Ligand Steric Hindrances Switch Bridging (μ<sub>2</sub>-I)···O,O to Two-Center I···O Halogen-Bonding Mode in the Assembly of Diketonate Copper(II) Species
Anton V. Rozhkov, Ivan V. Ananyev, Aleksandr A. Petrov, Bartomeu Galmés, Antonio Frontera, Nadezhda A. Bokach, Vadim Yu. Kukushkin
Abstract
The diketonate complex [Cu{OC(tBu)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-tBu groups; the geometry is stable in storage at 20–25 °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·C4H8O2, trans-1·1,4-FIB, and trans-1·1,3,5-FIB·C4H8O2 display the trans-geometry with the anti-tBu 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-1·1,4-FIB and trans-1·1,3,5-FIB·C4H8O2, the switch from the bridging (μ2-I)···O,O to two-center I···O halogen bonding is demonstrated. The theoretical study revealed that the energetic features of the (μ2-I)···O,O halogen bonding in [Cu(acetylacetonate)2]·1,4-FIB are similar to those of the I···O halogen bonding in 1·1,4-FIB. Variable-temperature XRD data (at 100, 150, 200, 250, and 300 K) for cis-1 and trans-1·1,4-FIB indicate that the infinite chains of molecules stabilized by I···O halogen bonding remain the main packing motif at all applied temperatures.