Konstantin A. Lyssenko

Density functional theory is straying from the path toward the exact functional

Whither the density in DFT calculations? The continuing development of density functional theory (DFT) has greatly expanded the size and complexity of molecules amenable to computationally tractable simulation. The conventional metric of success for new functionals has been the accuracy of their calculated energies. Medvedev et al. examined how well these functionals calculate electron density across a series of neutral and cationic atoms (see the Perspective by Hammes-Schiffer). Although historically the accuracies of energy and density have improved in tandem, certain recent functionals have sacrificed fidelity to the true density. Science, this issue p. 49; see also p. 28 Certain recent approaches to density functional theory have sacrificed fidelity to the true electron density. The theorems at the core of density functional theory (DFT) state that the energy of a many-electron system in its ground state is fully defined by its electron density distribution. This connection is made via the exact functional for the energy, which minimizes at the exact density. For years, DFT development focused on energies, implicitly assuming that functionals producing better energies become better approximations of the exact functional. We examined the other side of the coin: the energy-minimizing electron densities for atomic species, as produced by 128 historical and modern DFT functionals. We found that these densities became closer to the exact ones, reflecting theoretical advances, until the early 2000s, when this trend was reversed by unconstrained functionals sacrificing physical rigor for the flexibility of empirical fitting.

Highly Luminescent and Triboluminescent Coordination Polymers Assembled from Lanthanide β-Diketonates and Aromatic Bidentate O-Donor Ligands

The reaction of hydrated lanthanide hexafluoroacetylacetonates, [Ln(hfa)(3)(H(2)O)(2)], with 1,4-disubstituted benzenes afforded a new series of one-dimensional coordination polymers [Ln(hfa)(3)(Q)](∞), where Ln = Eu, Gd, Tb, and Lu and Q = 1,4-diacetylbenzene (acbz), 1,4-diacetoxybenzene (acetbz), or 1,4-dimethyltherephtalate (dmtph). X-ray single crystal analyses reveal [Ln(hfa)(3)(acbz)](∞) (Ln = Eu, Gd, Tb) consisting of zigzag polymeric chains with Ln-Ln-Ln angles equal to 128°, while the arrays are more linear in [Eu(hfa)(3)(acetbz)](∞) and [Eu(hfa)(3)(dmtph)](∞), with Ln-Ln-Ln angles of 165° and 180°, respectively. In all structures, Ln(III) ions are 8-coordinate and lie in distorted square-antiprismatic environments. The coordination polymers are thermally stable up to 180-210 °C under a nitrogen atmosphere. Their volatility has been tested in vacuum sublimation experiments at 200-250 °C and 10(-2) Torr: the metal-organic frameworks with acetbz and dmtph can be quantitatively sublimed, while [Ln(hfa)(3)(acbz)](∞) undergoes thermal decomposition. The triplet state energies of the ancillary ligands, 21,600 (acetbz), 22,840 (acbz), and 24,500 (dmtph) cm(-1), lie in an ideal range for sensitizing the luminescence of Eu(III) and/or Tb(III). As a result, all of the [Ln(hfa)(3)(Q)](∞) polymers display bright red or green luminescence due to the characteristic (5)D(0) → (7)F(J) (J = 0-4) or (5)D(4) → (7)F(J) (J = 6-0) transitions, respectively. Absolute quantum yields reach 51(Eu) and 56(Tb) % for the frameworks built from dmtph. Thin films of [Eu(hfa)(3)(Q)](∞) with 100-170 nm thickness can be obtained by thermal evaporation (P < 3 × 10(-5) Torr, 200-250 °C). They are stable over a long period of time, and their photophysical parameters are similar to those of the bulk samples so that their use as active materials in luminescent devices can be envisaged. Mixtures of [Ln(hfa)(3)(dmpth)](∞) with Ln = Eu and Tb yield color-tunable microcrystalline materials from red to green. Finally, the crystalline samples exhibit strong triboluminescence, which could be useful in the design of pressure and/or damage detection probes.

Reversible Addition of Alkynes to Gallium Complex of Chelating Diamide Ligand

Different alkynes add reversibly to the gallium complex of the dpp-Bian dianion. The reactions proceed with addition of the alkynes across the Ga-N-C fragment resulting in carbon-carbon and carbon-gallium bonds. In the case of 3 and 4 a full elimination of the alkyne takes place at T < 100 degrees C, whereas with adducts 5 and 6 it occurs at heating to ca. 200 degrees C.

“Higher density does not mean higher stability” mystery of paracetamol finally unraveled

Topological analysis of the experimental electron density distribution functions for two polymorphs of paracetamol showed that strong H-bonds are responsible for the higher stability of crystal phase I, weak interactions for the higher density of phase II. This made it possible to finally resolve the contradiction between the relative stabilities and the densities of the two paracetamol polymorphs.

Estimation of Dissociation Energy in Donor−Acceptor Complex AuCl·PPh3 via Topological Analysis of the Experimental Electron Density Distribution Function

The high-resolution X-ray diffraction analysis and plane-wave density functional theory were applied to the investigation of charge density distribution in the donor-acceptor complex of AuCl with PPh3. The approach allows us to estimate the atomic charges, the charge transfer, the energy of weak interactions (Au...H, Au...C, H...Cl, etc.), and Au-P bond energy directly from the experimental data.

Electron density distribution in stacked benzene dimers: a new approach towards the estimation of stacking interaction energies.

The potential energy surface for the benzene dimer in stacked conformations (84 points calculated) was computed at the MP2(FC)6-31+G(2d,2p) level of theory. Electron density (ED) distribution computed using the MP2(FC), B3LYP, and Hartree-Fock methods with the same basis set is studied in the frame of topological analysis. It is found that ED topology does not depend on the method of calculation. The values of the ED and its Laplacian in the cage critical point calculated using different methods are determined to be linearly dependent with the slope depending on basis set. Correlation equations based on these properties allow the interaction energy between benzene rings to be predicted with 8% mean relative error in the energy for the given region of the potential energy surface. This provides a new method for the estimation of stacking interaction energy using ED properties calculated with low level quantum-chemical methods.

Extremely short C–H⋯F contacts in the 1-methyl-3-propyl-imidazolium SiF6—the reason for ionic “liquid” unexpected high melting point

The synthesis and XRD investigation of hexafluorosilicate salt with 1-propyl-3-methyl imidazolium ([Pmim]+) cation is described. Analysis of crystal packing has revealed that an unexpectedly high melting point (mp, 210 °C) of salt resulted from the presence of extremely short interionic C(Im)H⋯F contacts in the crystal (1.94–2.42 A). The absence of strong C–H⋯F interaction for alkyl radicals led to high mobility of substituents and resulted in phase transition of the order–disorder type. The total energy of the CH⋯F interactions in the hypothetical [SiF6(Pmim)6]+4 cluster according to DFT calculation and topological analysis of the electron density distribution attains ca. 33 kcal mol−1.

Synthesis and structure of rhodium complexes with monoanionic carborane ligand [9-SMe2-7,8-C2B9H10]−

Abstract (Rhodacarborane)halide complexes [(η-9-SMe 2 -7,8-C 2 B 9 H 10 )RhX 2 ] 2 ( 4a : X=Cl; 4b : X=Br; 4c : X=I), which are analogous to [Cp*RhX 2 ] 2 , were synthesized by reaction of (η-9-SMe 2 -7,8-C 2 B 9 H 10 )Rh(cod) (cod=1,5-cyclooctadiene) with HX. Compounds 4 were used to prepare several sandwich and half-sandwich complexes containing (η-9-SMe 2 -7,8-C 2 B 9 H 10 )Rh fragment. 2e-Ligands destroy the dimeric structure of 4 to give the adducts (η-9-SMe 2 -7,8-C 2 B 9 H 10 )RhLX 2 , exemplified by preparation of (η-9-SMe 2 -7,8-C 2 B 9 H 10 )Rh(CO)I 2 and (η-9-SMe 2 -7,8-C 2 B 9 H 10 )Rh(PPh 3 )Cl 2 . The reaction of 4a with dppe in the presence of TlBF 4 affords the cationic complex [(η-9-SMe 2 -7,8-C 2 B 9 H 10 )Rh(dppe)Cl]BF 4 ( 7 BF 4 ). Sandwich complexes [(η-9-SMe 2 -7,8-C 2 B 9 H 10 )Rh(η-C 5 R 5 )]CF 3 SO 3 ( 11a CF 3 SO 3 : R=H; 11b CF 3 SO 3 : R=Me) were obtained by abstracting chloride from 4a by CF 3 SO 3 Ag with subsequent treatment with C 5 R 5 H. Complex 11b PF 6 was prepared by reaction of [Cp*RhCl 2 ] 2 with Na[9-SMe 2 -7,8-C 2 B 9 H 10 ]. Complex (η-9-SMe 2 -7,8-C 2 B 9 H 10 )Rh(η-7,8-C 2 B 9 H 11 ), containing two carborane ligands, was obtained by reaction of 4a with Tl[Tl(η-7,8-C 2 B 9 H 11 )]. Structures of 7 BF 4 and 11b PF 6 were confirmed by X-ray diffraction study.

Synthesis of Tetrazino‐tetrazine 1,3,6,8‐Tetraoxide (TTTO)

This study presents the first synthesis and characterization of a new high energy compound [1,2,3,4]tetrazino[5,6-e][1,2,3,4]tetrazine 1,3,6,8-tetraoxide (TTTO). It was synthesized in ten steps from 2,2-bis(tert-butyl-NNO-azoxy)acetonitrile. The synthetic strategy was based on the sequential closure of two 1,2,3,4-tetrazine 1,3-dioxide rings by the generation of oxodiazonium ions and their intramolecular coupling with tert-butyl-NNO-azoxy groups. The TTTO structure was confirmed by single-crystal X-ray.

Two Modifications Formed by "Sulflower" C16S8 Molecules, Their Study by XRD and Optical Spectroscopy (Raman, IR, UV-Vis) Methods

Sublimation of sulflower, octathio[8]circulene C 16S 8 ( 1), on heating under high vacuum ( approximately 10 (-5) Torr) leads to successive formation of two modifications: a white film ( 1W) and a red polycrystalline solid ( 1R). When kept at room temperature for several weeks, 1W spontaneously turns pink, reflecting the monotropic phase transition 1W --> 1R. The accurate molecular and crystal structure of 1R has been studied using low-temperature (100 K) high-resolution single crystal X-ray analysis. The C 16S 8 molecule in crystal is strictly planar with nearly equalized bonds of each type (C-C, C-S, and CC). The point symmetry group of the free molecule is D 8 h , and the crystal space group is P2 1/ n. These data allowed group-theoretical analysis of vibrational normal modes to be accomplished. Investigation of the charge density distribution of 1R including Baders AIM approach has revealed rather strong intermolecular S...S, S...C, and C...C interactions of charge transfer and pi-stacking types with overall lattice energy of 28.5 kcal/mol. The charge transfer due to the S...S interactions is the reason for the red coloration of 1R. The latter is reflected by its UV-vis spectrum exhibiting absorption bands in the visible region which are absent from that of 1W. Both modifications were studied comparatively by vibrational (Raman, IR) and electronic spectroscopies as well as XRD powder diffraction. All the results obtained are fully consistent and show that 1W is much less ordered than 1R with significantly weakened intermolecular interactions. Rationalizing of these results has led to an idea that 1W could be soluble, in contrast to 1R. Indeed, 1W appeared soluble in common solvents; this finding opens the way to the study of the chemistry of 1 and investigation of its electrooptical properties.