Alternating Ferro- and Antiferromagnetic Couplings in One-Dimensional Chain Hexachlorodicuprate(II), (MV)[CuCl3]2 (MV = Methyl Viologen)

To study quantum spin systems, we have investigated the magnetic properties of a one-dimensional chain magnet, (MV)[CuCl3]2 (MV = 1,1’-dimethyl-4,4’-bipyridinium). The chain structure of [Cu2C16]∞ is represented as an alternating inplane/ out-of-plane bridging system. From the analysis of magnetic susceptibility, we revealed the alternating ferro- /antiferromagnetic couplings in the chain, and estimated the two exchange coupling parameters between copper ions as J1/kB = –18.08(3) K and J2/kB = +1.33(17) K (defined as H = –2 Σ(Ji Si-1 ·Si + J2 Si .Si+1)). Additionally, the DFT calculations were performed, giving the exchange coupling constants as –16.78 K and +1.86 K. The calculated values are in good agreement with the experimental results. EPR spectra below 7 K revealed the triplet spin state in the copper(II) chain, indicating clearly the intrinsic ferromagnetic coupling, while the antiferromagnetic is dominant. It is concluded that (MV)[CuCl3]2 shows the quantum fluctuated one-dimensional spin system having alternating ferro- and antiferromagnetic couplings.