Heavy-Metal Aromatic and Conjugated Species: Rings, Oligomers, and Chains of Tin in Li<sub>9</sub><sub>-</sub><i><sub>x</sub></i>EuSn<sub>6+</sub><i><sub>x</sub></i>, Li<sub>9</sub><sub>-</sub><i><sub>x</sub></i>CaSn<sub>6+</sub><i><sub>x</sub></i>, Li<sub>5</sub>Ca<sub>7</sub>Sn<sub>11</sub>, Li<sub>6</sub>Eu<sub>5</sub>Sn<sub>9</sub>, LiMgEu<sub>2</sub>Sn<sub>3</sub>, and LiMgSr<sub>2</sub>Sn<sub>3</sub>
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The title compounds were synthesized from the elements by heating the corresponding mixtures at high temperature. Their structures were determined from single-crystal X-ray diffraction. Li9-xEuSn6+x, Li9-xCaSn6+x, Li5Ca7Sn11, and Li6Eu5Sn9 contain columns of stacked aromatic pentagons of Sn56- that are analogous to the cyclopentadienyl anion C5H5-. The pentagons are separated with Ca2+ or Eu2+ in the columns and resemble a polymeric metallocene. In addition to the columns, the isostructural Li9-xEuSn6+x and Li9-xCaSn6+x contain isolated tin atoms and bent tin trimers while Li5Ca7Sn11 and Li6Eu5Sn9 contain flat zigzag hexamers and flat zigzag infinite chains of tin, respectively. The isostructural LiMgEu2Sn3 and LiMgSr2Sn3 do not contain columns of pentagons but only flat zigzag infinite chains of tin. The aromaticity of the pentagons and the conjugation of the π-systems of the hexamers and the infinite chains are discussed. The title compounds are also characterized by magnetic and conductivity measurements.
