NaMoO 3 (IO 3 )(H 2 O): water molecule introduction induces strong second harmonic generation response, widened band gap and large anisotropy.

Exploring feasible tactics to induce the formation of non-centrosymmetric (NCS) structures, especially from centrosymmetric (CS) structures, is essential for the development of nonlinear optical crystals with more potential. An NCS alkali metal-containing molybdenum iodate hydrate, namely, NaMoO3 (IO3 )(H2 O), was designed based on the CS matrix NaMoO3 (IO3 ) via introducing a water molecule into the structure. The introduction of one crystalline water molecule results in the rearrangement of Λ-shaped cis -[MoO4 (IO3 )2 ] units, and the proper array of the cis -[MoO4 (IO3 )2 ] units in NaMoO3 (IO3 )(H2 O) results in its strong SHG response of 4.6 × KH2 PO4 . In addition, NaMoO3 (IO3 )(H2 O) exhibits a wider optical bandgap of 3.44 eV and a larger birefringence of 0.231 than its matrix. Furthermore, the framework of NaMoO3 (IO3 )(H2 O) is highly similar to that of α-KMoO3 (IO3 ), with water molecules assisting Na+ cations in occupying the position of K+ . However, due to the extra hydrogen bond of water molecules, the [MoO3 (IO3 )]∞ layers in NaMoO3 (IO3 )(H2 O) retain a parallel-stacking arrangement, different from the antiparallel arrangement of layers in α-KMoO3 (IO3 ) with a centric structure. This study confirms the feasibility of applying a water molecule to adjust the orientation of basic building block units to assemble an NCS structure based on CS crystals.