6. Spin crossover compounds are of great interest as a bistable system which wil

Question

6. Spin crossover compounds are of great interest as a bistable system which will respond to temperature. The most common class of compounds with this property are six-coordinate Fe(ll) complexes with ligands which are coordinated thru a nitrogen donor atom. Ligand 1 is an anionic, tridentate ligand, consisting of three different hetero-cyclic rings (pyridine, pyrazole and tetrazole) joined together which reacts with (Fe(H20)](BF42 to produce complex 2, whose crystal structure was determined at 180K and has a distorted octahedral geometry N-N N-N [Fe(H20)l(BFa 4)2 N-N NNI C12 CI cio NI1 1? 3 pts(b) Magnetic susceptibility measurements of the spin only magnetic moment, so, for complex 2 as a function of temperature are shown below Te 22°C Hso (BM) cooing 5 10 15 20 25 30 35 40 temperature (°C) The cooling and heating curves are shown for 2. How can we explain this magnetic behaviour?

Explanation / Answer

Answer for 6 (a).

KOtBu is functioning like a base which protonates the N from tetrazole ring.

Answer for (b).

In heating curve, at about 160 C, complex is showing spin crossover. Thus magnetic susceptibility increases suddenly and get saturated at critical temperature of 220 C . while in cooling curve, it is showing reversibility and follow the same path.

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