Four new Mo(Vl)-dioxo complexes of a family of N2X heteroscorpionate ligands are reported which, together with data already available for (Tp(R))(-), provide a unique example of a comprehensive set of isostructural, isoelectronic complexes differing only in one biologically relevant donor atom. A study of these complexes allows for a direct comparison of structural, spectroscopic, and oxygen atom transfer reactivity properties of the Mo(Vl)-dioxo center (of relevance to various families of molybdoenzymes) as a function of donor atom identity.