Infrared spectroscopic and theoretical studies of the OTiF2, OZrF2 and OHfF2 molecules with terminal oxo ligands

Abstract

The isolated group 4 metal oxydifluoride molecules OMF(2) (M = Ti, Zr, Hf) with terminal oxo groups are produced specifically on the spontaneous reactions of metal atoms with OF(2) through annealing in solid argon. The product structures and vibrational spectra are characterized using matrix isolation infrared spectroscopy as well as B3LYP density functional and CCSD(T) frequency calculations. OTiF(2) is predicted to have a planar structure while both OZrF(2) and OHfF(2) possess pyramidal structures, all with singlet ground states. Three infrared absorptions are observed for each product molecule, one M-O and two M-F stretching modes, and assignments of these molecules are further supported by the corresponding (18)O shifts. The molecular orbitals of the group 4 OMF(2) molecules show triple bond character for the terminal oxo groups, which are also supported by an NBO analysis. These molecular orbitals include a σ bond (O(2p) + Ti(sd hybrid)), a normal electron pair π bond (O(2p) + Ti(d)), and a dative π bond arising from O lone pair donation to the overlapping Ti d orbital. The M-O bond dissociation energies for OMF(2) are comparable to those in the diatomic oxide molecules. The OTiF intermediate is also observed through two slightly lower frequency bond stretching modes, and its yield is increased in complementary TiO + F(2) experiments. Finally, the formation of group 4 OMF(2) molecules is highly exothermic due to the weak O-F bonds in OF(2) as well as the strong new MO and M-F bonds formed.

A route to drastic increase of CO2 uptake in Zr metal organic framework UiO-66

“…3 can be ascribed to the shorter Ti-O 34 compared to Zr-O bonds. 35,36 The pore size distribution, obtained by a DFT fit to N 2 adsorption isotherms, shows two pore sizes at 6 Å and 9 Å, consistent with the tetrahedral and octahedral cages within UiO-66(Zr 100 ), respectively. 16 As Ti loading is increased, the tetrahedral cages remain unchanged, whereas the octahedral cages shrink by B1 Å and become increasingly broader in their distribution.…”

Porous Metal–Organic Frameworks for Carbon Dioxide Adsorption and Separation at Low Pressure

“…UiO-66­(Zr 100 ) showed two pore sizes at 6 and 9 Å, which represented tetrahedral and octahedral cages. With the increase of the Ti­(IV) ion dopant, the pore size of octahedral cages was shunk by ∼1 Å, which was due to the shorter Ti–O than Zr–O bands. , At 1 bar and 273 K, the CO 2 uptake of UiO-66­(Ti 56 ) was 4.00 mmol/g, which was 1.8 times that of pure UiO-66. Molecular simulation showed that charge transferred from metal ions to ligands followed by a decrease of pore size, which enhanced the CO 2 adsorption enthalpy of frameworks .…”

Crystallographic features of ammonium fluoroelpasolites: dynamic orientational disorder in crystals of (NH4)3HfF7 and (NH4)3Ti(O2)F5

“…If the compound composition corresponds to the formula (NH 4 ) 3 HfOF 5 , its vibrational spectra should contain the intensive band (both IR and Raman active) in the range 900 cm À1 , in accordance with the triple character (one + two ) of the Hf-O bond and a short distance of this bond (Gong et al, 2012). Similarly, the Ti-O bond has a triple character ( + 2) that ensures a rather short Ti-O distance in accordance with our structural determinations, and the Ti-O stretches appear at 870 and 897 cm À1 for (NH 4 ) 3 TiOF 5 and Rb 2 KTiOF 5 , respectively (Udovenko & Laptash, 2011).…”