K-Zn-MOF (
1) crystallizes in the rhombohedral space group
R3c (Tables S1 and S2 in Supporting information) and possesses an isoreticular structure to Na-Zn-MOF with 1D neutral hexagonal channels [
43]. The asymmetric unit consists of one-half crystallographically independent Zn
2+ ions and two one-half K
+ ions (denoted as K1 and K2, respectively). K1 ions participate in the assembly of helical Zn-O-K-O rod-shaped units that were bridged by FDA
2− to form 1D hexagonal channels (Fig. S1 in Supporting information), while K2 ions coordinate with two water molecules (Fig. S2 in Supporting information), which can be removed upon activation to generate OMSs, evidenced by powder X-ray diffraction (PXRD) profiles and thermogravimetric analysis (TGA) of activated
1 (Figs. S3 and S4 in Supporting information). Without considering K
+ ions, the topology analysis shows that the whole framework of
1 can be simplified to a typical NbO topology (Fig. S5 in Supporting information). To verify whether the bolt ligands can be anchored onto the OMSs, one-pot solvothermal reaction similar to the synthesis of
1 was performed, with the addition of fytpy or pytpy ligand at the beginning of the reaction. Single crystal X-ray diffraction (SCXRD) analyses suggest the molecular formula of the resulting complexes
2 and
3 to be [K
6Zn
3(fytpy)
2(FDA)
6] and [K
6Zn
3(pytpy)
2(FDA)
6], respectively (Tables S1 and S2). As shown in
Fig. 1, complexes
2 and
3 possess a similar three-dimensional (3D) framework as that of
1, but with the fytpy or pytpy ligand embedded into the 1D channels by replacing the water ligands of K2 ions (Figs. S6 and S7 in Supporting information). The distinctive distribution of hetero atoms (i.e., N and O) in fytpy and pytpy ligand leads to a subtle difference between the structures of
2 and
3. Specifically, the OMSs of K2 ions in
2 are two-thirds occupied by two N atoms from fytpy, while the rest OMSs are still retained due to the steric hindrance effect of furan ring. In contrast, the OMSs of K2 ions in
3 are all taken up by three N atoms from pytpy. Along with the trend in the occupied number of OMSs, the distance between the K2 ions accordingly decreases from 15.006 Å (for
1), to 14.986 Å (for
2) and 14.949 Å (for
3). The inserted ligands are stacked in a face-to-face fashion by the
π-
π interactions between the adjacent ligands. The intermolecular distances between fytpy are 3.751, 4.532, and 3.760 Å, slightly longer than those of pytpy (3.731, 4.434, and 3.731 Å) (Fig. S8 in Supporting information). Due to the insertion of fytpy or pytpy, the whole unit cell volume of
2 or
3 is contracted compared with
1. And
3 exhibits a higher thermal stability than that of
2 (Fig. S10 in Supporting information), likely ascribed to the full occupation of OMSs in
3. All the above results demonstrate the feasibility of anchoring the size-matching ligands onto the OMSs in the pore channels.