Experimental and theoretical study on vibrational spectra of nickel and zinc complexes of 5,10-diphenylporphyrin

Diboron Porphyrins: The Raman Signature of the In-Plane Tetragonal Elongation of the Macrocycle

We describe an unusual in-plane type of porphyrin core distortion, tetragonal elongation (TE), observed experimentally in diboron porphyrins. The vibrational spectra of several of these complexes exhibit shifts that we have assigned to this TE distortion by comparing experimental spectra with DFT computational findings. The influence of TE in porphyrin systems was isolated using DFT analysis of the well-known model compounds Ni(II)porphine and Zn(II)porphine, with the macrocycle ring constrained to eliminate the influence of out-of-plane (OOP) distortions. A significant down-shift in frequencies was observed for porphyrin normal vibrational modes, particularly the in-plane A_1g/B_1g modes that are dominated by contributions from stretching and bending of C_α-C_m coordinates. In contrast, TE had little effect on the v(Pyr_halfring) and δ(Pyr_def) modes, though the lowered symmetry of the system resulted in significant splitting of the B_2u and B_3u modes. The impact of the TE distortion upon the diboron porphyrin vibrational spectrum was probed experimentally using Raman spectroscopy of B₂O₂(BCl₃)₂(TTP), B₂OF₂(TTP), and B₂OPhOH₂(TTP) (TTP = 5,10,15,20-(tetra- p-tolyl)porphyrin). Comparing the experimentally obtained spectral signatures to the computational findings allowed us to assign the large shifts observed for the v₂ and v₃ modes to the TE distortion in diboron porphyrins.

Computational insights into the molecular interaction and ion-pair structures of a novel zinc-functionalized ionic liquid, [Emim][Zn(TFSI)₃]

The ion pair structures of a novel CO2 capture material in the form of a metal chelate anion-containing room temperature ionic liquid (IL), 1-ethyl-3-methylimidazolium tri[bis(trifluoromethylsulfonyl)imide]zincate(II), [Emim][Zn(TFSI)3], were elucidated by correlating the infrared spectra generated using density functional theory (DFT) calculations with the experimental spectrum derived from a room temperature infrared spectroscopic measurement. A free volume energy minimization algorithm revealed stable structures where the zinc ion forms an octahedral, homoleptic complex with the ligand bis(trifluoromethylsulfonyl)imide through coordination with the oxygen of the sulfone group, with 1-ethyl-3-methylimidazolium acting as the counterion. The method of analysis was built around 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [Emim][TFSI], involving direct comparison with published data, and extended to the more complex [Emim][Zn(TFSI)3] system. The DFT calculations reproduced the vibrational spectra of [Emim][Zn(TFSI)3] and [Emim][TFSI] using their optimized geometries, with correlation slopes of 0.9996 and 1.0022, respectively. Comparison of the vibrational modes of [Emim][TFSI] and [Emim][Zn(TFSI)3] provided insights into the ion pair structure of, and molecular interactions in the ILs analyzed.