Antonio Sousa

Electrochemical synthesis of metallic complexes of bidentate thiolates containing nitrogen as an additional donor atom

Abstract In this work, we describe the results obtained by our group on the synthesis of metallic thiolato complexes by the electrochemical oxidation of a sacrificial anode in a non-aqueous solution of the precursor ligand. In addition to its simplicity and high yield, the electrochemical method is both quick and selective, and provides a pathway to new compounds. The procedure has proven to be quite effective in obtaining mixed complexes in a single step by simply adding a second ligand to the cell. Our report is restricted to the synthesis and structural characterization of metallic compounds with heterocyclic thiones with diverse degrees of steric hindrance and containing, apart from sulfur, nitrogen atoms as donor atoms. The synthesis and structures of mixed complexes containing additional coligands such as 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), bis(diphenylphosphino)methane (dppm) or 1,2-bis(diphenylphosphino)ethane (dppe), are also described. A main part of the discussion is related to the influence of the steric hindrance and the presence of additional coligands on the degree of association of the metallic thiolates.

Electronic and steric effects in manganese Schiff-base complexes as models for the water oxidation complex in photosystem II. The isolation of manganese-(II) and -(III) complexes of 3- and 3,5-substituted N,N′-bis(salicylidene)ethane-1,2-diamine (H2salen) ligands

Manganese-(II) and -(III) complexes of substituted N,N′-bis(salicylidene)ethane-1,2-diamine (H2salen) ligands H2L (substituents are in the 3, 5 or 3,5 positions of the phenyl rings of the salen moiety) have been prepared and thoroughly characterised. The reaction of Mn(ClO4)2·6H2O with H2L in ethanol in air normally leads to manganese(III) complexes ligated by both the N2O2 ligand and water molecule(s). However, by employing electron-withdrawing substituents on the ligand, e.g. 3-Br,5-NO2, a manganese(II) complex can be obtained. A ‘borderline’ ligand is represented by the 5-NO2 derivative (nsalen), which produces a manganese(II) complex contaminated with a small amount of a manganese(III) species. Using a more rigorous oxidising agent in the synthesis, [Fe(η-C5H5)2][FeCl4], drives the reaction totally to a manganese(III) complex [Mn(nsalen)Cl(H2O)]. In addition to magnetic susceptibility studies, cyclic voltammetry has been employed. All the complexes exhibit an oxidation and reduction peak, the reversible character being confirmed by pulse voltammetry. Pulse voltammetry also confirmed the nature of the manganese(II) species [Mn(bnsalen)(H2O)2·2H2O [H2bnsalen =N,N′-bis(3-bromo-5-nitrosalicylidene)ethane-1,2-diamine] and that a slight amount of a manganese(III) species is present in [Mn(nsalen)(H2O)2]·2H2O. Six complexes have been crystallographically characterised. Despite the retention of an octahedral manganese environment in all of them, the supramolecular structures exhibit a wide diversity. The 3,5-dichloro and 5-bromo salen complexes containing co-ordinated water display combined π and hydrogen bonding, as well as dimerisation. The complex [{Mn(µ-dbsalen)(µ-O)}2](dbsalen = 3,5-dibromo derivative) offers an alternative bridging arrangement, and [Mn(bsalen)(MeOH)(OClO3)]·H2O (bsalen = 5-bromo derivative) highlights the versatility of the manganese centre in these systems where, unexpectedly, perchlorate is co-ordinated in place of a lattice water. A more subtle rearrangement of supramolecular structure is obtained in [Mn(nsalen)Cl(H2O)] where the usual combination of π- or hydrogen-bonding interaction is modified by the corresponding ability of the 5-NO2 substituent.

Spectral and structural studies of metal complexes of isatin 3-hexamethyleneiminylthiosemicarbazone prepared electrochemically

Abstract Cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II) and lead(II) complexes of isatin 3-hexamethyleneiminylthiosemicarbazone, [M(Ishexim)2], as well as a thallium(I) complex, [Tl(Ishexim)], have been prepared by electrochemical synthesis. The crystal structures of [Zn(Ishexim)2] and [Pb(Ishexim)2] have been solved, and the metal complexes have been characterized by their 1H and 13C NMR, IR, UV–Vis and mass spectra. Coordination of the Ishexim anions is via the imine nitrogen and thiolato sulfur atoms with evidence for weak interaction of the amide oxygen with the isatin portion of the ligand.

Synthesis and structural characterisation of new manganese(II) and (III) complexes. Study of their photolytic and catalase activity and X-ray crystal structure of [Mn(3-OMe, 5-Br-salpn)(EtOH)(H2O)]ClO4

Abstract New [MnIIL(H2O)2] and [MnIIIL(H2O)2]ClO4 complexes, where L are substituted N,N′-bis(salicylidene)propane-1,3-diamine (H2salpn) ligands have been prepared and thoroughly characterised by elemental analysis, IR and mass spectroscopy, conductivity and magnetic measurements at room temperature (and, in the case of 1, at variable temperature). Cyclic and normal pulse voltammetry measurements were also performed. All these studies support an octahedral geometry around the metal with the Schiff base in the equatorial plane acting as tetradentate and solvent molecules in the axial positions. Crystallographic characterisation of 6 confirms this geometry and shows a supramolecular structure involving π–π stacking and hydrogen bonding interactions. The ability to split water by these complexes and their catalase activity has also been studied.

Copper(I) complexes with 4,6-dimethylpyrimidine-2-thione (Hdmpymt); the crystal and molecular structure of [Cu6(dmpymt)6]

The complex [Cu6(dmpymt)6]·H2O was synthesised by electrochemical oxidation of copper in an acetonitrile solution of the neutral ligand 4,6-dimethylpyrimidine-2-thione (Hdmpymt). The reaction of [Cu6(dmpymt)6] with 1,2-bis(diphenylphosphino)methane (dppm) and 1,2-bis(diphenylphosphino)ethane (dppe) yielded compounds of general formulae [Cu(dmpymt)(dppm)] and [Cu2(dmpymt)2(dppe)3]. The molecular structure of [Cu6(dmpymt)6] was determined: the crystals are triclinic, space group P1, a= 11.432(3), b= 13.395(2), c= 15.694(4)A, α= 80.28(2), β= 87.75(2), γ= 73.87(2)° and Z= 2. The six copper atoms are arranged with distorted-octahedral geometry, each copper atom being trigonally co-ordinated to one nitrogen and two sulfur atoms of three different ligands. Infrared, 1H, 13C and 31P NMR spectral data are presented for all the compounds.

Electrochemical synthesis and crystal structure of silver(I) complexes with some heterocyclic thiones

Two silver(I) complexes, [{Ag(SR)}6][R1SH = 6-(tert-butyldimethylsilyl)pyridine-2-thione 1, R2SH = 3,6-bis(tert-butyldimethylsilyl)pyridine-2-thione 2], have been synthesized by electrochemical oxidation of the metal in an acetonitrile solution of the neutral heterocyclic thiones. The reaction of equimolar amounts of dppm [bis(diphenylphosphino)methane] with complexes 1 and 2 in dichloromethane resulted in the formation of [Ag4Cl4(dppm)2]3 and the elimination of RSCH2SR. Single-crystal X-ray analyses were performed for compounds 1, 3 and R2SCH2SR2.

Electrochemical synthesis of pyridine-2-thionato complexes of zinc(II) and cadmium(II) : the crystal structure of 1,10-phenanthroline-bis(pyridine-2-thionato)zinc(II)

Abstract Zinc and cadmium pyridine-2-thionato complexes, M(pyt)2, were prepared by direct electrochemical oxidation of the metal into a solution of pyridine-2-thione (pytH) in acetonitrile. Adducts of type [M(pyt)2L] (L = 2,2′-bipyridine or 1,10-phenanthroline) were obtained by addition of the ligand to the electrolyte phase. X-ray structure determination of [Zn(pyt)2phen] shows the molecule to have a distorted octahedral trans-ZnS2N4 core, with average bond distances of 2.182 A for ZnN(phen), 2.061 A for ZnN(pyt) and 2.586 A for ZnS. The vibrational, 1H and 13C NMR spectra of the compounds are discussed.

Synthesis of cobalt(II), nickel(II) and copper(II) complexes with 2-(2-hydroxyphenyliminomethyl)-1-(4-methyl-phenylsulfonamido)benzene and crystal structures of {bis(methanol)[2-(2′-N-tosylaminophenyl)iminomethyl]phenolato}nickel(II) and {bis(2,2′-bipyridine)[2-(2′-N-tosylaminophenyl)iminomethyl]phenolato}copper(II)

Abstract Electrochemical oxidation of metal anodes (cobalt, copper and nickel) in acetonitrile solutions of 2-(2-hydroxyphenyliminomethyl)-1-(4-methyl-phenylsulfonamido)benzene (H2L) gave [CoL], [CuL] and [NiL] complexes. When 1,10-phenanthroline (phen) or 2,2′-bipyridine (bipy) was added to the electrolytic cell, the mixed complexes [MLL′] (M=Co, Cu, L′=bipy or M=Ni, L′=phen) were obtained. A binuclear compound of composition [Ni2L2(MeOH)4] (1) was synthesized by reaction of the ligand H2L and nickel(II) acetate in methanol. X-ray structure determination showed the compound to be binuclear, with each nickel atom coordinated to two nitrogen and two bridging phenol oxygen atoms of two dianionic ligands and two methanol molecules, in an octahedral environment. The crystal structure of [CuLbipy] (2) was determined by X-ray diffraction; with the copper atom in a distorted bipyramidal environment defined by the two bipyridine nitrogen atoms and by the phenolic oxygen and the nitrogen atoms of the dianionic ligand. The electronic and vibrational spectral data of the complexes are discussed and related to the structure.

The electrochemical synthesis of neutral copper(II) complexes of schiff base ligands: The crystal structures of bis-{n-[2-(3-methylpyridyl)]-5-methoxysalicylideneiminato}copper(II) and bis-{n-[2-(6-metrylpyridyl)]-salicylideneiminato}copper(II)

Neutral copper(II) complexes of Schiff bases derived from substituted salicylaldehydes and 2-aminopyridine methyl derivatives have been synthesized by an electrochemical procedure. The crystal and molecular structure of bis{N-[2-(3-methylpyridyl)]-5-methoxysalicylideneiminato}copper(II) and of bis{N-[2-(6-methylpyridyl)]-salicylideneiminato}copper(II) have been determined by X-ray diffraction. The former compound crystallizes in the monoclinic space group C2/c with four molecules in the unit cell and cell constants a = 16.784(2), b = 16.344(2) and c = 11.211(2) A, and β = 124.08(1)°, while the other complex crystallizes in the monoclinic space group P21/c with two molecules in a cell of dimensions a = 12.456(1), b = 7.812(2) and c = 12.047(2) A, and β = 110.48(1)°. In both structures, the metals adopt square-planar coordination geometries and the pyridyl nitrogen atoms are not coordinated. The electronic and IR spectra of the complexes are discussed and related to the structure.

Electrochemical synthesis of benzothiazole-2-thionato complexes of nickel(II), zinc(II) and cadmium(II) : the crystal structure of 2,2'-bipyridine bis(benzothiazole-2-thionato)zinc(II)

The electrochemical oxidation of anodic metal (nickel, zinc or cadmium) in acetonitrile solutions of benzothiazole-2-thione (Hbztz) gave the compounds [M(bztz) 2 ] [M = nickel(II), zinc(II) and cadmium(II)]. When the oxidations were repeated in the presence of neutral ligands L′ (2,2′-bipyridine or 1,10-phenanthroline) the complexes [M(bztz) 2 L′] were obtained. The crystal structure of 2,2′-bipyridine bis(benzothiazole-2-thionato)zinc(II) was determined by X-ray diffraction. This compound consists of monomeric molecules in which the central ZnS 2 N 2 unit has a slightly distorted tetrahedral environment. The electronic, IR and 1 H and 13 C NMR spectra of the complexes are discussed and related to their structure.