Synthesis, characterization and thermal properties of trimetallic N3–CrCr⋯M–N3 azide complexes with M = Cr, Mn, Fe, and Co

Abstract

We report here two novel synthetic pathways toward the preparation of a family of trimetallic diazide compounds of the type Cr₂M(dpa)₄(N₃)₂, with M = Cr (10), Mn (4), Fe (5), and Co (11). Reaction of either Cr₂M(dpa)₄(OTf)₂ (for M = Mn and Fe) or [Cr₂M(dpa)₄(MeCN)₂](PF₆)₂ (for M = Cr and Co) with sodium azide in methanol leads to the formation of the corresponding diazide compounds, and single crystal X-ray diffraction measurements confirm the predicted structures. Compounds 4, 5, and 10 are all high-spin compounds, but 11 is a spin-crossover compound exhibiting low-spin behavior at low temperatures (∼100 K). Thermolytic characterization by DSC and TGA reveals an exothermic reaction corresponding to the loss of two dinitrogen molecules from compounds 5, 10, and 11. Further characterization by solution NMR measurements and cyclic voltammetry are also presented.