Synthesis, Structure, and Magnetic Properties of an Antiferromagnetic Spin-Ladder Complex: Bis(2,3-dimethylpyridinium) Tetrabromocuprate

The complex (2,3-dmpyH)2CuBr4 has been synthesized and its crystal packing determined by
single-crystal X-ray diffraction (2,3-dmpyH = 2,3-dimethylpyridinium). The compound crystallizes in the
triclinic space group P̄1. The crystal packing is characterized by the formation of a ladder structure for the
CuBr4 anions showing short Br···Br contacts. The rungs of the ladder are formed via a crystallographic
inversion center, while the rails are formed via unit cell translations. Variable temperature magnetic
susceptibility measurements agree very well with the ladder model [Jrung = −3.10 cm-1 (−4.34 K) and Jrail
= −6.02 cm-1 (−8.42 K)]. The assignment as a magnetic ladder is confirmed by first principles bottom-up
theoretical calculations which conclude that Jrung = −3.49 cm-1 (−4.89 K) and Jrail = −7.79 cm-1 (−10.9
K), in very good agreement with the experimental values. They also support the absence of additional
significant magnetic exchange within the crystals. Thus, (2,3-dmpyH)2CuBr4 represents the second reported
example of a weak-exchange limit magnetic ladder (that is, one in which the exchange along the rail is
stronger than that across the rung).