tellurido- ligands are often less stable and more difficult to prepare than their thio- analogues.
However a lot of different coordination compounds were found to be suitable as SSPs to
prepare metal chalcogenides, but the syntheses of starting materials are often complicated. Let
us point out dichalcogenido derivatives of R2PNHPR2. Complexes of both diseleno- and
ditelluroimidophosphinate ligands with cadmium and other p- or d-block metals were
prepared and successfully decomposed forming the corresponding selenides or tellurides [3].
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. In our previous work we have demonstrated that CdTe and HgTe may
be synthesized by a direct reaction of bis(diphenylphosphino)amine (PPA) with elemental
tellurium and cadmium carbonate, or mercury oxide, respectively [4]. In this process, the PPA
acts as a reducing agent for reduction of tellurium to telluride and also as a donor of protons
that react with the metal precursor. Using this approach the synthesis leads to simplification
because the whole reaction takes place in one step in an autoclave.
3-(Diphenylphosphino)propionic acid and its P=O and P=S analogues are commonly
known in organic chemistry as ligands for Cu-based catalysts of coupling reactions [5,6] and
in biochemistry as precursors for phosphine-containing peptides [7,8] or other interesting
biologically active compounds [9]. Nevertheless it also fits both our conditions to be used as a
precursor for metal chalcogenide synthesis. It contains an acidic proton that may react with
metal carbonate or oxide and also a phosphorus(III) atom that may reduce chalcogen to
chalcogenide.
In this study we present structures of known P=E derivatives of 3-
(diphenylphosphino)propionic acid (E = O and S). The seleno- analogue was also synthesized
and structurally characterized and the synthesis of P=Te analogue is discussed. Mainly, we
present a method of synthesis of cadmium, mercury and lead selenides and tellurides by a
direct, one-step reaction between elemental chalcogen, metal oxide or carbonate and 3-
(diphenylphosphino)propionic acid at temperatures below 200 °C.
2. Experimental
2.1 Materials and methods
All chemicals were purchased commercially and used without further purification.
NMR spectra were recorded on a Bruker Avance III 500 MHz spectrometer operating at
frequency 202.45 MHz (31P) and 95.38 MHz (77Se). 31P NMR chemical shifts are reported
relative to 85% H3PO4, 77Se NMR spectra were referenced against the secondary standard
SeO2 in D2O (chemical shift + 1303 ppm).
Powder X-ray diffration (PXRD) data were collected on a Rigaku SmartLab diffractometer
equipped with Cu fine focus tube (λKα1 = 1.54060 Å, λKα2 = 1.54443 Å and λKβ = 1.39225 Å).
Single crystal X-ray diffraction data were collected on a Rigaku diffractometer equipped with
rotating anode X-ray source (multilayered optics, MoKα radiation), partial χ axis goniometer,
CCD detector (Saturn 724+ HG) and Oxford Cryosystems cooling device. All diffraction
experiments were carried out at T = 120 K. Data were collected with CrystalClear [10]
software and processed with CrysAlisPro [11]. The structures were solved and refined using
SHELX software [12]. All C-H hydrogen atoms were placed at calculated positions and were
refined as riding, with their Uiso set to 1.2 Ueq of the carrier atom. All O–H hydrogen atoms
were refined as riding and rotating, with their Uiso set to 1.5 Ueq of the carrier atom.
2