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1.
The hydrophobic hydration processes have been analysed under the light of a mixture model of water that is assumed to be composed by clusters (W5)I, clusters (W4)II and free water molecules WIII. The hydrophobic hydration processes can be subdivided into two Classes A and B. In the processes of Class A, the transformation A(− ξwWI → ξwWII + ξwWIII + cavity) takes place, with expulsion from the bulk of ξw water molecules WIII, whereas in the processes of Class B the opposite transformation B(− ξwWIII − ξwWII → ξwWI − cavity) takes place, with condensation into the bulk of ξw water molecules WIII. The thermal equivalent dilution (TED) principle is exploited to determine the number ξw. The denaturation (unfolding) process belongs to Class A whereas folding (or renaturation) belongs to Class B. The enthalpy ΔHden and entropy ΔSden functions can be disaggregated in thermal and motive components, ΔHden = ΔHtherm + ΔHmot, and ΔSden = ΔStherm + ΔSmot, respectively. The terms ΔHtherm and ΔStherm are related to phase change of water molecules WIII, and give no contribution to free energy (ΔGtherm = 0). The motive functions refer to the process of cavity formation (Class A) or cavity reduction (Class B), respectively and are the only contributors to free energy ΔGmot. The folded native protein is thermodynamically favoured (ΔGfold ≡ ΔGmot < 0) because of the outstanding contribution of the positive entropy term for cavity reduction, ΔSred ? 0. The native protein can be brought to a stable denatured state (ΔGden ≡ ΔGmot < 0) by coupled reactions. Processes of protonation coupled to denaturation have been identified. In thermal denaturation by calorimetry, however, is the heat gradually supplied to the system that yields a change of phase of water WIII, with creation of cavity and negative entropy production, ΔSfor ? 0. The negative entropy change reduces and at last neutralises the positive entropy of folding. In molecular terms, this means the gradual disruption by cavity formation of the entropy-driven hydrophobic bonds that had been keeping the chains folded in the native protein. The action of the chemical denaturants is similar to that of heat, by modulating the equilibrium between WI, WII, and WIII toward cavity formation and negative entropy production. The salting-in effect produced by denaturants has been recognised as a hydrophobic hydration process belonging to Class A with cavity formation, whereas the salting-out effect produced by stabilisers belongs to Class B with cavity reduction.Some algorithms of denaturation thermodynamics are presented in the Appendices.  相似文献   

2.
Metal-oxygen bonding complexes (M = MgII, MnII, NiII, MoVI, WVI, PdII, SbIII, BiIII, FeIII, TiIV, KI, BaII, ZrIV and HfIV) with a hinokitiol (Hhino; 2-hydroxy-4-isopropylcyclohepta-2,4,6-trienone or β-thujaplicin) ligand, which has two unequivalent oxygen donor atoms, were synthesized and characterized by elemental analysis, TG/DTA, FT-IR and solution (1H and 13C) NMR spectroscopy. Single-crystal X-ray structure analysis revealed various molecular structures for the complexes, which were classified into several families of family, i.e. type A [MII(hino)2(L)]2 (M = MgII, MnII, NiII; L = EtOH or MeOH), with a dimeric structure consisting of one bridging hino anion, one chelating hino anion and one alcohol or water molecule, type B, with the octahedral, cis-dioxo, bis-chelate complexes cis-[MVIO2(hino)2] (M = MoVI, WVI), type C, with square planar complex [MII(hino)2] (M = PdII), type D, with tris-chelate, 7-coordinate complexes with one inert electron pair [MIII(hino)3] (M = SbIII, BiIII), type D′, with the bis-chelate, pseudo-6-coordinate complexes with one inert electron pair [MIII(hino)2X] (M = SbIII, X = Br), type E, with tris-chelate, 6-coordinate complexes with Δ and Λ isomers [MIII(hino)3] (M = FeIII), type E′ of bis-chelate, 6-coordinate complex [MIV(hino)2X2] (M = TiIV, X = Cl), type F, with water-soluble alkali metal salts [MI(hino)] (M = KI), and type H, with tetrakis-chelate, 8-coordinate complexes [MIV(hino)4](M = ZrIV, HfIV). These structural features were compared with those of metal complexes with a related ligand, tropolone (Htrop). The antimicrobial activities of these complexes, evaluated in terms of minimum inhibitory concentration (MIC; μg mL−1) in two systems, were compared to elucidate the relationship between structure and antimicrobial activity.  相似文献   

3.
Nitrite reduction to nitric oxide by heme proteins is drawing increasing attention as a protective mechanism to hypoxic injury in mammalian physiology. Here we probe the nitrite reductase (NiR) activities of manganese(II)- and cobalt(II)-substituted myoglobins, and compare with data obtained previously for the iron(II) analog wt MbII. Both MnIIMb and CoIIMb displayed NiR activity, and it was shown that the kinetics are first order each in [protein], [nitrite], and [H+], as previously determined for the FeII analog wt MbII. The second order rate constants (k2) at pH 7.4 and T = 25 °C, were 0.0066 and 0.015 M− 1 s− 1 for CoIIMb and MnIIMb, respectively, both orders of magnitude slower than the k2 (6 M− 1 s− 1) for wt MbII. The final reaction products for MnIIMb consisted of a mixture of the nitrosyl MnIIMb(NO) and MnIIIMb, similar to the products from the analogous NiR reaction by wt Mb. In contrast, the products of NiR by CoIIMb were found to be the nitrito complex CoIIIMb(ONO) plus roughly an equivalent of free NO. The differences can be attributed in part to the stronger coordination of inorganic nitrite to CoIIIMb as reflected in the respective MIIIMb(ONO) formation constants Knitrite: 2100 M− 1 (CoIII) and <~0.4 M− 1 (MnIII). We also report the formation constants (3.7 and 30 M− 1, respectively) for the nitrite complexes of the mutant metmyoglobins H64V MbIII(NO2) and H64V/V67R MbIII(ONO) and a Knitrite revised value (120 M− 1) for the nitrite complex of wt metMb. The respective Knitrite values for the three ferric proteins emphasize the importance of a H-bonding residue, such as His64 in the MbIII distal pocket or the Arg67 in H64V/V67R MbIII, in stabilizing nitrite coordination. Notably, the NiR activities of the corresponding ferrous Mbs follow a similar sequence suggesting that nitrite binding to these centers are analogously affected by the H-bonding residues.  相似文献   

4.
5.
Three new aqua magnesium phthalocyaninato complexes with 2-methoxyethylamine (MEA) in crystalline form have been obtained. The composition of the complexes depends on the crystallisation temperature. (MgPcH2O)2 · MEA (I) and (MgPcH2O)2 · 2MEA (II) were formed at about 170 °C and 80 °C, respectively, while room temperature (MgPcH2O)2 · 3MEA (III) was obtained. In all crystals the Mg atom is 4+1 coordinated, equatorially by four N-isoindole atoms of Pc ligand and axially by O atom of water molecule. The MgPc moiety is non-planar, the Mg(II) deviates by ∼0.5 Å from the N4-isoindole plane towards the oxygen atom of water molecule. The MEA molecules in the crystals interact via hydrogen bonds with coordinated water molecules of MgPcH2O. The arrangement of MgPcH2O and 2-methoxyethylamine molecules is determined by O-H?N and O-H?O hydrogen bonds and by π-π interactions. The thermogravimetric analyses show characteristic steeps responsible for the loss of MEA molecules (at lower temperature) and water (at higher temperature) and finally all the complexes transform into β-MgPc. From among the complexes only complex II exhibits an intense near-IR absorption band in the solid-state, while spectra in MEA solution are identical for all the complexes.  相似文献   

6.
The present paper describes a new tripodal ligand containing imidazole and pyridine arms and its first cis-[RuIII(L)(Cl)2]ClO4 complex (1). The crystal structure of 1 shows RuIII in a distorted octahedral geometry, in which two chloride ions, cis-positioned to each other, are coordinated besides the four nitrogen atoms from the tetradentate ligand L. The cyclic voltammogram of 1 exhibits three redox processes at −67, +73 and +200 mV versus SCE, which are attributed to the RuIII/RuII couple in the cis-[RuIII(L)(Cl)2]+, cis-[RuII(L)(H2O)(Cl)]+ and cis-[RuII(L)(H2O)2]2+, respectively. After chemical reduction (Zn(Hg) or EuII) only the cis-[RuII(L)(H2O)2]2+ species is observed in the cyclic voltammetry. Complex 1 absorbs at 470 nm (ε=1.4×103 mol−1 L cm−1), 335 nm (ε=7.9×103 mol−1 L cm−1), 301 nm (ε=6.7×103 mol−1 L cm−1) and 264 nm (ε=9.9×103 mol−1 L cm−1), in water solution (CF3COOH, 0.01 mol L−1, μ=0.1 mol L−1 with CF3COONa). Spectroelectrochemical experiments show a decrease of the bands at 335 and 301 nm, which are attributed to LMCT transitions from the chloride to the RuIII center and the appearance of a broad band at 402 nm ascribed to MLCT transition from the RuII center to the pyridine ligand. The lability of the water ligands in the cis-[RuII(L)(H2O)2]2+ species has been investigated using the auxiliary ligand pyrazine. Reactions in the presence of stoichiometric and excess of pyrazine yield the same species, cis-[RuII(L)(H2O)(pz)]2+, which exhibits a reversible redox process at 493 mV versus SCE and absorbs at 438 nm (ε=5.1×103 mol−1 L cm−1) and 394 nm (ε=4.2×103 mol−1 L cm−1). Experiments performed with a large excess of pyrazine gave a specific rate constant k1=(2.8±0.5)×10−2 M−1 s−1, at 25 °C, in CF3COOH, 0.01 mol L−1, μ=0.1 mol L−1 (with CF3COONa).  相似文献   

7.
The syntheses and comparative studies of the spectral, voltammetry and spectroelectrochemical properties of new manganese phthalocyanine complexes, tetra-substituted with diethylaminoethanethio at the peripheral (complex 3a) and non-peripheral positions (complex 3b) are reported. Solution electrochemistry of complex 3a showed quasi-reversible metal-based (MnIIIPc−2/MnIIPc2, E1/2 = −0.07 V vs. Ag|AgCl) and ring-based (MnIIPc−2/MnIIPc−3, E1/2 = −0.78 V vs. Ag|AgCl) reductions, but no ring-based oxidation. However, complex 3b showed weak irreversible ring-oxidation signal (Ep = +0.86 vs. Ag|AgCl). Reversible metal-based (MnIIIPc−2/MnIIPc−2, E1/2 = −0.04 V vs. Ag|AgCl) and ring-based (MnIIPc−2/MnIIPc−3, E1/2 = −0.68 V vs. Ag|AgCl) reductions were also observed for complex 3b. Spectroelectrochemistry was used to confirm these processes. Reduction process involving the metal (MnIIIPc−2/MnIIPc−2) was associated with the formation of manganese μ-oxo complex in complex 3a.  相似文献   

8.
An oxalate-bridged binuclear iron(III) complex, [(acac)2Fe(μ-ox)Fe(acac)2], (acac=acetylacetonate anion and ox2−=oxalate anion) was prepared. The complex crystallized as two types of crystals under different conditions: one had 1,2-dichloroethane as a solvent molecule of crystallization 2, the other did not 1. Both compounds have been characterized by X-ray crystallography, infrared spectroscopy, and thermogravimetric analysis. Compound 1 has also been characterized by UV-Vis and 1H NMR spectroscopies, mass spectrometry, and electrochemistry. In both crystals, each iron(III) is coordinated in an octahedral arrangement by the oxygen atoms of an oxalate-bridging ligand and four oxygen atoms belonging to peripheral acac ligands in an octahedral arrangement. The intermetallic distance of Fe?Fe is 5.4368(9) Å in 1 and 5.438(2) Å in 2. Two iron(III) ions in each crystal are bridged by the oxalate and both lie in the oxalate-plane. The results of thermal analyses imply that the thermal stability of 2 is lower than that of 1. Cyclic voltammograms of 1 in acetonitrile and dichloromethane at low temperature showed two consecutive, quasi-Nernstian, one-electron reduction steps corresponding to the reduction of FeIII-FeIII to FeIII-FeII followed by the reduction of FeIII-FeII to FeII-FeII. The electrochemical comproportionation constants (Kc) of the equilibrium (FeIII-FeIII) + (FeII-FeII) ? 2(FeIII-FeII) are 108.9 in acetonitrile medium and 108.5 in dichloromethane, respectively. The considerably large Kc values indicate that the main factor contributing to the stabilization of the FeIII-FeII mixed-valence state is electronic delocalization through the oxalate-bridge.  相似文献   

9.
The relationship between local thermal comfort, local skin wettedness (wlocal) and local galvanic skin conductance (GSC) in four body segments during two different exercise intensities was compared in 10 males. In a balanced order, participants walked at 35% VO2max for 45 min (WALK) (29.0±1.9°C, 29.8±3.6% RH, no wind) in one test and in a separate test ran at 70% VO2max for 45 min (RUN) (26.2±2.1°C, 31.1±7.0% RH, no wind). During both tests, participants wore a loose fitting 100% polyester long sleeve top and trouser ensemble with a low resistance to heat and vapour transfer (total thermal resistance of 0.154 m2 K W−1 and total water vapour resistance of 35.9 m2 Pa W−1). wlocal, change from baseline in GSC (ΔGSC) and local thermal comfort were recorded every 5 min. The results suggest that both wlocal and ΔGSC are strong predictors of thermal comfort during the WALK when sweat production is low and thermal discomfort minimal (r2>0.78 and r2>0.71, respectively). Interestingly, during the RUN wlocal plateaued at ~0.6 to 0.8 due to the high sweat production, whilst ΔGSC gradually increased throughout the experiment. ΔGSC had a similar relationship with thermal comfort to wlocal during the RUN (r2>0.95 and r2>0.94, respectively). Despite the strength of these relationships, the ability of wlocal to predict local thermal comfort accurately dramatically reduces in the exponential part of the curve. In a situation of uncompensated heat stress such as high metabolic rate in hot climate, where sweat production is high, ΔGSC shows to be a better predictor of local thermal comfort than wlocal. The wlocal data shows regional differences in the threshold which triggers local discomfort during the WALK than RUN; lower values are found for upper arms (0.22±0.03 and 0.28 ±0.22) and upper legs (0.22±0.11 and 0.22±0.10), higher values for upper back (0.30±0.12 and 0.36 ±0.10) and chest (0.27±0.10 and 0.39 ±0.32), respectively. However, no regional differences in the threshold of discomfort are found in the ?GSC data. Instead, the data suggests that the degree of discomfort experienced appears to be related to the amount of sweat within and around the skin (as indirectly measured by ΔGSC) at each body site.  相似文献   

10.
A study of the metal-to-metal charge-transfer (MMCT) transition within the binuclear cyano-bridged complexes cis-[L13CoIII(μ-NC)FeII(CN)5] (L13 = 12-methyl-1,4,7,10-tetraazacyclotridecan-12-amine), trans-[L14CoIII(μ-NC)FeII(CN)5] (L14 = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) and trans-[L15CoIII(μ-NC)FeII(CN)5] (L15 = 10-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine) has been carried out in electrolyte solutions at varying concentrations. Using these data, as well as the reaction free energies obtained from electrochemical measurements, the reorganisation and activation free energies for the forward and reverse thermal electron-transfer processes have been estimated. The changes of these parameters with the electrolyte concentration, as well as those of the energy of the maximum MMCT band and the reaction free energy, are mainly due to ion-pairing effects.  相似文献   

11.
The reactions of Ln(NO3)3 · xH2O, CoSO4 · 7H2O or ZnSO4 · 6H2O and 2-pyridylphosphonic acid under hydrothermal conditions result in heterometallic phosphonate compounds with formula [Ln2M3(C5H4NPO3)6] · 4H2O (Ln2M3; M = CoII or ZnII; Ln = LaIII, CeIII, PrIII, NdIII, SmIII, EuIII, GdIII, TbIII, DyIII). These compounds are isostructural and crystallize in a chiral cubic space group I213. Each structure contains the {LnO9} polyhedra and {MN2O4} octahedra which are connected by edge-sharing to form an inorganic open-framework structure with a 3-connected 10-gon (10, 3) topology. The nature of LnIII-CoII magnetic interactions in Ln2Co3 is investigated by a comparison with their LnIII-ZnII analogues. It is found that the LnIII-CoII interaction is weak antiferromagnetic for Ln = Ce and ferromagnetic for Ln = Sm, Gd, Tb and Dy. In the cases of Ln = Pr, Nd and Eu, no significant magnetic interaction is observed.  相似文献   

12.
Electrostatic interactions have a central role in some biological processes, such as recognition of charged ligands by proteins. We characterized the binding energetics of yeast triosephosphate isomerase (TIM) with phosphorylated inhibitors 2-phosphoglycollate (2PG) and phosphoglycolohydroxamate (PGH). We determined the thermodynamic parameters of the binding process (Kb, ΔGb, ΔHb, ΔSb and ΔCp) with different concentrations of NaCl, using fluorimetric and calorimetric titrations in the conventional mode of ITC and a novel method, multithermal titration calorimetry (MTC), which enabled us to measure ΔCp in a single experiment. We ruled out specific interactions of Na+ and Cl- with the native enzyme and did not detect significant linked protonation effects upon the binding of inhibitors. Increasing ionic strength (I) caused Kb, ΔGb and ΔHb to become less favorable, while ΔSb became less unfavorable. From the variation of Kb with I, we determined the electrostatic contribution of TIM−2PG and TIM−PGH to ΔGb at I = 0.06 M and 25 °C to be 36% and 26%, respectively. The greater affinity of PGH for TIM is due to a more favorable ΔHb compared to 2PG (by 19-24 kJ mol-1 at 25 °C). This difference is compatible with PGH establishing up to five more hydrogen bonds with TIM. Both binding ΔCps were negative, and less negative with increasing ionic strength. ΔCps at I = 0.06 M were much more negative than predicted by surface area models. Water molecules trapped in the interface when ligands bind to protein could explain the highly negative ΔCps. Thermodynamic binding functions for TIM−2PG changed more with ionic strength than those for TIM−PGH. This greater dependence is consistent with linked, but compensated, protonation equilibriums yielding the dianionic species of 2PG that binds to TIM, process that is not required for PGH.  相似文献   

13.
We report here the synthesis and properties of a family of mixed-valence cyanide-bridged dinuclear complex ions trans-[(L′L4RuII(μ-NC)FeIII(CN)5] (with L = pyridine or 4-dimethylaminopyridine (dmap) and L′ = pyridine, 4-methoxypyridine (meopy) or 4-dimethylaminopyridine)) whose properties could be adjusted smoothly by changing the acceptor properties of the solvent and the σ donor properties of the L′ pyridine ligand. In solution these complexes exhibit an intense solvent-dependent MM′CT (RuII → FeIII) absorption in the near infrared region. Analysis of this band in different complexes and solvents suggests an enhanced interaction as the energies of the metal centers come closer. From this trend the anion trans-[(dmap)5Ru(μ-NC)Fe(CN)5] (dmap = 4-dimethylaminopyridine) in water is expected to belong to the class II-III, but its spectral properties indicates a ground state with Ru(III)-Fe(II) character. The stabilization of this electronic isomer is probably related to the better donor properties of the hexacyanoferrate(II) moiety and its stronger interaction with water.  相似文献   

14.
Ferric human serum heme-albumin (heme-HSA) shows a peculiar nuclear magnetic relaxation dispersion (NMRD) behavior that allows to investigate structural and functional properties. Here, we report a thermodynamic analysis of NMRD profiles of heme-HSA between 20 and 60 °C to characterize its hydration. NMRD profiles, all showing two Lorentzian dispersions at 0.3 and 60 MHz, were analyzed in terms of modulation of the zero field splitting tensor for the S = 5/2 manifold. Values of correlation times for tensor fluctuation (τv) and chemical exchange of water molecules (τM) show the expected temperature dependence, with activation enthalpies of −1.94 and −2.46 ± 0.2 kJ mol−1, respectively. The cluster of water molecules located in the close proximity of the heme is progressively reduced in size by increasing the temperature, with Δ= 68 ± 28 kJ mol−1 and Δ= 200 ± 80 J mol−1 K−1. These results highlight the role of the water solvent in heme-HSA structure-function relationships.  相似文献   

15.
Substitution reaction of fac-[FeII(CN)2(CO)3I] with triphenylphosphine (PPh3) produced mono phosphine substituted complex cis-cis-[FeII(CN)2(CO)2(PPh3)I]. Crystal structure of the product showed that carbonyl positioned trans- to iodide was replaced by PPh3. The substitution reaction was monitored by quantitative infrared spectroscopic method, and the rate law for the substitution reaction was determined to be rate = k[[FeII(CN)2(CO)2(PPh3)I]][PPh3]. Transition state enthalpy and entropy changes were obtained from Eyring equation k = (kBT/h)exp(−ΔH/RT + ΔS/R) with ΔH = 119(4) kJ mol−1 and ΔS = 102(10) J mol−1 K−1. Positive transition state entropy change suggests that the substitution reaction went through a dissociative pathway.  相似文献   

16.
Structural changes between [OsIIL3]2+ and [OsIIIL3]3+ (L: 2,2′-bipyridine; 1,10-phenanthroline) and molecular and electronic structures of the OsIII complexes [OsIII(bpy)3]3+ and [OsIII(phen)3]3+ are discussed in this paper. Mid-infrared spectra in the ν(bpy) and ν(phen) ring stretching region for [OsII(bpy)3](PF6)2, [OsIII(bpy)3](PF6)3, [OsII(phen)3](PF6)2, and [OsIII(phen)3](PF6)3 are compared, as are X-ray crystal structures. Absorption spectra in the UV region for [OsIII(bpy)3](PF6)3 and [OsIII(phen)3](PF6)3 are dominated by very intense absorptions (ε = 40 000-50 000 M−1 cm−1) due to bpy and phen intra-ligand π → π transitions. In the visible region, relatively narrow bands with vibronic progressions of ∼1500 cm−1 appear, and have been assigned to bpy or phen-based, spin-orbit coupling enhanced, 1π → 3π electronic transitions. Also present in the visible region are ligand-to-metal charge transfer bands (LMCT) arising from π(bpy) → t2g(OsIII) or π(phen) → t2g(OsIII) transitions. In the near infrared, two broad absorption features appear for oxidized forms [OsIII(bpy)3](PF6)3 and [OsIII(phen)3](PF6)3 arising from dπ-dπ interconfigurational bands characteristic of dπ5OsIII. They are observed at 4580 and 5090 cm−1 for [OsIII(bpy)3](PF6)3 and at 4400 and 4990 cm−1 for [OsIII(phen)3](PF6)3. The bpy and phen infrared vibrational bands shift to higher energy upon oxidation of Os(II) to Os(III). In the cation structure in [OsIII(bpy)3](PF6)3, the OsIII atom resides at a distorted octahedral site, as judged by ∠N-Os-N, which varies from 78.78(22)° to 96.61(22)°. Os-N bond lengths are also in general longer for [OsIII(bpy)3](PF6)3 compared to [OsII(bpy)3](PF6)2 (0.010 Å), and for [OsIII(phen)3](PF6)3 compared to [OsII(phen)3](PF6)2 (0.014 Å). Structural changes in the ligands between oxidation states are discussed as originating from a combination of dπ(OsII) → π (bpy or phen) backbonding and charge redistribution on the ligands as calculated by natural population analysis.  相似文献   

17.
Two crystals of holmium(III) double-decker iodine doped phthalocyanines, HoPc2I5/3 (I) and HoPc2I (II), were grown directly in the reaction of holmium chips with 1,2-dicyanobenzene under versatile quantity of iodine at 180-160 °C. The complex I crystallises in the P4/mcc space group of tetragonal system, while the complex II crystallises in the P2/c space group of monoclinic system. The space group of P4/mcc and z = 1 requires that the Ho(III) atom is statistically disordered in the HoPc2I5/3 structure. The iodine atoms form linear symmetrical triiodide ions in I, while the I ions in II. Assignment of iodine species as in the HoPc2I5/3 and I in HoPc2I complexes point to the +5/9 and +1 oxidation state of the HoPc2 unit in these complexes. Thus one Pc macrocycle of the double-decker HoPc2 units has a non-integer oxidation state of −1.222 in I, while both Pc-rings are one-electron oxidised radical Pc in II. Magnetic susceptibilities of HoPc2I5/3 and HoPcI at room temperature are 4.56 × 10−2 and 5.12 × 10−2 emu/mol and the calculated magnetic moments are 10.46 and 11.08 μB, respectively. UV-Vis spectroscopic measurement of I and II in benzene solution were carried out and discussed.  相似文献   

18.
A seven-coordinate FeIII complex, [Fe(oda)(H2O)2(NO3)], was obtained after dissolving Fe(NO3)3 · 9H2O in an aqueous solution of oxydiacetic acid (H2oda) at room temperature. In the solid state, the FeIII center adopts a pentagonal bipyramid geometry with an {FeO7} core formed by a tridentate oda2− and a bidentate in the equatorial plane, and two axial water molecules. Magnetic measurements and EPR spectra revealed the presence of S = 5/2 FeIII centers with rhombic zero field splitting parameters (D = 0.81 cm−1, E/D = 0.33 ). Weak antiferromagnetic interactions with J ≈ −0.06 cm−1 operating between neighboring Fe ions connected through Fe-O-C-O?H-O-Fe paths are estimated using the molecular field approximation.  相似文献   

19.
Reaction of the five-coordinate trigonal-bipyramidal platinum(II) complex, [Pt(pt)(pp3)](BF4) (pt = 1-propanethiolate, pp3 = tris[2-(diphenylphosphino)ethyl]phosphine), with I in chloroform gave the five-coordinate square-pyramidal complex with a dissociated terminal phosphino group and an apically coordinated iodide ion in equilibrium. The thermodynamic parameters for the equilibrium between the trigonal-bipyramidal and square-pyramidal geometries, [Pt(pt)(pp3)]+ + I ? [PtI(pt) (pp3)], and the kinetic parameters for the chemical exchange were obtained as follows: , ΔH0 = − 10 ± 2.4 kJ mol−1, ΔS0 = − 36 ± 10 J K−1 mol−1, , ΔH = 34 ± 4.7 kJ mol−1, ΔS = − 50 ± 21 J K−1 mol−1. The square-planar trinuclear platinum(II) complex was formed by bridging reaction of one of the terminal phosphino groups of trigonal-bipyramidal [PtCl(pp3)]Cl with trans-[PtCl2(NCC6H5)2] in chloroform. From these facts, ligand substitution reactions of [PtX(pp3)]+ (X = monodentate anion) are expected to proceed via an intermediate with a dissociated phosphino group. The rate constants for the chloro-ligand substitution reactions of [PtCl(pp3)]+ with Br and I in chloroform approached the respective limiting values as concentrations of the entering halide ions are increased. These kinetic results confirmed the preassociation mechanism in which the square pyramidal intermediate with a dissociated phosphino group and an apically coordinated halide ion is present in the rapid pre-equilibrium.  相似文献   

20.
The reaction of [FeII(H2O)6](BF4)2 with tris(2-pyridylmethyl)amine (TPyA) and triethylamine in methanol under aerobic conditions forms [(TPyA)FFeIIIOFeIIIF(TPyA)](BF4)2 · 0.5MeOH (1), in which each Fe(III) ion is coordinated to a TPyA and an F ion as well as an oxo ion (O2−) linking two Fe(III) ions. 1 has offset face-to-face π-π interactions between the dimers, and possesses a supramolecular network structure. The magnetic susceptibility of 1 can be fit with g = 2.0, J/kB = − 153 K (106 cm−1), and θ = − 0.3 K [H = − 2JSa · Sb]. These indicate that very strong antiferromagnetic interactions occur via the oxo bridge within the Fe(III) dimer and weak antiferromagnetic interactions between the dimers.  相似文献   

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