For synthesis of Schiff's bases please read the paper below stated, there is explain maxiimal comprehensively (I hope) the capability of Schiff' systhetic road because of are inclöuded wide set of experimental conditions :
1. Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2013, 75, 211-221
Optical and nonlinear optical properties of new Schiff’s bases: experimental versus theoretical study of inclusion interactions, Bojidarka B. Ivanova, Michael Spiteller
For synthesis of Zn(II) complexes please read the papers:
2. Gas-phase CT-stabilized Ag(I) and Zn(II) metal–organic complexes – Experimental versus theoretical study, Polyhedron, 30,2011, 2564-2573
Marc Lamshöft, Jürgen Storp, Bojidarka Ivanova, Michael Spiteller
and
3. AgI and ZnII complexes with possible application as NLO materials – Crystal structures and properties, Polyhedron, 30, 2011, 241-245
Bojidarka Ivanova, Michael Spiteller
Under the shown conditions you would obtain as welll complexes with sulfa-drugs, which are objects of your interest because of it is avoided the formation of Zn(OH)2 under the increasing of the pH. At neutral pH o9r low pH values it has low probability to obtain complexes of Zn(II).
...for Zn(II) complexation with Schiff's bases you woulld try also the conditions in :
4. Structural and spectroscopic study of novel Ag(I) metal–organic complexes with dyes – Experimental vs. theoretical methods, Inorganica Chimica Acta, Volume 382, 2012, 96-104, M. Lamshöft, C. Stolle, J. Storp, B. Ivanova, M. Spiteller
Nevertheless that the report is on AgI-complexes, with Zn(II) also it yielded successful results. Furthermore the Zn(II) is with stable oxidation state, therefore, there has not the usual redox process of the metal ion like those of AgI/AgIII/Ag0.