Structural aspect of the adduct formation mechanism of metal β-diketonate complexes with macrocyclic polyethers. The structure of the intermediate—The 1:1 guest-host complex of calcium nitrate with 18-crown-6

We compare the structures of intermediate and final products in adduct formation of metal β-diketonate complexes with macrocyclic polyethers using [Ca(NO₃)₂(18C6)] (I) and [Ca(HFA)₂(18C6)] (II), where 18C6 is 18-crown-6 and HFA is hexafluoroacetylacetone. Adduct formation occurs by replacement of nitrate groups in I by HFA ligands with preservation of the coordination number of calcium and the conformation of the macrocycle but with variation in the coordination polyhedron of calcium. Both structures have the same packing mode: the centers of the complexes (Ca atoms) are located in the nodes of planar nets (Shlafly symbol 4⁴) forming two stories parallel to the shortest translations of the monoclinic cell in the same space group C2/c. Because of great size and nonisometricity of HFA ligands as compared to the nitrate group, the planar nets in (II) are well separated, and the tetragons are substantially distorted as compared to those in (I). This structural mechanism of adduct formation is supposed to be true for other complex-forming metals and β-diketonate ligands. X-ray structural analysis and interpretation of results. Synthesis of single crystals. Instute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 56–66, May–June, 1994. Translated by T. Yudanova