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、I）可调控2-卤代-3-羟基吡啶1、吡啶氮氧化物2以及2-卤代-3-氨基吡啶3的结晶过程，使其结晶于适用于非线性光学材料（nonlinear optical materials）的非中心对称空间群（noncentrosymmetric space groups）。尽管体系内的强氢键链（hydrogen-bond chains）呈反平行（antiparallel）排列，但弱卤间相互作用（interhalogen interaction）所形成的L型或V型构型，可引导固态（solid state）下的极性排列（polar alignment），即便对于偶极矩（μ）大于5.0德拜（D）的卤代吡啶氮氧化物2亦是如此。经评估的7种晶体结构中，有6种因卤间相互作用而结晶于极性/手性空间群（polar/chiral space groups），相较于非手性分子的非中心对称堆积概率仅为1/6的情况，该比例优势明显。