F. Cariati

Interaction of metal ions with humic-like models. Part. I. Synthesis, spectroscopic and structural properties of diaquabis(2,6-dihydroxybenzoato) copper(II) and hexaaquaM(II) bis(2,6-dihydroxybenzoate) dihydrate (M = Mn, Fe, Co, Ni, Cu and Zn)

Abstract Compounds of the type M(2,6-DHB) 2 ·8H 2 O (M = Mn, Fe, Co, Ni, and Zn; 2,6-DHB = 2,6-dihydroxybenzoate ion) and Cu(2,6-DHB) 2 (H 2 O) 2 were prepared and characterized by means of infrared and electronic spectroscopy, electron spin resonance and thermal analysis. For Cu(2,6-DHB) 2 (H 2 O) 2 ( 1 ) and Zn(2,6-DHB) 2 ·8H 2 O ( 2 ) the crystal structure was also determined by single-crystal X-ray diffraction methods. The compound ( 1 ) has a polymeric nature, the coordination around each copper atom being tetragonally-distorted octahedral, with two water oxygens [Cuue5f8O, 1.966(3) A] and two carboxyl oxygens [Cuue5f8O, 1.935(2) A] from 2,6-DHB molecules about the square plane and two phenolic groups from adjacent units in the axial positions. The structure of ( 2 ) consists of almost regular octahedral [Zn(H 2 O) 6 ] 2+ cations surrounded by 2,6-DHB anions. The remaining two water molecules are involved in hydrogen bonding with the coordinated water molecules. X-ray data show that all the M(2,6-DHB) 2 ·8H 2 O are isomorphous with ( 2 ). The thermal, spectroscopic and magnetic properties are interpreted on the basis of the crystal structures. In particular, the ESR and absorption data of the copper(II) compounds are compared with those of the salicylate complexes.

Mixed-valence effects in tellurium-molybdenum oxides

Abstract Powdered samples of α-Te2MoO7, TeMo5O16, α-TeO2 and MoO3 were studied by various spectroscopic techniques (XPS, IR, Raman, diffuse reflectance). Observed Mo(3d 1 2 –3d 5 2 and Te(3d 3 2 –3d 5 2 binding energies, combined with bond-strength bond-length calculations, indicate the presence of Te(IV) in both α-Te2MoO7 and TeMo5O16. In the latter compound some Mo(VI) valencies are trapped in specific cation sites whereas at other sites considerable Mo(V)-Mo(VI) mixing occurs; Mo(IV) contributions are ruled out. The class II mixed valence system TeMO5O16 is formally best described as TeO2·3MoO3·Mo2O5. Assignments of skeletal modes are suggested for MoO3, α-MoO3·H2O, α-Te2MoO7 and TeMo5O16.

Bis(triphenylphosphine)pyridine- and pyrazine-carboxylatecopper(I) complexes

Abstract Several complexes obtained by the reactions of tetrahydroboratebis(triphenylphosphine)copper(I) with pyridine(py)- and pyrazine(pyz)-carboxylic acids have been obtained and characterized by infrared spectra. Crystal structures of the L 2 Cu(3-py(CO 2 )) and the L 2 Cu(2,3-py(CO 2 )(COOH)) (L = triphenylphosphine) complexes have been determined. The L 2 CU(3-py(CO 2 )) complex has a polymeric structure in which each copper(I) atom is tetrahedrally coordinated to two molecules of triphenylphosphine and two nicotinate anions, one of which is bonded through the nitrogen atom and the other through the carboxylate group. The L 2 Cu(2,3-py(CO 2 )(COOH)) complex consists of tetrahedral monomeric units, in which the anion is coordinated through the nitrogen atom and unidentate ortho carboxylate group. The structures of the other complexes are proposed on the basis of their analytical and infrared data.

SPECTROSCOPIC ANALYSIS OF MIXED VALENCE MOLYBDENUM OXIDES

Abstract The cation valence state distribution in the higher molybdenum oxides Mo 18 O 52 , Mo 5 O 14 , Mo 17 O 47 and Mo 4 O 11 has been studied by means of XPS spectroscopy in combination with bond-length:bond-strength relationships. Tetrahedral oxomolybdenum positions are occupied by Mo(IV), but considerable Mo(V)ue5f8Mo(VI) mixing is found in the other polyhedra (octahedra and pentagonal bipyramids), as also suggested by the observed Mo(3d) binding energies. Assignments of skeletal modes for these class II mixed valence systems are suggested.

XPS photoelectron spectra of cluster compounds of gold

Abstract The XPS photoelectron spectra of mononuclear and polynuclear gold compounds of general formula AunLmXp (L = unsubstitured and para-substitutedtriphenylphosphine, X = anionic ligand) have been measured. The interpretation of the photoelectron data gives structural information on some clusters of unknown structure and also information on bonding properties in polynuclear gold compounds.

Magnetic investigations on some copper(II) N-acetyl- and N-benzoyl-alaninates

Abstract The magnetic properties of Cu(Ac-α-ala) 2 ·H 2 O, Cu(Bz-α-ala) 2 ·H 2 O and Cu(Bz-β-ala) 2 (Ac-α-ala = N-acetyl-DL-alaninate, Bz-α-ala = N-benzoyl-DL-alaninate, Bz-β-ala = N-benzoyl-β-alaninate ion) have been investigated by means of variable-temperature magnetic and ESR measurements. The magnetic behaviour of the compounds suggests binuclear structures with exchange integrals typical of copper acetate monohydrate-like complexes. Low-temperature ESR spectra of the powdered samples show triplet absorptions characteristic of axially symmetric (Cu(Ac-α-ala) 2 ·H 2 O and Cu(Bz-α-ala 2 ·H 2 O) or rhombically distorted (Cu(Bz-β-ala) 2 ) copper(II) carboxylate dimers. A polymeric structure is proposed for Cu(Bz-β-ala) 2 due to the detection of interdimer exchange between triplet states.

Spectroscopic investigation on the presence of OH in natural barrerite and in its collapsed phases

Barrerite, a zeolite with a stilbite-type framework, transforms on heating at 200–380° C and at 380–450° C into two new phases, called barrerite B and D respectively. After a few days barrerite B rehydrates to barrerite C. In the B and C heat-collapsed phases the aluminosilicate framework is interrupted by the statistical breaking of an oxygen bridge, giving rise to two partially occupied face-sharing tetrahedra. Near infrared (NIR) diffuse reflectance spectra show the absence of hydroxyls in natural barrerite and the presence of hydroxyls in its heat-collapsed phases. These results confirm the hypothesis that the fourth vertex of the tetrahedra generated from the breaking of the oxygen bridge is a hydroxyl. The presence of OH-bands in phase D suggests for this phase, as in the B and C phases, the presence of interrupted oxygen bridges.

Preparation, crystal structure and vibrational spectra of N-benzylpiperaziniumpentahalodimercury(II) complexes: (NbzpipzH)Hg2X5 (X = Cl, Br)

Abstract The preparation of new mercury(II) compounds, (NbzpipzH)Hg 2 X 5 (NbzpipzH = N-benzylpiperazinium monocation; X = Cl, Br) is reported. The determination of the structure of (NbzpipzH)Hg 2 Cl 5 by three-dimensional single-crystal X-ray analysis is described. The structure contains two different mercury atoms. One of them binds covalently two chlorine atoms and two bridged chlorine atoms with long contacts. The coordination around the other mercury is tetrahedrically distorted and involves one terminal and two bridged chlorine atoms and one molecule of N-benzylpiperazinium monocation. Far-infrared and Raman spectra are interpreted on the grounds of the crystal structure of compounds suggesting a relation between the values of a mercuryue5f8halogen stretching frequencies and the related bond distances.

Dehydration and re-hydration of the zeolites with 4-4-1 SBU's: near i.r. evidence for topological changes in heulandite I

Abstract Near infrared ( N i.r.) diffuse reflectance spectra show the absence of hydroxyls in natural heulandite and the presence of hydroxyls in its heat-collapsed phases B and I. These results, compared with analogous ones of barrerite and stellerite, indicated the impossibility for a framework, which has been interrupted by heat-induced dehydration, to re-form by rehydration the original topology of the natural phase. In general, there was a direct correlation between the amount of new T-O-T bridges and the mobility of the new framework.

Interaction of metal ions with humic-like models. Part 2. Thermal properties of hexaaquametal(II) bis(2,6-dihydroxybenzoate) dihydrate complexes

Abstract Compounds of formula M(2,6-DHB) 2 ·8 H 2 O [M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and 2,6-DHB = 2,6-dihydroxybenzoate anion), whose structure consists of hexaaquametal(II) cations and uncoordinated 2,6-DHB molecules, have been investigated by means of thermogravimetric (TG) analysis, differential scanning calorimetry (DSC), diffuse reflectance, and electron spin resonance (ESR). On heating, the outer-sphere arrangement is destroyed and M(2,6-DHB) 2 complexes are formed, those of Ni, Co and Cu exhibiting hexacoordination at the metal ions. It is shown that the first decomposition step of the anhydrous complexes involves the release of 2,6-dihydroxybenzoic acid and solid-state deprotonation of phenolic groups of the remaining DHB molecules to give, in certain cases, well-defined 1:1 M/L complexes [L = C 6 H 3 (OH)(O − )COO − ].