Chiral [Mn^IIMn^III₃M′] (M′=Na^I, Ca^II, Mn^II) and [Mn^IIMn^III₆Na^I₂] Clusters Built from an Enantiomerically Pure Schiff Base: Synthetic, Chiroptical, and Magnetic Properties

Abstract

From the reaction of manganese halides with the chiral Schiff bases obtained by condensation of o-vanillin and (R)- or (S)-phenylglycinol, 11 complexes based on pentanuclear cages with trigonal bipyramidal [Mn Mn M'] (M'=Na , Ca , Mn ) or enneanuclear [Mn Mn Na ] cores were synthesized. Structural, supramolecular chirality, and optical properties were explored. The magnetic properties of related systems were reviewed, and the magnetic response of the new systems was rationalized to the bond parameters.

Chiral Versus Non‐Chiral [MnIII6MnIINaI], [MnIII6MnII2NaI2] and [MnIII3MnIINaI] Clusters Derived from Schiff Bases or the Fight for Symmetry

“…The spectra of complexes 2 R and 2 S is very similar attending to the fact that ligands L2 2− and L3 2− have alkylic substituents that do not contribute to the π system of the ligands and thus do not modify the spectra in the high energy region, Figure . Comparison with the previously reported spectra for related complexes derived from H 2 L1 shows characteristic differences attributable to absorptions of the phenyl groups of the organic ligand at higher energies and similar transitions at lower energies related with the chiral cationic centers …”

“…For this kind of complexes based on the [Mn III 3 Mn II Na I ] core, the easy axis corresponding to the elongated bonds are always placed on the Mn III 3 plane and, its magnetic response can be ferro‐ or antiferromagnetic as a function of the ligands that link these positions bridging the Mn III 3 cations. As was previously described, any correlation can be found between the bond parameters inside the triangle and its magnetic response, indicating the relevant effect of the bridging ligands in that position. In contrast, all the reported systems with μ‐halides in these sites provide equilateral or quasi C 3 triangles and they promote ferromagnetic interaction in all reported cases.…”

“…In contrast with 2 R or the examples reported in the literature, complexes 3 Rac and 4 Rac show very weak antiferromagnetic coupling for the Mn II ⋅⋅⋅Mn III interactions mediated by one Mn II ‐ O ‐Mn III superexchange pathway. The previously studied complexes with [Mn III 3 Mn II Na I ] core have typically hexacoordinated cations but for 3 Rac and 4 Rac the divalent manganese cation is placed in a tetrahedral environment.…”

“…To do this, we have prepared (or completed from our previous publications) series of the racemic ( N Rac ) and chiral derivatives ( N R / N S ) of the ligands H 2 L1, H 2 L2, H 2 L3 and H 2 L4 (Scheme ), resulting the complexes [Mn III 6 Mn II Na I 2 (μ 3 ‐O) 2 Cl 6 (L1) 6 ] ( 1 Rac ), Na[Mn III 6 Mn II 2 Na I 2 (μ 3 ‐O) 2 (μ‐Cl) 3 Cl 6 (L2) 6 ] ( 2 Rac ), [Mn III 3 Mn II Na I (μ 3 ‐O)Cl 4 (L3) 3 ] ( 3 Rac , 3 R and 3 S ) and [Mn III 3 Mn II Na I (μ 3 ‐O)Cl 4 (L4) 3 ] ( 4 Rac ). 1 R and 1 S were previously reported and 2 R and 2 S were recently advanced as communication …”

Search for Structurally Resembled Mn/Ca Cubane Core of the Oxygen Evolving Complex of Photosystem II Yielded MnIV, MnIII3MnII and MnIII2CaII2Entities: Structure and Magnetism

“…A recent literature report of Ca II 2 Mn III 2 cubane core was built from 2‐(hydroxymethyl)pyridine and demonstrated slow magnetic relaxation [30] . Escuer group constructed Mn II Mn III 3 Ca core by employing a Schiff base obtained through condensation between o ‐vanillin and ( R )‐ or ( S )‐phynylglycinol [31] . Amino acids also served as successful candidates for constructing Ca/Mn species, [Mn 3 III Ca II ] and [Mn III 6 Ca II ], with structural closeness to the OEC bearing weak anti‐ferro/ferro magnetic interactions within the metal centers [32] …”