Table 2.

Logarithmic stepwise protonation constants of ${\text{P}}_3{\text{O}}_{10-n}{\left(\text{NH}\right)}_n^{5-}$ (n = 0, 2) anions^a determined by the pH profiles of ³¹P NMR chemical shifts of the anions in aqueous solutions^b, t = 25.0 ± 1.0 °C, I = 1.0 mol·L⁻¹ (NaNO₃)

	${\text{P}}_3{\text{O}}_{10}^{5-}$ End	${\text{P}}_3{\text{O}}_{10}^{5-}$ Mid	${\text{P}}_3{\text{O}}_8{\left(\text{NH}\right)}_2^{5-}$ End	${\text{P}}_3{\text{O}}_8{\left(\text{NH}\right)}_2^{5-}$ Mid
log10 K 1	7.01 (0.01)	7.02 (0.01)	9.05 (0.02)	8.97 (0.01)
log10 K 2	4.90 (0.01)	4.82 (0.01)	6.34 (0.04)	6.29 (0.02)
log10 K 3	1.09 (0.04)	0.98 (0.04)	3.15 (0.21)	2.96 (0.09)
log10 K 4	–c	–c	–d	1.69 (0.02)

^aValues in parentheses indicate standard deviations derived from the nonlinear least-squares approximation

^bIn the absence of D₂O for field-frequency locking

^cCorresponding species were scarcely formed

^dThis value could not be determined because of the slight change of the ³¹P NMR chemical shift due to the protonation of the anion