THERMODYNAMIC AND STRUCTURAL-PROPERTIES OF PALLADIUM(II) POLYNUCLEAR COMPLEXES OF AZAMACROCYCLES - CRYSTAL-STRUCTURE OF THE [PD2([24]ANEN8)](CLO4)4 COMPLEX

The formation of Pd2+ Complexes of [18]aneN6 (1,4,7,10,13,16-hexaazacyclooctadecane), [21]aneN7 (1,4,7,10,-13,16,19-heptaazacyclohenicosane), and [24]aneN8 (1,4,7,10,13,16,19,21-octaazacyclotetracosane)in solution has been studied by microcalorimetry and H-1 and C-13 NMR. As previously reported (Bencini, A.; Bianchi, A.; Dapporto, P.; Garcia-Espana, E.; Micheloni, M.; Paoletti, P.; Paoli, P. J. Chem. Soc., Chem. Commun. 1990,1382) [18]aneN6 and [21]aneN7 form both mono- and binuclear complexs, while [21]aneN7 forms also a trinuclear complex [Pd3-([21]aneN7-H)Cl3]2+ in which an amino group of the ligand deprotonates bridging two Pd2+ ions. In the present work only the formation of a binuclear complex of [24]aneN8 has been observed. These complexes are very stable due to favorable enthalpic and entropic contributions. The crystal structure of [Pd2([24]aneN8)](ClO4)4 (Pcab, a = 15.874(8) angstrom, b = 13.070(16) angstrom, c = 16.454(7) angstrom, V = 3414(5) angstrom3, Z = 4, R = 0.082, R(w) = 0.066) has been solved by X-ray analysis. In the centrosymmetric [Pd2([24]aneN8)]4+ complex cation the two palladium ions, located 5.447(4) angstrom apart, are coordinated by four nitrogen atoms of the macrocycle in a distorted squared geometry. The palladium ions are 0.145(1) angstrom out of the donor atoms' mean plane. NMR data suggest that the rigidity observed in this crystal structure, as well as in that of [Pd2([18]aneN6)Cl2](ClO4)2, is almost maintained in solution. In the case of the complex [Pd3([21]aneN7-H)Cl3]2+, Signals at ca. 70 ppm, which could be diagnostic for the deprotonation of an amino group in this type of compounds, have been observed.