Magnetic and EPR Spectroscopic Studies of Thiolate Bridged Divalent Ni, Pd, and Pt Ions Capped with VO(N 2 S 2 ) Metalloligands

Reactions of the metallodithiolate complex VO(bme-dach) (hereafter abbreviated as V, where bme-dach = N,N'-bis(2-mercaptoethyl)-1,4-diazacycloheptane) with [PdII(CH₃CN)₄](BF₄)₂ and [PtII(CH₃CN)₄](BF₄)₂ yield the V-M-V trimetallic compounds [VPdV](BF4)2 (2) and [VPtV](BF4)2 (3). Reaction of a similar metalloligand, VO(bme-daco) (hereafter abbreviated as V' where bme-daco = N,N'-bis(2-mercaptoethyl)-1,5-diazacyclooctane) with [NiII(CH₃CN)₆](BF₄)₂ afforded the related salt [V'NiV'](BF4)2 (1). X-ray structural analyses revealed that cations in 1, 2, and 3 adopt a stairstep C2h structure consisting of two terminal VO(N₂S₂) moieties bridged via thiolate sulfur to the group 10 metal ions. Weak ferromagnetic superexchange coupling (J = 0.282 cm⁻¹ for 1, 0.954 cm⁻¹ for 2, and 1.372 cm⁻¹ for 3) was observed between the two S = 1/2 VIV centers separated by distances in the range of 5.9-6.3 Å, with J values varying following the order Ni < Pd < Pt. Frozen-solution EPR spectra measured on the more soluble [BArF₂₄]⁻ (BArF₂₄⁻ = tetrakis((3,5-trifluoromethyl)phenyl)borate) analogues revealed that the [VPtV]²+ cation exhibits a 15-line hyperfine splitting of 225 MHz at g = 4 in parallel mode, confirming exchange coupling between the two ⁵¹V, I = 7/2 nuclei. Density-functional theory (DFT) calculations indicate an S = 1 ground state for 1-3. These results demonstrate that the choice of paramagnetic metallodithiolate ligand and diamagnetic bridge in such trimetallic species influences the sign and magnitude of magnetic interactions.