From 1D chain to 3D network: Tuning hybrid II-VI nanostructures and their optical properties

In an effort to make semiconductor nanomaterials with tunable properties, we have deliberately designed and synthesized a family of novel organic - inorganic hybrid nanocomposites based on II-VI semiconductors with structures ranging from one-dimensional (1-D) chain to two-dimensional layer (2-D) to three-dimensional (3-D) framework. All nanostructures exhibit strong quantum confinement effect (QCE), while possessing a perfectly periodic arrangement. The optical absorption experiments show that all compounds generate a very large blue shift in the absorption edge (1.0-2.0 eV) due to the strong QCE. More significantly, their band edge shift and optical properties can be tuned by changing the dimensionality of inorganic motifs as well as overall crystal structures. Raman studies reveal that not only do these structures have distinctly different vibrational signatures from those of the II-VI host semiconductors, but they also differ significantly from each other as a result of changes in dimensionality. The crystal structures of these nanocomposite materials have been characterized by single crystal and/or powder X-ray diffraction methods. [ZnTe(pda)] (1; pda = propanediamine) is composed of 1-D chains of [ZnTe] with pda chelating to Zn atoms. [ZnTe(N₂H₄)] (2; N₂H₄ = hydrazine) and [ZnTe(ma)] (3; ma = MeNH₂ = methylamine) are two-dimensional (2-D) layered structures containing [ZnTe] slabs and terminal hydrazine (2) or methylamine (3) molecules. The crystal structures of [CdSe(en)_0.5] (4; en = ethylenediamine) and [CdSe(pda)_0.5] (5) are 3-D networks containing [CdSe] slabs bridged by bidentate organic diamine molecules. Crystal data for 1: Orthorhombic, space group Pbcm, a = 9.997(2), b = 6.997(1), c = 10.332(2) Å, Z = 4. For 2: Monoclinic, space group P2₁, a = 4.2222(6), b = 6.9057(9), c = 7.3031 (10) Å, β = 98.92(8)°, Z = 2. For 3: Orthorhombic, Pbca, a = 7.179(1), b = 6.946(1), c = 18.913(4) Å, Z = 8. For 4: Orthorhombic, Pbca, a = 7.0949(3), b = 6.795(3), c = 16.7212(8) Å, Z = 8. For 5: Orthorhombic, Cmc2₁, a = 20.6660(12), b = 6.8900(4), c = 6.7513(4) Å, Z = 8.