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 4 K 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. Show more