Magnetic Interactions Mediated by Diamagnetic Cations in [Mn₁₈<b>M</b>] (<b>M</b> = Sr²⁺, Y³⁺, Cd²⁺, and Lu³⁺) Coordination Clusters

We previously reported how the synthesis of [Mn^III₁₂Mn^II₇(μ₄-O)₈(μ₃-η¹-N₃)₈(HL¹)₁₂(MeCN)₆]­Cl₂·10MeOH·MeCN (<b>1</b>), which has a Mn₁₉ core corresponding to two supertetrahedral {Mn^II₄Mn^III₆} units sharing a common Mn^II vertex, can be modified such that the central octacoordinate Mn^II ion can be replaced by metal ions more likely to favor this coordination geometry such as Dy^III as exemplified in the compound [Mn^III₁₂Mn^II₆Dy^III(μ₄-O)₈(μ₃-Cl)_6.5(μ₃-N₃)_1.5(HL)₁₂(MeOH)₆]­Cl₃·25MeOH (<b>2</b>). Here, we report a systematic survey of the effects of incorporating various diamagnetic metal ions <b>M</b>ⁿ⁺ into this central position. We chose diamagnetic ions with electron configurations with fully occupied or completely empty frontier orbitals in order to gauge the effect on the overall magnetic behavior. The syntheses, structures, and magnetic properties of the heterometallic aggregates [Mn^III₁₂Mn^II₆Sr^II(μ₄-O)₈(μ₃-η¹-N₃)_7.5(μ₃-η¹-Cl)_0.5(HL¹)₁₂(MeCN)₆]­Cl₂·15MeOH (<b>3</b>), [Mn^III₁₂Mn^II₆Y^III(μ₄-O)₈(μ₃-η¹-N₃)₈(HL¹)₁₂(MeCN)₆]­(NO₃)₃·11MeOH (<b>4</b>), [Mn^III₁₂Mn^II₆Cd^II(μ₄-O)₈(μ₃-η¹-N₃)_6.8(μ₃-η¹-Cl)_1.2(HL¹)₁₂(MeCN)₆]­(CdCl₄)_0.25Cl_1.5·14.5MeOH (<b>5</b>), and [Mn^III₁₂Mn^II₆Lu^III(μ₄-O)₈(μ₃-η¹-N₃)_6.5(μ₃-η¹-Cl)_1.5(HL²)₁₂(MeCN)₆]­Cl₃·3H₂O·7MeOH·MeCN (<b>6</b>) (H₃L¹ = 2,6-<i>bis</i>(hydroxymethyl)-4-methylphenol, H₃L² = 2,6-<i>bis</i>(hydroxymethyl)-4-fluorophenol) are reported. The aggregates were prepared in one-pot self-assembly reactions of H₃L¹ (or H₃L²), MnCl₂·4H₂O or Mn­(NO₃)₂·4H₂O, NaOAc·3H₂O or Et₃N, and NaN₃ in the presence of the appropriate diamagnetic metal salt in MeCN/MeOH mixtures. Compounds <b>3</b>–<b>6</b> crystallize isotypically to <b>1</b> in the trigonal space group <i>R3̅</i> with <i>Z</i> = 3. The effects on the magnetic properties were investigated, paying attention to the presence of any weak coupling mediated by the diamagnetic cations between the two {Mn^II₃Mn^III₆} <i>S</i> = 39/2 subunits. In the Cd²⁺ compound <b>5</b>, the two {Mn^II₃Mn^III₆} units are magnetically isolated. In <b>3</b>, <b>4</b>, and <b>6</b>, the diamagnetic Sr²⁺, Y³⁺, and Lu³⁺ cations mediate weak antiferromagnetic interactions between the two {Mn^II₃Mn^III₆} subunits. DFT calculations show that the inter-{Mn^II₃Mn^III₆} interactions in the Mn₁₈<b>M</b> systems are attributable to the electronic structure of the central diamagnetic cation, with systems containing trivalent central cations showing stronger antiferromagnetic interactions than those with isoelectronic divalent cations