Accurate Crystal Structures of C12H9CN, C12H8(CN)2, and C16H11CN Valence Isomers Using Nonspherical Atomic Scattering Factors.

Fourteen crystal structures, mostly from good-quality datasets but including some marginal and twinned exemplars, from a series of novel polycyclic benzo- and naphtho-fused organic nitriles are presented and accurately described, including some related structures of a bromo-substituted and partially hydrogenated analogues. These structures represent a considerable increase in the number of published structures within their archetypes. This work highlights the significant advancement in structural refinement software proffered by NoSpherA2, which enables Hirshfeld Atom Refinement (HAR) of the structures within Olex2 v1.5. This results in the determination of C-H bond lengths with near to neutron diffraction accuracies at far lower experimental cost, and with an average improvement in C-C bond precision of 42% compared to Independent Atom Model refinements. H-atoms (apart from disordered components) refined well with anisotropic displacement parameters. Nonclassical H-bonding (C-H···N≡C) in this series is analyzed, and dipolar nitrile-nitrile interactions (C≡N···C≡N) in three major motifs described by (Wood, P. A. Acta Cryst. B, 2008, 64, 393-396) are found in 9 out of 13 nitrile-containing compounds of this series, a much higher proportion than the global average of 21% of nitrile-containing compounds. The HAR/NoSpherA2 approach shows increasing benefits with better data quality without apparent discontinuities.

A tetrabromo-1,4-ethanonaphthalene and related dibromo-1,4-ethenonaphthalene.

(1RS,3RS,4RS,10SR)-2,2,3,10-Tetrabromo-1,2,3,4-tetrahydro-1,4-ethanonaphthalene, C12H10Br4, (I), is the first structure to be reported with four Br atoms bound to a 1,4-ethanonaphthalene framework and also the first which possesses three Br atoms in exo positions. Interactions between the Br atoms [three short intramolecular Br...Br distances of 3.1094 (4), 3.2669 (4) and 3.4415 (5) Å] have little effect on the C-C bond lengths but lead to significant twisting of the cage structure compared with the parent hydrocarbon, which is expected to be fully eclipsed at the two saturated C2H4 bridge positions. Chemically related (1SR,4RS)-2,3-dibromo-1,4-ethenonaphthalene, C12H8Br2, (II), obtained by double dehydrobromination of (I), represents the first structure of any halogen-substituted benzobarrelene. This cis-dibromide shows little evidence of steric congestion at the double bond [Br...Br = 3.5276 (8) Å] as a consequence of the large C-C-Br angles [average C=C-Br angle = 126.15 (10)°].

(5Z,7Z,9Z)-5,10-Di-bromo-benzo[8]annulene.

In the structure of the title compound, C12H8Br2, the two bromine substituents are oriented exo to the boat-shaped cyclo-octa-tetra-ene at the two ring sites that are ß to the ring fusion positions. The average Br-C bond distance is 1.919 (2) Å, the average distance for C=C double bonds that are Br substituted is 1.328 (2) Å, while the other two double-bond distances are 1.327 (2) and 1.398 (2) Šfor the non-fused and fused bonds, respectively. Each type of ring inter-atomic distance is within s.u. of the average values for the four known structures, including the title compound, of benzo-fused cyclo-ocata-tetra-enes that are not coordinated to a metal atom. The crystal structure features short Br⋯Br [3.6620 (3) Å] and C⋯H [2.834 (2) and 2.841 (2) Å] contacts.

Dimethyl 7-meth-oxy-tetra-cyclo-[6.4.0.0(2,4).0(3,7)]dodeca-1(12),5,8,10-tetra-ene-3,4-dicarboxyl-ate.

The title compound, C(17)H(16)O(5), is a previously unreported substituted semibulvalene cage compound (that is, a tricyclic hydro-carbon formed from one cyclo-propane and two cyclo-pentene rings which also has one double bond fused to a benzene ring). It has one meth-oxy substituent attached to the bridgehead C atom that links only the two cyclo-pentene rings and two methyl carboxyl-ate groups located on the C atom shared by all three non-benzene rings and that shared only between the cyclo-propane and the cyclo-pentene rings. The stereochemistry of the two enanti-omers (racemate) that assemble in each unit cell is RRRS and SSSR. In the crystal, mol-ecules are linked via C-H⋯O hydrogen bonds and C-H⋯π inter-actions, forming double-layered sheets lying perpendicular to the a axis.

exo-10,11-Dibromo-tricyclo-[6.3.1.0]dodeca-2,4,6,9-tetra-ene.

The title compound, C(12)H(10)Br(2), is a bridged ring system based on a homobenzonorbornadiene framework. The exo configuration of one of the Br atoms was previously assigned via NMR correlations and has now been confirmed by the geometry of the solid-state structure. The compound features a Br-C-C-Br torsion angle of 66.68 (12)°, whereby the C atoms in the calculation are respectively sp(3)- and sp(2)-hybridized.