Field-induced slow magnetic relaxation in low-spin S = 1/2 mononuclear osmium(v) complexes

Abstract

Photochemical reactions of (PPh₄)[Os^VI(N)(L)(CN)₃] (NO₂-OsN) with piperidine and pyrrolidine afforded two osmium(V) hydrazido compounds, (PPh₄)[Os^V(L)(CN)₃(NNC₅H₁₀)] ([PPh₄]1) and (PPh₄)[Os^V(L)(CN)₃(NNC₄H₈)] ([PPh₄]2), respectively. Their structures consist of isolated, mononuclear distorted octahedral osmium anions that are well-separated from each other by PPh₄⁺. Their low spin S = 1/2 and L = 1 ground state was confirmed by magnetometry and DFT calculations. Interestingly, both compounds exhibit slow magnetic relaxation under a bias dc-field. These osmium(V) complexes are potentially useful building-blocks for the construction of molecule-based architectures with interesting magnetic properties. In contrast, the structurally related (PPh₄)[Os^III(L)(CN)₃(NH₃)] ([PPh₄]3), which also has a low-spin S = 1/2 ground state but with a different electronic configuration (5d⁵), does not exhibit slow magnetic relaxation, due to the absence of any orbital moment (L = 0). Furthermore, the structurally different osmium(V) hydrazido compound reported by Meyer, [Os^V(tpy)(Cl)₂(NNC₅H₁₀)](PF₆) (4[PF₆]), also does not exhibit slow magnetic relaxation due possibly to a change in magnetic anisotropy from axial for [PPh₄]1 and [PPh₄]2 to planar.