Jolanda Giusti

One-dimensional polymeric chlorocadmate(II) systems of N-methylpiperazinium and N,N′-dimethylpiperazinium compounds: synthesis, structural and thermal properties

The chlorocadmate(II) systems of (H2me2pipz)[Cd2Cl6(H2O)2] (1) and (H2mepipz)2[Cd3Cl10(H2O)] (2) (L = me2pipz = N,N′-dimethylpiperazine; L′ = mepipz = N-methylpiperazine) were prepared and their structural and thermal properties investigated. Compound 1 is monoclinic, space group P21/c, a = 7.664(1), b = 7.472(4), c = 15.347(1) A, β = 99.468(7)°, Z = 2, R = 0.024. The crystal structure consists of organic cations and infinite one-dimensional chains of [CdCl3(H2O)]n3− anions. Each Cd atom is octahedrally surrounded by bridged and terminal chlorine atoms and by a water molecule, which is in trans position with respect to the terminal chlorine atom. Inter- and intrachain hydrogen bond interactions between the terminal chlorine atoms and the water molecules contribute to the crystal packing. Compound 2 is orthorhombic, space group Cmc21, a = 15.286(3), b = 13.354(3), c = 13.154(3) A, R = 0.023. The crystal structure consists of organic dications and infinite chains of [Cd2Cl6(CdCl4H2O]n4− units running along the [001] axis. Each unit is formed of regularly alternate six-coordinated Cd atoms, one of them linking one pentacoordinated Cd atom which completes its coordination througha water molecule. A strong hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential scanning calorimetry measurements did not show the presence of any structural phase transitions. The structures are compared with those of (H2pipz)[Cd2Cl6(H2O)2] (3), (H2mepipz)[Cd2Cl6(H2O)2]·H2O (4) and (H2mepipz)[Cd2Cl6] (5) (L = pipz = piperazine, L′ = mepipz = N-ethylpiperazine).

Trans-2-styrylbenzothiazole complexes with mercury(II) halides. Synthesis, characterization and X-ray crystal structure of diiodobis(trans-2-styrylbenzothiazole)mercury(II)

Abstract The synthesis of trans-2-styrylbenzothiazole (L) and of its complexes with mercury(II) halides is reported. Complexes with the formulae [Hg2(L)Cl4], [Hg(L)Br2], [Hg(L)2I2] and [Hg(L)I2] were isolated and characterized by conventional chemical analysis, electronic and IR spectra and by thermal analysis. For one of these complexes, [Hg(L)2I2], the X-ray crystal structure was also determined. The complex consists of discrete [Hg(L)2I2] units in which mercury, located on a two-fold axis, shows a distorted tetrahedral coordination and the ligand molecules are bonded via nitrogen atoms with HI = 2.61(2) A and HgN = 2.36(1) A bond distances.

SYNTHESIS, THERMAL AND ELECTRICAL CHARACTERIZATION OF 2-METHYLPENTANE-1,5-DIAMMONIUM TETRACHLOROCADMATE(II) WITH PEROVSKITE-LIKE STRUCTURE

Abstract This paper repotts the synthesis and the structural, thermal and electrical characterization of the 2-methyl-pentane-1,5-diammonium bidimensional chlorocadmate(II) system with perovskite-like structure. Its structure consists of layers of CdCl6 corner-sharing octahedra extending in the ab plane. Interposed sheets of organic dications link adjacent layers through hydrogen bonding and contribute to the crystal packing. The presence of a methyl group on the C(4) atom of the organic chain is considered responsible for the thermal stability of the compound between room and melting temperature (605 K). The compound behaves as an electrical insulator at low temperature approaching semiconducting values at higher temperature. These results are also compared with those found for other structurally similar compounds.

Thermal stability of some potassium dibenzo-18-crown-6 solid compounds: KX(DB18C6) (X=NCS, Br, I, NO3). Differential scanning calorimetry and X-ray investigations

Abstract The thermal stability of the compounds KX(DB- 18C6) (X = NCS, Br, I, NO3; DB18C6 = dibenzo-18- crown-6) has been determined by differential scanning calorimetry. Only the KNCS(DB18C6) complex melts congruently; the iodide and the nitrate compounds, when melting, undergo a partial dissociation into their components. The compound KI(DB18C6)- C2H5OH, when heated, loses the ethanol molecule without any dissociation. A KBr(DB18C6)3CHCl3 compound was isolated; it dissociates into its components by evaporation of the solvate molecules. Crystals of the compounds KNCS(DB18C6) are monoclinic, space group P21/n with a = 19.107(8), b = 27.085(5),c = 8.559(5) A, β = 101.96(4),° and Z = 8. The structure was solved by the heavy atom method. Refinement of the atomic parameters by least-squares gave a final R factor of 0.127 (Rw = 0.116). The structure consists of independent complex molecules of KNCS(DB18C6) in which the potassium ion is coordinated by the six oxygen atoms of the crown ether and by the nitrogen atom of the thiocyanate ion.

Analysis by differential scanning calorimetry of the KNCS/dibenzo-18-crown-6 system: Phase diagram and enthalpy changes

Abstract The phase diagram of the system KNCS/dibenzo-18-crown-6 (DB18C6) was determined by DSC analysis. A 1:1 complex, congruently melting at 245°C, is formed, which is not miscible with the components in the solid phase and is miscible with the crown ether, but not with KNCS, in the liquid phase. The enthalpies of melting of the complex and of its components were determined and the relative entropy changes were calculated. The enthalpy of formation of the complex from its components in the different states was determined and discussed.

Polymeric 1-D linear-chain piperidinium and morpholinium trichlorocadmates (II): synthesis and structural, thermal and electrical properties

Abstract The crystal structures of two polymeric 1-D linear-chain piperidinium and morpholinium trichlorocadmates(II) have been determined. The CdCl 3 (pdH) ( pdH = piperidinium cation) salt is orthorhombic with the following space group and lattice constants: A ma2, a = 6.770(1) A , b = 18.421(6) A , c = 7.642(1) A , Z = 4. Its structure consists of piperidinium cations and polymeric 1-D endless chains of triangular-face sharing distorted octahedral (CdCl 6 ) 4− ions, joined via three bridging chlorine atoms. The CdCl 3 (mfH) ( mfH = morpholinium cation) salt is orthorhombic with the following space group and lattice constants: P212121 , a = 17.524(4) A , b = 14.368(3) A , c = 7.000(1) A , Z = 4. Its structure consists of zwitterionic 1-D linear Cd 2 Cl 6 (mfH) 2 chains in which two unequivalent cadmium atoms, Cd(1) surrounded by six chlorine atoms and Cd(2) by four chlorine atoms and two oxygen coordinated morpholinium cations, are present. Alternate CdCl 4 (cis-Cl 2 ) and CdCl 4 (cis-O 2 ) distorted octahedra share edges by two chlorine atoms, forming chains of Cd 2 Cl 6 (mfH) 2 units, running along the z axis. The compounds are also investigated by means of thermal, optical microscopy, X-Ray powder spectra and d.c. and a.c. electrical measurements. In particular for the CdCl 3 (mfH) salt the two phase transitions appearing at 201 and 211°C are tentatively explained on the basis of the above cited measurements. Correlations among the different parameters and the known structures of these materials are also drawn.

Thermal behaviour of [N(2-ammoniumethyl) piperazinium] pentachlorocuprate(II) dihydrate

The thermal behaviour of single-crystals of the title compound has been investigated by means of thermal methods supported by optical microscopy. A complex change takes place on heating. After the loss of the two water molecules, leading to an amorphous phase, recrystallization takes place. This results in a solid (probably an anhydrous form) which reacts further, through partial liquefaction, to yield a red crystalline product whose structure has been characterized via X-ray powder spectra and electronic and IR spectroscopy.ZusammenfassungDas thermische Verhalten von Einkristallen der Titelverbindung wurden mittels thermischer Methoden und optischer Mikroskopie untersucht. Beim Erhitzen verläuft ein komplexer Prozeß. Nach dem zu einer amorphen Phase führenden Verlust von zwei Wassermolekülen findet eine Rekristallisation statt. Dabei wird eine feste Substanz, wahrscheinlich in wasserfreier Form, erhalten, die über partielle Verflüssigung unter Bildung eines roten kristallinen Produktes weiterreagiert, dessen Struktur durch Röntgenpulverspektren sowie Elektronen- und Infrarotspektroskopie charakterisiert wurde.РезюмеТермическое поведен ие монокристаллов ря да соединений исследов ано термическими методами, дополненны х оптической микроск опией. При нагревании этих крис таллов протекают сложные пр евращения. Потеря дву х молекул воды приводит к образ ованию аморфной фазы с после дующей ее кристаллиз ацией. Это может быть следствие м того, что твердая, вероятно, безводная форма реаг ирует дальше с частичным ра зжижением, образуя красный крис таллический продукт, структура которого была устано влена с помощью рентгеновских спект ров, электронных спек тров поглощения и ИК спект роскопии.

Structural, thermal and microscopic studies of potassium cryptate K(222)NCS·H2O

Abstract The crystals of the title compound are isomorphous with the Rb and Cs analogues and have cell constants a = 14.365(3), b = 8.310(2), c = 22.251(5), a = 107.45(5)°, space group P 2 a and Z = 4. The potassium ion is coordinated by the two nitrogen atoms and the six oxygen atoms of the ligand. Structural analysis indicates that the cryptate conformation is very similar to that of the Rb compound, but differs from that of the KI complex. The thermal behaviour of K(222)NCS·H2O crystalline powder was investigated by DSC. After dehydration, the anhydrous material undergoes two reversible phase transitions before melting at 428 K. These findings were confirmed by microscopic observation of single crystals between crossed polarizers. Enthalpic and entropic changes are reported, and comparison between the entropies of fusion of the ligand and the complex is discussed in terms of ligand rigidity.

Correlation between thermal stability and molecular and crystal structure in a series of potassium–dibenzo-18-crown-6 solid compounds

The compounds [K(NO3)L](L = 6,7,9,10,17,18,20,21-octahydrodibenzo[b,k][1,4,7,10,13,16]-hexaoxacyclo-octadecin) and [K(Hpht)L](Hpht = hydrogenphthalate) have been studied by differential scanning calorimetry and single-crystal X-ray analyses. Both the complexes undergo, upon melting, a partial dissociation into their components. The enthalpy of melting of [K(NO3)L] is fairly high (14.6 kcal mol–1) and equal, within experimental error, to the enthalpy of melting of the free ligand, L. The entropy of melting of the complex reflects an increased stiffening in the complexed crown ether molecule with respect to the free ligand. Crystals of [K(NO3)L] and of [K(Hpht)L] are monoclinic, space group P21/c with a= 15.054 4(7), b= 20.575(2), c= 14.259(l)A, β= 97.655(5)°, Z= 8; and orthorhombic, space group P212121 with a= 15.990(2), b= 17.915(1), c= 9.314(1)A, Z= 4 respectively. Refinement of the atomic parameters by least squares gave a final R factor of 0.0544 (R′= 0.0590) and of 0.0622 (R′= 0.0735) respectively. Both the structures consist of independent complex molecules {two in an asymmetric unit for [K(NO3)L]} in which the potassium ion is surrounded by eight oxygen donor atoms, six from L and two from the anions. The nitrate ion acts as a symmetrically bonded bidentate ligand [K ⋯ O 2.832(4), 2.836(4) and 2.815(4), 2.790(4)A] while Hpht is asymmetrically bonded [K ⋯ O 2.729(9), 3.168(8)A]. The potassium ions are pulled 0.631(1) and 0.465(1)A from the least-squares plane through the six oxygen donors of L, towards the nitrate ion, and 0.592 A toward the hydrogenphthalate ion. The comparison of these complexes with the NCS derivative shows the existence of a correlation between their thermal stability and the displacement of the potassium ion from the donor ring.