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

Reactions of the metallodithiolate complex VO(bme-dach) (hereafter abbreviated as V, where bme-dach = <i>N</i>,<i>N</i>'-bis(2-mercaptoethyl)-1,4-diazacycloheptane) with [Pd^II(CH₃CN)₄](BF₄)₂ and [Pt^II(CH₃CN)₄](BF₄)₂ yield the V-<i>M</i>-V trimetallic compounds <b>[VPdV](BF</b>_<b>4</b>)_<b>2</b> <b>(2)</b> and <b>[VPtV](BF</b>_<b>4</b>)_<b>2</b> <b>(3)</b>. Reaction of a similar metalloligand, VO(bme-daco) (hereafter abbreviated as V' where bme-daco = <i>N</i>,<i>N</i>'-bis(2-mercaptoethyl)-1,5-diazacyclooctane) with [Ni^II(CH₃CN)₆](BF₄)₂ afforded the related salt <b>[V'NiV'](BF</b>_<b>4</b>)_<b>2</b> <b>(1)</b>. X-ray structural analyses revealed that cations in <b>1</b>, <b>2</b>, and <b>3</b> adopt a stairstep C_2h structure consisting of two terminal VO(N₂S₂) moieties bridged via thiolate sulfur to the group 10 metal ions. Weak ferromagnetic superexchange coupling (<i>J</i> = 0.282 cm^-1 for <b>1</b>, 0.954 cm^-1 for <b>2</b>, and 1.372 cm^-1 for <b>3</b>) was observed between the two <i>S</i> = 1/2 V^IV centers separated by distances in the range of 5.9-6.3 Å, with <i>J</i> 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 <b>[VPtV]²</b>^<b>+</b> cation exhibits a 15-line hyperfine splitting of 225 MHz at <i>g</i> = 4 in parallel mode, confirming exchange coupling between the two ⁵¹V, <i>I</i> = 7/2 nuclei. Density-functional theory (DFT) calculations indicate an <i>S</i> = 1 ground state for <b>1</b>-<b>3</b>. 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.