Crystal engineering using very short and linear C(sp)–H⋯N hydrogen bonds: formation of head-to-tail straight tapes and their assembly into nonlinear optical polar crystals

Abstract

The crystallization of 4-ethynylpyridine (1) and 4-(4-ethynylphenyl)ethynylpyridine (2) leads to C(sp)-HN hydrogen bonded straight tapes that further assemble into polar crystals, in the case of 2, and show intense powder SHG response, 8 times more efficient than crystalline urea.