Silver complexes with triazolopyrimidine ligands containing an exocyclic oxygen atom: X-ray evidence for an unusual tautomeric form

The crystal structures of the silver complexes [Ag-2(5HtpO)(2)][NO3](2) 1, [Ag-2(5HtpO)(2)][ClO4](2). 2H(2)O 2 and {[Ag(7HtpO)]ClO4}(n) 3, where the l igands are the triazolopyrimidine derivatives 4,5-dihydro-5-oxo[1,2,4]triaz olo[1,5-a]pyrimidine (5HtpO) and 4,7-dihydro-7-oxo[1,2,4]triazolo[1,5-a]pyr imidine (7HtpO), are described. 1 and 2 are binuclear compounds, with two l igands bridging two silver atoms through their nitrogen atoms at positions 3 and 4. The ligand in these compounds is in an unusual tautomeric form wit h its acidic proton attached to the exocyclic oxygen atom, which influences its geometric and spectroscopic (infrared) properties. On the other hand, the ligand 7HtpO in compound 3 is in its usual tautomeric form and binds tw o different silver atoms through its nitrogen atoms in positions 1 and 3, b uilding infinite -Ag-7HtpO-Ag-7HtpO- chains.