Single-crystal diffraction analysis reveals the two MOFs are isostructural in spite of their different metal centers and space groups (
HL-5: Ni
2+,
C2/
m;
HL-6: Co
2+,
P1). Therefore, in the following description,
HL-6 is selected to show their structures. As illustrated in Fig. S1b (Supporting information), the asymmetric unit of
HL-6 contains three Co(Ⅱ) centers (Co1, Co2, and Co3), one L
3- ligand, three bpb ligands and two water molecules. All Co(Ⅱ) ions are six-coordinated (two N atoms and four O atoms) with octahedral geometry (Table S2 in Supporting information) calculated by
SHAPE 2.1 [
39] and two vertexes of the octahedron are occupied by the two N atoms from different bpb ligands with four O atoms forming the equatorial plane. However, for Co1 and Co2, coordinated O atoms are from two isophthalate groups of L
3- ligands and two water molecules, while for Co3, the four O atoms are all from the third carboxylate groups of two different L
3- ligands. The Co—O bond distances are from 2.081(2) Å to 2.140(2) Å, and the Co—N bonds range from 2.102(3) Å to 2.159(3) Å. In addition, the coordination angles around Co(Ⅱ) ions are in the range of 61.33(10)°–180.0° (Table S3 in Supporting information). Each L
3- ligand acting as a 3-connected linker in a
μ3-
η1:
η1:
η2 coordination mode (two monodentate and one chelate, Fig. S1c in Supporting information), connects three Co(Ⅱ) ions, resulting in the formation of a two-dimensional (2D) honeycomb layer structure (
Fig. 1a), which is further partitioned by the coordination between 1/3 of the bpb ligands and Co3 centers (
Fig. 1b). Then, the rest 2/3 bip ligands, which coordinate with Co1 and Co2 centers, respectively, link the 2D layers together to form a three-dimensional (3D) "pillaredlayer" framework (
Fig. 1c). Moreover, since the large voids in one single framework, three identical and independent single frameworks are entangled with each other to generate the final three-fold interpenetrated framework of
HL-6 (
Fig. 1d). The solvent accessible volume is 23.6% (526.8 Å
3 per unit cell volume), as estimated by PLATON [
40]. Finally, topology of the framework of
HL-6 is also analyzed, and it reveals a (3, 4, 4)- connected 3-nodal
sqc306 type 3D net with a point symbol of {6·7
2}
2{6
4·7·8}
2{7
4·10·11} (Fig. S1d in Supporting information) by considering L
3-, Co1 or Co2, and Co3 as three-, four-, fourconnected nodes, respectively.