Synthesis and Characterization of Inorganic and Coordination Compounds
Synthesis and Characterization of Inorganic and Coordination Compounds
This domain examines whether you can make a coordination compound reproducibly and prove what you have made. Expect air-sensitive technique, ligand-field reasoning, and interpretation of several independent characterisation methods.
Core rules
- Choose the technique that matches the sensitivity: Schlenk line and cannula for air/moisture-sensitive solutions, glovebox for solids, freeze-pump-thaw for degassing. Dry THF/Et2O over Na/benzophenone, CH2Cl2 over CaH2; confirm water by Karl Fischer.
- Control the metal source: hydrated salts introduce water, counterions change solubility, and trace acid can protonate basic ligands.
- Use ligand-field and HSAB arguments. Pt(II) trans influence order: CO, CN⁻, C2H4, PR3 > Cl⁻. Irving–Williams order gives stability Cu²⁺ > Zn²⁺ > Ni²⁺ > Co²⁺ > Fe²⁺ > Mn²⁺. d⁹ Cu(II) shows Jahn–Teller elongation; d⁸ Ni(II) can be tetrahedral or octahedral.
- Prove composition with elemental analysis (C,H,N), ICP-OES/AAS for the metal, and ion chromatography or AgNO3 titration for ionic halide. IR shows ligand coordination (C=O shift, M–O/M–N modes), UV-Vis shows d–d and charge-transfer bands, molar conductivity gives the ion count, and magnetic susceptibility (Evans method) gives unpaired electrons. Single-crystal XRD is definitive.
Worked example
A cobalt(III) complex analyses as [Co(NH3)5Cl]Cl2, M = 250.4 g mol⁻¹. You weigh 0.100 g (0.399 mmol) and precipitate chloride with excess AgNO3, obtaining 0.114 g AgCl (M = 143.3 g mol⁻¹; 0.796 mmol). The ratio Cl⁻:complex is 2.0:1, so the compound is a 2:1 electrolyte, consistent with one bound and two ionic chlorides. Molar conductivity in water would be near 250 S cm² mol⁻¹, not the ~120 expected for a 1:1 salt.
Traps
Reading the formula as the structure; ignoring lattice solvent in elemental analysis; using magnetic moment alone to assign geometry; oxidising air-sensitive Cu(I) or Fe(II) during workup; reporting a yield without purity evidence.