Developing a “Highway Code” To Steer the Structural and Electronic Properties of Fe^III/Dy^III Coordination Clusters

In the recently established field of 3d/4f coordination cluster (CC) chemistry several burning questions still need to be addressed. It is clear that combining 3d and 4f metal ions within a coordination cluster core has the potential to lead to electronic structures that will be very difficult to describe but can also be extremely interesting. Furthermore, understanding why certain core topologies seem to be favored is difficult to predict. Here we show that the secondary coordination sphere provided by the ligands influences the favored product, as demonstrated for the compound [Fe₄Dy₂(μ₃-OH)₂(<i>n-</i>bdea)₄­(C₆H₅CO₂)₈]·MeCN (<b>1</b>), which has a 2Fe:2Dy:2Fe core and was made using [Fe^III₃O­(C₆H₅)­CO₂)­(L)₃]⁺ as starting material plus Dy­(NO₃)₃ and <i>N</i>-<i>n</i>-butyl-diethanolamine (<i>n-</i>bdeaH₂), compared with the compound made using a methyl meta-substituent (R) on the phenyl ring of the benzoate, [Fe^III₃O­(C₆H₄Me)­CO₂)­(L)₃]⁺ as starting material, which resulted in the “square-in-square” compound [Fe₄Dy₄(μ₃-OH)₄(<i>n-</i>bdea)₄­(O₂CC₆H₄CH₃)₁₂]·MeCN (<b>2</b>) when using ambient conditions. Changing reaction conditions from ambient to solvothermal leads to “double-propeller” compounds [Fe₄Dy₄(μ₄-O)₃(<i>n-</i>bdea)₃­(C₆H₅CO₂)₁₂]·13MeCN (<b>3</b>) and [Fe₄Dy₄(μ₄-O)₃(<i>n-</i>bdea)₃­(O₂CC₆H₄CH₃)₁₂]·MeCN (<b>4</b>) forming with this core, resulting irrespective of the substitution on the iron benzoate starting material. Furthermore, compounds <b>1</b> and <b>2</b> can be transformed into compounds <b>3</b> and <b>4</b>, respectively, using a solvothermal method. Thus, compounds <b>3</b> and <b>4</b> appear to be the thermodynamically most stable species. The factors steering the reactions toward these products are discussed. The electronic structures have been investigated using magnetic and Mössbauer studies. All compounds are cooperatively coupled 3d/4f systems, with compound <b>1</b> showing single-molecule magnet behavior