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Racemic Compound FormationversusConglomerate Formation with [M(bpy)3](PF6)2 (M = Ni, Zn, Ru); Lattice Energy Minimisations and Implications for Structure Prediction

“…In the β-modification Tshaped πϪπ interaction [36Ϫ38] contacts along the racemic columns with colinear C 3 axes are observed, while in the γ-type shifted π-stacks occur along the complex cation columns running along c (Figure 5a and 5c in ref. [1] respectively). Since these two mutual arrangements also allow for an effective penetration of adjacent molecules, it cannot even be decided from geometry alone whether these CϪH···π-interactions have to be realised or just happen to be there because of the complementarity of molecular surfaces and thus packing efficiency.…”

“…These molecular structures may vary due to experimental errors and, more importantly, due to tiny conformational changes induced by the interplay of intramolecular and intermolecular forces, which in turn is dependant on temperature. To explore the effect of such methodical uncertainties in the molecular structures on the results of the lattice energy minimisations, the lattice energy for γ-[Ni(bpy) 3 ](PF 6 ) 2 was calculated for two starting structures which were determined at the same temperature (200 K) using two data sets sampled on different crystals [γ 200 (1) and γ 200 (2) [1] ]. The lattice energies for these two starting structures determined at the same temperature differ by less than 0.5 kJ/mol.…”

“…The lattice energies for these two starting structures determined at the same temperature differ by less than 0.5 kJ/mol. To investigate minor modifications in the molecular shapes induced by temperature-dependant packing requirements the lattice energy for the racemic [Ru(bpy) 3 ](PF 6 ) 2 structures was not only calculated for the α-type (105 K, α 105 ) [25] and the β-structure determined by Rillema at 294 K (β 294 ), [22] but also for a structure determined at an intermediate temperature (200 K, β 200 ), [1] that is still well above the onset of the phase transition to the low-temperature modification. The variation of the calculated lattice energies increases by up to 2 kJ/mol.…”

“…QuadrupoleϪ quadrupole interactions from the π electrons are not explicitly included into the electrostatic model, but they get subsumed into the monopoleϪmonopole interactions. Also, the assumed isotropic atomϪatom form for the repulsion appears to be adequate to describe the stacking of aromatic rings as observed in the γ-structure [1] even though the charge density in these regions is known not to be spherical. [35] This satisfying result encourages further interpretation with respect to crystal engineering.…”

“…The preceding paper [1] describes such a system. With [M(bpy) 3 ](PF 6 ) 2 (M ϭ Ni, Zn, Ru) three different polymorphs are observed.…”