Abstract
A heterometallic metal−organic framework (MOF) of [Cd6Ca4(BTB)6(HCOO)2(DEF)2(H2O)12]∙DEF∙xSol (1, H3BTB = benzene-1,3,5-tribenzoic acid; DEF = N,N′-diethylformamide; xSol. = undefined solvates within the pore) was prepared by solvothermal reaction of Cd(NO3)2·4H2O, CaO and H3BTB in a mixed solvent of DEF/H2O/HNO3. The compatibility of these two divalent cations from different blocks of the periodic table results in a solid-state structure consisting of an unusual combination of a discrete V-shaped heptanuclear cluster of [Cd2Ca]2Ca′ and an infinite one-dimensional (1D) chain of [Cd2CaCa′]n that are orthogonally linked via a corner-shared Ca2+ ion (denoted as Ca′), giving rise to an unprecedented branched-chain secondary building unit (SBU). These SBUs propagate via tridentate BTB to yield a three-dimensional (3D) structure featuring a corner-truncated P41 helix in MOF 1. This outcome highlights the unique topologies possible via the combination of carefully chosen s- and d-block metal ions with polydentate ligands.
Highlights
[Cd3 (BTB)2 (DEF)4 ]·2(DEF)0.5 [62,63], as we and others have demonstrated that the heterometallic combinations of Cd/Zn, Cd/Co, and Zn/Co are readily tolerated in linear trimetallic cluster secondary building unit (SBU) [26,66]
The thermally unstable nature of metal−organic framework (MOF) 1 prevented us from studying its surface area via gas adsorption, and our preliminary experiments suggested that MOF 1 exhibits no adsorption of N2 at 77 K (Supplementary Figure S2), presumably due to the collapse of the 3D
The isolation of MOF 1 exemplified the usefulness of s-block metal ions for the MOF assembly
Summary
Heterometallic metal−organic frameworks (MOFs) merge the traits of two or more different metal ions in one ordered array with synergistic advantages that can be applied to catalysis [1,2,3,4,5,6,7,8], gas adsorption [9,10,11,12,13], bioimaging [14,15,16], and other applications [17,18,19,20,21]. The flexible coordination geometries of these ions and the ionic forces between the metal ions and ligands (relative to dative bonds between a typical d-block metal ion and the ligand) may permit novel framework topologies. Some of these s-block metal ions (e.g., Li+ ) have additional advantages of being inexpensive and relatively non-toxic [12,50,61]. The structure of MOF 1 is dramatically different from, and much more delicate than, all the literature examples that are exclusively from the assembly of Cd2+ with BTB ligands [62,63,64,65]
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