Infrared spectra of silver complexes with 2-aminopyridine and crystal structure of the 4:3 aminopyridine-silver nitrate compound

The 43 complex formed between 2-aminopyridine (ampy) and AgNO₃ belongs to the orthorhombic space groupPccn. The unit cell of dimensionsa=7.992(4),b=16.788(5),c=21.034(8) Å contains four formula units. The structure was refined on 998 nonzero reflections toR=0.038. The crystal contains the dimeric Ag₃(ampy)₄]³⁺ cation. Two of the three independent Ag atoms are each coordinated to two ampy ligandsvia the heterocyclic nitrogen lone pair (mean Ag-N=2.18 Å), and the N-Ag-N angle in this ampy-Ag-ampy]⁺ unit is 154.0°. By using the two available amino groups, the ampy-Ag-ampy]⁺ unit acts as a bidentate ligand, and two such units related by a twofold axis achieve a roughly tetrahedral environment of NH₂ lone pairs about the third Ag atom (mean Ag-N=2.39 Å). The infrared spectra of Ag₃(ampy)₄](NO₃)₃, Ag(ampy)₂]ClO₄, Ag₃(ampy-H)₂]NO₃, and Ag₃(ampy-H)₂]ClO₄, and those of their amino-deuterated derivatives, are discussed. Diagnostic regions are proposed to identify coordinationvia the amino group and the heterocyclic nitrogen atom.