Octanuclear Aluminum(III) and Iron(III) Phosphonate Cages Encapsulating Two Na^I Ions

Hydrothermal reactions of aluminum(III) nitrate or iron(III) nitrate with N,N-dimethylaminomethane-1,1-diphosphonic acid (H₄L) and sodium hydroxide lead to two novel isostructural octanuclear metal phosphonate cages encapsulating two Na^I ions, namely, [Al₈Na₂(HL)₂(H₂L)₁₀(H₂O)₆]·20H₂O (1) and [Fe₈Na₂(HL)₂(H₂L)₁₀(H₂O)₆]·22H₂O (2). The molecular structure of 1 can be viewed as a three-in-one cluster, in which a central zeolite D6R SBU lookalike aluminophosphonate cage is capped by two symmetry-related aluminophosphonate tetrahedral cages above and below and such a tetrahedral cage, being composed of four zeolite S6R SBU lookalike aluminophosphonate rings, further hexadentately traps one Na⁺ ion in its cavity.