Third Unique Polymorph of bis(2,9-Dimethyl-1,10-phenanthroline)-Copper(I) tetrafluoroborate, [Cu(dmp)2](BF4)

Polymorphic behavior has significant consequences in solid-state properties relevant to functional materials and pharmaceutical applications. This study reports the single-crystal X-ray structure of a new third unique polymorph of the photoluminescent compound [Cu(dmp)2](BF4) (dmp = 2,9-dimethyl-1,10-phenanthroline). A detailed analysis of how this new polymorph compares with the two previously reported polymorphs was carried out including intramolecular metrics (τ4, twisting, flattening, rocking measures) and intermolecular differences (π-stacking, Hirshfeld surfaces). The new polymorph reported here has larger twisting and flattening distortions from an idealized tetrahedral geometry and the largest displacement of Cu from one dmp plane than the other polymorphs. This new polymorph also exhibits enhanced π-stacking that leads to more dense packing than previous reported polymorphs. Hirshfeld surface comparisons are consistent with a larger percentage of C…C short contacts and lower percentage of C…H contacts present in this new polymorph. The variability of intra- and intermolecular differences within this family of three polymorphs compared demonstrates the large degree of flexibility of both the coordination sphere and packing, even with the expected rigid planar bis-bidentate dmp binding to copper. As the polymorphs each show unique inter- and intramolecular features, differences in solid-state properties including solid-state photoluminescence are expected. This demonstrates the importance of phase purity in the construction of solid-state device applications.