Tossing and turning: guests in the flexible frameworks of metal(III) dicarboxylates

Single crystals of Ga(OH)(C(8)H(4)O(4)).0.74C(8)H(6)O(4) (2) and Ga(OH,F)(C(8)H(4)O(4)).0.74C(8)H(6)O(4) (3) were obtained under hydrothermal conditions. The structures of 2 and 3 have the same topological framework as the previously reported aluminum 1,4-benzenedicarboxylate (BDC), Al(OH)(C(8)H(4)O(4)).0.7C(8)H(6)O(4) (1). The frameworks are built by interconnecting M-OH-M chains (M = Al, Ga) with BDC anions to form large diamond-shaped one-dimensional channels filled with additional H(2)BDC guest molecules occupying disordered positions in the channels. Upon removal of H(2)BDC, other guest molecules such as H(2)O and pyridine can be inserted. In this work, we present a study of the intercalation of aromatic guests (BDC and pyridine) into frameworks of 1-3 by liquid and vapor diffusion into the empty channels of 1 and by single-crystal-to-single-crystal solvothermal guest exchange for 2 and 3. In the case of Al(OH)BDC and Ga(OH,F)BDC, two interconvertible, guest-concentration-dependent phases with different orientations of the pyridine guests have been observed, while only one pyridine orientation is found in Ga(OH)BDC.