Synthesis and characterization of magnesium and zinc complexes of 1,4,7-triazacyclononane-N-acetate. Potential models for the active site of RuBisCo

Reaction of the tetradentate pendant-arm macrocycle 1,4,7-triazacyclononane -N-acetate (L) with Zn(O3SCF3)(2) or Mg(O3SCF3)(2) in alcohol produces the six-coordinate complexes [ZnL(H2O)]O3SCF3.C2H5OH (1) and [MgL(H2O)(2)]O3SCF 3 (2). Compounds 1 and 2 were characterized by single-crystal X-ray crystal lography. The complex cation of 1 forms a polymeric chain with zinc centers bridged in a syn, anti fashion by acetate pendant arms. The complex cation of 2 is mononuclear, with two adjacent coordination sites on magnesium occ upied by water molecules. These labile coordination sites may provide a bin ding site for activation of substrates in functional modeling of magnesium enzymes such as RuBisCo. H-1 and C-13 NMR spectroscopy demonstrates that L remains bound to magnesium in methanol solution. Crystal data: 1, orthorhom bic, space group P2(1)2(1)2(1), a = 9.0536(7), b = 14.3750(11), c = 14.4741 (11) Angstrom, V = 1883.7(2) Angstrom(3), Z = 4, R = 0.041, 2, orthorhombic , space group P2(1)2(1)2(1), a = 8.5949(3), b = 13.9694(4), c = 14.0076(5) Angstrom, V = 1681.83(10) Angstrom(3), Z = 4, R = 0.0248. (C) 2000 Elsevier Science S.A. All rights reserved.