Heteropentanuclear {Ru(II)Cu(II)₄} Kuratowski Complexes Assembled from a Ruthenium(II) Precursor Complex to Study Competing Exchange Interactions in M(II)(ta)₂ Networks [ta(−) = 1,2,3-Triazolate]

We report a directed two-step synthesis toward pentanuclear Kuratowski complexes. First, six 5,6-dimethylbenzo[1,2,3]triazole ligands (Me₂btaH) are coordinated to a single Ru(II) ion, providing a topologically ideal template for the addition of further metal ions. The synthesis and crystal structures of [RuCu₄X₄(Me₂bta)₆] [X = acetylacetonate (acac) and tris(3,5-dimethyl-1-pyrazolyl)borate (Tp*)] are described. Both represent new members of the family of so-called Kuratowski (K_3,3) complexes. The coordination units feature triazolato-bridged metal-centered {MM₄} tetrahedra, which are known for frustrated magnetic interactions in both complexes and metal–organic frameworks. The novel Ru(II)-centered complexes were synthesized in order to investigate the influence of the presence or absence of a paramagnetic central metal ion in the Kuratowski complex. Superconducting quantum interference device and electron spin resonance measurements demonstrate that small deviations in bond lengths and valence angles can lead to the formation of pairs of magnetic exchange-coupled Cu(II) ions. Which Cu(II) ions pair up can be predicted in Jahn–Teller active compounds by the overlap of the respective orbitals. These data are compared with those gleaned for M(II)(ta)₂ (ta = 1,2,3-triazolate) lattices, in which structurally similar {MM₄} tetrahedra constitute the secondary building units.