Crystal Packing Driven Comparable Thermal Expansion of Polymorphs of a Tripodal Molecule and Guest-Dependent Expansion of Its Isostructural Solvates

The tripodal molecule 2,4,6-triethyl-1,3,5-tris­(phenoxymethyl)­benzene (A) has three polymorphic forms, of which the single-crystal structures are known for two, the monoclinic form I (A-1), and the triclinic form II (A-2). Between 118 and 298 K, the volumetric thermal expansions of A-1 (172(4) × 10^–6 K^–1) and A-2 (183(9) × 10^–6 K^–1) are comparable, even though A-1 exhibits a positive thermal expansion along all principal directions whereas A-2 exhibits a uniaxial negative thermal expansion of −29(2) × 10^–6 K^–1 along the minor principal axis, X1_{A‑2,(−212)}. The comparable volumetric thermal expansion of the polymorphs A-1 and A-2 is attributed to their comparable average Ueq (Ueq̅) and percent change of Ueq̅ with temperature. The molecule A forms a pair of isostructural 1:1 channeled solvates with tetrahydrofuran (A-3) and tetrachloromethane (A-4). Between 118 and 253 K, A-3 registers a high volumetric expansion of 375(32) × 10^–6 K^–1 while A-4 registers an expansion of 212(9) × 10^–6 K^–1. The volumetric expansions of both solvates, A-3 and A-4, are higher than those of the polymorphs due to the contribution of the respective lattice occluded solvents. The structures of all four systems are sustained by the π···π stacking, C–H···π, and C–H···O interactions, and the respective thermal expansions can be correlated with the intermolecular interactions.