Addition of Activated Acetylenes to Coordinated Polysulfide Ligands. 2.¹ Synthesis of the Fe₂[S₂C₂(COOCH₃)₂]₄^2- Dithiolene Complex by the Addition of CH₃OOCCΞeCCOOCH₃ to the (Fe₂S₁₂)^2- Anion. Crystal and Molecular Structure of (Ph₄P)₂Fe₂[S₂C₂(COOCH₃)₂]₄

The reaction of (Ph₄P)₂Fe₂S₁₂ and CH₃OOCCΞCCOOCH₃ in dimethylformamide (DMF) in a 1:2 molar ratio proceeds readily to afford the new (Ph₄P)₂Fe₂[S₂C₂(COOCH₃)₂]₄,2DMF complex in 69% yield. The complex crystallizes in the triclinic space group PI (Z = 2) with one molecule per unit cell. The cell dimensions are a = 12.343 (4) Å, b = 13.710 (5) Å, c = 14.787 (8) Å, a = 63.79 (4)°, β = 68.23 (4)°, and γ = 85.32 (3)°. Intensity data were collected with a P3F Nicolet automated diffractometer using the θ-2θ scan mode. All the non-hydrogen atoms were refined anisotropically. Full-matrix least-squares refinement of 351 parameters on 2886 data gave final R^w = 7.03% and R = 5.15%. The hydrogen atoms were incuded in their calculated positions but were not refined. The anion is located on the crystallographic center of symmetry with the [Fe(S2C2(COOCH3)2)2]~ fragment as the asymmetric unit. The Fe(III) atoms are found in a tetragonal-pyramidal coordination environment with one basal sulfur S(3) on one Fe atom serving as the axial ligand for the other centrosymmetrically related Fe atom. The Fe-S(l) and Fe-S(2) basal bond lengths of the terminal ligand are 2.230 (2) Å. The other two basal Fe-S(3) and Fe-S(4) bonds of the bridging ligand are 2.256 (2) and 2.243 (2) Å, respectively. The axial bridging Fe-S(3)' bond length is 2.466 (2) Å. Solution electronic spectral, electrochemical, NMR spectroscopic, and magnetic studies show that the dimeric structure is preserved in weakly dielectric media while in highly polar coordinating media the axial bridging interactions within the dimer are replaced by solvent coordination and the monomeric structure prevails with the system in a paramagnetic S = 3/2 state. The magnetic moments range from 3.78 to 1.87 μ_B in different solutions in the order Me₂SO ~ DMF > CH₃CN > CH₂C₁₂. EPR spectra at 93 K in DMF and Me₂SO show absorptions characteristic of a S = 3/2 spin ground state.