The Use of a Bis(phenylpyrazolyl)pyridyl Ligand to Prepare [Mn4] and [Mn10] Cage Complexes

Abstract

Many branches in molecular magnetism live on the production of novel transition-metal (TM) coordination clusters. This has been the source of high-spin molecules, most single-molecule magnets (SMMs), or the possible future qubits for quantum computing. Without doubt, the great advances made in these areas have benefited, for the most part, from the preparation of molecules through so-called “serendipitous self-assembly”. Even though the designed preparation of clusters with predetermined structures and properties is highly desirable, it continues to be a huge synthetic challenge. Therefore, there is no reason to think that the “nonpredictable” approach will cease to be instrumental in the near future. For this, synthetic coordination chemists will keep providing original methods of preparation of polynuclear TM complexes. Typically, these are produced from reactions involving one or more small ligands with donor atoms capable of bridging metals, normally exhibiting several potential coordination modes. By contrast, the synthesis of large multidentate ligands with numerous donor atoms is far less common in this context. We have recently prepared a new ligand with two aligned hydroxyphenylpyrazolyl units separated by a pyridine group (2,6-bis[5-(2-hydroxyphenyl)pyrazol-3-yl]pyridine, H4L, Scheme 1). [10] Hydroxyphenylpyrazolyl derivatives or related pyrazolinoles have proven to be excellent ligands for the assembly of TM clusters with novel structures. The build up of more than one such moiety on the same molecule promises to be an open door to a variety of unprecedented architectures. Ligand H4L is well suited, for example, to stimulate the aggregation of a sequence of five closely spaced metals within a cluster (Scheme 2B). We report herein very promis-