Distances between M + from the geometric center of C18 (d0, in Å), distances between M + and the nearest and farthest C atoms of C18 (d1 and d2, in Å), point group (PG), NPA charge of M + [q(M + ), in e], and the max Wiberg bond order of M + C a The difference between d1 and d2, Δd = d2 -d1, in Å.