Synthesis and Characterisation of Luminescent [Cr^III₂L(μ‐carboxylato)]³⁺ Complexes with High‐Spin S=3 Ground States (L=N₆S₂ donor ligand)

Abstract

The synthesis, structure, magnetic, and photophysical properties of two dinuclear, luminescent, mixedligand [Cr III 2 L(O 2 CR)] 3 + complexes (R = CH 3 (1), Ph (2)) of a 24membered binucleating hexa-aza-dithiophenolate macrocycle (L) 2À are presented. X-ray crystallographic analysis reveals an edge-sharing bioctahedral N 3 Cr(μ-SR) 2 (μ 1,3 -O 2 CR)CrN 3 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 À 1 (1), + 34.8(4) cm À 1 (2), H = À 2JS 1 S 2 ) are significantly larger than in related bis-μalkoxido-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 A 2 ! 2 T 1 (ν 2 ) bands (λ exc = 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/CH 2 Cl 2 glasses, Φ L = 0.44 � 0.02 (for 1), Φ L = 0.45 � 0.02 (for 2).

Fifty Years of Inorganic Biomimetic Chemistry: From the Complexation of Single Metal Cations to Polynuclear Metal Complexes by Multidentate Thiolate Ligands

“…The [Cr (III) 2 ( L14 Me )(O 2 CR)] 3+ complexes exhibited ferromagnetic coupling between the Cr (III) centers. Here the magnitude of the coupling was three times higher than in other dinuclear Cr (III) complexes ( J= +24.2(2) cm −1 for the complex with formiate coligand and J= +34.8(4) cm −1 for the complex with benzoate coligand) [63b] …”