Biomedical subjects
Publications and source records attributed to Narcis Avarvari.
A new diazine tetratopic helicand, H4L, is obtained from 3-formylsalicylic acid and hydrazine. The reaction between H4L and cobalt(II) perchlorate, iron(III) perchlorate, and sodium carbonate leads to triple-stranded tetranuclear anionic helicates, [L3Co(II)2Fe(III)2]2-, which are connected through Na ions, resulting in chiral coordination polymers, [L3Na2Fe2Co2(H2O)4(EtOH)2].3H2O.
The coordination ability of the electroactive TTF-based chelating ligand 5,5'-bis(4,5-bis(thiomethyl)-4'-carbamoyltetrathiafulvalene)-2,2'-bipyridine (L) has been tested with Cu(I) and Cu(II) centres. [(L)2Cu(I)](PF6), [(L)2Cu(II)](OTf)2 and [(L)Cu(II)(DMF)3](OTf)2 have been synthesized. A single-crystal X-ray analysis was performed on [(L)Cu(II)(DMF)3](OTf)2, showing a distorted octahedral geometry around the Cu(II) centre, and the formation of dimeric units in the solid state through weak coordination in apical position of an amide oxygen atom from a neighbouring complex. Magnetic data show that the paramagnetic metallic centres are isolated, in agreement with the solid-state structure. Electrochemical measurements were performed on the three complexes and in all cases the Cu(I)/Cu(II) and TTF/TTF+*/TTF2+ redox processes were observed.
Electroactive molecular materials precursors are obtained through coordination chemistry of the hexarhenium cluster core [Re(6)Se(8)](2+) on the six available apical positions with redox-active phosphines bearing tetrathiafulvalene- or ferrocene-based moieties. Single-crystal X-ray diffraction study and electrospray mass spectrometry ascertain the synthesis of these hexasubstituted electroactive clusters, containing up to 12 redox active sites. Cyclic voltammetry experiments demonstrate that these compounds can be reversibly oxidized at rather low potentials, thus allowing an easy access to the corresponding radical species which should provide new conducting and/or magnetic molecular materials.
Nickel dithiolene complexes symmetrically appended with hydrogen-bond donor/acceptor functionalities such as imide, amide, or cyano/amide groups have been synthesized by a straightforward method of wide applicability starting from one single precursor. Single-crystal X-ray structures reveal the occurrence of one type of ribbon common to all compounds that is based on a recurrent self-complementary intermolecular hydrogen-bonded ring motif linking the symmetrically substituted complexes.
A metallic behavior characterizes a first complete series of 2:1 AsF6- mixed-valence chiral salts of (R)-, (S)-, and racemic (+/-)-tetrathiafulvalene methyl-oxazoline derivatives. The enhanced conductivity of the pure enantiomeric salts, when compared with that of the racemic one, is the likely consequence of the structural disorder observed in the latter.
The heteroleptic neutral radical dithiolene complexes CpNi(dmit)., CpNi(dsit). and CpNi(dmid).(dmit=1,3-dithiole-2-thione-4,5-dithiolate; dsit=1,3-dithiole-2-thione-4,5-diselenolate; dmid=1,3-dithiole-2-one-4,5-dithiolate) are obtained from the reaction of (Cp2Ni)BF4 with either (n-Bu4N)[Ni(dmit)2] and (n-Bu4N)[Ni(dmid)2] or PhSb(dmit) and PhSb(dsit), respectively. The three complexes reduce reversibly to the corresponding Ni(II) anions and oxidize reversibly to the cationic state. As deduced from DFT calculations performed on CpNi(dmit)., the SOMO of these complexes is essentially localized on the dithiolene moiety with little metal contribution. CpNi(dsit). is isostructural with CpNi(dmit). and crystallizes in the monoclinic system, space group P2(1). In the solid-state structures of both CpNi(dmit). and CpNi(dsit)., molecules interact through a three-dimensional set of intermolecular interactions mediated by short SS, SeSe and SSe contacts, as confirmed from the temperature and field dependence of the magnetic susceptibility by the observation of an antiferromagnetic ground state below T(Neel)=27 K in CpNi(dmit)., 18 K in CpNi(dsit).. Finally, CpNi(dmid). crystallizes in the orthorhombic system, space group Pnma. Molecules organize into uniform chains through the stacking of the dmid moieties in a sigma-type face-to-face overlap.
Electrospray ionization mass spectrometry was used for the analysis of functionalized rhenium clusters such as [Re6Se8(o-Me2TTFPPh2)6]2+ (1), {Re6Se8[(o-Me2TTF)2PPh]6}2+ (2) and [Re6Se8(MePPh2)6]2+ (3). The high-resolution mass spectra of the intact clusters, performed in dichloromethane, confirm the identification of the compounds by comparison with the theoretical isotopic distributions. Low-resolution full-scan mass spectra recorded at increasing desolvation cone voltage values allow the study of the intrinsic reactivity of ionic species. The survival yield curves illustrating the bimolecular reactivity of 1 and 2 suggest that a bisdimethyltetrathiafulvalene(phenyl)phosphine ligand increases the stability of the functionalized ML6(2+) cluster 2. In the case of the 3, instead of loss of a neutral ligand, ligand exchange is observed either with traces of water present in dichloromethane or with acetonitrile used as solvent.
Electrochemical and theoretical investigations demonstrate through-bond interactions between two TTF moieties fused to a 1,4-dihydro-1,4-diphosphinine, for which the single crystal X-ray structure of the cis isomer is described together with that of a mixed-valent, charge-localized, radical cation salt with Mo6O19(2-), obtained upon electrocrystallization of the same cis isomer.
The solid-state chemistry of a series of seven ortho-bis(alkylamido)ethylenedithiotetrathiafulvalene derivatives EDT-TTF-(CONHR)2 (R=Me, 1; Et, 2; Pr, 3; Bu, 4; Pent, 5; Hex, 6; and Bz, 7), in their neutral and one-electron-oxidized, radical cation states, was investigated with an eye on the topology of intra- and intermolecular hydrogen-bond motifs. In the case of neutral, monomolecular solids, an intramolecular N--H.O hydrogen bond seals a constrained seven-membered ring for 1, 2, 3, and 7, which is disrupted in butyl derivative 4 in favor of an antiparallel ladder at the expense of any intramolecular hydrogen bond. In the solid-state, the competition between intra- and intermolecular hydrogen bonding observed in solution depends on the packing of the molecules. Electrocrystallization of methyl derivative 1 with ReO4- or ClO4-, two anions of different volumes but otherwise identical charge and symmetry, revealed a fine sensitivity of the constrained seven-membered ring to the internal chemical pressure exerted by the anion. [1]2 *+ReO4 (sigmaRT=8.5 S cm(-1), activation energy Delta=600 K at high temperature) and beta"-[1]2 *+ClO4 (sigmaRT=0.03 S cm(-1), Delta=1600 K; under pressure at room temperature, the conductivity increases by three orders of magnitude up to 17 kbar with a linear variation of the activation energy with pressure, Delta=aP with a=0.202 10(6) K kbar(-1)) have vastly different architectures, dimensionalities, electronic structures, and collective properties, a consequence of the presence of the closed or open structural isomers in one or the other. This exemplifies the flexibility of functionalized TTF derivatives, even when the functional group is directly attached to the electro-active core. This allows an analogy to be drawn with tetrafunctionalized metallocenes, in which such flexibility has already been observed. The experimental data are supported by theoretical calculations of the energy profile of a model molecule on rotation of the amido groups.
A novel Cu(II)-Mn(II) hexanuclear complex of formula [[MnCuL](3)(tma)](ClO(4))(3).8H(2)O [H(2)L = macrocyclic Robson proligand; H(3)tma = trimesic acid] has been obtained by connecting three heterobinuclear [Cu(II)Mn(II)L](2+) cationic species through the trimesate anion. The complex exhibits a C(3) rotational symmetry, imposed by the geometry of the bridging ligand. The interaction within each Mn(II)-Cu(II) pair is antiferromagnetic (J = -16.7 cm(-1)). A weak ferromagnetic coupling among the three S = 2 resulting spins through the tricarboxylato bridge leads to a S = 6 ground spin state, for which the spin polarization mechanism is responsible.
Amidopyridine and -2,2'-bipyridine derivatives of EDT-TTF and BTM-TTF (EDT=ethylenedithio, BTM=bis(thiomethyl), TTF=tetrathiafulvalene) have been synthesized and crystallographically characterized. In the solid state, the different supramolecular organization of all these donors results from the competition between the intermolecular interactions, that is, van der Waals, hydrogen-bonding, pi-pi stacking, and donor-acceptor interactions. The electron-donating properties of the new donors have been investigated by cyclic voltammetry measurements. A radical cation salt, formulated [EDT-TTF-CONH-m-Py](.) (+)[PF(6)](-), has been prepared by electrocrystallization and its crystal structure determined by X-ray analysis. Square planar dicationic complexes with the same donor and M(II)L(2) fragments (M=Pd, Pt, L(2)=bis(diphenylphosphino)propane (dppp) or bis(diphenylphosphino)ethane (dppe)) have been synthesized and one of them, containing the Pd(dppp) unit, has been structurally characterized. The conformation of the complex in the crystalline state is anti, with the coexistence of the dl racemic pair of enantiomers.
The redox active ligand EDT-TTF-CONH-3-pyridine undergoes a [2 + 2] cycloaddition upon irradiation with polychromatic light, an unprecedented single-crystal-to-single-crystal transformation for a TTF derivative.
Attempted thallium triflate abstraction of chloride anions from the MCl(2) complexes of the unsaturated chelating diphosphines o-dimethyl-bis(diphenylphosphino)tetrathiafulvalene (P2) (M = Pd, Pt) and cis-1,2-bis(diphenylphosphino)ethylene (dppen) (M = Pd) affords, surprisingly, a Tl(OTf) adduct in the case of (P2)PdCl(2) and (P2)PtCl(2), with no chloride abstraction, and a dicationic bis(palladium) bis(triflate) salt in the case of (cis-dppen)PdCl(2), in which only one Cl anion was removed. The crystal structures of these complexes were determined by X-ray analysis, which established the formulations (P2)MCl(2).Tl(OTf) (M = Pd, Pt) and [(dppen)PdCl](2)(OTf)(2), respectively. These compounds can be seen as possible intermediates in the general chloride abstraction process between (P-P)MCl(2) (M = Pd, Pt) and thallium triflate.
Reaction of the lithium salt of EDT-TTF-2-(4-methyl)oxazoline with chloro-diphenylphosphine afforded the novel redox active chiral chelating ligands, EDT-TTF-phosphino-oxazolines, for which a palladium (II) dichloride complex was synthesized and structurally characterized.
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The deliberate design of a series of single crystals of conducting two-dimensional radical cation salts of o-bis(amide)-appended ethylenedithiotetrathiafulvalene, beta'-[EDT-TTF-(CONH(2))(2)](2)X (X = HSO(4)(-), ClO(4)(-), ReO(4)(-), or AsF(6)(-)) and of their parent monocomponent solid EDT-TTF-(CONH(2))(2) is demonstrated and allows us to reach a level of prediction of the structure of molecular conductors. Their conductivity is activated with a gap of 1650 K and a sizable room-temperature conductivity of 0.15 S.cm(-)(1) (for X = ClO(4)(-)) and a singular spin susceptibility for a beta'-type salt that, in addition, changes very remarkably with the anion. The key design element is that of a recurrent, puckered ribbon constructed out of self-complementary, hydrogen-bonded amide...amide ring motifs whose minute modulations of curvature and shape throughout the series have been shown to correlate to very remarkable differences in the intrastack beta(HOMO)(-)(HOMO) interaction energies and changes in the density of states at the Fermi level and on to important differences of spin susceptibility behavior in a system where electron correlations are significant. The coupled activation of structure, electron interactions, and magnetic susceptibility discovered and discussed throughout the paper is unprecedented and is seen as a genuine expression of interfacial hydrogen-bond interactions onto the collective electronic properties.
Geometries, aromatic character, Mulliken charge distribution, and MO diagrams of 1,2-aza-, 1,3,2-diaza-, 1,3-aza-, and 1,3,5-diazaphosphinines have been calculated and compared to those of phosphinine and pyridine. This study reveals that the introduction of nitrogen atoms at the position adjacent to phosphorus significantly reduces the aromatic delocalization and induces a [1,4] dipolar character through an increase of the positive charge on the P atom. This phenomenon does not occur in 1,3-aza- and 1,3,5-diazaphosphinines, which exhibit a poor dipolar character. This comparison confirms the high reactivity of 1,3,2-diazaphosphinines toward alkynes. A [4 + 2] cycloaddition reaction between these two types of diazaphosphinines and acetylene has been modelized. Calculated geometries of the resultant [4 + 2] diazabarrelene cycloadducts and that of their respective transition states reveal that, especially with 1,3,2-diaza isomers, the cycloaddition proceeds via a disymmetrical pathway that involves the preliminary formation of the P-C bond.