Magnetic properties of octa- and heptadeca-nuclear heterometallic Co$^{\textrm{{II}}}$-Ln$^{\textrm{{III}}}$ complexes derived from the ligand 6-chloro-2-hydroxypyridine

Four isostructural heterometallic octanuclear complexes have been synthesized of general formulae [{CoII}4LnIII4({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 [{CoII}11DyIII6({OH})14(chp)14(piv)8({NO}3)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 motifs. {DC} magnetic susceptibility measurements for the \{{CoII}4LnIII4\} family of compounds (1 ??? 4) reveals that the diamagnetic Y analogue \{{CoII}4YIII4\} (1) displays antiferromagnetic exchange interactions between the Co-Co ions. An overall decrease in the susceptibility (??{MT}) is then observed upon lowering the temperature for \{{CoII}4GdIII4\} (2) and \{{CoII}4TbIII4\} (3), while the \{{CoII}4DyIII4\} (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 \{{CoII}11DyIII6\} follows a similar profile to compound 4 revealing a small increase in ??{MT} at low temperatures, with the observation of possible {SMM} behaviour as observed via low temperature ???tails??? of peaks in the out-of-phase susceptibilities.