Extended Data Figure 7: IR spectra of complexes 3–6 after heating at different temperatures.

a, Complexes 3–6 after heating at 60 °C for 0.5 h, denoted as 3′–6′, respectively. cyclo-N₅^– remains after the partial loss of water, as shown in the highlighted regions. b, Complexes 3–6 heated at 110 °C for 0.5 h, denoted as 3″–6″, respectively. The signal for N₃^– indicates that cyclo-N₅^– decomposed under these conditions. c–e, Temperature-dependent IR spectra of 4–6 in air. Significant decomposition of cyclo-N₅^– occurs at 95, 65 and 100 °C, respectively.