Relationship between the thermally induced reorientations of aromatic solvate molecules in Cu(hfac)2-nitroxide breathing crystals and the character of the magnetic anomaly

A new group of "breathing" crystals has been synthesized. These are aromatic solvates of the copper(II) hexafluoroacetylacetonate complex with spin-labeled pyrazole Cu(hfac)(2)L·0.5Solv, where L is 2-(1-butyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl and Solv is benzene, toluene, ethylbenzene, propylbenzene, butylbenzene, styrene, o-xylene, m-xylene, p-xylene, 1,4-bis(trifluoromethyl)benzene, 1-methyl-4-ethylbenzene, 1-methyl-4-vinylbenzene, 1,4-diethylbenzene, 1,2,3-trimethylbenzene, or 1,2,4-trimethylbenzene. The main feature of Cu(hfac)(2)L·0.5Solv single crystals is their remarkable mechanical stability and ability to undergo thermally induced structural rearrangements accompanied by spin-crossover-like phenomena. The structures of Cu(hfac)(2)L·0.5Solv solvates are similar and based on mutually parallel {Cu(hfac)(2)L}(∞) heterospin chains with a "head-to-head" motif. The localization of voids with guest molecules being the same in all crystals, the temperature dependence of the effective magnetic moment (μ(eff)) for Cu(hfac)(2)L·0.5Solv is determined by the structure of the guest molecules, along which the polymer chains are "gliding" when the temperature changes. When the temperature decreased from 300 to 100-50 K, μ(eff) decreased, abruptly or gradually, from 2.7-2.4 to ~1.8 β for the majority of Cu(hfac)(2)L·0.5Solv except the solvates with benzene, toluene, and 1,4-bis(trifluoromethyl)benzene. When Cu(hfac)(2)L·0.5C(6)H(6) and Cu(hfac)(2)L·0.5CH(3)-C(6)H(5) were cooled to 50 K, μ(eff) decreased to ~2.1-2.2 β. When Cu(hfac)(2)L·0.5(1,4-(CF(3))(2)-C(6)H(4)) was cooled to 50 K, μ(eff) initially decreased from ~2.7 to 1.9 β and then abruptly increased to ~2.4 β. A single-crystal X-ray diffraction analysis of each solvate within a temperature range wider than the range of magnetic anomaly temperatures revealed a complex interrelated dynamics of the aromatic solvent guest molecules and heterospin chains. The dynamics largely depended on the orientation of the solvent guest molecules relative to the polymer chains. An analysis of the thermally induced phase transformations revealed a relationship between the structural rearrangement of Cu(hfac)(2)L·0.5Solv and the form of the magnetic anomaly on the μ(eff)(T) curve and between the structural rearrangement of the solvate and the temperature of the magnetic effect.     

Equilibrium Compositions of HF Solutions in <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylformamide

For HF solutions in DMF, concentration-dependent fractions of DMF molecules (α(DMF)) that remain unassociated and that enter heteroassociates (HAs) of 1 : 1, 4 : 1, and 12 : 1 molecular stoichiometries were obtained by two independent methods, namely, from an analysis of IR spectra and by calculating the material balance. The experimental way was shown to be enough exact in determining the ratio between the solvent molecules in four different states up to ~83 mol % HF. The equilibrium compositions of HF–DMF solutions were estimated over the entire range of concentrations. Starting with [HF] of ~25 mol %, more than one-half HF molecules are associated, and at [HF] of ~50–92 mol %, at least 90% of the HF molecules are associated. The equilibrium composition of HF–organic solvent (Solv) solutions in which HAs of 1 : 1, 1 : 4, and 1 : 12 molecular stoichiometries are formed, can be described by a single set of α(HF–Solv) versus concentration plots.     

Composition of heteroassociates formed in a binary liquid system HF-Et<Subscript>2</Subscript>O

IR spectra and densities of solutions in a binary liquid system (BLS) HF-Et₂O were measured for the first time for the molar ratios of the components ranging from 1: 12 to 14: 1 and 31: 1, respectively. An analysis of the concentration dependences of the normalized (to the total number of moles of the BLS components in 1 L) absorbance and excess density of the studied solutions revealed that they contained heteroassociates with stoichiometric ratios of the molecules of 1: 2, 2: 1, 4: 1, and 11–12: 1. The concentration range in which each associate is formed in the binary mixture HF-Et₂O was estimated for all the associates. The results obtained were compared with the data on the HF: Solv ratios (Solv is solvent) in molecular complexes that prevail in the seven BLS HF-organic solvent studied earlier. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1833–1839, September, 2008.     

The Relationship of the Energy of Interaction of Alkali Metal Cations with an Aprotic Solvent Molecule with Quantum Topological Electron Density Characteristics

The optimal geometry and wave functions of the complexes [M(Solv)]⁺ (M = Li, Na, K; Solv is an aprotic solvent molecule) were calculated and the topological characteristics of the electron density distribution at the (3,–1) critical points (CP) of ion–molecule bonds were analyzed by the density functional theory in the B3LYP/6-31+G(d, p) approximation. The parametric dependences for the energy of ion–molecule bonds in terms of the local kinetic and potential electron energy densities at the bond CTs were proposed.     

Solubility of <Emphasis Type="Italic">d</Emphasis>-element salts in organic and aqueous–organic solvents: II. Effect of halocomplex formation on solubility of cobalt bromide and chloride and nickel chloride

Solubility of salts in the systems MCl₂–H₂O–Solv (M = Co, Ni) and CoBr₂–H₂O–Solv (Solv = dimethyl sulfoxide, dimethyl formamide, and dimethyl acetamide) at 25°C was measured experimentally. Dominating species of cobalt and nickel halides existing in various concentration regions were identified by analysis of electron absorption spectra. It was shown that the major factor defining solubility is the interaction of halocomplexes of metal ions with solvent molecules.     

Modelling catalytic turnover frequencies in ionic liquids: the determination of the bimolecular rate constant for solvent displacement from [(C6H6)Cr(CO)2Solv] in 1-n-butyl-3-methylimidazolium hexafluorophosphate

The bimolecular rate constant for solvent displacement, k(2), from [(C(6)H(6))Cr(CO)(2)Solv] by an incoming ligand has been determined in the room temperature ionic liquid, [bmim][PF(6)], and is compared to that for the same process in cyclohexane and dichloroethane.     

Solubility of <Emphasis Type="Italic">d</Emphasis>-elements salts in organic and aqueous-organic solvents: III. Influence of intermolecular association on solubility of cadmium bromide and iodide

Solubility in the systems CdX₂–H₂O–Solv (X = Br, I; Solv = dimethyl sulfoxide, N,N-dimethyl acetamide, N,N-dimethyl formamide, and 1,4-dioxane) at 25°C was measured by the isothermal saturation method. A relation between the shape of the solubility isotherm and the structure of the binary solvent depending on its composition was found. Positions of solubility maxima and isotherms inflection points in the most cases correlate with destruction of intermolecular associates formed by solvent components.     

Thermally induced magnetic anomalies in solvates of the bis(hexafluoroacetylacetonate)copper(II) complex with pyrazolyl-substituted nitronyl nitroxide

We succeeded in synthesizing of a whole family of isostructural solvates of the copper(II) hexafluoroacetylacetonate complex with pyrazolyl-substituted nitronyl nitroxide (L): Cu(hfac)2L x 0.Solv. The main feature inherent in nature of Cu(hfac)2L x 0.5 Solv single crystals is their incredible mechanical stability and ability to undergo reversible structural rearrangements with temperature variation, accompanied by anomalies on the mu(eff(T)) dependence. Structural investigation of the complexes over a wide temperature range before and after the structural transition and the ensuing magnetic phase transition showed that the spatial peculiarities of the solvent molecules incorporated into the solid govern the character of the mu(eff(T)) dependence and the temperature region of the magnetic anomaly. Thus, doping of crystals with definite solvent molecules could be used as an efficient method of control over the magnetic anomaly temperature (T(a)). The investigation of this special series of crystals has revealed the relationship between the chemical step and the magnetic properties. It was shown that "mild" modification of T(a) for Cu(hfac)2L x 0.5 Solv required a much smaller structural step than the typical change of one -CH2- fragment in a homologous series in organic chemistry. Quantum-chemical calculations with the use of X-ray diffraction data allowed us to trace the character of changes in the exchange interaction parameters in the range of the phase transition. In the temperature range of the phase transition, the exchange parameter changes substantially. The gradual decrease in the magnetic moment, observed in most experiments during sample cooling to T(a), is the result of the gradual increase in the fraction of the low-temperature phase in the high-temperature phase.     

Composition of heteroassociates formed in HF-pyridine and HF-formamide binary liquid systems

The IR spectra and the densities of solutions in HF-pyridine and HF-formamide binary liquid systems were measured over a wide range of mole ratios HF: Solv (Solv is the organic solvent). The composition of heteroassociates (HA) formed in these systems was determined by analysis of the concentration dependences of normalized (to the total number of moles per 1 L) optical density in the IR region and the excess density of the binary mixtures under study. The HA with the stoichiometric ratio 3: 1 are present in the HF-Py system at all studied mole ratios of the components (from 1: 12 to 20: 1). The 1: 2 HA were found in the dilute solutions, whereas the >6: 1 HA were revealed in the concentrated solutions. The HA with the stoichiometric ratio 4: 1 were found in HF-formamide system. The results obtained were compared with the known data on the composition of HA formed in the binary liquid systems HF-DMF, HF-Me₂CO, and HF-MeCN. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1281–1287, July, 2007.     

Heterometallic modular metal-organic 3D frameworks assembled via new tris-β-diketonate metalloligands: nanoporous materials for anion exchange and scaffolding of selected anionic guests

The modular engineering of heterometallic nanoporous metal-organic frameworks (MOFs) based on novel tris-chelate metalloligands, prepared using the functionalised β-diketone 1,3-bis(4'-cyanophenyl)-1,3-propanedione (HL), is described. The complexes [M(III)L(3)] (M=Fe(3+), Co(3+)) and [M(II)L(3)](NEt(4)) (M=Mn(2+), Co(2+), Zn(2+), Cd(2+)) have been synthesised and characterised, all of which exhibit a distorted octahedral chiral structure. The presence of six exo-oriented cyano donor groups on each complex makes it a suitable building block for networking through interactions with external metal ions. We have prepared two families of MOFs by reacting the metalloligands [M(III)L(3)] and [M(II)L(3)](-) with many silver salts AgX (X=NO(3)(-), BF(4)(-), PF(6)(-), AsF(6)(-), SbF(6)(-), CF(3)SO(3)(-), tosylate), specifically the [M(III)L(3)Ag(3)]X(3)·Solv and [M(II)L(3)Ag(3)]X(2)·Solv network species. Very interestingly, all of these network species exhibit the same type of 3D structure and crystallise in the same trigonal space group with similar cell parameters, in spite of the different metal ions, ionic charges and X(-) counteranions of the silver salts. We have also succeeded in synthesising trimetallic species such as [Zn(x)Fe(y)L(3)Ag(3)](ClO(4))((2x+3y))·Solv and [Zn(x)Cd(y)L(3)Ag(3)](ClO(4))(2)·Solv (with x+y=1). All of the frameworks can be described as sixfold interpenetrated pcu nets, considering the Ag(+) ions as simple digonal spacers. Each individual net is homochiral, containing only Δ or Λ nodes; the whole array contains three nets of type Δ and three nets of type Λ. Otherwise, taking into account the presence of weak Ag-C σ bonds involving the central carbon atoms of the β-diketonate ligands of adjacent nets, the six interpenetrating pcu networks are joined into a unique non-interpenetrated six-connected frame with the rare acs topology. The networks contain large parallel channels of approximate hexagonal-shaped sections that represent 37-48% of the cell volume and include the anions and many guest solvent molecules. The guest solvent molecules can be reversibly removed by thermal activation with retention of the framework structure, which proved to be stable up to about 270°C, as confirmed by TGA and powder XRD monitoring. The anions could be easily exchanged in single-crystal to single-crystal processes, thereby allowing the insertion of selected anions into the framework channels.     

Using molecular simulation to predict solute solvation and partition coefficients in solvents of different polarity

A methodology is proposed for the prediction of the Gibbs energy of solvation (Δ(Solv)G) based on MD simulations. The methodology is then used to predict Δ(Solv)G of four solutes (namely propane, benzene, ethanol and acetone) in several solvents of different polarities (including n-hexane, n-hexadecane, ethylbenzene, 1-octanol, acetone and water) while testing the validity of the TraPPE force field parameters. Excellent agreement with experimental data is obtained, with average deviations of 0.2, 1.1, 0.8 and 1.2 kJ mol(-1), for the four solutes respectively. Subsequently, partition coefficients (log P) for forty different solute/solvent systems are predicted. The a priori knowledge of partition coefficient values is of high importance in chemical and pharmaceutical separation process design or as a measure of the increasingly important environmental fate. Here again, the agreement between experimental data and simulation predictions is excellent, with an absolute average deviation of 0.28 log P units. However, this deviation can be decreased down to 0.14 log P units, just by optimizing partial atomic charges of acetone in the water phase. Consequently, molecular simulation is proven to be a tool with strong physical basis able to predict log P with competitive accuracy when compared to the popular statistical methods with weak physical basis.     

Tuning the Spin‐Crossover Behaviour of a Hydrogen‐Accepting Porous Coordination Polymer by Hydrogen‐Donating Guests

A Hoffman‐like coordination polymer with appreciable porosity and uncoordinated pyridyl groups, namely, [Fe(2,5‐bpp){Au(CN)₂}₂] ? x Solv (2,5‐bpp=2,5‐bis(pyrid‐4‐yl)pyridine; Solv=solvent), was synthesised and characterised. A series of fascinating spin‐crossover behaviours with abrupt, stepwise and hysteretic features were obtained by exchange with a range of protic solvents (ethanol, n‐propanol, isopropyl alcohol, sec‐butanol and isobutanol). Guest–host hydrogen‐bonding interactions involving the H‐accepting site of the framework are primarily responsible for the pronounced cooperativity of these spin‐crossover behaviours. Meanwhile, the tunable critical temperatures over a range of about 130 K are presumably attributable to a certain degree of competition between internal pressure and local electronic influences of solvents.     

Photoluminescence of the Coordination Zinc Compounds with 3-Methyl-4-Formyl-1-Phenylpyrazol-5-one Acylhydrazones

Russian Journal of Coordination Chemistry - New coordination zinc compounds based on 3-methyl-4-formyl-1-phenylpyrazol-5-one acylhydrazones [Zn(L)(CH3COO)Solv] (Solv is H2O (I), Py (II)) are...     

Ionization and Complexing Properties of Hyperbranched Polyester Poly[3-(2-aminoethyl)amino)]propionate

Syntheses of a polydentate ligand based on the second-generation hyperbranched polyester containing 3-(2-aminoethyl)amino]propionate groups and its metal complex with copper(II) ions have been elaborated. In view of the IR, electronic absorption, and EPR spectroscopy data, it has been suggested that the coordination sites in the metal-polymer complex are paramagnetic sites with the CuN4Solv2 or CuN2O2Solv2 composition (Solv = H2O, DMSO).     

Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectra

Cluster ions such as [Cat+X+nM](+) (n = 0-4); [Cat-H+nM](+) (n = 1-3); and [2(Cat-H)+X+nM](+) (n = 0-2), where Cat, X, and M are the dication, anion, and neutral salt (CatX(2)), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H](+), one-electron reduction of the dication to form Cat(+.), demethylation of the paraquat cation to form [Cat-CH(3)](+), and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H](+) and its clusters) and odd-electron (mostly Cat(+)) ions in ESI mass spectra of these pesticides. The [Cat+n. Solv](2+) doubly charged cluster ions, where n 相似文献   

Halide ligand-more than just sigma-donors? A structural and spectroscopic study of homologous organonickel complexes

The isoleptic organonickel complexes [(bpy)Ni(Mes)X] (bpy ) 2,2'-bipyridine; Mes ) 2,4,6-trimethylphenyl; X ) F,Cl, Br, or I, and for comparison X ) OMe and SCN) have been investigated by multiple spectroscopic means.Their structures have been determined in part by single-crystal X-ray diffraction, the full series by extended X-ray absorption fine structure. The long-wavelength charge transfer absorptions (mainly metal-to-ligand charge transfer)obtain contributions from the mesityl coligand but are almost invariable upon variation of X. UV-vis spectroscopy allowed investigation of the solvolysis reaction [(bpy)Ni(Mes)X] + Solv a [(bpy)Ni(Mes)(Solv)]+ + X-, which occurs very fast for X ) I (k ) 0.176(4) M(-1) s(-1)) or Br but very slow for X ) Cl (k ) 5.18(5) x 10(-5) M(-1) cm(-1))or F. Quantum chemical (density functional theory) calculations on the geometry, electronic states, and electronic transitions (time-dependent density functional theory) are very helpful for detailed insight into the role the X coligands play in these complexes. The combination of methods reveals rather strong, highly covalent Ni-X bonds for all halide coligands but marginal pi-donation.     

A New Class of Ruthenium Carbene Complexes: Synthesis and Structures of Highly Efficient Catalysts for Olefin Metathesis

Cationic Ru^II carbene complexes with tBu₂PCH₂PtBu₂ (dtbpm) as a chelating ligand, which are accessible by chloride abstraction from neutral precursors [(κ²-dtbpm)Cl₂Ru=CHR] with trimethylsilyl triflate, are established as highly efficient ring opening metathesis polymerization catalysts (see scheme). Solv=solvent.     

Ungewöhnliche Molekülstrukturen für Platin(II)-at-Komplexe

Unusual Structures of Platinum(II)-ate Complexes X-ray investigations at Pt^II-ate complexes of the type “Li₂[Pt(CH₃)₄](Solv.)₂” revealed a new structure type of organometallic compounds of platinum(II). The synthesis of the highly reactive compounds [Li₂{Pt(CH₃)₄}(Solv.)₂]_n (Solv. = Et₂O, THF, n = 2; TMEDA, PMDTA; n = 1) as well as studies by NMR and DTA will be described.     

Features of the solvation of meso-triphenylcorrole in organic solvents according to calorimetry

Enthalpies of dissolution of meso-triphenylcorrole are measured according to calorimetry in solvents with various polarities and electron donor abilities, the values of which are more exothermic than those for porphyrins of similar structure. The most negative values Δ_sol H ^○ are found in a medium of polar electron donor solvents, due to the formation of H-associates of the H₃(ms-Ph)₃Cor · Solv type with chemically active NH-bonds of macrocycles; the concentration dependences of the enthalpy of dissolution of tetrapyrrols in DMF and DMSO are determined for the first time. It is shown that the value of the enthalpy of moving from standard solvent to DMF agrees with the heat of vaporization of solvent from H-associate H₃(ms-Ph)₃Cor · DMF obtained earlier, which characterizes the energy of specific corrole-solvent interaction.     

Solvent-dependent tautomerism of the inverted isomer of <Emphasis Type="Italic">meso</Emphasis>-tetraphenylporphine: Effect of the polarity of the medium

It is found that aza-imino tautomerism (a ? b) of the inverted porphyrinoids and its mechanism are, along with the stability of tautomeric forms in the Solv–B system, determined by the nature of a base B and the polarity of a solvent Solv. It is shown that the transition from the C₆H₆–B system to MeCN–B is characterized by an approximate doubling of stability constants K_T of the imine form (b), and by a change of the number of molecules B involved in the process (from two to one). According to quantum-chemical data (DFT, B3LYP, CC-pVDZ) and the results from spectral measurements (electronic absorption spectra, EAS), the stability of tautomer b (imino form) falls in the series of solvents DMF > Py ~ Et₂NH > MeCN > Me₂CO, and tautomer a is to a lesser extent stabilized in the given media by electron donors through the formation of hydrogen bonds (except for Me₂CO: DMF > Py ? Me₂CO ? MeCN, Et₂NH).