Fe(III) quinolylsalicylaldimine complexes: a rare mixed-spin-state complex and abrupt spin crossover.

A new synthesis of (8-quinolyl)-5-methoxysalicylaldimine (Hqsal-5-OMe) is reported and its crystal structure is presented. Two Fe(III) complexes, [Fe(qsal-5-OMe)(2)]Cl⋅solvent (solvent = 2 MeOH⋅0.5 H(2)O (1) and MeCN⋅H(2)O (2)) have been prepared and their structural, electronic and magnetic properties studied. [Fe(qsal-5-OMe)(2)]Cl⋅2 MeOH⋅0.5 H(2)O (1) exhibits rare crystallographically independent high-spin and low-spin Fe(III) centres at 150 K, whereas [Fe(qsal-5-OMe)(2)]Cl⋅ MeCN⋅H(2)O (2) is low spin at 100 K. In both structures there are extensive π-π and C-H⋅⋅⋅π interactions. SQUID magnetometry of 2 reveals an unusual abrupt stepped-spin crossover with T(1/2) = 245 K and 275 K for steps 1 and 2, respectively, with a slight hysteresis of 5 K in the first step and a plateau of 15 K between the steps. In contrast, 1 is found to undergo an abrupt half-spin crossover also with a hysteresis of 10 K. The two compounds are the first Fe(III) complexes of a substituted qsal ligand to exhibit abrupt spin crossover. These conclusions are supported by (57) Fe Mössbauer spectroscopy. Both complexes exhibit reversible reduction to Fe(II) at -0.18 V and irreversible oxidation of the coordinated qsal-5-OMe ligand at +1.10 V.

(8-Amino-quinoline-κ(2)N,N')bis-(1,1,1,5,5,5-hexa-fluoro-pentane-2,4-dionato-κ(2)O,O')cobalt(II).

In the title compound, [Co(C(5)HF(6)O(2))(2)(C(9)H(8)N(2))], the Co(II) centre exhibits a pseudooctahedral coordination geometry, comprising two N-atom donors from the bidentate amino-quinoline ligand and four O-atom donor atoms from two bidentate chelating 1,1,1,5,5,5-hexafluoropentane-2,4-dionate ligands. In the crystal, molecules are linked via pairs of N-H⋯O hydrogen bonds, forming inversion dimers. These dimers are further connected through π-π interactions between neighbouring quinoline rings [centroid-centroid distance = 3.472 (2) Å], and stack along the c axis.

Slow relaxation of magnetization in a bis-mer-tridentate octahedral Co(ii) complex.

Reaction of a rigid tridentate ligand o-[(1H-imidazol-2-yl)methylideneamino]phenol (2-H2imap) with Co(ClO4)2 in the presence of NaN3, or Co(NO3)2 without a base yields [CoII(2-Himap)2] 1 and [CoIII(2-Himap)2]NO3·MeOH 2, respectively. Both complexes exhibit a mer-octahedral geometry with the cobalt centre being distorted along an octahedral-trigonal prismatic pathway. The packing in 1 and 2 is dominated by H-bonding forming 2D sheets and 1D chains, respectively. Detailed dc and ac magnetic studies indicate that 1 is a field-induced single-ion magnet (SIM) with D = 36.7 cm-1 and E = 2.0 cm-1. Extensive ab initio calculations support these conclusions and suggest that relaxation of the magnetization occurs principally through direct quantum tunnelling in the ground state, with the Raman process dominant in an applied field. This contrasts with the recently reported series of mer-[Co(L)2] (L = monoanionic NNO donor ligand; Inorg. Chem., 2017, 56, 6056-6066) complexes where D is negative, as these compounds have a more ambiguous geometry, and highlights the importance of supramolecular interactions in subtly altering the coordination sphere thereby impacting the magnetic behaviour.

Self-assembly of a mixed-valence FeII-FeIII tetranuclear star.

A unique self-assembled mixed-valence FeII-FeIII tetranuclear star has been comprehensively characterised showing a large magnetic anisotropy at the peripheral FeII centres, ferromagnetic coupling between the iron centres and field-induced SMM behaviour.