Assessment of Iron-Based Spin-Orbit Coupling Effects in Pt-Fe Heterobimetallic Lantern Complexes via 57Fe Mössbauer Spectroscopy.

A series of heterobimetallic lantern complexes, [PtFe(SOCR)4(pyX)] where R = Me, X = H (1), X = NH2 (2), X = SMe (3); R = Ph, X = H (4), X = NH2 (5), X = SMe (6), have been prepared and characterized spectroscopically. Compounds 1, 4, and 5 are reported herein for the first time. The high-spin iron(II) sites of 1-6 have been investigated using 57Fe Mössbauer spectroscopy. Although the isomer shift of these species is nearly identical, their quadrupole splitting exhibits a much larger variation. Moreover, the zero-field Mössbauer spectra of 3-5 show surprising changes over time which are likely indicative of small structural distortions. The field dependent Mössbauer study of 1 and 6 revealed a zero field splitting (ZFS) characterized by a relatively large and positive D value. The combined Density Functional Theory (DFT) and ab initio Complete Active Space Self-Consistent Field (CASSCF) investigation of 1-6 indicates that their ground state is best described using a linear combination of {|xz⟩, |yz⟩} states. Our theoretical analysis suggests that the ZFSs and magnitude of the quadrupole splitting of 1-6 are determined by the spin-orbit coupling of the three lowest orbital states which have a T2g parentage.