Studies on the iodine complexes of pyridine picolines and aminopyridine by constant activity method

The iodine complexes of pyridine, -, β-, γ- picolines, 2-aminopyridine and 2,2′-bipyridine in cyclohexane were studied by the constant activity method, their spectral characteristics and thermodynamic parameters were determined. The equilibrium constants, molar extinction coefficients of the charge-transfer band maxima, _CT, at 25°C and heats of complexation, ΔH°, are respectively as follows:

1. (a) pyridine-iodine, 107 dm³mol^?1 24200 dm³mol^?1m^?1 and 31 KJ/mol;

2. (b) -picoline-iodine, 172 dm³mol^?1m^?1, 49700 dm³mol^?1m^?1 and 33 KJ/mol;

3. (c) β-picoline-iodine, 243 dm³mol^?1, 50300 dm³mol^?1m^?1 and 35 KJ/mol;

4. (d) γ-picoline-iodine, 342 dm³mol^?1, 55900 dm³mol^?1m^?1 and 41 KJ/m;

5. (e) 2-aminopyridine-iodine, 427 dm³mol^?1, 60800 dm³mol^?1m^?1 and 47 KJ/mol;

6. (f) 2,2′-bipyridine-iodine, 6.0 dm³mol^?1,?, 21 KJ/mol.

The values of the blue shifted iodine band maxima of the above mentioned donors and their molar extinction coefficients are, 420 nm (1450 dm³mol^?1m^?1), 419 nm (1470 dm³mol^?1m^?1), 418 nm (1640 dm³mol^?1m^?1), 417 nm (1570 dm³mol^?1m^?1), 410 nm (1574 dm³mol^?1m^?1) and 452 nm (1370 dm³mol^?1m^?1) respectively. The oscillator strengths and transition dipole moments of the blue-shifted iodine bands are characterised.