Effect of Aromatic System Expansion on Crystal Structures of 1,2,5-Thia- and 1,2,5-Selenadiazoles and Their Quaternary Salts: Synthesis, Structure, and Spectroscopic Properties.

Rational manipulation of secondary bonding interactions is a crucial factor in the construction of new chalcogenadiazole-based materials. This article reports detailed experimental studies on phenanthro[9,10-c][1,2,5]chalcogenadiazolium and 2,1,3-benzochalcogenadiazolium salts and their precursors. The compounds were synthesized, characterized employing NMR and UV-Vis spectroscopy. TD-DFT calculations were also performed. The influence of the size of the aromatic system on the molecular motifs formed by the compounds in the solid state has been studied by means of single-crystal X-ray diffraction. In case of the salts, the nature of an anion was also taken into consideration. The results show that cyclic [E···N]2 supramolecular synthon connects neighboring molecules of phenanthro[9,10-c][1,2,5]chalcogenadiazoles, with a relatively large aromatic system, in dimers regardless of the chalcogen atom in the molecule. Both N-methyl-2,1,3-benzothiadiazolium and N-methylphenanthro[9,10-c][1,2,5]chalcogenadiazolium cations have a strong affinity for triflate and iodide anions, therefore the formation of S···N or Se···N secondary bonding interactions is observed only in two out of the eight quaternary salts. Less coordinating anions must be used to enable the building blocks studied to form cyclic [E···N]2 synthons. Moreover, for two of the triflate salts, which are isostructural, a new supramolecular motif has been observed.

Helicity discrimination in N,N'-dibenzoyl-1,2,3,4,7,8,9,10-octahydro-1,10-phenanthrolines and their thiono- and selenocarbonyl analogues by inclusion complexation with chiral diols.

X-ray crystallographic analysis of the title compounds revealed that they assume a folded helical conformation of an approximate C2 symmetry in the solid state. Dithioamide 5b, diselenoamide 5c and monoselenoamide 5d were resolved to enantiomers by inclusion crystallization with optically active diols (TADDOLs). The absolute configuration of the guest molecules in the complexes 5b·6a, 5c·6a and 5d·6a was assigned as P. The optical activity of the resolved compounds is manifested by their CD spectra showing relatively strong Cotton effects in the region of thionoamide and selenoamide n­π* transition. The optically active thiono- and selenoamides are configurationally labile compounds and gradually racemize in solution but they are stable in the form of the inclusion complexes. The first-order kinetics of the racemization in solution allowed us to assign the racemization barriers by the spectropolarimetric measurements.

Helicity discrimination in diaryl dichalcogenides generated by inclusion complexation with chiral hosts.

Inclusion complexation of diaryl dichalcogenides with either cholic acid or chiral diols results in their helicity discrimination and an induction of optical activity that can be detected by solid-state CD measurements.

Enantiomeric resolution of N,N'-dimethyldithiodianthranilide through diastereomeric silver(I) complex. Circular dichroism spectra, racemization barrier, and molecular self-assembly.

Planar chiral N,N'-dimethyldithiodianthranilide (2b) was resolved to enantiomers through a diasteromeric complex with easily accessible silver(I) (1S)-camphorosulfonate (3). The (-)-2b enantiomer was assigned the R absolute configuration from the X-ray crystal structure of the silver complex. The compound is configurationally stable and its racemization occurs through boat-to-boat ring inversion (DeltaG(double dagger) = 36.5 +/- 0.2 kcal mol(-1) at 438 K). The analysis of the CD spectrum of the title compound showed that the n-pi* Cotton effect sign is determined by the helicity of the skewed thiobenzamide chromophore. The molecules of 2b are unable to achieve efficient crystal packing by themselves and easily form inclusion complexes with toluene or pentafluorophenol.

Conformational properties, chiroptical spectra, and molecular self-assembly of 2,3-piperazinodiones and their dithiono analogues.

A family of chiral cyclic oxamides was prepared by the condensation of optically active 1,2-diamines with diethyl oxalate. Thionation of the products with Lawesson's reagent afforded a series of chiral 2,3-piperazinedithiones. Molecular geometries of the title compounds were studied with the use of quantum mechanical DFT calculations and were compared to the X-ray crystallographic results. The heterocyclic six-membered ring adopted a half-chair conformation with the C-5 substituent preferably at the equatorial position, whereas a substitution at the nitrogen atoms resulted in domination of the axial form in the conformational equilibrium. The opposite helicity of the twisted oxamide chromophore in the axial and equatorial conformers led to the opposite signs of the Cotton effects corresponding to two pi-pi* electronic transitions. The CD signs can be predicted by a simple helicity rule. The same rule is valid for 2,3-piperazinodithiones, where a substitution of sulfur for oxygen in the carbonyl groups results in bathochromic shifts of the absorption and CD bands. The crystal packing analysis of several 2,3-piperazinodiones revealed that strong NH...O=C intermolecular hydrogen-bonding interactions generating the chain motif resulted in the formation of 3-D networks as well as with the use of the cyclic hydrogen-bond motif tape structures.

Supramolecular structures of bis-thionooxalamic acid esters derived from (+/-)-cyclohexane-1,2-diamine and (+/-)-1,2-diphenylethylenediamine.

The bis-thionooxalamic acid esters trans-(+/-)-diethyl N,N'-(cyclohexane-1,2-diyl)bis(2-thiooxamate), C14H22N2O4S2, and (+/-)-N,N'-diethyl (1,2-diphenylethane-1,2-diyl)bis(2-thiooxamate), C22H24N2O4S2, both consist of conformationally flexible molecules which adopt similar conformations with approximate C2 rotational symmetry. The thioamide and ester parts of the thiooxamate group are significantly twisted along the central C-C bond, with the S=C-C=O torsion angles in the range 30.94 (19)-44.77 (19) degrees. The twisted s-cis conformation of the thionooxamide groups facilitates assembly of molecules into a one-dimensional polymeric structure via intermolecular three-center C=S...NH...O=C hydrogen bonds and C-H...O interactions formed between molecules of the opposite chirality.

N,N'-Bis(2-pyridyl)benzene-1,2-diamine.

Hindered rotation about the partial double C-N bonds between the amine and pyridine moieties in the title molecule, C16H14N4, results in two different conformations of the N-aryl-2-aminopyridine units. One, assuming an E conformation, is involved in a pair of N-H...N hydrogen bonds that generate a centrosymmetric R2(2)(8) motif. The second, adopting a Z conformation, is not engaged in any hydrogen bonding and is flattened, the dihedral angle between the benzene and pyridine rings being 12.07 (7) degrees. This conformation is stabilized by an intramolecular C-H...N interaction [C...N = 2.9126 (19) A, H...N = 2.31 A and C-H...N = 120 degrees ].

Planar chiral dianthranilide and dithiodianthranilide molecules: optical resolution, chiroptical spectra, and molecular self-assembly.

Planar chiral dianthranilide (1) was resolved to enantiomers with use of (-)-(1S,4R)-camphanoyl chloride as a chiral derivatizing agent. The (+)-1 enantiomer was assigned the S absolute configuration from the X-ray crystal structure of its N,N'-dicamphanoyl derivative. Optical resolution of dithionodianthranilide (2) was accomplished by inclusion crystallization with (R,R)-1,2-diaminocyclohexane, and the X-ray structure of the corresponding adduct revealed the (-)-2stereoisomer has the R configuration. A slow boat-to-boat ring inversion (DeltaG(++) = 24.1 +/- 0.1 kcal mol(-1)) causes racemization of (+)-1 in solution as manifested by a gradual decrease of the CD spectrum whereas, (-)-2 is configurationally stable at these conditions. The analysis of the CD spectra of the title compounds showed that the n-pi* Cotton effect signs are determined by the helicity of the skewed benzamide and thiobenzamide chromophores. The solid-state structures of the racemic and homochiral forms of 1 and 2 show different self-assembly patterns: the racemate (+/-)-1 prefers the cyclic R(2)(2)(8) hydrogen bond motif, whereas the crystalline DMSO solvates of (+/-)-1 and (+)-1 consist of 1D homochiral hydrogen-bonded assemblies generated by the C(6) motif. In the case of dithionolactams (+/-)-2 and (-)-2 two types of 1D networks were observed: in the racemate they are generated by the centrosymmetric R(2)(2)(8) and R(2)(2)(12) hydrogen bond motifs, whereas the molecules in the homochiral crystals are connected solely with use of the strongly nonplanar R(2)(2)(8) motif.

2,4,6-Trimethylbenzamide.

The crystal structure of the title compound, C(10)H(13)NO, displays an infinite one-dimensional network composed of primary amide molecules connected by N-H...O[double bond]C hydrogen bonds involving the anti NH amide H atoms, thus generating a C(4) motif. This network is additionally stabilized by a weak N-H...pi interaction between the syn-oriented amide H atom and the aromatic ring of a neighbouring molecule. The distance between the H atom and the ring centroid is 2.50 A. The amide group and the aryl moiety are nearly perpendicular, forming an intramolecular dihedral angle of 84.69 (6) degrees.

Creation of hydrogen bonded 1D networks by co-crystallization of N,N'-bis(2-pyridyl)aryldiamines with dicarboxylic acids.

The preparation and crystal structures of fourteen complexes of N,N'-bis(2-pyridyl)aryldiamines with dicarboxylic acids and two complexes with squaric acid are reported. The recognition between the carboxylic acids and the 2-aminopyridine units occurs through the formation of the cyclic R(2)2 (8) hydrogen bond motif, whereas squaric acid creates the analogous R(2)2 (9) motif. In the 1:1 complexes the cyclic motifs generate infinite hydrogen-bonded 1D networks with the alternating component molecules. These networks are further organised into densely packed layers assembled through weaker C-H...O interactions. Analysis of the intermolecular interactions in these complexes led us to the synthesis of N,N'-bis(2-pyridyl)-2,2'-oxybis(aminobenzene) (5) which acts as a tritopic receptor of the carboxylic group and forms exclusively 2:1 complexes with dicarboxylic acids.

Hydrogen-bonded one-dimensional networks in 1:1 complexes of N,N'-bis(2-pyridyl)aryldiamines with anilic acid.

The 1:1 complexes N,N'-bis(2-pyridyl)benzene-1,4-diamine-anilic acid (2,5-dihydroxy-1,4-benzoquinone) (1/1), C(16)H(14)N(4).C(6)H(4)O(4), (I), and N,N'-bis(2-pyridyl)biphenyl-4,4'-diamine-anilic acid (1/1), C(22)H(18)N(4).C(6)H(4)O(4), (II), have been prepared and their solid-state structures investigated. The component molecules of these complexes are connected via conventional N-H.O and O-H.N hydrogen bonds, leading to the formation of an infinite one-dimensional network generated by the cyclic motif R(2)(2)(9). The anilic acid molecules in both crystal structures lie around inversion centres and the observed bond lengths are typical for the neutral molecule. Nevertheless, the pyridine C-N-C angles [120.9 (2) and 120.13 (17) degrees for complexes (I) and (II), respectively] point to a partial H-atom transfer from anilic aicd to the bispyridylamine, and hence to H-atom disorder in the OHN bridge. The bispyridylamine molecules of (I) and (II) also lie around inversion centres and exhibit disorder of their central phenyl rings over two positions.

(S)-trans-cyclohexane-1,2-dicarboximide.

The molecule of the title compound, C(8)H(11)NO(2), contains a strained bicyclic system with a significantly twisted imide chromophore. The five-membered ring fragment containing the imide function is strongly puckered and adopts a half-chair conformation. The six-membered ring has a slightly distorted chair conformation. The molecules are joined by strong N-H.O and weak C-H.O hydrogen bonds into infinite chains.

Enantioselective Inclusion Complexation of N-Nitrosopiperidines by Steroidal Bile Acids.

N-nitrosamines, whose chirality is solely due to hindered rotation about the N-N bond, are enantioselectively enclathrated by the crystal host matrices of cholic or deoxycholic acid, as evidenced by X-ray crystallography (see structure in picture) and CD spectra.

Structure, Conformation, and Stereodynamics of N-Nitroso-2,4-diaryl-3-azabicyclo[3.3.1]nonanes and N-Nitroso-2,4-diaryl-3-azabicyclo[3.3.1]nonan-9-ones(1).

The variable temperature (1)H, (13)C, and (19)F NMR spectra were measured for the title N-nitrosamines. The observed unusually low N-N rotation barriers (12-15 kcal/mol) result from a significant deviation of the nitrosamino system from planarity. A pyramidal character of the amino nitrogen was confirmed by the X-ray crystal structures of two compounds and by bathochromic shifts of the n-pi absorption bands in the UV spectra. The nonplanarity of the nitrosamino moiety is due to the strong pseudoallylic A((1,3)) strain caused by the steric interaction of the NNO group with the neighboring aryl substituents fixed in the equatorial positions of the bicyclic skeleton. In addition, the barriers to the C-C rotation of aryl groups were examined at temperatures lower than required to "freeze" the N-N rotation and different DeltaG() values were observed for the aryls oriented syn and anti to the nitroso oxygen.