GROUP-13 METAL-INDUCED COORDINATION VARIATION OF THE BIS(2-PYRIDYL)AMIDE LIGAND IN SOLUTION AND IN THE SOLID-STATE

Ligands containing aromatic nitrogen heterocycles play a leading role in the molecular self assembling processes that lead to macromolecular architectures. The inductive effect of various metal fragments on tho se building blocks has not yet been studied systematically. To evaluat e this effect we synthesized the homologous series of Group-13 metal c omplexes [Me(2)AIPy(2)N] (1), [Me2GaPy2N] (2), [Me2InNPy2](2) (3), and [Me2TINPy2](infinity) (4) (Py = 2-NC5H4), and characterized them by l ow-temperature X-ray structure analysis and N-15-NMR spectroscopy in s olution. The electronic equivalence of the central and the ring nitrog en atoms leaves the energetic hyperface of the anion quite flat, and t he electron density is polarized according to the requirements of the metal. In the aluminum and the gallium complexes 1 and 2 the metal cen ter is coordinated exclusively through the nitrogen atoms within the p yridyl rings. The complexes with these hard metals are close-contact i on pairs. in the indium complex 3 the cis-cis orientation gives rise t o a dimeric structure, while the unprecedented cis-trans arrangement i n the thallium compound 4 leads to a polymeric structure. The complexe s 3 and 4 have to be regarded as separated ion pairs of Me2M+ cations and Py2N- anions without any covalent bonds between the anionic moiety and the dimethylmetal cations, even in the solid state. The series of complexes proves the bis(2-pyridyl)amide to be an excellent self-adap ting ligand. These findings are substantiated by NMR-spectroscopic stu dies in solution. Not only do the steric requirements of N heteroaroma tic ligands have to be considered in molecular self-assembling process es but also the inductive effect of the different metal fragments.