Polymers Therefore, lanthanide ions have become good


Polymers are
defined as large and heavy molecule, or macromolecule, composed of many repeated subunits which
are linked by covalent bond. Coordination
polymers are unlimited systems that are developed by metal ions and organic
ligands as fundamental units linked via covalent bonds and other weak chemical bonds.

The crystal
engineering of coordination compounds (coordination polymers  (CPs), metal-organic frameworks  (MOFs) has turned out as great research area.
Moreover, it also takes significant attention in realm of various applications from molecular magnetism, photoluminescence,
catalysis; non linear optics (NLO) materials, spin crossover materials, micro
magnets, medical applications like drug delivery and implantable devices and gas storage/adsorption to materials science.2–13 Actually, special interest in design of coordination polymers is the
search in their interesting properties and applications. For example, luminescent effect
of polymeric networks has attracted much interest because of their potential
applications in photoelectronic devices or as fluorescent sensors and probes.
Indeed, the coordination polymers often expose more stability (thermal- and
solvent-resistant) than the pure organic ligands and may affect the emission
wavelength of these organic molecules.14–17 The further example can be third-order
non linear optics  materials (NLO) in realm of CPs and MOFs which
are currently interest of  many research
groups since they can be used for a number of photonic applications, for
example, optical signal processing, optical communication, optical computing,
electrooptic modulation, optical limiting effect, etc.18–20 In principle, in
comparison with traditional NLO materials, the metal atom in coordination
polymers introduces more sublevels into the energy hierarchy, which makes
possible that more allowed electronic transition takes place, hence a larger
NLO effect can be observed. 20–23. In perspective of magnetic effect, many coordination
polymers and metal-organic frameworks of transition metals have been reported
in past two decades. 24–31 For example,   the magnetic properties of lanthanide coordination
polymers are also studied, because many Ln(III) ions, such as Tb(III), Dy(III), or Ho(III) exhibit the strong unquenched orbital angular
momentum that result in magnetic anisotropy, originating from unpaired 4f
electrons. Therefore, lanthanide ions have become good candidates to synthesize
single-molecule magnets (SMM) and single-chain magnets (SCM).32–35 Besides many interesting
properties of coordination polymers, it is worth to note that the metal organic
frameworks (MOFs) have emerged strong potential adsorption and being as  catalysts due to their porous nature, easily
tunable and tailored structures and chemical functionality which ease diffusion
and interfacial contact between active sites and reagents. 37–39

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term ”coordination polymer” was ?rst used by J. C. Bailar in 1964, since he
found the similarities between organic polymers with inorganic compounds which
can be considered as polymeric species. In comparison, he made rules for the
architecture and the required properties of new species which involved metal
ions and organic ligands. 40 In addition a certain number of principal
differences between CPs and polymers must be considered in order to avoid confusion.
1) Despite polymers usually exhibit a certain size distribution due to variable
chain lengths, MOFs, usually characterized in the solid state and they possess
in?nite metal­ligand assemblies which extend into one, two or three dimensional
networks (Figure 1). 41 2) A
polymer is combined by many small molecules known as monomer units via covalent
bonds, while a coordination polymer network is generally based upon
coordinative bonds. Coordinative bonds are formed in equilibrium which
may be more on the side of the products and less of the starting materials. For
both, weak intermolecular interactions may affect on the overall arrangement
and in?uence the properties. 3) As a consequence, in solution, polymers may be
identi?ed by their chain length, while for MOFs or CPs the identity of polymeric
structure depends on various factors. For instance, on the solvent, the
temperature, pH, the pressure etc., i.e.  Which  in?uence
stability. 4) While polymers, because of the connection of an immense number of
monomers, may own properties which cause elastomers, duroplasts, or
thermoplasts. The coordination polymer networks are usually in solid state and
crystalline, hence they are well-ordered in the long range .The latter leads to
the fact that the structure of MOFs and CPs is usually well-known and their
structure can be shown from single crystal x-ray data.42