A trinuclear platinum-cobalt acetate-bridged complex {PtII(acac)}2CoII(μ-OOCMe)4: Synthesis and structure

Article abstract of DOI:10.1016/j.inoche.2007.05.006

Reaction of the platinum(II) acetylacetonate Pt(acac)₂ with Co(OOCMe)₂ · 4H₂O in air produced the Pt^II-Co^II heterodimetallic complex {Pt^II(acac)}₂Co^II(μ-OOCMe)₄ as established by single-crystal X-ray diffraction.

Full text of DOI:10.1016/j.inoche.2007.05.006

Inorganic Chemistry Communications 10 (2007) 956–958
www.elsevier.com/locate/inoche
A trinuclear platinum–cobalt acetate-bridged
complex {PtII(acac)}2CoII(l-OOCMe)4: Synthesis and structure
Natalia Yu. Kozitsyna, Alexander E. Gekhman, Sergei E. Nefedov,
*
Michael N. Vargaftik , Ilya I. Moiseev
N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky Prospect 31, Moscow 119991, Russian Federation
Received 16 March 2007; accepted 6 May 2007
Available online 18 May 2007
Abstract
Reaction of the platinum(II) acetylacetonate Pt(acac)2 with Co(OOCMe)2 Æ 4H2O in air produced the PtII–CoII heterodimetallic com-
plex {PtII(acac)}2CoII(l-OOCMe)4 as established by single-crystal X-ray diffraction.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Platinum; Cobalt; Heterodimetallic complex; Acetate-bridging complex; X-ray structure
Heterobimetallic platinum(II)–cobalt(II) complexes
attract attention as promising precursors for platinum–
cobalt mixed-metal materials and alloys, which find wide
use as materials for catalysis [1–3], high coercivity magnets
[4], storing information [5] and jewelry [6]. Traditionally
these materials are produced by fusion of the component
metals or reduction of mixtures of the corresponding metal
salts. Alternatively, a Pt–Co alloy could be prepared from a
heterobimetallic PtIICoII carboxylate-bridged precursor, by
analogy with the earlier reported [7] Pd–Zn nanoalloy
obtained by easy reduction of the acetate complex PdII(l-
OOCMe)4ZnII(OH2) under mild conditions (5–10% H2/He,
150–250 ꢁC). However, none of the structurally charac-
terized heterometallic PtII–CoII carboxylate complexes
have been documented so far. The only precedent is the
synthesis of the platinum(IV)-based heterodimetallic car-
in this work we used platinum(II) bis(acetylacetonate) (1)
[9] as the initial reagent.
Herein we report the synthesis of a PtII–CoII heterodi-
metallic complex {PtII(acac)}2CoII(l-OOCMe)4 (2) by the
reaction of platinum(II) bis(acetylacetonate) and cobalt(II)
acetate [10].
ð1Þ
X-ray diffraction study [11] of 2 · C6H6 showed that
molecule 2 (Fig. 1) bent with a Pt–Co–Pt angle of 71.3ꢁ.
The central CoII atom is coordinated to four O atoms of
two pairs of l-OOCMe ligands (Co–O: 2.008(5);
boxylate-bridged complex PtIVCoII(l,g2-OOCCMe3)4-
2
˚
2.040(5) A), forming a slightly distorted tetrahedron. Each
(OOCCMe3)2(OH)2(HOOCCMe3)4 prepared from the
platinum blue [Pt(OOCMe)2.5]n in 10% yield [8]. Another
potential starting material, platinum(II) acetate, is not
commercially available and is difficult to synthesize. Hence,
PtII atom has a square-plane coordination, being connected
to the CoII atom by pairs of acetate bridges (Pt–O:
˚
2.008(5), 2.011(5); Ptꢀ ꢀ ꢀCo: 2.7513(8) A) and complement-
ing the coordination sphere by two O atoms of bidentate
˚
acetylacetonate anions (Pt–O: 1.974(5), 1.976(5) A).
*
Formally reaction (1) seems to be a ligand exchange
resulting in the replacement of acacꢁ ligand for MeCOOꢁ
Corresponding author. Tel.: +7 095 955 4865; fax: +7 095 954 1279.
E-mail address: mvar@igic.ras.ru (M.N. Vargaftik).
1387-7003/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2007.05.006

N.Yu. Kozitsyna et al. / Inorganic Chemistry Communications 10 (2007) 956–958
957
Fig. 1. Molecular structure of the complex {PtII(acac)}2CoII(l-OAc)4 (2) with thermal ellipsoids drawn at 50% probability level.
anion followed by combing two Pt(acac)+ cations with
CoðOOCMeÞ4 anion. However, we found that reaction
the Russian Academy of Sciences for Basic Research ‘‘Pur-
poseful Synthesis of Inorganic Substances and Creation of
Related Functional Materials’’.
2ꢁ
(1) strongly requires air oxygen, while no reaction between
1 and Co(OOCMe)2 Æ 4H2O occurs in Ar atmosphere [10].
The reaction seems to be rather complicated, implying
the involvement of the oxidative CoII/O2 system in the
mechanism. Intermediate CoIII species formed in this sys-
tem could remove the acacꢁ ligand (e.g., by its free radical
oxidation to MeCOOH) from the PtII coordination sphere,
facilitating the entry of CoII acetate into the coordination
vacancies thus formed. This assumption is supported by
our observation that acetates of such unoxidizable metals
as ZnII and NiII do not react with 1. For instance, when
1 was attempted to react with Zn(OOCMe)2 Æ 2H2O both
in air and under Ar [15], no heterometallic complex was
obtained, but the crystal solvate 1 · 2MeCOOH (3)
(according to X-ray diffraction data [16]) was recovered
from the reaction mixture.
Appendix A. Supplementary material
CCDC 640718 and 640719 contain the supplementary
crystallographic data for 2 and 3. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at
doi:10.1016/j.inoche.2007.05.006.
References
Thus, the chelating acac ligand strongly bound to PtII is
not substituted in such acidic media as MeCOOH via its
protonation, but can be replaced in the oxidative CoII/O2
system.
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The authors thank the Russian Foundation for Basic
Research (Projects Nos. 05-03-32683, 05-03-32794, 06-03-
32578 and 06-03-08173), the Program of President of the
Russian Federation for Support of Leading Russian Scien-
tific Schools (Grant NSh-4959.2006.03) and the Program of
[7] O.P. Tkachenko, A. Yu. Stakheev, L.M. Kustov, I.V. Mashkovsky,
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for all non-hydrogen atoms. The hydrogen atoms in the structure
were placed geometrically and included in the structure factor
calculation in the riding motion approximation. All calculations were
performed with the use of the SAINT [13] and SHELXTL-97 [14]
program packages.
[10] Chemicals (K2PtCl4, Co(OOCMe)2 Æ 4H2O and acetylacetone, all of
reagent grade, purchased from Reakhim, Russia) and solvents (acetic
acid, benzene and n-hexane, all special purity grade, purchased from
Acros, Belgium) were used as-received. Platinum(II) acetylacetonate
Pt(acac)2 was prepared by the reaction of K2PtCl4 with acetylacetone
in alkaline solution according to [9]. Synthesis of 2 · C6H6:Pt(acac)2
(100 mg, 0.25 mmol) and Co(OOCMe)2 Æ 4H2O (62 mg, 0.25 mmol)
were magnetically stirred under reflux in acetic acid (10 ml) in Ar
atmosphere. No reaction was observed for 2 h, which was evidenced
by unchanged colour of solution. When air was admitted through a
condenser, the solution began to change its colour from pink to red-
violet. The reaction solution was refluxed under air for 2 h, cooled,
filtered and reduced in vacuo to 2 ml. Benzene (ca. 0.3 ml) was added
and the solution was kept to crystallize at room temperature for 24 h.
The red-violet crystals of 2 (12 mg) were separated from the mother
liquor, washed with cold benzene and used for X-ray diffraction
study. The mother liquor was evaporated to dryness, the residue was
dissolved in hot benzene and precipitated with hexane. Total yield
79 mg (65% based on Pt). Found: C, 29.81; H, 3.29%. For
Pt2CoC24O32H12 calc: C, 29.98; H, 3.35. IR (KBr pellet, m/cmꢁ1):
1587m, 1533s, 1421s, 1349w, 1286w,1205w, 1105w, 1026w, 792m,
703m, 687m.
[12] G.M. Sheldrick, SADABS, 1997, Bruker AXS Inc., Madison, WI-
53719, USA.
[13] SMART V5.051 and SAINT V5.00, Area detector control and
integration software, 1998, Bruker AXS Inc., Madison, WI-53719,
USA.
[14] G.M. Sheldrick, SHELXTL-97 V5.10, 1997, Bruker AXS Inc.,
Madison, WI-53719, USA.
[15] Reaction of 1 with ZnII acetate: Pt(acac)2 (100 mg, 0.25 mmol) and
Zn(OOCMe)2 Æ 2H2O (56 mg, 0.25 mmol) were stirred under reflux in
acetic acid (10 ml) either under Ar or with admission of air through a
condenser for 2 h. In both cases an invariably yellow-green solution
was cooled, filtered and reduced in vacuo to 2 ml. After cooling of the
solution to 10 ꢁC, the unstable in air crystals of crystal solvate
1 · 2MeCOOH (3, 87 mg, 0.22 mmol) were separated from the
mother liquor and used for the X-ray diffraction study. Analogous
reaction of
1 with Ni(OOCMe)2 Æ 4H2O recovered the starting
material only.
[16] X-ray structure analysis of 3: SMART APEX, CCD-detector k(Mo
˚
Ka) = 0.71073 A, graphite monochromator, x-scanning, 2hmax = 60ꢁ,
˚
C
14H22O8Pt, M = 513.4, triclinic, space group P1, a = 6.9501(8) A,
˚
˚
b = 7.6631(9) A, c = 9.1030(11) A, a = 79.999(2)ꢁ, b = 85.771(2)ꢁ,
3
˚
c = 64.610(2)ꢁ, V = 431.34(9) A (120 K), Z = 1, Dcalc = 1.976
[11] X-ray structure analysis of 2 · C6H6: SMART APEX, CCD-detector
g/cm3, 3976 measured reflections, 2040 [R(int) = 0.0472] independent
k(Mo Ka) = 0.71073 A, graphite monochromator, x-scanning,
reflections with F2 > 2r(I), l = 8.169 mmꢁ1
, R1 = 0.0249, wR2 =
˚
2hmax = 60ꢁ, C24H34CoO12Pt2, M = 963.62, monoclinic, space group
0.0476. Corrections for absorption were made by SADABS [12].
The structure was solved by the direct method and refined by the full-
matrix least squares method for F2 with anisotropic parameters for all
non-hydrogen atoms. The hydrogen atoms in the structure were
placed geometrically and included in the structure factor calculation
in the riding motion approximation. All calculations were performed
with the use of the SAINT [13] and SHELXTL-97 [14] program
packages.
˚
˚
˚
C2/c, a = 15.0106(16) A, b = 15.3091(17) A, c = 13.9119(15) A,
3
˚
b = 117.306(2)ꢁ, V = 2840.7(5) A (120 K), Z = 4, Dcalc = 2.253
g/cm3, 16,123 measured reflections, 4074 [R(int) = 0.0635] indepen-
dent reflections with F2 > 2r(I), l = 10.462 mmꢁ1
, R1 = 0.0384,
wR2 = 0.0529. Corrections for absorption were made by SADABS
[12]. The structure was solved by the direct method and refined by the
full-matrix least squares method for F2 with anisotropic parameters