Giant Heterometallic [Mn36Ni4]0/2− and [Mn32Co8] “Loops-of-Loops-and-Supertetrahedra” Molecular Aggregates (2019)

We report the synthesis, crystal structures and magnetic properties of the giant heterometallic [Mn<sub>36</sub>Ni<sub>4</sub>]<sup>2-/0</sup> (compounds <b>1</b>, <b>2</b>)/[Mn<sub>32</sub>Co<sub>8</sub>] (compound <b>3</b>) "loops-of-loops-and-supertetrahedra" molecular aggregates and of a [Mn<sub>2</sub>Ni<sub>6</sub>]<sup>2+</sup> compound (cation of <b>4</b>) that is structurally related with the cation co-crystallizing with the anion of <b>1</b>. In particular, after the initial preparation and characterization of compound [Mn<sub>2</sub>Ni<sub>6</sub>(μ<sub>4</sub>-O)<sub>2</sub>(μ<sub>3</sub>-OH)<sub>3</sub>(μ<sub>3</sub>-Cl)<sub>3</sub>(O<sub>2</sub>CCH<sub>3</sub>)<sub>6</sub>(py)<sub>8</sub>]<sup>2+</sup>[Mn<sub>36</sub>Ni<sub>4</sub>(μ<sub>4</sub>-O)<sub>8</sub>(μ<sub>3</sub>-O)<sub>4</sub>(μ<sub>3</sub>-Cl)<sub>8</sub>Cl<sub>4</sub>(O<sub>2</sub>CCH<sub>3</sub>)<sub>26</sub>(pd)<sub>24</sub>(py)<sub>4</sub>]<sup>2-</sup> (<b>1</b>) we targeted the isolation of (i) both the cationic and the anionic aggregates of <b>1</b> in a discrete form and (ii) the Mn/Co analog of [Mn<sub>36</sub>Ni<sub>4</sub>]<sup>2-</sup> aggregate. Our synthetic efforts toward these directions afforded the discrete [Mn<sub>36</sub>Ni<sub>4</sub>] "loops-of-loops-and-supertetrahedra" aggregate [Mn<sub>36</sub>Ni<sub>4</sub>(μ<sub>4</sub>-O)<sub>8</sub>(μ<sub>3</sub>-O)<sub>4</sub>(μ<sub>3</sub>-Cl)<sub>8</sub>Cl<sub>2</sub>(O<sub>2</sub>CCH<sub>3</sub>)<sub>26</sub>(pd)<sub>24</sub>(py)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>2</b>), the heterometallic Mn/Co analog [Mn<sub>32</sub>Co<sub>8</sub>(μ<sub>4</sub>-O)<sub>8</sub>(μ<sub>3</sub>-O)<sub>4</sub>(μ<sub>3</sub>-Cl)<sub>8</sub>Cl<sub>2</sub>(μ<sub>2</sub>-OCH<sub>2</sub>CH<sub>3</sub>)<sub>2</sub>(O<sub>2</sub>CCH<sub>3</sub>)<sub>28</sub>(pd)<sub>22</sub>(py)<sub>6</sub>] (<b>3</b>) and the discrete [Mn<sub>2</sub>Ni<sub>6</sub>]<sup>2+</sup> cation [Mn<sub>2</sub>Ni<sub>6</sub>(μ<sub>4</sub>-O)<sub>2</sub>(μ<sub>3</sub>-OH)<sub>4</sub>(μ<sub>3</sub>-Cl)<sub>2</sub>(O<sub>2</sub>CCH<sub>3</sub>)<sub>6</sub>(py)<sub>8</sub>](ClO<sub>4</sub>)(OH) (<b>4</b>). The structure of <b>1</b> consists of a mixed valence [ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mtext>Mn</mml:mtext></mml:mrow> <mml:mrow><mml:mn>28</mml:mn></mml:mrow> <mml:mrow><mml:mtext>III</mml:mtext></mml:mrow> </mml:msubsup> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mtext>Mn</mml:mtext></mml:mrow> <mml:mrow><mml:mn>8</mml:mn></mml:mrow> <mml:mrow><mml:mtext>II</mml:mtext></mml:mrow> </mml:msubsup> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mtext>Ni</mml:mtext></mml:mrow> <mml:mrow><mml:mn>4</mml:mn></mml:mrow> <mml:mrow><mml:mtext>II</mml:mtext></mml:mrow> </mml:msubsup> </mml:math> ]<sup>2-</sup> molecular aggregate that contains two <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mtext>Mn</mml:mtext></mml:mrow> <mml:mrow><mml:mn>8</mml:mn></mml:mrow> <mml:mrow><mml:mtext>III</mml:mtext></mml:mrow> </mml:msubsup> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mtext>Ni</mml:mtext></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> <mml:mrow><mml:mtext>II</mml:mtext></mml:mrow> </mml:msubsup> </mml:math> loops separated by two <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mtext>Mn</mml:mtext></mml:mrow> <mml:mrow><mml:mn>6</mml:mn></mml:mrow> <mml:mrow><mml:mtext>III</mml:mtext></mml:mrow> </mml:msubsup> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mtext>Mn</mml:mtext></mml:mrow> <mml:mrow><mml:mn>4</mml:mn></mml:mrow> <mml:mrow><mml:mtext>II</mml:mtext></mml:mrow> </mml:msubsup> </mml:math> supertetrahedral units and a [ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mtext>Mn</mml:mtext></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> <mml:mrow><mml:mtext>III</mml:mtext></mml:mrow> </mml:msubsup> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mtext>Ni</mml:mtext></mml:mrow> <mml:mrow><mml:mn>6</mml:mn></mml:mrow> <mml:mrow><mml:mtext>II</mml:mtext></mml:mrow> </mml:msubsup> </mml:math> ]<sup>2+</sup> cation based on two [Mn<sup>III</sup> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mtext>Ni</mml:mtext></mml:mrow> <mml:mrow><mml:mn>3</mml:mn></mml:mrow> <mml:mrow><mml:mtext>II</mml:mtext></mml:mrow> </mml:msubsup> </mml:math> (μ<sub>4</sub>-O)(μ<sub>3</sub>-OH)<sub>1.5</sub>(μ<sub>3</sub>-Cl)<sub>1.5</sub>]<sup>4+</sup> cubane sub-units connected through both mono- and tri-atomic bridges provided by the μ<sub>4</sub>-O<sup>2-</sup> and carboxylate anions. The structures of <b>2</b>-<b>4</b> are related to those of the compounds co-crystallized in <b>1</b> exhibiting however some differences that shall be discussed in detail in the manuscript. Magnetism studies revealed the presence of dominant ferromagnetic interactions in <b>1</b>-<b>3</b> that lead to large ground state spin (S<sub>T</sub>) values for the "loops-of-loops-and-supertetrahedra" aggregates and antiferromagnetic exchange interactions in <b>4</b> that lead to a low (and possibly zero) S<sub>T</sub> value. In particular, dc and ac magnetic susceptibility studies revealed that the discrete [Mn<sub>36</sub>Ni<sub>4</sub>] aggregate exhibits a large S<sub>T</sub> value ~ 26 but is not a new SMM. The ac magnetic susceptibility studies of the [Mn<sub>32</sub>Co<sub>8</sub>] analog revealed an extremely weak beginning of an out-of-phase tail indicating the presence of a very small relaxation barrier assignable to the anisotropic Co<sup>2+</sup>ions and a resulting out-of-phase ac signal whose peak is at very low T.