Two co-crystalline M(hfac)2(IPhIN)2·M(hfac)2 (M = Mn, Co) compounds with a bis(iminoylnitroxide) biradical: structure and magnetism

Abstract

1-Iodo-3,5-bis(4′,4′,5′,5′-tetramethyl-4′,5′-dihydro-1H-imidazole-1′-oxyl)benzene (IPhIN = L) forms co-crystalline [M(hfac)₂(IPhIN)₂]·[M(hfac)₂] coordination complexes (M = Mn, Co) with [Mn(hfac)₂] and [Co(hfac)₂]. In each system only one of the iminoylnitroxide radical moieties is coordinated as part of the [M(hfac)₂(IPhIN)₂] structural units; the metal ions do not coordinate the radical nitrogen atoms, but rather the nitroxide oxygen to form a cis NO–M–ON grouping in a hexacoordinate ligand sphere. Solvate water molecules in the lattice provide an important driving force for assembly of the co-crystal structures in the cobalt(II) derivative; an additional factor is the formation of halogen bonds between hfac CF₃ groups and the IPhIN iodine atom. The paramagnetic susceptibility (χ_M) versus temperature (T) measurements showed antiferromagnetic exchange downturns at lower temperature. Based on the crystal structures of the complexes, the χ_MT versus T data were modelled using a paramagnetic contribution from the [M(hfac)₂] fragment, an exchange interaction J₁ within the L–M–L fragment, plus an intramolecular radical–radical interaction J₂ within the IPhIN biradical unit. For the Mn(II) complex, a good fit was obtained for g_Mn = 2.14(1), g_rad = 2.0 (fixed), J₁ = −311(9) cm⁻¹ and J₂ = 11.1(7) cm⁻¹. A reasonable fit for the cobalt compound was obtained for g_Co = 2.72(1), g_rad = 2.0 (fixed), J₁ = −400(5) cm⁻¹, J₂ = 28.3(3) cm⁻¹ with a generalized zero field splitting parameter D = 64(2) cm⁻¹.