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58 Chapter 4
4.1 Introduction
4.1.1 Solid solutions
Among the well-known mixed-component MOFs, the class of MOF solid solutions (also
known as molecular substitutional alloys) attract huge attention. It implies MOFs where to
two or more types of the related components (either linkers, metals, or both) are
randomly mixed within single-phased framework. Remarkably, this often allows the fine
modulation of the MOF’s functionalities and properties. Considering the nature of the
mixed components, MOF solid solutions could be sub-divided mainly into two groups:
linker-based and metal-based MOF solid solutions. The first group covers MOF solids
where two or more homologous linkers (usually of similar size and functionality) are
integrated in various proportions while the structural integrity of MOF is preserved. The
metal-based MOF solid solutions will be discussed in details in Chapter 5 and involve
mixed-metal frameworks where ions of one metal type is partly isomorphous substituted
by the other metal ions.
Figure 4.1. Mixed-linker approaches to the formation of MOF solid solutions. Magenta balls, metal
nodes; cyan sticks, parent linker; green sticks, isostructural mixed-linker; wine short sticks,
truncated mixed-linker; violet sticks, heterostructural mixed-linker. Inspired by the reports of
Bunck [127] and Fang et al. [137]
Approaches for the synthesis of linker-based MOF solid solutions go basically into three
directions depending on the utilized linker mixtures (Figure 4.1): [127]
i) isostructural mixed-linker (IML) approach where mixed linkers feature identical linking
geometry. [123-124, 209-212]