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J Am Chem Soc ; 130(26): 8261-70, 2008 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-18533720


The oxychalcogenides A2F2Fe2OQ2 (A = Sr, Ba; Q = S, Se), which contain Fe2O square planar layers of the anti-CuO2 type, were predicted using a modular assembly of layered secondary building units and subsequently synthesized. The physical properties of these compounds were characterized using magnetic susceptibility, electrical resistivity, specific heat, (57)Fe Mossbauer, and powder neutron diffraction measurements and also by estimating their exchange interactions on the basis of first-principles density functional theory electronic structure calculations. These compounds are magnetic semiconductors that undergo a long-range antiferromagnetic ordering below 83.6-106.2 K, and their magnetic properties are well-described by a two-dimensional Ising model. The dominant antiferromagnetic spin exchange interaction between S = 2 Fe(2+) ions occurs through corner-sharing Fe-O-Fe bridges. Moreover, the calculated spin exchange interactions show that the A2F2Fe2OQ2 (A = Sr, Ba; Q = S, Se) compounds represent a rare example of a frustrated antiferromagnetic checkerboard lattice.

Inorg Chem ; 45(2): 917-22, 2006 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-16411731


We could predict the structure of a new family of compounds Ae(2)F(2)SnX(3) (Ae = Sr, Ba; X = S, Se) from the stacking of known 2D building blocks of the rock salt and fluorite types. With a high-temperature ceramic method we have then succeeded to synthesize the four compounds Ba(2)F(2)SnS(3), Ba(2)F(2)SnSe(3), Sr(2)F(2)SnS(3), and Sr(2)F(2)SnSe(3). The structure refinements from X-ray powder diffraction patterns have confirmed the structure predictions and showed their good accuracy. The structure of the four compounds results from the alternated stacking of fluorite [Ae(2)F(2)] (Ae = Sr, Ba) and distorted rock salt [SnX(3)] (X = S, Se) 2D building blocks. As shown by band structure calculations, these blocks behave as a charge reservoir and a charge acceptor, respectively. Sr(2)F(2)SnS(3) and Ba(2)F(2)SnS(3) are transparent with optical gaps of 3.06 and 3.21 eV, respectively. However, an attempt to obtain a transparent conductor by substituting Ba per La in Ba(2)F(2)SnS(3) was unsuccessful.