Polymeric silver(I) complexes of the multinucleating ligand 4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine. Analogous hydrogen-bonded structures in the crystal and vapour phases of the ligand

Abstract

X-Ray crystallography showed that the crystal structure of Hmtpo (4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine) is built up of hydrogen-bonded polymeric chains, whereas mass spectroscopy and solution ¹⁵N NMR spectroscopy suggested the existence of a dimeric structure comprising eight-membered · · · H–N –C–N · · · H–N –C–N rings in less condensed phases. On the other hand, the reaction between the silver(I) salts AgX (X = NO₃, ClO₄ or ½SO₄) and Hmtpo yielded polymeric complexes. The compounds have been structurally characterised by IR spectroscopy and X-ray crystallography. The X-ray results show that the compounds containing the Hmtpo derivative in its neutral form comprise infinite one-dimensional chains, in which the ligand bridges the metal centres through N(1) and N(3) donor atoms. The presence of an additional soft and bulky ligand such as triphenylphosphine in [{AgX(µ-Hmtpo-κ²N ¹ ,N ³)(PPh₃)}_n ] (X = NO₃ or ClO₄) partially changes the tendency to form polymeric complexes, lengthening the Ag–N(1) bond distance by 0.35 Å. Finally, deprotonation of Hmtpo results in an additional available coordination position at N(4), the ligand bridging three metal centres in [{Ag₃(µ₃-mtpo-κ⁴N  ¹,N ³,N  ⁴,O⁷)₂(HSO₄)(H ₂O)₂]·H₂O}_n ]. The new co-ordination mode results in the formation of eight-membered Ag–N–C–N–Ag–N–C–N rings, which give rise to short intermetallic contacts of 3.078(1) Å. The structures of free Hmtpo in the solid state and the postulated vapour-phase structure are compared to those of linear co-ordinated silver(I) complexes.

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