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The title compound was synthesized in an attempt to produce stacked benzene-like Sn6 6- rings separated by alkaline-earth cations in analogy with the recently reported stacks of aromatic cyclopentadienyl-like Sn 5 6- in Na8BaSn 6 (in addition to isolated Sn 4- anions). The resulting compound, synthesized from a stoichiometric mixture of the elements at high temperature, has the “correct” stoichiometry with six tin atoms and six positive charges. However, the rings of Sn 6 6- are puckered into chair-type cyclohexanes that are interconnected into isolated cylindrical tubes stuffed with Ca2+ between the rings. Such tubes, if fused to each other, form the hexagonal diamond structure. The new compound is electronically balanced according to magnetic and four-probe resistivity measurements. Reported are also the synthesis and properties of Na 10EuSn12 and Na10YbSn12 which are isostructural with the known Na 10CaSn12.

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.

The title compounds were prepared by direct reactions of the corresponding elements at high temperature. They are isostructural with each other (monoclinic, P2(1)/m, Z = 2; Na(8)BaPb(6), a = 13.116(4), b = 5.351(1), and c = 16.166(5) A, beta = 108.07(2) degrees; Na(8)BaSn(6), a = 12.897(4), b = 5.362(1), and c = 16.826(5) A, beta = 108.19(2) degrees; Na(8)EuSn(6), a = 12.912(2), b = 5.220(1), and c = 15.721(2) A, beta = 108.09(1) degrees ) and contain isolated, flat, and aromatic pentagonal rings of Sn(5)(6)(-) and Pb(5)(6)(-) as well as isolated anions of Sn(4)(-) and Pb(4)(-). According to four-probe conductivity measurements, the tin compounds, Na(8)BaSn(6) and Na(8)EuSn(6), are semiconducting with band gaps of 0.11 and 0.09 eV, respectively, and are therefore electronically balanced. Magnetic measurements show that Na(8)BaSn(6) is diamagnetic while Na(8)EuSn(6) is paramagnetic and undergoes two transitions at low temperatures.

We report the synthesis, structure, spectroscopic properties, charge and thermal transport, and electronic structure of a new member of the Zintl family, Yb(5)Al(2)Sb(6). The compound crystallizes in the Ba(5)Al(2)Bi(6) structure type and requires the addition of Ge or Si in the synthesis, which appears to act as a catalyst. Yb(5)Al(2)Sb(6) has an anisotropic structure with infinite anionic double chains cross-linked by Yb(2+) ions. Polycrystalline ingots of Yb(5)Al(2)Sb(6) prepared in the presence of 0.5 mol equiv of Ge showed room-temperature conductivity, thermopower, and thermal conductivity of approximately 1100 S/cm, approximately 20 microV/K, and approximately 3.8 W/m.K, respectively. Investigations of other solid solutions of Yb(5)Al(2)Sb(6), doping effects, and chemical modifications are discussed. Sr only partially replaces Yb in the structure leading to Sr(0.85)Yb(4.15)Al(2)Sb(6). Electronic structure calculations performed using a highly precise full-potential linearized augmented plane wave method within the density functional theory scheme show the presence of a negative band gap and suggest incomplete electron transfer and a metallic character to the compound.

The title compounds were prepared by direct reactions of the corresponding elements at high temperature. They are isostructural and crystallize in the chiral orthorhombic space group P212121 (Li2Ce5Sn7: a = 6.273(1), b = 13.839(2), and c = 17.467(2) A; Li2Pr5Sn7: a = 6.241(1), b = 13.762(2), and c = 17.367(1) A; Li2Sm5Sn7: a = 6.262 (1), b = 13.809(1), and c = 17.432(1) A; Li2Eu5Sn7: a = 6.165(1), b = 13.562(2), and c = 17.128(1) A). The structure contains isolated Sn7 oligomers that resemble the carbon core of an open-chain heptane molecule C7H16. Although these heptamers are stacked along the a axis at a distance that is comparable to the distances within the heptamer, electronic structure calculations show that this intermolecular contact is nonbonding for a formal charge of 16- or higher per heptamer. A hypothetical lower charge of 14-, on the other hand, leads to positive and substantial bond-overlap population that would result in branched infinite chains of infinity[Sn714-]. Magnetic measurements of the Ce and Pr compounds indicate a 3+ oxidation state for the rare-earth cations and, therefore, 17 available electrons from the cations per formula unit. According to four-probe conductivity measurements, the compounds are metallic.

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. Li(9)(-)(x)()EuSn(6+)(x)(), Li(9)(-)(x)()CaSn(6+)(x)(), Li(5)Ca(7)Sn(11), and Li(6)Eu(5)Sn(9) contain columns of stacked aromatic pentagons of Sn(5)(6)(-) that are analogous to the cyclopentadienyl anion C(5)H(5)(-). The pentagons are separated with Ca(2+) or Eu(2+) in the columns and resemble a polymeric metallocene. In addition to the columns, the isostructural Li(9)(-)(x)()EuSn(6+)(x)() and Li(9)(-)(x)()CaSn(6+)(x)() contain isolated tin atoms and bent tin trimers while Li(5)Ca(7)Sn(11) and Li(6)Eu(5)Sn(9) contain flat zigzag hexamers and flat zigzag infinite chains of tin, respectively. The isostructural LiMgEu(2)Sn(3) and LiMgSr(2)Sn(3) do not contain columns of pentagons but only flat zigzag infinite chains of tin. The aromaticity of the pentagons and the conjugation of the pi-systems of the hexamers and the infinite chains are discussed. The title compounds are also characterized by magnetic and conductivity measurements.