Synthesis and Characterisation of Luminescent [CrIII2L(μ‐carboxylato)]3+ Complexes with High‐Spin S=3 Ground States (L=N6S2 donor ligand). Issue 60 (6th October 2021)

• Record Type: Journal Article
• Authors: Börner, Martin; Klose, Jennifer; Gutierrez Suburu, Matias E.; Strassert, Cristian A.; Yang, Fangshun; Monakhov, Kirill Yu.; Abel, Bernd; Kersting, Berthold
• Is Part Of: Chemistry. Volume 27:Issue 60(2021)
• Page Start: 14899
• Page End: 14910
• Publication Date: 2021-10-06
• Subjects: crystal structures -- dinuclear chromium(III) complexes -- luminescence -- magnetic properties -- thiolato ligand; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202102079
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The synthesis, structure, magnetic, and photophysical properties of two dinuclear, luminescent, mixed‐ligand [Cr III 2 L(O2 CR)] 3+ complexes (R=CH3 (1 ), Ph (2 )) of a 24‐membered binucleating hexa‐aza‐dithiophenolate macrocycle (L) 2− are presented. X‐ray crystallographic analysis reveals an edge‐sharing bioctahedral N3 Cr( μ ‐SR)2 ( μ 1, 3 ‐O2 CR)CrN3 core structure with μ 1, 3 ‐bridging carboxylate groups. A ferromagnetic superexchange interaction between the electron spins of the Cr 3+ ions leads to a high‐spin ( S =3) ground state. The coupling constants ( J =+24.2(1) cm −1 (1 ), +34.8(4) cm −1 (2 ), H=−2 J S1 S2 ) are significantly larger than in related bis ‐ μ ‐alkoxido‐ μ ‐carboxylato structures. DFT calculations performed on both complexes reproduce both the sign and strength of the exchange interactions found experimentally. Frozen methanol‐dichloromethane 1 : 1 solutions of 1 and 2 luminesce at 750 nm when excited into the 4 LMCT state on the 4 A2 → 2 T1 (ν2 ) bands (λexc =405 nm). The absolute quantum yields ( Φ L ) for 1 and 2 were found to be strongly temperature dependent. At 77 K in frozen MeOH/CH2 Cl2 glasses, Φ L =0.44±0.02 (for 1 ), Φ L =0.45±0.02 (for 2 ). Abstract : The synthesis of mixed‐ligand chromium(III) complexes, [Cr III 2 L(O2 CR)] 3+, where L represents a macrocyclic binucleating hexaamine‐dithiophenolato ligand and R=Me or Ph, has been achieved. The complexes exhibit a relatively strong intramolecular ferromagnetic exchange interaction that leads to an S =3 spin ground state ( J ∼24–34 cm −1 ). The complexes emit at 750 nm ( Φ L =45 %) by excitation into the intense LMCT and d‐d* bands.