Structurally distinct homoleptic anthracene complexes, [M(C ₁₄H₁₀)₃]^2-, M = titanium, zirconium, hafnium: Tris(arene) complexes for a triad of transition metals

(Figure Presented) Being positive about anions: Hydrocarbon complexes containing negative-valent Hf are obtained for the first time as tris(polyarene)hafnates(2-), polyarene = anthracene (An) and naphthalene, where the latter functions as a synthon for the unknown atomic Hf^2- (see scheme, cot = 1,3,5,7-cyclooctatetraene). Tris(anthracene)metalates(2-) of Ti and Zr were also accessed,which completes an unprecedented triad of tris(arene)metal complexes.