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 ligands are the triazolopyrimidine derivatives 4,5-dihydro-5-oxo[1,2,4]triazolo[1,5-a]pyrimidine (5HtpO) and 4,7-dihydro-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine (7HtpO), are described. 1 and 2 are binuclear compounds, with two ligands bridging two silver atoms through their nitrogen atoms at positions 3 and 4. The ligand in these compounds is in an unusual tautomeric form with 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 two different silver atoms through its nitrogen atoms in positions 1 and 3, building infinite -Ag-7HtpO-Ag-7HtpO- chains.