Elsevier

Polyhedron

Volume 28, Issue 11, 6 July 2009, Pages 2097-2102
Polyhedron

Cadmium thiosemicarbazide complexes as precursors for the synthesis of nanodimensional crystals of CdS

https://doi.org/10.1016/j.poly.2009.02.046Get rights and content

Abstract

The single X-ray structures of the thiosemicarbazide complexes [Cd(NH2CSNHNH2)Cl2]n·H2O (A) and [Cd(NH2CSNHNH2)2Cl2]n (B) are reported. Both compounds have been found to be effective as single source precursors for the preparation of CdS nanomaterials. Thermal decomposition of the precursors in hexadecylamine (HDA) results in the formation of nanorods of different dimensions. The powder X-ray diffraction patterns of the nanodimensional materials reveal differences in the phases of the CdS synthesized from the two complexes. The particles synthesized from both precursors show quantum confinement effects in their absorption spectra, with the evidence of a broad defect emission in their photoluminescence spectra.

Graphical abstract

Anisotropic cadmium sulfide nanocrystals have been prepared from two thiosemicarbazide complexes. Thermal decomposition of the precursors in hexadecylamine (HDA) results in the formation of nanorods of different dimensions. The powder X-ray diffraction patterns of the nanodimensional materials reveal differences in the phases of the CdS synthesized from the two complexes. Transmission Electron Microscopy (TEM) was used to study the morphology of the final materials.

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Introduction

Rods of semiconductor nanoparticles were prepared by Alivisatos et al. [1] by adding hexylphosphonic acid (HPA) in an attempt to modify crystal growth. Numerous reports on the synthesis of metal chalcogenide nanorods, including those of CdSe [2], CdTe [3] and CdS [4], [5], [6], [7], followed. Peng et al. have studied various factors that influence the formation of particles with non-spherical morphologies for CdSe [8]. Their work suggests that the nature of the precursor, the rate of nucleation and the nature of the capping agent are all potential factors affecting particle morphology. We have recently shown that the ratio of surface area to volume [7] and feed ratios are significant parameters in the formation of these small particles [9]. In Peng’s work, cadmium chalcogenide (CdE; E = S, Se) nanoparticles were synthesized using CdO and Cd(O2CCH3)2 together with an alkylphosphonic acid. The study showed that the rod shaped particles formed in reactions with high monomer concentrations. At intermediate monomer concentrations the nanoparticles grow to give a mixture of spheres and rods. At low monomer concentrations the particles are exclusively close to spherical. There have been relatively few reports of the preparation of nanorods of CdS by colloidal routes [10], [11], [12], [13], [14], [15], [16], [17], and such work remains of current interest.

Group IIB metal complexes of thiosemicarbazides and thiosemicarbazones have been themselves identified as compounds which have potential for applications as non-linear optic materials [18], [19]. Cadmium complexes of these ligands are thermally stable with large second harmonic generation (SHG) efficiencies [20], [21].

Here we report the synthesis and structure of two cadmium complexes containing the thiosemicabazide ligand, and the preparation of CdS rods via their thermal decomposition in hexadecylamine (HDA). Thiosemicarbazide has been shown to be a good ligand for a range of metals, including zinc, mercury, cadmium and nickel [22], [23]. Furthermore the related bis-bromo complex is also known for cadmium [24]. This earlier work suggests that these complexes offer an excellent opportunity for the study of the effects of the ligand system on the formation of nanomaterials.

Section snippets

Materials

Ethanol, methanol, toluene, chloroform, thiosemicarbazide (analytical grade), hexadecylamine (HDA), tri-n-octylphosphine and cadmium chloride (analytical grade) were purchased from Aldrich. All the reagents were used as purchased without further purification.

Physical measurements

Absorption spectra were measured on a Helios B UV-spectrophotometer in chloroform in a 1 cm path length cell. Photoluminescence measurements were carried out on a Horiba Fluorolog-3 (FL3-22) in chloroform with a 1 cm path length. The p-XRD

Structure of complex (A) [Cd(NH2CSNHNH2)Cl2]n·H2O

The structure of complex A (Fig. 1) is very similar to that reported by Woode et al. [28], showing only a small variation in the unit cell with a similar bonding arrangement. The compound crystallises into the monoclinic Cc space group. Complex B (Fig. 2), on the other hand, crystallises in the monoclinic C2/c space group. The lattice of complex B consists of infinite chains of CdCl4 units linked into CdL2 units via a Cd–S–Cd bridge (L is a thiosemicarbazide). The chloride ions lie almost

Conclusions

Cadmium thiosemicarbazide complexes are useful precursors for the preparation of anisotropic cadmium sulfide nanomaterials. Furthermore the nature of the precursor and the ease of thermal decomposition can significantly affect the morphology of the final products.

Supplementary data

CCDC 602904 and 602905 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected].

Acknowledgements

We would like to thank the EPSRC, RCUK and the NRF South Africa for funding, that made this work possible.

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