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2 General introduction<br />
The aim of this chapter is to give a general introduction on the research progress of metalorganic<br />
frameworks (MOFs) including the origin of MOFs, their chemistry, structural<br />
features, synthetic approaches, modification on the structure as well as their applications.<br />
2.1 Origin of MOFs - Coordination polymers<br />
In 1833, J. J. Berzelius firstly use the term “polymer” to describe any compound that could<br />
be formulated as consisting of multiple units of a basic building block. [1] Later, Werner for<br />
the first time, proposed the correct structure [Co(NH3)6]Cl3 for coordination compounds<br />
containing complex ions in 1893, which developed the groundwork for the study of<br />
coordination polymers (CPs). In 1916, to define dimers and trimers of various cobalt(II)<br />
ammine nitrates, the term “CPs” was firstly employed by Y. Shibata [2] and has been<br />
continuously used in the scientific literature since the 1950's. Moreover, the first review<br />
on CPs was published in 1964. [3] The International Union of Pure and Applied Chemistry<br />
(IUPAC) Red Book of inorganic nomenclature from 2005 gives the following definition of<br />
coordination compounds: “A coordination compound is any compound that contains a<br />
coordination entity. A coordination entity is an ion or neutral molecule that is composed of<br />
a central atom, usually that of a metal, to which is attached a surrounding array of atoms<br />
or groups of atoms, each of which is called a ligand”. [4] Consequently, CPs can be<br />
conceptually considered as coordination compounds with extended arrays structures of<br />
one, two or three dimensions (Figure 2.1). [5] Typically, CP consists of two central<br />
components: metal ions (serving as connectors) and ligands (serving as linkers). Apart<br />
from these two components, blocking ligands, counter-anions, non-bonding guests or<br />
template molecules can be also included (Figure 2.2). The number and orientation of the<br />
binding sites (i.e. coordination numbers and geometries) are the important<br />
characteristics of the connectors and linkers. Their combination in numerous ways via a<br />
self-assembly enables the formation of practically an infinite number of CPs (Figure 2.1).