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

A series of heterobimetallic lantern complexes, [PtFe(SOCR) 4 (pyX)] where R = Me, X = H ( 1 ), X = NH 2 ( 2 ), X = SMe ( 3 ); R = Ph, X = H ( 4 ), X = NH 2 ( 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 57 Fe 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 T 2g parentage.