As shown in Table , there are four sites with C I and C II structures. These sites contain at least one pocket with large available volume, which hosts the C I structures, while the C II structures are found between two pockets with smaller available volume. The energy diagrams for two sample sites are shown in Figure The energy diagram for Site 1 is reported in Figure . This site has one small pocket where the ring is located, P a , with angles θ αβ = 76 ○ and ϕ αβ = 133 ○ . The other pockets have: θ βγ = 103 ○ and ϕ βγ = 160 ○ for P b , and θ γα = 108 ○ and ϕ γα = 123 ○ for P c . Contrary to the usual trend, three C II structures were found in the pocket P c because the lowfrequency Nb --O wagging motion points towards this pocket.