Square Grid Metal–Chloranilate Networks as Robust Host Systems for Guest Sorption

Abstract

Reaction of the chloranilate dianion with Y(NO₃ )₃ in the presence of Et₄ N⁺ in the appropriate proportions results in the formation of (Et₄ N)[Y(can)₂ ], which consists of anionic square-grid coordination polymer sheets with interleaved layers of counter-cations. These counter-cations, which serve as squat pillars between [Y(can)₂ ] sheets, lead to alignment of the square grid sheets and the subsequent generation of square channels running perpendicular to the sheets. The crystals are found to be porous and retain crystallinity following cycles of adsorption and desorption. This compound exhibits a high affinity for volatile guest molecules, which could be identified within the framework by crystallographic methods. In situ neutron powder diffraction indicates a size-shape complementarity leading to a strong interaction between host and guest for CO₂ and CH₄ . Single-crystal X-ray diffraction experiments indicate significant interactions between the host framework and discrete I₂ or Br₂ molecules. A series of isostructural compounds (cat)[M^III (X-an)₂ ] with M=Sc, Gd, Tb, Dy, Ho, Er, Yb, Lu, Bi or In, cat=Et₄ N, Me₄ N and X-an=chloranilate, bromanilate or cyanochloranilate bridging ligands have been generated. The magnetic properties of representative examples (Et₄ N)[Gd(can)₂ ] and (Et₄ N)[Dy(can)₂ ] are reported with normal DC susceptibility but unusual AC susceptibility data noted for (Et₄ N)[Gd(can)₂ ].