binding energy of Zn2+ ligands

 Dear CCL'ers,
I am looking for literature describing the influence of the basicity of metal ion ligands (ideally Zn2+ ligands) on the binding energy.
For example, I would expect the binding energy for an imidazole to be more favorable than for an imidazole with an electron withdrawing substituent, let's say an -SO2-group.
 Can somebody point me to articles on this matter?
 Thanks a lot in advance,
 Oliver Hucke, Dr.
                               Health Sciences Building - K418C
 University of Washington      1959 NE Pacific St.
 Dept. of Biochemistry         phone: (206) 685 7046
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 Seattle, WA 98195-7742        email: ohucke[at]