Structural Variation in Mellitate Complexes of First-Row Transition Metals: What Chance for Design?

Eight compounds of Co, Ni, and Cu with mellitate ligands display a wide variety of structures with metal–mellitate coordination polymer dimensionality 0–3. Usually mellitate is fully deprotonated (mel6–), but there is one example of Hmel5– and one of H2mel4–. [M3(mel)(OH2)12]·6H2O (M = Co or Ni) are chain polymers with octahedral M, while [Cu7(OH2)19(OH)2(mel)2]·9H2O has a 2D polymer sheet structure with square-based pyramidal Cu. Addition of KOH produces different compounds. Two incorporate K+ in the structures: K+2(OH2)5[{Ni(OH2)5}2(mel)]2–·2H2O contains discrete nickel–mellitate anionic units, and K+2(OH2)6[{Cu(OH2)3}2(mel)]2–·H2O has a copper–mellitate two-dimensional (2D) polymeric anion. For Co the product is [Co(OH2)6]2+[{Co(OH2)4}5(mel)2]2–·4H2O, with a 2D polymeric anion and discrete cations. A gel-supported synthesis leads to [Cu3(OH2)10(Hmel)][Cu2(OH2)6(Hmel)]·7H2O, with two different copper–mellitate polymeric sheets arranged alternately in a stack. [{Cu(OH2)(EtOH)(4,4′-bipy)}2(H2mel)] contain...