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1.  The syntheses and structures of ‘3+2’ and ‘2+2+1’ oxorhenium mixed-ligand complexes employing 8-hydroxy-5-nitroquinoline as the bidentate N,O donor ligand 
Inorganica chimica acta  2000;308(1-2):80-90.
The syntheses and structural characterizations of a series of novel ‘3+2’ and ‘2+2+1’ mixed-ligand complexes carrying 8-hydroxy-5-nitroquinoline (HL) as the bidentate N,O donor atom system are reported. Thus one-pot reactions of [ReOCl3(PPh3)2] with dianionic tridentate ligands H2Ln (where H2L1=HOC6H4-2-CH=NC6H4-2-OH; H2L2=HOC6H4-2-CH=N–C6H4-2-SH; H2L3=HOC6H4-2-CH=NN=C(NHC6H5)–SH; H2L4=2-CH2OH–C5H3N-6-CH2SH; and H2L5=2-CO2H–C5H3N-6-CO2H) and HL afforded a series of ‘3+2’ oxorhenium complexes of the type [ReO(H2Ln)(L)] 2–6, which exhibit distorted octahedral geometries. Crystals of 1 are monoclinic space group C2/c, a=16.702(1), b=14.275(1), c=22.363(2) Å, β=108.083(1)° V=5068.2(7) Åβ and Z=8; those of 2 are monoclinic space group P21/n, a=8.5093(4) b=38.518(2), c=11.6092(5) Å, β=97.708(1)°, V=3770.7(3) Å3 and Z=8; those of 5 are triclinic, space group P1−, a=7.5899(8), b=10.322(1), c=11.905(1) Å, α=78.636(2)°, β=74.229(2)°, γ=71.391(2)°, V=844.3(2) Å3, and Z=2. Upon reaction of 2,6-pyridinedimethanol (H2L6) with the intermediate complex [ReOCl2(L)(PPh3)] (1), only one of the two methylene hydroxy group was deprotonated and a new ‘2+2+1’ complex [ReO(OCH3)(HL6)(L)]·CH3OH (7) was obtained. Crystal data for 7: monoclinic P21/n, a=12.0579(6), b=11.0993(6), c=14.9262(8) Å, β=107.872(1)°, V=1901.2(2) Å3, and Z=8. In the preparation of complex 3, cleavage of the C=N bond of the Schiff base H2L2 was observed and the ‘2+2+1’ complex 8 [ReO(PPh3)(η2-NHC6H4-2-S)(L)]·CH2Cl2 having 2-aminothiophenol as a dianionic bidentate ligand was isolated. Crystals of 8 are monoclinic space group C2/c, a=25.627(2), b=8.1305(6) c=31.404(2) Å β=96.147(1)°, V=6505.7(8) Å3, and Z=8. Reduction of HL to 8-hydroxy-5-aminoquinoline was realized during the formation of complex 6, and a new complex 9 was thus isolated involving the coordination of two sets of N,O donor atoms from L and 8-hydroxy-5-aminoquinoline while a methoxy oxygen atom completes the octahedral coordination geometry. Crystals of 9 are monoclinic space group P21/n, a=7.5330(6), b=15.095(1), c=16.394(1) Å, β=99.690(2)°, V=1837.7(3) Å3, and Z=4.
PMCID: PMC2893356  PMID: 20592939
Crystal structures; Rhenium complexes; Oxo complexes; N,O donor ligand complexes
2.  Spectroscopic, Thermal and Biological Studies on Some Trivalent Ruthenium and Rhodium NS Chelating Thiosemicarbazone Complexes 
The synthetic, spectroscopic, and biological studies of sixteen ring-substituted 4-phenylthiosemicarbazones and 4-nitrophenyl-thiosemicarbazones of anisaldehyde, 4-chlorobenzaldehyde, 4-fluorobenzaldehyde, and vanillin with ruthenium(III) and rhodium(III) chlorides are reported here. Their structures were determined on the basis of the elemental analyses, spectroscopic data (IR, electronic, 1H and 13C NMR) along with magnetic susceptibility measurements, molar conductivity and thermogravimetric analyses. Electrical conductance measurement revealed a 1 : 3 electrolytic nature of the complexes. The resulting colored products are monomeric in nature. On the basis of the above studies, three ligands were suggested to be coordinated to each metal atom by thione sulphur and azomethine nitrogen to form low-spin octahedral complexes with ruthenium(III) while forming diamagnetic complexes with rhodium(III). Both ligands and their complexes have been screened for their bactericidal activities and the results indicate that they exhibit a significant activity.
PMCID: PMC1852900  PMID: 17505530
3.  Synthesis, Characterization, and Biological Activity of N1-Methyl-2-(1H-1,2,3-Benzotriazol-1-y1)-3-Oxobutan- ethioamide Complexes with Some Divalent Metal (II) Ions 
A new series of Zn2+, Cu2+, Ni2+, and Co2+ complexes of N1-methyl-2-(1H-1,2,3-benzotriazol-1-yl)-3-oxobutanethioamide (MBOBT), HL, has been synthesized and characterized by different spectral and magnetic measurements and elemental analysis. IR spectral data indicates that (MBOBT) exists only in the thione form in the solid state while 13C NMR spectrum indicates its existence in thione and thiole tautomeric forms. The IR spectra of all complexes indicate that (MBOBT) acts as a monobasic bidentate ligand coordinating to the metal(II) ions via the keto-oxygen and thiolato-sulphur atoms. The electronic spectral studies showed that (MBOBT) bonded to all metal ions through sulphur and nitrogen atoms based on the positions and intensity of their charge transfer bands. Furthermore, the spectra reflect four coordinate tetrahedral zinc(II), tetragonally distorted copper(II), square planar nickel(II), and cobalt(II) complexes. Thermal decomposition study of the complexes was monitored by TG and DTG analyses under N2 atmosphere. The decomposition course and steps were analyzed and the activation parameters of the nonisothermal decomposition are determined. The isolated metal chelates have been screened for their antimicrobial activities and the findings have been reported and discussed in relation to their structures.
PMCID: PMC2268950  PMID: 18364993
4.  Mixed-Valence Nickel-Iron Dithiolate Models of the [NiFe]-Hydrogenase Active Site 
Inorganic Chemistry  2012;51(4):2338-2348.
A series of mixed-valence iron-nickel dithiolates is described. Oxidation of (diphosphine)Ni(dithiolate)Fe(CO)3 complexes 1, 2, and 3 with ferrocenium salts affords the corresponding tricarbonyl cations [(dppe)Ni(pdt)Fe(CO)3]+ ([1]+), [(dppe)Ni(edt)Fe(CO)3]+ ([2]+) and [(dcpe)Ni(pdt)Fe(CO)3]+ ([3]+), respectively, where dppe = Ph2PCH2CH2PPh2, dcpe = Cy2PCH2CH2PCy2, pdtH2 = HSCH2CH2CH2SH and edtH2 = HSCH2CH2SH. The cation [2]+ proved unstable, but the propanedithiolates are robust. IR and EPR spectroscopic measurements indicate that these species exist as Cs-symmetric species. Crystallographic characterization of [3]BF4 shows that Ni is square planar. Interaction of [1]BF4 with P-donor ligands (L) afforded a series of substituted derivatives of type [(dppe)Ni(pdt)Fe(CO)2L]BF4 for L = P(OPh)3 ([4a]BF4), P(p-C6H4Cl)3 ([4b]BF4), PPh2(2-py) ([4c]BF4), PPh2(OEt) ([4d]BF4), PPh3 ([4e]BF4), PPh2(o-C6H4OMe) ([4f]BF4), PPh2(o-C6H4OCH2OMe) ([4g]BF4), P(p-tol)3 ([4h]BF4), P(p-C6H4OMe)3 ([4i]BF4), PMePh2 ([4j]BF4). EPR analysis indicates that ethanedithiolate [2]+ exists as a single species at 110 K, whereas the propanedithiolate cations exist as a mixture of two conformers, which are proposed to be related through a flip of the chelate ring. Mössbauer spectra of 1 and oxidized S = ½ [4e]BF4 are both consistent with a low-spin Fe(i) state. The hyperfine coupling tensor of [4e]BF4 has a small isotropic component and significant anisotropy. DFT calculations using the BP86, B3LYP, and PBE0 exchange-correlation functionals agree with the structural and spectroscopic data, suggesting that the SOMOs in complexes of the present type are localized in a Fe(i)-centered d(z2) orbital. The DFT calculations allow an assignment of oxidation states of the metals and rationalization of the conformers detected by EPR spectroscopy. Treatment of [1]+ with CN- and compact basic phosphines results in complex reactions. With dppe, [1]+ undergoes quasi-disproportionation to give 1 and the diamagnetic complex [(dppe)Ni(pdt)Fe(CO)2(dppe)]2+ ([5]2+), which features square-planar Ni linked to an octahedral Fe center.
PMCID: PMC3288512  PMID: 22304696
5.  Cd(II) and Pb(II) complexes of the polyether ionophorous antibiotic salinomycin 
The natural polyether ionophorous antibiotics are used for the treatment of coccidiosis in poultry and ruminants. They are effective agents against infections caused by Gram-positive microorganisms. On the other hand, it was found that some of these compounds selectively bind lead(II) ions in in vivo experiments, despite so far no Pb(II)-containing compounds of defined composition have been isolated and characterized. To assess the potential of polyether ionophores as possible antidotes in the agriculture, a detailed study on their in vitro complexation with toxic metal ions is required. In the present paper we report for the first time the preparation and the structure elucidation of salinomycin complexes with ions of cadmium(II) and lead(II).
New metal(II) complexes of the polyether ionophorous antibiotic salinomycin with Cd(II) and Pb(II) ions were prepared and structurally characterized by IR, FAB-MS and NMR techniques. The spectroscopic information and elemental analysis data reveal that sodium salinomycin (SalNa) undergoes a reaction with heavy metal(II) ions to form [Cd(Sal)2(H2O)2] (1) and [Pb(Sal)(NO3)] (2), respectively. Abstraction of sodium ions from the cavity of the antibiotic is occurring during the complexation reaction. Salinomycin coordinates with cadmium(II) ions as a bidentate monoanionic ligand through the deprotonated carboxylic moiety and one of the hydroxyl groups to yield 1. Two salinomycin anions occupy the equatorial plane of the Cd(II) center, while two water molecules take the axial positions of the inner coordination sphere of the metal(II) cation. Complex 2 consists of monoanionic salinomycin acting in polydentate coordination mode in a molar ratio of 1: 1 to the metal ion with one nitrate ion for charge compensation.
The formation of the salinomycin heavy metal(II) complexes indicates a possible antidote activity of the ligand in case of chronic/acute intoxications likely to occur in the stock farming.
PMCID: PMC3184049  PMID: 21906282
6.  Synthesis and Characterization of New Palladium(II) Thiosemicarbazone Complexes and Their Cytotoxic Activity against Various Human Tumor Cell Lines 
The palladium(II) bis-chelate complexes of the type [Pd(TSC1-5)2] (6–10), with their corresponding ligands 4-phenyl-1-(acetone)-thiosemicarbazone, HTSC1 (1), 4-phenyl-1-(2′-chloro-benzaldehyde)-thiosemicarbazone, HTSC2 (2), 4-phenyl-1-(3′-hydroxy-benzaldehyde)-thiosemicarbazone, HTSC3 (3), 4-phenyl-1-(2′-naphthaldehyde)-thiosemicarbazone, HTSC4 (4), and 4-phenyl-1-(1′-nitro-2′-naphthaldehyde)-thiosemicarbazone, HTSC5 (5), were synthesized and characterized by elemental analysis and spectroscopic techniques (IR and 1H- and 13C-NMR). The molecular structure of HTSC3, HTSC4, and [Pd(TSC1)2] (6) have been determined by single crystal X-ray crystallography. Complex 6 shows a square planar geometry with two deprotonated ligands coordinated to PdII through the azomethine nitrogen and thione sulfur atoms in a cis arrangement. The in vitro cytotoxic activity measurements indicate that the palladium(II) complexes (IC50 = 0.01–9.87 μM) exhibited higher antiproliferative activity than their free ligands (IC50 = 23.48–70.86 and >250 μM) against different types of human tumor cell lines. Among all the studied palladium(II) complexes, the [Pd(TSC3)2] (8) complex exhibited high antitumor activity on the DU145 prostate carcinoma and K562 chronic myelogenous leukemia cells, with low values of the inhibitory concentration (0.01 and 0.02 μM, resp.).
PMCID: PMC3874341  PMID: 24391528
7.  Synthesis, spectroscopic, coordination and biological activities of some organometallic complexes derived from thio-Schiff base ligands 
Graphical abstract
Synthesis, spectroscopic, coordination and biological activities of some organometallic complexes derived from thio-Schiff base ligands
•Thio Schiff base complexes derived from mono- and diacetyl ferrocene were synthesized.•The complexes are characterized by different spectroscopic techniques.•The complexes have different varieties of geometrical structures.•Biochemical studies were studied.
Two series of mono- and binuclear complexes cyclic or acyclic thio-ferocine Schiff base ligands, derived from the condensation of 2-aminobenzenthiol (L) with monoacetyl ferrocene in the molar ratio 1:1 or in the molar ratio 1:2 for diacetyl ferocine have been prepared. The condensation reactions yield the corresponding Schiff Base ligands, HLa-Maf and H2Lb-Daf. The chelation of the ligands to metal ions occurs through the sulfur of the thiol group as well as the nitrogen atoms of the azomethine group of the ligands. HLa-Maf acts as monobasic bidentate or dibasic tetradentate, while H2Lb-Daf behaves as twice negatively cargend tetradentate ligand. The structures of these ligands were elucidated by elemental analysis, infrared, ultraviolet–visible spectra, as well as 1H NMR spectra. Reactions of the Schiff bases ligands with ruthenium(III), oxovanadium(IV) and dioxouranium(VI) afforded the corresponding transition metal complexes. The properties of the newly prepared complexes were analyse by elemental analyses, infrared, electronic spectra, 1H NMR as well as the magnetic susceptibility and conductivity measurement. The metal complexes exhibits different geometrical arrangements such as octahedral and square pyramidal coordination. Schiff base ligands and their metal complexes were tested against two pathogenic bacteria as Gram-positive and Gram-negative bacteria as well as one kind of fungi to study their biological activity. All the complexes exhibit antibacterial and antifungal activities against these organisms.
PMCID: PMC3826106  PMID: 24070648
Monoacetylferrocene; 1,1′-Diacetylferrocene; Thio-Schiff base; Metal complexes; Spectroscopy; Biological activity
8.  Luminescent Di and Polynuclear Organometallic Gold(I)-M (Au2, {Au2Ag}n and {Au2Cu}n) Compounds Containing Bidentate Phosphanes as Active Antimicrobial Agents 
The reaction of new dinuclear gold(I) organometallic complexes containing mesityl ligands and bridging bidentate phosphanes [Au2(mes)2(μ-LL)] (LL = dppe: 1,2-Bis(di-phenylphosphano)ethane 1a, and water-soluble dppy: 1,2-Bis(di-3-pyridylphosphano)ethane 1b) with Ag+ and Cu+ lead to the formation of a family of heterometallic clusters with mesityl bridging ligands of the general formula [Au2M(μ-mes)2(μ-LL)]A (M = Ag, A = ClO4−, L-L = dppe 2a, dppy 2b; M = Ag, A = SO3CF3−, L-L = dppe 3a, dppy 3b; M = Cu, A = PF6−, L-L = dppe 4a, dppy 4b). The new compounds were characterized by different spectroscopic techniques and mass spectrometry The crystal structures of [Au2(mes)2(μ-dppy)] 1b and [Au2Ag(μ-mes)2(μ-dppe)]SO3CF3 3a were determined by a single-crystal X-ray diffraction study. 3a in solid state is not a cyclic trinuclear Au2Ag derivative but it gives an open polymeric structure instead, with the {Au2(μ-dppe)} fragments “linked” by Ag(μ-mes)2 units. The very short distances of 2.7559(6) Å (Au-Ag) and 2.9229(8) Å (Au-Au) are indicative of gold-silver (metallophillic) and aurophilic interactions. A systematic study of their luminescence properties revealed that all compounds are brightly luminescent in solid state, at room temperature (RT) and at 77 K, or in frozen DMSO solutions with lifetimes in the microsecond range and probably due to the self-aggregation of [Au2M(μ-mes)2(μ-LL)]+ units (M= Ag or Cu; LL= dppe or dppy) into an extended chain structure, through Au-Au and/or Au-M metallophylic interactions, as that observed for 3a. In solid state the heterometallic Au2M complexes with dppe (2a–4a) show a shift of emission maxima (from ca. 430 to the range of 520–540 nm) as compared to the parent dinuclear organometallic product 1a while the complexes with dppy (2b–4b) display a more moderate shift (505 for 1b to a max of 563 nm for 4b).
More importantly, compound [Au2Ag(μ-mes)2(μ-dppy)]ClO4 2b resulted luminescent in diluted DMSO solution at room temperature. Previously reported compound [Au2Cl2(μ-LL)] (L-L dppy 5b) was also studied for comparative purposes. The antimicrobial activity of 1–5 and AgA (A= ClO4−, OSO2CF3−) against Gram-positive and Gram-negative bacteria and yeast was evaluated. Most tested compounds displayed moderate to high antibacterial activity while heteronuclear Au2M derivatives with dppe (2a–4a) were the more active (MIC 10 to 1 μg/mL). Compounds containing silver were ten times more active to Gram-negative bacteria than the parent dinuclear compound 1a or silver salts. Au2Ag compounds with dppy (2b, 3b) were also potent against fungi.
PMCID: PMC3371653  PMID: 22334444
luminescent; gold-silver; gold-copper; antimicrobial; synergism
9.  Synthesis and Biological Activity of Manganese (II) Complexes of Phthalic and Isophthalic Acid: X-Ray Crystal Structures of [Mn(ph)(Phen)2(H2O)]· 4H2O, [Mn(Phen)2(H2O)2]2(Isoph)2(Phen)· 12H2O and {[Mn(Isoph)(bipy)]4· 2.75biby}n(phH2 = Phthalic Acid; isoph = Isophthalic Acid; phen = 1,10-Phenanthroline; bipy = 2,2-Bipyridine) 
Metal-Based Drugs  2000;7(5):275-288.
Manganese(II) acetate reacts with phthalic acid (phH2) to give [Mn(ph)]·0.5H2O (1). Reaction of 1 with 1,10-phenanthroline produces [Mn(ph)(phen)]·2H2O (2) and [Mn(ph)(phen)2(H2O)]·4H2O (3). Reaction of isophthalic acid (isophH2) with manganese(II) acetate results in the formation of [Mn(isoph)]·2H2O (4). The addition of the N,N-donor ligands 1,10-phenanthroline or 2,2'-bipyridine to 4 leads to the formation of [Mn2 (isoph)2(phen)3)]·4H2O (5), [(Mn(phen)2(H2O)2]2(isoph)2(phen)·12H2O (6) and {[Mn(isoph)(bipy)]4·2.75 biby}n (7), respectively. Molecular structures of 3, 6 and 7 were determined crystallographically. In 3 the phthalate ligand is bound to the manganese via just one of its carboxylate groups in a monodentate mode with the remaining coordination sites filled by four phenanthroline nitrogen and one water oxygen atoms. In 6 the isophthalates are uncoordinated with the octahedral manganese center ligated by two phenanthrolines and two waters. In 7 the Isophthalate ligands act as bridges resulting in a polymeric structure. One of the carboxylate groups is chelating a single manganese with the other binding two metal centres in a bridging bidentate mode. The phthalate and isophthalate complexes, the metal free ligands and a number of simple manganes salts were each tested for their ability, to inhibit the growth of Candida albicans. Only the “metal free” 1,10-phenanthroline and its manganese complexes were found to be active.
PMCID: PMC2365232  PMID: 18475957
10.  Synthesis, Structure, Electrochemistry, and Spectral Characterization of Bis-Isatin Thiocarbohydrazone Metal Complexes and Their Antitumor Activity Against Ehrlich Ascites Carcinoma in Swiss Albino Mice 
Metal-Based Drugs  2007;2008:362105.
The synthesis, structure, electrochemistry, and biological studies of Co(II), Ni(II), Cu(II), and Zn(II) complexes of thiocarbohydrazone ligand are described. The ligand is synthesized starting from thiocarbohydrazide and isatin. It is evident from the IR data that in all the complexes, only one part of the ligand is coordinated to the metal ion resulting mononuclear complexes. The ligand coordinates essentially through the carbonyl oxygen of the isatin fragment, the nitrogen atom of the azomethine group, and sulfur atom after deprotonation to give five membered rings. H1 NMR spectrum of the ligand shows only one set of signals for the aromatic protons, while the NH of isatin and NH of hydrazone give rise to two different singlets in the 11–14 ppm range. The formulations, [Cu(L)Cl]·2H2O, [Cu(L)(CH3COO)]·2H2O, [Ni(L)Cl], [Ni(L)(CH3COO)], [Co(L2)], and [Zn(L2)]·2H2O are in accordance with elemental analyses, physical, and spectroscopic measurements. The complexes are soluble in organic solvents. Molar conductance values in DMF indicate the nonelectrolytic nature of the complexes. Copper complex displays quasireversible cyclic voltametric responses with Ep near −0.659 v and 0.504 v Vs Ag/AgCl at the scan rate of 0.1 V/s. Copper(II) complexes show a single line EPR signals. For the observed magnetic moment and electronic spectral data possible explanation has been discussed. From all the available data, the probable structures for the complexes have been proposed. The compounds synthesized in present study have shown promising cytotoxic activity when screened using the in vitro method and at the same time were shown to have good activity when tested using the Ehrlich ascites carcinoma (EAC) model. The antimicrobial screening showed that the cobalt complex possesses enhanced antimicrobial activity towards fungi.
PMCID: PMC2259242  PMID: 18320020
11.  Synthesis, characterization, electrospinning and antibacterial studies on triphenylphosphine-dithiphosphonates Copper(I) and Silver(I) complexes 
The novel amido and O-ferrocenyldithiophosphonates [FcP(S)(SH)(NHR1)] (Fc = Fe(η5-C5H5)(η5-C5H4), R1 = 1-(4-fluorophenylethyl and benzyloxycyclopentyl) and [FcP(S)(OR2)S−][H3N+C(CH3)3] (R2 = myrtanyl) were synthesized by the reaction of [(FcPS2)]2 (Fc = Fe(η5-C5H5)(η5-C5H4)) and chiral amines, such as (S)–(−)-1-(4-fluorophenylethyl) amine and (1S,2S)-(+)-benzyloxycyclopentyl amine, and of (1S), (2S), (5S)-myrtanol in toluene. The reaction of ferrocenyldithiophosphonates and [Cu(PPh3)2]NO3 or AgNO3 and PPh3 gave rise to copper(I) and silver(I) complexes in THF. [Ag2{FcP(OMe)S2}2(PPh3)2] and [Cu(PPh3)2]NO3 were embedded into nanofibers and their antimicrobial activities on fibers were also investigated.
The compounds have been characterized by elemental analyses, IR, NMR (1H-, 31P-) spectroscopy as well as MS measurements. Nanofibers were obtained by electrospinning method which is the simplest and most effective method to produce nanoscale fibers under strong electrical field. Antimicrobial activity of the compound 5, [Ag2{FcP(OMe)S2}2(PPh3)2], and [Cu(PPh3)2]NO3 on fibers were studied.
In this study, the new dithiophosphonate ligands were synthesized and utilized in the preparation of copper(I) and silver(I) complexes with ferrocenyldithiophosphonate and triphenylphosphine. Then, the compounds [Ag2{FcP(OMe)S2}2(PPh3)2] and [Cu(PPh3)2]NO3 were added into the PAN solutions (Co-PAN dissolved in dimethylacetamide) and the solutions were electrospun onto microscope slides and PP meltblown surfaces. Antimicrobial activity of the compounds [Ag2{FcP(OMe)S2}2(PPh3)2] and [Cu(PPh3)2]NO3 on fibers were determined in vitro against two indicator strains; M. luteus NCIB and E. coli ATCC25922. The obtained results indicated that these metals showed moderate level antimicrobial activities.
PMCID: PMC4004045  PMID: 24629061
Dithiophosphonates; Triphenylphosphine; Copper(I) and Silver(I) complexes; Nanofiber; Electrospinning; Antibacterial
12.  Re(V) and Re(III) Complexes with Sal2phen and Triphenylphosphine: Rearrangement, Oxidation and Reduction 
Reactions of ReV, tetradentate Schiff base complexes with tertiary phosphines have previously yielded both rearranged ReV and reduced ReIII complexes. To further understand this chemistry, the rigid diiminediphenol (N2O2) Schiff base ligand sal2phen (N,N’-o-phenylenebis(salicylaldimine)) was reacted with (n-Bu4N)[ReOCl4] to yield trans-[ReOCl(sal2phen)] (1). On reaction with triphenylphosphine (PPh3), a rearranged ReV product cis-[ReO(PPh3)(sal2phen*)]PF6 (2), in which one of the imines was reduced to an amine during the reaction, and the reduced ReIII products trans-[ReCl(PPh3)(sal2phen)] (4) and trans- [Re(PPh3)2(sal2phen)]+ (5) were isolated. Reaction of sal2phen with [ReCl3(PPh3)2(CH3CN)] resulted in the isolation of [ReCl2(PPh3)2(salphen)] (3). The compounds were characterized using standard spectroscopic methods, elemental analyses and single crystal X-ray crystallography.
PMCID: PMC3059235  PMID: 21079821
13.  Metal-Based Antibacterial and Antifungal Agents: Synthesis, Characterization, and In Vitro Biological Evaluation of Co(II), Cu(II), Ni(II), and Zn(II) Complexes With Amino Acid-Derived Compounds 
A series of antibacterial and antifungal amino acid-derived compounds and their cobalt(II), copper(II), nickel(II), and zinc(II) metal complexes have been synthesized and characterized by their elemental analyses, molar conductances, magnetic moments, and IR, and electronic spectral measurements. Ligands (L1)−(L5) were derived by condensation of β-diketones with glycine, phenylalanine, valine, and histidine and act as bidentate towards metal ions (cobalt, copper, nickel, and zinc) via the azomethine-N and deprotonated-O of the respective amino acid. The stoichiometric reaction between the metal(II) ion and synthesized ligands in molar ratio of M : L (1 : 1) resulted in the formation of the metal complexes of type [M(L)(H2O)4]Cl (where M = Co(II), Cu(II), and Zn(II)) and of M : L (1 : 2) of type [M(L)2(H2O)2] (where M = Co(II), Cu(II), Ni(II), and Zn(II)). The magnetic moment data suggested for the complexes to have an octahedral geometry around the central metal atom. The electronic spectral data also supported the same octahedral geometry of the complexes. Elemental analyses and NMR spectral data of the ligands and their metal(II) complexes agree with their proposed structures. The synthesized ligands, along with their metal(II) complexes, were screened for their in vitro antibacterial activity against four Gram-negative (Escherichia coli, Shigella flexeneri, Pseudomonas aeruginosa, and Salmonella typhi) and two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and for in vitro antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani, and Candida glaberata. The results of these studies show the metal(II) complexes to be more antibacterial/antifungal against one or more species as compared to the uncomplexed ligands. The brine shrimp bioassay was also carried out to study their in vitro cytotoxic properties. Five compounds, (3), (7), (10), (11), and (22), displayed potent cytotoxic activity as LD50 = 8.974 × 10−4, 7.022 × 10−4, 8.839 × 10−4, 7.133 × 10−4, and 9.725 × 10−4 M/mL, respectively, against Artemia salina.
PMCID: PMC1800917  PMID: 17497020
14.  catena-Poly[[[bis­(N,N-dimethyl­formamide)iron(II)]-{μ-2,2′-bis­(diphenyl­phosphino­yl)-N,N′-[(1R,2R)-cyclo­hexane-1,2-di­yl]dibenzamide}] bis­(perchlorate) N,N-dimethyl­formamide disolvate] 
The title extended solid coordination compound, {[Fe(C44H40N2O4P2)(C3H7NO)2](ClO4)2·2C3H7NO}n, was crystallized un­ex­pectedly from the reaction mixture containing the Trost ligand (1R,2R)-(+)-1,2-diamino­cyclo­hexane-N,N′-bis­(2′-di­phenyl­phosphinobenzo­yl) and Fe(ClO4)2·6H2O in a 1:1 ratio in dimethyl­formamide (DMF) under reflux conditions. The polymeric complex is characterized by FeII metal centers that are coordinated by two oxidized Trost ligands, each coordinated in a bidentate fashion in a square plane, along with two DMF mol­ecules above and below the plane [average Fe—ODMF = 2.086 (4) Å], forming an overall pseudo-octa­hedral geometry. The Trost ligand binds adjacent FeII centers, each FeII being bound through the O atom of one of the phosphine oxides [average Fe—OPPh2 = 2.115 (4) Å] and the carbonyl O atom of the adjacent amide [average Fe—Oamide = 2.192 (3) Å]. Disorder is observed in the co-solvated solvent: there are two DMF mol­ecules per FeII centre, which were modeled as one DMF mol­ecule with complete occupancy and the other being modeled in two positions with equal occupancy. Disorder was also observed with one of the perchlorate anions, which was modeled in two positions with 0.75:0.25 occupancy.
PMCID: PMC2971940  PMID: 21578561
15.  (Acetato-κO)(acetato-κO,O′)bis­(1,3-diazinane-2-thione-κS)cadmium(II) 
In the title complex, [Cd(CH3COO)2(C4H8N2S)2], the CdII cation is coordinated by three acetate O atoms and two S atoms of Diaz [Diaz = 1,3-diazinane-2-thione = 3,4,5,6-tetra­hydro­pyrimidine-2(1H)-thione]. The CdII coordination is augmented by one considerably longer Cd—O bond of 2.782 (3) Å to a carboxyl­ate O atom. The resulting coordination polyhedron around the CdII cations can be described as a highly distorted octa­hedron. The Diaz ligand and the acetate anions are linked by N—H⋯O hydrogen-bonding inter­actions.
PMCID: PMC3515111  PMID: 23284338
16.  Molecular Oxygen and Sulfur Reactivity of a Cyclotriveratrylene (CTV) Derived Trinuclear Copper(I) Complex 
Inorganic chemistry  2009;48(17):8342-8356.
Our continuing efforts into developing copper coordination chemistry relevant to dioxygen-processing copper proteins has led us to design and synthesize a cyclotriveratrylene (CTV)-based trinucleating ligand, CTV-TMPA, which employs tetradentate tris(2-pyridylmethyl)-amine chelates (TMPA) for their copper ion binding sites. Binding of three copper ions per CTV-TMPA unit was established by various chemical and spectroscopic methods such as UV-vis and resonance Raman (rR) spectroscopies. The following complexes were observed: A tricopper(I) complex [(CTV-TMPA)CuI3]3+ (1), a CO adduct [(CTV-TMPA)CuI3(CO)3]3+ (1-CO; ν(C=O) = 2094 cm−1), a triphenylphosphine adduct [(CTV-TMPA)CuI3(PPh3)3]3+ (1-PPh3), a tricopper(II) complex [(CTV-TMPA)CuII3]3+ (1-Ox) and its tris-monochloride or tris-monobromide adducts. Also, introduction of dioxygen to the −80 °C solutions of 1 leads to O2-adducts, the first example of a synthetic copper complex which can stabilize a mononuclear CuII-superoxo and dinuclear peroxo species simultaneously within one complex {[Cu] = 1.53 mM in THF: (μ-1,2-peroxo complex, λmax = 543 (ε 9650) nm): ν(O-O) = 825 ((Δ18O2) = −47) cm−1; ν(Cu-O) = 506 ((Δ18O2) = −26) cm−1: (superoxo complex, λmax = 427 (ε 3150) nm): ν(O-O) = 1129 ((Δ18O2) = −60) cm−1; ν(Cu-O) = 463 ((Δ18O2) =−27) cm−1}. Elemental sulfur reacts reversibly with 1 leading to a (proposed) hexanuclear species [{(CTV-TMPA)CuII3}2(μ-1,2-S22−)3]6+ (1-S) {λmax = 544 (ε 7270 nm }, possessing one dicopper(II)-disulfide structural type: {THF solvent) ν(S-S) = 489 ((Δ34S) = −10) cm−1; ν(Cu-S) = 506 ((Δ34S) = −5) cm−1}. Derivation of spectroscopic, structural and chemical conclusions were aided by the study of a close mononuclear analogue with one pyridyl group of the TMPA parent possessing a 6-CH2OCH3 substituent, this being part of the CTV-TMPA architecture.
PMCID: PMC2917907  PMID: 19663454
17.  (Sulfasalazinato-κO)bis­(triphenyl­phosphine-κP)copper(I) 
The title mixed-ligand copper(I) complex, [Cu(C18H13N4O5S)(C18H15P)2], was synthesized via solvothermal reaction of [Cu(PPh3)2(MeCN)2]ClO4 and sulfasalazine [systematic name: 2-hydr­oxy-5-(2-{4-[(2-pyridylamino)sulfon­yl]phen­yl}diazen­yl)benzoic acid]. The mononuclear complex displays a trigonal coordination geometry for the Cu(I) atom, which is surrounded by two P-atom donors from two different PPh3 ligands and one O-atom donor from the monodentate carboxyl­ate group of the sulfasalazinate ligand. The latter ligand is found in a zwitterionic form, with a deprotonated amine N atom and a protonated pyridine N atom. Such a feature was previously described for free sulfasalazine. The crystal structure is stabilized by C—H⋯O, C—H⋯N, N—H⋯N and O—H⋯O hydrogen bonds.
PMCID: PMC2979139  PMID: 21579036
18.  Novel Zinc(II) Complexes of Heterocyclic Ligands as Antimicrobial Agents: Synthesis, Characterisation, and Antimicrobial Studies 
The synthesis and antimicrobial activity of novel Zn(II) metal complexes derived from three novel heterocyclic Schiff base ligands 8-[(Z)-{[3-(N-methylamino)propyl]imino}methyl]-7-hydroxy-4-methyl-2H-chromen-2-one, 2-[(E)-{[4-(1H-1,2,4-triazol-1-ylmethyl)phenyl]imino}methyl]phenol, and (4S)-4-{4-[(E)-(2-hydroxybenzylidene)amino]benzyl}-1,3-oxazolidin-2-one have been described. These Schiff base ligands and metal complexes are characterised by spectroscopic techniques. According to these data, we propose an octahedral geometry to all the metal complexes. Antimicrobial activity of the Schiff base ligand and its metal complexes was studied against Gram negative bacteria: E. coli and Pseudomonas fluorescens, Gram positive bacteria: Staphylococcus aureus, and also against fungi, that is, C. albicans and A. niger. Some of the metal complexes show significant antifungal activity (MIC < 0.2 μg/mL). The “in vitro” data has identified [Zn(NMAPIMHMC)2]·2H2O, [Zn(TMPIMP)2]·2H2O, and [Zn(HBABO)2]·2H2O as potential therapeutic antifungal agents against C. albicans and A. niger.
PMCID: PMC3953498  PMID: 24707242
19.  Poly[ethano­lbis(μ3-2-thio­xo-1,2-dihydro­pyridin-1-olato)dilithium(I)] 
The title compound, [Li2(C5H4NOS)2(C2H6O)]n, having two formula units in the asymmetric unit, forms infinite chains of Li2O2 rhombi along b, consisting of four independent Li and O atoms. Metal binding to 2-thio­oxo-1,2-dihydro­pyridin-1-olate occurs in a bidentate fashion via O and S, and in a monodentate manner via the N-oxide O atom. π–π Inter­actions between polymeric chains are evident from centroid-to-centroid distances of pyridine­thione fragments of 3.461 (6)–3.607 (6) Å. The N—O and C—S bond lengths are distinctively different from those in hitherto investigated NiII, ZnII and (H3C)2TlIII complexes of 2-thio­oxo-1,2-dihydro­pyridin-1-olate, but correlate with those reported for 1-hydr­oxy- and 1-alkoxy­pyridine-2(1H)-thio­nes in the solid state.
PMCID: PMC2960834  PMID: 21201855
20.  Synthesis, Characterization, and Cytotoxic Activity of New Lanthanum(III) Complexes of Bis-Coumarins 
Complexes of lanthanum(III) with bis-coumarins: 3,3′-benzylidene-bis(4-hydroxy-2H-1-benzopyran-2-one) (H2L1) and bis(4-hydroxy-2-oxo-2H-chromen-3-yl)-(1H-pyrazol-3-yl)-methane (H2L2) were synthesized by reaction of lanthanum(III) salt and the ligands, in amounts equal to metal : ligand molar ratio of 1 : 2. The complexes were prepared by adding an aqueous solution of lanthanum(III) salt to an aqueous solution of the ligand subsequently raising the pH of the mixture gradually to circa 5.0 by adding dilute solution of sodium hydroxide. The lanthanum(III) complexes with bis-coumarins were characterized by different physicochemical methods—elemental analysis, IR-, 1H-, and 13C-NMR-spectroscopies, and mass spectral data. The spectral data of lanthanum(III) complexes were interpreted on the basis of comparison with the spectra of the free ligands. This analysis showed that in the La(III) complexes, the ligands coordinated to the metal ion through both deprotonated hydroxyl groups. On the basis of the ν(C=O) red shift observed, participation of the carbonyl groups in the coordination with the metal ion was also suggested. In the present study, we performed a cytotoxic-effects screening of the lanthanum complexes with H2L1 and H2L2 in a panel of human tumor cell lines, using the standard MTT-dye reduction assay for cell viability. The panel consisted of the acute myeloid leukemia-derived HL-60 and the chronic myeloid leukemia-derived BV-173. Following a 24- hour treatment of BV-173 cells with lanthanum complex of H2L1 at 100 or 200 μM led to a DNA-laddering. The findings suggest that the observed cytotoxicity of the lanthanum complex of H2L1 on BV-173 is at least partly mediated through induction of programmed cell death.
PMCID: PMC1686302  PMID: 17497005
21.  Bis(2,2′-bipyridine)[1,9-bis(diphenylphos­phanyl)-1,2,3,4,6,7,8,9-octahydropyrim­ido[1,2-a]pyrimidin-5-ium]ruthenium(II) hexa­fluorido­phosphate dibromide di­chloro­methane disolvate monohydrate 
In the cation of the title complex, [Ru(C31H32N3P2)(C10H8N2)2](PF6)(Br)2·2CH2Cl2·H2O, the ruthenium ion is coordinated in a distorted octa­hedral geometry by two 2,2′-bi­pyridine (bpy) ligands and a chelating cationic N-di­phenyl­phosphino-1,3,4,6,7,8-hexa­hydro-2-pyrimido[1,2-a]pyrimidine [(PPh2)2-hpp] ligand. The tricationic charge of the complex is balanced by two bromide and one hexa­fluorido­phosphate counter-anions. The compound crystallized with two mol­ecules of di­chloro­methane (one of which is equally disordered about a Cl atom) and a water mol­ecule. In the crystal, one of the Br anions bridges two water mol­ecules via O—H⋯Br hydrogen bonds, forming a centrosymmetric diamond-shaped R 4 2(8) motif. The cation and anions and the solvent mol­ecules are linked via C—H⋯F, C—H⋯Br, C—H⋯Cl and C—H⋯O hydrogen bonds, forming a three-dimensional network.
PMCID: PMC3884983  PMID: 24454158
22.  Synthesis, Spectral Characterization, and Biological Evaluation of Transition Metal Complexes of Bidentate N, O Donor Schiff Bases 
New series of three bidentate N, O donor type Schiff bases (L1)–(L3) were prepared by using ethylene-1,2-diamine with 5-methyl furfural, 2-anisaldehyde, and 2-hydroxybenzaldehyde in an equimolar ratio. These ligands were further complexed with Co(II), Cu(II), Ni(II), and Zn(II) metals to produce their new metal complexes having an octahedral geometry. These compounds were characterized on the basis of their physical, spectral, and analytical data. Elemental analysis and spectral data of the uncomplexed ligands and their metal(II) complexes were found to be in good agreement with their structures, indicating high purity of all the compounds. All ligands and their metal complexes were screened for antimicrobial activity. The results of antimicrobial activity indicated that metal complexes have significantly higher activity than corresponding ligands. This higher activity might be due to chelation process which reduces the polarity of metal ion by coordinating with ligands.
PMCID: PMC4134787  PMID: 25147493
23.  Synthesis, Characterization, and Reactivities of Manganese(V)-Oxo Porphyrin Complexes 
The reactions of manganese(III) porphyrin complexes with terminal oxidants, such as m-chloroperbenzoic acid, iodosylarenes, and H2O2, produced high-valent manganese(V)-oxo porphyrins in the presence of base in organic solvents at room temperature. The manganese(V)-oxo porphyrins have been characterized with various spectroscopic techniques, including UV-vis, EPR, 1H and 19F NMR, resonance Raman, and X-ray absorption spectroscopy. The combined spectroscopic results indicate that the manganese(V)-oxo porphyrins are diamagnetic low-spin (S = 0) species with a longer, weaker Mn-O bond than in previously reported Mn(V)-oxo complexes of non-porphyrin ligands. This is indicative of double bond character between the manganese(V) ion and the oxygen atom, and may be attributed to the presence of a trans-axial ligand. The [(Porp)MnV=O]+ species are stable in the presence of base at room temperature. The stability of the intermediates is dependent on base concentration. In the absence of base, (Porp)MnIV=O is generated instead of the [(Porp)MnV=O]+ species. The stability of the [(Porp)MnV=O]+ species also depends on the electronic nature of porphyrin ligands; [(Porp)MnV=O]+ complexes bearing electron-deficient porphyrin ligands are more stable than those bearing electron-rich porphyrins. Reactivity studies of manganese(V)-oxo porphyrins revealed that the intermediates are capable of oxygenating PPh3 and thioanisoles, but not olefins and alkanes at room temperature. These results indicate that the oxidizing power of [(Porp)MnV=O]+ is low in the presence of base. However, when the [(Porp)MnV=O]+ complexes were associated with iodosylbenzene in the presence of olefins and alkanes, high yields of oxygenated products were obtained in the catalytic olefin epoxidation and alkane hydroxylation reactions. Mechanistic aspects, such as oxygen exchange between [(Porp)MnV=16O]+ and H218O, are also discussed.
PMCID: PMC2915770  PMID: 17263410
24.  Dibromidobis[1-(2,4,6-trimethyl­phen­yl)-1,4,5,6-tetra­hydro­pyrimidine-κN 3]palladium(II) 
In the title complex, [PdBr2(C13H18N2)2], the PdII atom is situated on an inversion center. The tetra­hydro­pyrimidine group of the N-(2,4,6-trimethyl­phen­yl)-1,4,5,6-tetra­hydro­pyrimidine ligand is twisted from the square (PdN2Br2) coordination plane with a C—N—Pd—Br torsion angle of 81.8 (4)°; this is different from the angle of 43.47 (14)°, reported in a closely related structure, dichloridobis(1-methyl-1,4,5,6-tetra­hydro­pyrimidine)­palladium(II).
PMCID: PMC3050419  PMID: 21522581
25.  A Study of Mo(4+)Quinoxalyl-Dithiolenes as Models for the Non-Innocent Pyranopterin in the Molybdenum Cofactor 
Inorganic Chemistry  2011;50(20):9804-9815.
A model system for the molybdenum cofactor has been developed that illustrates the non-innocent behavior of a N-heterocycle appended to a dithiolene chelate on molybdenum. The pyranopterin of the molybdenum cofactor is modeled by a quinoxalyl-dithiolene ligand (S2BMOQO) formed from reaction of a molybdenum tetrasulfide and a quinoxalyl alkyne. The resulting complexes TEA[Tp*MoX(S2BMOQO)] (1, X = S; 3, X = O; TEA = tetraethylammonium; Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) undergo a dehydration-driven intramolecular cyclization within the quinoxalyl-dithiolene forming Tp*MoX(pyrrolo-S2BMOQO) (2, X= S; 4, X= O). 4 can be oxidized by one electron to produce the Mo(5+) complex 5. In a preliminary report of this work evidence from X-ray crystallography, electronic absorption and resonance Raman spectroscopies, and DFT bonding calculations revealed that 4 possesses an unusual asymmetric dithiolene chelate with significant thione-thiolate character. The results described here provide a detailed description of the reaction conditions that lead to formation of 4. Data from cyclic voltammetry, additional DFT calculations and several spectroscopic methods (infrared, electronic, resonance Raman, electron paramagnetic resonance) have been used to characterize the properties of members in this suite of five Mo(S2BMOQO) complexes and further substantiate the highly electron-withdrawing character of the pyrrolo-S2BMOQO ligand in 2 and 4. This study of the unique non-innocent ligand S2BMOQO provides examples of the roles that the N-heterocycle pterin can play as an essential part of the molybdenum cofactor. The versatile nature of dithiolene appended by heterocycles may aid in modulating the redox processes of the molybdenum center during the course of enzyme catalysis.
PMCID: PMC3268461  PMID: 21894968

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