Ferromagnetic manganese “cubes”: from PSII to single-molecule magnets

Abstract

The reaction of Mn(O₂CMe)₂·2H₂O with Me-saoH₂ (Me-saoH₂ = 2-hydroxyphenylethanone oxime) in MeCN forms the complex [Mn(III)₄(Me-sao)₄(Me-saoH)₄] (1) in good yields. Replacing Me-saoH₂ with Naphth-saoH₂ (Naphth-saoH₂ = 2-hydroxy-1-napthaldoxime) in the presence of CH₃ONa forms the complex [Mn(III)₄(Naphth-sao)₄(Naphth-saoH)₄] (2) in low yields, while the reaction between Mn(ClO₄)₂·6H₂O, Et-saoH₂ (Et-saoH₂= 2-hydroxypropiophenone oxime) and NBu₄OH in MeCN gives the complex [Mn(III)₄(Et-sao)₄(Et-saoH)₄] (3) in moderate yields. All three tetrametallic cages exclusively contain Mn(III) centres arranged in a "cube"-like topology, in which the metal centres are connected by -N-O(oximate) groups. The magnetic properties of 1-3 are near identical, revealing the presence of only ferromagnetic interactions between the metal ions leading to high-spin ground states of S = 8. The complexes display frequency dependent out-of-phase signals in ac susceptibility studies and, in the case of 1 single-molecule magnetism has been observed by means of single-crystal hysteresis loop measurements.

Synthesis and Properties of Complexes with Unusual {MnIII4} and {MnII4} Cages

“…However, assuming H 2 O and MeOH molecules beside Cl – ligands, the formal oxidation state would indeed be +II and thus not producing any distortion. A comparison between the geometric parameters of the cage in 2 with those observed in 1a and 1b , as well as with the reported “ferromagnetic cubes”,5 quite decisively leads to the conclusion that the Jahn–Teller distortion is visible in the {Mn III 4 } complexes in 1 , but not in 2 (Table S2). An indication for the presence of methanol/water ligands in 2 is the tendency of the crystals to lose solvent.…”

“…Hydrogen atoms are omitted for clarity, except those involved in intramolecular hydrogen bonds (denoted by dashed lines O–H ··· O). The non‐hydrogen atom labeling scheme for the sake of comparison, has beenadopted from the CCDC entry for compound described in 5…”

“…Recently, Inglis et al carried out a study on a series of ferromagnetic complexes with similar [Mn 4 ] distorted cubes of the general formula [Mn III 4 ( R ‐sao) 4 ( R ‐saoH) 4 ] ( R = Me, Napth, Et) 5. This provided a better insight into this class of compounds, however, overlooking antiferromagnetic compound B .…”

Tetranuclear Manganese Complex Incorporating 2‐Pyridyloximate Ligand: Synthesis, Crystal Structure and Magnetic Property

“…In the reported tetranuclear Mn II clusters, the Mn 4 cores mainly displayed tetrahedral or linear zig‐zag topology 19,20,23,24. The tetra‐face‐capped tetrahedral topology displayed by 1 is very sparse in the manganese/oximate coordination complexes 30…”

Cube‐like 12‐MC‐4 and Offset Stacked 10‐MC‐3 Metallacrowns: Synthesis, Structure, and Magnetic Properties

“…Interestingly, the [Mn4] unit has assembled with four neighboring [Mn4]' ( 1b ) units by C–H ··· π interactions [C2–H2] ··· π (C133, C134, C135, C136, C137, C142) H ··· centroid 2.838 Å, C ··· centroid 3.682 Å, C–H ··· centroid 138°; [C48–H48] ··· π (C1, C2, C3, C4, C5, C10) H ··· centroid 2.874 Å, C ··· centroid 2.784 Å, C–H ··· centroid 174° and C–H ··· O hydrogen bonds [C78–H78 ··· O32, H ··· O 2.472 Å, C ··· O 3.175 Å, C–H ··· O 133°] forming an undulated net running (Figure a). The [Mn4]' units have also assemble with four [Mn4] through nine C–H ··· π interactions and a π ··· π [(C37, C38, C39, C40, C41, C46) (C145, C146, C147, C148, C149, C154)], π ··· π centroid 3.923 Å (Figure b) …”