Precisely tunable magnetic phase transition temperature, TC, through the formation of a molecular alloy in [NixPt1-x(mnt)2](-)-based spin systems (mnt(2-) = maleonitriledithiolate, x = 0.09-0.91).

Nine molecular substitutional alloys with formula [Cl-BzPy][NixPt1-x(mnt)2] (x = 0.09-0.91) were prepared by mixing the isostructural [Cl-BzPy][Ni(mnt)2] and [Cl-BzPy][Pt(mnt)2] in acetonitrile according to the molar ratio of x/(1 - x), where mnt(2-) = maleonitriledithiolate, Cl-BzPy(+) = 1-(4'-chloro-benzyl)pyridinium. Each alloy compound is isostructural with the parent compounds and shows a magnetic transition; the TC decreases linearly with the molar fraction x, indicating that TC is precisely tunable in this alloy system.