Cordination Compounds Essay

* FLEXIDENTATE CHARACTER OF POLYDENTATE LIGANDS* Poly dentate ligands fetch flexi dentate character in the sense that all donors atoms may not form coordinate bonds with the central metal atom or ion. For deterrent example EDTA which is the hexa dentate ligand similarly 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 well replaced by other ligands is called a labile complex. * GEOMETRY OF CuX42- IONS* The halide complex of Cu (2) shows two different stereo chemistries. In (NH4)2CuCl4, CuCl42- ion is squ ar planar, but Cs2CuCl4 and Cs2CuBr4, the CuX42- ions have a slightly squashed tetrahedral shape. Tetrahedral CuCl42- ions nuclear number 18 orange whereas, squ are planar CuCl42- ions are yellow in colour. * GREATER STABILITY OF Co(+3) COMPLEXES THAN Co(+2) COMPLEXES * Co+2 ions are very stalls & are difficult to oxidise. Co+3 ions are less stable and are readily reduced by irrigate to Co2+. In contrast Co(+2) are less stable and are readily oxidised 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 system OR EFFECTIVE ATOMIC NUMBER (EAN) RULE* Sidgwick put in the lead a rule to explain the stability of complexes on the basis of trenchant 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 appalling gas.Thus, from the calculation presumption in the table below, Fe(CN)64- is more stable than Fe(CN)63- though this rule is found to be applicable in many cases, merely it fails in no. Of cases as illustrated by last two examples given in the table belowcomplex Oxidation state nuclear number Co-ordination number EAN Co(NH3)63+ +3 27 6 27-3+26=36, i.e. KrFe(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