Synthesis, characterization and thermal properties of trimetallic N3-Cr[quadruple bond]Cr···M-N3 azide complexes with M = Cr, Mn, Fe, and Co.

We report here two novel synthetic pathways toward the preparation of a family of trimetallic diazide compounds of the type Cr(2)M(dpa)(4)(N(3))(2), with M = Cr (10), Mn (4), Fe (5), and Co (11). Reaction of either Cr(2)M(dpa)(4)(OTf)(2) (for M = Mn and Fe) or [Cr(2)M(dpa)(4)(MeCN)(2)](PF(6))(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.