Investigations of the Coordination Chemistry of Molybdenum with Facultative Tetradentate Ligands Possessing N₂S₂ Donor Sets. 3. Crystal and Molecular Structures of [MoO₂(SCH₂CH₂NMe(CH₂)_nNMeCH₂CH₂S)], n = 2 or 3, and [MoO₂(SC₆H₄NHCH₂CH₂NHC₆H₄S)] and a Comparison to the Structure of [MoO₂(SCH₂CH₂NHCH₂CH₂SCH₂CH₂S)], a Complex with the NS₃ Donor Set

The structures of four MoO₂Y complexes where Y²⁻ is a linear tetradentate ligand containing N and S donor atoms are reported. The reaction of Mo(VI) starting materials with stoichiometric amounts of the appropriate YH₂ ligand produced the MoO₂Y complexes in good yield. The relevant crystallographic parameters for the title complexes are presented in Table I and summarized herein. [MoO₂(SCH₂CH₂N(CH₃)CH₂CH₂N(CH₃)CH₂CH₂S)], [MoO₂L], crystallized in the triclinic space group P1̄ with unit cell dimensions a = 7.169 (2) Å, b = 14.369 (4) Å, and c = 13.572 (4) Å and α = 95.72 (3)°, β = 97.12 (2)°, and γ = 111.80 (2)°, with Z = 4, to give a calculated density of 1.75 g/cm³ (observed density of 1.74 g/cm³). The structure was solved on the basis of 2609 reflections with F_o ≥ 6σ(F_o) and refined to final R values of 0.080 and 0.084. [MoO₂(SCH₂CH₂N(CH₃)CH₂CH₂CH₂N(CH₃)CH₂CH₂S)], [MoO₂L′], crystallizes as yellow prisms in the monoclinic space group C2/c with unit cell dimensions a = 8.992 (3) Å, b = 12.468 (3) Å, and c = 12.204 (2) Å and β = 104.7 (1)°. The measured density of 1.72 g/cm³ was in good agreement with the value of 1.75 g/cm³ calculated on the basis of 4 molecules in the unit cell. The structure has been solved and refined to R values of 0.040 and 0.067 based on 1335 reflections with F_o ≥ 6σ(F_o). [MoO₂(SC₆H₄NHCH₂CH₂NHC₆H4S)], [MoO₂L″], crystallizes in the monoclinic crystal system, space group P2₁/n, with unit cell dimensions a = 11.202 (3) Å, b = 11.468 (4) Å, and c = 16.033 (3) Å with β = 105.83 (2)° and Z = 4 to give a calculated density of 1.58 g/cm³ (observed density of 1.55 g/cm³). Structure solution and refinement were based on 4325 reflections with F_o ≥ 6σ(R_o) to give final R values of 0.051 and 0.044. The complex [MoO₂(SCH₂CH₂NHCH₂CH₂SCH₂CH₂S)], [MoO₂(SNSS)], crystallizes in the orthorhombic space group Pbca, with unit cell dimensions a = 13.787 (2) Å, b = 14.920 (2) Å, and c = 10.665 (2) Å, with Z = 8 and a calculated density of 1.84 g/cm³ (observed density of 1.85 g/cm³). Structure refinement based on 1870 unique reflections with F_o ≥ 6.σ(F_o) converged to R values of 0.028 and 0.023. The structural studies reveal that the molecules possess the usual cis-dioxo MoO₂²⁺ core and that the ligands are present as tetradentate donors coordinating through thiolate sulfur and amine nitrogen groups and, in the case of [MoO₂(SNSS)], through thioether sulfur also. The structure of [MoO₂L] reveals two crystallographically independent molecules in the asymmetric unit with nonequivalent Mo-S or Mo-N bond distances, in contrast to other structures with the MoO₂²⁺ core. On the other hand, [MoO₂L′] displays crystallographically equivalent Mo-S distances, but an unusually long Mo-N bond length of 2.486 (5) Å. Comparison of the above two structures to that of the related species [MoO₂″] suggests that minor ligand variations cause significant differences in the static structural behavior of the Mo(VI) complexes. The effects of drastic changes in the nature of the ligand donor groups are revealed in the structure of [MoO₂(SNSS)], where an amine nitrogen donor has been replaced by a thioether sulfur. The most notable feature of the structure is the Mo-S(thioether) bond distance of 2.708 (1) Å. The geometries of the title complexes are compared to those previously reported for species containing the MoO₂²⁺ core.