The catalytic synthesis of 1,3-diaminopropane from 1,3-propanediol and ammonia was studied in a continuous fixed-bed reactor in the pressure range 50 to 150 bar. The unsupported Co-based catalysts applied were characterized by N₂physisorption, XRD, XPS, TPR, and ammonia adsorption using pulse thermal analysis and DRIFT spectroscopy. The latter investigations revealed that the best catalyst, 95 wt% Co–5 wt% Fe, contained only very weak acidic sites, unable to chemisorb ammonia. The absence of strong acidic and basic sites was crucial to suppress the various acid/base-catalyzed side reactions (retro-aldol reaction, hydrogenolysis, alkylation, disproportionation, dimerization, oligomerization). Other important requirements for improved diaminopropane formation were the use of excess ammonia (molar ratio NH₃/diol>20) and the presence of the metastable β-Co phase. A small amount of Fe additive could efficiently hinder the transformation of this phase into the thermodynamically stable α-Co phase and thus prevent catalyst deactivation up to 10 days on stream. Application of supercritical ammonia almost doubled the selectivity to amino alcohol and diamine. The selectivity enhancement in the near-critical region is attributed to elimination of the interphase mass transport limitations and to the resulting higher surface ammonia concentration.

A new modifier, 2-phenyl-9-deoxy-10,11-dihydrocinchonidine, has been synthesized for the enantioselective hydrogenation of ketopantolactone and α-ketoesters over chirally modified Pt/alumina. The results indicate flat adsorption of cinchonidine with the quinoline ring oriented parallel to the surface and, furthermore, give some insight into the conformation of the modifier within the transition state complex. Comparison of the structures and catalytic behaviors of 9-deoxycinchonidine and the new modifier allows to exclude the previously proposed perpendicular or tilted adsorption of the quinoline ring via the N atom.

Cinchona alkaloids play a major role as chiral auxiliaries in asymmetric catalysis. Acetic acid is known to be an excellent solvent in the enantioselective hydrogenation over chirally modified platinum metals. The crucial interaction between the chiral auxiliary and the solvent has been investigated using the cinchonidine–acetic acid pair. Solutions containing cinchonidine and acetic acid were studied by means of NMR and IR spectroscopy as well as by ab initio Hartree–Fock calculations. In the presence of the acid cinchonidine is protonated at the quinuclidine N and adopts an open conformation where the quinuclidine N points away from the quinoline moiety. In the most stable 1∶1 and 2∶1 acetic acid–cinchonidine complexes both the N–H⁺ and O–H groups of cinchonidine are involved in hydrogen bonding. The most stable 1∶1 complex is found to be cyclic. The relative arrangement of the N–H⁺ and O–H groups of protonated cinchonidine is ideally suited to bind an acetate anion, and the interaction hardly affects the cinchonidine conformation. Several 2∶1 acid–base complexes coexist in solution. The IR spectra give evidence for the existence of a 2∶1 cyclic complex. Calculated structures, relative energies and vibrational frequencies are in good agreement with the experiment. The findings rationalise the importance of the O–H group of cinchonidine for the enantiodifferentiation in the enantioselective hydrogenation of α,β-unsaturated carboxylic acids over cinchonidine-modified Pd.

The mechanism of enantiodifferentiation in the hydrogenation of alkenoic acids over cinchona-modified Pd has been investigated using the tiglic acid → 2-methyl-butanoic acid transformation as test reaction. Application of simple derivatives of cinchonidine, modified at the (C-9)–OH and/or the quinuclidine nitrogen, proved that both functional groups are involved in the enantiodiscriminating step. Addition of a strong base (1,8-diazabicyclo[5.4.0]undec-7-ene, DBU) to tiglic acid prior to hydrogenation revealed that one cinchonidine molecule interacts with a dimer of tiglic acid on the metal surface. Ab initio calculations corroborate the existence of an energetically favored acid dimer–cinchonidine intermediate stabilized by hydrogen bonding, involving both the OH and the quinuclidine nitrogen of cinchonidine.

In contrast to high-spin ferrous paramagnetic heme proteins, the chemical shifts of the heme protons are very unusual in the ferrocytochromes c‘. Magnetic susceptibility studies ofRhodobacter capsulatus ferrocytochrome c‘ in frozen solutions have been performed and indicate an S = 2 spin state and a large negative axial (D) zero-field splitting parameter (−18.3 cm^-1) as well as a significant rhombic (E) value (−4.9 cm^-1). The ¹H and ¹⁵N resonances have been extensively assigned by TOCSY−HSQC, NOESY−HSQC, and HSQC−NOESY−HSQC 3-D heteronuclear experiments performed on a 8 mM sample labeled with ¹⁵N. Based on short-range and medium-range NOEs and H^N exchange rates, the secondary structure consists of four helices: helix-1 (3−30), helix-2 (34−49), helix-3 (78−97), and helix-4 (103−117). The ¹⁵N, H^N, and H^α chemical shifts of the reduced (or ferro) state are compared to those previously assigned for the diamagnetic carbon monoxide complex form. From the chemical shift differences between these redox states, the orientation and the anisotropy of the paramagnetic susceptibility tensor have been determined using the crystallographic coordinates of the ferric state. Values of −23 and −3 cm^-1 have been inferred for D and E, and the z-axis of the tensor is tilted approximately 30° from the normal to the heme. The paramagnetic chemical shifts of the heme protons have been determined and split up into Fermi shift and the dipolar shift contributions. The pattern of the contact shifts is very unusual, exhibiting a 2-fold symmetry, and is discussed in terms of molecular orbital interactions between the porphyrin macrocycle and the imidazole ring.

Barium in BaMgF[4] and in Ba[6]Mg[7]F[26] can be partially replaced by Sr or Eu. The single crystal structural analysis of the title compounds (a = 409.06 pm, b = 1452.7 pm, c = 579.02 pm, space group Cmc2[1] for Ba[0.78(3)]Eu[0.22(3)]MgF[4] [Z = 2, R[w] = 0.023 for 998 reflections] and a = 583.47 pm, b = 1209.09 pm and c = 1506.56 pm, space group Immm for Ba[5.20(6)]Eu[0.80(6)]Mg[7]F[26]) MgF[4] [Z = 2, R[w] = 0.019 for 2694 reflections] confirms the substitution of barium by europium. A split refinement of the substituted barium site in both crystals reveals a trend of europium to get closer to the nearest fluoride neighbors by simultaneously reducing the coordination sphere.

Crystals of composition Ba₇F₁₂Cl₂ were obtained by a reaction at room temperature between Ba²⁺/Cl^-/F^- in a gel of agar-agar/water. The hexagonal crystals have space group P6, a=1064.69(8), c=417.89(5)pm, V=410.24(8) 106 pm3 and Z=1. The anions form a propeller type network located in tunnels parallel to the chex axis; the chloride ions are located at the center on the propeller axes. The Ba²⁺ ions are coordinated by a (distorted) tricapped trigonal environment of fluoride and chloride anions. Disorder is present for one particular Ba²⁺ site. The average structure is isotypic with the structure of Pb₇F₁₂Cl₂.

Short range correlations of the distribution of high spin (HS) and low spin (LS) states show up in thermal spin transition curves, decay curves of the light induced metastable HS state (LIESST state), and in structural features during the spin transitions. Correlations are due to short range interactions between the spin crossover molecules. Short range interactions may compete with omnipresent long range interactions and give rise to interesting spin transition phenomena. In this paper, the effect of correlations on the thermal spin transition in the mixed crystal system [Fe_xZn_1−x(pic)₃]Cl₂·EtOH (pic=picolylamine) is discussed. In particular the step in the thermal transition curve is a direct consequence of such correlations. In addition, the decay of the metastable HS state of the pure iron compound at ca. 20 K can be significantly changed by preparing metastable HS states with a random distribution over the lattice sites. Both experiments could be well reproduced by Monte Carlo simulations. In the orthorhombic modification of the compound Fe[5NO₂-sal-N(1,4,7,10)]([2,2′-(2,5,8,11-tetraazadodeca-1,11-diene-1,12-diyl)4-nitrophenolato] (2-)-N2, N2′,N2′′,N2′′′,O1, O1′]Fe(II)) a commensurable superstructure has been found. This compound represents the first example of a stable infinite range correlation of the spin states over the lattice sites.

The propagation of the high-spin (HS) → low-spin (LS) relaxation at 53 K in a single crystal of the iron (II) spin-crossover compound [Fe(ptz)₆](BF₄)₂ was followed by photography, after inducing the local photoexcitation to the metastable HS state at 20 K using the single wavelength (457 nm Ar^± ion laser) irradiation. The photoinduced formation of the HS—LS patterns with a characteristic diameter of some 0.1 mm was observed to occur inhomogeneously at a macroscopic scale already during photoexcitation. The contrast between the HS (transparent) and the LS (purple) regions was amplified during relaxation. The effect is described in terms of a transient instability, for which a microscopic model in the mean-field approximation is proposed. The mechanism for the development of patterns at the macroscopic scale is discussed.

As shown from the crystal structure, the oxygen atom of Ph₃P=CH---C(O)CH₃ forms both intra and intermolecular hydrogen bonds. X-irradiation of this compounds produces a room-temperature-stable radical which was studied by single crystal EPR/ENDOR spectroscopy. Comparison of the experimental hyperfine couplings with those obtained from ab initio calculations shows that the radical cation Ph₃P⁺---CH=C(OH)CH₂ is formed under radiolysis. The principal directions of the hyperfine tensors indicate that, in this process, some of the hydrogen bonds are broken and that the radical undergoes a drastic reorientation around the Ph₃P---C bond.

Li2S, cubic, Fiiβm (No. 225), a = 5.7158(1) A, V= 186.7 A3, Z = 4, REi(F) = 0.009, Rv.(F) = 0.009, T= 293 K.

We have studied the binding of two organic cations, an iminium (IM) and a guanidinium (GU), to a cyclophane host P^4--4Na⁺, using molecular dynamics simulations and free energy calculations. A proper treatment of the long-range electrostatic forces is essential for the stability of these highly charged complexes, and a simple cutoff at 12 Å results in an artifactual dissociation of the IM−P^4--4Na⁺ complex. Since the host is highly aromatic and the guests cationic, cation−π interactions play an important role in the complex stability. In free energy calculations, using a simple additive force field, we calculate that the relative free energy of association of IM and GU binding to the host is 2.3 kcal/mol favoring IM, which is of the correct sign but 1.4 kcal/mol too small in magnitude. Differences in van der Waals interaction energies are mainly responsible for the different binding strengths, and the host adopts different shapes when accommodating IM compared to GU. To approximately estimate the contribution to the complex stability from the polarization energy, we calculated the in vacuo interaction energies in the two complexes, using a nonadditive force field, previously shown to accurately describe alkali cation−aromatic interaction energies in vacuo. Adding the contribution from the polarization energy upon forming the two complexes in this calculation to the estimate from the free energy calculation, we obtain an improved relative binding free energy (−4.0 kcal/mol), which is in close agreement with the experimental value of −3.7 kcal/mol.

Persistent spectral hole burning was performed on the ⁷F₀–⁵D₁ transition of Sm²⁺ in thin films of SrFCl. Depending on the substrate and the growth conditions, a total hole depth between 47% and 70% was reached. The holes were Lorentzians of width 4(±0.3) cm⁻¹. The time evolution of the hole depth was studied. It is described by two exponentials: a short time decay (t₁ = 0.37 days) and a long time decay (t₂ = 20.4 days) with a 20% infinite time limit. One- and two-photon burning mechanisms act.

Electronic energy transfer from [Cr(ox)₃]^3- (ox = oxalate) in three-dimensional (3D) anionic oxalate networks to encapsulated [Cr(bpy)₃]³⁺ (bpy = 2,2‘-bipyridine) cations at 1.5 K was investigated by time-resolved luminescence spectroscopy. Two series of mixed crystals of nominal compositions [NaAl_1-xCr_x(ox)₃][Rh_0.99Cr_0.01(bpy)₃]ClO₄ (x = 0, 0.01, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, and 1) and [NaAl_0.99Cr_0.01(ox)₃][Rh_1-yCr_y(bpy)₃]ClO₄ (y = 0, 0.01, 0.02, 0.03, 0.04, and 0.05) were utilized. Energy transfer from [Cr(ox)₃]^3- to [Cr(bpy)₃]³⁺ occurs by two mechanisms. Rapid, short-range transfer (k_et > 10⁶ s^-1) is attributed to superexchange coupling between the Cr³⁺ ions via π overlap of the oxalate and bipyridine ligands. In addition, at low [Cr(ox)₃]^3- concentrations (nominally x = 0.01) a very much slower process with a maximum k_et ≈ 200 s^-1 is identified in the time-resolved spectra and attributed to a dipole−dipole mechanism. Furthermore, the resonant [Cr(ox)₃]^3- to [Cr(ox)₃]^3- energy migration previously reported by von Arx et al. (Phys. Rev. (1996), B54, 15800) assists [Cr(ox)₃]^3- to [Cr(bpy)₃]³⁺ transfer as the [Cr(ox)₃]^3- concentration increases.

In iron(II) spin-crossover compounds, the transition from the ¹A₁ low-spin state at low temperatures to the ⁵T₂ high-spin state at elevated temperatures is accompanied by a large increase in metal-ligand bond lengths. The resulting elastic interactions may be pictured as an internal pressure which is proportional to the concentration of the low-spin species. Because pressure stabilises the low-spin state relative to the high-spin state this results in a positive feedback. Thermal transition curves in neat iron(II) spin-crossover compounds are thus invariable much steeper than in diluted mixed crystals, and the high-spin→low-spin relaxation following the light-induced population of the high-spin state at low temperatures is self-accelerating. Strong interactions give rise to a thermal hysteresis, and light-induced bistabilities may be observed for compounds with initially a high-spin ground state and the potential for a light-induced population of the low-spin state. For such compounds, the increasing internal pressure may stabilise the low-spin state sufficiently so that it becomes the molecular ground state above some critical light-induced low-spin fraction. Secondary effects of the elastic interactions include crystallographic phase transitions, inhomogeneous distributions of sites, and anomalies such as steps in the transition curve.

The formalism of the Kohn–Sham equations with constrained electron density is extended to the spin-polarized case. The isotropic hyperfine coupling constants (A_iso(Mg)) of Mg⁺ embedded in a Ne or Ar matrix represented using a cluster are calculated and compared to that of free Mg⁺. For the largest basis set used, the calculated values (222.9 and 210.4 gauss for Ar and Ne, respectively) agree with experimental measurements (222.4 and 211.6). The shifts of A_iso(Mg) relative to the values for free Mg⁺ are rather basis-set-independent.

The ground- and excited-state properties of both [Ru(bz)₂]²⁺ and crystalline bis(η⁶-benzene)ruthenium(II) p-toluenesulfonate are investigated using the density functional theory. A symmetry-based technique is employed to calculate the energies of the multiplet structure splitting of the singly excited triplet states. For the crystalline system, a Buckingham potential is introduced to describe the intermolecular interactions between the [Ru(bz)₂]²⁺ system and its first shell of neighbor molecules. The overall agreement between experimental and calculated ground- and excited-state properties is good, as far as the absolute transition energies, the Stokes shift, and the geometry of the excited states are concerned. The calculated d-d excitation energies of the isolated cluster are typically 1000-2000 cm^-1 too low. An energy lowering is obtained in a_1g → e_1g(³E_1g) excited state when the geometry of [Ru(bz)₂]²⁺ is bent along the e_1u Renner-Teller active coordinate. It vanishes as the crystal packing is taken into account.

The adsorption of methanol on the (110) surface of γ-alumina was investigated using both ab initio and density functional theory quantum chemical methods. A [Al₃O₉H₁₀]⁺ cluster model comprising one tetrahedral and two octahedral aluminum cations were used to describe the surface and the mechanism of adsorption of methanol. This has allowed us to rationalize the stable structures of adsorbate and the mode of bonding. The IR frequency shifts between the gas phase and the adsorbed species were also calculated and they exhibit good agreement with experiment.

The structure and stretching frequency of the CO molecule physisorbed on the MgO(100) surface were investigated using the recently developed formalism of Kohn-Sham equations with constrained electron density (KSCED). The KSCED method makes it possible to divide a large system into two subsystems and to study one of them using Kohn-Sham-like equations in which the effective potential takes into account the interactions between subsystems. Compared to the standard Kohn-Sham formalism, the KSCED method involves an additional functional due to the non-additivity of the kinetic energy. The surface was represented using a cluster ((MgO₅)⁸⁻ or Mg₉O₉) embedded in an array of electric point-charges. The KSCED calculations led to a blue-shift of the stretching frequency of the C-down adsorbed CO molecule amounting to 47–21 cm⁻¹ depending on the distance from the surface. At the C–Mg distance of 2.42 Å, which corresponds to a typical minimum of the potential energy curve derived from supermolecule Kohn-Sham calculations applying gradient-corrected functionals, the KSCED frequency shift amounts to 35 cm⁻¹ in excellent agreement with the most recent experiments. The CO stretching frequency of the O-down adsorbed CO molecule is red-shifted. The effects of cluster size and choice of the functionals on the KSCED frequencies, geometries and energies were analyzed. For C–Mg distances varying between 2.3 and 3.0 Å, changing the cluster size affects the frequencies by less than 4 cm⁻¹ and the CO bond length by less than 0.0003 Å. At C–Mg distances larger than 2.4 Å, the change of the cluster size negligibly affects the KSCED interaction energies. The KSCED formalism makes it possible to study directly the effects associated with relaxation of the surface's electron density upon adsorbing CO. It is shown that these effects might contribute up to 30% of the KSCED interaction energy, but that they do not result in significant changes of either the geometries or frequencies.

A study of the dynamics of electronic energy transfer (EET) in arrays containing three, four, and six tetraphenylporphine units connected with phenylethynyl spacers is reported. For arrays containing the same chromophores, the EET rate constant was determined from the reorientational dynamics of the transition dipole using the crossed grating technique. EET time constants ranging from 150 ps up to 33 ns were measured, depending on the distance between the chromophores and on the metal ion complexed in the porphyrins. For the trimeric planar arrays, the interchromophoric distance varies by a factor of 2, while the ratio of the through space to through bond distances is constant. By comparing the measured EET rate constants with those calculated using Förster theory, the contributions of the Coulombic, through space, mechanism and of the exchange, through bond, mechanism could be estimated. For the arrays with the shortest spacer (through space distance of 23 Å), EET occurs through both exchange and Coulombic interactions with a ratio of about 3:1. This ratio increases up to about 10 as the distance is increased to 34.5 Å. At 46.5 Å, the ratio decreases and it appears that the Coulombic interaction becomes the dominant mechanism at longer distances. In the tetrahedral compound, the presence of a central saturated carbon strongly alters the electronic conducting properties of the spacer and makes the exchange mechanism inoperative.

The deactivation of the S₁(π,π^*) excited state of nickel tetraphenylporphine has been investigated using various transient grating techniques. By measuring the density changes of the sample occurring during this process, the excited state, that is responsible for the ground state recovery time of 250 ps, was determined to lie 1.18±0.13 eV above the ground state. This value suggests that this state is the¹(d,d) state.

The solvation dynamics of an organic dye, IR140, in methanol, ethanol, and in a series of six alkanenitriles has been investigated using the transient grating technique. In all solvents, the dynamics exhibit ultrafast, almost solvent-independent, components ascribed to inertial solvation, and a slower viscosity-dependent component, due to diffusive solvation. The relative amplitudes of these components depend on both the solvent and on the wavelength at which the experiment is performed. The contribution of inertial motion increases with decreasing size of the solvent molecules and with decreasing wavelength. It appears that diffusive motion is associated with a loose solvent shell, while inertial motion dominates when the solvation layer is dense.

A "CO-like matrix", showing coordination analogous to that of carbonyl groups, is provided by silacalix[4]phosphinine macrocycles. Reaction with Au^I leads to the first gold(I) complexes of macrocycles, which can be reduced with sodium or potassium to the paramagnetic gold(0) complexes (an example is shown), as evidenced by cyclic voltammetry and EPR spectroscopy.

Single crystals of the new host Ba₁₂F₁₉Cl₅ doped with Eu²⁺ were grown and studied by electron paramagnetic resonance (EPR) and luminescence emission spectroscopy. Three different Eu²⁺ sites were observed. Two of them had orthorhombic point symmetry while the last one was monoclinic. Physico-chemical and symmetry arguments allowed us to establish correspondence between the different Eu²⁺centres and the host cation lattice sites. All three centres presented in their ground state important crystal field splitting. The 80 K luminescence emission spectrum consisted of one broad unsymmetrical f-d band peaking at 22 700 cm^-1. No 4f-4f transitions of the Eu²⁺ ion were observed between room temperature and 80 K.

We have studied the solid-liquid equilibrium of the system Sr_1–yBa_yFCl_1–xBr_x using DTA and X-ray diffraction techniques. The entire composition range in this system yields solid solutions which crystallize in the PbFCl (Matlockite) structure type. The melting points of the entire composition range have been parametrized (within 5°C rms error) using a biquadratic fit of the available data obtained by experiment and from the literature.