**4. Reducing topologies can easily deliver deep insights into the structures**

The structural details of nanoscopic frameworks are often difficult to perceive. Some basic discussion may be made even with the structures completely ignored, but we already have seen many limitations to that. Understanding the structure is necessary to provide more thorough explanations for the chemical trends appearing

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ranges.

*Ionothermal Synthesis of Metal-Organic Framework DOI: http://dx.doi.org/10.5772/intechopen.79156*

beyond the trees, and lastly, tour around that forest.

of any laws governing them, acquisition of more data is necessary.

metal clusters, just like vertices and edges of a mathematical 3D figure.

**4.2 Structure explains the popularity of [RMI][metal(BTC)] topology**

Some of the most commonly occurring structures need attention, not only because they will be frequently met in trials of novel conditions, but also they will provide a valuable starting point in relating to other structures occurring in the same system to understand the correlations like the ones we have visited.

The topology [RMI][Metal(BTC)] occurs in most metal systems that have been reported and in the highest frequency. With this topology as an example, we will show how a complex structure may be simplified. This way, details unnecessary for understanding of the topology can be ignored and attention may be more easily focused on the topology itself. The characteristics that may vary within the topology without changing it include coordination modes, bond angle, and bond in certain

and **7** actually have the exact same framework.

The simplification illustrated in **Figure 5** exemplifies the power of reduction in brining different structures together. Although it could have been inferred from the same molecular formulas, a great number of structures introduced in **Tables 4**, **5**

**4.1 Metals atoms tend to exist in clusters**

in the organised systems of ionothermally prepared MOFs, including many unusual cases unexplainable by simple intuition. Just like organic chemistry cannot be approached without molecular formulas, inorganic chemistry cannot be explained without framework structures. We would like to dedicate this chapter to suggest a method to break down the complications of nanoscopic structures to see the forest

In order to bring down the structures to simpler diagrams, the patterns, or segments of atoms, that occur frequently throughout the framework must be well noticed. After taken the knowledge of the building blocks, we will look into a representative building to see how the blocks are assembled to a building. It is obvious that the organic linker will stay as it is used before the reaction in most structures, as it is very difficult for the benzene ring to disassemble in our BTC example. One thing, however, may fluctuate greatly from structure to structure: the coordination mode. Often there are many atoms, or sites, that are capable of coordinating to metal atoms, but almost always, not all of them do. It is very difficult to predict which coordination mode the ligand will take, since even under the same topology, the ligands are found to take structures with many different coordination modes [1, 30, 31]. Attempts have been made to collectively study coordination modes [34], but for successful discovery

In collaboration with the coordination modes, though it is difficult to distinguish causation from correlation at this level, the reaction environment determines the shape in which the metal atoms exist in the framework. From **Tables 4**, **5** and **7**, it has been shown the nuclear types the metal atoms take in the framework, but the concept has never been visited yet. This 'nucleus' is a small collection of metal atoms and atoms from the organic ligand coordinating to them and is more commonly called 'metal clusters' because many metal atoms are found together in most structures. These metal clusters are one of the most important character to determine the topology of MOFs, and the frameworks are named as binuclear, trinuclear, etc. according to the number metal atoms present in the metal cluster. If small variations within the same topology are ignored, the framework can be viewed as a collection of simple connections between the unvarying organic ligand and the

*(H2O)2]. Combinations that have not been reported were left blank.*

were even different after all.

lated to be 21.8 Å3

**Table 6.**

[PMI] and [BMI].

in the cobalt system.

**into the structures**

the increase in the cation size that caused it. However, a question that never has been addressed in previous systems was, is the difference between [EMI] to [PMI] the same as that between [PMI] and [BMI]? In other words, they are gradual, but are they in scale? They both differ by a carbon, and carbon–carbon bond length is nearly universally conserved. It seems they should differ only by an iota, if they

*A table for the system of framework synthesised with cadmium-BTC system arranged similarly to Table 1.*

**Co(OAc)2·H3BTC Cl Br I** [EMI] — α1 [25] — [PMI] — β1 [30] — [BMI] — β2 [31] — *Each labels denote, α1-[EMI]2[Co3(BTC)2(OAc)2], β1- [PMI]2[Co2(BTC)2(H2O)2], and β2 -[BMI]2[Co2(BTC)2*

The *in situ* conformations of the guest cations were taken and subjected to computational analysis [31]. The difference in volume between [EMI] and [PMI] was calcu-

, the difference between

, which is significantly larger than 14.9 Å3

[PMI] and [BMI]. It is apparent that this difference arose from the bent conformation of the butyl chain of [BMI] cation; the distance between the terminal carbon to the first carbon in the chain was 2.918°A in compound β2, exceeding 2.567°A of compound β1 only by a small difference. The carbon–carbon bond is free to rotate about each other, but the β-class framework is stable enough to fix the conformation severely bent as they appear; a remarkable example of the framework influencing the property of the solvent. Moreover, just because it appears as the same one step on the table does not mean the actual size difference between the ionic species is the same. Even though β1 and β2 structures belong to the same topology class, they may have minor differences like the ones described in the manganese system. Even by a small bit, [BMI] is still larger than [PMI] and is expected to exert pressure on the framework towards retaining a larger void volume. However, this straightforward prediction is actually far from the truth. The β-topology framework is so rigid that the void volume and the framework volume stay nearly unchanged for

It also deserves some attention that the β-topology occurs very rare in other metal systems, suggesting that it is not so chemically favoured in many other environments [31]. While the rigidity of the framework can also be viewed as how favoured it is over other possible outcomes, it is interesting that this rare topology is so strongly preferred in the system and in cobalt system only. Also, attempts to synthesise crystalline frameworks with [PEMI]Br and [HMI]Br in the system all failed but only acquired amorphous solids. This further supports the absence of any other stable framework possible in the cobalt system. Additional studies must follow to provide explanations for the strikingly different preference of framework

The structural details of nanoscopic frameworks are often difficult to perceive. Some basic discussion may be made even with the structures completely ignored, but we already have seen many limitations to that. Understanding the structure is necessary to provide more thorough explanations for the chemical trends appearing

**4. Reducing topologies can easily deliver deep insights** 

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in the organised systems of ionothermally prepared MOFs, including many unusual cases unexplainable by simple intuition. Just like organic chemistry cannot be approached without molecular formulas, inorganic chemistry cannot be explained without framework structures. We would like to dedicate this chapter to suggest a method to break down the complications of nanoscopic structures to see the forest beyond the trees, and lastly, tour around that forest.
