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.