Self-Organization into Preferred Sites by Mg^II, Mn^II, and Mn^III in Brucite-Structured M₁₉ Cluster

The search for functional materials, for example those aiming at microelectronics, magnetic recording, and catalysis, often ventures into mixed metal systems to achieve optimization of the properties. Thus, understanding site preference and self-organization is crucial but hard to implement. Herein, we present a system whereby Mg^II, Mn^II, and Mn^III ions selectively locate exact positions within the Brucite-structured cluster, Mn₁₃Mg₆, [Mn^III⊂Mg^II₆⊂Mn^II₉Mn^III₃( L)₁₈(OH)₁₂(N₃)₆](ClO₄)₆·12CH₃CN, H L = 1-(hydroxymethyl)-3,5-dimethylpyrazolate). The Mn^III being small (78 pm) takes up the core position; while 6 Mg^II (86 pm) are located in the inner ring, and the 9 large Mn^II (97 pm) and 3 Mn^III occupy the outer ring. The factors (a) ionic radii, (b) regularity in coordination geometry, oxophilicity, and softness of Mg^II compared to Mn^II, and (c) Jahn-Teller distortion of Mn^III may all be implicated synergistically. Electrospray ionization mass spectrometry reveals the M₁₉ disc remains an integral unit when crystals are dissolved, and exchange between Mg and Mn occurs within the disc during its formation. Diamagnetic Mg^II doping insulates the magnetic exchange between the central Mn^III and those in the outer ring, thus giving an overall antiferromagnetic exchange interaction between nearest-neighbors of the outer ring. The work reveals the underlying rule for site-preference of main group metal versus transition metal in disc-like Brucite-structured cluster and provides an elegant new avenue to assemble heterometallic clusters in a stepwise fashion.