Magnetic Behavior of Heterometallic Wheels Having a [Mn^IV₆M₂O₉]¹⁰⁺ Core with M = Ca²⁺ and Sr²⁺

Abstract

Two new heterometallic Mn(IV)-M(2+) compounds with formula [Mn6M2O9(4-(t)BuC6H4COO)10(4-(t)BuC6H4COOH)5] (M = Ca(2+) (1), Sr(2+) (2)) have been crystallized. The core of both compounds consists of a planar Mn6 ring, where the Mn(IV) ions are alternatively bridged by (μ3-O)2(μ-RCOO) and (μ4-O)(μ-RCOO)2 ligands, and the two alkaline earth ions are located to both sides of the wheel, linked to the oxo bridges, generating three fused [Mn2M2O4](4+) cuboids. These compounds show a net antiferromagnetic behavior, more important for 2 (Sr(2+)) than for 1 (Ca(2+)). The fitting of the experimental data was performed with the support of DFT calculations, considering four different exchange pathways: two between adjacent Mn(IV) ions (J1 and J2) and two between nonadjacent Mn(IV) ions (J3 and J4). The results of the analysis show that J1 and J2 are of the opposite sign, the ferromagnetic contribution corresponding to the [Mn2(μ4-O)(μ-RCOO)2](4+) unit (J2). The influence of the M(2+) ions in the magnetic behavior is analyzed for 1 and 2 and for three hypothetical models with the structural parameters of 1 containing Mg(2+), Sr(2+) or without the M(2+) ions. In spite of the diamagnetic character of the alkaline earth ions, their influence on the magnetic behavior has been evidenced and correlated with their polarizing effect. Moreover, the magnetic interactions between nonadjacent ions are non-negligible.

Bismuth for Controlled Assembly/Disassembly of Transition-Metal Oxo Clusters, Defining Reaction Pathways in Inorganic Synthesis and Nature

“…This synthesis yielded a Bi 3+and K + -capped hexamer ring, fully formulated as [Mn IV 6 Bi 2 -KO 9 (CH 3 COO) 10 (H 2 O) 3 (NO 3 ) 2 ](CH 3 COOH) 2 (NO 3 )• 5H 2 O (Mn 6 Bi 2 ; Figure 1; see the Experimental Section for details about the synthesis). The Mn 6 ring had been crystallized previously: (1) bicapped with Ca/Sr 2+ and ligated with butylbenzoic acid, 53 (2) bicapped with Ce IV and ligated with butylphosphate and acetate, 54 and (3) bicapped with Bi 3+ and ligated with ethyl acetate. 55 Mn 6 Bi 2 crystallizes in the monoclinic space group C2/m (see Table S1 for crystallographic details).…”

Hollow Sr/Rh-codoped TiO2 photocatalyst for efficient sunlight-driven organic compound degradation

“…Hence, Sr 2+ could be present on the TiO 2 surface as Sr-O clusters. 24,25 Fig . 3B shows the ultraviolet-visible (UV-vis) spectra of hollow Sr/Rh-TiO 2 -550, hollow Sr/Rh-TiO 2 -900, and bulk Rh-TiO 2 -900.…”