J.M. Salas-Peregrin

Transition metal complexes with monodeprotonated isoorotic and 2-thioisoorotic acids: Crystal structure, spectral and magnetic study, and antimicrobial activity

Abstract The reaction, in ethanol or water medium, of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), and Pt(II) ions with isoorotic and 2-thioisoorotic acids (H 3 L) has allowed the isolation of complexes with the general formula M II (H 2 L) 2 ·2H 2 O. These were characterized by means of elemental analysis, spectral techniques (UV-Vis-NIR, IR, EPR, 13 C and 1 H NMR), magnetic moments, and conductivity measurements. The molar conductivities in dimethylsulphoxide indicate the non-ionic nature of isolated compounds. The most common coordination mode of uracil monoanions seems to be a O4-OCO bidentate scheme which leads to a six-membered chelate ring. Complexes of first row transition ions display an octahedral structure, whereas for Pd(II) and Pt(II) compounds a square-planar structure is suggested. The MO 6 octahedral structure has been corroborated from the single crystal x-ray study of bis-isoorotato-diaquazinc(II). This compound is monoclinic, space group P2 1 /c, with a = 5.067(5) A, b = 15.072(4) A, c = 11.239(8) A, β = 125.80(9)°, V = 696(1) A 3 , and Z = 2. The structure was solved by means of the heavy atom method from the zinc special position. Full matrix refinements based on F o were performed to R = 0.060 for 1884 data. The structure consists of discrete [Zn(H 2 CU) 2 (H 2 O) 2 ] units in which the Zn(II) ion is octahedrally MO 6 coordinated by two bidentate O4-OCO isoorotato ligands (MO, 2.033 and 2.039 A) and two water molecules occupying the axial positions (MO w , 2.170 A). Likewise, a previous study of biological activity of these complexes against several bacteria and yeasts was carried out. In general, complexes with the 2-thioisoorotato ligand possess greater antimicrobial activity than those with the isoorotate ligand, specially in the case of cobalt(II) complexes.

Synthesis and structural studies on metal nitrate complexes with 1,3-dimethyllumazine and 1,3,6,7-tetramethyllumazine: crystal structure of two new cobalt(II) and copper(II) three-dimensionally hydrogen-bonded complexes and a cadmium(II) complex with unusual geometry

Abstract In absolute methanol medium, M II (NO 3 ) 2 (M = Co,Ni,Cu,Zn and Cd) react with 1,3-dimethyllumazine (DLM) and 1,3,6,7-tetramethyllumazine (DLMD) (lumazine = (1 H ,3 H )-pteridin-2,4-dione) to give complexes with general formula M II (NO 3 ) 2 (pteridine) 2 · n H 2 O. These compounds have been characterized by means of the analytical techniques (elemental analysis and thermogravimetry), spectral methods (IR, 13 C and 1 H NMR, UV-Vis-NIR, EPR) and magnetic measurements (77–290 K). Single-crystal X-ray diffraction studies have been made on the complexes [Co(DLM) 2 (H 2 O) 2 ](NO 3 ) 2 ·2H 2 O, [Cu(DLMD) 2 (H 2 O) 2 ](NO 3 ) 2 ·2H 2 O and [Cd(NO 3 ) 2 (DLMD) 2 ]. Cobalt and copper complexes crystallize in the monoclinic system (space group P 2 1 / n , Z = 2) with a = 8.746(1), b = 13.584(2), c = 10.997(1) A , β = 94.89(1)°, V = 1301.8(3) A 1 , and R = 0.057 for 3787 independent reflections with l >2 σ (1) and 202 parameters (Co/DLM complex) and a = 8.9929(7), b = 1.0574(9), c = 11.9242(7) A , β = 98.124(5)°, V = 1492.3(2) A 1 , and R = 0.039 for 2612 independent reflections with l >2 σ ( l ) and 230 parameters (Cu/DLMD complex). In both complexes, the metal ion occupies an inversion center and exhibits an octahedral coordination. The Co(II) coordination octahedron is tetragonally flattened, but the Cu(II) coordination is rhombically distorted. The equatorial plane consists of two N(5) and two O(4) atoms of pteridine ligands and the two axial sites are occupied by two oxygen atoms from the coordinated water molecules. The monomeric units together with non-coordinated water molecules and nitrate anions are involved in a complex three-dimensional H-bond network. The cadmium complex crystallizes in the monoclinic system (space group P 2 1 / c , Z = 2) with a = 8.5689(4), b = 18.5279(9), c = 8.6209(3) A , β = 106.894(3)°, V = 1309.6(1) A 3 , and R = 0.030 for 1260 independent reflections with l >2 σ ( l ) and 192 parameters. The structure consists of monomeric centrosymmetric units in which the cadmium atom is eight-coordinated by four nitrate oxygen atoms of two bidentate nitrate anions and two N(5)-O(4) lumazine bidentate ligands. The geometry of the coordination polyhedron could be described as an octahedron whose equatorial plane is formed by two bidentate N(5)-O(4) pteridine ligands and whose apical positions each seem to be split into two coordination positions occupied by bidentate nitrate ligands.

Kinetics and mechanism of the oxidation of D-galactono-1,4-lactone by CrVI and CrV

Abstract The oxidation of d -galactono-1,4-lactone by CrVI yields d -lyxonic acid, carbon dioxide and Cr3+ as final products when an excess of sugar acid over CrVI is used. The redox reaction occurs through CrVI → CrIII and CrVI → CrV → CrIII paths. The complete rate law for the CrVI oxidation reaction is expressed by −d [CrVI] \dt = (k0+kH [H+] ) [gal] [CrVI] , where k0 = (31±3) ×10−4 M−1 s−1 and kH = (99±5) ×10−4 M−2 s−1, at 40°C. CrV is formed in a rapid step by reaction of the CO·− 2 radical with CrVI. CrV reacts with the substrate faster than does CrVI. The CrV oxidation follows the rate law : −d [CrV] \dt = ( k ′ 0 +k ′ H [H+] ) [gal] , where k ′ 0 = (15±2) ×10−3 M−1 s−1 and k ′ H = (34±4) ×10−3 M−2 s−1, at 40°C. The EPR spectra show that several intermediate [Cr (O) (gala) 2] − linkage isomers are formed in rapid pre-equilibria before the redox steps.

Crystal structure, raman and 57Fe mo¨ssbauer spectra of the FeII complex of iso-orotic acid

Abstract The crystal structure of [Fe(H 2 isoor) 2 (H 2 O) 2 ]·2H 2 O has been solved by single-crystal X-ray diffractometry. Thermogravimetric analysis shows simultaneous loss of all water molecules between 120 and 266°C, followed immediately by a rapid degradation of the compound. A comparative analysis of the Raman spectra of the complex with that of free-iso-orotic acid allowed a straightforward assignment of the vibrations of the ligand groups involved in coordination. The 57 Fe Mo¨ssbauer spectrum of the complex confirms the presence of a high-spin Fe II ion and the distortion of the octahedral Fe II environment.

Studies on pyrimidine, derivative complexes: spectroscopy, thermal behaviour and crystal structure of μ-dichloro-μ-sulphur-chloro(4,6-diamino-1,2-dihydro-2-thiopyrimidine-N3,S2) cadmium(II) monohydrate

Abstract The crystal structure of Cd(DATP)Cl2·H2O has been determined by X-ray diffraction methods. It crystallizes in the tetragonal space group I41cd with a = 24.296(7), c = 7.108(9) A, V = 4196(4) A3, and Z = 16. The structure has been solved by Patterson and Fourier syntheses and refined by full-matrix least-squares procedure to R = 0.049 for 1688 observed reflections. The crystal does not contain individual Cd(DATP)Cl2·H2O neutral molecules. Cadmium atoms show a coordination number of six. On the basis of the molecular structure of the Cd(DATP)Cl2·H2O complex the most significant IR bands have been assigned in the 4000-600 cm−1 range. Likewise, the v(CdN), v(CdS) and v(CdX) bands were assigned by comparing the IR spectra of the Cd(DATP)Cl2·H2O and Cd(DATP)2Br2 complexes in the 600–180 cm−1 range. Finally, by using an IR technique for the identification of intermediates, a thermal decomposition mechanism for the Cd(DATP)Cl2·H2O complex has been proposed.

Thermal studies on purine complexes. III. Palladium complexes of xanthine and some xanthine derivatives

Abstract Some complexes |PdL 2 Cl 2 | (where L = xanthine, theophylline, theobromine, 3,8-dimethylxanthine, caffeine and 1,3,8-trimethylxanthine) have been prepared in acid medium. Their structure has been established from IR and 1 H-NMR data. The thermal behaviour of these complexes has been studied by TG, DTG and DSC techniques. Heats of dehalogenation have been calculated from the DSC curves.

Palladium, platinum, cadmium, and mercury complexes with neutral isoorotic and 2-thioisoorotic acids: IR and NMR spectroscopies, thermal behavior and biological properties

Seven complexes containing neutral isoorotic and 2-thioisoorotic acids, as well as thiocyanate and chloride anions as lignands, have been synthesized and characterized by means of both spectral (IR, 1H, and 13C NMR) and thermal (TG and DSC) methods, as well as conductivity measurements. Spectral data suggest that any binding metal-ligand mode for uracil derivatives is not easy to propose. Therefore, isoorotic ligands must link through some oxygen atom. Likewise, 2-thioisoorotic acid seems to be [N,S] bonded in Pd(II) and Pt(IV) complexes, whereas for Hg(II) complex a distorted tetrahedral HgCl2S2 structure has been proposed. In the cadmium complex, the metal ion exhibits a CdCl2O2 coordination sphere. Antimicrobial activities of the complexes against Pseudomonas sp, E. coli, Proteus sp, Salmonella sp, Micrococcus sp, Staphylococcus sp, Bacillus sp and Candida sp were performed as a previous step in the study of their biological activity.

Mixed complexes of 5-nitrosouracil derivatives: Synthesis and structural study of 6-amino-1,3-dimethyl-5-nitrosouracilato (N5,N6)-aqua-2,2′-bipyridine (N,N′)-copper(II) perchlorate hydrate and 2,2′-bipyridine (N,N′)-chloro-1,3-dimethylviolurato (N5,O6)-copper(II) hemihydrate

Abstract The mixed [Cu(DANU)(bipy)(H2O)]ClO4·H2O (1) and [Cu(DMV)(ipyl)Cl]·1/2H2O (2) complexes have been isolated from the reaction, in water/EtOH medium, of copper(II) perchlorate and chloride with 6-amino-1,3-dimethyl-5-nitrosouracil (HDANU) and 2,2′-bipyridine (bipy). It is noteworthy that, in the second complex, the uracil ligand is the 1,3-dimethyl-violurato monoanion (DMV), appeared from the hydrolysis of HDANU. In addition to X-ray diffraction studies, these compounds have been characterized from IR and EPR spectra and magnetic measurements (77–290 K). The crystal lattice of 1 is made up of discrete square pyramidal [Cu(DANU)(bipy)(H2O)]+ cations, a disordered perchlorate group and a water molecule. The coordination geometry about the metal centre is square pyramidal (N4+O). The basal positions are occupied by a bidentate DANU ligand, coordinated through the N15 and N16 donor positions, and a bipyridine ligand. A water molecule (CuO1W 2.193(3) A) occupies the apical site. The compound 2 presents a similar molecular structure to that of 1 with the copper centre lying in a N3O+Cl environment. In this case, the basal positions are occupied by a bipy ligand and a DMV ligand coordinated through the N15 and O16 donor positions, instead of the DANU ligand found in the previous compound. The apical position is occupied in this case by a chlorine atom (CulCll 2.413(2) and Cu2C12 2.389(2) A).

Thermal studies on purine complexes. IV. Thermal behaviour of some tetrachloroaurates of xanthine derivatives

Abstract Gold compounds [LH + 2 ][AuCl 4 ] (where LH = theophylline, theobromine, 3,8-dimethylxanthine, caffeine and 1,3,8-trimethylxanthine) were prepared in acid medium, and characterized on the basis of IR, 1 H-NMR and magnetic studies. The thermal behaviour of these salts was studied using TG, DTG and DSC techniques. Heats of dehalogenation were calculated from DSC curves. These heats fluctuate between 81.8 and 184.3 kJ mole −1 .

Thermal studies on purine complexes. I. Thermal behaviour of some xanthine complexes of cobalt(II), copper(II) and cadmium(II)

Abstract Cobalt, copper and cadmium xanthinate tetrahydrates have been prepared in aqueous medium, and characterized on the basis of elemental analysis, IR and 1 HNMR studies. The thermal behaviour of these compounds has been studied using TG, DTG and DSC techniques. Heats of dehydration have been calculated from DSC curves.