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Featured researches published by D. A. Clemente.


Inorganica Chimica Acta | 1985

Interaction of metal ions with humic-like models. Part 5. The crystal and molecular structure of diaquabis(2,6-dihydroxybenzoato)-dioxouranium(VI) octahydrate ☆

Giovanni Micera; L.Strinna Erre; Franco Cariati; D. A. Clemente; Armando Marzotto; M. Biagini Cingi

Abstract The crystal and molecular structure of the complex [UO 2 (DHB) 2 (H 2 O) 2 ]·8H 2 O (DHB = 2,6-di- hydroxybenzoato) has been determined from single- crystal X-ray analysis and refined to a final R value of 0.033 for 3620 observed reflections. The complex crystallizes in the monoclinic system, space group C 2/ m , with a = 6.704(3), b = 20.171(6), c = 9.454(4) A and Z = 2. The coordination about the uranyl group, which is linear, involves two bidentate carboxylate groups and two water molecules in trans positions giving rise to an irregular hexagonal bipyramid. Intra- molecular hydrogen bonds between phenolic and carboxylate groups forming six-membered rings allow the molecule to be nearly planar. Spectroscopic (IR, NMR and electronic absorption) data and thermal properties of the compound are also reported.


Molecular Crystals and Liquid Crystals | 1983

Crystal Structure of Biphenyl-1,2,4,5-Tetracyanobenzene 1:1 CT Complex and EPR Investigation of Photoexcited Triplet Excitons

Luigi Pasimeni; Graziano Guella; Carlo Corvaja; D. A. Clemente; Marco Vicentini

Abstract The crystal structure of biphenyl and 1,2,4,5-tetracyanobenzene 1:1 charge transfer complex has been determined at room temperature. The crystals belong to the triclinic system with space group CI, a = 9.592(6) A, b = 12.359(9) A, c = 7.335(5) A, α = 94.17(6)°, β = 96.50(8)° and γ = 89.07(7)° with two complexes per unit cell. The increase of the zero-field splitting tensor of photoexcited triplet excitons with increasing temperature has been discussed in terms of two early proposed models. In the former approach a thermal equilibrium between two triplet states was assumed. In the second the variation of the fine structure tensor elements was attributed to changes of the charge transfer character of the triplet state as a consequence of the temperature dependent molecular packing in the crystal. Experimental evidences are in favor of this latter model.


Inorganica Chimica Acta | 1981

Crystal structure of 2:1 molecular complexes of caffeine with hexaaquamagnesium(II) bromide and hexaaquamanganese(II) triiodide iodide

Marina Biagini Cingi; Anna Maria Manotti Lanfredi; Antonio Tiripicchio; Giuliano Bandoli; D. A. Clemente

Abstract The crystal structures of (C 8 H 10 N 4 O 2 ) 2 Mg(OH 2 ) 6 Br 2 (I) and (C 8 H 10 N 4 O 2 ) 2 Mn(OH 2 ) 6 I·I 3 (II) have been determined by X-ray diffraction methods; crystals of I are triclinic, space group P 1 , with Z = 1, in a unit cell of dimensions: a = 9.620(7), b = 10.779(8), c = 7.645(6) A , α = 107.03(7), β = 108.88(7), γ = 72.71(8)°; crystals of II are monoclinic, space group P 2 1 /n, with Z = 4, in a unit cell of dimensions a = 12.406(8), b = 29.652(12), c = 9.419(6) A , β = 108.39(7)°. The structures of I and II have been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.046 for I and 0.090 for II. Both compounds contain octahedral hexaaquametal(II) cations, uncoordinated caffeine molecules and bromide anions in I and triiodide and iodide anions in II, held together by a network of hydrogen bonds. The triiodide anions are unsymmetrical [I(1)I(2) = 2.89, I(2)I(3) = 2.95 A , I(1)I(2)I(3) = 178°], arranged in linear systems with a weak ‘head-to-tail’ interaction, the distance being of 3.62 A .


Inorganica Chimica Acta | 1985

Interaction of metal ions with humic-like models. Part 6. Molecular structure, spectral and thermal properties of diaquabis(2,6-dimethoxybenzoato)dioxouranium(VI) monohydrate

Giovanni Micera; L.Strinna Erre; Franco Cariati; D. A. Clemente; Armando Marzotto; Giovanni Valle

The crystal and molecular structure of [UO 2 (DMB) 2 (H 2 O) 2 ]·H 2 O (DMB = 2,6-dimethoxybenzoate), complex I , has been detcrmined by X-ray diffraction and refined to a final R value of 0.0411. The compound belongs to the space group P 2 1 / a with cell constants a = 12.649(4), b = 14.418(5), c = 13.460(4) A and Z = 4. As in the analogous complex [UO 2 (DHB) 2 (H 2 O) 2 ]·8H 2 O (DHB = 2,6- dihydroxybenzoate), compound II , the uranyl ion is bound to two bidentate carboxylate groups and two water molecules, but the point-symmetry is lower because the carboxylates, and the water molecules, are in vicinal positions. The lack of hydrogen- bonds between carboxylate groups and ortho -methoxy substituents and, possibly, steric factors account for the rotation of the phenyl rings with respect to the equatorial plane of the metal, the dihedral angle between the ‘best planes’ being about 77°. Detectable changes in the bond distances and angles within the carboxylate groups are produced by the non-planarity of the ligand. Spectroscopic and thermal properties of complexes I and II are also compared.


Acta Crystallographica Section C-crystal Structure Communications | 1997

Piperazine (and derivatives) platinum(II) complexes : Trans-bis(N-methylpiperazine-N,N')platinum(II) dichloride tetrahydrate

Armando Marzotto; D. A. Clemente; Giovanni Valle

The title compound, trans-[L 2 Pt II ] 2+ .2Cl - .4H 2 O, (L = N-methylpiperazine), [Pt(C 5 H 12 N 2 ) 2 ]Cl 2 .4H 2 O, has been synthesized in the course of our work on complexes formed by the Pt 2+ ion with piperazine derivatives. X-ray diffraction analysis showed that two N-methylpiperazine molecules bind one Pt 2+ ion in such a way that the two methyl groups lie in opposite directions with respect to the Pt atom. The coordination around the Pt atom is square planar with four N atoms occupying the coordination sites, and the coordination plane is perfectly planar because the Pt atom lies on a centre of symmetry. This type of coordination imposes a boat conformation on the six-membered N-methylpiperazine ring. As found in other N-methylpiperazine complexes, the molecule has a local mirror plane coincident with the square-planar coordination plane and nearly bisecting the piperazine six-membered ring.


Acta Crystallographica Section C-crystal Structure Communications | 1993

Structure of aquachloro[tris(2-aminoethyl)amine]nickel(II) chloride monohydrate

Armando Marzotto; D. A. Clemente; Giovanni Valle

[Ni(C 6 H 18 N 4 )(H 2 O)Cl]Cl.H 2 O, M r = 311.88, monoclinic, P2 1 /a, a=14. 117 (2), b=11.040 (2), c=8.828 (1) A, β=106.8 (2) o , V=1317 (1) A 3 , Z=4, D x =1.57 Mg m -3 , λ(Mo Kα)=0.7107 A, μ=1.879 mm -1 , F(000)=656, T=293 K, R=0.030 for 2756 independent reflections [Fu >3σ(F o )]. The Ni atom is octahedrally surrounded by the four N atoms of the tren [tris(2-aminoethyl)amine] ligand, N(CH 2 CH 2 NH 2 ) 3 , one chloride ion and one water molecule. The second chloride ion and the second water molecule are not bound to Ni II and contribute only to the crystal packing stabilization


Molecular Crystals and Liquid Crystals | 1984

Crystal Structure of Diphenylacetylene-Tetracyanobenzene 1:1 CT Complex and Spin Polarization of Triplet Exciton and of Trans-Stilbene Triplet Trap

Luigi Pasimeni; Carlo Corvaja; D. A. Clemente

Abstract The crystal structure of diphenylacetylene and 1, 2, 4, 5-tetracyanobenzene 1:1 charge transfer complex has been determined at room temperature. pe crystals belong to the monoclinic system with space group C2/m, a = 9.632(4) A, b = 12.403(6) A, c = 8.131(4) A, β = 101.59(4)° with two translationally equivalent complexes per unit cell. EPR spectra of photoexcited mobile and trapped triplet species were recorded. The nature of the trap has been investigated and attributed to the trans-Stilbene-TCNB 1:2 CT complex. The analysis of the orientation dependence of polarized spectra of exciton and trap has shown that spin polarization is provided by ISC in which the TCNB is involved. Excitation transfer to the trap takes place by preseming alignment of the spin states.


Journal of Applied Crystallography | 1980

Program for crystal setting and data reduction on a PW 1100 diffractometer using a simple method based on real space

M. Biagini Cingi; Giuliano Bandoli; D. A. Clemente; Antonio Tiripicchio

A simple method, based on real space, is described to calculate on a PW 1100 diffractometer D and RD vectors for anisotropic extinction corrections. and for every 0 (0 = rotation around the reciprocal vector). This problem has already been solved for other diffractometers in reciprocal space (Coppens, Leiserowitz & Rabinovich, 1965; Coppens, 1970) and has been re-examined for the PW 1100, using a simple procedure in real space.


Acta Crystallographica Section C-crystal Structure Communications | 1999

Cobalt(II) complexes of piperazine and derivatives: 1-methylpiperazin-4-ium trichloro(1-methylpiperazine-N4)cobaltate(II)

Armando Marzotto; D. A. Clemente; Giovanni Valle

The title compound, (C 5 H 13 N 2 )[CoCl 3 (C 5 H 12 N 2 )], contains a Co II ion coordinated to three Cl atoms and to the unmethylated N atom of N-methylpiperazine in a distorted tetrahedral geometry. The six-membered ring of both the coordinated and free N-methylpiperazine molecules possesses the more stable chair conformation. In addition, other tautomeric forms may be present in small amounts in the crystals.


Acta Crystallographica Section C-crystal Structure Communications | 1998

Platinum(II) Complexes of Piperazine (and Derivatives): trans-Dichlorobis(N-methylpiperazine-N')platinum(II)

Armando Marzotto; D. A. Clemente; Giovanni Valle

The neutral title complex, trans-[PtCl2(C5H12N2)2], has been synthesized in the course of our studies on piperazine derivative complexes with platinum(II). This complex is square-planar and isomorphous with the analogous palladium(II) complex, and exhibits the same molecular, but not crystallographic, structure as trans-[PtCl2(C5H13N2)2]Cl2.2H2O, [(C5H13N2) is N-methylpiperazinium(+1)]. The six-membered ring is in the chair conformation and binds platinum(II) through the unmethylated N1—H nitrogen, which is sterically less hindered than the methylated one. The molecule has a local pseudo-mirror plane nearly coincident with the square-planar coordination plane and nearly bisecting the piperazine ring.

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