What is the ratio of metal salt : Ligand : Solvent we need to follow to get a MOF in Hydrothermal synthesis.
Answering such a question would mean to write down an entire book, as there are a very large number of variables that one should take into account when approaching the synthesis of a MOF.
Of course the ligand:metal: solvent ratio is one of these, but temperature, pH, nature of the solvent (polarity, boiling point, ability to form hydrogen bonds), nature of the ligand (coordinating group, shape, symmetry, flexibility), nature of the metal (preferred coordination geometry, oxidation number), reaction time are other variables that have a strong influence on the synthesis process.
As a consequence, being able to determine a priori the best experimental conditions for obtaining a MOF is very difficult, and the discovery of new MOFs is basically a trial and error process. This is why, in order to span a wide range of variables in a fast manner, many groups use high throughput methods, which allow to run dozens of syntheses in different conditions at the same time.
It depends on the metal center, the ligand connectivity and the desired material topology. For example if you expect from the chemical formula for the ligand to be in a lets say 1:3 metal to ligand then it is ok if you keep that ratio in your reaction quantities with a bit larger quantity for the ligand. In my synthesis i usually keep a 1 to 1,5 ratio ligand to metal because the Ligand is the expensive one.... But in general keep in mind that you have to go back to basics in order to see whats the relation beetween the two. Now for the solvent although the quantity can change a lot... usually it doesnt. What it affects is the generation of crystallization centers. In general the more delute the reaction mixture the biggest the crystals. So a normal quantity used is somewhere between 1 to 30 ml. Just keep in mind of the water content in your solvent.
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