FORMATION OF QUANTUM-SIZE SEMICONDUCTOR PARTICLES IN A LAYERED METAL PHOSPHONATE HOST LATTICE

Quantum-size ZnSe, PbS, CdS, and CdSe particles 30-50 angstrom in diameter were grown in the interlamellar region of the layered host material Zr(O3PCH2CH2CO2H)2 by reaction of H2S or H2Se with M(II)[Zr-(O3PCH2CH2CO2)2]. Diffraction from the PbS particles indicated the rocksalt structure, whereas CdSe adopts the zincblende structure and grow with the [111] zone axis parallel to the host layering direction. CdSe crystallites within a single host platelet are oriented relative to each other, even though the crystallinity of the host is destroyed during particle growth. Little or no reaction was found under similar conditions with M(II)[Zr(PO4)2]. It is postulated that M(II)[Zr(O3PCH2CH2CO2)2], prepared by dehydration of M(II)[Zr(O3PCH2CH2CO2)2].xH2O (x almost-equal-to 1.4) has an open structure that allows for interlamellar diffusion of H2S and H2Se. Contraction of the layer axis upon dehydration is significantly smaller for M(II)[Zr(O3PCH2CH2CO2)2].xH2O than for M(II)[Zr(PO4)2].yH2O. For comparison, an analogously layered compound, Zn[Zn(O3PCH2CH2CO2)]2.3H2O, was prepared and structurally characterized. This compound crystallizes in orthorhombic space group Pbcn (No. 60) with a = 5.126 (1), b = 10.837 (2), c = 28.596 (9) angstrom, V = 1588.5 angstrom-3, Z = 4, R = 0.028, R(W) = 0.033 for 1567 unique reflections with F(o) > 3-sigma(F(o)). The structure contains one set of zinc atoms four-coordinated by oxygen atoms of the phosphonate groups and another set five-coordinated by oxygen atoms of the carboxyl groups and lattice water molecules. The repeating unit is Zn/O3PCH2CH2CO2/Zn(H2O)3/O2CCH2CH2PO3/Zn... along the layering (c axis) direction. Complete dehydration of this compound causes a relatively small decrease in the layer spacing, from 28.6 to 28.0 angstrom.