Chiral Resolution of a Mn³⁺ Spin Crossover Complex

Abstract

Enantiopure Δ and Λ forms of the spin crossover Mn 3+ chelate complex [Mn{5-OCF 3 -sal 2 (323)}] + were prepared by co-crystallization with the (R,R) and (S,S) forms of the chiral spiroborate anion bis[1,1′-binaphthyl-2,2′-diolato]boron. The absolute structures of the enantiomers were established by X-ray crystallography at 100 K and at 293 K. The enantiomeric [a]

Homochiral Mn3+ Spin-Crossover Complexes: A Structural and Spectroscopic Study

“…A check of the CCDC database reveals that only 6 of the 78 unique [Mn(R-Sal 2 323)] + complexes 30 published before 2021 crystallize adventitiously in a chiral space group, 31 − 36 with a seventh example targeted by introduction of a chiral anion. 37 The interplay between SCO and chirality 38 − 58 is increasingly recognized as an important route to switchable nonlinear optical (NLO) materials 51 , 59 − 64 and spin-state dependent changes in optical activity may also constitute an economic and low energy route to follow SCO in sensing applications. Here we use circular dichroism to confirm the spontaneous resolution in the case of the ClO 4 – complex ( 1 ) and to demonstrate that the complex is stable toward racemization in solution.…”

Modulation of Mn3+ Spin State by Guest Molecule Inclusion

“…Hydrogen-bonding is a particularly effective tool in modulating SCO and this approach was successfully used to generate an extended homochiral 2D sheet of mixed valence Fe 2+ /Fe 3+ sites, which exhibited SCO and light induced excited spin state trapping (LIESST) [36]. In our own work with the [Mn(R-sal 2 323)] + series of Schiff base complexes, we have established that thermal SCO is possible in the less studied d 4 ion Mn 3+ [37][38][39][40][41][42][43][44][45][46]. The hexadentate ligand type used in this approach results from condensation of 1,2-bis(3-aminopropylamino)ethane with a substituted 2-hydroxybenzaldehyde, and the ligand series may be abbreviated as R-Sal 2 323 to indicate the 323 alkyl connectivity in the starting tetraamine and the substitution (R) on the phenolate ring.…”

“…Complexes ( 1) and (2) crystallize isostructurally in monoclinic space group P2 1 /c with Z = 4 where the asymmetric unit contains a full [MnL 1 ] + cation and one full triflate or one full hexafluorophosphate anion, respectively, Figure 2. The hexadentate Schiff base ligand chelates the Mn 3+ centre in pseudo octahedral geometry with two trans-phenolate donors, O1 and O3, two cis-amine and two cis-imine donor atoms, in the same way as previously observed for manganese complexes with this ligand type [37][38][39][40][41][42][43][44][45][46]48]. Residual electron density in both data sets was modelled as part occupancy water molecules using Platon SQUEEZE [47].…”

Spin-crossover materials: Getting the most from x-ray crystallography

“…52,53 The chiral functionality may emerge from different possibilities : use of chiral ligands (such as macrocyclic ligands with asymmetric substituents) in a mononuclear complex, 54 use of chelating ligands which twist around the metal center (such as for the [Fe(phen) 3 ] complex), 52,53,55 confining SCO molecules in chiral host framework, 56 or co-crystalizing SCO molecules with chiral counterions. 57 Chiral SCO materials of different architectures have been reported…”

“…in the literature: chiral SCO metal-organic frameworks, 58 chiral SCO mononuclear complexes [52][53][54][55]57 , chiral SCO polymeric chains. 59 Synthesis with equimolar racemic composition of the two enantiomers usually pack in a centrosymmetric space group, or crystallize as inversion twins.…”