This paper addresses the general question: what are the significant guest properties selected by this host when interacting with guest molecules in the liquid phase, resulting in cocrystallization of the host and guest? In particular, to what extent do pi electrons in a guest molecule effect its potential as a guest? Werner clathrates of the host [Ni(NCS)(2)(4-ViPy)(4)] with mixtures of tetrahydrofuran (THF) and cyclic hydrocarbons as guests have been synthesised and their structures elucidated. Clathrate (1): [Ni(NCS)(2)(4-ViPy)(4)](1.78 THF)(0.22 cyclohexane), crystallizes in the orthorhombic space group P-bcn a = 9.976(6), b = 20.630(25), c = 19.861(4)Angstrom, V = 4087 Angstrom(3), Z = 4, R = 0.087 for 1461 reflections; (2): [Ni(NCS)(2)(4-ViPy)(4)](1.76 THF)(0.24 cyclohexene), P-bcn, a = 9.987(7), b = 20.614(4), c = 19.898(4)Angstrom, V = 4096 Angstrom(3), Z = 4, R = 0.084 for 1304 reflections; (3): [Ni(NCS)(2)(4-ViPy)(4)](0.48 THF)(0.52 1,3-cyclohexadiene), tetragonal I4(1)/a, a = 16.898(3), b = 16.898(3), c = 26.463(6)Angstrom, V = 7556 Angstrom(3), Z = 8, R = 0.120 for 1698 reflections; (4): [Ni(NCS)(2)(4-ViPy)(4)](0.36 THF)(1.04 1,4-cyclohexadiene I4(1)/a, a = 16.986(4), b = 16.986(4), c = 25.896(15)Angstrom, V = 7472 Angstrom(3), Z = 8, R = 0.103 for 2025 reflections; (5): [Ni(NCS)(2)(4-ViPy)(4)](0.35 THF)(1.05 benzene), I4(1)/a, a = 17.102(10), b = 17.102(10), c = 25.498(8)Angstrom, V = 7458 Angstrom(3), Z = 8, R = 0.118 for 2200 reflections; (6): [Ni(NCS)(2)(4-ViPy)(4)](3 benzene), triclinic P $($) over bar$$ 1, a = 10.432(24), b = 11.155(9), c = 21.581(7)Angstrom, alpha = 78.70(5), beta = 82.60(7), gamma = 74.09(13)degrees, V = 2361 Angstrom(3), Z = 2, R = 0.078 for 3427 reflections. Host-guest ratios and, for mixtures of guests, guest1/guest2 ratios, were elucidated by density and NMR. We show that the conformational freedom of the substituted pyridines is not the primary reason for the clathrating ability of Werner hosts. All six structures show no host-guest interaction at the level of van der Waals interactions. As non-bonding interactions are not observed between the host and guest, this study shows that the above host's selectivity by enclathration of particular guest molecules cannot be accounted for by solid state structural analysis.
