phosphate hydrate complexes of singly and doubly charged magnesium ions: Structure,energies, and spin states

For mixed magnesium phosphate hydrate complexes containing Mg²⁺ and Mg⁺ cations and HPO₄²⁻, HPO₄⁻, and H₂P₂O₇²⁻ anions, theoretical analysis of the electronic structure and energies has been performed at the model level in order to predict the actual role of these systems in various reactions that occur in the catalytic sites of ATP synthesizing enzymes. The calculations (DFT/B3LYP, MP2 with the 6–31G* basis set) of isolated aqua complexes Mg(H₂O) _n ^p (n = 1−6, p = 0, +1, +2) show that their relative stability monotonically increases with increasing n in each series and sharply decreases at a given n in going from the charged systems of Mg²⁺ (4–16 eV) and Mg⁺ (2–7 eV) to the neutral systems of Mg (<2 eV). An even higher stability is predicted for mixed magnesium complexes. The energies of fragmentation of mixed Mg²⁺ complexes into singlet phosphate and Mg²⁺-containing fragments at n = 0–4 are within 6–27 eV, and the energies of fragmentation into the corresponding radical ions are within 3–10 eV; for the Mg⁺ complexes, the fragmentation energies are also high (6–14 eV). The reasons for the enhanced stability of the complexes of both types have been analyzed with allowance for the predicted specific features of the electron density redistribution upon complex formation. Typical changes in the geometry of the P- and Mg-containing fragments caused by formation of mixed complexes have been discussed in the framework of the vibronic model of heteroligand systems. The high stability of all mixed magnesium complexes relative to various fragmentation products presumably rules out any dissociative processes in them in the course of ATP synthesis with the participation of phosphorylating enzymes.     

Understanding Stability Trends along the Lanthanide Series

The stability trends across the lanthanide series of complexes with the polyaminocarboxylate ligands TETA^4? (H₄TETA=2,2′,2′′,2′′′‐(1,4,8,11‐tetraazacyclotetradecane‐1,4,8,11‐tetrayl)tetraacetic acid), BCAED^4? (H₄BCAED=2,2′,2′′,2′′′‐{[(1,4‐diazepane‐1,4‐diyl)bis(ethane‐2,1‐diyl)]bis(azanetriyl)}tetraacetic acid), and BP18C6^2? (H₂BP18C6=6,6′‐[(1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane‐7,16‐diyl)bis(methylene)]dipicolinic acid) were investigated using DFT calculations. Geometry optimizations performed at the TPSSh/6‐31G(d,p) level, and using a 46+4fⁿ ECP for lanthanides, provide bond lengths of the metal coordination environments in good agreement with the experimental values observed in the X‐ray structures. The contractions of the Ln³⁺ coordination spheres follow quadratic trends, as observed previously for different isostructural series of complexes. We show here that the parameters obtained from the quantitative analysis of these data can be used to rationalize the observed stability trends across the 4f period. The stability trends along the lanthanide series were also evaluated by calculating the free energy for the reaction [La( L )]^n+/?_(sol)+Ln³⁺_(sol)→[Ln( L )]^n+/?_(sol)+La³⁺_(sol). A parameterization of the Ln³⁺ radii was performed by minimizing the differences between experimental and calculated standard hydration free energies. The calculated stability trends are in good agreement with the experimental stability constants, which increase markedly across the series for BCAED^4? complexes, increase smoothly for the TETA^4? analogues, and decrease in the case of BP18C6^2? complexes. The resulting stability trend is the result of a subtle balance between the increased binding energies of the ligand across the lanthanide series, which contribute to an increasing complex stability, and the increase in the absolute values of hydration energies along the 4f period.     

Synthesis,crystal structures,fluorescence, electrochemiluminescent properties,and Hirshfeld surface analysis of four Cu/Mn Schiff-basecomplexes

Four new complexes [Cu(L¹)₂]_n ( 1 ), [Mn(L¹)₂]_n ( 2 ), [Cu(L²)₂]_n ( 3 ), [Mn(L²)₂]_n ( 4 , HL¹ = 2-(((4H-1,2,4-triazol-4-yl)imino)methyl)-4,6-dichlorophenol; HL ² = 2-(((4H-1,2,4-triazol-4-yl)imino)methyl)-4,6-dibromophenol) were synthesized by microreaction bottle method. Complexes 1 and 3 and 2 and 4 are isomorphous heterostructures having the same molecular structure. The structures of 1 – 4 were characterized using single X-ray diffraction, Fourier-transform infrared spectroscopy, powder X-ray diffraction, and thermogravimetric analysis, and their potential applications were analyzed by detecting their fluorescence and electrochemical luminescence (ECL). Hirshfeld surface analysis indicates that X···H (X = Br, Cl) interactions play a crucial role in stabilizing the self-assembly process of 1 – 4 , which show highly intense ECL in N,N-dimethylformamide solution and high thermal stability.     

Molecular modeling for Cu(II)‐aminopolycarboxylate complexes: Structures,conformational energies,and ligand binding affinities

A ligand field molecular mechanics (LFMM) force field (FF) has been developed for d⁹ copper(II) complexes of aminopolycarboxylate ligands. Training data were derived from density functional theory (DFT) geometry optimizations of 14 complexes comprising potentially hexadentate N₂O₄, tetrasubstituted ethylenediamine (ed), and propylenediamine cores with various combinations of acetate and propionate side arms. The FF was validated against 13 experimental structures from X‐ray crystallography including hexadentate N₂O₄ donors where the nitrogens donors are forced to be cis and bis‐tridentate ONO ligands which generate complexes with trans nitrogen donors. Stochastic conformational searches for [Cu{ed(acetate)_n (propionate)_4‐n}]^2?, n = 0–4, were carried out and the lowest conformers for each system reoptimized with DFT. In each case, both DFT and LFMM predict the same lowest‐energy conformer and the structures and energies of the higher‐energy conformers are also in satisfactory agreement. The relative interaction energies for n = 0, 2, and 4 computed by molecular mechanics correlate with the experimental log β binding affinities. Adding in the predicted log β values for n = 1 and 3 suggest for this set of complexes a monotonic decrease in log β as the number of propionate arms increases. © 2013 Wiley Periodicals, Inc.     

Einzentrum-Modellrechnungen an Germaniumhydriden vom Typ GeHn,GeH n + und GeH n − (n = 3,4 oder 5)

Zusammenfassung Nach der Einzentrummethode werden für eine Reihe von Germaniumwasserstoffverbindungen vom Typ GeH _n , GeH _n ⁺ und GeH _n ^– (n = 3, 4 oder 5) Wellenfunktion, geometrische Struktur, Energie des Molekülgrundzustandes und Bindungsabstände berechnet. Für das German-Molekül GeH₄ wird darüber hinaus die Bindungsenergie, die Ionisierungsenergie und die Protonenaffinität erstmals bestimmt.

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OCE-calculations on germanium hydrides of the type GeH_n, GeH _n ⁺ and GeH _n ^– (n = 3, 4 or 5)

OCE-Calculations are reported for molecular wavefunctions, molecular symmetries, ground state energies and bond distances of some germanium hydrides of the type GeH _n , GeH _n ⁺ and GeH _n ^– (n = 3, 4 or 5). Further on the binding energy, first ionization potential and proton affinity are obtained for GeH₄.

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Resume Par la méthode monocentrique, pour quelques hydrures de germanium du genre GeH _n GeH _n ⁺ et GeH _n ^– (n = 3,4 on 5) sent calculées la fonction d'onde, la structure moléculaire, l'énergie de l'état fondamental et les longueurs de liaison. Pour la molécule GeH₄ sent déterminés l'energie de liaison, le potential d'ionisation et l'affinité protonique la première fois.

     

A density functional theory study on boundary of “superreduced” transition metal carbonyl anions [M(CO)n](M=Cr, n=5, 4, 3, z=2, 4, 6; M=Mn, n=5, 4, 3, z=1, 3, 5; M=Fe, n=4, 3, 2, z=2, 4, 6; M=Co, n=4, 3, 2, z=1, 3, 5)

A nonlocal density functional theory (DFT) method has been applied to the calculations on optimized geometry, Mulliken atomic net charges and interatomic Mulliken bond orders as well as total bonding energies (E) in the binary transition metal carbonyl anions with different reduced states [M(CO)_n]^z− (M=Cr, n=5, 4, 3, z=2, 4, 6; M=Mn, n=5, 4, 3, z=1, 3, 5; M=Fe, n=4, 3, 2, z=2, 4, 6; M=Co, n=4, 3, 2, z=1, 3, 5). For comparison of relative stability, a relative stabilization energy D is defined as D=E([M(CO)_n]^z−)−nE(CO). The calculated C–O distances are lengthened monotonously with the increase of the anionic charge, but the M–C distances are significantly lengthened only in the higher reduced states. The relative stabilization energy calculated is a considerable negative value in the lower reduced states, but a larger positive value in the higher reduced states. The DFT calculations show that with the increase of the anionic charge, the Mulliken net charges on the M, C, and O atoms all increase, however, an excess of the anionic charge is mainly located at the central metal atom. The calculated C–O Mulliken bond orders decrease consistently with the increase of the anionic charge, but the M–C bond orders exhibit an irregular behavior. However, the total bond orders calculated clearly explain the higher reduced states to be considerably unstable. From analysis of the calculated results, it is deduced that the stability of the binary transition metal carbonyl anions [M(CO)_n]^z− studied are associated with the coordination number n and the anionic charge z, further, it is possible for the anions studied to be stable if n≥z, conversely, it is impossible when n<z.     

Formation of positive cluster ions LinBr (n = 2–7) and ionization energies studied by thermal ionization mass spectrometry

Clusters of the type Li_nX (X = halides) can be considered as potential building blocks of cluster‐assembly materials. In this work, Li_nBr (n = 2–7) clusters were obtained by a thermal ionization source of modified design and selected by a magnetic sector mass spectrometer. Positive ions of the Li_nBr (n = 4–7) cluster were detected for the first time. The order of ion intensities was Li₂Br⁺ > Li₄Br⁺ > Li₅Br⁺ > Li₆Br⁺ > Li₃Br⁺. The ionization energies (IEs) were measured and found to be 3.95 ± 0.20 eV for Li₂Br, 3.92 ± 0.20 eV for Li₃Br, 3.93 ± 0.20 eV for Li₄Br, 4.08 ± 0.20 eV for Li₅Br, 4.14 ± 0.20 eV for Li₆Br and 4.19 ± 0.20 eV for Li₇Br. All of these clusters have a much lower ionization potential than that of the lithium atom, so they belong to the superalkali class. The IEs of Li_nBr (n = 2–4) are slightly lower than those in the corresponding small Li_n or Li_nH clusters, whereas the IEs of Li_nBr are very similar to those of Li_n or Li_nH for n = 5 and 6. The thermal ionization source of modified design is an important means for simultaneously obtaining and measuring the IEs of Li_nBr (n = 2–7) clusters (because their ions are thermodynamically stable with respect to the loss of lithium atoms in the gas phase) and increasingly contributes toward the development of clusters for practical applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Metal–Nitrosyl complexes as a source of new vasodilators: Strategies derived from systematic chemistry and nitrosyl ligand reactivity

A series of nitrosyl complexes of empirical formula K_n[M(CN)₅NO], where M = V, Cr, Mn and Co and n = 3, or M = Mo and n = 4, have been prepared which are notional analogues of the widely used vasodilator sodium nitroprusside. Their reactivity towards common nucleophiles (OH^?, NH₂R, NHR₂, HS^? and RS^?), acid and photolysis has been investigated to elucidate the desired properties required of new metal nitrosyls which may have some potential as new non-cyanide-based vasodilators.     

Revisiting the structural and electronic properties of neutral,mono- and di-anionic titanium-doped silicon clusters TiSin0/−/2− (n = 6-16)

The systematic structures search for neutral and Zintl anionic Ti-doped silicon clusters TiSi_n^0/−/2− (n = 6-16) have been carried out using the ABCluster global search technique combined with a double-hybrid density functional method. Based on the predicted energies, adiabatic electron affinities, vertical detachment energies and the consistency between simulated and experimental photoelectron spectroscopy, the true global minimum structures are confirmed. The results show that structural growth pattern of neutral TiSi_n clusters is from linked structures (n = 10-12) to encapsulated configurations (n = 13-16). In contrast, the evolution pattern of Zintl anionic TiSi_n^−/2− clusters begins with the pentagonal bipyramid structure (n = 6). As the Si atoms increase, these Si atoms attach to the surface adjacent to Ti atom, and gradually surround Ti atom. Eventually, the encapsulated structure is formed when n = 12. Moreover, two extra electrons not only perfect the structure of TiSi₁₂ but also improve its chemical and thermodynamic stability.     

Quantum‐Chemical and Electrochemical Investigation of the Electrochemical Windows of Halogenated Carborate Anions

The range of electrochemical stability of a series of weakly coordinating halogenated (Hal=F, Cl, Br, I) 1‐carba‐closo‐dodecaborate anions, [1‐R‐CB₁₁X₅Y₆]^? (R=H, Me; X=H, Hal, Me; Y=Hal), has been established by using quantum chemical calculations and electrochemical methods. The structures of the neutral and dianionic radicals, as well as the anions, have been optimized by using DFT calculations at the PBE0/def2‐TZVPP level. The calculated structures are in good agreement with existing experimental data and with previous calculations. Their gas‐phase ionization energies and electron affinities were calculated based on their optimized structures and were compared with experimental (cyclic and square‐wave) voltammetry data. Electrochemical oxidation was performed in MeCN at room temperature and in liquid sulfur dioxide at lower temperatures. All of the anions show a very high resistance to the onset of oxidation (2.15–2.85 V versus Fc^0/+), with only a minor dependence of the oxidation potential on the different halogen substituents. In contrast, the reduction potentials in MeCN are strongly substituent dependent (?1.93 to ?3.32 V versus Fc^0/+). The calculated ionization energies and electron affinities correlate well with the experimental redox potentials, which provide important verification of the thermodynamic validity of the mostly irreversible redox processes that are observed for this series. The large electrochemical windows that are afforded by these anions indicate their suitability for electrochemical applications, for example, as supporting electrolytes.     

Redox potential of iron–sulfur clusters as a model of the Desulfovibrio vulgaris center

A theoretical study of Heisenberg exchange and double exchange effects in clusters with four and six iron ions has been performed for [Fe₄ S₃ O] ^m+, [Fe₄ S₄]^m+ (where m = 3, 2), and [Fe₆ S₆] ⁿ⁺ (where n = 5, 4) ions as models of the Desulfovibrio vulgaris iron–sulfur centers. Assuming that the redox potential mostly depends on the Heisenberg spin coupling and the resonance delocalization, we performed an analysis of the reduction process for the [Fe₄ S₃ O] ^3+/2+, [Fe₄ S₄] ^3+/2+, and [Fe₆ S₆] ^5+/4+ ions and showed that the redox potential can be calculated as a difference between average spin energies of the tetravalent and pentavalent double cubane superclusters. For the Heisenberg parameter of J₁ = 20 cm^-1, the redox potential amounts to about 0.03 V.It complies with close to zero experimental values of the redox potential.Electronic Supplementary Material: Supplementary material is available in the online version of this article at     

Study of small chlorine‐doped potassium clusters by thermal ionization mass spectrometry

The theoretical calculations have predicted that nonmetal‐doped potassium clusters can be used in the synthesis of a new class of charge‐transfer salts which can be considered as potential building blocks for the assembly of novel nanostructured material. In this work, K_nCl (n = 2–6) and K_nCl_n?1 (n = 3 and 4) clusters were produced by vaporization of a solid potassium chloride salt in a thermal ionization mass spectrometry. The ionization energies (IEs) were measured, and found to be 3.64 ± 0.20 eV for K₂Cl, 3.67 ± 0.20 eV for K₃Cl, 3.62 ± 0.20 eV for K₄Cl, 3.57 ± 0.20 eV for K₅Cl, 3.69 ± 0.20 eV for K₆Cl, 3.71 ± 0.20 eV for K₃Cl₂ and 3.72 ± 0.20 eV for K₄Cl₃. The K_nCl⁺ (n = 3–6) clusters were detected for the first time in a cluster beam generated by the thermal ionization source of modified design. Also, this work is the first to report experimentally obtained values of IEs for K_nCl⁺ (n = 3–6) and K_nCl_n?1⁺ (n = 3 and 4) clusters. The ionization energies for K_nCl⁺ and K_nCl_n?1⁺ clusters are much lower than the 4.34 eV of the potassium atom; hence, these clusters should be classified as ‘superalkali’ species. Copyright © 2012 John Wiley & Sons, Ltd.     

A DV-Xα study on the electronic structures of cubane-like iron-sulfur cluster compounds

The electronic structures of six cubane-like cluster compounds of the type [Fe₄S₄L₄]ⁿ (L = SH, OH, and Cl, n=-2 and ?3; L=NO, n = 0 and ?1) have been calculated by using DV-X_α method, and the bonding properties are discussed with emphasis on the ligand effect on cluster bonding. The comparisons of MO energies and cluster charge distributions with the experimental data are made, and the differences between the early studies and the present one are also briefly commented.     

Theoretical studies on structures and electronic spectra of linear carbon chains C2nH+ (n = 1−5)

The density functional theory (DFT) and the complete active space self‐consistent‐field (CASSCF) method have been used for full geometry optimization of carbon chains C_2nH⁺ (n = 1–5) in their ground states and selected excited states, respectively. Calculations show that C_2nH⁺ (n = 1–5) have stable linear structures with the ground state of X³Π for C₂H⁺ or X³Σ^? for other species. The excited‐state properties of C_2nH⁺ have been investigated by the multiconfigurational second‐order perturbation theory (CASPT2), and predicted vertical excitation energies show good agreement with the available experimental values. On the basis of our calculations, the unsolved observed bands in previous experiments have been interpreted. CASSCF/CASPT2 calculations also have been used to explore the vertical emission energy of selected low‐lying states in C_2nH⁺ (n = 1–5). Present results indicate that the predicted vertical excitation and emission energies of C_2nH⁺ have similar size dependences, and they gradually decrease as the chain size increases. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Structures and thermochemistry of ions formed by methane chemical ionization of Fe(CO)5. Site of protonation and determination of Fe?H and Fe?CO bond dissociation energies of HFe(CO)n+ ions

High-energy collisional activation mass spectrometry of HFe(CO)₅⁺ ions shows that Fe(CO)₅ is protonated on the iron atom rather than on one of the ligands. This finding is supported by ab initio quantum chemical calculations. The value of the proton affinity of Fe(CO)₅ was measured by high-pressure mass spectrometry to be 857 kJ mol^?1. The Fe? CO bond dissociation energies for HFe(CO)_n⁺ (n = 1–5) were measured by energy-variable low-energy collisional activation mass spectrometry. The Fe? H bond dissociation energies in HFe(CO)_n⁺ ions were also determined. A synergistic effect on the strengths of the Fe? H and Fe? CO bonds in HFe(CO)⁺ is noticed. It is demonstrated that the electronically unsaturated species HFe(CO)_n⁺ (n = 3, 4) formed in exothermic proton-transfer reactions with Fe(CO)₅ form adducts with CH₄. Adducts between C₂H₅⁺ or C₃H₅⁺ and Fe(CO)_n are observed. These adducts are probably formed in direct reactions between the respective carbocations and Fe(CO)₅.     

Structural stability and evolution of terbium-doped silicon clusters and influence of 4f → 5d electronic transition mechanism on magnetism and appearance of photoelectron spectroscopy for TbSin0/− (n = 6-18) clusters

The global minimal structures of terbium-doped Si clusters and their anions TbSi _n^0/− (n = 6-18) are confirmed by employing the ABCluster unbiased global search technique combined with a B2PLYP double-hybrid density functional and comparing consistency of simulated and experimental photoelectron spectroscopy (PES). The results demonstrated that structural evolution patterns for neutral clusters prefer Tb-substitutional to Tb-encapsulated configuration starting from n = 16. While for the corresponding anionic clusters, the growth pattern adopts Tb-linked structures to encapsulated motif. The Natural Population Analysis revealed that the 4f electrons of Tb atom in TbSi _n^0/− (n = 6-18) clusters participate in bonding. The way to participate in bonding is one 4f electron transition to 5d orbital ([Xe]6s²4f⁹ → [Xe]6s²4f⁸5d¹), which significantly affects the cluster's magnetism and appearance of PES. The total magnetic moments of neutral TbSi _n and the corresponding anions maintain at 7 μB and 6 μB, respectively, which are larger than that of an isolated Tb atom. The HOMO-LUMO energy gap, relative stability, and chemical bonding analysis demonstrated that superatomic TbSi₁₆⁻ cluster is a magic cluster with fine thermodynamic and moderate chemical stability.     

Energetic stability and electronic properties of exohedral derivatives of C20: C20Xn (X = H,F, Cl; n = 1–4)

Exohedral derivatives of the smallest fullerene, C₂₀, with the general formula of C₂₀X_n (X = H, F, Cl; n = 1–4) have been systematically investigated to evaluate the energetic stability of these molecular structures and determine their respective electronic properties. Analysis of the theoretical results indicate that the addition of exohedral atoms increase the stability of the caged‐structure to varying degrees according to the predicted HOMO‐LUMO gaps, ionization energies, and electron affinities. Further support for increasing stability is deduced from the calculated reaction and binding energies of the exohedral atoms. © 2012 Wiley Periodicals, Inc.     

Density functional study on highly energetic organic azides with empirical formula Cn(N3)m

The structural, electronic, and thermodynamical properties of C_n(N₃)_m (n = 1–7) (m = 4, 6) organic azides have been investigated using Density Functional Calculations. The ground state structures of organic azides were compared with C_nH_m (n = 1–7) (m = 4, 6) cumulenes which shows their higher relative stability. The stability and reactivity of organic azides were analyzed by calculating the HOMO-LUMO gap, binding energies, and harmonic frequencies of the azides. The binding energy and formation energy of C_n(N₃)_m (n = 1–7) (m = 4, 6) organic azides suggest their energetic stability. The structural analysis of the azide group in C_n(N₃)_m (n = 1–7) (m = 4, 6) organic azide shows a tendency to stabilize at a maximum separation between functional azide groups. Ionization potential, electron affinities, and global hardness have been computed for C_n(N₃)_m (n = 1–7) (m = 4, 6) organic azides and the odd–even alternation rule was observed. The molecular dynamic simulation performed at 300 K for 1 fs confirms organic azide's structural stability at room temperature, except for C₄(N₃)₄, and the members of their family can be synthesized.     

Modellrechnungen an einigen Siliziumwasserstoffverbindungen vom Typ SiHn,SiH n + und SiH n − nach der Einzentrenmethode

Zusammenfassung Es werden molekulare Struktur, Energie des Grundzustandes, Bindungsabstände, Bindungsenergie, Ionisierungsenergie und Protonenaffinität der Siliziumwasserstoffverbindungen SiH _n , SiH _n ⁺ und SiH_n ^– (n=3, 4 oder 5) nach der Einzentrenmethode berechnet.

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OCE-calculations on some silicon hydrides of the type SiH _n , SiH _n ⁺ and SiH _n ^–

OCE-Calculations are reported for molecular structures, ground state energies, bond distances, binding energies, ionization potentials and proton affinities of the silicon hydrides SiH _n , SiH _n ⁺ and SiH _n ^– (n=3, 4 or 5).

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Résumé Calcul par la méthode monocentrique de la structure moléculaire, de l'énergie de l'état fondamental, des longueurs de liaison, des énergies de liaison, des potentiels d'ionisation et des affinités protoniques pour les hydrures de silicium SiH _n , SiH _n ⁺ et SiH _n ^– (n=3, 4 ou 5).