Ray J. Butcher

Spectroscopic, structural and antibacterial properties of copper(II) complexes with bio-relevant 5-methyl-3-formylpyrazole N(4)-benzyl-N(4)-methylthiosemicarbazone

The coordination behaviour of the title ligand, 5-methyl-3-formylpyrazole N(4)-benzyl-N(4)-methylthiosemicarbazone(HMPz4BM), is reported with solid state isolation of copper(II) complexes, [Cu(HMPz4BM)X2] (X = Cl, Br, NO3, ClO4 and BF4) which have been spectroscopically and structurally characterised. I.r. data for the free ligand and its Cu(II) complexes indicate that HMPz4BM exhibits a neutral NNS tridentate function via the pyrazolyl nitrogen(tertiary), azomethine nitrogen and thione sulphur. Electronic spectral data are suggestive of a square pyramidal environment for the seemingly pentacoordinated Cu(II) species. E.s.r parameters (RT and LNT) of the reported copper(II) complexes are indicative of a dxx2–y2 ground state for the reported species. Cyclic voltammograms of Cu(II) complexes show a quasireversible CuII/CuIII couple and also an irreversible CuII/CuI couple. X-ray crystallography of a representative species, [Cu(HMPz4BM)(NO3)2] (C2/c, monoclinic ), has unambiguously documented the conjectural findings from i.r. data that coordinating sites of the title ligand are pyrazolyl (tertiary)nitrogen, azomethine nitrogen and the thione sulphur (NNS); and the oxygen of one of the nitrate ions has occupied the basal plane; the fifth coordination position has been occupied by the oxygen of another nitrate ion in a square pyramidal geometry. The antibacterial properties of the ligand and its copper(II) complexes studied on microorganism, Staphylococcus aureus have pointed out that most of the complexes have higher activities than that of the free ligand.

The preparation and characterization of bis-chelated nickel(II) complexes of the 6-methylpyridine-2-carboxaldehyde Schiff bases of S-alkyldithiocarbazates and the X-ray crystal structure of the bis {S-methyl-β-N- (6-methylpyrid-2-yl)- methylenedithiocarbazato}nickel(II) complex

Abstract New nickel(II) complexes of general formula, [Ni(NNS)2] (NNS− = uninegatively charged tridentate ligands formed by condensation of 6-methyl-2-formylpyridine with S-methyl- and S-benzyldithiocarbazates) have been prepared and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic evidence support a distorted octahedral structure for these complexes. The crystal and molecular structure of the bis{S-methyl-β-N-(6-methylpyrid-2-yl)methylenedithiocarbazato}nickel(II) complex has been determined by X-ray diffraction studies. The complex has a distorted octahedral structure with the ligands coordinated to the nickel(II) ion as uninegatively charged tridentate chelating agents via the pyridine nitrogen, the azomethine nitrogen and the mercaptide sulphur atoms. The distortion from the regular octahedral geometry is ascribed to the stereochemical limitations imposed by the planar tridentate ligands.

Novel chiral organoselenenyl halides stabilized by Se···N nonbonded interactions: synthesis and structural characterization

The first examples of structurally characterized chiral organoselenenyl halides stabilized by Se···N intramolecular interactions are described. The existence of strong nonbonded Se···N interactions in the solid state as well as in solution was unambiguously determined by single-crystal X-ray analysis and 77 Se NMR spectroscopy.

Complexes of N(4)-cyclohexylsemicarbazones and N(4)-cyclohexylthiosemicarbazones derived from 2-formyl-, 2-acetyl- and 2-benzoylpyridine

Abstract2-Formyl-, 2-acetyl- and 2-benzoylpyridine N(4)-cyclohexylsemicarbazone and N(4)-cyclohexylthiosemicarbazone complexes of cobalt(II, III), nickel(II) and copper(II) have been prepared and characterized by molar conductivities, magnetic susceptibilities and spectroscopic techniques. For many of the complexes, coordination is by the neutral ligand, the main exceptions being the cobalt(III) complexes of the three thiosemicarbazones and three of the benzoylpyridine derivatives. Thus, bonding is via the pyridyl nitrogen, azomethine nitrogen and thione/thiolato sulfur. The five-coordinate copper(II) complex of 2-acetylpyridine N(4)-cyclohexylthiosemicarbazone, [Cu(HAc4CHex)Cl2], approaches square pyramidal stereochemistry with the basal Cu—Cl bond significantly shorter than the apical Cu—Cl bond.

The preparation and characterization of mono- and bis-chelated cadmium(II) complexes of the di-2-pyridylketone Schiff base of S-methyldithiocarbazate (Hdpksme) and the X-ray crystal structure of the [Cd(dpksme)2] · 0.5 MeOH complex

New cadmium(II) complexes of empirical formulae, [Cd(dpksme)X] (dpksme = anionic form of the Schiff base; X = NCS−, Cl−, I−) and [Cd(dpksme)2] · 0.5MeOH, respectively have been prepared and characterized. The mono-ligated cadmium(II) complexes, [Cd(dpksme)X] are four-coordinate and tetrahedral but the bis-ligand complex, [Cd(dpksme)2] · 0.5MeOH is six-coordinate and octahedral. The crystal and molecular structure of [Cd(dpksme)2] · 0.5MeOH has been determined by X-ray diffraction. The complex has a distorted mer-octahedral structure in which the ligands are coordinated as uninegatively charged tridentate chelating agents via the pyridine nitrogen atoms, the azomethine nitrogen atoms and the thiolate sulfur atoms. The distortion from regular octahedral geometry is ascribed to the restricted bite angles of the ligands. The Schiff base and its cadmium(II) complexes exhibit mild antibacterial activities against Shigella dysenteriae, Bacillus cereus, Staphylococcus aureus and Escherichia coli. They are also mildly fungitoxic against the phytopathogenic fungi, Alternaria alternata and Macrophomina phaseolina.

Synthesis and characterization of manganese(II) and iron(III) d5 tripodal imidazole complexes. Effect of oxidation state, protonation state and ligand conformation on coordination number and spin state

The 1 : 3 Schiff base condensates of tris(2-aminoethyl)amine (tren) or tris(3-aminopropyl)amine (trpn) with 4-methyl-5-imidazolecarboxaldehyde, H3L1 and H3L2, respectively, were generated in situ and used to prepare complexes with manganese(II) and iron(III). The resultant complexes, [MnH3L1](ClO4)2, [MnH3L1](ClO4)2.EtOH.H2O, [MnH3L2](ClO4)2, [FeH3L1](ClO4)3.1.5(EtOH) and [FeHL1](I3) (0.525)(I)(0.475).2.625H2O, have been characterized by EA, IR, ES MS, variable temperature magnetic susceptibility, X-ray crystallography, and Mössbauer spectroscopy for the iron complexes. The three manganese(II) complexes are high spin with [MnH3L2](ClO4)2 exhibiting coordination number seven while the others are six coordinate. [FeH3L1](ClO4)3.1.5(EtOH) has two iron sites, a seven coordinate and a pseudo seven coordinate site. The complex is high spin at room temperature but exhibits a magnetic moment that decreases with temperature corresponding to conversion of one of the sites to low spin. [FeHL1](I3) (0.525)(I)(0.475).2.625H2O is low spin even at room temperature. In the present complexes the apical nitrogen atom, N(ap), of the tripodal ligand is pyramidal and directed toward the metal atom. The data show that the M-N(ap) distance decreases as the oxidation state of the metal increases, as the number of bound imidazole protons on the ligand increases, and as the number of carbon atoms in the backbone of the ligand (tren vs. trpn) increases. In a limiting sense, short M-N(ap) distances result in high spin seven coordinate mono capped octahedral complexes and long M-N(ap) distances result in low spin six coordinate octahedral complexes.

Synthesis and characterization of some four- and five-coordinate copper(II) complexes of 6-methyl-2-formylpyridinethiosemicarbazone (HNNS) and the X-ray crystal structures of the [Cu(NNS)(CH3COO)(H2O)] and [Cu (HNNS) (H20) (S04)) - H2O complexes

Abstract Copper(II) complexes of general formula, [Cu(NNS)(H2O)xX] · nH2O (NNS− = uninegatively charged tridentate thiosemicarbazone ligand formed from 6-methyl-2-formylpyridine; X = NCS−, CH3COO−, N3−; x = 0,1; n = 0.5, 1) and [Cu(HNNS)(H2O)(SO4)] · H20 have been synthesized and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic evidence support a square-planar structure for the [Cu(NNS)X] (X = NCS−, N3−) complexes and a five-coordinate structure for the [Cu(HNNS)(H2O)(SO4)] · H2O complex. The crystal structures of the [Cu(NNS)(CH3COO)(H2O)] and [Cu(HNNS)(H2O)(SO4)] · H2O complexes have been determined by X-ray diffraction. The acetato complex has a distorted square-pyramidal geometry with the thiosemicarbazone ligand acting as a uninegatively charged tridentate NNS chelating agent and the fourth and fifth coordination positions of the copper(II) ion are occupied by a unidentate acetate and water ligand, respectively. The sulphato-complex is also five-coordinate with the thiosemicarbazone coordinated as a neutral NNS ligand and the fourth and fifth coordination sites are occupied by a water molecule and a unidentate sulphate ligand, respectively.

Preparation, characterization and antifungal properties of nickel(II) complexes of tridentate ONS ligands derived from N-methyl-S-methyldithiocarbazate and the X-ray crystal structure of the [Ni(ONMeS)CN]·H2O complex

Nickel(II) complexes of general empirical formula, NiLX·nH2O (L = deprotonated form of the Schiff base formed by condensation of N-methyl-S-methyldithiocarbazate with 2-hydroxybenzaldehyde or 5-bromo-2-hydroxybenzaldehyde; X = Cl−, Br−, NCS−, AcO− or CN−; n = 0, 1) have been prepared and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic data support a square-planar structure for these complexes. The crystal structure of the [Ni(ONMeS)CN]·H2O complex (ONMeS = anionic form of the 2-hydroxybenzaldehyde Schiff base of N-methyl-S-methyldithiocarbazate) has been determined by X-ray diffraction. The complex has a distorted square-planar structure in which the Schiff base is coordinated to the nickel(II) ion as a uninegatively charged anion coordinating via the phenolic oxygen atom, the azomethine nitrogen atom and the thione sulfur atom. The fourth coordination position is occupied by a cayano ligand. The antifungal properties of the Schiff bases and their nickel(II) complexes were studied against three plant pathogenic fungi. The ligands display moderate fungitoxicities against these organisms but their nickel(II) complexes are less active than the free ligands.

Synthesis and characterization of a spin crossover iron(II)–iron(III) mixed valence supramolecular pseudo-dimer exhibiting chiral recognition, hydrogen bonding, and π–π interactions

Reaction of iron(II) and the 3 : 1 Schiff base condensate of 5-methylpyrazole-3-carboxaldehyde and tris(2-aminoethyl)amine in air gives a pseudo-dimer complex with a triple helix structure made of Δ–Δ and Λ–Λ pairings of spin crossover iron(II) and low spin iron(III) cations that are held together by three π–π and hydrogen bonding interactions.

Synthesis of organochalcogens stabilized by intramolecular non-bonded interactions of sterically unhindered 2-phenyl-2-oxazoline

The synthesis and characterization of low-valent organoselenium and -sulfur compounds incorporating sterically unhindered 2-phenyl-2-oxazoline are described. Organylselenenyl halides, RSeX (X = Cl, Br, I) were prepared from diselenide and the benzyl selenide derivative was synthesized by the reaction of in situ generated lithium arylselenolate, OxSe−Li+ (Ox = 2-phenyl-2-oxazoline) with benzyl chloride. These compounds in general show strong Se⋯N intramolecular interactions as compared with the substituted oxazoline analogues. Bis[2-(2-oxazolinylphenyl)] disulfide and [2-(2-oxazolinyl)phenyl]benzyl sulfide were synthesized by the ortho-lithiation method and characterized by 1H and 13C NMR spectroscopy. The S⋯N intramolecular interactions were confirmed by single crystal X-ray crystallography.