STERICALLY HINDERED, SADDLE-SHAPED COMPLEXES OF PALLADIUM(II) AND PLATINUM(II) AND THEIR REACTION WITH IODINE

The synthesis and characterization of I2 reaction products of palladium(ll) and platinum(II) with the tetraaza ma crocycle tetrabenzo[b, f, j, n][l, 5, 9, 13] tetraazacyclohexadecine (TAAB) from [M(TAAB)][BF4]2 are described. X-ray structural results for [Pd(TAAB)][BF4]2 show the complex to crystallize in the monoclinic space group P21/c with unit cell dimensions a = 16.927 (6) A, b = 1 1.757 (7) A, c = 15.559 (4) A, and ² = 118.87 (2)°. The immediate coordination sphere of the palladium consists of the four nitrogens situated on a saddle-shaped surface with the palladium located essentially in the center. The ligand system is decidedly saddle shaped, with the benzo groups forming cavities 2.70 A deep above and below the PdN4 surface. In the presence of I2 these complexes react to form a complex with the stoichiometry [M(TAAB)] [I3]2, 7. The presence of I3 - and absence of I2 were confirmed by both far-infrared and Raman spectroscopy. Mid-infrared and EPR evidence substantiates that ligand oxidation has not occurred. Electrical conductivity measurements using dc two-probe techniques indicate an unusual pressure dependence, whereby up to a 1000-fold increase in conductivity at up to 10 kbar pressure is noted. Single-crystal conductivity measurements for [Pt(TAAB)] [13)2.7 indicate conductivities on the order of the partially oxidized bisdioximates (10-4 Ω-1 cm-1 while the palladium analogue is considerably less (10-7 cm-1). © 1979, American Chemical Society. All rights reserved.