Ligand Steric Hindrances Switch Bridging (μ2-I)•••O,O to Two-Center I•••O Halogen-Bonding Mode in the Assembly of Diketonate Copper(II) Species

The diketonate complex [Cu{OC(Bu-t)CC(H)O}(2)] (1) and its cocrystals with 1,4-diiodotetrafluorobenzene (1,4-FIB), 1,3,5-triiodotrifluorobenzene (1,3,5-FIB), and 1,4-dioxane were studied by X-ray diffraction. In the solid state, 1 exhibits the cis-geometry with syn-Bu-t groups; the geometry is stable in storage at 20-25 degrees C or even in heating in the solid state, solutions, or sublimation. The DFT modeling for isolated molecules of cis- and trans-1 revealed that the cis-form is only slightly more energetically favorable. However, cocrystals trans-1 center dot C4H8O2, trans-1 center dot 1,4-FIB, and trans-1 center dot 1,3,5-FIB center dot C4H8O2 display the trans-geometry with the anti-Bu-t substituents; the comparison of the geometries revealed the facile crystal-packing-driven cis-to-trans isomerization of 1 upon the cocrystal growth. Compared to the cocrystals of the unsubstituted [Cu(acetylacetonate)(2)] complex with the FIBs, in the assembled architectures of trans-1 center dot 1,4-FIB and trans-1 center dot 1,3,5-FIB center dot C4H8O2, the switch from the bridging (mu(2)-I)center dot center dot center dot O,O to two-center I center dot center dot center dot O halogen bonding is demonstrated. The theoretical study revealed that the energetic features of the (mu(2)-I)center dot center dot center dot O,O halogen bonding in [Cu(acetylacetonate)(2)]center dot 1,4-FIB are similar to those of the I center dot center dot center dot O halogen bonding in 1 center dot 1,4-FIB. Variable-temperature XRD data (at 100, 150, 200, 250, and 300 K) for cis-1 and trans-1 center dot 1,4-FIB indicate that the infinite chains of molecules stabilized by I center dot center dot center dot O halogen bonding remain the main packing motif at all applied temperatures.

Automated summary

The study revealed the stability and isomerization of different geometries of a copper diketonate complex in the solid state and cocrystals, as well as the halogen bonding interactions in the cocrystal structures.