Crystal structures of the clathrate inclusion compounds formed by the host bis(isothiocyanato) tetrakis (4-methylpyridine) iron (II) with benzene,m-xylene andp-xylene as guests

Single crystal X-ray structures of three 1 : 1 (guest: host) compounds in which the Fe(NCS)₂ (4-methylpyridine)₄ complex is the host component and benzene,m-xylene andp-xylene are the respective guest components, are reported. The crystals of the inclusion compounds are tetragonalI4₁/a, with:a = 17.08(1),c = 23.66(3) Å (benzene clathrate);a = 17.17(1),c = 24.02(2) Å (m-xylene clathrate) anda = 17.12(1),c = 23.93(3) Å (p-xylene clathrate);Z = 8. The host complex molecule has the octahedral type of coordination of the N₆ donor system. The isothiocyanate ligands are intrans positions and related by twofold axial symmetry. The symmetry axis runs diagonally between the neighbouring, equatorial 4-methylpyridine (MePy) ligands. The two symmetrically independent McPy ligands form angles ofca. 45 and 55° with the equatorial Fe-N₄ plane. The absorption sites for guest molecules lie on centres of symmetry. Non-centrosymmetricm-xylene molecules occupy these sites randomly distributed over two orientations related by symmetry. The structures belong to the class oforganic zeolites since the cavities occupied by the guest molecules are interconnected to form a three-dimensional network.