CHEM2402 | Chemistry Practical

Added on - Feb 2020

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Chemistry2IntroductionThis is the existence of coordination of chemical compounds which contain similarcomposition but differing with the connectivity of the metal to a ligand. There are differentprototype of ligand which will give rise to linkage isomers; These may include the following;Nitrite ( NO2-), Sulfite ( SO32-) and thiocynate (SeCN-)[ CITATION Rob142 \l 1033 ].Most of theselinkage isomers are generally violet in colour. That is, they contain the violet colored ion[(NH3)5Co-SCN]2+and the orange colored ion [(NH3)5Co-NCS]2+. In the three best examples arealmost the same but the only different in them is what atoms the ligands (molecular ligands)binds to the central ion. These ligand should contain more than one donor atom and it must bindto ion in one place[ CITATION Fre111 \l 1033 ].Linkage isomers contains are two or some case more than two coordination compoundsfor which a donor atom of at least one of the ligand is not the same[ CITATION Cha112 \l 1033 ].That is to say, the linkage between the atoms are not the same. Some ligand may form linkageisomers as illustrated in the table below and they contain different physical properties anddifferent chemical properties;For [Co(NH3)4(NO2)Cl]+, it should be noted that the N of the nitrite group is linkageto the Co atoms, and the nitrite group which is written as NO2in its molecular formula
Chemistry3and not ONO , having N atom adjacent to the Co symbol which illustrate that the N as opposedto O is the donor atom, and we need to note the octahedral structure of the ligand[ CITATIONGeo151 \l 1033 ].Cationic cabalt complex always occurs in two separable isomers (linkageisomers) of the complex ion;(NH3)5(NO2)]2+[ CITATION Jam15 \l 1033 ]. When donation is to metalcenter fromnitrogen, the complex is referred to as a nitro-complex but when the donation is to a metalcenter from oxygen the whole complex is known as nitrito-complex . And these two are illustrated inthe figure below;The formula of the complex ion are the same but the properties of the complex sometimes maybe different.For [Co(NH3)4(ONO)Cl]+ we need to note that one of oxygen atom O of the nitritecategory is linked to the Co atom. And in this case the nitrite group is written as `` ONO `` in themolecular formula as opposed to what we say earlier NO2. With the O atom adjacent to the Cosymbol it illustrates that the O atom is actually the donor and here we have to note the octahedralstructure as well[ CITATION Luk10 \l 1033 ].For this the different in how the ligand linked to themetal, for the first isomer in the below diagram, the ligand to the metal is by an electron pair onthe nitrogen, while in another isomer, the ligand linked to the metal via an electron pair on one ofthe oxygen atom.
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