Single-Chain Magnet Behavior in an Alternated One-Dimensional Assembly of a MnIII Schiff-Base Complex and a TCNQ Radical

An alternated 1:1 chain compound of a MnIII salen derivative and the TCNQ monoradical was synthesized: [Mn(5‐TMAMsaltmen)(TCNQ)](ClO4)2 (1) (TCNQ=tetracyano‐p‐quinodimethane; 5‐TMAMsaltmen=N,N′‐(1,1,2,2‐tetramethylethylene) bis(5‐trimethylammoniomethylsalicylideneiminato)). Compound 1 has a zigzag chain structure packed with adjacent chains with an interchain Mn⋅⋅⋅Mn distance of over 8 Å. As compound 1 contains no crystallization solvent, the void spaces between chains are occupied only by ClO4− counter ions. Compound 1 has a structure reminiscent of what has been observed in the family of MnIII(porphyrin)‐TCNE or ‐TCNQ compounds reported previously by Miller and co‐workers and we demonstrate herein its unique single‐chain magnet behavior among this family of compounds. The direct current (dc) magnetic measurements established the one‐dimensional nature of compound 1 with an antiferromagnetic exchange coupling, J/kB≈−96 K, between the MnIII ion and TCNQ radical and with an activated correlation length (Δξ=26.5 K) at low temperatures (50–15 K). The slow relaxation of the magnetization was shown in compound 1 by the field hysteresis of the magnetization observed below 3.5 K (with a coercive field up to 14 kOe at 1.8 K). Single‐crystal magnetization measurements demonstrated the uniaxial symmetry of this compound and allowed an estimation of the anisotropy field, Ha≈97 kOe. The absence of magnetic ordered phase or spin‐glass behavior was established by heat‐capacity calorimetry measurements that exhibit no abnormality of Cp between 0.5 K and 10 K. The study of the magnetization relaxation by combined ac (alternating current) and dc techniques showed that compound 1 possesses a single relaxation time (τ). As the consequence of the finite size of the chain, the temperature dependence of τ presents two activated regimes above and below 4.5 K with τ01=2.1×10−10 s, Δτ1=94.1 K and τ02=6.8×10−8 s and Δτ2=67.7 K, respectively. The detailed analysis of these dynamics properties together with the correlation length, allows an unambiguous demonstration of the single‐chain magnet behavior in 1. A new one‐dimensional ferrimagnetic arrangement of MnIII ions and the tetracyano‐p‐quinodimethane (TCNQ) radical has been obtained in [Mn(5‐TMAMsaltmen)(TCNQ)](ClO4)2 (see picture) (5‐TMAMsaltmen=N,N′‐(1,1,2,2‐tetramethylethylene) bis(5‐trimethylammoniomethylsalicylideneiminato)), which exhibits single‐chain magnet behavior as shown by the detailed analysis of its thermodynamic an