Insight into understanding magnetic transition quite sensitive to nonmagnetic impurity in a one-dimensional S=1/2 regular linear chain system

A series of isomorphic salts [CN-BzPy][CuxNi1-x(mnt)(2)] (x = 0-1; CN-BzPy(+) = 1-(4 '-cyanobenzyl)pyridinium, mnt(2-) = maleonitriledithiolate) were prepared and characterized by microanalysis (C, H and N elements), IR and Raman spectroscopy, TG, and powder X-ray diffraction techniques. All salts crystallize in the monoclinic space group P2(1)/n with similar cell parameters, and both [M(mnt)(2)](-) (M = Ni or Cu) anions and CN-BzPy(+) cations form segregated and regular stacks. The thermal stabilities of the salts are enhanced with reducing cell volume in [CN-BzPy][CuxNi1-x(mnt)(2)] (x = 0-1). Intriguingly, a spin-Peierls-type transition occurs at T-C approximate to 191 K in the parent salt [CN-BzPy][Ni(mnt)(2)]; however, this vanishes in solid solutions even at x = 0.005, indicating that it is quite sensitive to being doped by a nonmagnetic impurity. Both the overlap integral of magnetic orbitals and spin density distribution analyses demonstrate that the antiferromagnetic couplings in a [Ni(mnt)(2)](-) stack are realized mainly through spatial dipole-dipole type interactions between the NiS4 cores of adjacent [Ni(mnt)(2)](-) anions, which are strongly related to the intermolecular NiMIDLINE HORIZONTAL ELLIPSISNi, NiMIDLINE HORIZONTAL ELLIPSISS and SMIDLINE HORIZONTAL ELLIPSISS separations. The functions of the shortest intermolecular NiMIDLINE HORIZONTAL ELLIPSISNi, NiMIDLINE HORIZONTAL ELLIPSISS and SMIDLINE HORIZONTAL ELLIPSISS distances as x changes indicate that a sharp increase occurs in a solid solution even at too low a concentration of nonmagnetic impurity (x = 0.005), suggesting that the spin-Peierls-state collapsing in solid solution is relevant to the sudden increase of intermolecular NiMIDLINE HORIZONTAL ELLIPSISNi, NiMIDLINE HORIZONTAL ELLIPSISS and SMIDLINE HORIZONTAL ELLIPSISS distances between neighboring [Ni(mnt)(2)](-) anions, leading to a rapid alteration of magnetic dipole-dipole interactions.

Automated summary

A series of isomorphic salts were prepared and characterized in this study. The thermal stabilities of the salts were found to increase with decreasing cell volume. Furthermore, the spin-Peierls transition observed in the parent salt disappeared upon doping with a nonmagnetic impurity.