Koordination von Rhodium(III), Iridium(III) und Kupfer(II) mit dem potentiell vierzähnigen Akzeptorliganden Bis(1‐methylimidazol‐2‐yl)glyoxal (big)

Coordination of Rhodium(III), Iridium(III), and Copper(II) with the Potentially Tetradentate Acceptor Ligand Bis(1‐methylimidazol‐2‐yl)glyoxal (big) Bis(1‐methylimidazol‐2‐yl)glyoxal (big) which has hitherto not been used in coordination chemistry crystallizes to form two perpendicular 1‐methylimidazol‐2‐yl‐carbonyl molecular halves. Out of the various possibilities for mono‐ and bis‐chelate coordination the N,N′‐alternative with a seven‐membered chelate ring is realized in Cp*Cl(big)Rh](PF₆) as evident from crystal structure analysis. The iridium analogue reacts under hydration of big and elimination of HCl to form a complex cation Cp*(bigOH)Ir]⁺ which dimerizes in the crystal through hydrogen bonding and contains one five‐ and one six‐membered chelate ring involving the alcoholate‐O. Cu(ClO₄)₂ and the ligand big yield a complex ion Cu(big)₂]²⁺ with an ESR spectrum that suggests the coordination of the central metal by four N atoms in an approximately planar setting.