V. A. Logvinenko

CONTACT STABILIZATION OF HOST COMPLEX MOLECULES DURING CLATHRATE FORMATION: THE PYRIDINE-ZINC NITRATE AND THE PYRIDINE-CADMIUM NITRATE SYSTEMS

Abstract Clathrate formation ranges of the phase diagrams of two binary systems Py-Zn(NO3)2 and Py-Cd(NO3)2 (Py = pyridine) were studied. A clathrate of composition [MPy4(NO3)2]·2Py (M = Zn, Cd) was observed in each of the systems. The space group Ccca (orthorhombic system) and the parameters of the unit cells of both clathrates were determined by X-ray analysis of their single crystals. The data obtained show them to be isostructural with the clathrate [NiPy4(NO3)2]·2Py whose structure is known and suggest the actual presence of the host molecules trans-[MPy4(NO3)2] (M = Zn,Cd) inside the clathrate phases. Host complexes do not form as separate compounds but can only arise in clathrate phases due to contact stabilization by the guest molecules. Both Zn- and Cd-clathrates are of constant composition and melt incongruently at 62.3(6) and 106.0(5)°C, respectively, yielding the complexes [ZnPy3(NO3)2] and [CdPy3(NO3)2], these melting congruently at 131.4(5) and 169.5(5)°C, respectively. During thermal decomp...

Spin crossover in iron(II) complexes with tris(pyrazol-1-yl)methane

Mononuclear iron(II) coordination compounds with tris(pyrazol-1-yl)methane (HC(Pz)3) described as [Fe{HC(Pz)3}2]A2 × nH2O, where A = Cl−, Br−, I−, 1/2 SO42−, n = 0–7, were synthesized. The compounds were studied by static magnetic susceptibility measurements, IR and UV/Vis spectroscopy, and powder X-ray diffraction. The crystal and molecular structures of all compounds were determined by single crystal X-ray diffraction.

Vapour pressure of 4-methylpyridine (MePy) over [Ni(MePy)4(NCS)2]·y(MePy) and [Cu(MePy)4(NCS)2]·2/3(MePy) clathrates during their dissociation

Strain measurement and quasiequilibrium thermogravimetry were used to study the dissociation processes of two clathrates, [Ni(MePy)4(NCS)2]·(MePy) and [Cu(MePy)4(NCS)2]·2/3(MePy), accompanied by the liberation of MePy into the gaseous phase. In the Ni clathrate dissociation process in the temperature range 298–368 K the liberated MePy was redistributed between the solid clathrate and gaseous phases; the MePy vapour pressure over the clathrate is a function of temperature and the guest contenty, which agrees with the presence in the MePy-[Ni(MePy)4(NCS)2] system of a wide range of β-clathrate solutions, [Ni(MePy)4(NCS)2]·y(MePy). The same methods used to study the Cu clathrate dissociation resulted in conclusions different from those obtained for the dissociation process of the above clathrate: the process is described by the equation [Cu(MePy)4(NCS)2]·2/3(MePy)solid =[Cu(MePy)2(NCS)2]solid+22/3(MePy)gas; the temperature dependence of the Mepy vapour pressure over the solid sample does not depend on its composition, which points to the absence from the system of solid solutions based on the clathrate. Standard changes of the enthalpy, entropy, and isobaric-isothermal reaction potential for the temperature range 292–325 K are equal to 178.6±1.7 kJ (mole of clathrate)−1, 463±5.6 J (mole of clathrate)−1 K−1, and 40.4±2.4 kJ (mole of clathrate)−1, respectively.

Study of the thermal decomposition processes of clathrate compounds

The decompositions of the clathrate compounds [M(NCS)2(4-MePy)4]·nG (whereM=Mn, Co, Ni or Cd;G=4-methylpyridine (4-MePy), benzene or xylenes) were studied on a Q-derivatograph under quasi-equilibrium conditions and with linear heating. These clathrates can be divided into two groups, in which the loss of guest is either (I) accompanied by destruction of the host complex, or (II) occurs before decomposition of the host complex. Kinetic parameters were obtained.ZusammenfassungDie Zersetzung von Clathrat-Verbindungen der Zusammensetzung [M(NCS)2(4-MePy)4]·nG (M=Mn, Co, Ni, Cd;G=4-Methylpyridin (4-MePy), Benzen, o-,m, p-Xylen) wurde mittels Q-Derivatograph unter Quasi-Gleichgewichtsbedingungen und bei linearer Aufheizung untersucht.Die studierten Clathrate lassen sich in zwei Gruppen einteilen, je nachdem ob die Abgabe des Gastmoleküls G entweder vor oder unter Gleichzeitiger Zerstörung des Wirtskomplexes erfolgt. Kinetische Parameter wurden ermittelt.РЕЗЮМЕС помощью Q-дериватогр афа в квазиравновесн ых условиях и в условиях линейного нагрева изучено разл ожение клатратных со единений состава [M(NCS)2(4-MePy)2]·nG, гдеM дв ухвалентные марганец, кобальт, ник ель и кадмий, аG — 4-мбтил пиридин, бензол и ксилолы. Изученные клатраты м огут быть разделены п о тому признаку, что потеря м олекул внедрения сопровождается разл ожением комплекса ил и же процесс выделения таких моле кул происходит перед разложением ко мплекса. Установлены кинетические параме тры происходящих реа кций.

Thermodynamic Dissociation Constants for [MPy4(NO3)2]*2Py Clathrates (M=Mn, Co, Ni, Cu)

Abstract Stoichiometry and thermodynamic parameters of the title clathrates dissociation have been studied with thermoanalytical and strain method techniques. The [MPy4(NO3)2]*2Py (M = Mn, Co, Ni) clathrates dissociate with collapsing clathrate porous phase and destruction of the host complex to give the respective tripyridine complexes and gaseous pyridine. The [CuPy4(NO3)2]*2Py dissociates with collapsing clathrate phase but giving the host [CuPy4(NO3)2] complex as individual phase, with the tripyridine complex forming in further course of decomposition. The comparison of the thermodynamic dissociation parameters for the [MPy4(NO3)2]*2Py series with M = Mn, Co, Ni, Cu, Zn and Cd shows that the differences in the stability of the compounds do not correlate with structural parameters of the clathrates but depend on the nature of the metal cation in the host complex. Thermodynamic stability of these clathrate phases follows the general sequence of stabilty for complexes of the 3d transition metals known as Irwing-Williams sequence: MnZn. These results disclose the main issue of instability of the [MPy4(NO3)2]*2Py clathrates as instability of the respective host complexes.

Solid State Coordination Chemistry. The quantitative thermoanalytical study of thermal dissociation reactions

Physicalo-chemical importance of the quantitative study of kineticliability of coordination compounds in thermal dissociation processes is considered. Muchattention is given to the proof of the physicalo-chemical meaning and validity of kineticparameters calculated from thermoanalytical data. Experimental data (thermal dissociation ofcoordination compounds and clathrates with such a matrix) are discussed.

[MPy4(NCO)2]-2Py clathrates (M = M(II) = Mn, Fe, Co, Ni, Cu, Zn, Cd; Py = pyridine)

The title compounds form an iso structural series and are isomorphic with other [MPy4X2]-2Py clathrates (XRD, KM4 diffractometer, cell parameters and space group Ccca from 17–80 reflections). In the clathrate [NiPy4(NCO)2]-2Py studied in detail (XRD, CAD-4 diffractom eter, λCuKα, Ω/2θ scan mode, θmax = 78‡, 990 strong reflections, 104 parameters, R = 0.053), the host molecule has 222 symmetry, and the twofold axes run along the coordination bonds. The transoctahedral environment of nickel consists of six nitrogen atoms of four pyridine and two isocyanate ligands. The coordination polyhedron is slightly distorted due to changes in the bond lengths. The molecule has a propeller conformation. The guest molecules lie in the cavities of the crystal structure in conformity with the van der Waals type of packing. The host complex [NiPy4(NCO)2] (XRD, CAD-4 diffractometer, 4615 strong reflections, 560 parameters, R-0.037) crystallizes in the triclinic crystal system (space group P1) with two independent asymmetric molecules in the unit cell. The molecular structure is analogous to that in the ciathrate phase, but the coordination angles are severely distorted; one of the molecules acquires a distorted propeller conformation, and the other, a centrosvmmetric conformation, which is less favorable. While being structurally identical, the [MPy4(NCO)2]-2Py clathrates differ heavily in the properties. The first four complexes dissociate to host complexes, and their thermal stability changes in the sequence Mn< Fe< Co< Ni; the Cu and Zn clathrates decompose in one step to dipyridine complexes with decomposition of host complexes. Decomposition of the Cd ciathrate follows one of these patterns depending on conditions. The results are compared with those for other known systems. Synthetic procedures are given.

Clathrate Formation and Phase Equilibria in the Pyridine-Cadmium Nitrate System

Preparative, thermal (DTA, TGA), solubility, strain and spectral (Raman) techniques were used to study clathrate and complex formation in the pyridine (Py)-cadmium nitrate system. Three compounds have been isolated and studied: the clathrate compound [CdPy4(NO3)2] · 2Py (I), the complex [CdPy3(NO3)2] (II) and a compound of composition ‘Cd(NO3)2·7/4Py’ (III), of unknown nature. The phase diagram of the system has been determined for the concentration and temperature range 0–66 mass-% Cd(NO3)2 and −100 to +200 °C, respectively. ClathrateI undergoes polymorphous conversion at −51.8(4) °C and melts incongruently at 106.0(5) °C, forming complexII. CompoundsII andIII melt congruently at 165.5(4) and 191(1) °C, respectively. The complexes [CdPy4(NO3)2] (the host phase) and [CdPy2(NO3)2] are not observed in the system. The nature and thermodynamic parameters of the dissociation of clathrate I have been determined. For the process 1/13[CdPy4)NO3)2] · 2Pysolid = 1/3[CdPy3(NO3)2]solid + Pygas in the range 290–360K δHo = 54.9(3) kj/mole, ΔS298o = 142(1) J/(mole K), ΔG298o = 12.5(5) kJ/mole.

Preparation of metal-polymer composites through the thermolysis of Fe(II), Co(II), and Ni(II) maleates

Metal-polymer composites have been prepared through the thermolysis of the [M1(H2O)2(C4H2O4)] · H2O (M1 = Co(II), Ni(II)) neutral maleates and [M2(H2O)4(C4H3O4)2] (M2 = Fe(II), Co(II), Ni(II)) acid maleates. In the polymer matrix of the Fe-containing composite, we identified metal, Fe2O3, and Fe3O4 particles, with slight densification of the matrix around them. The polymer matrix of the cobalt maleate-derived composite contained four types of nanoparticles: α-Co, β-Co, and CoO in polymer shells and Co3O4 with no polymer shell. The decomposition of the nickel maleates yielded homogeneous nickel nanoparticles (4–5 nm) covered with two to five graphene layers. The Co-containing composite was found to be a dielectric. The Ni-containing composite exhibited variable range hopping conduction in the range T ≤ 50 K.

Transition-metal bimaleates and their solid solutions: Synthesis, structural, and thermoanalytical study

Transition-metal hydrogen maleates of composition M(C4H3O4)2 · 4H2O, where M = Mn, Fe, Co, and Ni, and their solid solutions were synthesized and characterized by X-ray crystallography, IR spectroscopy, mass spectrometry, and thermal analysis. X-ray crystallography and IR spectroscopy showed that both intramolecular and intermolecular H-bonds exist in these compounds. The generation of continuous substitutional solid solutions with cation substitution in these compounds was studied. The thermolysis mechanism was studied for both transition-metal hydrogen maleates and their solid solutions. The composite produced by thermolysis is stable up to 1200°C in flowing helium.