A preformed 1-D {Cu II2}n helical chain as precursor to a decanuclear 0-D {Cu II8Mn II2} cluster: synthesis, structure and magnetism

Abstract

The Schiff base ligand, N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH₂), was initially employed in both homometallic Cu^II and heterometallic Mn^II/Cu^II coordination chemistry. A 1-D helical chain, [Cu^II₂(sacb)₂(MeOH)]_n (1), and a decanuclear 0-D heterometallic cluster, [Cu^II₈Mn^II₂(OH)₄(sacb)₈(H₂O)₂] (2), were synthesized and fully characterized. Complex 2 is one of the two highest nuclearity Mn^II/Cu^II complexes reported to date and exhibits a unique {Cu₈Mn₂(μ₃-OH)₄(μ-OR)₆(μ₃-OR)₂(μ-O₂CR)₂}⁶⁺ core composed of two oppositely oriented pentanuclear {Cu₄Mn} units, each featuring two vertex-sharing {Cu₂Mn} triangles. The presence of the {Cu₂(sacb)₂} fragment in both species suggests a templating role of the preformed chain 1 in the assembly of molecular cluster 2. Variable-temperature dc magnetic susceptibility studies reveal predominant antiferromagnetic interactions between Cu^II⋯Mn^II and Cu^II⋯Cu^II centers, with exchange coupling constants: J₁ = −16.5(1) cm⁻¹, J₂ = −35.1(5) cm⁻¹ and J₃ = +0.7(3) cm⁻¹. These findings highlight the utility of preformed oligonuclear and polymeric 3d-metal species as building blocks for the preparation of heterometallic 3d/3d′ polynuclear complexes with novel architectures and tailored physicochemical properties.