Synthesis, Structure, and Compositional Tuning of the Layered Oxide Tellurides Sr₂MnO₂Cu_{2- x}Te₂ and Sr₂CoO₂Cu₂Te₂

The synthesis and structure of two new transition metal oxide tellurides, Sr₂MnO₂Cu_1.82(2)Te₂ and Sr₂CoO₂Cu₂Te₂, are reported. Sr₂CoO₂Cu₂Te₂ with the purely divalent Co²⁺ ion in the oxide layers has magnetic ordering based on antiferromagnetic interactions between nearest neighbors and appears to be inert to attempted topotactic oxidation by partial removal of the Cu ions. In contrast, the Mn analogue with the more oxidizable transition metal ion has a 9(1)% Cu deficiency in the telluride layer when synthesized at high temperatures, corresponding to a Mn oxidation state of +2.18(2), and neutron powder diffraction revealed the presence of a sole highly asymmetric Warren-type magnetic peak, characteristic of magnetic ordering that is highly two-dimensional and not fully developed over a long range. Topotactic oxidation by the chemical deintercalation of further copper using a solution of I₂ in acetonitrile offers control over the Mn oxidation state and, hence, the magnetic ordering: oxidation yielded Sr₂MnO₂Cu_1.58(2)Te₂ (Mn oxidation state of +2.42(2)) in which ferromagnetic interactions between Mn ions result from Mn^2+/3+ mixed valence, resulting in a long-range-ordered A-type antiferromagnet with ferromagnetic MnO₂ layers coupled antiferromagnetically.