Various structural features, such as proton disorder or noncovalent interactions, determine the existence of switchable nonlinear optical properties under varying external conditions. Thus, for the single crystal of diiodobutenyl‐bis‐thioquinolinium triiodide with the bridge hydrogen atom, previously characterized under ambient conditions by C2/c symmetry, we have measured Raman spectra in the temperature range from 298 K down to 113 K. Variations in low‐wavenumber region of Raman spectra at temperatures below 153 K have been attributed to the change of the bridge hydrogen atom position in the [NHN]+ fragment, thus lowering the crystal symmetry from C2/c to Cc. Quantum chemical calculations in the solid state for noncentrosymmetric Cc structure predict high hyperpolarizability and second‐order electric susceptibilities, comparable to those of modern nonlinear optical materials. This indicates the emergence of nonlinear optical properties in the low‐temperature phase of the studied crystal. Copyright © 2017 John Wiley & Sons, Ltd.

The staple role of hydrogen and halogen bonds in crystalline (E)-8-((2,3-diiodo-4-(quinolin-8-ylthio)but-2-en-1-yl)thio)quinolin-1-ium triiodide Abstract The crystal structure of (E)-8-((2,3-diiodo-4-(quinolin-8-ylthio)but-2-en-1-yl)thio)quinolin-1-ium triiodide, determined at 100 K in the space group C2/c, contains the bridge hydrogen bond [NÁÁÁHÁÁÁN] ? linking two neighboring quinolinium fragments; the distance NÁÁÁN is 2.6927(15) Å . The experimental difference Fourier maps at 293 and 100 K lead to a conclusion about the dynamic nature of the H atom disorder. Calculated vibrational modes obtained for the same compound in the space groups C2/c and Cc are in agreement with the experimental Raman spectrum in the low-frequency region; together, they are consistent with a previous supposition about the dynamic nature of the H atom disorder. We have found that the cation-anion interactions are realized through the charge-assisted iodine-iodine halogen bond.

Source of material 8-(propargyloxy)quinoline was obtained by the reaction of 8-quinolinol with propargylbromide in acetone/K 2 CO 3 with reflux. Asolutionof8-(propargyloxy)quinoline (0.145g,1mmol) in 5 mL of dichloromethane wasm ixed with 0.762 go fi odine( 3 mmol) in 15 mL of dichloromethane. Dark purplesingle crystals for the X-ray diffraction study were obtained after keeping the mixture at room temperatureinclosed flask for 48 hours, yield: 0.447 g(55 %). Experimental detailsPosition of theHatoms were calculated based on geometric criteria(C-H=0.97 Å, 0.93 Åand 0.85 Åfor methylene, aromatic and methine atoms,respectively)than have been placed in their calculatedposition andrefined isotropicallyusing arider modelwith U iso (H)=1.2U eq (C). The resulting six-membered ring is partially planar, where the C10 atom of the methylene group is slightly out of plane. The crystal structure confirms the closure of the ring between O1 and N1 atoms, where formed C11-N1 bond is covalent (1.451(5) Å).T he C11-C12 bond, that is associated with sixmember ring, has double bond character with abond distance of 1.324(6) Å. TheC12-I1 bond (2.082(4) Å) significantly deviated from mean plane of quinolinium moiety, the C11-C12-I1 angle is 123.6(3)°. Crystal packing is formedbymultiple interactions of [C 12 H 9 INO] + cations, triiodide and iodine molecules. Theorganic cationspackcould be represented as the dimeric association establishedbyap-p interaction.The fusedrings aresituated in opposite directions and lie nearly parallel to oneanother;the closest centroid-centroidd istance is 3.51(6)Å .T he dimers ares urroundedbytriiodide anions and iodine molecules. The geometry of triiodide is almost linear, I2-I3 and I3-I4 distancesa re Z. Kristallogr. Discussion

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Two kinds of iodine-iodine halogen bonds are the focus of our attention in the crystal structure of the title salt, C12H8ClINO(+)·I3(-), described by X-ray diffraction. The first kind is a halogen bond, reinforced by charges, between the I atom of the heterocyclic cation and the triiodide anion. The second kind is the rare case of a halogen bond between the terminal atoms of neighbouring triiodide anions. The influence of relatively weakly bound iodine inside an asymmetric triiodide anion on the thermal and Raman spectroscopic properties has been demonstrated.