Coordination Compounds

Coordination compounds — like haemoglobin, chlorophyll, vitamin B12 and countless industrial catalysts — are molecules in which a central metal atom or ion is bonded to a set of surrounding ligands. This chapter, worth a reliable 6-9 Board marks and 3-4 JEE/NEET questions a year, builds the whole subject from Werner's pioneering theory of primary and secondary valencies. We define the key terms (ligands, denticity, coordination number, coordination sphere), learn the IUPAC rules for writing formulas and names, and explore the rich isomerism of these compounds — structural (linkage, coordination, ionisation, solvate) and stereoisomerism (geometrical cis-trans and optical). We then study bonding through two models: Valence Bond Theory (hybridisation, inner vs outer orbital complexes, and magnetic behaviour) and Crystal Field Theory (the splitting of d orbitals in octahedral and tetrahedral fields, $\Delta_o$, the spectrochemical series, high-spin vs low-spin complexes, and crystal field stabilisation energy). We explain why complexes are coloured and magnetic, look at the synergic bonding in metal carbonyls, the stability of complexes and the chelate effect, and finish with the many applications of coordination chemistry. Every formula, structure and exam-favourite comparison is covered.