Cordination Compounds Essay

* FLEXIDENTATE CHARACTER OF POLYDENTATE LIGANDS* Poly rough ligands have flexi dentate character in the sense that all donors atoms may not form coordinate bonds with the central metal atom or ion. For example EDTA which is the hexa dentate ligand also acts as tetra dentate or penta dentate in certain complexes. Similarly sulphate ion, which is a bi dentate ligand, also acts as a mono dentate ligand in certain complexes, e.g. in Co(SO4)(NH3)5Cl. * LABILE COMPLEXES* A complex in which the ligands can be easily replaced by other ligands is called a labile complex. * GEOMETRY OF CuX42- IONS* The halide complex of Cu (2) shows devil different stereo chemistries. In (NH4)2CuCl4, CuCl42- ion is squargon planar, but Cs2CuCl4 and Cs2CuBr4, the CuX42- ions have a slightly squashed tetrahedral shape. Tetrahedral CuCl42- ions are orange whereas, square planar CuCl42- ions are yellow in colour. * GREATER STABILITY OF Co(+3) COMPLEXES THAN Co(+2) COMPLEXES * Co+2 ions are very stable & are diff icult to oxidise. Co+3 ions are slight stable and are readily reduced by water to Co2+. In contrast Co(+2) are less stable and are readily modify to Co(+3) complexes, i.e. Co(3) are very stable. This is because CFSE of Co(+3) with d6 configuration is higher than Co(+2) with d7 configuration. * SIDGWICK THEORY OR EFFECTIVE ATOMIC NUMBER (EAN) RULE* Sidgwick put forward a rule to explicate the stability of complexes on the basis of effective atomic number as follows- EAN of metal in complex= atomic number oxidation state+2 co-ordination number A stable complex is formed if the EAN is equal to the atomic number of the next noble gas.Thus, from the calculation given in the table below, Fe(CN)64- is to a greater extent stable than Fe(CN)63- Though this rule is found to be applicable in many cases, yet it fails in no. Of cases as illustrated by last two examples given in the table belowcomplex Oxidation state Atomic number Co-ordination number EAN Co(NH3)63+ +3 27 6 27-3+26=36, i.e. K rFe(CN)64- +2 26 6 26-2+26=36, i.e. KrPtCl62- +4 78 6 78-4+26=86, i.e. RnFe(CN)63- +3 26 6 26-3+26=35Ag(NH3)21+ +1 47 2 47-1+22=50