We introduce the
concept of domain building blocks (DBBs) as an
effective approach to increasing the diversity and complexity of metal–organic
frameworks (MOFs). DBBs are defined as distinct structural or compositional
regions within a MOF material. Using the DBB approach, we illustrate
how an immense number of multivariate MOF materials can be prepared
from a small collection of molecular building blocks comprising the
distinct domains. The multivariate nature of the MOFs is determined
by the sequence of DBBs within the MOF. We then apply this approach
to the construction of a rich library of UiO-67 stratified MOF (sMOF)
particles consisting of multiple concentric DBBs. We discuss and highlight
the negative consequences of linker exchange reactions on the compositional
integrity of DBBs in the UiO-67 sMOFs and propose and demonstrate
mitigation strategies. We also demonstrate that individual strata
can be specifically postsynthetically addressed and manipulated. Finally,
we demonstrate the versatility of these synthetic strategies through
the preparation of sMOF–nanoparticle composite materials.
The T point group symmetry of rare earth (RE) metal clusters RE(μ-OH)(COO) makes them attractive building blocks for creating metal-organic frameworks (MOFs) with controllable topologies. Herein, we describe the design and synthesis of a series of isoreticular MOFs featuring pcu topology [MOF-1114(RE) and MOF-1115(RE)] with variable rare earth metal ions (RE = Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) and linear amino-functionalized dicarboxylate linkers of different lengths. In total, we report 22 MOFs that vary in both composition and structure yet share the same RE(μ-OH) cluster motif. We demonstrate that these pcu MOFs are cationic and that anion exchange can be used to affect the MOF properties. We also investigate the luminescence properties of a representative member of this MOF series [MOF-1114(Yb)] that exhibits near-infrared emission. We show that the excitation energy for Yb sensitization can be carefully adjusted to lower energy via covalent postsynthetic modification at the amino group sites within the MOF.
Using diverse building blocks, such as different heterometallic clusters, in metal-organic framework (MOF) syntheses greatly increases MOF complexity and leads to emergent synergistic properties. However, applying reticular chemistry to syntheses involving more than two molecular building blocks is challenging and there is limited progress in this area. We are therefore motivated to develop a strategy for achieving systematic and differential control over the coordination of multiple metals in MOFs. Herein, we report the design and synthesis of a diverse series of heterobimetallic MOFs with different metal ions and clusters severally distributed throughout two or three inorganic secondary building units (SBUs). By taking advantage of the bifunctional isonicotinate linker and its derivatives, which can coordinatively distinguish between early and late transition metals, we control the assembly and topology of up to three different inorganic SBUs in one-pot solvothermal reactions. Specifically, M(μ-O) (μ-OH)(CO) (M = Zr, Hf, Dy) SBUs are formed along with metal-pyridyl complexes. By controlling the geometry of the metal-pyridyl complexes, we direct the overall topology to produce eight new MOFs with fcu, ftw, and previously unreported trinodal pfm crystallographic nets.
Dye RE3+-MOF hybrid exhibits both NIR excitation and emission within the biological diagnostic window, highlighting its potential for biological imaging.
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