Coordination complexes have emerged as a powerful tool in the fight against environmental pollution. These versatile compounds, formed by metal ions bonded to organic or inorganic ligands, play a crucial role in addressing some of the most pressing environmental challenges of our time. From removing heavy metals from water sources to breaking down toxic pollutants, coordination complexes offer innovative and efficient solutions for environmental remediation. Their unique chemical properties enable them to interact with and neutralize harmful substances, making them indispensable in the quest for a cleaner, safer environment.
Author: Mishal Hayat
Coordination complexes
Compounds having one central metal attached to the ligand through coordinate covalent bond is known as coordination compounds. Ligand may be atoms, ions or molecules having lone pair which is donated to the central metal in complex. Transition metals has a specialty of vacant d orbital, due to this empty orbital it can accommodate many changes and has a wide spread applications in different fields. It may be used as catalysts, in medicinal field, material science, environmental remediation, nano technology etc.
TYPES OF COORDINATION COMPLEXE
Perfect or Penetrating Complex
In a perfect complex, the complex ion is either completely stable, that is, undissociated or is very feebly dissociated in solution. For example:
K4 [Fe(CN)6] → 4K+ + [Fe(CN)6]4- ⇌ Fe2+ + 6CN–
Imperfect or Normal Complex
In an imperfect complex, the complex ion is either less stable or dissociates appreciably. For example:
K2 [Cd(CN)4 ] → 2K+ + [Cd(CN)4] 2– ⇌ Cd2+ + 4CN –
Ligands
►The molecules and ions that surround the metal ion in a complex are known as ligands or complexing agents.
►An atom or group of atoms which bind to the central metal atom or ion through lone pair of electrons present on its donor atom.
►Depending on number of pairs donated by different atoms, it is of following types.
Monodentate | Bidentate | tridentate | tetradentate | pentadentate | hexadentate |
NH2 CN– -OH | ►C2 O4 –2 (Oxalato) ►H2 NCH2 COO– (Glycinato) ►H2 NCH2 CH2 NH2 or en (Ethylenediammine) ►Bipyridyl (bipy) | H2 N (CH2 ) 2 NH (CH2 ) 2 NH2 Diethylenetriammine (dien) Terpyridyl (terpy) | ►Triethylenetetraamine or trien ►Triaminotriethylamine or tren ►Nitriloacetato | Ethylene diamminetriacetate | Ethylenediamminetetra acetate (EDTA) |
PREPARATION OF COMPLEXE
By Substitution Reactions
Substitution reaction means to replace ligands in a reactant they may occur through associative, dissociative or interchange mechanism.
[Cu(H2O)SO4+4NH3→[Cu(NH3 )4 SO4+4H2O]
By Direct Combinations
In direct combination complexes refer to reaction between different ligands or other complexes to form a new complex. In this type of reaction metal center or ligand is involve some time both take part in reaction.
PtCl4 + 2KCl → K2 [PtCl6 ]
By Redox Reactions
Change in oxidation number of the metal complexes occur, it may outer electron sphere or inner electron sphere
CoCl2 + 2NH4 Cl + 10 NH3 + H2O2 → 2[Co (NH3) 6 ] Cl3 + 2H2O
Applications
Our environment is facing many challenges including climate change, pollution from industries to air as well as to water etc., for all these problems coordination compounds play a vital role in heavy metal removal, air purification, biodegradation, sensing and detection, and many more.
Heavy metal removal
industrial waste water is a key issue for most of the aquatic life to resolve this issue coordination complexes play a vital role. As discuss above complexes is of two type one is labile other is stable these heavy metals are attached to the ligands it may be strong or weak field ligand, and through attachment it may remove from the water. When heavy metals such as Ni(II), Cr(III), Cu(II), Hg(II), Cd(II) and Pb(II) bind to the ligand(s), the environmental fate and toxicity of heavy metals can be significantly influenced. Different separation techniques were then perform including ion exchange adsorption membrane filtration etc.,
Air purification
some of MOFs (metal organic framework), zeolites, polymeric coordination, metal oxide are used for air purification. Particulate matter, VOC heavy metals etc., are forming a stable complex through adsorption, absorption or catalytic oxidation. These process are highly selective, low cost and efficient.
Sensing and detection
some of coordination complexes may also used in various sensing and detecting platforms, they detect gases like O2 CO NO etc., biomolecules for example DNA, RNA, glucose etc., it may also detect some ions including Na+ k+ ca+ etc., PH sensing, fluorescence sensing, electrochemical sensing, magnetic sensing etc.
Also read: Molarity Calculations
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