Zero-field splitting & spin states of photoactive pyridinophanesupported Ni(II)Cl2 complexes
Year: 2026
Type: preprint
Abstract: A combination of High-Frequency and -Field Electron Paramagnetic Resonance (HFEPR), Far-Infrared Magnetospectroscopy (FIRMS), and computational modeling allows for the determination of typically elusive zero-field splitting parameters (ZFS). When supported by our tridentate pyridinophane backbone, square pyramidal NiIICl2 exhibits a pure S = 1 triplet spin system with notable axial splitting (D), easy-plane axial anisotropy (D > 0), and small but nonzero rhombic splitting (E). While the bidentate-supported square planar NiIICl2 analog is classically expected to reside in an S = 0 singlet state, we observe 44% of the sample exhibiting S = 1 triplet character with similar magnitudes of axial splitting as the tridentate version, but with reduced rhombic splitting due to the vacant z-axis. The mixed-spin character is computationally resolved through density functional theory (DFT) and complete active space self-consistent field theory (CASSCF), which predict similar energy S = 1 and S = 0 states, corroborated by SQUID showing temperature-independent paramagnetism (TIP) and potential mixing of the singlet and triplet states. Combining HFEPR, FIRMS, DFT, and CASSCF is a promising method to extract ZFS parameters for complex spin systems, especially for near-axial systems where a slight perturbation in the z-axis results in small but nonzero rhombic character.
Source: ChemRxiv
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7170243764