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 FeII 1-x NiII x series (0≤x≤1) show an innocent composition dependence, where the blocking temperature of slow relaxation decreases monotonically as FeII is replaced by less anisotropic NiII . The FeII 1-x CoII x series show an unexpected antagonistic blending effect on slow relaxation: blending FeII and CoII tends to depress the spin dynamics, and the bimetallic materials with intermediate composition show significantly lower blocking temperature than both FeII and CoII materials. This is quite the opposite of what happens in the Co1-x Nix series, where CoII and NiII seem to have a synergetic effect so that slow relaxation in bimetallic systems can be promoted to higher temperature than both CoII and NiII materials.