Effects of Metal Blending in Random Bimetallic Single-Chain Magnets: Synergetic, Antagonistic, or Innocent

A family of isomorphous three-dimensional metal–organic frameworks based on bimetallic (FeCo, FeNi, and CoNi) chains with random metal sites have been prepared and magnetically characterized. The solid-solution-type bimetallic materials inherit intrachain ferromagnetic interactions and single-chain-magnet (SCM) behaviors from the homometallic parent materials. Interestingly, different composition dependence of magnetic behaviors has been found. The Fe^II_1−xNi^II_xseries (0≤x≤1) show an innocent composition dependence, where the blocking temperature of slow relaxation decreases monotonically as Fe^IIis replaced by less anisotropic Ni^II. The Fe^II_1−xCo^II_xseries show an unexpected antagonistic blending effect on slow relaxation: blending Fe^IIand Co^IItends to depress the spin dynamics, and the bimetallic materials with intermediate composition show significantly lower blocking temperature than both Fe^IIand Co^IImaterials. This is quite the opposite of what happens in the Co_1−xNi_xseries, where Co^IIand Ni^IIseem to have a synergetic effect so that slow relaxation in bimetallic systems can be promoted to higher temperature than both Co^IIand Ni^IImaterials.