José-Vicente Folgado

Synthesis and structural, spectroscopic and magnetic characterization of iron(II) and iron(III) complexes of N-2-pyridinylcarbonyl-2-pyridinecarboximidate

Abstract One iron(II) complex of N -2-pyridinylcarbonyl-2-pyridinecarboximidate monoanion (bpca), [Fe(bpca) 2 ]·H 2 O ( 1 ), and three iron(III) complexes, [Fe(bpca)Cl 2 (H 2 O)]·(CH 3 ) 2 CO ( 2 ), [Fe(bpca) 2 ](NO 3 )·1.67H 2 O ( 3 ), [Fe(bpca) 2 ](ClO 4 ) ( 4 ), have been prepared and characterized by means of IR, UV-Vis and EPR spectroscopy and magnetic susceptibility measurements, where appropriate. The crystal structures of 1 – 3 have been determined from single crystal X-ray data, showing that the metallic ions are surrounded in all cases by distorted octahedral coordination spheres. From magnetic measurements it is evident that compounds 1 and 3 are practically in the low-spin state at room temperature, compound 2 is in the high-spin state in all the range of measured temperatures and compound 4 shows spin-crossover behaviour. Crystal data for 1 : space group P 2 1 / c , a =8.827(1), b =8.941(2), c =28.957(4) A, β=95.90(1)°, Z =4; for 2 : space group P 2 1 / c , a =8.293(2), b =13.779(2), c =15.884(4) A, β=98.22(1)°, Z =4; for 3 : space group P 1 , a =8.840(1), b =10.713(1), c =14.989(1) A, α=71.16(1), β=73.43(1), γ=82.67(1)°, Z =2.

Crystal and molecular structure and electronic properties of [Cu(bbimpy)(H2O)2(ONO2)](NO3)· H2O (bbimpy = 2,6-bis(2-benzimidazolyl)pyridine)

Abstract The crystal structure of the complex [Cu(bbimpy)(H2O)2(ONO2)](NO3)·H2O(bbimpy = 2,6-bis(2-benzimidazolyl)pyridine) has been determined by X-ray diffraction methods. It crystallises in the monoclinic space group P2 1 n , with Z = 4 in a cell of dimensions a = 13.350(1), b = 7.820(1), c = 21.484(1) A , β = 92.26(1)° . The structure is built up of [Cu(bbimpy)(H2O)2(ONO2)]+ cations, NO3− anions and crystal lattice water molecules, with a 4 + 1 + 1 pseudo-octahedral geometry for the CuN3OO′O″ chromophores. In the EPR spectrum exchange coupling between Cu(II) chromophores of different orientation is observed, and molecular g values, compatible with the crystallographic data, could be calculated.

Spectroscopic studies and crystal structure of bis(N-2-pyridinylcarbonyl-2-pyridinecarboximidato) manganese(II) monohydrate: Zero-field splitting param

Abstract The X-ray crystal structure of bis(N-2-pyridinylcarbonyl-2-pyridinecarboximidato)manganese(II) monohydrate, Mn(BPCA)2·H2O, has been determine

Crystal structure, magnetic and spectroscopic properties of the bis(dimethyl sulfoxide) adduct of tetra-μ-formato-dicopper(II), a new tetracarboxylato-bridged copper(II) dimer

Abstract The crystal and molecular structure of a new tetracarboxylato-bridged copper(II) dimer, the bis(dimethyl sulfoxide)tetrakis(μ-formato)dicopper(II) has been determined by X-ray diffraction methods. It crystatlizes in the tetragonal space group I41/a, with Z=8 in a cell of dimensions a=17.688(2), c=10.408(1) A. The structure is built up of centrosymmetric neutral dimers [Cu2(HCOO)4(dmso)2], where four bidentate carboxylate anions form syn-syn bridges between the metal atoms which are in a 4 + 1 environment. Magnetic susceptibility data show that the copper atoms are strongly antiferromagnetically coupled with J=−434 cm−1. The obtained triplet-singlet energy gap is compared with those reported for a series of related dimers. Finally, the ESR spectrum shows characteristic features of a triplet state with a non-negligible zero field splitting, being typical of the copper(II) dimeric tetracarboxylates.

Low-temperature synthesis, structure and magnetoresistance ofsubmicrometric La1-xKxMnO3+δperovskites

The use of a precursor-based synthetic method, namely, the freeze-drying of acetic acid solutions, allows the preparation, at temperatures as low as 600 °C, of single phase perovskites in the solid solution series La 1-x K x MnO 3+δ . This soft treatment of the precursors yields products constituted of homogeneous nanometric particles (30–50 nm). Samples prepared at 1000 °C remain single phase forx=0.00, 0.05, 0.10 and 0.15, and are constituted by submicrometer homogeneous particles, without deviation from nominal stoichiometries upon heating. Their crystal structures were refined by the Rietveld method from X-ray powder diffraction data. Ac susceptibility, magnetization, resistivity and magnetoresistivity measurements have allowed us to establish, for the first time, relevant points of the electronic phase diagram of an alkali-metal-doped lanthanide manganate system.

X-ray crystal structure and electronic properties of chlorobis(mepirizole)copper(II) tetrafluoroborate (mepirizole = 4-methoxy-2-(5-methoxy-3-methyl-1H-pyrazol-1-yl)-6-methylpyrimidine)

Abstract The crystal structure of [Cu(mep)2Cl](BF4)[mep = 4-methoxy-2-(5-methoxy-3-methyl-1H-pyrazol-1-yl)-6-methylpyrimidine] has been determined by X-ray diffraction. The crystal structure is built up of [Cu(mep)2Cl]+ cations and BF4− anions. The structure of the cation involves a five-coordinated CuN4Cl chromophore, with a stereochemistry near to a compressed trigonal bypyramid (TBP) but with a significant degree of distortion towards the square pyramidal (SP) topology. The EPR spectrum is indicative of a mixed dz2/dx2 − y2 ground state for the copper(II) ions, in agreement with the structural data.

ESR study of thianthrenium radical cation within acid zeolites

Abstract Thianthrene (E ox = 1.47 V vs NHE) has been adsorbed into a series of zeolites beta (s) and ZSM-5 in the NH 4 + or H + forms, having different particle size and Si/Al ratio. The resulting population of generated thianthrenium radical cation was determined by a combination of diffuse reflectance and ESR spectroscopies. From the results obtained it can be concluded: i) the process takes predominantly place in the interior of the voids (XPS measurements and lack of influence of the particle size); ii) ZSM-5 is more efficient than zeolite s; iii) no strong acid sites are required (both NH 4 + and H + forms produced very similar spin concentrations); iv) the zeolite framework acts isolating the organic spins, thus avoiding diamagnetic coupling (zeolite samples do obey Curie law); and v) the population of oxidizing sites increases with the aluminum content of the zeolite.

Exchange interactions through hydrogen-bond bridges. Crystal structure, spectroscopic characterisation and magnetic properties of the complex [{Cu(en)}2(μ-egta)]·4H2O (H4egta = 3,12-bis(carboxymethyl)-6,9-dioxa-3,12-diazatetradecanedionic acid)

Abstract The structure and spectroscopic and magnetic properties of [{Cu(en)} 2 (μ-egta)]·4H 2 O (H 4 egta = 3,12-bis(carboxymethyl)-6–9-dio 3,12-diazatetradecanedioic acid) are described. The compound is built of centrosymmetric neutral dimeric {[Cu(en)} 2 (μ-egta)] entities linked through hydrogen bonds involving water molecules. -NH 2 groups and -CO 2 groups, affording a three-dimensional framework. The egta anion displays an opened-up structure acting as a bridging ligand between two copper atoms. The coordination geometry about the metal atoms can be viewed as 4 + 1 + 1 (CuN 3 OO′O″ chromophores). The EPR spectra are indicative of an essentially d v−v ground state for the copper(II) ions. Magnetic susceptibility measurements in the range 1.8–200 K show weak antiferromagnetic exchange interactions (2 J ≡ = 1.51(1) cm −1 . The observed behaviour is discussed based on the crystal structure and compared with that observed in the related compound {(Cu(H 2 O)} 2 (μ-egta)]·2H 2 O. From this study, the triatomic NH…O bridges between the dimeric [{Cu(en)} 2 (μ-egta)] units are thought to be the suitable pathway for the exchange interaction.

Stereochemistry of [Cu(Tridentate Ligand)2] entities. crystal and molecular structure and electronic properties of [Cu(tedpa)2](PF6)2 (tedpa = N,N,N′N′-tetraethyl pyridinedicarboxamide)

Abstract The crystal and molecular structure of [Cu(tedpa) 2 ](PF 6 ) 2 have been determined by X-ray diffraction methods. The compound is built up of cationic [Cu(tedpa) 2 ] 2+ and PF 6 groups. The coordination geometry about the copper atom can be described as an elongated and strongly distorted octahedron (CuN 2 O 3 O′ chromophore). The EPR powder spectrum is slightly orthorhombic and from the g values and the partially resolved hyperfine components some covalency and molecular parameters have been estimated. EPR single crystal experiments indicate that the g -tensor axes follow the molecular bonds. Copyright

Crystal and molecular structure and electronic properties of [Cu(HBIP) (BIP) (ONO2)] (HBIP = 3,3-bis(2-imidazolyl)propionic acid)

Abstract The crystal and molecular structure of the complex [Cu(HBIP) (BIP)ONO2] (HBIP = 3,3-bis(2-imidazolyl)propionic acid) has been determined by X-ray methods. It crystallises in the monoclinic space group C2/c, Z=4, a=11.350(2), b=13.156(2), c=14.225(2) A , s=95.36(2)°, V=2114.8(6) A 3 . The CuN4O chromophore could be considered as an intermediate between the trigonal bipyramid (TBP) and square pyramid (SP). Neighbouring molecules of the complex are bound by very strong hydrogen bonds, as short as 2.478 A, between COO− and COOH groups. Electronic and EPR spectra are consistent with the crystallographic data.