Thermochemistry of adducts of some bivalent transition metal bromides with aniline

The compounds [MBr₂(an)₂] (where M is Mn(II), Fe(II), Co(II), Ni(II), Cu(II) or Zn(II); an = aniline) were synthesized and characterized by melting points, elemental analysis, thermal studies, and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and aniline in methanol, aqueous 1.2 M HCl or 25% (v/v) aqueous 1.2 M HCl in methanol were measured. The following thermochemical parameters for the adducts have been determined by thermochemical cycles: the standard enthalpies for the Lewis acid/base reactions (Δ_rH°), the standard enthalpies of formation (Δ_fH°), the standard enthalpies of decomposition (Δ_DH°), the lattice standard enthalpies (Δ_MH°) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH°(g)). The mean bond dissociation enthalpies of the M(II)-nitrogen bonds () and the enthalpies of formation of the adducts from the ions in the gaseous phase: M²⁺_(g) + Br⁻_(g) + an_(g) → [MBr₂(an)₂]_(g), (Δ_fiH°) have been estimated.     

Thermochemistry of adducts of some bivalent transition metal bromides with pyridine

The compounds [MBr₂(py)₂] (where M is Mn(II), Co(II), Ni(II), Cu(II) or Zn(II); py = pyridine) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyridine in 25% (v/v) 1.2 M aqueous HCl in methanol were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH^θ), the standard enthalpies of formation (Δ_fH^θ), the standard enthalpies of decomposition (Δ_DH^θ), the lattice standard enthalpies (Δ_MH^θ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH^θ(g)). The mean bond dissociation enthalpies of the M(II)-nitrogen bonds have been estimated as well as the enthalpies of the adducts formation in the gaseous phase.     

Layered hybrid organic-inorganic Co(II) alkylphosphonates. Synthesis, crystal structure and magnetism of the first two members of the series: Co[(CH3PO3)(H2O)] and Co[(C2H5PO3)(H2O)]

Co[(CH₃PO₃)(H₂O)] (1) and Co[(C₂H₅PO₃)(H₂O)] (2) were prepared by the hydrothermal method and isolated as blue-violet platelet crystals. They were characterized by X-ray diffraction, FT-IR, TGA-DSC techniques and their magnetic properties studied by a dc-SQUID magnetometer. Compound (1) shows an hybrid layered structure, made of alternating inorganic and organic layers along the a-direction of the unit cell. The inorganic layers contain Co(II) ions six-coordinated by five phosphonate oxygen atoms and one from the water molecule. These layers are separated by bi-layers of methyl groups and van der Waals contacts are established between them. In compound (2), the layered hybrid structure is rather similar to that described for compound (1), but the alternation of the inorganic and organic layers is along the b-direction of the unit cell. The magnetic behavior of (1) and (2) as function of temperature and magnetic field was studied. The compounds obey the Curie-Weiss law at temperatures above 100 K, the Curie C, and Weiss θ constants for the methyl derivative being and and for the ethyl derivative and , respectively. The observed magnetic moments for Co atom at room temperature (i.e. μ_eff=5.18 and 5.38 BM, respectively) are higher than those expected for a spin-only value for high spin Co(II) (S=3/2), revealing a substantial orbital contribution to the magnetic moment. The negative values of θ are an indication of the presence of antiferromagnetic exchange couplings between the near-neighbors Co(II) ions, within the layers. [Co(C_nH_2n+1PO₃)(H₂O)] (n=1,2) are 2D Ising antiferromagnets at low temperatures.     

Thermochemistry of adducts of some bivalent transition metal bromides with 4-chloroaniline

The compounds [MBr₂(p-clan)₂] (where M is Mn(II), Fe(II), Co(II), Ni(II), Cu(II) or Zn(II); p-clan = 4-chloroaniline) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of solution of the adducts, metal(II) bromides and 4-chloroaniline in methanol, 1.2 M aqueous HCl or 25% (v/v) 1.2 M aqueous HCl in methanol were measures and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH°), the standard enthalpies of formation (Δ_fH°), the standard enthalpies of decomposition (Δ_DH°), the lattice standard enthalpies (Δ_MH°) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH°(g)). The mean bond dissociation enthalpies of the metal(II)-nitrogen coordinated bonds and the enthalpies of adduct formation in the gaseous phase have been estimated.     

Standard molar enthalpies of formation of Ln(C9H6NO)2(C2H3O2) (Ln: Nd, Sm)

Using an on-line solution-reaction isoperibol calorimeter, the standard molar enthalpies of reaction for the general thermochemical reaction: LnCl₃·6H₂O(s) + 2C₉H₇NO(s) + CH₃COONa(s) = Ln(C₉H₆NO)₂(C₂H₃O₂)(s) + NaCl(s) + 2HCl(g) + 6H₂O(l) (Ln: Nd, Sm), were determined at T=298.15 K, as  kJ mol^−l, respectively. From the mentioned standard molar enthalpies of reaction and other auxiliary thermodynamic quantities, the standard molar enthalpies of formation of Ln(C₉H₆NO)₂(C₂H₃O₂)(s) (Ln: Nd, Sm), at T=298.15 K, have been derived to be: −(1494.7±3.3) and −(1501.5±3.4) kJ mol^−l, respectively.     

U(IV)/LN(III) unexpected mixed site in polymetallic oxalato complexes. Part II. Substitution of U(IV) for Ln(III) in the new oxalates (N2H5)Ln(C2O4)2·nH2O (Ln=Nd, Gd)

Two new hydrazinium lanthanide(III) oxalates, (N₂H₅)[Nd(C₂O₄)₂(H₂O)]·4H₂O (1) and (N₂H₅)[Gd(C₂O₄)₂(H₂O)]·4.5H₂O (2) have been prepared and their crystal structures determined by single-crystal X-ray diffraction. The crystal structures were solved by the direct methods and Fourier difference techniques, and refined by a least-squares method on the basis of F² for all unique reflections. Crystallographic data: 1, triclinic, space group , , b=9.762(4), , α=62.378(5), β=76.681(5), γ=73.858(5), Z=2, R₁=0.0335 for 172 parameters with 3430 reflections with I?2σ(I); 2, triclinic, space group , , b=9.51(3), , α=62.11(4), β=76.15(5), γ=73.73(5), Z=2, R₁=0.0325 for 172 parameters with 1742 reflections with I?2σ(I). The two isotypic structures are built from a three-dimensional (3D) arrangement of lanthanide and oxalate ions. The lanthanide atom is coordinated by eight oxygen atoms from four tetradentate oxalate ions and one aqua oxygen. Alternating lanthanide and oxalate ions form six-membered rings that delimit tunnels running down three directions and occupied by hydrazinium and water molecules. Starting from these lanthanide(III) compounds two isotypic mixed Ln(III)/U(IV) oxalates, (N₂H₅)_0.75[Nd_0.75U_0.25(C₂O₄)₂(H₂O)]·4.5H₂O (3) and (N₂H₅)_0.75[Gd_0.75U_0.25(C₂O₄)₂(H₂O)]·4H₂O (4), are obtained by partial substitution of Ln(III) by U(IV) in the nine-coordinated site, the charge excess being compensated by removal of monovalent ions from the tunnels. Finally, using Na⁺ gel, two mixed Ln(III)/U(IV) sodium oxalates, Na_0.5[Nd_0.5U_0.5(C₂O₄)₂(H₂O)]·3H₂O (5) and Na_0.65[Gd_0.65U_0.35(C₂O₄)₂(H₂O)]·4.5H₂O (6) have been obtained without any change in the 3D framework.     

Thermochemical study of two anhydrous polymorphs of caffeine

The mean values of the standard massic energy of combustion of caffeine in phase I (or alpha) and in phase II (or beta) measured by static-bomb combustion calorimetry in oxygen, at T = 298.15 K, are Δ_cu^° (C₈H₁₀O₂N₄, I) = −(21823.27 ± 0.68) J · g⁻¹ and Δ_cu^° (C₈H₁₀O₂N₄, II) = −(21799.96 ± 1.08) J · g⁻¹, respectively.The standard (p^° = 0.1 MPa) molar enthalpy of formation in condensed phase for each form was derived from the corresponding standard molar enthalpies of combustion as, and .The difference between the standard enthalpy of formation of the two polymorphs in condensed phase was also evaluated by using reaction-solution calorimetry. The obtained result, 2.04 ± 0.25 kJ · mol⁻¹, is in agreement, within the uncertainty, with the difference between the molar enthalpies of formation obtained from combustion experiments (4.5 ± 3.2) kJ · mol⁻¹, which can be considered as an internal test for consistency of the results.A value for the standard enthalpy of formation of caffeine in the gaseous state was proposed: , estimated from the values of the standard enthalpies of formation of both crystalline forms obtained in this work, and the data on standard enthalpies of sublimation collected from the literature.     

Solvothermal synthesis of new metal organic framework structures in the zinc-terephthalic acid-dimethyl formamide system

Two new metal organic framework (MOF) structures have been obtained from the Zn-terephthalic acid (H₂BDC)-dimethyl formamide (DMF) system and examined by single-crystal X-ray diffraction: Zn(C₈H₄O₄)(C₃H₇NO), 1, monoclinic C2/m, a=11.1369(5), b=14.0217(7), , β=106.316(1)°, , , Z=4, R₁=0.060, wR₂=0.169, S=1.27; Zn(HCO₂)₃(C₂H₈N), 2, trigonal , a=8.1818(1), , , , Z=6, R₁=0.014, wR₂=0.039, S=1.11. Contrary to previously published structures in the same system, the crystals were obtained by solvothermal synthesis at 381 K. Structure 1 consists of 2-D layers stacked in an offset manner to accommodate DMF moieties coordinated to Zn²⁺ within voids in adjacent layers. Structure 2 consists of a 3-D network constructed from Zn²⁺ ions bridged by deprotonated formic acid moieties. Over time, the structure of 1 rearranges to Zn(C₈H₄O₄)(C₃H₇NO)(H₂O) [monoclinic P2₁/n, a=6.6456(2), b=15.2232(5), , β=104.110(2)°, , , Z=4, R₁=0.048, wR₂=0.100, S=1.07], which is identical to the known MOF-2 structure, obtained by crystallization at ambient conditions. The three structures were determined from crystals with similar crystal habits picked from a single solvothermal synthesis batch. The study demonstrates that MOF syntheses can give not only multiple crystal structures under different conditions, but also that numerous different structures, including some that are metastable, can be formed under identical conditions.     

Cu(II) complex of an abiotic receptor as highly selective fluorescent sensor for acetate

A copper complex having quinoline moiety as fluorophore has been synthesized. The anion recognition behavior of the receptor and its copper complex has been studied in acetonitrile and in acetonitrile: H₂O (95:5 v/v). The copper complex shows high selectivity toward acetate over other anions studied such as F⁻, Cl⁻, Br⁻, I⁻, OAc⁻, dl-malate, l-mandelate, benzoate, isophthalate, , and .     

Thermochemistry of some adducts of Indium(III) chloride with neutral donors

The [InCl₃(L) _n ] (where L is 2,2′-bipyridine (bipy), 2,2′-bipyridine N,N′-dioxide (bipyNO), N,N-dimethylacetamide (dma), urea (u), thiourea (tu) or 1,1,3,3-tetramethylthiourea (tmtu); n = 1.5, 3 or 4) were synthesized and characterized by melting points, elemental analysis, thermal analysis and IR spectroscopy. The enthalpies of dissolution of the adducts, Indium(III) chloride and ligands in 1.2 M aqueous HCl were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_r H ^θ), the standard enthalpies of formation (Δ_f H ^θ), the lattice standard enthalpies (Δ_M H ^θ), and the standard enthalpies of decomposition (Δ_D H ^θ).     

Solvothermal synthesis, crystal structure, magnetic and luminescent properties of (H3O)6·[Co4(H2O)4(HPMIDA)2(PMIDA)2)]·2H2O

A cobalt phosphonate (H₃O)₆·[Co₄(H₂O)₄(HPMIDA)₂(PMIDA)₂)]·2H₂O, 1, has been synthesized from a mild solvothermal reaction of Co(II) ion with N-(phosphonomethyl)iminodiacetic acid (H₄PMIDA). Compound 1 crystallizes in the triclinic space group with cell parameters of , , , α=93.06(3)°, β=99.66(3)°, γ=90.34(3)° and Z=1. Compound 1 shows a novel tetra-nuclear molecular structure. In the crystal lattice, molecules of 1 hydrogen bond to each other to form two-dimensional (2D) layers, which are further linked together by the co-crystallized H₂O molecules and H₃O⁺ counter ions through hydrogen bonding to form the 3D supramolecular network. Thermogravimetric analysis, IR spectrum, magnetic susceptibility and luminescent spectra are given.     

Cu(II) complex of a flexible tripodal receptor as a highly selective fluorescent probe for iodide

A Cu(II) complex of a tripodal receptor bearing an anthracene moiety on one pod as a fluorophore was synthesized. The anion recognition behavior of the Cu(II) complex was evaluated in CH₃CN/H₂O (95:5, v/v), resulting in an extremely high selectivity for iodide over other anions such as F⁻, Cl⁻, Br⁻, , CH₃COO⁻, and . The Cu(II) complex acts as a selective probe for estimating iodide even in the presence of other anions without any interference.