Using Halogen···Halogen Interactions to Direct Noncentrosymmetric Crystal Packing in Dipolar Organic Molecules

Halogen atoms Cl, Br, and I steer crystallization of 2-halo-3-hydroxypyridine 1, pyridine-N-oxides 2, and 2-halo-3-aminopyridine 3 in noncentrosymmetric space groups efficient for nonlinear optical materials. Whereas the strong hydrogen-bond chains
are aligned antiparallel, the L- or V-geometry of weak interhalogen interaction steers polar alignment in the solid state, even for high dipole
moment (μ) halogenated N-oxides 2 (μ > 5.0 D). Six out of seven structures evaluated crystallize in polar/chiral space groups due to
interhalogen interactions compared to the one in six probability of noncentrosymmetric packing for achiral molecules.

卤素原子Cl、Br和I在非中心对称空间群中引导2-卤-3-羟基吡啶1、吡啶-N-氧化物2以及2-卤-3-氨基吡啶3的结晶，这些空间群对非线性光学材料尤为有效。尽管强烈的氢键链呈反平行排列，但弱卤素间相互作用形成的L-或V-几何构型仍能引导固态中的极性排列，即使对于具有高偶极矩（μ）的卤素化N-氧化物2（μ > 5.0 D）也是如此。在评估的七个结构中，有六个由于卤素间相互作用而在极性/手性空间群中结晶，相比之下，非手性分子在六方非中心对称堆积中的概率为六分之一。