LIPOPHILIC COORDINATION-COMPOUNDS - ALUMINUM, GALLIUM, AND INDIUM COMPLEXES OF 1-ARYL-3-HYDROXY-2-METHYL-4-PYRIDINONES

A series of 1-aryl-3-hydroxy-2-methyl-4-pyridinones and tris(1-aryl-3-hydroxy-2-methyl-4-pyridinonato) aluminum(III), -gallium(III), and -indium(III) complexes have been prepared and completely characterized. The pyridinones have a variety of aryl substituents at the ring nitrogen atom (phenyl, p-tolyl, p-methoxyphenyl, p-nitrophenyl). The complexes have been studied by a number of techniques including n-octanol/water partitioning, potentiometry, and single-crystal X-ray diffraction. The uncomplexed ligands have log (n-octanol/water partition coefficients) (log p) greater than 1, except for the p-nitrophenyl case; the log p values are significantly higher in the complexes (> 2, except for the p-nitrophenyl cases). The complexes of 3-hydroxy-2-methyl-1-phenyl-4-pyridinone with aluminum (III), gallium (III), and indium (III) have been characterized by potentiometric (glass electrode) titration. The equilibria have been examined at 25.0 +/- 0.1-degrees-C (and 37.0 +/- 0.1-degrees-C for Al) at an ionic strength of mu- = 0.15. This ligand forms Ml(n) complexes (n = 1-3) of high stability; at 25-degrees-C the overall stability constants beta-3 for the 3:1 complexes are 10(30.7) (M = Al3+), 10(36.3) (Ga3+), and 10(31.1) (In3+). At ligand to metal ratios greater-than-or-equal-to 1, the ligands prevent M(III) hydrolysis at millimolar concentrations, even under slightly basic conditions, and the effective formation constants (beta-3eff) for the metal ions at physiological pH are 10(24.7) (M = Al3+), 10(30.3) (Ga3+), and 10(25.1) (In3+). Crystals of the ML3.5.5H2O complexes C39H36MN3O6.5.5H2O) (where M is Al or Ga, respectively, and L is the anion of 3-hydroxy-2-methyl-1-p-tolyl-4-pyridinone) are isomorphous and isostructural, crystallizing in the trigonal space group p3BAR1c with Z = 4, a = 16.2990 (8), 16.2817 (8) angstrom, and c = 16.784 (2), 16.948 (2) angstrom. The structure of the Al complex was solved by direct methods, and the structure of the Ga complex was solved by starting with the coordinates for Al complex. The two structures were refined by full-matrix least-squares procedures to R = 0.040 and 0.036 for 1593 and 1665 reflections with I greater-than-or-equal-to 3-sigma-(I), respectively. They form fac geometries incorporating hydrogen-bonding water molecules that bridge the metal chelating ligand oxygen atoms. These water molecules are all that remain of the exoclathrate array that is formed with smaller N substituents.