EFFECT OF POLYMORPHISM ON THE LUMINESCENT PROPERTIES ON SILVER(I) NITRATE COMPLEXES WITH 2-AMINO-5-PHENYLPYRAZINE

The reaction between AgNO3 and 2-amino-5-phenylpyrazine (L) at a molar ratio Ag:L = 1.5:1 (synthesis time 3-4 h) in the acetonitrile solution leads to the formation of [AgL2NO3] complex (1). According to the single crystal X-ray diffraction data, two L molecules are coordinated to each silver atom through the N1 atom of the pyrazine ring and one NO3- anion. Polymorph 2 is obtained by the reaction between AgNO3 and L at a 1:2 molar ratio and a short synthesis time (3-30 min). Complex 2 consists of two moieties ([AgL2](+) and [AgL2(NO3)(2)]-) in which silver atoms have different coordination environments: almost linear and distorted tetrahedral respectively. In photoluminescence spectra of the solid complexes, two emission bands are observed, which appear after light irradiation with different wavelengths. Upon the excitation in the range of 300-400 nm, both complexes exhibit blue emission (lambda(max) = 445 nm for 1, lambda(max)= 430 nm for 2). Upon the excitation with lambda(ex) = 440-500 nm, green emission is observed (lambda(ex) = 545 nm for 1, lambda(max) = 530 nm for 2). Both bands are characterized by the biexponential decay kinetics with nano- and microsecond lifetimes of the excited state.