Magnetic properties of octa- and heptadeca-nuclear heterometallic CoII–LnIII complexes derived from the ligand 6-chloro-2-hydroxypyridine

Abstract

Four isostructural heterometallic octanuclear complexes have been synthesized of general formulae [CoII4LnIII4(OH)4(chp)10(acac)6]·solv (Ln=Y (1), Gd (2), Tb (3) and Dy (4); solv=0.5MeCN for 1, 2 and 4 and Et2O for 3), where Hchp=6-chloro-2-hydroxypyridine and acac−=acetylacetonate. A fifth complex of formula [CoII11DyIII6(OH)14(chp)14(piv)8(NO3)4(MeCN)4]·2H2O (5) was also isolated using the Hchp ligand with pivalic acid as a co-ligand. X-ray crystallographic studies reveal that complexes 1–4 all display a central planar butterfly motif consisting of the four LnIII ions, with the CoII ions “capping” around the periphery of the butterfly. Compound 5 displays a complex metallic core with an unusual disc-like motif capped by two non-planar butterfly units. DC magnetic susceptibility measurements for the {CoII4LnIII4} family of compounds (1–4) reveals that the diamagnetic Y analogue {CoII4YIII4} (1) displays antiferromagnetic exchange interactions between the Co–Co ions. An overall decrease in the susceptibility (χMT) is then observed upon lowering the temperature for {CoII4GdIII4} (2) and {CoII4TbIII4} (3), while the {CoII4DyIII4} (4) complex displays a decrease before a small increase at the lowest temperatures measured, indicating a ferrimagnetic ground state. AC susceptibility measurements reveal an absence of any SMM behaviour for 1–3 but show the onset of slow magnetic relaxation below 4K in the case of 4. The DC and AC behaviour of complex 5 {CoII11DyIII6} follows a similar profile to compound 4 revealing a small increase in χMT at low temperatures, with the observation of possible SMM behaviour as observed via low temperature ‘tails’ of peaks in the out-of-phase susceptibilities.