The thermodynamic properties of the [(Me<Subscript>3</Subscript>Si)<Subscript>7</Subscript>C<Subscript>60</Subscript>]<Subscript>2</Subscript> fullerene complex

The temperature dependence of the heat capacity C _p ^o of the [(Me₃Si)₇C₆₀]₂ fullerene complex was measured for the first time using precision adiabatic vacuum calorimetry over the temperature range 6.7–340 K and high-accuracy differential scanning calorimetry at 320–635 K. For the most part, the error in the C _p ^o values was about ±0.5%. An irreversible endothermic effect caused by the splitting of the dimeric bond between fullerene fragments and the thermal decomposition of the complex was observed at 448–570 K. The thermodynamic characteristics of this transformation were calculated and analyzed. Multifractal analysis of the low-temperature (T < 50 K) heat capacity was performed, and conclusions were drawn concerning the character of the heterodynamicity of the structure. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o (T) ? H ^o (0), S ^o (T) ? S ^o (0), and G ^o (T) ? H ^o (0) over the temperature range from T → 0 to 445 K and estimate the standard entropy of formation of the compound from simple substances at 298.15 K. The standard thermodynamic properties of [(Me₃Si)₇C₆₀]₂ are compared with those of the (C₆₀)₂ dimer, the [(η⁶-Ph₂)₂Cr]⁺[C₆₀]^?? fulleride, and the initial C₆₀ fullerene.     

A Quantum Chemical Study of C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>, C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Molecules and Fe@C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Endocomplex

(U)PBE0/cc-pVDZ method is used to study the structure of C₆₀Cl₃₀, C₆₀(OH)₃₀ molecules and Fe@C₆₀(OH)₃₀ endocomplex. The triplet state of the endocomplex is shown to be the lowest in energy among its four states corresponding to different spin multiplicities and positions of Fe nucleus within the fullerene cavity. This state is characterized by bonding between the iron atom and one of two benzenoid cycles of the carbon cage, six internuclear Fe–C distances (208 pm), and 1s²2s²2p⁶3s²3p⁶3d^7.24s^0.14p^0.3 electron configuration of iron with spin population of 2.36.     

Synthesis of fullerene C<Subscript>60</Subscript> monoadducts. Cyclopropanation of C<Subscript>60</Subscript> with sulfonium ylides

3′H-Cyclopropa[1,9](C₆₀-I_h)[5,6]fullerene-3′-carboxylic acid can be synthesized in a good yield by cyclopropanation of fullerene C₆₀ with 2-(dimethyl-λ⁴-sulfanylidene)acetates provided that the ester residue is readily hydrolyzable in acid medium.     

Crystal and molecular structure of [Au(C<Subscript>14</Subscript>H<Subscript>24</Subscript>N<Subscript>4</Subscript>)][H<Subscript>3</Subscript>O](ClO<Subscript>4</Subscript>)<Subscript>4</Subscript>

The crystal and molecular structure of doubly protonated tetraazamacrocyclic complex of gold(III) [Au(C₁₄H₂₄N₄)][H₃O](ClO₄)₄ has been determined. The crystals are monoclinic: a = 11.158(2) Å, b = 8.243(1) Å, c = 14.756(2) Å; β = 98.65(1)°, V = 1341.8(3) ų, Z = 2, ρ(calc) = 1.134 g/cm³, space group P2₁/n. The structure is built of almost flat centrosymmetrical Au(C₁₄H₂₄N₄)]³⁺ and [H₃O]⁺ cations and [ClO₄]^? anions. The gold atom is coordinated with four nitrogen atoms of the ligand forming a flat square. The coordinated ligand is protonated at its γ-carbon atoms of the two six-membered chelate rings. The Au-N bond lengths are almost identical (the mean value is 1.994 Å). The six-membered rings of the complex contain C=N diimine bonds. The [H₃O]⁺ oxonium ion has H-bonds with the oxygen atoms of perchlorate ions.     

Carbon in boron carbide: The crystal structure of B<Subscript>11.4</Subscript>C<Subscript>3.6</Subscript>

A single crystal of boron carbide obtained from a self-propagating high-temperature synthesis (SHS) product was studied by X-ray crystallography: B_11.4C_3.6, a = 5.594(2) Å, c = 11.977(7) Å, V = 324.6(7) ų, space group R3m, Z = 3, ρ_calcd = 2.56 g/cm³, R = 0.048. The content of carbon in the single crystal was estimated at ～24 at % from analysis of the unit cell parameters, bond lengths, and the volume of B_{12 ? x} C _x icosahedra, which demonstrated the possibility of obtaining by SHS carbon-rich boron carbide crystals due to the substitution of carbon atoms for boron atoms in icosahedra. Comparison of the X-ray crystallographic data for single crystals of boron carbide with the results of quantum-chemical calculations (an ab initio method (the 3–21G basis set) with geometry optimization) showed that the C-B-C group in a crystal has a nonlinear structure.     

Crystal and molecular structures and luminescence properties of [Eu(Cin)<Subscript>3</Subscript>]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> complex

The crystal structure of europium cinnamate of the composition [Eu(Cin)₃] _n (Cin is cinnamic acid anion C₉H₇O ₂ ^? ) was determined by X-ray crystallography (a = 22.626(1) Å, c = 7.7330(7) Å, space group R3/c, Z = 3, ρ_calc = 1.448 g/cm³). The coordination polyhedron of Eu atoms is a distorted trigonal prism with three centered square faces. The structure is built of infinite polymeric chains [Eu(Cin)₃] _n running along the c axis and linked by van der Waals and π stacking interactions. Luminescent characteristics of the compound were determined.     

Structure of arsenic 8-mercaptoquinolinate: Synthesis and crystal structure of arsenic 4-methoxy-8-mercaptoquinolinate As[C<Subscript>9</Subscript>H<Subscript>5</Subscript>(OCH<Subscript>3</Subscript>)NS]<Subscript>3</Subscript>

Arsenic 4-methoxy-8-mercaptoquinolinate As[C₉H₅(4-OCH₃)NS]₃ (I) was synthesized and studied by X-ray diffraction. Crystals are trigonal: space group R3, a = b = 13.9867(4) Å, c = 12.4991(5) Å, γ = 120°, V = 2117.58(12) ų, ρ = 1.519 g/cm³, Z = 3. An arsenic atom in the crystal structure occupies a special position on axis 3. The structural unit of the crystal (neutral complex I) has symmetry C3. 4-Methoxy-8-mercaptoquinoline acts as a bidentate (N,S-) ligand. The coordination polyhedron of the arsenic atom is a symmetric octahedron (3S + 3N) or, with allowance for the lone electron pair, ψ-one-capped octahedron (3S + 3N + E). Bond lengths are as follows: As-S, 2.3179(7)Å; As…N 2.688(3) Å. The geometries of coordination polyhedra of arsenic atoms are compared in the crystal structures of As(C₉H₆NS)₃, As[C₉H₅(2-CH₃)NS]₃, and As[C₉H₅(4-CH₃)NS]₃.     

Synthesis and magnetic properties of quasi-unidimensional oxide Sr<Subscript>6.3</Subscript>Rh<Subscript>2.35</Subscript>Mn<Subscript>2.35</Subscript>O<Subscript>15</Subscript>

Attempts of the synthesis in air of complex oxides Sr₃RhMnO_x and Sr₄Rh_1.5Mn_1.5O_x resulted in revealing formation of a new oxide phase Sr_6.3Rh_2.35Mn_2.35O₉ related to quasi-unidimensional family A_3n+3m A′ _n B_3m+n O_9m+6n at n = 1 and m = 1. Its structural characteristics and magnetic properties are studied. X-ray data of the obtained phase is indicated on the basis of trigonal cell (spatial group P321) with the parameters: a 9.6239(4) Å; c ₁ 4.1130(4) Å, c ₂ 2.4946(2) Å. Manganese and rhodium exist in the compound as the cations Mn⁴⁺, Rh³⁺ and Rh⁴⁺, as follows from the data of measuring of magnetic susceptibility in the range 2–300 K.     

High-temperature heat capacity and thermodynamic properties of pyrovanadate Pb<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> and orthovanadate Pb<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The heat capacities of Pb₂V₂O₇ and Pb₃(VO₄)₂ as a function of temperature in the range 350–965 K have been studied by the differential scanning calorimetry method. The C_P = f(T) curve for Pb₂V₂O₇ is described by the equation C_p = (230.76 ± 0.51) + (73.60 ± 0.50)×10^-3T ? (18.38 ± 0.54)×10⁵T^-2 in the entire temperature range. For Pb₃(VO₄)₂, there is a well-pronounced extreme point in the C_P = f(T) curve at T = 371.5 K, which is caused by the existence of a structural phase transition. The thermodynamic properties of the oxide compounds have been calculated.     

X-ray diffraction study of CsZn<Subscript>2</Subscript>Br<Subscript>5</Subscript>

CsZn₂Br₅ crystals are studied by X-ray diffraction. The compound crystallizes in the monoclinic system with the unit cell parameters a = 6.8880(12) Å, b = 10.4703(19) Å, c = 6.5197(9) Å, β = 108.25°, V = 446.55 ų, ρ_calcd = 4.960 g/cm³. Refractive indices are n _p = 1.640 and n _p = 1.754.     

Synthesis and characterization of a new monophosphate (C<Subscript>6</Subscript>H<Subscript>16</Subscript>N<Subscript>2</Subscript>)(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) ų, Z = 1, and D_x = 1.565 g cm^?3. The crystal structure has been determined and refined to R = 0.030 and R _w(F ²) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H₂PO₄] _n ^n? chains with (C₆H₁₆N₂)²⁺ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, ¹³C and ³¹P MAS NMR spectroscopies and Ab initio calculations.     

Electrochemical oxidation and reduction of osmium and iridium complexes with fullerene C<Subscript>60</Subscript>

The electrochemical oxidation and reduction of a series of complexes of platinum-group metals (Os, Ir, and Rh) with fullerene C₆₀ with common formula C₆₀[ML _n ] (ML _n is the metal and the metal-bonded ligands) in the tetrahydrofuran solution are studied using the method of cyclic voltammetry. The effect of metal and ligands on the variations in the redox properties of complexes and stability of anions, which are formed in the reduction, is considered. It is shown that all complexes studied are reduced more difficultly than free fullerene, and the reduced forms of metallofullerenes are less stable as compared with free fullerene anions.     

Quantum-chemical study of ytterbium fluorides and of complex F<Subscript>2</Subscript>YbF<Subscript>2</Subscript>CeF<Subscript>2</Subscript>

The structural parameters of the (²Σ⁺//C_∞v)-YbF, (¹A₁//C_2v)-YbF2, (²A₂^′//D_3h)-YbF₃, (¹Ag//D_2h)-YbF₂Yb, (¹Ag//C_2h)-FYbF₂YbF, (¹A₁//C_2v)-FYbF₂YbF, (¹A₁//C_2v)-YbF₂YbF₂, (³B_3u//D_2h)-F₂YbF₂YbF₂, (²A′//C_s)-FYbF₂YbF₂, and (³B₂//С_2v)-F₂YbF₂CeF₂ molecules have been determined. Disproportionation of ytterbium monofluoride (2YbF → YbF₂ + Yb + 0.46 eV) is less exothermic than dimerization (2YbF → YbF₂Yb + 2.10 eV). The bond energy of the ytterbium difluoride molecules in the trans dimer (2.93 eV) exceeds those in the cis dimer (2.86 eV) and the coaxial dimer (1.66 eV). Ytterbium trifluoride dimerizes exothermically (2.95 eV) without spin pairing. The dipole and quadrupole moments of the molecules as well as the charges and spin populations of the atoms and the valence electron configurations of the lanthanides have been calculated.     

Paramagnetic centers related to Al,Sc, In,and Nb impurities in KTiOAsO<Subscript>4</Subscript>crystals

Electron paramagnetic resonance (EPR) is applied to study Al-, Sc-, In-, and Nb-doped KTiOAsO₄ (KTA) crystals. Paramagnetic hole centers O^? are observed after ionizing irradiation of KTA crystals. These centers are, as a rule, unstable at room temperature and are slowly annealed for about two weeks. Oxygen ions are bridging two cations in KTA. Near the impurity, two p-orbitals of oxygen atoms participate in covalent bonding with cations, whereas the third p-orbital remains free and under the radiation effect captures the hole thus forming the paramagnetic center of M ⁿ⁺-O^?-M^(n?1)+ (here M ⁿ⁺ is the lattice cation and M^(n?1)+ is the impurity cation of Al, In, Sc, or Nb). In the centers investigated the specific principal direction of the g-factor g ～ 2 is normal to the M ⁿ⁺-O^?-M^(n?1)+ plane, and the main value of g _max falls in this plane. The direction of the O^?-M^(n?1)+ bond is close to the selected direction of the hyperfine interaction with the impurity ion. The models of six hole centers and the found parameters of EPR spectra are discussed.     

Synthesis,structure, physicochemical properties,and solid-phase thermolysis of Co<Subscript>2</Subscript>Sm(Piv)<Subscript>7</Subscript>(2,4-Lut)<Subscript>2</Subscript>

Heterometallic pivalate Co₂Sm(Piv)₇(2,4-Lut)₂ (1) was prepared for the first time and structurally characterized at 293 and 160 K. Antiferromagnetic exchange interactions are dominant in complex 1. This compound experiences a first-order phase transition within 210–260 K. A set of thermodynamic functions was obtained for this complex (C _p , H _T ⁰ - H ₁₈₀ ⁰ , and S _T ⁰ ), and parameters were determined for solid-phase thermolysis where samarium cobaltate SmCoO₃ is the only product.     

Matrix Assisted and/or Laser Desorption Ionization Quadrupole Ion Trap Time-of-Flight Mass Spectrometry of WO<Subscript>3</Subscript> Clusters Formation in Gas Phase. Nanodiamonds,Fullerene, and Graphene Oxide Matrices

The formation of W _x O _y ^+●/-● clusters in the gas phase was studied by laser desorption ionization (LDI) and matrix assisted laser desorption ionization (MALDI) of solid WO₃. LDI produced (WO₃) _n ^{+ ●/- ●} (n = 1-7) clusters. In MALDI, when using nano-diamonds (NDs), graphene oxide (GO), or fullerene (C₆₀) matrices, higher mass clusters were generated. In addition to (WO₃) _n ^-● clusters, oxygen-rich or -deficient species were found in both LDI and MALDI (with the total number of clusters exceeding one hundred ≈ 137). This is the first time that such matrices have been used for the generation of(WO₃) _n ^+●/-● clusters in the gas phase, while new high mass clusters (WO₃) _n ^-● (n = 12-19) were also detected.

Open image in new window

Graphical Abstract

     

Synthesis and crystal structure of a 1D coordination polymer [Cd(NITpPy)<Subscript>2</Subscript>(N(CN)<Subscript>2</Subscript>)<Subscript>2</Subscript>)]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

A novel one-dimensional chain complex [Cd(NITpPy)₂(N(CN)₂)₂)] _n (NITpPy = 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) has been synthesized and characterized structurally. It crystallizes in the triclinic space group P \(\bar 1\) with a = 7.1742(13), b = 9.4913(17), c = 13.208(2) Å, α = 71.020(2)°, β=87.308(2)°, γ = 70.503(2)°, V = 799.8(3) ų, C₂₈H₃₂CdN₁₂O₄, Mr = 713.06, Z = 1, ρ _c = 1.48 g/cm³, μ(MoK _α) = 0.736 mm^?1, F(000) = 364, R = 0.0275 and wR = 0.0605 for 2702 observed reflections with I > 2σ(I). The crystal structure consists of infinite chains of [Cd(NITpPy)₂(N(CN)₂)₂)] units linked by dicyanamide anions [N(CN)₂]^?. Each Cd²⁺ ion is six-coordinated with the geometry of a distorted octahedron.     

New polymorph of CaHPO<Subscript>4</Subscript> (monetite): synthesis and crystal structure

A novel form of anhydrous dicalcium phosphate CaHPO₄ (monetite) is synthesized hydrothermally and characterized by single crystal X-ray diffraction. It crystallizes in the orthorhombic space group Ccm2₁ with a = 6.242(1) Å, b = 6.994(2) Å, c = 7.003(3) Å, V = 305.73(16) ų and it has four independent unit formulas in the unit cell (Z = 4). A three-dimensional crystal structure can be described by {HPO₄}_n infinite zigzag chains linked by Ca–O bonds. The comparison to the crystal structures of other polymorphs is given.     

Synthesis and crystal structure of (<Emphasis Type="Italic">o</Emphasis>-Diaminobenzene)<Subscript>2</Subscript> Zn(OAc)<Subscript>2</Subscript>

The treatment of o-diaminobenzene with Zn ( OAc )₂ · 2H₂O in alcohol results in the formation of mononuclear bis(o-diaminobenzene)diacetate Zinc, Zn[C₈H₁₁N₂O₂]₂. Its structure was determined by X-ray diffraction analysis. The complex is also characterized by elemental analysis, ¹H NMR and IR. The crystal is monoclinic space group C2, parameters: a = 16.297(5), b = 4.775(3), c = 11.664(5) Å, β = 97.646(5)°, λ = 1.54184 Å, V = 899.6(7) ų, Z = 2, ρ _c = 1.476 g/cm³, M _r = 399.75, F(000) = 416.0, R ₁ = 0.0594, wR ₂ = 0.1439 for 995 observed reflections with I > 2σ(I).     

Three- and four-coordinated silver(I) ions in the coordination polymers [Ag(Me<Subscript>4</Subscript>Pyz)<Subscript>2</Subscript>]PF<Subscript>6</Subscript> and [Ag(2,3-Et<Subscript>2</Subscript>Pyz)<Subscript>2</Subscript>]PF<Subscript>6</Subscript>

The coordination polymers [AgPF₆(Me₄Pyz)₂] (I) and [AgPF₆(2,3-Et₂Pyz)₂] (II) were synthesized, and their structures were determined. Crystals of I are monoclinic, space group C2/c, a = 10.213(2) Å, b = 16.267(3) Å, c = 12.663(3) Å, β = 92.90(3)°, V = 2102.1(7) ų, ρ_calcd = 1.660 g/cm³, Z = 4. The structure of I is built of polymeric zigzag [Ag(C₈H₁₂N₂)] _∞ ⁺ chains and octahedral [PF₆] anions. The coordination polyhedron of the Ag⁺ ion is a flat triangle. Crystals of II are tetragonal, space group P \(\bar 4\)2(1)/c,a = b = 10.641(1) Å, c = 18.942(1) Å, V = 2144.6(2) ų, ρ_calcd = 1.627 g/cm³, Z = 4. In the structure of II, 2D cationic layers of fused square rings exist; the rings consist of four Ag⁺ cations linked by four bridging ligands of diethylpyrazine Et₂Pyz. The coordination polyhedron of the Ag⁺ ion is an irregular four-vertex polyhedron.