Tris(1,10‐phenanthroline‐κ2N,N′)cadmium(II) bis(perchlorate) 3.5‐hydrate: a water chain stabilized by perchlorate anions

The title compound, [Cd(C₁₂H₈N₂)₃](ClO₄)₂·3.5H₂O, contains a cross‐shaped one‐dimensional channel along the c axis which encapsulates an ordered water chain. This water chain features a centrosymmetric cyclic water hexamer unit with a chair‐like conformation. Neighbouring hexamers are linked by bridging water molecules. The host perchlorate anions recognize and stabilize the guest water chain via three kinds of hydrogen‐bond patterns, leading to the formation of a complex one‐dimensional {[(H₂O)₇(ClO₄)₄]⁴⁻}_n anionic chain. One perchlorate acts as a single hydrogen‐bond acceptor dangling on the chain, the second perchlorate on the chain serves as a double hydrogen‐bond acceptor for only one water molecule to form an R₂²(6) ring, where both entities lie on a twofold axis, while the third perchlorate, which also lies on a twofold axis, accepts two hydrogen bonds from two equivalent water molecules and is involved in the construction of an R₆⁵(14) ring.