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 Bader's 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.

A disiladicarbene, (Cy-cAAC)2Si2 (2), was synthesized by reduction of Cy-cAAC:SiCl4 adduct with KC8. The dark-colored compound 2 is stable at room temperature for a year under an inert atmosphere. Moreover, it is stable up to 190 °C and also can be characterized by electron ionization mass spectrometry. Theoretical and Raman studies reveal the existence of a Si═Si double bond with a partial double bond between each carbene carbon atom and silicon atom. Cyclic voltammetry suggests that 2 can quasi-reversibly accept an electron to produce a very reactive radical anion, 2(•-), as an intermediate species. Thus, reduction of 2 with potassium metal at room temperature led to the isolation of an isomeric neutral rearranged product and an anionic dimer of a potassium salt via the formation of 2(•-).

The molecular design of spin‐crossover complexes relies on controlling the spin state of a transition metal ion by proper chemical modifications of the ligands. Herein, the first N,N’‐disubstituted 2,6‐bis(pyrazol‐3‐yl)pyridines (3‐bpp) are reported that, against the common wisdom, induce a spin‐crossover in otherwise high‐spin iron(II) complexes by increasing the steric demand of a bulky substituent, an ortho‐functionalized phenyl group. As N,N’‐disubstituted 3‐bpp complexes have no pendant NH groups that make their spin state extremely sensitive to the environment, the proposed ligand design, which may be applicable to isomeric 1‐bpp or other families of popular bi‐, tri‐ and higher denticity ligands, opens the way for their molecular design as spin‐crossover compounds for future breakthrough applications.

The aromaticity of three-membered monoheterocycles containing a group 14 or 4 element was investigated by using modern aromaticity criteria: structural, electronic (FBO), optical (vibrational spectroscopy), energetic (ISE), and magnetic (NICS-scan, GIMIC). The results of all methods used show that the group 14 compounds are aromatic, with cyclopropene exhibiting σ aromaticity, whereas sila-and germacyclopropenes X 2 EC 2 R 2 exhibit pseudo-π aromaticity due to the interaction of the CC π bond orbital with the low-lying vacant antibonding σ* orbital of the X 2 E fragment (E = Si, Ge). At the same time, the results of MO and magnetic descriptor calculations testify against the aromaticity of group 4 cyclopropenes Cp 2 MC 2 R 2 (M = Ti, Zr, Hf). Thus, a fundamental dissimilarity in bonding schemes and electronic structure was disclosed between 1-heterocyclopropenes containing E = C, Si, Ge atoms and those containing M = Ti, Zr, Hf atoms, the latter molecules being in essence π complexes of acetylene.

Pincer complexes featuring readily tunable tridentate ligand frameworks comprise one of the most actively studied classes of organometallic and metalorganic compounds and find extensive use in catalysis, organic synthesis, materials science, and other fields of chemistry and allied disciplines. Currently growing attention is devoted to non-classical ligand scaffolds, such as functionalized carboxamides, which offer multiple options for directed structural modifications. In this study, the reactions of (methylsulfanyl)acetyl and propanoyl chlorides with 2-(aminomethyl)pyridine, 2-(2-aminoethyl)pyridine, 8aminoquinoline and 2-(diphenylthiophosphoryl)aniline afford a series of new pincer-type ligands based on functionalized carboxamides. The ligands obtained readily undergo direct cyclopalladation under the action of PdCl 2 (NCPh) 2 in dichloromethane at room temperature, resulting in Pd(II) pincer complexes with N,N,S-and S,N,S-donor sets. Importantly, some of the cyclopalladated derivatives can also be produced efficiently under solvent-free conditions according to the approach recently developed by our group. The complexes obtained have been tested for cytotoxicity against several human cancer cell lines and catalytic activity in the model Suzuki reaction. The results have been compared to those for the related Pd(II) pincer complexes to define the main structure-activity relationships and to outline the most promising structures for further investigations. Yield: 87 mg (95%). M.p. > 225°C (dec.). 1 H NMR (400.13 MHz, CDCl 3 , δ, ppm): 2.73 (ddd, 1H, CH 2 , 2 J HH = 1.9 Hz, 3 J HH = 16.8 Hz, 3 J HH = 7.3 Hz), 3.15 (ddd, 1H, CH 2 S(O), 2 J HH = 2.2 Hz, 3 J HH = 16.8 Hz, 3 J HH = 11.4 Hz), 3.36 (ddd, 1H, CH 2 , 2 J HH = 1.9 Hz, 3 J HH = 13.0 Hz, 3 J HH = 11.4 Hz), 3.47 (ddd, 1H, CH 2 S(O), 2 J HH = 2.2 Hz, 3 J HH = 13.0 Hz, 3 J HH = 7.3 Hz), 3.51 (s, 3H, Me), 5.03 and 5.22 (ABq, 2H, CH 2 Py, J AB = 20.3 Hz), 7.35-7.39 (m, 1H, H(C4)), 7.48 (d, 1H, H(C2), 3 J HH = 7.9 Hz), 7.91 (dt, 1H, H(C3), 3 J HH = 7.9 Hz, 4 J HH = 1.6 Hz), 9.05 (d, 1H, H(C5), 3 J HH = 5.4 Hz).13

The reactions of picolinyl and 4-chloropicolinyl chlorides with methyl esters of S-methyl-l-cysteine, l- and d-methionine, and l-histidine afforded a series of functionalized carboxamides, which readily formed pincer-type complexes upon interaction with PdCl(NCPh) in solution under mild conditions. The direct cyclopalladation of the ligands derived was also accomplished in the solid phase, in particular, mechanochemically, although it was complicated by the partial deactivation of the starting amides. The resulting complexes with 5,5- and 5,6-membered fused metallocycles were fully characterized by IR and NMR spectroscopy, including variable-temperature and 2D-NMR studies. In the case of some cysteine- and methionine-based derivatives, the realization of κ-N,N,S-coordination was supported by X-ray diffraction. The cytotoxic effects of these complexes were examined on HCT116, MCF7, and PC3 human cancer cell lines as well as HEK293 as a representative of normal cells. The comparative studies allowed us to determine that the presence of the sulfide ancillary donor group is crucial for cytotoxic activity of this type of Pd(II) complexes. The main structure-activity relationships and the most promising palladocycles were outlined. The additional studies by gel electrophoresis revealed that 4-chloropicolinyl derivatives, despite the nature of an amino acid, can bind with DNA and inhibit topoisomerase I activity.

A series of benzannulated N-heterocyclic compounds containing divalent 14 group atoms, CH(NR)E, E = C, Si, Ge, Sn, Pb, have been studied by various experimental (vibrational and UV-vis spectroscopy) and theoretical (NICS, ISE, ACID) techniques. The methods used confirm 10 π-electron delocalization (aromaticity) in these heterocycles, however, the aromaticity sequences estimated by the criteria based on different physical properties do not coincide.

2D-coordination redox-active networks bearing t-Bu-substituted anilic bridged ligands and lanthanide ions were synthesized and characterized.