Crystal structure of the dinitratotetrakis(pyridine)nickel(II) clathrate with pyridine as guest, [NiPy4(NO3)2]·2Py

The structure of the NiPy₄(NO₃)₂]·2Py clathrate was determined by single crystal X-ray diffraction analysis (KM-4 diffractometer, λMoK_a radiation, graphite monochromator, ω/2θ scan mode, θ_max=30°, 640 reflections, R=0.065). Orthorthombic base-centered unit cell, space group Ccca, a=12.148(5), b=15.019(4), c=16.96(1) Å, Z=4C₃₀H₃₀N₈NiO₆, d_calc=1.411 g/cm³. The structure is of island type and consists of distorted octahedral trans-NiPy₄(NO₃)₂] (host) and pyridine (guest) molecules. The Ni(II) cation coordinated by four nitrogens of the pyridine ligands and two oxygens of the nitrato groups lies in the special position 222; the twofold axes coincide with the directions of the metal-ligand bonds. The guest pyridine molecules lie on the twofold axes that are parallel to the c axes and are oriented in such a way that the total dipole moment of the guest subsystem is zero.