Site Exchange Process Research Articles

Diffusion-Controlled Rotation of Triptycene in a Metal-Organic Framework (MOF) Sheds Light on the Viscosity of MOF-Confined Solvent.

Artificial molecular machines are expected to operate under conditions of very low Reynolds numbers with inertial forces orders of magnitude smaller than viscous forces. While these conditions are relatively well understood in bulk fluids, opportunities to assess the role of viscous forces in confined crystalline media are rare. Here we report one such example of diffusion-controlled rotation in crystals and its application as a probe for viscosity of MOF-confined solvent. We describe the preparation and characterization of three pillared paddlewheel MOFs, with 9,10-bis(4-pyridylethynyl)triptycene 3 as a pillar and molecular rotator, and three axially substituted dicarboxylate linkers with different lengths and steric bulk. The noncatenated structure with a bulky dicarboxylate linker (UCLA-R3) features a cavity filled by 10 molecules of N,N-dimethylformamide (DMF). Solid-state 2H NMR analysis performed between 293 and 343 K revealed a fast 3-fold rotation of the pillar triptycene group with the temperature dependence consistent with a site exchange process determined by rotator-solvent interactions. The dynamic viscosity of the MOF-confined solvent was estimated to be 13.3 N·s/m2 (or Pa·s), which is 4 orders of magnitude greater than that of bulk DMF (8.2 × 10–4 N·s/m2), and comparable to that of honey.

Excited States of Nucleic Acids Probed by Proton Relaxation Dispersion NMR Spectroscopy.

In this work an improved stable isotope labeling protocol for nucleic acids is introduced. The novel building blocks eliminate/minimize homonuclear 13C and 1H scalar couplings thus allowing proton relaxation dispersion (RD) experiments to report accurately on the chemical exchange of nucleic acids. Using site‐specific 2H and 13C labeling, spin topologies are introduced into DNA and RNA that make 1H relaxation dispersion experiments applicable in a straightforward manner. The novel RNA/DNA building blocks were successfully incorporated into two nucleic acids. The A‐site RNA was previously shown to undergo a two site exchange process in the micro‐ to millisecond time regime. Using proton relaxation dispersion experiments the exchange parameters determined earlier could be recapitulated, thus validating the proposed approach. We further investigated the dynamics of the cTAR DNA, a DNA transcript that is involved in the viral replication cycle of HIV‐1. Again, an exchange process could be characterized and quantified. This shows the general applicablility of the novel labeling scheme for 1H RD experiments of nucleic acids.

Excited States of Nucleic Acids Probed by Proton Relaxation Dispersion NMR Spectroscopy

AbstractIn this work an improved stable isotope labeling protocol for nucleic acids is introduced. The novel building blocks eliminate/minimize homonuclear 13C and 1H scalar couplings thus allowing proton relaxation dispersion (RD) experiments to report accurately on the chemical exchange of nucleic acids. Using site‐specific 2H and 13C labeling, spin topologies are introduced into DNA and RNA that make 1H relaxation dispersion experiments applicable in a straightforward manner. The novel RNA/DNA building blocks were successfully incorporated into two nucleic acids. The A‐site RNA was previously shown to undergo a two site exchange process in the micro‐ to millisecond time regime. Using proton relaxation dispersion experiments the exchange parameters determined earlier could be recapitulated, thus validating the proposed approach. We further investigated the dynamics of the cTAR DNA, a DNA transcript that is involved in the viral replication cycle of HIV‐1. Again, an exchange process could be characterized and quantified. This shows the general applicablility of the novel labeling scheme for 1H RD experiments of nucleic acids.

Crystal Fluidity Reflected by Fast Rotational Motion at the Core, Branches, and Peripheral Aromatic Groups of a Dendrimeric Molecular Rotor.

Low packing densities are key structural features of amphidynamic crystals built with static and mobile components. Here we report a loosely packed crystal of dendrimeric rotor 2 and the fast dynamics of all its aromatic groups, both resulting from the hyperbranched structure of the molecule. Compound 2 was synthesized with a convergent strategy to construct a central phenylene core with stators consisting of two layers of triarylmethyl groups. Single crystal X-ray diffraction analysis confirmed a low-density packing structure consisting of one molecule of 2 and approximately eight solvent molecules per unit cell. Three isotopologues of 2 were synthesized to study the motion of each segment of the molecule in the solid state using variable temperature quadrupolar echo (2)H NMR spectroscopy. Line shape analysis of the spectra reveals that the central phenylene, the six branch phenylenes, and the 18 periphery phenyls all display megahertz rotational dynamics in the crystals at ambient temperature. Arrhenius analysis of the data gives similar activation energies and pre-exponential factors for different parts of the structure. The observed pre-exponential factors are 4-6 orders of magnitude greater than those of elementary site-exchange processes, indicating that the dynamics are not dictated by static energetic potentials. Instead, the activation energies for rotations in the crystals of 2 are controlled by temperature dependent local structural fluctuations and crystal fluidity.

Boryl-Dihydrideborate Osmium Complexes: Preparation, Structure, and Dynamic Behavior in Solution

The metal fragment Os(CO)(PiPr3)2 stabilizes boryl-dihydrideborate species, which can be viewed as snapshots of states of B–H oxidative addition of a R2BH molecule and frustrated B–H bond activation of a second one. Complex OsH2(η2-CH2═CHEt)(CO)(PiPr3)2 (2) shows a tendency to dissociate the olefin. The resulting dihydride OsH2(CO)(PiPr3)2 (3) rapidly coordinates catecholborane (HBcat) and pinacolborane (HBpin) to give the corresponding σ-borane derivatives OsH2(η2-HBR2)(CO)(PiPr3)2 (BR2 = Bcat (4), Bpin (5)). Complex 4 reacts with a second molecule of HBcat to release H2 and to afford the octahedral boryl dihydride borate derivative Os(Bcat)(κ2-H2Bcat)(CO)(PiPr3)2 (6), which undergoes a thermally activated Bcat site exchange process in solution. Borane displaces catecholborane from the dihydride-borate of 6 to generate the boryl-tetrahydrideborate Os(Bcat)(κ2-H2BH2)(CO)(PiPr3)2 (7). This compound and the Bpin counterpart Os(Bpin)(κ2-H2BH2)(CO)(PiPr3)2 (8) have also been prepared by reaction of the corres...

The initial oxidation of poly-crystalline aluminum studied with x-ray photoelectron spectroscopy

The initial oxidation of poly-crystalline aluminum is investigated using x-ray photoelectron spectroscopy (XPS). The total oxygen coverage and the oxidic oxygen coverage are obtained from the O 1s and Al 2p peaks in the XPS spectra. A linear relationship is found between the total oxygen coverage and the oxidic oxygen coverage. The critical oxygen coverage representing the start of the nucleation process is determined to be 0.07 ± 0.02. It is proposed that the site-exchange process is caused by a repulsive interaction between a chemisorbed oxygen island and the aluminum substrate and the strength of this interaction increases with the size of the oxygen island. Based on this consideration, a simple model is introduced, which predicts a linear relationship between the total oxygen coverage and the oxidic oxygen coverage, in agreement with the experimental observation.

New defect-crystal-chemical approach to non-Vegardianity and complex defect structure of fluorite-based MO 2–LnO 1.5 solid solutions (M 4+ = Ce, Th; Ln 3+ = lanthanide) : Part II: Detailed local-structure and ionic-conductivity analysis

In Part I a new lattice-parameter ( a 0(ss)) model for the entitled so-called defect-fluorite solid solutions (ss) was proposed; this clarified their markedly non-Vegardian a 0(ss) behavior as a macroscopic manifestation of their microscopic defect (V O)-related local structure, in particular the non-random oxygen coordination around the cations of CN(Ln 3+) ≠ CN(M 4+). In this Part II the proposed model was further applied to analyse their controversial detailed local-structure and ionic-conductivity behavior. The combination of the CN(Ln 3+, M 4+) data with ‘restricted (non-)randomness’ of defect-fluorite oxides can provide almost a full set of their mutually non-random cation (M 4+, Ln 3+) ↔ anion (O 2−, V O) coordination-structure data, such as oxygen 8, 7 and 6-fold coordinated cation (M 4+, Ln 3+) concentrations and dopant (Ln 3+) n(= 0–4)-fold coordinated anion (V O, O 2−) concentrations. This can also provide a new consistent description of ionic-conductivity maximum behavior in low- y range as a multiple V O ↔ O 2− site-exchange process in and between differently dopant (Ln 3+)-associated anion sites. Thus, together with the a 0(ss)-analysis results obtained in Part I, the present model is proposed as a new quantitative a 0(ss) model for these defect-fluorite oxides and as a new direct link to their complex defect (local) structure. Possible further elaborations and application extensions of the present model in the future are also discussed both from the basic theoretical and material sides.

Evidence for Effective p(Z)−π(Ar) Conjugations (Z = S, Se, and Te, as Well as Z = O) in 9-(Arylchalcogenyl)triptycenes: Experimental and Theoretical Investigations

The p(Z)-pi(Ar) conjugations must operate fully in the ground states of 9-(arylchalcogenyl)triptycenes (p-YC(6)H(4)ZTpc:1 (Z = O), 2 (Z = S), 3 (Z = Se), and 4 (Z = Te)), where the p-YC(6)H(4) group is placed in the bisected area between two phenyl planes of the triptycyl group with the parallel orientation. The ground-state geometries, which we call (A: pl), are confirmed by X-ray analysis. However, the conjugations never operate in the transition states between (A: pl) and/or the topomeric structures (A': pl'), where the Z-C(Tpc) bond is perpendicular to the plane. The site-exchange processes correlate to the conjugations. Temperature-dependent (1)H NMR spectra are analyzed for 2 and 3 to demonstrate the effective p(Z)-pi(Ar) conjugations. The activation energies for the interconversion between (A: pl) and (A': pl') (GR: gear process) were obtained for 2 (DeltaG(GR)(2)) and 3 (DeltaG(GR)(3)). DeltaG(GR)(3) correlate well with DeltaG(GR)(2), and DeltaG(GR)(2) are well analyzed by the Hammett-type dual parameters. DeltaG(GR)(2) and DeltaG(GR)(3) are demonstrated to be controlled by the resonance interaction of the p(Z)-pi(C(6)H(4))-p(Y) conjugations. QC calculations are performed on the ground and exited states of 1-4, which clarify the effective p(Z)-pi(C(6)H(4))-p(Y) conjugations for Z of heavier atoms.

Site blocking and CO/sulfur site exchange processes on stepped Pt surfaces

The influence of preadsorbed sulfur on the adsorption of CO on Pt(355) and Pt(322) isinvestigated systematically for sulfur precoverages between 0.02 and 0.30 ML by in situ x-rayphotoelectron spectroscopy of the C 1s and S 2p core levels. The two surfaces have thesame nominal terrace width of 5 atomic rows, but different step orientation. For both, atlow temperatures (130 and 150 K), S preferentially adsorbs at the steps and passivates themfor CO adsorption. The required S precoverage is significantly smaller for Pt(322), becauseof the lower number of steps as a result of the S-induced double-step formation. Uponheating, population of step sites with CO occurs due to irreversible CO/S siteexchange. At low S precoverages, the characteristic transition temperatures of165 K for Pt(355) and 245 K for Pt(322) are significantly different, indicating ahigher activation barrier for the CO/S site exchange process for Pt(322). Formedium to high S precoverages the transition temperature stays unchanged forPt(322) but increases for Pt(355). The observed behavior is attributed to a kineticpassivation of the steps by sulfur at low temperatures, which is lifted upon heating.

E-Selective Allyl Transfer Reaction in a μ-η1:η2-Crotylplatinum−Cobalt Complex

Oxidative addition of the Co−C bond of Co(η3-CH2CHCHR)(CO)3 (R = Ph (2a), Me (2b)) to Pt(styrene)(dppe) (1) gives (dppe)(μ-η1:η2-RCH═CHCH2)Pt−Co(CO)3 (R = Ph (3a), Me (3b)). The E-isomer of 3b showed fluxionality due to a site exchange process between the allyl carbon and Co at Pt and complete E-selective allyl transfer reaction from platinum to cobalt, which was accelerated by addition of acrylonitrile or PPh3, whereas the Z-isomer had a rigid structure and showed lower reactivity.

Kinetic passivation of steps with sulfur and CO/S site exchange processes on stepped Pt surfaces

We studied the influence of preadsorbed sulfur on the adsorption of CO on Pt(3 5 5) and Pt(3 2 2) by in situ X-ray photoelectron spectroscopy. At low temperatures, no adsorption of CO at steps is found, indicating a passivation by sulfur. Upon heating, population of step sites with CO occurs. This behavior is attributed to a kinetic passivation of the steps by sulfur at low temperatures, which is lifted upon heating. The characteristic transition temperatures of 185 K for Pt(3 5 5) and 240 K for Pt(3 2 2) are significantly different, due to a higher activation barrier for the CO/S site exchange process for Pt(3 2 2).

Structure and properties of mullite—A review

Mullite has achieved outstanding importance as a material for both traditional and advanced ceramics because of its favourable thermal and mechanical properties. Mullite displays various Al to Si ratios referring to the solid solution Al 4+2 x Si 2−2 x O 10− x , with x ranging between about 0.2 and 0.9 (about 55 to 90 mol% Al 2O 3). Depending on the synthesis temperature and atmosphere mullite is able to incorporate a number of transition metal cations and other foreign atoms. The crystal structure of mullite is closely related to that of sillimanite, which is characterized by chains of edge-connected AlO 6 octahedra running parallel to the crystallographic c-axis. These very stiff chains are cross-linked by tetrahedral chains consisting of (Al,Si)O 4 tetrahedra. In more detail: Parallel to a the tetrahedra are linked to the relatively short more stiff Al–O(A, B) bonds, whereas parallel b they are linked parallel to the relatively long more compliant Al–O(D) bonds. In mullite some of the oxygen atoms bridging the tetrahedra are removed for charge compensation. This gives rise to the formation of oxygen vacancies and of T 3O groups (so-called tetrahedral triclusters). The anisotropy of the bonding system of mullite has a major influence on the anisotropy of its physical properties. For example: • the highest longitudinal elastic stiffness is observed parallel c, but lower ones parallel a and especially parallel b, • the maximum of the thermal conductivity occurs parallel c, but maller ones parallel a and especially parallel b, • large thermal expansion especially parallel b, • fastest crystal growth and highest corrosion parallel c. Heat capacity and thermal expansion measurements of mullite display reversible anomalies in the temperature range between about 1000 and 1200 °C. It is believed that tetrahedral cations, bridging O atoms, and O vacancies undergo dynamical site exchange processes at high temperatures. At lower temperatures the dynamic disorder may transform to a static one. Diffraction experiments revealed that also partially ordered states may exist.

Synthesis, structure, photophysical and electrochemical behavior of 2-amino-anthracene triosmium clusters

The reactions of 2-amino-anthracene with [Os3(CO)10(CH3CN)2] have been studied and the products structurally characterized by spectroscopic, X-ray diffraction, photophysical and electrochemical techniques. At room temperature in CH2Cl2 two major, isomeric products are obtained [Os3(CO)10(μ-η2-(N-C(1))-NH2C14H8)(μ-H)] (1, 14%) and [Os3(CO)10(μ-η2-(N-C(3))-NHC14H9)(μ-H)] (2, 35%) along with a trace amount of the dihydrido complex [Os3(CO)9(μ-η2-(N-C(3))-NHC14H8)(μ-H)2] (3). In refluxing tetrahydrofuran only complexes 2 and 3 are obtained in 24% and 28%, respectively. A separate experiment shows that complex 1 slowly converts to 2 and that the rearrangement is catalyzed by adventitious water and involves proton transfer to the anthracene ring. Complex 1 is stereochemically non-rigid; exhibiting edge to edge hydride migration while 2 is stereochemically rigid. Complex 3 is also stereochemically non-rigid showing a site exchange process of the magnetically nonequivalent hydrides typical for trinuclear dihydrides. Interestingly, 2 decarbonylates cleanly to the electronically unsaturated 46e− cluster [Os3(CO)9(μ3-η2-(N-C(3))-NHC10H9)(μ-H)] (4, 68%) in refluxing cyclohexane, while photolysis of 2 in CH2Cl2 yields only a small amount of 3 along with considerable decomposition. The mechanism of the conversion of 1 to 2 and the dependence of the product distribution on solvent are discussed. All four compounds are luminescent with compounds 1–3 showing emissions that can be assigned to radiative decay associated with the anthracene ligand. Complexes 1–3 all show irreversible 1e− reductions in the range of −1.85–2.14V while 4 shows a nicely reversible 1e− wave at −1.16V and a quasi-reversible second 1e− wave at −1.62V. Irreversible oxidations are observed in the range from +0.35 to +0.49V. The relationship between the cluster ligand configurations and the observed electrochemical and photochemical behavior is discussed and compared with that of the free ligand.

Substitution Reactions at a Bridging Silicon Ligand. Formation of a Bis(μ-silylene) Complex Containing a Trifluoroacetoxy Group. Mechanistic Studies of the Site-Exchange Process of the Hydride Ligands

Treatment of a bis(μ-diphenylsilyl) complex, {Cp*Ru(μ-η2-HSiPh2)}2(μ-H)(H) (2a, Cp* = η5-C5Me5), with trifluoroacetic acid in toluene resulted in introduction of a trifluoroacetoxy group on a bridg...

Experimental and theoretical study of intramolecular exchange in Ir2Rh2(CO)12and Ir4(CO)11(µ-SO2)

As observed by variable-temperature and -pressure 13C NMR, intramolecular carbonyl scrambling in Ir2Rh2(CO)12 and Ir4(CO)11(micro-SO2) proceeds via a 'change of basal face' mechanism. In both cases the site exchange process has a positive activation volume suggesting that the transition states contain longer M-M distances compared to ground states of Cs symmetry. Transition state structures have been located by density functional calculations including relativistic effects. These structures contain a new symmetry plane which interchanges the indistinguishable starting and final geometries. Both transition state structures contain one significantly elongated M-M distance, bearing the bridging ligand unaffected by the site exchange. Differences in molecular volumes of ground and transition state geometries as calculated from Connolly surfaces and electron densities confirm the volume expansion in both cases. The sign of the activation volume is therefore a good criterion for distinguishing between the two main site exchange processes occurring in tetrahedral d9 carbonyl clusters, i.e. the 'change of basal face' process and the 'merry-go-round' process, as the latter presents a negative activation volume.

Cβ−H Activation of Aldehydes Promoted by an Osmium Complex

Evidence for the Cβ−H bond activation of aldehydes is shown. Complex (1) reacts with benzaldehyde and p- and m-substituted benzaldehydes to give (R = H (2), OCH3 (3, 5, 6), CF3 (4, 7)), which result from the C−H activation of one ortho-C−H bond. Reactions of 1 with 3-furaldehyde and 1-cyclohexene-1-carboxaldehyde lead to (8) and (9), respectively. 1H NMR spectroscopic studies indicate that the OsH2 unit of 2−9 forms elongated dihydrogen systems with H−H separations ranging between 1.41 and 1.50 A. Furthermore, the hydrogen atoms undergo thermally activated site exchange processes with ΔG⧧ between 9 and 12 kcal·mol-1 and quantum exchange coupling. Complexes 2, 5, and 8 have been characterized by X-ray diffraction analysis.

Activation of C(sp2)−H and Reduction of CE (E = CH, N) Bonds with an Osmium-Hexahydride Complex: Influence of E on the Behavior of RCHE-py Substrates

The hexahydride complex OsH6(PiPr3)2 (1) reacts with 2-vinylpyridine to give the trihydride derivative (2). The β- and γ-positions of the pyridine ring are quantitatively and selectively deuterated by addition of 1 (5%) to toluene-d8 and benzene-d6 solutions of 2. Under hydrogen atmosphere, 2 reacts with HBF4·OEt2 to afford [HNC5H4-o-Et]BF4 and regenerate 1. Under argon atmosphere, the addition of HBF4·OEt2 to dichloromethane solutions of 2 leads to the hydride-dihydrogen (3), which catalyzes the hydrogenation of 2-vinylpyridine to 2-ethylpyridine. In dichloromethane 3 evolves into the neutral chloro-dihydrogen compound (4). Complex 1 also reacts with N-methylene-2-pyridinamine and (E)-N-(phenylmethylene)-2-pyridinamine. The reaction with the first pyridinamine leads to a 3:1 mixture of the trihydride complexes (5) and (6), while the reaction with the second one selectively affords (7). Similarly to 2, the addition of 1 (5%) to toluene-d8 and benzene-d6 solutions of 6 produces the quantitative and selective deuteration of the β- and γ-positions of the pyridine ring. The addition of HBF4·OEt2 to diethyl ether solutions of 5 leads to (8). Isotope labeling experiments suggest that the reduction of the CC double bond of 2-vinylpyridine takes place by concerted addition of a dihydrogen ligand, while the reduction of the CN double bond of N-methylene-2-pyridinamine occurs by sequential addition of H- and H+. In solution the hydride ligands of these compounds undergo two different site exchange processes. Their activation parameters have been calculated by 1H NMR spectroscopy. Complexes 2, 3, and 5 have been characterized by X-ray diffraction analyses.

Ortho-CH Activation of Aromatic Ketones, Partially Fluorinated Aromatic Ketones, and Aromatic Imines by a Trihydride-Stannyl-Osmium(IV) Complex

Complex (1) reacts with acetophenone and benzophenone to give (R = CH3 (2), Ph (3)). In the solid state, the structure of 2 determined by X-ray diffraction analysis can be described as a pentagonal bipyramid with the phosphorus atoms of the phosphines occupying axial positions. In solution the hydride ligands of 2 and 3 undergo a thermally activated site exchange process. The activation parameters for the exchange are ΔH⧧ = 11.9 ± 0.5 kcal·mol-1 and ΔS⧧ = −0.7 ± 1.2 cal·mol-1·K-1 for 2 and ΔH⧧ = 11.8 ± 0.2 kcal·mol-1 and ΔS⧧ = −2.6 ± 1.9 cal·mol-1·K-1 for 3. The reaction of 1 with perdeuterated benzophenone affords the hydride-deuteride (3-d10), suggesting that the activation takes place on the monohydride intermediate OsH(SnPh2Cl)(PiPr3)2. The reaction pathway for the formation of this intermediate is evaluated by DFT calculations. Complex 1 also reacts with 2,3,4,5,6-pentafluorobenzophenone, 2-fluoroacetophenone, and benzophenone imine. The reactions with the partially fluorinated ketones give (4) and (5). In solution, the hydride ligands of 4 and 5 also exchange their positions. In this case, the activation parameters are ΔH⧧ = 12.6 ± 0.5 kcal·mol-1 and ΔS⧧ = −2.9 ± 1 cal·mol-1·K-1 for 4 and ΔH⧧ = 11.2 ± 0.4 kcal·mol-1 and ΔS⧧ = −2.8 ± 1.1 cal·mol-1·K-1 for 5. The reaction of 1 with benzophenone imine leads to (6), which has been characterized by X-ray diffraction analysis. The structure reveals an intramolecular Cl···H−N hydrogen bond between the chlorine bonded to the tin atom and the hydrogen of the imine. Treatment of 6 with KOH affords (7). The X-ray diffraction analysis of 7 shows a intramolecular O···H−N hydrogen bond and intermolecular HO···H interactions between the oxygen and the O−H hydrogen atom of two adjacent molecules in the crystal. DFT calculations on the model compounds (2t) and (X = Cl (6t), OH (7t)) have allowed the complete determination of the hydride positions in 2, 6, and 7 and the full characterization of the hydrogen bonds in 6 and 7.

Modelling americium sorption onto colloids: effect of redox potential

An analytical expression that evaluates the effect of the pH and the redox potential (Eh) was developed for studying the sorption of actinides onto colloids. It includes surface complexation with one type of surface site and ion exchange processes, and its formulation yields to a distribution coefficient (Kd) as function of the pH (hydrolysis) and Eh (redox sensitive species). The formulation considers also the values of the stability and hydrolysis constants for all species in solution and sorbed at the surface, and makes use of semi-empirical correlations between hydrolysis and surface complexation constants, for each colloid surface. The presence of complexing ligands in solution (such as carbonates) was also taken into account. The model was applied to the sorption of americium onto Al2O3, FeOOH and SiO2 colloids, in the presence and in the absence of carbonates in solution. From model testing it was shown that Am(III) sorption does not undergo redox change under natural conditions, as was expected. When carbonates are present in solution the calculated values of the distribution coefficient were lower than those calculated in the absence of carbonates, and no redox effect was detected. The distribution coefficient (Kd) values obtained with the developed model are in agreement with values reported for the sorption of americium onto colloids. It is known that in the water stability region Am(III) and their hydroxides are the only stable species; however, for the model application, all the possible redox couples of americium were considered. Moreover, this model is applicable to study the sorption of other redox sensitive elements.

Theoretical Study for the Site Exchange Mechanism of Anionic 5-Coordinate Pt(II) Complexes with Halide, [PtX(hfac)2]- (X=Cl,Br,I, hfac=hexafluoroacetylacetonate).

DFT calculations of the intra molecular site exchange process in square pyramidal five coordinate complexes, [PtX(hfac)2]- (hfac = 1, 1, 1, 5, 5, 5-hexafluoro-2, 4-pentanedionate, X = Cl, Br, I), were performed. The calculation reproduces well the X-ray molecular structures and the trigonal bipyramidal transition state energies of three possible paths, two of which actually seem to function, show that the order of the trans effect of halide ligands is Cl Br > I, which is in accordance with the experimental results.