Pseudopolymorphism of [2,5-bis-(2-pyridyl)pyrazine]ferrocenyl-(methyl)boron hexafluorophosphate

Two pseudopolymorphs of [2,5-bis(2-pyridyl)pyrazine]ferrocenyl(methyl)boron hexafluorophosphate have been determined at 173 K, namely the diethyl ethe r hemisolvate, [Fe(C5H5)(C20H17BN4)]PF6.0.5C(4)H(10)O, (I), which forms red crystals with Z' = 1, and the acetonitrile hemisolvate, [Fe(C5H5)(C20H17BN 4)]PF6.0.5CH(3)CN, (II), which yields green-brown crystals with Z' = 2. Des pite the different crystal packing, the cations in (I) and (II) are similar . The 2,5-bis(2-pyridyl)pyrazine moiety is almost planar and displays bendi ng along its long axis compared with free 2,5-bis(2-pyridyl)pyrazine. It is remarkable that both crystals were obtained from the same acetonitrile/die thyl ether solution.