Yeni piridin-karboksamid schiff bazı ve Nİ(II), CU(II) ve CD(II) komplekslerinin sentezi, spektral karakterizasyonu ve antioksidan aktivite çalışmaları Synthesis, spectral characterization and antioxidant activity studies of new pyridine-carboxamide schiff base and its NI(II), CU(II) and cCD(II) complexes