Homonuclear Compounds Research Articles

Lanthanide-Based Coordination Polymers Molecular Alloys Stability: A Thermochemical Approach

In this study, we investigate the thermodynamics of lanthanide-based coordination polymer molecular alloys. We demonstrate that if lanthanide ions have many chemical similarities, the solubility of homo-lanthanide-based coordination polymers can vary significantly from one lanthanide ion to another. Indeed, we experimentally determine the solubility constants of a series of isostructural homo-lanthanide coordination polymers, with general chemical formula [Ln2(bdc)3(H2O)4]∞ with Ln = La-Er plus Y and where bdc2- symbolizes 1,4-benzene-di-carboxylate. Then, we extend the study to two series of isostructural molecular alloys with general chemical formula [Ln2xLn'2-2x(bdc)3(H2O)4]∞ with 0 ≤ x ≤ 1 based either on heavy ([Eu2xTb2-2x(bdc)3(H2O)4]∞) or light ( [Nd2xSm2-2x(bdc)3(H2O)4]∞) lanthanide ions. We found that whatever the solubility difference of the homo-nuclear compounds is, the configurational entropy is the main driving force of the stabilization of molecular alloys.

Description of covalent bond in terms of generalized charges: potential and dissociation energy of homonuclear compound

The theory of generalized charges is an asymptotic approximation of quantum mechanics for interatomic forces. It is based on the model of multicomponent electron gas, which extends the Thomas–Fermi model of inhomogeneous electron gas to pair electronic states. The present research takes in consideration the participation of the field of generalized charges in interatomic bonds. Herein, the definition of generalized charges (GC) by means of the overlap integral of the wave functions of valence electrons is given, and properties of GC are found out. Equations are derived for the potential and length of a homopolar bond, and dependence of these parameters on the generalized charges is shown. The dissociation energy of a diatomic molecule is expressed in terms of the nuclear charges, the function and multiplicity of the covalent bond, the angular momentum, and the vibrational energy of the binding electrons. The parametrization rules are substantiated and an a priori calculation of the dissociation energy of diatomic homonuclear molecules is carried out against the electronic configuration of the bond electrons and the nuclear charge. The calculation results for homonuclear compounds of the elements of the first four rows of the periodic table are shown to be of satisfactory accuracy.

The ratio of chemical bond components in metals and nonmetals and their classification into conductors, semiconductors and dielectrics

The article considers the influence of chemical bond components (covalent character CC, metallic character CM and ionic character CI, in %) in homo- and heteronuclear substances and materials on their classification into classes of electrical conductivity: conductors, semiconductors and dielectrics. Consideration of the influence of the chemical bond type (via CC, CM, CI) on the nature of the electrical conductivity properties of homo- and hetero compounds and respective materials showed the influence of all three components of the chemical bond on it. As a result, it became possible to classify homonuclear compounds of elements by electrical properties into three groups of materials: conductors - CC < CM; semiconductors - CC ≍ or > CM; dielectrics - CC > CM. A good correlation of the ratio of these components with the values of their electrical resistivity, the width of the band gap and the type of conductivity was established. It was found that the increase in electrical conductivity in heteronuclear binary materials, in general, is determined by the growth of CM.

Lanthanide-Based Coordination Polymers with a 4,5-Dichlorophthalate Ligand Exhibiting Highly Tunable Luminescence: Toward Luminescent Bar Codes.

Reactions in water of 4,5-dichlorophthalate (dcpa2-) with the heaviest lanthanide ions lead to a family of compounds with the general chemical formula [Ln2(dcpa)3(H2O)5·3H2O]∞, where Ln = Tb-Lu, Y. The synthesis, crystal structure, thermal behavior, and luminescent properties of this series of homonuclear compounds are described. Additionally, this family can be extended to isostructural heteronuclear compounds that can contain some light lanthanide ions and therefore present some original photophysical properties. These compounds show potential interest as multiemissive materials (visible and infrared light between 450 and 1600 nm) and could find application as luminescent bar codes.

Influence of Photoinduced Electron Transfer on Lanthanide-Based Coordination Polymer Luminescence: A Comparison between Two Pseudoisoreticular Molecular Networks

The luminescent properties of two families of heteronuclear lanthanide-containing coordination polymers are compared. These families have general chemical formulas [Ln2-2xLn'2x(ip)3(H2O)9·6H2O]∞ and [Ln2-2xLn'2x(aip)2(H2O)10·(aip)·4H2O]∞ where H2ip and H2aip stand for isophthalic acid and 5-amino-isophthalic acid, respectively, and where Ln and Ln' are one of the lanthanide ions between Sm(3+) and Dy(3+). Heteronuclear compounds that belong to each family are isostructural to the already reported homonuclear compounds [Gd2(ip)3(H2O)9·6H2O]∞ and [Eu2(aip)2(H2O)10·(aip)·4H2O]∞, respectively. These two crystal structures are very similar. However, despite similar chemical formulas, similar crystal structures, and similar hydration rates, these two families of compounds present very different luminescent properties that have thus been deeply investigated. This study demonstrates that these different optical behaviors can be attributed to the presence of a PET (photoinduced electron transfer) mechanism that is only present in the amino-isophthalate-containing coordination polymers.

Structure of the La12GdEuB6Ge2O34 borogermanate as probed by NMR and IR spectroscopy

The structure of fine crystalline borogermanate La12GdEuB6Ge2O34 has been studied by NMR and IR spectroscopy. It has been demonstrated that this compound is isostructural to the homonuclear Ln14B6Ge2O34 compounds (Ln = Pr-Gd) and crystallizes in space group P31. The rare-earth elements have been distributed over the LnOn polyhedra in La12GdEuB6Ge2O34 by analogy with the known structures. Lanthanum can occupy positions with CN 7–10, and the symmetry of these LnOn coordination polyhedra is not higher than C2v. In the La12GdEuB6Ge2O34 structure, the LnOn coordination polyhedra are formed by oxygen atoms of oxo groups and anions, some of the oxygen atoms being shared by LnOn polyhedra. The BO3 and GeO4 groups in the structure are also bridging, i.e., are involved in bonding of LnOn polyhedra. One of the B-O bonds in La12EuGd(BO3)6(GeO4)2O8 is elongated as compared with the B-O bond lengths in homonuclear compounds Pr14(BO3)6(GeO4)2O8 and Nd14(BO3)6(GeO4)2O8. In the La12GdEuB6Ge2O34 structure, germanium is located in isolated GeO4 tetrahedra with distorted Td symmetry. The local symmetry of lanthanum in fine crystalline La12GdEuB6Ge2O34 have been assessed using 139La NMR (B0 = 7.04 T, room temperature). For comparison, binary lanthanum compounds with a simpler structure— LaBO3, La(BO2)3, and La2GeO5—have been used. The spectra of all compounds are rather broad (ν1/2 = 180–240 kHz). The 139La NMR spectra of the LaBO3, La(BO2)3, and La12GdEu(BO3)6(GeO4)2O8 borates show a signal at (1080 ± 40) ppm, which is absent in the spectrum of La2GeO5. The shape of the 139La NMR spectra of La12GdEu(BO3)6(GeO4)2O8 and LaBO3 is characterized by the second-order quadrupole splitting with a downfield shoulder. The similarity of these spectra points to close 139La NMR chemical shifts of La12GdEu(BO3)6(GeO4)2O8 and LaBO3. No quadrupole splitting was observed in the spectra of La(BO2)3 and La2GeO5.

Iónico, covalente y metálico

This study presents the history of the conceptual development of a model which integrates and distinguishes three types of primary bonds. A triangle is obtained by plotting two of any different variables of the electronegativity for binary compounds. This allows the segregation of the well defined ionic, covalent and metallic compounds into three regions. The aims of this work are: 1. To popularize the model and to encourage its use among the students; 2. To display its advantages and limits; 3. To infer the impact of the model on: a) The classification of the compounds primarily covalent, ionic and metallic; b) The concept of the intermediate bonding between covalent and metallic for homonuclear compounds and among covalent, ionic and metallic for heteronuclear ones, and c) The definition of a criterion to divide between ionic and covalent compounds.

The Electronic Structure of Inorganic Benzenes: Valence Bond and Ring-Current Descriptions

Valence bond (VB) theory and ring-current maps have been used to study the electronic structure of inorganic benzene analogues X(6)H(6) (X = C (1), Si (2)), X(6) (X = N (3), P (4)), X(3)Y(3)H(6) (X,Y = B,N (5), B,P (6), Al,N (7), Al,P (8)), and B(3)Y(3)H(3) (Y = O (9), S (10)). It is shown that the homonuclear compounds possess benzene-like character, with resonance between two Kekulé-like structures and induced diatropic ring currents. Heteronuclear compounds typically show localization of the lone pairs on the electronegative atoms; Kekulé-like structures do not contribute. Of the heteronuclear compounds, only B(3)P(3)H(6) (6) has some benzene-like features with a significant contribution of two Kekulé-like structures to its VB wave function, an appreciable resonance energy, and a discernible diatropic ring current in planar geometry. However, relaxation of 6 to the optimal nonplanar chair conformation is accompanied by the onset of localization of the ring current.

Hydrogen Shift Isomerization Study of Doubly Bonded Compounds between Heavy Group 15 Elements HXYH (X,Y = As, Sb, and Bi)

The lowest singlet and triplet potential energy surfaces of H-shift isomerization for HXYH (X,Y = As, Sb, and Bi) systems have been explored through ab initio calculations. The geometries of the various isomers were determined at the QCISD/LANL2DZdp level of theory and confirmed to be minima by vibrational analysis. Our model calculations indicate that the range of π-bond strength is 12−20 kcal/mol, as indicated by the singlet−triplet gap of the HXYH molecules. The hydrogen-shifted isomers H2XY in the singlet state are considerably unstable than the singlet-state parent isomers by 24−49 kcal/mol. The triplet isomers are comparable in stability with respect to the parent singlet molecules, HXYH, within 3 kcal/mol for X lighter than Y. The gap increases to 8 kcal/mol for the homonuclear compounds with X = Y. It increases further to 17 kcal/mol for X heavier than Y.

Isostructural cobalt(II) and zinc(II) complexes of the N, N-bis(carboxymethyl)-β-alaninato(3−) ion. Crystal structure of the cobalt(II) derivative, [Co(H 2O) 6][Co 2L 2(H 2O) 2]·4H 2O

Homonuclear compounds [M(H 2O) 6[M 2L 2(H 2O) 2]·4H 2O (M(II)Co(II) or Zn(II), L 3−=anion of N, N-bis(carboxymethyl)-β-alanine or ((2-carboxyethyl)imino)diacetic acid) have been synthesized and characterized by chemical analysis, magnetic susceptibility data and/or IR spectra, thermal analysis and X-ray diffraction method. They are isostructural and crystallize in the triclinic system, space group P 1 with Z=1. The crystal structure was determined for the cobalt(II) compound ( a=8.732(7)- b=9.751(6), c=9.918(5) Å, α=99.96(4), β=110.88(5), γ=103.79(5), V=734.6Å 3, D meas=1.80 g cm −3, D exp=1.80 g cm −3,μ=1.767 mm − (MoKα)). Final R=0.034 and R w=0.043 for 3145 independent observed reflections. This compound consists of both centrosymmetric hexaaquocobalt(II) cations (Co(1)-OW(1)=2.046(2), (Co(1)-OW(2)=2.077(2), Co(1)-OW(3)=2.119(2) Å) and anions [Co 2L 2(H 2 O) 2] 2−, and non-coordinated water molecules. In the homodinuclear chelate anions, each cobalt(II) atom is bonded to one water molecule (Co( 2)-OW(4)=2.098(2) Å) and one tetradentate chelating ligand L 3− (Co(2)−N=2.134(2), Co(2)−O(5)=2.113(2), Co(2)−O(13)=2.081 (2), Co(2)-O(23)=2.101(2) Å). The dimer has an imposed C i symmetry. One carboxylate oxygen atom from the β-alanine arm acts as a bridge between the two cobalt atoms so completing the octahedral coordination of cobalt. The values of the distances Co(2)−Co(2 i) and the angle at the oxygen atom Co(2)−O(5)−Co(2 i) are 3.2934(7) Å and 103.5(1) o respectively.

ChemInform Abstract: Macrocyclic Complexes with Lanthanoid Salts. Part 38. Synthesis and Luminescence Study of Homo‐ and Heterobinuclear Complexes of Lanthanoids with a New Cyclic Compartmental Schiff Base.

AbstractThe complexes (IV) are obtained by an in situ procedure outlined in the scheme for the homonuclear compounds (IVa).

Infrared spectroscopic studies on metal carbonyl compounds. XX. Assignment in the CO stretching region of the binuclear mixed carbonyl compound MnRe(CO) 10; force and interaction constants calculation by a parametric rotational method

The infrared spectrum and complete assignment of the reinvestigated mixed carbonyl MnRe(CO) 10, in the CO stretching region is reported, with special emphasis on the weak isotopic bands. The frequencies and assignment are compared with those of the homo-nuclear compounds M2(CO) 10 (M = Mn, Tc and Re) 3. The force and interaction constants have been calculated in a CO factored force field by a parametric rotational method 4 applied for the presence of a species of fourth order, with the introduction of constraints in the eigenvector matrix.