.alpha.,.alpha.',.alpha.''-Tripyridyl 1148-79-4 2,2',2''-Terpyridine 2,2',2''-Terpyridyl 2,2',2''-Tripyridine 2,2',2''-Tripyridyl 2,2':6',2''-Terpyridine 2,6-Bis(2-pyridyl)pyridine Ba 2799 NSC3905 Tripyridine Tripyridyl