Ivan S. Bushmarinov

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.

Lanthanide 9-anthracenate: solution processable emitters for efficient purely NIR emitting host-free OLEDs

Searching for new NIR emitting materials, lanthanide 9-anthracenates Ln(ant)3 were synthesized and thoroughly characterized. Ytterbium 9-anthracenate Yb(ant)3, that demonstrated the highest NIR luminescence efficiency, was successfully used as an emission layer of a host-free OLED and its electroluminescence quantum efficiency, corresponding to the sole band at 1000 nm, reached 0.21%. This performance could be achieved due to the high quantum yield of Yb(ant)3, which reached 1.5% and was increased up to 2.5% by partial Yb3+ substitution with Lu3+, as well as its high electron mobility due to the extended stacking in its crystal structure. The first gadolinium-based PHOLED was prepared based on Gd(ant)3.

Electrocatalysis in MIRC reaction strategy: facile stereoselective approach to medicinally relevant spirocyclopropylbarbiturates from barbituric acids and activated olefins

The combined electrolysis of barbituric acids and benzylidenemalononitriles or benzylidenecyanoacetates in methanol in an undivided cell in the presence of sodium bromide results in efficient MIRC (Michael-initiated ring-closure) formation of the corresponding spirocyclopropylbarbiturates in 45–93% yield. The electrocatalytic reaction proceeds smoothly under neutral and mild conditions with benzylidenemalononitriles or benzylidenecyanoacetates bearing both electron-donating and electron-withdrawing groups. NMR and single X-ray diffraction studies indicate that the electrocatalytic MIRC transformation of barbituric acids and benzylidenecyanoacetates results in the stereoselective formation of spirocyclopropanes with an (E)-configuration of aryl and alkoxycarboxylate substituents. The implication of electrocatalysis in the MIRC reaction strategy allows the combination of the synthetic virtues of both methods and accounts for an efficient approach to medicinally relevant spirocyclopropylbarbiturates avoiding inconvenient direct use of molecular halogen or halogenated substrates in accordance with the concepts of modern green chemistry.

Highly Luminescent, Water‐Soluble Lanthanide Fluorobenzoates: Syntheses, Structures and Photophysics, Part I: Lanthanide Pentafluorobenzoates

Highly luminescent, photostable, and soluble lanthanide pentafluorobenzoates have been synthesized and thoroughly characterized, with a focus on Eu(III) and Tb(III) complexes as visible emitters and Nd(III) , Er(III) , and Yb(III) complexes as infrared emitters. Investigation of the crystal structures of the complexes in powder form and as single crystals by using X-ray diffraction revealed five different structural types, including monomeric, dimeric, and polymeric. The local structure in different solutions was studied by using X-ray absorption spectroscopy. The photoluminescence quantum yields (PLQYs) of terbium and europium complexes were 39 and 15 %, respectively; the latter value was increased almost twice by using the heterometallic complex [Tb0.5 Eu0.5 (pfb)3 (H2 O)] (Hpfb=pentafluorobenzoic acid). Due to the effectively utilized sensitization strategy (pfb)(-) →Tb→Eu, a pure europium luminescence with a PLQY of 29 % was achieved.

Novel 1,5,3-dithiazepanes: three-component synthesis, stereochemistry, and fungicidal activity

Three-component heterocyclization of hydrazine with formaldehyde and ethane-1,2-dithiol gave previously unknown 3,3′-bi(1,5,3-dithiazepane). Its stereochemistry was determined by X-ray diffraction. The reaction with higher aliphatic aldehydes RCHO (R = Me, Et, Prn, and Bun) yielded 2,4-dialkyl-3-alkylideneamino-1,5,3-dithiazepanes. The stereochemistry of the latter was determined by 1H and 13C NMR spectroscopy and confirmed by quantum chemical calculations. Heterocyclizations of phenylhydrazine and benzylhydrazine with ethane-1,2-dithiol gave 3-amino-1,5,3-dithiazepanes only with CH2O and MeCHO as the aldehyde component. 3,3′-Bi(1,5,3-dithiazepane) and its N-adduct with MeI were found to exhibit fungicidal activity against microscopic fungi.

The azide anion as a building block in crystal engineering from a charge density point of view

The geometrical preferences of hydrogen bonds with azide anion are studied using topological analysis of experimental and calculated electron density distribution. The comparison of electron localization function (ELF) and QTAIM analysis shows the reasons behind the apparent unidirectionality of azide anions lone pairs. The similarity between hydrogen and coordinated bonds involving azide species is demonstrated via the analysis of the CSD.

Neuroprotective Activity of (+)-(S)-2-[(1S,5R)-(3,7-Dioxo-2,4,6,8-Tetraazabicyclo[3.3.0]oct-2-yl)]-4-methylthiobutanoic acid

A study of the neurotropic, neuroprotective, and antioxidant action of the enantiomers and racemate of 2-[(3,7-dioxo-2,4,6,8-tetraazabicyclo[3.3.0]oct-2-yl)]-4-methylthiobutanoic acid synthesized in a stereoselective reaction of (R)-, (S)-, or (R,S)-N-carbamoylmethionine with 4,5-dihydroxyimidazolidine-2-one showed that only (+)-(S)-2-[(1S,5R)-(3,7-dioxo-2,4,6,8-tetraazabicyclo[3.3.0]oct-2-yl)]-4-methylthiobutanoic acid had neuroprotective properties. X-ray structure analysis showed that the predominating racemate of glycolurils is crystallized from aqueous solutions as a conglomerate. Antioxidant activity was not detected.

Comb-shaped liquid crystalline stereoregular cyclolinear methylsiloxane copolymers: synthesis, behaviour in bulk and behaviour in monolayers

Stereoregular cyclolinear organosiloxane copolymers containing vinyl groups with diorganosiloxane spacers as well as cyclohexasiloxane fragments were synthesised. Comb-shaped liquid crystalline (LC) cyclolinear polymethylsiloxanes with mesogenic side groups were prepared by hydrosilylation of stereoregular cyclolinear organosiloxane copolymers with (4′-cyanobiphenyl-4-yl)-11-(1,1,3,3-tetramethyldisiloxyl)undecanoate in the presence of the Karstedt catalyst. The chemical structure of the copolymers synthesised was confirmed by proton and silicon nuclear magnetic resonance spectroscopies and infrared spectroscopy. Their phase behaviour was characterised by differential scanning calorimetry, X-ray analysis and optical polarising microscopy. It was shown that the appearance of the LC state, the temperature range of its existence and polymesomorphism are determined by the molecular mass of the copolymer and by the content of the mesogenic groups. The introduction of three mesogenic groups per monomer unit results in polymesomorphic transitions. The tacticity of the backbone influences the interchain distances in the comb-shaped LC cyclolinear methylsiloxane copolymers. Studying the Langmuir films of the stereoregular LC methylsiloxane copolymers revealed that different types of molecular arrangements could be observed depending on the number of mesogenic groups attached. LC copolymers having three mesogens per monomer unit demonstrate a two-stage monolayer collapse.

Electronic structure of cesium butyratouranylate(VI) as derived from DFT-assisted powder X-ray diffraction data.

Investigation of chemical bonding and electronic structure of coordination polymers that do not form high-quality single crystals requires special techniques. Here, we report the molecular and electronic structure of the first cesium butyratouranylate, Cs[UO(2)(n-C(3)H(7)COO)(3)][UO(2)(n-C(3)H(7)COO)(OH)(H2O)], as obtained from DFT-assisted powder X-ray diffraction data because of the low quality of crystalline sample. The topological analysis of the charge distribution within the quantum theory of atoms-in-molecules (QTAIM) space partitioning and the distribution of electron localization function (ELF) is reported. The constancy of atomic domain of the uranium(VI) atom at different coordination numbers (7 and 8) and the presence of three ELF maxima in equatorial plane of an uranyl cation attributed to the 6s and 6p electrons were demonstrated for the first time. Details of methodologies applied for additional verification of the correctness of powder XRD refinement (Voronoi atomic descriptors and the Morse restraints) are discussed.

Tuning of the double-well potential of short strong hydrogen bonds by ionic interactions in alkali metal hydrodicarboxylates

Short strong hydrogen bonds within crystals of sodium and potassium hydrofumarates were investigated by means of high-resolution and multitemperature X-ray diffraction studies. Various parameters, including geometry data, displacement parameters and cation–anion interaction energy, are considered to discuss hydrogen atom disorder. The influence of cation–anion interactions, being mainly electrostatic in nature, on the H-bond peculiarities is discussed. Equations interlinking the distance and energy of metal-oxygen interactions are introduced for carboxylates of sodium and potassium.