*2.4. Single-Crystal X-ray Diffraction*

Crystals were collected under oil and mounted in oil. Data was collected using Cu radiation on a STOE STADIVARI diffractometer, using a 200 K Pilatus detector at 293 K. The ShelXT intrinsic phasing method and ShelXL least squares method were used for structure solution and refinement, respectively (Table 1, Figures 1 and 2). Details regarding the structure solution and refinement procedures are described in Appendix A, while further detailed structural information for this structure is given in Tables S5–S9 in the Supplementary Materials.


### **Table 1.** Crystal data and structure refinement for O(*i*PrNH)2PO)2.

**Figure 1.** (**a**) Molecular structure obtained for O((*i*PrNH)2PO)2 the hydrogen bonding N3–H1···N2 (blue) and the weak hydrogen bonding observed as C32–H32A···O3 and C41–H41A···O1 (red)(generated using Olex2 [23]); (**b**) molecular diagram for O((*i*PrNH)2PO)2 (generated using ChemSketch [24]).

**Figure 2.** Unit cell for O((*i*PrNH)2PO)2 viewed along the b-axis (generated in Mercury [25]).
