Paolo Dapporto

Manganese(iii) Formate: A Three-Dimensional Framework That Traps Carbon Dioxide Molecules**

Carbon dioxide, formic acid, and water molecules are trapped in the crystal lattice of manganese(III) formate (see 1), which was obtained by reducing permanganate with formic acid. Each CO2 guest molecule exhibits four C-H⋅⋅⋅O-C-O interactions with the three-dimensional host framework of Mn(HCOO)3 units. Compound 1 undergoes an antiferromagnetic phase transition at 27 K.

Selective recognition of carboxylate anions by polyammonium receptors in aqueous solution. Criteria for selectivity in molecular recognition

The interaction in aqueous solution of the polyammonium receptor 1,4,7,10,13,16,19-heptaazacyclohenicosane (8, [21]aneN7) with the carboxylic species, 1,2-benzenedicarboxylic (1), 1,3-benzenedicarboxylic (2), 1,2,3-benzenetricarboxylic (3), 1,3,5-benzenetricarboxylic (4), cis,cis-1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic (5), cis,trans-1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic (6), and citric (7) acids has been followed by potentiometry and cyclic voltammetry at 298.1 K in 0.15 mol dm–3 NaClO4, as well as by NMR spectroscopy. The analysis of the potentiometric and electrochemical data show the formation of 1:1 adducts. A novel method based on both potentiometry and cyclic voltammetry to establish selectivity patterns in systems presenting different protonation possibilities is introduced. Preorganization of the substrates in a shape complementary to the receptor yields interesting features such as the selective recognition of 5 over its epimer 6 and recognition of the dicarboxylic species 1 and 2 over the tricarboxylic ones 6 and 7.

Study of the Thermal Properties of Pr(III) Precursors and Their Implementation in the MOCVD Growth of Praseodymium Oxide Films

A praseodymium adduct, Pr(hfa) 3 .diglyme [(H-hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentandione, diglyme = CH 3 O(CH 2 CH 2 O) 2 CH 3 )] has been synthesized. It has been applied as a Pr source for the metallorganic chemical vapor deposition (MOCVD) of praseodymium containing films on silicon substrate and compared with Pr(tmhd) 3 [(H-tmhd = 2,2,6,6-tetramethyl-3,5-heptandione)] precursor. Physical and thermal properties of both Pr(hfa) 3 .diglyme and Pr(tmhd)3 precursors have been fully analyzed and their efficacy as MOCVD precursors for the growth of praseodymium oxide films have been fully tested. Depending on the oxygen partial pressure (p O2 ), different praseodymium oxide phases have been obtained.

Interaction of lead(II) with highly-dentate linear and cyclic polyamines

The interaction of Pb2+ with the macrocyclic amines 1,4,7,10,13,16-hexaazacyclooctadecane (L1), 1,4,7,10,13,16,19-heptaazacyclohenicosane (L2), 1,4,7,10,13,16,19,22-octaazacyclotetracosane (L3), 1,4,7,10,13,16,19,22,25-nonaazacycloheptacosane (L4), 1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane (L5), 1,4,7,10,13,16,19,22,25,28,31-undecaazacyclotritriacontane (L6) and 1,4,7,10,13,16,19,22,25,28,31,34-dodecaazacyclohexatriacontane (L7) belonging to the [3k]aneNg series and with their related open-chain, terminally methylated polyamines 1,14-bis(methylamino)-3,6,9,12-tetraazatetra-decane (L8), 1,17-bis(methylamino)-3,6,9,12,15-pentaazaheptadecane (L9), 1,20-bis(methylamino)-3,6,9,12,15,18-hexaazaicosane (L10) and 1,23-bis(methylamino)-3,6,9,12,15,18,21-heptaazatricosane (L11) has been studied by potentiometry at 298.1 K in 0.15 mol dm–3 NaClO4. The cyclic amines L1 and L2 form only mononuclear complexes, while L3–L5 can form both mono- and bi-nuclear species. The largest amines of this series L6 and L7 form bi- and tri-nuclear lead(II) complexes. Of the open-chain ligands, L8 forms only mononuclear complexes, while L9–L11 form both mono- and bi-nuclear species. The crystal structure of the solid compound [Pb2L5][ClO4]4 has been solved by X-ray diffraction analysis [space group P21/n, Z= 2, a= 9.052(9), b= 11.400(9), c= 18.689(8)A, β= 94.42(6)°, R= 0.082 and R′= 0.068]. It shows that both Pb2+ ions are tightly co-ordinated to four nitrogens of the macrocycle (Pb–N ranging from 2.27 to 2.71 A). A fifth nitrogen and three oxygens of two perchlorate anions are weakly interacting at much larger distances (Pb–N 3.04; Pb–O 2.98, 3.38, 3.41 A). The complex cation is situated around a crystallographic symmetry centre. The arrangement of the eight atoms around the lead ion is rather asymmetric leaving a zone free from co-ordinated donor atoms which is believed to be occupied by a lone pair of electrons.

Di-and tri-palladium(II) polyazacycloalakane complexes. A case of deprotonated secondary nitrogen in solution and in solid state

Crystal structures of di- and tri-nuclear palladium(II) complexes with the azamacrocycles[18]aneN6 and [21]aneN7 have been solved by X-ray analysis; in the case of the trinuclear complex deprotonation of a secondary amino group occurs, both in solution and in the solid state.

CRYSTAL STRUCTURES OF COMPLEXES OF AMMONIUM AND POTASSIUM HEXAFLUOROPHOSPHATE WITH DIBENZO-18-CROWN-6. MOLECULAR MECHANICS STUDIES ON THE UNCOMPLEXED MACROCYCLE

Abstract Crown ether complex formed by the dibenzo-18-crown-6 (DB18C6) macrocycle with ammonium and potassium hexafluorophosphate have been prepared and their crystal structures have been determined by single crystal X-ray analyses. The ammonium compound consists of a 2:1 mixture of NH4 (DB18C6)PF6 and free DB18C6 ligand (compound 1). Crystals are monoclinic, space group P21/c with a=12.638(2), b=13.118(4), c=20.927(9) A , β=106.21(2)°, V=3331(2) A 3 and Z=4 (R=0.0457) . The ammonium cation interacts with the six oxygen atoms of the crown ether and with two fluorine atoms of a PF6− anion. The potassium derivative (compound 2) consists of K(DB18C6)PF6 units. Crystals are monoclinic, space group P2/c, with a=15.744(8), b=7.945(3), c=37.59(2) A , β=94.27(4)° , V=4689(4) A 3 and Z=8 (R=0.0786) . The potassium atoms of the three independent complexes are linked to the six oxygen atoms of the DB18C6 ligand and to fluorine atoms of two PF6− anions. Molecular mechanics calculations were performed on the uncomplexed DB18C6 molecule by using the MM2 force field.

Viable route for the synthesis of the anhydrous Co(hfac)2 adduct with monoglyme: a useful precursor for thin films of CoO

The [Co(hfac)2·CH3OCH2CH2OCH3] adduct was synthesised and investigated by X-ray crystal structure, mass spectra, TG-DTG thermal measurements and infrared transmittance spectroscopy. X-Ray single crystal data provide evidence of a slightly distorted octahedral cobalt cation, coordinated with four oxygen atoms of two hfac anions and two oxygens of the monoglyme molecule. Deposition experiments, in a low-pressure horizontal hot-wall reactor, on optically transparent SiO2 substrates, using the title complex, resulted in CoO films. XRD measurements show that CoO consists of cubic, highly oriented, crystals. The surface atomic composition of the films was investigated by XPS. No fluorine contamination was detected.

(PdCl4)2– inclusion into the deca-charged polyammonium receptor (H10[30]aneN10)10+([30]aneN10= 1,4,7,10,13,16,19,22,25,28-deca-azacyclotriacontane)

The title decaprotonated deca-azamacrocycle encapsulates the tetrachloropalladate(II) anion forming a ‘super complex’ whose crystal structure has been determined.

Conformational and Database Study on the Intramolecular CH...π Aromatic Bond and Its Possible Influence on the Stereochemistry of Polypeptide Chains

The presence of intramolecular CH...π aromatic bonds in organic molecules has been analyzed by means of CSD searches. In particular, molecules containing aromatic and methyl groups have been examined as a function of the length of the chain separating the interacting groups. The type of bonds in the chain and its geometry have also been taken into account. The maximum number of CH...π interactions have been found for five-membered chains joining the aromatic and methyl moieties. In addition, this interaction seems favored when the chain contains two sp2 hybridized atoms. The interactions involving polypeptides have been carefully examined. Interest has focused on compounds containing both aromatic and methylic residues, i.e., a combination of phenylalanine (phe), tyrosine (tyr), and tryptophan (trp) with alanine (ala), valine (val), leucine (leu), and isoleucine (ile). The maximum number of CH...π interactions have been found when five atoms constituted the chain, i.e., in the sequences phe–ala and ala–phe.

Structural aspects of the protonation of small cages. Preparation of the new aza-cage 12,17-dimethyl-1,9,12,17-tetra-azabicyclo[7.5.5]nonadecane (L). Thermodynamic studies on solution equilibria. Crystal structures of [H2L][CoCl4] and [H2L1][CoCl4] salts

The synthesis and characterization of the new aza-cage 12,17-dimethyl-1,9,12,17-tetra-azabicyclo-[7.5.5]nonadecane (L) are described. The basicity behaviour in both aqueous and water–DMSO (50 : 50, mol : mol) solutions has been investigated by potentiometric and microcalorimetric (25 °C, 0.15 mol dm–3 NaCl) techniques. L behaves, in aqueous solution, as a fairly strong base (log K1= 12.00; ΔH1⊖=–54.0 kJ mol–1; TΔS1⊖= 14.5 kJ mol–1) in the first protonation step and as a moderate base in the second step (log K2= 7.86 ΔH2⊖=–44.8 kJ mol–1; TΔS2⊖ca. 0). The enthalpic and entropic contributions are discussed in terms of molecular topology and translational entropy. The CuII ion is encapsulated by L, the electronic spectra being diagnostic of a square-planar structure. The molecular structures of the diprotonated salts [H2L][CoCl4] and [H2L1][CoCl4](L1 = 5,12,17-trimethyl-1,5,9,12,17-penta-azabicyclo[7.5.5]nonadecane) have been determined by single-crystal X-ray analysis.Crystals of [H2L][CoCl4] are orthorhombic, space group pbn21, with a= 9.311 (3)A, b= 15.480(2)A, c = 16.636(6)A, and Z= 4. Final R values of 0.043 (Rw= 0.037) for 1 358 observed reflections. X-Ray analysis shows that the protonation occurs on the N–CH3 groups. Each hydrogen atom of the NH+–CH3 interacts with the two bridgehead nitrogen atoms.The compound [H2L1][CoCl4] crystallizes in a monoclinic unit cell (space group P21) with lattice constants a= 8.877(3)A, b= 14.088(8)A, c= 10.122(5)A, β= 105.51 (4)°, and Z= 2. Final R values of 0.064 (Rw= 0.049) for 2 374 observed reflections. In this case the conformation of the diprotonated cage is different and the protonation probably occurs at one of the two methylated nitrogens and at the apical nitrogen atom.