*2.4. Single-Crystal X-ray Diffraction (SCXRD)*

Single crystals of DIC-Na hydrates and anhydrate were prepared by the method described in Section 2.2, and the SCXRD data were collected using R-AXIS RAPID (Rigaku Tokyo, Japan) with Mo Kα radiation (*λ* = 0.71075 Å). Data reduction and correction were performed using RAPID-AUTO (Rigaku) with ABSCOR (T. Higashi Rigaku, Tokyo, Japan). The space group was determined using PLATON [40]. The structure was solved using a dual-space algorithm of *SHELXT* [41] and then refined on *F* <sup>2</sup> using *SHELXL*-2017/1 [42]. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms attached to oxygen (water) and nitrogen atoms were found in the differential Fourier map. The water hydrogen atoms were refined using standard distance restraints and constrained isotropic thermal parameters. The hydrogen atoms attached to nitrogen were refined with lax distance restraints of 0.88 Å and thermal parameters set to 1.2 times those of the parent atom. Other hydrogen atoms were located in the geometrically calculated position and refined using the riding model. The 3D structures of the molecules were drawn using Mercury 4.3.1 [43].
