Role of NEt₄⁺ in Orienting and Locking Together [M₂lig₃]^2– (6,3) Sheets (H₂lig = Chloranilic or Fluoranilic Acid) to Generate Spacious Channels Perpendicular to the Sheets

Abstract

In the presence of the Et4N+ cation the chloranilate dianion (can2–) associates with a range of divalent cations, M2+, to yield an isomorphous series of crystalline compounds of composition (Et4N)2[M2(can)3] (M = Mg, Mn, Fe, Co, Ni, Cu, and Zn). The fluoranilate dianion (fan2–) likewise affords the closely related (Et4N)2[Zn2(fan)3]. The structures of (Et4N)2[Zn2(can)3], (Et4N)2[Fe2(can)3], and (Et4N)2[Zn2(fan)3] were determined by single crystal X-ray diffraction. Powder X-ray diffraction indicates that all the members of the can2– series are isomorphous. The structure of (Et4N)2[Zn2(fan)3] is very closely related to the structures of the can2– compounds. The [M2(can)32–]n component is present as chicken-wire-like sheets with (6,3) topology. The Et4N+ cation binds sheet to sheet and aligns them so that the large holes within the sheets are arranged one above another, thereby generating spacious channels running perpendicular to the sheets. The solvent molecules present in the channels are ill-defined and easily removed. The (Et4N)2[M2(can)3] structure remains intact after desolvation. The void spaces are calculated to be ∼39% in the case of the can2– compounds and ∼43% in (Et4N)2[Zn2(fan)3]. Substantial amounts of CO2 are sorbed at 273 K by (Et4N)2[Zn2(can)3] and (Et4N)2[Zn2(fan)3]. Spectroscopic evidence supports the presence of at least some of the chloranilate in the radical trianion form in (Et4N)2[Fe2(can)3].