Bis(pyrazolylethyl) ether ligation to zinc and cobalt: Meridional vs facial coordination and the suitability of such ligands in providing a NNO donor set for modeling bioinorganic aspects of zinc chemistry

The structures of bis(pyrazolylethyl) ether derivatives of zinc and cobalt, namely [eta(3)-O(CH(2)CH(2)pz(Pri2))(2)]Zn(NO3)(2) and [eta(3)-O(CH(2)CH(2)PzMe(2))(2)]CO(NO3)(2), have been determined with a view to addressing the applicability of such ligands in modeling bioinorganic aspects of zinc chemistry. Specific consideration is given to the possibility that bis(pyrazolylethyl) ether ligands may provide an NNO donor system which may model aspects of the binding of zinc to protein backbones in enzymes such as thermolysin. The structural studies demonstrate that the bis(pyrazolylethyl) ether ligands do indeed coordinate via each of their NNO functionalities but that the relationship to the enzyme is limited by the adoption of meridional rather than facial coordination geometries. [eta(3)-O(CH(2)CH(2)Pz(Pri2))(2)]Zn(NO3)(2) is monoclinic, P2(1)/c (No. 14), with a = 11.619(2) Angstrom, b = 14.380(3) Angstrom, c = 16.757(2) Angstrom, beta = 90.44(2)degrees, and Z = 4. [eta(3)-O(CH(2)CH(2)pz(Me2))(2)]Co(NO3)(2) is monoclinic, C2/c (No. 15), with a = 17.136(3) Angstrom, b = 10.505(2) Angstrom, c = 11.121(2) Angstrom, beta = 104.62(3)degrees, and Z = 4.