The synthesis of three new heterometallic CoIII-DyIII planar butterfly coordination complexes are reported of molecular formulae [DyIII2CoIII2(OH)2(teaH)2(acac)6]·MeCN (3), [DyIII2CoIII2(OH)2(bdea)2(acac)6]·2H2O (4) and [DyIII2CoIII2(OH)2(edea)2(acac)6]·2H2O·4MeCN (5) (teaH3 = triethanolamine, bdeaH2 = N-n-butyldiethanolamine, edeaH2 = N-ethyldiethanolamine and acacH = acetylacetone) each of which display single-molecule magnet (SMM) behaviour. Importantly these new compounds are related to several {Co2IIIDy2III} SMM compounds allowing for the study of the effect that the subtle changes in structure have on the SMM properties. Ab-initio calculations are performed on 3 – 5, as well as on the related structural derivatives in order to gain insight on the effect the structural changes have on the dynamic magnetic behaviour.