (M = Al, Ga, In and Cr) results in the isolation of four novel dinuclear complexes [Al(μ-L)Cl₂]₂ (1), [Ga(μ-L)Cl₂]₂ (2), [In(μ-L)Br₂(H₂O)]₂·2thf (3) and [Cr(μ-L)Cl₂(H₂O)]₂·1.5thf (4) in good yields. The new complexes have been characterized with the aid of analytical and spectroscopic studies. A single crystal X-ray structure determination in each case confirms the dimeric structure for all the complexes in the solid-state. The pyrazole ethanol ligand binds to the metal through both pyrazole nitrogen and bridging alkoxide oxygen terminals with the formation of a central M₂O₂ core involving the ethoxide anion. The metal(III) center is pentacoordinated in compounds 1 and 2, while it is hexacoordinated in compounds 3 and 4.     

Synthesis and spectroscopic properties of cobalt(III) complexes of some aroyl hydrazones: X-ray crystal structures of one cobalt(III) complex and two aroyl hydrazone ligands

Cobalt(III) complexes of diacetyl monooxime benzoyl hydrazone (dmoBH₂) and diacetyl monooxime isonicotinoyl hydrazone (dmoInH₂) have been synthesized and characterized by elemental analyses and spectroscopic methods. The X-ray crystal structures of the two hydrazone ligands, as well as that of the cobalt(III) complex [Co^III(dmoInH)₂]Cl·2H₂O, are also reported. It is found that in the cobalt(III) complexes the Co(III) ion is hexa-coordinated, the hydrazone ligands behaving as mono-anionic tridentate O,N,N donors. In the [Co^III(dmoInH)₂]Cl·2H₂O complex, the amide and the oxime hydrogens are deprotonated for both the ligands, while the isonicotine nitrogens are protonated. In the [Co^III(dmoBH)₂]Cl complex, only the amide nitrogens are deprotonated. It is shown that the additional hydrogen bonding capability of the isonicotine nitrogen results in different conformation and supramolecular structure for dmoInH₂, compared to dmoBH₂, in the solid state. Comparing the structure of the [Co^III(dmoInH)₂]Cl·2H₂O with that of the Zn(II) complex of the same ligand, reported earlier, it is seen that the metal ion has a profound influence on the supramolecular structure, due to change in geometrical dispositions of the chelate rings.