A Mixed-Ligand Approach for Spin-Crossover Modulation in a Linear FeII Coordination Polymer

In this work, we present a family of Fe-II coordination polymers of general formula [Fe(btzx)(3-3x)(btix)(3x)(ClO4)(2) with interesting spin-crossover properties. These coordination polymers have been synthesized using chemical mixtures of two different but closely related ligands, 1,4-bis(tetrazol-1-ylmethyl)benzene (btzx) and 1,4-bis(triazol-1-ylmethyl)benzene (btix), and the effect of a gradual substitution of the ligand in the spin transition temperature has been investigated. Several chemical mixtures have been structurally characterized by X-ray powder diffraction indicating a clear critical amount in the composition of the mixture after which mixed phases rather than a single phase comprising mixed components are observed. Importantly, this approach causes the appearance of a new transition at lower temperatures that is not present in the pure [Fe(L)(3)](ClO4)(2) systems.