Observation of divergent isotope effects as well as metal ion-modulated TC and spin-canting nature in isostructural supramolecular magnets

Abstract

The ion-pair complexes of [4-NH₂-PyH][M(mnt)₂] (M = Pt for 1 and Ni for 3) and their deuterated analogues [4-NH₂-PyD][M(mnt)₂] (M = Pt for 2 and Ni for 4) are isostructural with each other. Four complexes crystalline in monoclinic space group C2/c, whose asymmetric unit consists of two halves of [M(mnt)₂]⁻ anions and one cation, show quite similar cell parameters and almost identical packing structures as well. In the crystals of 1–4, two types of crystallographically inequivalent [M(mnt)₂]⁻ anions construct individual layers, which are separated by the cation layer; the supramolecular networks are formed via the H-bonding interactions between the [M(mnt)₂]⁻ and 4-NH₂-PyH⁺ (or 4-NH₂-PyD⁺) ions as well as the weakly π⋯π stacking interactions between the [M(mnt)₂]⁻ anions. The four isostructural complexes exhibit canted antiferromagnetism, arising from the non-collinearity of the magnetic moments between the crystallographically inequivalent anion layers, with T_C ≈ 14.8 K for 1, 13.6 K for 2, 7.7 K for 3 and 8.8 K for 4, respectively. Ac magnetic susceptibility measurements revealed that 1 and 2 show spin canting, while 3 and 4 show hidden-spin canting characteristics. The isostructural 1 and 3 were deuterated to give the divergent isotope effects on the cell volume and T_C.