Preparation and characterization of selected metal heavier chalcogenides



Student: Václav Kubát

Supervisor: doc. RNDr. Josef Novosad, CSc.



Metal selenides and tellurides are modern inorganic materials with a variety of applications,
mainly in optical devices such as solar cells, but also in thermoelectrical devices and others [1].
There is considerable interest in studying various methods for the synthesis of these compounds,
above all in a nanoscopic form.

One of the early methods uses a solvothermal reaction between Me[2]Cd and
trioctylphosphinechalcogenide (TOPE, E = S, Se or Te) to produce CdE [2]. This route is quite
efficient, but requires high temperatures and utilization of toxic organometallic compounds.
Another possibility is decomposition of single-source precursors (SSPs), i.e. coordination
compounds that contain both metal (as a central atom) and chalcogen (as a donor atom of the
ligand). The SSPs approach uses lower temperatures and less toxic chemicals compared to the
solvothermal reactions, but it introduces a new difficulty. The ligand and thereafter the complex
must be prepared and isolated, so the whole process of metal chalcogenide synthesis is  rather
complicated [3].


In our work we developed a new synthetic approach for the preparation of metal selenides and
tellurides. Combinig advantages of both mentioned methods we use a direct reaction between a metal
source (metal carbonate or oxide), elemental chalcogen and a phosphine (Ph[2]PNHPPh[2] or
Ph[2]PCH[2]CH[2]COOH) to prepare the appropriate chalcogenide. The resulting chalcogenide is
produced in one synthetic step as the whole process takes place in an autoclave.

As major part of the lecture the chemical nature of the process will be discussed. P-chalcogeno
derivatives of Ph[2]PCH[2]CH[2]COOH were synthesized and structurally characterized as they most
likely are key intermediates of the metal chalcogenide formation reactions. We presume that after a
redox reaction between the phosphine and chalcogen a complex between metal cation and the
P-chalcogen species is formed and it immediately decomposes forming a chalcogenide. We have
demonstrated that our reaction system can be used for the preparation of cadmium, mercury and lead
selenides and tellurides. The products are obtained in very good yields and according to PXRD and
EDX analyses also in good purity. At last, reaction temperatures used for our process are below 200
°C.











References


[1]    M. Afzaal, P. O´Brien, J. Mater. Chem. 16 (2006) 1597 – 1602.

[2]    C.B. Murray, D.J. Norris, M.G. Bawendi, J. Am. Chem. Soc. 115 (1993) 8706 – 8715.

[3]    M. Afzaal, M.A. Malik, P. O´Brien, J. Mater. Chem. 20 (2010) 4031 – 4040.