Investigations of the Coordination Chemistry of Molybdenum with Facultative Tetradentate Ligands Possessing N₂S₂ Donor Sets. 4. Crystal and Molecular Structures of [Mo₂O₃(C₈H₁₈N₂S₂)₂] and [Mo₂O₄(C₉H₂₂N₂S₂)₂]

The reaction of [MoO₂(acac)₂] with a twofold excess of N,N′-dimethyl-N,N′-bis(β-mercaptoethyl)ethylenediamine (LH₂) gives the deep purple compound [Mo₂O₃(C_gH₁₈N₂S₂)], [Mo₂O₃L₂], in low yield. X-ray crystallography shows that the molecule possesses a trans planar [formula omitted]⁴⁺ core and that the ligand is present as a tetradentate, coordinating through sulfur and nitrogen donors. The complex crystallizes in space group Pcab with cell parameters a = 15.318 (3) Å, b = 17.957 (4) Å, and c = 18.298 (4) Å. The measured density of 1.70 g/cm³ was in good agreement with the value of 1.72 g/cm³ calculated on the basis of eight molecules in the unit cell. The structure has been refined to R₁ = 0.042 and R₂ = 0.048 on the basis of 2413 unique reflections with F_o ≥ 6σ(F_o). The analogous reaction of [MoO₂(acac)₂] with the ligand N,N′-dimethyl-N,N′-bis(β-mercaptoethyl)propylenediamine (L′H₂) yields orange prisms of the compound [Mo₂O₄(C₉H₂₂N₂S₂)₂], [Mo₂O₄(L′H)₂]. The complex crystallizes in the monoclinic space group P2₁/a with unit cell dimensions a = 15.155 (5) Å, b = 12.446 (5) Å, and c = 16.195 (6) Å, and β = 101.99 (1)° with Z = 4 to give a calculated density of 1.55 g/cm³ (observed density 1.54 g/cm³). The structure was solved on the basis of 1907 unique reflections with F_o ≥ 6σ(F_o) and refined to final R values of 0.059 and 0.083. The complex possesses the Mo₂O₄²⁺ core with molybdenum atoms coordinating to the thiolate sulfurs of the L′ ligand. The unusual feature of the structure is that the two ligand amine nitrogens are not coordinated to the molybdenum, resulting in the 14-membered ring (CH₂)₃N(CH₂)₂SMoOMoS(CH₂)₂N. One of the L′H nitrogens is protonated to produce a six-membered H-N-C-C-C-N ring with a chair conformation, and the ligand itself assumes an overall chair conformation.