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The crystal structures of two polymorphs of a phenazine hexacyanoferrate(II) salt/cocrystal, with the formula (Hphen)3[H2Fe(CN)6][H3Fe(CN)6]·2(phen)·2H2O, are reported. The polymorphs are comprised of (Hphen)2[H2Fe(CN)6] trimers and (Hphen)[(phen)2(H2O)2][H3Fe(CN)6] hexamers connected into two‐dimensional (2D) hydrogen‐bonded networks through strong hydrogen bonds between the [H2Fe(CN)6]2− and [H3Fe(CN)6]− anions. The layers are further connected by hydrogen bonds, as well as through π–π stacking of phenazine moieties. Aside from the identical 2D hydrogen‐bonded networks, the two polymorphs share phenazine stacks comprising both protonated and neutral phenazine molecules. On the other hand, the polymorphs differ in the conformation, placement and orientation of the hydrogen‐bonded trimers and hexamers within the hydrogen‐bonded networks, which leads to different packing of the hydrogen‐bonded layers, as well as to different hydrogen bonding between the layers. Thus, aside from an exceptional number of symmetry‐independent units (nine in total), these two polymorphs show how robust structural motifs, such as charge‐assisted hydrogen bonding or π‐stacking, allow for different arrangements of the supramolecular units, resulting in polymorphism. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure of [4‐damp])2[Cl4Q]3 (4‐damp=4‐dimethylamino‐N‐methylpyridinium, Cl4Q=tetrachloroquinone) salt is built up from slipped columnar stacks of quinoid rings composed of closely bound trimers with the intra‐trimer separation distance of 2.84 Å and total charge of −2 whereas the inter‐trimer distance is 3.59 Å. The individual rings exhibit partial negative charges that are distributed unevenly among the three Cl4Qs in the trimer. The strong interactions within a trimer (Cl4Q)32− have a partially covalent character with two‐electron/multicentered bonding, that is extended over three rings, plausibly termed as “pancake bonding”. The electron pairing within this multicentre bond leads to the fact that the crystals are diamagnetic and act as insulators. The studies of the structure and nature of bonding are based on X‐ray charge density analysis and density functional theory. [ABSTRACT FROM AUTHOR]

The structural parameters and semiconductivity of crystals with stacked 5,6-dichloro-2,3-dicyanosemiquinone (DDQ) radicals were studied for a series of the first nine salts of DDQ with substituted N-ethyl- and N-methylpyridinium cations. Structures with stacks of equidistant radicals (interplanar separation ＜3.3 Å) are fairly good semiconductors (10−9 S cm−1), while those with Peierls-distorted stacks comprising diamagnetic dimers of radicals (interplanar separations are ＜3.1 Å within the dimers and ＞3.4 Å between the dimers) are insulators. DFT calculations indicate the covalent character (pancake bonding) of the interactions between the DDQ radical anions. The inductive effects of electronegative substituents (halogeno and cyano) on the quinoid ring stabilise the radicals, but also increase the HOMO–LUMO gap, resulting in lower electrical conductivity. [ABSTRACT FROM AUTHOR]

The reactions of N -arylalkyl derivatives of iminodiacetamide (Bnimda, Peimda, Ppimda; Bn = benzyl, Pe = 2-phenylethyl; Pp = 3-phenylprop-1-yl) with copper(II) sulfate and sodium perchlorate in aqueous solutions were investigated. Three new copper(II) complexes [Cu(Bnimda) 2 ](ClO 4 ) 2 ( 1 ), [Cu(Peimda) 2 ](ClO 4 ) 2 ( 2 ) and [Cu(Ppimda) 2 ](ClO 4 ) 2 ·2H 2 O ( 3 ) were prepared and characterized by infrared spectroscopy and thermal analysis (TG/DTA). Complex 2 was found to be explosive upon heating. The octahedral coordination environments around the copper(II) ions in complexes 1 and 3 consist of two O , N , O ′-tridentate N -arylalkyliminodiacetamide ligands, with imino N atoms in trans -position. Molecules are interconnected by extensive hydrogen bonding between the amide moieties and perchlorate ions or water molecules, forming 3D networks in both structures. However, the difference in the hydrophobic chain lengths leads to significant differences in the hydrogen bonding motifs in the two structures. The molecular geometry and infrared spectra of these complexes were also studied by DFT calculations using B3LYP/6-311G(d,p) computational model. The calculated spectra and molecular geometry agree very well with the experimental results despite the extensive hydrogen bonding frameworks which are present in the crystal structures of these compounds. [ABSTRACT FROM AUTHOR]

In order to study the effect of halogen bond on tautomerism in β-diketones in the solid-state, we have prepared a series of cocrystals derived from an asymmetric β-diketone, benzoyl-4-pyridoylmethane (b4pm), as halogen bond acceptor and perfluorinated iodobenzenes: iodopentaflourobenzene (ipfb), 1,2-, 1,3- and 1,4-diiodotetraflorobenzene (12tfib, 13tfib and 14tfib) and 1,3,5-triiodo-2,4,6-trifluorobenzene (135titfb). All five cocrystals are assembled by I···N halogen bonds involving pyridyl nitrogen and iodoperfluorobenzene iodine resulting in 1:1 (four compounds) or 1:2 (one compound) cocrystal stoichiometry. Tautomer of b4pm in which hydrogen atom is adjacent to the pyridyl fragment was found to be more stable in vacuo than tautomer with a benzoyl hydroxyl group. This tautomer is also found to be dominant in the majority of crystal structures, somewhat more abundantly in crystal structures of cocrystals in which additional I···O halogen bond with the benzoyl oxygen has been established. Attempts have also been made to prepare an equivalent series of cocrystals using a closely related asymmetric β-diketone, benzoyl-3-pyridoylmethane (b3pm); however, all attempts were unsuccessful, which is attributed to more effective crystal packing of b3pm isomer compared to b4pm, which reduced the probability of cocrystal formation. [ABSTRACT FROM AUTHOR]