A Polar Titanium–Organic Chain with a Very Large Second-Harmonic-Generation Response

A noncentrosymmetric (NCS) titanium–organic compound, [H2N­(CH3)2]­TiO­{[NC5H3(CO2)2]­[NC5H4(CO2)]} (CAUMOF-18), has been synthesized by a solvothermal reaction. The aligned unidimensional polar chain structure of CAUMOF-18 consisting of corner-shared distorted TiO5N2 pentagonal bipyramids is attributed to strong hydrogen-bonding and π–π interactions. CAUMOF-18 reveals a very strong second-harmonic-generation efficiency of 400 times that of α-SiO2 and is phase-matchable (type I). Water-molecule-driven reversible centricity conversion and topotactic transformation to TiO2 microrods for CAUMOF-18 are also presented.