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 metalmellitate coordination polymer dimensionality 0-3. Usually mellitate is fully deprotonated (mel(6-)), but there is one example of Hmel(5-) and one of H(2)mel(4-). [M-3(mel)(OH2)(12)]center dot 6H(2)O (M = Co or Ni) are chain polymers with octahedral M, while [Cu-7(OH2)(19)(OH)(2)(mel)(2)]center dot 9H(2)O 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-)center dot 2H(2)O contains discrete nickel-mellitate anionic units, and K-2(+)(OH2)(6)[{Cu(OH2)(3)}(2)(mel)](2-)center dot 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-)center dot 4H(2)O, with a 2D polymeric anion and discrete cations. A gel-supported synthesis leads to [Cu-3(OH2)(10)-(Hmel)][Cu-2(OH2)(6)(Hmel)]center dot 7H(2)O, with two different copper-mellitate polymeric sheets arranged alternately in a stack. [{Cu(OH2)(EtOH)(4,4'-bipy)}(2)(H(2)mel)] contains a three-dimensional copper-mellitate network with hexagonal channels, occupied by 4,4'-bipyridyl molecules coordinated to Cu at one end and hydrogen bonded to H(2)mel(4-) at the other. While some of these features are familiar from other structures, some are new, raising the question of how far design principles can be applied to the synthesis of mellitate complexes.