.gamma.,.gamma.'-Bipyridyl .gamma.,.gamma.'-Dipyridyl 4,4'-Bipyridine 4,4'-Bipyridyl 4,4'-Dipyridine 4,4'-Dipyridyl 4,4'-Dipyridyl hydrate 4,4-Bipyridyl 4,4-Dipyridyl 4-(4-Pyridyl)pyridine 553-26-4 NSC404423