Method for producing aqueous preparations of complexes of platinum group metals
The invention relates to a method for producing aqueous preparations of complexes of platinum group metals (PGM) Pt, Pd, Rh and Ir having the general formula [M A /M B /M C (L) a (H 2 O) b (O 2 —) c (OH − ) d] (OH—) e (H + ) f , wherein M A =Pt II or Pd II , M B =Pt IV , M C =Rh or Ir, L is a neutral monodentate or bidentate donor ligand, and a is an integer between 1 and 4 (or 2) and/or between 1 and 6 (or 3), b is an integer between 0 and 3 (or 5), c is an integer between 0 and 3 (or 4), d is an integer between 0 and 3 (or 5), e is an integer between 0 and 2 (or 3 or 4) and f is an integer between 0 and 4 (or 5). In the method according to the invention, the hydroxo complexes H 2 P d (OH) 4 (in the case of M A =Pd II ), H 2 Pt(OH) 6 (in the case of M A =Pt II and M B =Pt IV ) or H 3 M C (OH) 6 (for M C =Rh III Ir III ) are converted in the presence of the donor ligands, wherein at least one hydroxo group of the hydro complex is exchanged. Preferably, the reaction occurs at temperatures in the range of 40 to 110° C. with a reaction time of between 2 and 24 hours, wherein, where MA=PtII, the conversion additionally occurs in the presence of a reduction agent. The method optionally further comprises an exchange of OH anions bound outside of the complex sphere with other anions (e.g. hydrogen carbonate or carbonate anions). The aqueous preparations contain PGM complexes such as [Pt(en) 2 ](OH) 2 , [Pt(EA) 4 ](OH) 2 or [Rh(NH 3 ) 6 ](OH) 3 and are used to produce electroplating baths, heterogeneous catalysts or metal powders, for example.
1. A process for producing electroplating baths, for producing heterogeneous catalysts, for preparing further complexes or for preparing metal powders, which comprises the steps:
providing water-containing preparations of complexes of the platinum group metals (PGM) having the general formula (1)
[M A (L) a (H 2 O) b (O 2− ) c (OH − ) d ](OH − ) e (H + ) f (1)
where
M A =platinum (Pt) or palladium (Pd) in the oxidation state +2 and
L=an uncharged monodentate or bidentate donor ligand and
a=an integer from 1 to 4 (for monodentate donor ligands) or an integer from 1 to 2 (for bidentate donor ligands),
b=an integer from 0 to 3,
c=an integer from 0 to 3,
d=an integer from 0 to 3,
e=an integer from 0 to 2 and
f=an integer from 0 to 4
and the platinum group metal M A has the coordination number 4,
wherein the hydroxo complexes H 2 Pd(OH) 4 (in the case of M A =Pd) or H 2 Pt(OH) 6 (in the case of M A =Pt) are in each case reacted with an uncharged donor ligand L, where at least one hydroxo group of the hydroxo complex concerned is replaced and in the case of M A =Pt the reaction is carried out in the presence of a reducing agent,
reacting formulation of the water-containing preparations or the complexes of the platinum group metals (PGM) present therein to give electroplating baths, heterogeneous catalysts, further complexes or metal powders.
2. The process as claimed in claim 1 , wherein the step of reaction or formulation of the water-containing preparations or the complexes of the platinum group metals (PGM) present therein comprises a reaction selected from the group consisting of reduction of a complex of the PGM, oxidation of a complex of the PGM, ligand exchange of a complex of the PGM and combinations thereof.
3. The process as claimed in claim 1 , wherein the indices a-f in the general formulae (1), (2) and (3) are selected so that the resulting PGM complexes are electrically neutral.
4. The process as claimed in claim 1 , wherein ammonia or ligands from the group consisting of monoalkylamines, dialkylamines, trialkylamines, monoalkanolamines, dialkanolamines, trialkanolamines, monoarylamines, diarylamines, triarylamines, trialkylphosphines, triarylphosphines, trialkoxyphosphines, triaryloxyphosphines or mixtures thereof are used as monodentate donor ligands.
5. The process as claimed in claim 1 , wherein the nitrogen-containing ligands ammonia, ethanolamine, ethylamine, diethylamine, isopropanolamine or mixtures thereof are used as monodentate donor ligands.
6. The process as claimed in claim 1 , wherein the nitrogen-containing ligands ethylenediamine, o-phenylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1,2-propylenediamine or mixtures thereof are used as bidentate donor ligands.
7. The process as claimed in claim 1 , wherein the replacement of the OH groups in the hydroxo complexes H 2 Pd(OH) 4 , H 2 Pt(OH) 6 or H 3 M c (OH) 6 (in the case of M c =Rh III or Ir III ) by the uncharged donor ligands L is incomplete and the resulting compounds of the general formulae (1), (2) or (3) continue to contain aquo (H 2 O), oxo (O 2− ) or hydroxo (OH − ) ligands.
8. The process as claimed in claim 1 , wherein hydrogen, an H 2 /N 2 mixture, hydrazine (N 2 H 4 ), oxalic acid (H 2 C 2 O 4 ), formaldehyde (HCHO) or formic acid (HCOOH) or mixtures thereof are used as reducing agent in the case of M A =platinum(II).
9. The process as claimed in claim 1 , wherein the water-containing preparations contain organic solvents.
10. The process as claimed in claim 1 , wherein the concentration of the platinum group metals M A , M B or M c in the water-containing preparation is in the range from 0.5 to 15% by weight.