[C(NH₂)₃]₂MoO₂F₄·H₂O: Unique Chinese-Knot Structure Revealing Superior Nonlinear-Optical Properties

A novel organic–inorganic hybrid guanidine fluoromolybdate, [C(NH₂)₃]₂MoO₂F₄·H₂O, was successfully synthesized via our proposed cation–anion synergetic interaction strategy. The title compound features a unique Chinese-knot structure constructed by hydrogen-bonding interactions, which induces an all-around improvement of the optical band gap, second-harmonic-generation effect, and phase-matchable ability compared with the reported fluoromolybdates, demonstrating that it is a promising UV nonlinear-optical material.