Looking at the pre-peak region of NixCo1-x-struvite mixtures and their heated mixtures, Ni 2+ forms a near-ideal octahedral coordination in the crystalline NixCo1-x-struvite structure and in the heated products regardless of the Ni#, as is indicated by a low pre-peak intensity (ESI: Figure , Table ,S9). In contrast, Co 2+ shows a slightly higher degree of distortion with increasing Ni content in the struvite structure (precursor Ni0.8Co0.2-struvite and App = 0.032(2) vs. Ni0.2Co0.8-struvite and App = 0.025(1)). In the heated products the degree of distortion decreases with lower Ni# (heated Ni0.8Co0.2-struvite App = 0.046(2) vs. heated Ni0.2Co0.8-struvite App = 0.034(2)). Based on XRD results (Figure ), NixCo1-x-struvites decomposes to an amorphous phase, as a single phase in Ni-rich compositions above Ni# > 0.5 and as a secondary phase at values of 0.2 < Ni# ≤ 0.5. Subsequently to that, M-dittmarite recrystallizes at Ni# ≥ 0.5 as a primary phase and it is the only occurring phase below Ni# <0.2 (ESI: Table and). Hence, Ni 2+ tends to be incorporated in the amorphous phase, while Co 2+ favors the crystalline M-dittmarite structure. Surprisingly, the distortion degree of Ni 2+ barely changes in all observed structures, in the precursor M-struvite, M-dittmarite or in the amorphous phase. In contrast, Co 2+ forms a more distorted non-centrosymmetric coordination environment than Ni 2+ in the pure compounds and the distortion increases even more in the mixed NixCo1-x-ones with higher Ni content (ESI: Table and).