Alfonso Castiñeiras

Spectral and structural studies of iron(III), cobalt(II,III) and nickel(II) complexes of 2-pyridineformamide N(4)-methylthiosemicarbazone

Abstract Reduction of 2-cyanopyridine by sodium in dry methanol in the presence of N(4)-methylthiosemicarbazide produces 2-pyridineformamide N(4)-methylthiosemicarbazone, HAm4M. Complexes with iron(III), cobalt(II,III) and nickel(II) have been prepared and characterized by molar conductivities, magnetic susceptibilities and spectroscopic techniques. In addition, the crystal structures of HAm4M, [Ni(Am4M)(OAc)], [Fe(Am4M)2]ClO4 and [Co(Am4M)2]ClO4 have been solved. Coordination is via the pyridyl nitrogen, imine nitrogen and thione or thiolato sulfur when coordinating as the neutral and anionic ligand, respectively.

Complexes of Ni(II) and Cu(II) with ofloxacin. Crystal structure of a new Cu(II) ofloxacin complex.

Several coordination compounds formed between Ni(II) or Cu(II) with ofloxacin have been synthesised and characterised. According to elemental chemical analysis and FT-IR spectroscopy data, direct reaction of Ni(II) and Cu(II) salts with ofloxacin leads to formation of precipitates for which mass spectrometry demonstrates their polymeric nature. However, crystalline [Cu(oflo)2(H2O)].2H2O is formed if the reaction is carried out in the presence of ammonia. This complex crystallises in the triclinic system, space group P-1 with a=9.2887(12), b=11.2376(14), c=17.874(2) A, alpha=92.12(3), beta=95.39(3), gamma=91.71(3) degrees and Z=2. The local geometry around the Cu(II) ion is a slightly distorted square base pyramid. Electronic spectra, magnetic susceptibility measurements and EPR spectra of the synthesised complexes indicate a tetragonal environment.

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.

Synthesis, characterization, and crystal structure of [Cu(cinoxacinate)2] · 2H2O complex: A square-planar CuO4 chromophore. Antibacterial studies

The structural and spectroscopic properties of a new copper (II) complex of cinoxacin (HCx) have been investigated. The complex [Cu(Cx)2].2H2O crystallizes in the monoclinic system, space group P2(1)/c. The cell dimensions are: a = 7.998(2), b = 7.622(1), c = 18.955(6) A, beta = 94.38(2) degree, V = 1154.6(6) A3, Z = 2. The structure was refined to R = 0.051. The crystal is composed of [Cu(Cx)2] units and uncoordinated water molecules. The Cu(II) ion, at a center of symmetry, is coordinated to two cinoxacinate (Cx) ligands related by the inversion center. Each cinoxacinate acts as bidentate ligand bonded to the cation through its carboxylate oxygen atom and through its exocyclic carbonyl oxygen atom, resulting in a CuO4 chromophore in a crystallographically planar configuration. The complex was screened for its activity against several bacteria, showing the same antimicrobial activity as the corresponding ligand.

Synthesis, characterization and antifungal activity of group 12 metal complexes of 2-acetylpyridine-4N-ethylthiosemicarbazone (H4EL) and 2-acetylpyridine-N-oxide-4N-ethylthiosemicarbazone (H4ELO)

Abstract Reaction of group 12 metal halides in ethanol with the thiosemicarbazones 2-acetylpyridine-4N-ethylthiosemicarbazone (H4EL) and 2-acetylpyridine-N-oxide-4N-ethylthiosemicarbazone (H4ELO) produced the compounds [M(H4EL)X2] and [M(H4ELO)X2] [M=Zn(II), Cd(II) or Hg(II), X=Cl, Br or I]. The ligands and complexes were characterized by elemental analysis and by IR and NMR (1H, 13C, 113Cd, 199Hg) spectroscopy, and the structures of H4ELO·H2O and the complexes [Cd(H4EL)I2]·2DMSO, [Hg(H4EL)Br2]–DMSO, [Zn(H4ELO)Cl2] and [Zn(H4ELO)Br2] were determined by X-ray diffraction. The metal centers in the complexes have coordination number five, H4EL and H4ELO behaving as neutral NNS- and ONS-tridentate ligands, respectively. The coordination polyhedra are close to tetragonal pyramids, the degree of distortion towards trigonal bipyramids was estimated by τ calculation. Against the pathogenic fungi Aspergillus niger and Paecilomyces variotii, the mercury complexes of H4ELO had activities that at some doses exceeded that of nystatin.

The crystal structure and hydrolysis equilibrium of triphenyl(2-mercapto-1-methylimidazolato)tin(IV)

Abstract The title compound was prepared from 1-methyl-2(3H)-inidazolinethione and triphenyltin(IV) hydroxide, and its crystal structure was determined by X-ray diffraction. The crystal consists of discrete molecules with the tin atom coordinated to one carbon atom of each of the three phenyl groups and to the sulfur atom of the deprotonated ligand. An SnN interaction [2.920(3) A] slightly distorts the tin coordination geometry from that of a perfect tetrahedron. NMR spectroscopy was used to study the hydrolysis of this compound in CDC13.

Structural and spectral characterization of transition metal complexes of 2-pyridineformamide N(4)-dimethylthiosemicarbazone

Abstract Sodium in dry methanol reduces 2-cyanopyridine in the presence of N(4)-dimethylthiosemicarbazide to produce 2-pyridineformamide N(4)-dimethylthiosemicarbazone, HAm4DM. Complexes with iron(III), cobalt(III), nickel(II), copper(II), palladium(II) and platinum(II) have been prepared and characterized by spectroscopic techniques. In addition, the crystal structures of [Ni(Am4DM)(OAc)], [Ni(Am4DM)(CH3CN)]ClO4, [Cu(Am4DM)(OAc)] and [Pt(Am4DM)(DMSO)]Cl·2H2O are included. Coordination of the anionic thiosemicarbazone ligand is via the pyridyl nitrogen, imine nitrogen and thiolato sulfur atoms. The acetato groups in [Ni(Am4DM)(OAc)] and [Cu(Am4DM)(OAc)] are coordinated as monodentate ligands by one oxygen and the other oxygen interacts intermolecularly with the amide NH2 function of Am4DM. Coordination of the DMSO molecule in [Pt(Am4DM)(DMSO)]Cl·2H2O is through sulfur to give an essentially planar cation.

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.

Three new modes of adenine-copper(II) coordination: interligand interactions controlling the selective N3-, N7- and bridging μ-N3,N7metal-bonding of adenine to different N-substituted iminodiacetato-copper(II) chelates

Abstract The reaction of Cu2CO3(OH)2, various N-substituted-iminodiacetic acids [RN(CH2CO2H)2)] and adenine (AdeH) in water yields crystalline samples of mixed-ligand copper(II) complexes of formulas [Cu(A)(N7AdeH)(H2O)]·H2O (A=N-methyl- or N-ethyl-iminodiacetato(2−); compounds 1 and 2, respectively), [Cu(B)(N3AdeH)(H2O)]·H2O (B=N-benzyl- or N-(p-methylbenzyl)-iminodiacetato(2−); compounds 3 and 4, respectively) as well as [Cu4(pheida)4(μ-N3,N7AdeH)2(H2O)4]·2H2O (pheida=N-phenethyl-iminodiacetato(2−)). Crystal structures of the acid H2pheida and compounds 1–5 are reported. H2pheida acid exhibits a typical zwitterionic structure. Copper(II) compounds were also studied by TG analysis (with FT-IR study of the evolved gasses), IR, electronic and ESR spectra and magnetic susceptibility data. The N-alkyl- or N-benzyl-like-iminodiacetato(2−) ligands (A or B) give complexes with Cu(II)/(A or B)/AdeH equimolar ratio, whereas pheida yields an unexpected tetranuclear compound with a 2:2:1 Cu(II)/pheida/AdeH molar ratio. In 1 and 2 AdeH binds to the metal by N7, whereas in 3 and 4 the N3 atom is used. An unexpected bridging μ-N3,N7AdeHdicopper(II) binding mode is found in the tetra-nuclear compound 5 (without interligand π,π-stacking interactions). These AdeHCu(II) binding modes have not been referred in the literature before. The difference in AdeHCu(II) binding modes in compounds 1 or 2 and 3 or 4 is rationalised on the basis of the absence or presence of a flexible N-benzyl-like substituent in the iminodiacetato(2−) ligand skeleton, which prevents or permits the interligand π,π-stacking interactions.

Coordination behaviour of sulfanilamide derivatives.: Crystal structures of [Hg(sulfamethoxypyridazinato)2], [Cd(sulfadimidinato)2(H2O)]·2H2O and [Zn(sulfamethoxazolato)2-(pyridine)2(H2O)2]

Abstract Hg(II), Cd(II) and Zn(II) complexes with the ligands sulfadimethoxine, sulfamethoxypyridazine, sulfadiazine, sulfamerazine, sulfadimidine and sulfamethoxazole have been prepared and characterised by spectral data. 1H and 13C NMR have been used to interpret the structural characteristics of the complexes in solution. The X-ray crystal structures of [Hg(sulfamethoxypyridazinato)2] (2a), [Cd(sulfadimidinato)2(H2O)]·2H2O (4b) and [Zn(sulfamethoxazolato)2(py)2(H2O)2] (6d) have been determined. In complex 2a the Hg(II) ion lies on an inversion centre and exhibits linear coordination by two sulfonamidic nitrogen atoms [Hg–N(1)=2.071(4) A] of the two deprotonated sulfamethoxypyridazinato ligands. The polymeric Cd(II) complex (4b) exhibits a high distorted-octahedral geometry, involving the sulfonamidic nitrogen [Cd–N(1)=2.328(6); Cd–N(1′)=2.326(6) A] and the heterocyclic N(3)/N(2′) [Cd–N(3)=2.307(6) A; Cd–N(2′)=2.426(6) A] of two bidentate sulfadimidine ligands, the terminal amino N(4′b) [Cd–N(4′b)=2.379(7) A] of a third sulfadimidine which is bonded to an adjacent Cd(II), and the O(3) atom of a coordinated water molecule [Cd–O(3)=2.334(6) A]. In complex 6d the geometry around the Zn(II) ion can be described as a slightly distorted compressed octahedron. Two pyridine [Zn–N(16)=2.1841(17) A] and two isoxazole N atoms [Zn–N(2)=2.1736(15) A] are located in the equatorial plane and two oxygen atoms of two water molecules [Zn–O(4)=2.0984(14) A] are placed in the apical positions. IR and NMR spectral studies suggest a similar behaviour of the Cd(II) and Zn(II) complexes, both in solid state and solution, and different to the corresponding Hg(II) complexes. Thus 1H and 13C NMR spectra, in DMSO-d6, of Cd(II) and Zn(II) compounds show coordination mainly through the heterocyclic nitrogen while the corresponding Hg(II) derivatives seem to be coordinated through the sulfonamidic nitrogen.