**Appendix A**

### *Appendix A.1. Single Crystal X-ray Diffraction Experimental Description*

Single crystals of C12H32N4O3P2 [O(*i*PrNH)2PO)2] were [Layering CHCl3 solution with 30–40 petroleum ether]. A suitable crystal was selected and [Collected in oil and frozen] on a STOE STADIVARI diffractometer. The crystal was kept at 293 K during data collection. Using Olex2 [1], the structure was solved with the ShelXT [2] structure solution program using Intrinsic Phasing and refined with the ShelXL [3] refinement package using Least Squares minimisation. CCDC 2055906 contains the supplementary crystallographic data for this paper. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures.


Crystal structure determination of [O(*i*PrNH)2PO)2]

Crystal Data for C12H32N4O3P2 (*M* = 342.35 g/mol): orthorhombic, space group *Pca*21 (no. 29), *a* = 20.342(2) Å, *b* = 5.0495(6) Å, *c* = 19.103(3) Å, *V* = 1962.2(4) Å3, *Z* = 4, *T* = 295 K, μ(CuKα) = 2.133 mm<sup>−</sup>1, *Dcalc* = 1.159 g/cm3, 43032 reflections measured (8.696◦ ≤ 2Θ ≤ 137.27◦), 3317 unique (*R*int = 0.0557, Rsigma = 0.0226) which were used in all calculations. The final *R*1 was 0.0408 (I > 2σ(I)) and *wR*2 was 0.1075 (all data).

*Appendix A.2. Refinement Model Description*

> Number of restraints—1, number of constraints—unknown. Details:


2a. Ternary CH refined with riding coordinates: C10(H10), C20(H20), C30(H30), C40(H40)

2b. Idealised Me refined as rotating group: C31(H31A,H31B,H31C), C11(H11A,H11B,H11C), C41(H41A,H41B,H41C), C42(H42A,H42B,H42C), C12(H12A,H12B,H12C), C22(H22A, H22B,H22C), C32(H32A,H32B,H32C), C21(H21A, H21B,H21C)
