Structural Variation in Novel Double Salts of Silver Acetylide with Silver Nitrate:  Fully Encapsulated Acetylide Dianion in Different Polyhedral Silver Cages

The reaction of silver acetylide with silver nitrate at 80 °C yielded a mixture of the known compounds Ag2C2·6AgNO3 (1) and Ag2C2·5.5AgNO3·0.5H2O (2), which have different crystal habits and could be manually separated. Ag2C2·5AgNO3 (3) was obtained serendipitously as a mixed product together with 1 from the addition of AgNO3 to a solution of the double salt of Ag2C2 with CF3COOAg at 80 °C. Ag2C2·AgNO3 (4) was obtained by carrying out a hydrothermal reaction at 105 °C. Complexes 2 and 3 contain a monocapped octahedral silver cage and a monocapped trigonal prismatic silver cage, respectively, each fully entrapping an acetylide dianion. In complex 4, silver octahedra each encapsulating an acetylide dianion are connected by linking their equatorial edges along the a and b directions to form a slab, and the sharing of apexes between adjacent slabs along the c direction then generates a three-dimensional network. The bonding interaction between the acetylide dianion, which exhibits triple-bond character, and the cage silver atoms in complexes 1−4 is of the mixed σ,π-type, except that with a few silver atoms mainly σ bonding or π bonding can be clearly recognized. The different structural alternatives adopted by this series of related complexes suggests that a higher molar composition of silver acetylide in a double salt favors the formation of a network of edge- and vertex-sharing silver polyhedra that approaches the unknown crystal structure of silver acetylide.