New Hydrogen Peroxide Adducts of Alkali Metal Tetracyanoplatinates
A2[Pt(CN)4] · H2O2 (A = K, Rb, Cs)
Claus Mu¨hle, Eva-Maria Peters, and Martin Jansen
Max-Planck-Institut fu¨r Festko¨rperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
Reprint requests to Prof. Dr. Martin Jansen. Fax: ++49-0711-6891502. E-mail: m.jansen@fkf.mpg.de
Z. Naturforsch. 2009, 64b, 111 – 115; received October 13, 2008
Dedicated to Professor Otto J. Scherer on the occasion of his 75th birthday
The title compounds have been synthesized by adding hydrogen peroxide to an aqueous solu-
tion of A2[Pt(CN)4] (A = K, Rb, Cs). They grow as yellow needles after concentrating and cooling
◦
to 4 C. The structures were elucidated from single crystal analysis. The isostructural compounds
crystallize monoclinically, in space group C2/c with Z = 4. K2Pt(CN)4 · H2O2: a = 13.3751(7), b =
◦
3
˚
˚
11.2713(6), c = 6.5461(3) A, β = 105.432(1) , V = 951.3(3) A . Rb2Pt(CN)4 · H2O2: a = 13.6103(2),
◦
3
˚
˚
b = 11.6759(1), c = 6.5683(7) A, β = 106.588(2) , V = 1000.3(2) A . Cs2Pt(CN)4 · H2O2: a =
◦
3
˚
˚
13.9569(2), b = 12.2023(2), c = 6.5857(9) A, β = 107.590(3) , V = 1069.1(2) A . As a remark-
able feature, the hydrogen bonds O–H···N vary significantly with the cation size: in the Cs compound
the O–H bonds are weakest, and the N···H interactions are strongest. All three compounds were
characterized by differential thermal analysis, thermogravimetry and infrared spectroscopy.
Key words: Crystal Structure, Alkali Metal Tetracyanoplatinate, Hydrogen Peroxide,
Infrared Spectroscopy
Introduction
sive review has been given by Williams in [4], in-
cluding reports on Rb1.6[Pt(CN)4] · 2 H2O [5] and
Cs1.75[Pt(CN)4] · y H2O [4]. We have continued in
this field [6, 7] focusing on getting more information
about the partially oxidized cyanoplatinates, in partic-
ular how they form. Our attempts to synthesize the
rubidium-deficient cyanoplatinate following the con-
ventional route suggested by Levy [2] and Williams
[5] sometimes resulted in the formation of yellow nee-
dles of an unknown phase. We found out that hydro-
gen peroxide in such instances did not oxidize plat-
inum at neutral conditions, instead yellow needles
form which are hydrogen peroxide adducts of the for-
mula A2[Pt(CN)4] · H2O2 (A = K, Rb, Cs). Here we
report on their structure analyses by X-ray crystallo-
graphy, and characterization of the new adducts by in-
frared spectroscopy (IR), thermogravimetry (TG) and
differential thermal analysis (DTA).
Substantial progress in the cyanoplatinate chem-
istry has been marked by the structural character-
ization of partially oxidized salts by Krogmann in
the 1960ies [1]. He revealed a significant contrac-
tion of the Pt–Pt distances in the oxidized products
K2[Pt(CN)4]X0.33 · y H2O (X = Cl, Br) to distances
˚
as short as 2.88 A [1], which is only slightly longer
˚
than in metallic platinum (2.77 A), suggesting signif-
icant bonding interactions between the partially filled
Pt dz orbitals. The oxidized cyanoplatinates thus can
2
be considered as one-dimensional metals, in accor-
dance with their relatively high electron conductiv-
ity. The first experiments to obtain partially oxidized
potassium cyanoplatinates by adding hydrogen per-
oxide and sulfuric acid to respective aqueous solu-
tions were performed by Levy [2] at the beginning
of the 20th century. In 1968, Krogmann [3] solved
the structure and determined the composition of the
product to be K1.74[Pt(CN)4] · 1.8 H2O, exhibiting a
Experimental Section
Synthesis
˚
Pt–Pt distance of 2.96 A. Since Krogmann’s pio-
neering work the amazing structure-property correla-
tions in this class of compounds have been treated
K2[Pt(CN)4] · 3 H2O was obtained from K2[PtCl4]
(Chempur, 99.9 %) and KCN as described previously [6, 8].
in a huge number of publications. A comprehen- This salt was recrystallized three times from water to re-
c
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