The role of water molecules in formation of heterometallic palladium acetate complexes with cerium and neodymium

Article abstract of DOI:10.1134/S0036023611030156

The reactions of palladium(II) acetate with neodymium(III) and cerium(III) acetates in acetic acid containing a specified amount of water have been studied. The following homo- and heterometallic com- plexes have been synthesized and characterized by X-ray diffraction: Nd₂(μ-OOCMe) ₂(μ,η ²-OOCMe)₂(η ²- OOCMe)₂(HOOCMe)₂(OH₂)₂ · 4HOOCMe, [Pd(μ-OOCMe)₄Ce(OH₂)₂(μ,η ²-OOCMe)]₂ · 2HOOCMe · 6H₂O, [Pd(μ-OOCMe)₄Ce(OH₂)₂(μ,η ²-OOCMe)]₂ · 14H₂O, [Pd(μ-OOCMe) 4M(HOOCMe)₂(OH₂)₂]+ [Pd(μ-OOCMe)4M(μ- OOCMe)₄Pd]^- · 2MeCOOH · 1.5H₂O (M = Nd, Ce), and {[Pd(μ- OOCMe)₄Ce(OOCMe)₄]₂ [Pd₄(μ-OOCMe)₄]₂(μ₄-O) ₈CePd₄}(OH)₃ · 27H₂O. From kinetic and structural data and optical spectra of reaction solutions, the conclusion was drawn that hydrolytic processes play a decisive role in complexation reactions. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S0036023611030156

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 3, pp. 357–374. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © S.E. Nefedov, N.Yu. Kozitsyna, N.S. Akhmadullina, N.V. Cherkashina, M.N. Vargaftik, I.I. Moiseev, 2011, published in Zhurnal Neorganicheskoi Khimii,
2011, Vol. 56, No. 3, pp. 399–416.
COORDINATION COMPOUNDS
The Role of Water Molecules in Formation of Heterometallic
Palladium Acetate Complexes with Cerium and Neodymium
S. E. Nefedov, N. Yu. Kozitsyna, N. S. Akhmadullina, N. V. Cherkashina,
M. N. Vargaftik, and I. I. Moiseev
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
eꢀmail; wahr36@gmail.com
Received June 4, 2010
Abstract—The reactions of palladium(II) acetate with neodymium(III) and cerium(III) acetates in acetic
acid containing a specified amount of water have been studied. The following homoꢀ and heterometallic comꢀ
plexes have been synthesized and characterized by Xꢀray diffraction: Nd2(
OOCMe)2(HOOCMe)2(OH2)2 4HOOCMe, [Pd( ꢀOOCMe)4Ce(OH2)2(
6H2O, [Pd( ꢀOOCMe)4Ce(OH2)2( 14H2O, [Pd(
2ꢀOOCMe)]2 ꢀOOCMe)4M(HOOCMe)2(OH2)2]+
[Pd( ꢀOOCMe)4M( 2MeCOOH 1.5H2O (M = Nd, Ce), and {[Pd(
ꢀOOCMe)4Pd]–
OOCMe)4Ce(OOCMe)4]2 [Pd4( ꢀOOCMe)4]2( 4ꢀO)8CePd4}(OH)3 27H2O. From kinetic and structural
μ
ꢀOOCMe)2(
μ
,
η
2ꢀOOCMe)2(
η
2ꢀ
⋅
μ
μ
,
η
2ꢀOOCMe)]2
⋅
2HOOCMe
⋅
μ
μ
,
η
⋅
μ
μ
μ
⋅
⋅
μ
ꢀ
μ
μ
⋅
data and optical spectra of reaction solutions, the conclusion was drawn that hydrolytic processes play a deciꢀ
sive role in complexation reactions.
DOI: 10.1134/S0036023611030156
The properties of palladiumꢀbased heterometallic solutions, as well as the composition and structures of
1
nanocomposites, alloys, and polyfunctional catalysts
depend on the nature of precursor compounds. As
the reaction products.
such, either metals per se, or mixtures of palladium
and other metal complexes, which are then subjected
to reductive thermolysis, are commonly used [1–5].
Recently, we synthesized a new extraordinary class of
complexes containing a palladium atom and an addiꢀ
tional transition, mainꢀgroup, or rare earth metal
atom linked by carboxylate bridges [6–10]. Such comꢀ
plexes were synthesized in high (nearly quantitative)
EXPERIMENTAL
Glacial acetic acid (chemically pure, Reakhim,
Russia) containing 1.3% (0.72 mol/L) of water was
purified by freezing with subsequent fractional distillaꢀ
tion with triacetyl borate. A weighed sample of water
was introduced into the reaction mixture. The water
content was monitored by GLC.
yields by reacting palladium(II) acetate Pd3(
μꢀ
Palladium(II) acetate Pd3(OOCMe)6 was obtained
by oxidation of palladium black (prepared by reducing
PdCl2 (chemically pure, Reakhim, Russia) with
sodium borohydride) by concentrated nitric acid in
glacial acetic acid as described in [14], purified from
impurities of Pd(II) nitrito complexes by boiling in
glacial acetic acid in the presence of a fresh portion of
palladium black until the termination of NO2 evoluꢀ
tion, and recrystallized from hot acetic acid. The salts
OOCMe)6 ( with acetates of corresponding addiꢀ
1
)
tional metals. A specific feature of these compounds is
their ability to transform into catalytically active
nanosized heterometallic clusters and particles upon
reductive thermolysis under mild conditions [10, 11].
To optimize the synthesis conditions of heterobiꢀ
metallic complexes Pd(μꢀOOCMe)4 M(OH2, NCMe)
in acetic acid, we recently studied the kinetics of this
reaction and found that the reaction of complex 1 with
Ce(OOCMe)3
⋅
4H2O and Nd(OOCMe)3 1.5H2O (both
⋅
transition metal acetates (M = СоII, NiII, CuII) in
anhydrous acetic acid is extremely slow, but it is signifꢀ
icantly accelerated in the presence of even small water
amounts [12, 13].
of special purity grade, Reakhim, Russia) were used as
purchased.
Electronic absorption spectra were recorded on a
Varian Cary 50 spectrophotometer with a standard
builtꢀin adjustable Peltier thermostat in a quartz cell
In this work, we studied the kinetics of the reaction
of palladium acetate
Nd(OOCMe)3 and Ce(OOCMe)3 in acetic acid conꢀ
taining specified amount of water (0.03–
4.95 mol/L) and the UV and visible spectra of reaction
1 with rare earth acetates
(10 mm) with a magnetic stirrer at 25–80°C ( 0.1°C)
.
1
a
Preliminary communication, see S. E. Nefedov, N. Yu. Kozitꢀ
sina, M. N. Vargaftik, et al., Inorg. Chem. Commun. (2011).
357

358
NEFEDOV et al.
Elemental analysis was carried out on a Carlo Erba
For Pd2Ce2C24O34H58 anal. calcd. (%): C, 20.83;
CHN analyzer. The IR spectra were recorded as KBr H, 4.22. Found (%): C, 20.78; H, 4.15.
IR (KBr,
, cm–1): 3438 s br, 2939 w, 1641 s, 1557
ν
pellets on Nicolet Nexus and Specord Mꢀ80 spectroꢀ
photometers.
vs br, 1412 vs br, 1340 m, 1050 w, 1022 w, 937 w, 692 m,
668 m, 619 w.
[Pd(
μ
ꢀOOCMe)4Ce]2(
μ
,
η
2ꢀOOCMe)2(H2O)4
⋅
XꢀRay Crystallography
14H2O (6b). A suspension of Pd3(OOCMe)6(100 mg,
0.445 mmol as calculated for Pd(OOCMe)2) and
The Xꢀray diffraction experiment was carried out
on a Bruker SMART APEX II diffractometer with a
Ce(OOCMe)3 4H2O (173 mg, 0.445 mmol) in acetic
⋅
CCD detector (graphite monochromator, Mo
K radiꢀ
α
acid (5 mL) was stirred at 90°С until complete dissoluꢀ
tion (1 h). The solvent was completely removed on a
rotary evaporator, and the residue was dried in vacuo
(30 Torr) at temperature not exceeding 50°С. Then,
2 mL of H2O was added to the dry residue. The resulting
yellow solution was allowed to stand in an open beaker at
room temperature for 4 days and then was placed into a
refrigerator (~5°С) for 12 h. The resulting yellow plateꢀ
like crystals of 6b were separated by decantation. The
yield of 6b was 166 mg (53% as calculated for Pd).
For Pd2Ce2C20O38H66 anal. calcd. (%): C, 20.83;
H, 4.22. Found (%): C, 20.78; H, 4.15.
ation,
λ
= 0.71073
Å,
ω
scan). The collected reflection
intensities were processed with the SAINT [15] and
SADABS [16] program packages. The structures were
solved by direct methods and refined by the fullꢀmatrix
leastꢀsquares method on F2 with anisotropic thermal
parameters for all nonꢀhydrogen atoms, using the
SHELXTL97 program package [17] and refined with
the SHELXTL97 program [17]. All hydrogen atoms
were placed in geometrically calculated positions and
refined as riding on their bonded atoms.
Crystal data, refinement details, and bond lengths
and bond angles for complexes 2a, 6a, 6b, 7, 8, and 9
are listed in Tables 1–7.
Full tables of atomic coordinates, bond lengths,
ans bond angles were deposited with the Cambridge
Crystal Data Center (CCDC 775582–775587).
IR (KBr,
, cm–1): 3438 s br, 2939 w, 1641 s, 1557
ν
vs br, 1412 vs br, 1340 m, 1050 w, 1022 w, 937 w, 692 m,
668 m, 619 w.
[Pd(
OOCMe)4M(
(M = Nd (7), Ce (8))
(100 mg, 0.445 mmol as calculated for Pd(OOCMe)2
and Nd(OOCMe)3 1.5H2O (78 mg, 0.222 mmol) in
μ
ꢀOOCMe)4M(HOOCMe)2(OH2)2]+[Pd(
μ
ꢀ
μ
ꢀOOCMe)4Pd]–
A suspension of Pd3(OOCMe)6
⋅ 2MeCOOH ⋅ 1.5H2O
.
)
Synthesis of Complexes
⋅
Synthesis of Nd2(
OOCMe)2 (HOOCMe)2(OH2)2
Commercial Nd(OOCMe)3 1.5H2O(389 mg, 1.1 mmol)
was dissolved in 5 mL of hot (80 ) acetic acid (conꢀ
μ
ꢀOOCMe)2(
μ
,
η
2ꢀOOCMe)2(
η
2ꢀ
acetic acid (1.4 mL) was stirred at 90°С until complete
dissolution (1 h). The reaction mixture was filtered
and allowed to stand at room temperature for 12 h.
⋅
4HOOCMe (2a).
⋅
°С
The resulting yellow crystals of
7 were separated by
taining 0.083% (0.04 mol/L) H2O. The solution was
concentrated to 2 mL and left in an open beaker at
room temperature for 5 days. The resulting light lilac
crystals were separated by decantation. The yield of 2a
was 360 mg (93% as calculated for Nd).
decantation. An additional portion of crystals was
obtained by concentration of the supernatant in air at
room temperature. The yield of
calculated for Nd).
7 was 81 mg (45% as
For Pd2Nd4C64O71H118 anal. calcd. (%): C, 23.73;
H, 3.67. Found (%): C, 23.69; H, 3.64.
For Nd2C24H46O26 anal. calcd. (%): C, 27.74; H,
4.46. Found (%): C, 26.95; H, 4.22.
IR (KBr,
, cm–1): 3426 s br, 2940 w, 1710 w, 1643
ν
IR (KBr,
, cm–1): 2372 w, 2332 w, 1684 w, 1664 m,
ν
s sh, 1561 vs br, 1419 vs br, 1341 m, 1289 w, 1051 w,
1022 w, 940 w, 695 m, 669 m, 622 m.
1650 m br (νas(CO)), 1416 w (νs(CO)), 1264 w, 1052 m,
1020 w, 948 m, 672 s, 612 m, 468 w.
The isostructural Pd–Ce complex [Pd(
OOCMe)4Ce(HOOCMe)2
(OH2)2]+[Pd(
OOCMe)4Ce( 2MeCOOH 1.5H2O
ꢀOOCMe)4Pd]–
was prepared analogously with a yield of 65 mg (36% as
μ
ꢀ
[Pd(
2HOOCMe
Pd3(OOCMe)6 (100 mg, 0.445 mmol as calculated for
Pd(OOCMe)2) and Ce(OOCMe)3 4H2O (173 mg,
μ
ꢀOOCMe)4Ce]2(
μ
,
η
2ꢀOOCMe)2(H2O)4
suspension of
⋅
μꢀ
⋅
6H2O (6a).
A
μ
⋅
⋅
(8)
⋅
calculated for Ce).
0.445 mmol) in acetic acid (1 mL) was stirred at 90°С
until complete dissolution (1 h). The yellow reaction
solution was allowed to stand in an open beaker at
room temperature for 5 days. The resulting yellow
crystals suitable for Xꢀray diffraction were separated by
decantation. An additional portion of crystals of 6a
was obtained after keeping the supernatant in a refrigꢀ
erator (~15°С) for 12 h. The yield of 6a was 231 mg
(75% as calculated for Pd).
For Pd6Ce4C64O71H118 anal. calcd. (%): C, 23.85;
H, 3.69. Found (%): C, 23.79; H, 3.63.
IR (KBr,
, cm–1): 3423 s br, 2935 w, 1707 w, 1641
ν
s sh, 1559 vs br, 1417 vs br, 1339 m, 1288 w, 1049 w,
1020 w, 937 w, 692 m, 668 m, 620 m.
{[Pd(
μ4ꢀO)8MPd4}(OH)3
suspension of Pd3(OOCMe)6 (200 mg, 0.89 mmol as
μ
ꢀOOCMe)4M(OOCMe)4]2[Pd4(μꢀOOCMe)4]2
(
⋅
27H2O (M = Ce (9), Nd (10)). A
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

THE ROLE OF WATER MOLECULES IN FORMATION
359
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

360
NEFEDOV et al.
Table 2. Selected bond lengths and bond angles for complex 2a
Bond
d
, Å
Bond
d, Å
Nd(l)–Nd(lA)
Nd(l)–O(2)
Nd(l)–O(4)
Nd(l)–O(6)
Nd(l)–O(6A)a
4.0174(4)
2.524(2)
2.423(2)
2.3942(19)
2.614(2)
Nd(l)–O(1)
Nd(l)–O(3)
Nd(l)–O(5)
Nd(l)–O(7)
Nd(l)–O(9)
2.520(2)
2.516(2)
2.476(2)
2.501(2)
2.422(2)
Angle
ω
, deg
Angle
ω
, deg
O(9)Nd(l)Nd(lA)a
O(5)Nd(l)Nd(lA)a
O(3)Nd(l)Nd(lA)a
O(2)Nd(l)Nd(lA)a
68.04(5)
68.85(5)
84.91(5)
110.32(5)
O(4)Nd(l)Nd(lA)a
O(7)Nd(l)Nd(lA)a
O(l)Nd(l)Nd(lA)a
O(6A)Nd(l)Nd(lA)a
140.49(6)
136.80(5)
116.75(5)
34.83(4)
a
Symmetry codes used for generation of equivalent atoms: –x + 1, –y + 1, –z + 2.
Table 3. Selected bond lengths and bond angles for complex 6a
Bond
d
, Å
Bond
d, Å
Ce(l)–Pd(l)
Pd(l)–O(3)
Pd(l)–O(7)
Ce(1)–O(4)
Ce(1)–O(8)
Ce(1)–O(9A)a
Ce(1)–O(11)
3.4117(3)
1.996(2)
1.999(2)
2.551(2)
2.556(2)
2.687(2)
2.5117(19)
Pd(l)–O(1)
Pd(l)–O(5)
Ce(1)–O(2)
Ce(1)–O(6)
Ce(1)–O(9)
Ce(1)–O(10)
Ce(1)–O(12)
2.003(2)
1.989(2)
2.493(2)
2.471(2)
2.5173(19)
2.579(2)
2.5666(19)
Angle
ω
, deg
Angle
ω
, deg
O(2)Ce(1)Pd(1)
O(9)Ce(1)Pd(1)
O(8)Ce(1)Pd(1)
O(10)Ce(1)Pd(1)
O(1)Pd(1)Ce(1)
O(7)Pd(1)Ce(1)
59.59(5)
124.10(5)
60.32(5)
124.51(4)
92.30(6)
92.42(6)
O(11)Ce(1)Pd(1)
O(4)Ce(1)Pd(1)
O(12)Ce(1)Pd(1)
O(9A)aCe(1)Pd(1)
O(3)Pd(1)Ce(1)
Ce(1)O(9)Ce(1)a
112.91(5)
60.24(5)
113.76(4)
173.65(4)
92.23(6)
117.88(7)
a
Symmetry codes used for generation of equivalent atoms: –x + 3, –y + 1, –z – 1.
calculated for Pd) and Ce(OOCMe)3
⋅
4H2O (173 mg, crystals of
9
were formed. The crystals of complex 9
were separated from lighter crystals of 6b by vigorous
shaking and repeated decantation into a clean flask.
The crystals of 9 remaining on the bottom of the reacꢀ
tion flask were washed with cold water to remove the
traces of complex 6b. Complex 6b separated by decanꢀ
tation was filtered off and dried at room temperature.
Further removal of water from the mother liquor
afforded an additional amount of complex 6b. The
yield of 6b was 141 mg (~45% as calculated for Ce).
0.445 mmol) in acetic acid (5 mL) was stirred at 90°С
until complete dissolution (1 h). The solvent was comꢀ
pletely removed on a rotary evaporator, and the resiꢀ
due was dried in vacuo (30 Torr) at temperature not
exceeding 50°С for 15 min. The solid residue was
extracted with water (1 mL and 0.5 mL 2). Each porꢀ
×
tion was heated at 60°С for 15 min and rapidly filtered
while warm. The combined aqueous extract was
allowed to stand in an open flask at room temperature
for 5 days. Within this period of time, yellow platelike
For Pd2Ce2C20O38H66 anal. calcd. (%): C, 29.83;
crystals of 6b and a small amount of bright red rhombic H, 4.22. Found (%): C, 20.78; H, 4.15.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

THE ROLE OF WATER MOLECULES IN FORMATION
Table 4. Selected bond lengths and bond angles for complex 6b
361
Bond
d
, Å
Bon
d
d, Å
Ce(1)–Pd(1)
Pd(1)–O(3)
Pd(1)–O(7)
Ce(1)–O(4)
Ce(1)–O(8)
Ce(1)–O(9A)a
Ce(1)–O(11)
3.4099(2)
Pd(1)–O(1)
Pd(1)–O(5)
Ce(1)–O(2)
Ce(1)–O(6)
Ce(1)–O(9)
Ce(1)–O(10)
Ce(1)–O(12)
2.0113(13)
1.9997(13)
2.4792(13)
2.6150(13)
2.5198(12)
2.5459(13)
2.5716(13)
1.9985(13)
1.9994(13)
2.5153(13)
2.4559(13)
2.7144(13)
2.4831(13)
Angle
ω
,
deg
Angle
ω
, deg
O(2)Ce(1)Pd(1)
O(4)Ce(1)Pd(1)
O(10)Ce(1)Pd(1)
O(12)Ce(1)Pd(1)
O(9A)Ce(1)Pd(1)
O(3)Pd(1)Ce(1)
O(7)Pd(1)Ce(1)
59.77(3)
59.17(3)
121.69(3)
115.59(3)
170.55(3)
92.17(4)
92.41(4)
O(8)Ce(1)Pd(1)
O(11)Ce(1)Pd(1)
O(9)Ce(1)Pd(1)
O(6)Ce(1)Pd(1)
O(1)Pd(1)Ce(1)
O(5)Pd(1)Ce(1)
58.30(3)
112.16(3)
126.27(3)
60.09(3)
90.87(4)
91.68(4)
a
Symmetry codes used for generation of equivalent atoms: –x + 1, –y + 1, –z – 1.
IR (KBr,
1412 vs br, 1340 m, 1050 w, 1022 w, 937 w, 692 m, 668 m, structurally characterized: anhydrous Nd(OOCMe)3
619 w. [22] and crystal hydrate Се(СH3СОО)3 0.7Н2О [23].
The yield of
ν
, cm–1): 3438 s br, 2939 w, 1641 s, 1557 vs br, 2010) [21], only two NdIII and CeIII acetates have been
⋅
To elucidate the structure of the complexes involved in
the reaction under consideration, we obtained neodyꢀ
mium(III) acetate single crystals by recrystallization
9
was 30 mg (~5% as calculated for Pd).
For Pd14Ce3C48O86H129 anal. calcd. (%): C, 14.44;
H, 3.26. Found (%): C, 14.39; H, 3.29.
of commercial Nd(OOCMe)3 1.5H2O (2) from acetic
⋅
IR (KBr,
, cm–1): 3436 s br, 2925 w, 2854 w, 1639 s sh,
ν
acid containing 0.083% (0.04 mol/L) H2O. According
1561 vs br, 1449 s sh, 1414 vs br, 1339 m, 1046 w, 1021 w,
937 w, 695 w, 668 w, 619 w.
Red crystals of Pd–Nd complex 10 were obtained
in 3% yield by an analogous procedure. Unit cell
to Xꢀray diffraction data (Fig. 1, Tables 1, 2), in the
Nd2(
(HOOCMe)2(OH2)2
NdIII atoms are linked by two
μ
ꢀOOCMe)2(
μ
,
η
2ꢀOOCMe)2( 2ꢀOOCMe)2
η
⋅
4HOOCMe (2a
)
crystal, two
ꢀacetate
μ,η
2ꢀ and two
μ
parameters (
= 90 = 90
0.04 0.02 0.02 mm) crystals of 10 (scan time, 120 s;
78 reflections in the range 2.54 –18.72 ).
a
= 32.1(5)
Å,
b
= 32.1(5)
Å, c = 34.2(8) Å,
bridges (Nd–O(3), 2.516(2) Å; Nd–O(6), 2.3942(19) Å,
Nd–O(6A), 2.614(2) Å; Nd–O(5), 2.476(2) Å;
Nd–O(9), 2.422(2) Å) with a nonbonding Nd···Nd
distance of 4.0174(4) Å.
α
°,
β
°
,
γ
= 120°)) were measured for small
(
×
×
θ
°
°
For Pd14Nd3C48O86H129 anal. calcd. (%): C, 14.39;
H, 3.25. Found (%): C, 14.34; H, 3.27.
The metal–oxygen distances in
2ꢀacetate ligands
η
are nearly the same (Nd–O(1), 2.520(2) Å; Nd–O(2),
2.524(2) Å). The terminal acetic acid molecule (Nd–
O(7), 2.501(2) Å) is involved in intramolecular hydroꢀ
gen bonds with the O(5) atom of the bridging acetate
ligand (O(8)···O(5) 2.580(2) Å); in addition, the coordiꢀ
nation sphere of each neodymium atom is completed
with a water molecule (Nd–O(4), 2.423(2) Å), so that
the overall CN of Nd atoms is nine. The unit cell of
IR (KBr,
, cm–1): 3412 s br, 2924 w, 2854 w, 1630 w,
ν
1555 vs br, 1440 w sh, 1411 vs br, 1340 m, 1065 w, 1042 w,
949 w, 695 w, 620 w br.
RESULTS AND DISCUSSION
Initial Rare Earth Acetates
The composition and structure of rare earth aceꢀ complex 2a contains four solvation molecules of acetic
tates depends noticeably on both the solvent (acetic acid: two of them are linked through short hydrogen
acid, water, etc.) and the conditions of single crystal bonds with the coordinated water molecules and the
growth [18–20]. According to CSD (ver. 5.31, Feb. oxygen atom of the
η
2ꢀcoordinated acetate anion
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

362
NEFEDOV et al.
Table 5. Selected bond lengths and bond angles for complex 7
Bond
d
, Å
Bond
d, Å
Nd(1)–Pd(1)
Nd(2)–Pd(3)
Pd(1)–O(3)
Pd(1)–O(7)
Pd(2)–O(11)
Pd(2)–O(15)
Pd(3)–O(19)
Pd(3)–O(23)
Nd(1)–O(4)
Nd(1)–O(8)
Nd(1)–O(12)
Nd(1)–O(16)
Nd(2)–O(20)
Nd(2)–O(24)
Nd(2)–O(27)
Nd(2)–O(30)
3.3289(9)
3.3018(9)
1.986(7)
1.996(7)
2.010(6)
1.995(6)
1.999(6)
1.985(6)
2.445(6)
2.466(6)
2.471(5)
2.479(6)
2.423(6)
2.438(6)
2.499(6)
2.480(6)
Nd(1)–Pd(2)
Pd(1)–O(1)
Pd(1)–O(5)
Pd(2)–O(9)
Pd(2)–O(13)
Pd(3)–O(17)
Pd(3)–O(21)
Nd(1)–O(2)
Nd(1)–O(6)
Nd(1)–O(10)
Nd(1)–O(14)
Nd(2)–O(18)
Nd(2)–O(22)
Nd(2)–O(25)
Nd(2)–O(29)
3.4650(9)
1.981(6)
1.986(6)
1.988(5)
2.021(5)
2.009(7)
2.004(7)
2.479(6)
2.448(6)
2.487(6)
2.445(6)
2.384(7)
2.425(6)
2.471(6)
2.481(6)
Angle
ω
, deg
Angle
ω
, deg
O(14)Nd(1)Pd(1)
O(6)Nd(1)Pd(1)
O(12)Nd(1)Pd(1)
O(2)Nd(1)Pd(1)
O(14)Nd(1)Pd(2)
O(6)Nd(1)Pd(2)
O(12)Nd(1)Pd(2)
O(2)Nd(1)Pd(2)
Pd(1)Nd(1)Pd(2)
O(20)Nd(2)Pd(3)
O(24)Nd(2)Pd(3)
O(30)Nd(2)Pd(3)
O(27)Nd(2)Pd(3)
O(3)Pd(1)Nd(1)
O(7)Pd(1)Nd(1)
O(15)Pd(2)Nd(1)
O(13)Pd(2)Nd(1)
O(19)Pd(3)Nd(2)
O(17)Pd(3)Nd(2)
119.08(14)
60.69(13)
121.03(14)
60.76(15)
58.00(14)
121.41(13)
58.99(14)
117.21(15)
177.08(2)
61.14(15)
61.29(15)
127.40(15)
123.44(13)
93.11(19)
90.6(2)
O(4)Nd(1)Pd(1)
O(8)Nd(1)Pd(1)
O(16)Nd(1)Pd(1)
O(10)Nd(1)Pd(1)
O(4)Nd(1)Pd(2)
O(8)Nd(1)Pd(2)
O(16)Nd(1)Pd(2)
O(10)Nd(1)Pd(2)
O(18)Nd(2)Pd(3)
O(22)Nd(2)Pd(3)
O(25)Nd(2)Pd(3)
O(29)Nd(2)Pd(3)
O(1)Pd(1)Nd(1)
O(5)Pd(1)Nd(1)
O(9)Pd(2)Nd(1)
O(11)Pd(2)Nd(1)
O(23)Pd(3)Nd(2)
O(21)Pd(3)Nd(2)
59.83(13)
62.36(16)
122.21(13)
124.75(13)
118.10(13)
119.70(16)
57.73(13)
58.17(13)
63.02(16)
61.50(15)
125.31(13)
126.17(15)
92.8(2)
92.54(18)
92.27(17)
91.05(17)
92.2(2)
91.87(17)
90.60(16)
91.86(19)
90.0(2)
92.47(19)
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

THE ROLE OF WATER MOLECULES IN FORMATION
Table 6. Selected bond lengths and bond angles for complex 8
363
Bond
d
, Å
Bond
d, Å
Ce(1)–Pd(1)
Ce(2)–Pd(3)
Pd(1)–O(3)
Pd(1)–O(7)
Pd(2)–O(11)
Pd(2)–O(15)
Pd(3)–O(19)
Pd(3)–O(23)
Ce(1)–O(4)
Ce(1)–O(8)
Ce(1)–O(12)
Ce(1)–O(16)
Ce(2)–O(20)
Ce(2)–O(24)
Ce(2)–O(27)
Ce(2)–O(30)
3.3399(4)
3.3178(4)
1.977(3)
1.997(3)
2.013(2)
2.002(2)
1.998(3)
1.996(3)
2.486(3)
2.503(3)
2.506(3)
2.520(3)
2.458(3)
2.465(3)
2.537(3)
2.529(3)
Ce(1)–Pd(2)
Pd(1)–O(1)
Pd(1)–O(5)
Pd(2)–O(9)
Pd(2)–O(13)
Pd(3)–O(17)
Pd(3)–O(21)
Ce(1)–O(2)
Ce(1)–O(6)
Ce(1)–O(10)
Ce(1)–O(14)
Ce(2)–O(18)
Ce(2)–O(22)
Ce(2)–O(25)
Ce(2)–O(29)
3.4895(3)
1.989(3)
1.992(3)
1.998(2)
2.018(2)
1.997(3)
2.008(3)
2.522(3)
2.488(3)
2.530(3)
2.477(3)
2.431(3)
2.468(3)
2.508(3)
2.528(3)
Angle
ω
,
deg
Angle
ω
, deg
O(14)Ce(1)Pd(1)
O(6)Ce(1)Pd(1)
O(12)Ce(1)Pd(1)
O(2)Ce(1)Pd(1)
O(14)Ce(1)Pd(2)
O(6)Ce(1)Pd(2)
O(12)Ce(1)Pd(2)
O(2)Ce(1)Pd(2)
Pd(1)Ce(1)Pd(2)
O(20)Ce(2)Pd(3)
O(22)Ce(2)Pd(3)
O(29)Ce(2)Pd(3)
O(27)Ce(2)Pd(3)
O(l)Pd(1)Ce(1)
O(7)Pd(1)Ce(1)
O(15)Pd(2)Ce(1)
O(13)Pd(2)Ce(1)
O(17)Pd(3)Ce(2)
O(21)Pd(3)Ce(2)
119.68(6)
60.42(6)
121.68(6)
61.08(7)
57.71(6)
121.76(6)
58.76(6)
116.79(7)
177.344(9)
61.19(7)
60.84(6)
126.56(7)
121.65(6)
92.77(9)
90.90(9)
92.38(7)
91.16(7)
90.49(9)
92.68(8)
O(4)Ce(1)Pd(1)
O(8)Ce(1)Pd(1)
O(16)Ce(1)Pd(1)
O(10)Ce(1)Pd(1)
O(4)Ce(1)Pd(2)
O(8)Ce(1)Pd(2)
O(16)Ce(1)Pd(2)
O(10)Ce(1)Pd(2)
O(18)Ce(2)Pd(3)
O(24)Ce(2)Pd(3)
O(25)Ce(2)Pd(3)
O(30)Ce(2)Pd(3)
O(3)Pd(1)Ce(1)
O(5)Pd(1)Ce(1)
O(9)Pd(2)Ce(1)
O(11)Pd(2)Ce(1)
O(23)Pd(3)Ce(2)
O(19)Pd(3)Ce(2)
59.91(6)
62.45(6)
122.20(6)
124.91(6)
118.54(6)
119.10(6)
57.30(6)
57.71(6)
62.47(8)
61.16(7)
124.38(6)
128.82(7)
93.52(9)
92.99(9)
92.39(7)
90.66(7)
92.42(9)
92.30(8)
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

364
NEFEDOV et al.
Table 7. Selected bond lengths and bond angles for complex 9
Bond
d
, Å
Bond
d, Å
Ce(1)–Pd(1)
Ce(1)–Pd(2)
Ce(1)–Pd(3)
Ce(1)–Pd(4)
Ce(2)–Pd(7)
Pd(1)–Pd(4)
Pd(3)–Pd(4)
Ce(1)–O(2A)a
Ce(1)–O(4A)a
Pd(1)–O(2)
Pd(2)–O(4)
Pd(3)–O(4)
Pd(4)–O(3A)a
Pd(5)–O(3)
Pd(6)–O(4)
3.3543(5)
3.3622(5)
3.3423(5)
3.3473(5)
3.3338(7)
3.0569(7)
3.0793(8)
2.339(4)
2.333(5)
1.992(5)
1.995(5)
1.991(5)
1.996(5)
2.018(4)
2.015(5)
Ce(1)–Pd(lA)a
Ce(1)–Pd(2A)a
Ce(1)–Pd(3A)a
Ce(1)–Pd(4A)a
Pd(l)–Pd(2)
Pd(2)–Pd(3)
Ce(1)–O(1)
3.3543(5)
3.3622(5)
3.3424(5)
3.3472(5)
3.0905(8)
3.0691(7)
2.336(5)
2.324(4)
1.991(4)
2.000(5)
1.990(4)
1.995(5)
2.008(5)
2.017(4)
Ce(1)–O(3)
Pd(1)–O(1)
Pd(2)–O(2)
Pd(3)–O(3A)a
Pd(4)–O(1)
Pd(5)–O(2)
Pd(6)–O(lA)a
Angle
ω
, deg
Angle
ω
, deg
Pd(1)Pd(2)Ce(1)
Pd(1)Pd(4)Ce(1)
Pd(3)Pd(2)Ce(1)
Pd(2)Pd(3)Ce(1)
Pd(3)Ce(1)Pd(4)
Pd(3A)Ce(1)Pd(4)
Pd(4)Ce(1)Pd(4A)a
Pd(1)Pd(4)Pd(3)
Pd(2)Pd(3)Pd(4)
Pd(1)O(1)Pd(4)
Pd(4)O(1)Pd(6A)a
Pd(4)O(1)Ce(1)
Pd(1)O(2)Pd(2)
Pd(2)O(2)Pd(5)
Pd(2)O(2)Ce(1)
Pd(3A)O(3)Pd(4A)a
Pd(4A)O(3)Pd(5)
Pd(4A)aO(3)Ce(1)
Pd(3)O(4)Pd(2)
Pd(2)O(4)Pd(6)
Pd(2)O(4)Ce(1)
62.470(13)
62.966(14)
62.436(14)
63.073(14)
54.814(14)
125.184(13)
180.0
Pd(2)Pd(1)Ce(1)
Pd(3)Pd(4)Ce(1)
Pd(4)Pd(1)Ce(1)
Pd(4)Pd(3)Ce(1)
Pd(3)Ce(1)Pd(3A)a
Pd(3)Ce(1)Pd(4A)a
Pd(3A)aCe(1)Pd(4A)a
Pd(3)Pd(2)Pd(1)
Pd(4)Pd(1)Pd(2)
Pd(1)O(1)Pd(6A)a
Pd(1)O(1)Ce(1)
Pd(6A)O(1)Ce(1)
Pd(1)O(2)Pd(5)
Pd(1)O(2)Ce(1)
Pd(5)O(2)Ce(1)
Pd(3A)aO(3)Pd(5)
Pd(3A)O(3)Ce(l)
Pd(5)O(3)Ce(l)
62.726(14)
62.511(14)
62.752(14)
62.676(14)
180.0
125.189(14)
54.814(13)
91.66(2)
92.11(2)
88.05(2)
88.07(2)
100.2(2)
126.8(2)
119.9(2)
101.32(19)
103.48(19)
125.5(2)
100.92(19)
101.5(2)
120.4(2)
101.20(18)
102.70(18)
125.3(2)
101.28(19)
101.15(19)
120.8(2)
101.27(18)
102.89(18)
126.0(2)
101.28(19)
100.7(2)
Pd(3)O(4)Pd(6)
Pd(3)O(4)Ce(1)
Pd(6)O(4)Ce(1)
119.8(2)
100.96(19)
103.66(18)
101.7(2)
a
Symmetry codes used for generation of equivalent atoms: –x – 1/3, –y + 1/3, –z – 2/3.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

THE ROLE OF WATER MOLECULES IN FORMATION
365
C(10)
The above data suggest that, under the reaction
conditions, the initial neodymium acetate form is a
C(12A)
binuclear structural moiety Nd2(
η
with the known Xꢀray crystallographic data on NdIII
μ
ꢀOOCMe)2(
μ
,
2ꢀ
η
OOCMe)2(
2ꢀOOCMe)2 of complex 2a. By analogy
C(9)
O(10)
C(6A)
O(11)
H(41)
C(11A)
O(12A)
O(13A)
and CeIII acetates [22, 23], we can assume that comꢀ
O(8A)
H(8D)
mercial cerium(III) acetate (3) is crystallized from
acetic acid to form a similar binuclear complex.
C(5A)
H(10)
O(9)
H(12G)
C(8A)
O(4)
C(7A)
O(7A)
O(5A)
C(4)
O(2)
H(42)
Reaction Kinetics
O(3)
O(6)
C(3)
C(2)
O(1A)
C(2A)
Nd(1)
The reaction of complex 1 with neodymium(III) or
O(6A)
C(1)
O(1)
Nd(1A)
cerium(III) acetate leads to the appearance in the optiꢀ
cal spectrum of a new absorption band at 340–360 nm
→
C(1A)
C(3A)
O(3A)
O(7)
C(4A)
(corresponding to the 1Alg
lEg transition of Pd atom),
O(2A)
H(42A)
C(8)
which is typical of monoꢀ and binuclear PdII comꢀ
C(7)
O(4A)
H(12)
O(12)
O(5)
H(8)
O(9A)
plexes and is absent in the spectrum of trinuclear comꢀ
H(10D)
O(10A)
H(41A)
C(5)
O(8)
plex
plexes give rise to only weak
1
[24, 25]. In this region, the NdIII and CeIII comꢀ
f–f(d) bands almost not
C(11)
O(13)
responding to changes in the coordination sphere of a
rare earth metal [26–28]. The course of reaction was
monitored by observing the electronic spectra in the
range 200–600 nm. Depending on the reaction time,
the spectrum of the reaction mixture in acetic acid
with a low water content (0.03–0.05 mol/L) (Figs. 2a,
2b) shows two isosbestic points (305 and 583 nm for
the PdII + NdIII reaction and 304 and 385 nm for the
PdII + CeIII reaction).
O(11A)
C(9A)
C(6)
C(12)
C(10A)
Fig. 1. Molecular structure of the complex Nd (
μ
ꢀ
2
2
2
OOCMe) (
μ
,
η
ꢀOOCMe) ( ꢀOOCMe) (HOOCMe)
η
2
2
2 2
(OH )
⋅
4HOOCMe (2а) (50% probability thermal ellipꢀ
2 2
Both reactions are considerably promoted by addꢀ
ing water. As the water content increases (up to
~5 mol/L), the isosbestic points are blurred. The
absorbance–time curves at 340 nm (for the PdII + NdIII
reaction) and 343 nm (for the PdII + CeIII reaction) are
linearized well in semilogarithmic coordinates, which
is evidence of firstꢀorder kinetics (Figs. 3a, 3b).
soids).
(
O(4)···O(11) 2.747(2), O(2)···O(10) 2.615(2) Å), and the
other two molecules have hydrogen bonds with the
other oxygen atoms of the
anions (O(1)···O(12) 2.643(2) Å).
η
2ꢀcoordinated acetate
(а)
(b)
340 min
0.8
0.6
0.4
0.2
0
120 min
0.6
0.4
0.2
0
10 min
0 min
1 min
300
0 min
400
Wavelength, nm
500
300
400
500
600
Wavelength, nm
Fig. 2. Time evolution of the absorption spectrum of reaction solutions at 80°С: (a) the reaction of
1
with
2
at the initial concenꢀ
–3
–3
trations
(b) the reaction of
ning at 1 min intervals.
[1
] = 0.30
×
10 mol/L, [Nd(OOCMe) ] = 0.90 10 mol/L, and [H O] = 0.03 mol/L, scanning at 10 min intervals;
×
0
3 0
2
–3
–3
1
with
3
at
[
1
] = 0.30
×
10 mol/L, [Ce(OOCMe) ] = 0.90 10 mol/L, and [H O] = 0.05 mol/L, scanꢀ
×
0
3 0
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

366
NEFEDOV et al.
(а)
Time, min
40
(b)
Time, min
0
20
60
80
0
20
40
60
80
log A
Δ
log
Δ
A
0.8
1
1
–0.3
–0.6
–0.9
–1.2
–1.5
–0.3
–0.6
–0.9
–1.2
–1.5
0.75
0.60
0.45
0.30
0.15
0.7
0.6
0.5
0.4
0.3
0.2
2
2
0
20 40 60 80 100 120
Time, min
0
25 50 75 100 125 150 175
Time, min
–3
Fig. 3. Kinetic curves of the reaction at 80°С. (a) The reaction of
1
with
2
, scanning at 340 nm,
[
1
] = 0.30 10 mol/L, [2] =
×
0
0
–3
0.90
tation; (b) the reaction of
0.05 mol/L, ( ) accumulation curve of the reaction product and (
×
10 mol/L, and [H O] = 0.04 mol/L, (
1
) accumulation curve of the reaction product and (
2
×
) semilogarithmic represenꢀ
10 mol/L, and [H O] =
2
1
–3
–3
with
3, scanning at 343 nm,
[
1
] = 0.30
×
10 mol/L,
[
3
] = 0.90
0
0
2
1
2) semilogarithmic representation.
The kinetic curves for both reactions are almost concentration of
identical, except that cerium(III) acetate reacts thrice complex
. At higher PdII concentrations, k1 increases
as fast as neodymium(III) acetate. The rate constant k1 roughly linearly with an increase in the concentration
1; i.e., the reaction has zero order in
1
for both reactions increases linearly with an increase in of
the water concentration in the reaction solution (Fig. 4).
An analogous dependence was observed previously for
1
and the reaction obeys firstꢀorder kinetics:
k1 ].
An analogous situation is observed for neodymium(III)
acetate. At low concentrations (
10–3 mol/L), the reacꢀ
w
=
[1
reactions of complex
[11].
1 with divalent 3dꢀmetal acetates
≤
tion rate either does not depend on the NdIII concenꢀ
tration or even slightly decreases, and at higher NdIII
concentrations, the reaction is accelerated and is firstꢀ
order in NdIII acetate; as a result, at rather high pallaꢀ
dium concentrations, the reaction obeys secondꢀorder
kinetics:
The presence of the ordinate segment intercepted
by the plot (Fig. 4) points to the existence of a reaction
path independent of the water content. In addition, k1
is a complicated function of the concentration of palꢀ
ladium acetate 1 and rare earth acetates (Figs. 5a, 5b).
At low initial PdII concentrations (<10–3 mol/L),
the k1 rate constant almost does not depend on the
w = k1[1][2].
The experimental points in Figs. 5a and 5b can be
approximated, within the error of measurements, by a
parabola or another more complex curve; it is worth
noting than inflections in Figs. 5a and 5b are observed
in the range of equivalent concentrations of PdII and
NdIII acetates.
The above features of the reaction kinetics and the
observed blurring of the isosbestic points with an
increase in the water concentration in a reaction
medium indicate that water molecules are involved in
formation of both the reaction intermediates and
products. Inasmuch as the initial reagents and the
products have close but not identical optical spectra,
the observed kinetic pattern is insufficiently informaꢀ
tive.
0.12
0.10
0.08
0.06
0.04
0.02
0
0.8 1.0
0.6
0.4
1.2
0.2
[H2O], mol/L
Therefore, we preparatively obtained and structurꢀ
ally characterized by Xꢀray diffraction the reaction
products isolated from reaction mixtures with a differꢀ
Fig. 4. Rate constant
k vs. the water concentration for the
1
reaction of 1 with 2 at 80°С.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

THE ROLE OF WATER MOLECULES IN FORMATION
367
0.039
(а)
(b)
0.10
0.08
0.06
0.04
0.02
0.036
0.033
0.030
0.027
0.024
0.021
0
5
10 15 20 25 30
10 , mol/L
0
10
20
[Nd]
30
40
50
4
4
[Pd]
×
×
10 , mol/L
II
III
Fig. 5. Rate constant
k
vs. the initial concentrations of (a) Pd and (b) Nd acetates.
1
ent water content with the aim of comparing the specꢀ Ce(1)–O(9A), 2.688(2) Å; Ce(1)–O(10), 2.579(2) Å)
tra of their solutions with the spectra of the reaction (Fig. 6, Tables 3, 4).
mixtures.
Xꢀray diffraction showed that water plays an imporꢀ
tant role not only in reaction kinetics but also in the
Reaction Products
structure of reaction products. In the unit cell of comꢀ
plex 6a, the solvation acetic acid and water molecules
form a complicated system of intermolecular hydroꢀ
gen bonds (Fig. 7).
Previously [7, 8], we showed that the reaction of
equimolar amounts of complex
1.5 H2O ([PdII]0 : [NdIII]0 = 1 : 1) in hot acetic acid
afforded the complexes Pd2Nd2(μꢀOOCMe)8 (
2ꢀ
OOCMe)2(THF)2 and [Pd( ꢀOOCMe)4
Nd(OH2)( 2HOOCMe ( , in which
2ꢀOOCMe)]2
two asymmetric “Chinese lanterns” are linked by
2ꢀacetate bridges (Scheme 1).
1
with Nd(OOCMe)3
⋅
μ,η
In the crystal of 6a, the MeCOOH solvation moleꢀ
cules are involved in hydrogen bonds with the coordiꢀ
nated O(12) atom (O(12)···O(13), 2.725(4) Å), and the
H2O solvation molecules (O(17)···O(14), 2.610(4) Å)
form short contacts with the Pd atom (O(17)···Pd
3.608(3) Å) and the oxygen atom of the bridging
MeCOO– anion of a neighboring Pd–Ce complex
(
4
)
μ
μ
,
η
⋅
5)
μ,η
(
O(17)···O(1), 2.789(3) Å; O(17)···O(3), 2.748(4) Å). The
Me
C
Me
C
L
second H atom of the coordinated water molecule
(O(12)) is linked by a hydrogen bond with the O(16)
solvation molecule (O(12)···O(16), 2.731(4) Å), which
is also bonded to the bridging oxygen atoms coordinated
with the cerium atoms of two neighboring complex molꢀ
ecules (O(16)···O(10), 2.731(4) Å; O(16)···O(9A),
O(11A), 3.265(4), 3.246(4) Å) and the O(15) solvation
water molecule (O(16)···O(15), 2.912(4) Å) that forms
hydrogen bonds with the coordinated H2O molecule
of the third complex molecule (Fig. 7).
Me
O
O
O
Nd
O
C
Me
C
O
Me
C
O
O
Pd
O
O
O
O
O
O
C
O
C
Pd
Nd
O
O
C
O
O
Me
O
O
Me
Me
L
C
C
Me
Scheme 1. Structure of complexes
and (L = H O) [8].
Me
4
(L = THF) [7]
5
2
An analogous reaction of
1 with cerium(III) aceꢀ
tate followed by complete removal of the solvent and
dissolution of the reaction product in water yields the
[Pd(
complex (6b), which have almost the same molecular
geometry as 6a Pd···Ce, 3.4100(2) Å; Pd–O,
1.999(1)–2.011(1) Å; Ce–O, 2.457(1)–2.616(1) Å;
Ce(1)–O(9), 2.521(1) Å; Ce(1)–O(9A), 2.714(1) Å;
μ
ꢀOOCMe)4 Ce(OH2)2(
μ
,
η
2ꢀOOCMe)]2
14Н2О
⋅
In the present work, we found demonstrated that
an analogous reaction of complex with cerium(III)
acetate
in hot acetic acid at ([PdII]0 : [CeIII]0 = 1 : 1
yields the [Pd( ꢀOOCMe)4Ce(OH2)2(μ
2ꢀOOCMe)]2
2HOOCMe 6Н2О complex (6a) (Fig. 5, Tables 4, 5).
1
(
3
μ
,η
⋅
⋅
Its geometry is rather close to the geometry of comꢀ Ce(1)–O(10), 2.546(1)Å;Ce–Ow 2.483(1), 2.571(1) Å).
plexes and (Pd–Ce, 3.4117(3) Å; Ce–O, However, Xꢀray crystallography shows that complex
4
5
2.469(2)–2.556(2) Å; Ce(1)–O(9), 2.518(2) Å; 6b does not contain solvation molecules of acetic acid.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

368
NEFEDOV et al.
C(2A)
C(1A)
С(8)
H(11A)
O(11)
H(12C)
C(4A)
H(11B)
O(2A)
C(7)
O(1A)
O(3A)
O(12A)
C(10A)
O(8)
O(7)
С(6)
H(12D)
C(3A)
O(4A)
C(9A)
O(10)
C(5)
O(6)
O(5)
O(9A)
Pd(1A)
Ce(1)
Ce(1A)
Pd(1)
O(9)
O(6A)
O(4)
C(5A)
O(5A)
C(7A)
C(3)
C(9)
O(10A)
H(12B)
O(3)
O(6A)
C(4)
O(11A)
H(11C)
O(7A)
O(12)
O(1)
C(10)
O(2)
O(8A)
H(12A)
H(11D)
C(1)
C(2)
C(8A)
2
Fig. 6. Molecular structure of the complexes [Pd(
μ
ꢀOOCMe) Ce(OH ) (
μ
,
η
ꢀOOCMe)]
×
2HOOCMe
×
6Н О (6a) and
2
4
2 2
2
2
[Pd(
μ
ꢀOOCMe) Ce(OH ) (
μ
,
η
ꢀOOCMe)]
×
14Н О (
6b
) (50% probability thermal ellipsoids).
4
2 2
2
2
Ce(1K)
O(5AF)
O(17E)
O(17C)
O(9F)
O(3F)
Pd(1R)
O(13B)
O(14B)
O(16B)
O(16F)
O(8I)
O(12R)
O(17F)
O(12C)
O(15E)
O(15F)
Ce(1D)
O(13C)
O(11Q)
Ce(1C)
O(14C)
O(16C)
O(11J)
O(12I)
O(9AE)
O(9B)
O(15H)
Pd(1J)
O(11I)
O(12J)
O(16D)
O(9E)
O(15A)
O(14D)
O(9AH)
O(11B)
O(6A)
O(13D)
O(11B)
O(17A)
O(12A)
O(15C)
O(11H)
O(16A)
O(16E)
O(15D)
O(12P)
O(14E)
Pd(1B)
O(9AD)
O(17B)
O(13E)
Pd(1H)
Fig. 7. A fragment of the crystal packing of 6а with participation of hydrogen bonds.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

THE ROLE OF WATER MOLECULES IN FORMATION
369
(а)
Pd(1K)
Pd(1L)
O(5F)
Pd(1G)
O(10G)
O(11K)
Ce(1H)
O(12L)
O(19D)
O(18D)
O(11G)
O(16G)
O(13B)
O(18A)
O(17A)
O(12H)
O(19B)
O(15G)
O(17C)
O(15C)
O(14D)
O(16E)
O(17G)
O(16C)
O(15D)
O(14B)
O(17D)
O(13A)
O(16A)
O(18G)
O(15A)
O(12E)
O(11F)
O(18C)
Ce(1E)
O(10F)
O(11B)
Ce(1A)
Ce(1B)
Pd(1E)
Pd(1A)
(b)
Ce(1G)
Ce(1H)
Pd(1H)
Pd(1G)
Pd(1C)
Pd(1D)
O(13A)
O(1AA)
Ce(1A)
Pd(1B)
Pd(1N)
O(7I)
O(7AB)
Pd(1A)
O(7C)
O(7AA)
Ce(1R)
Ce(1B)
Pd(1R)
Pd(1E)
Pd(1Q)
Ce(1Q)
O(1I)
O(13D)
Pd(1P)
Pd(1L)
Pd(1K)
Fig. 8. A fragment of the crystal packing of 6b with intermolecular Hꢀbonds: (a) frontal view and (b) side view.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

370
NEFEDOV et al.
C(18)
C(17)
С(8)
C(10)
H(29A)
C(7)
C(6)
O(18)
O(8)
O(10)
O(7)
C(9)
O(17)
H(29B)
O(9)
O(29)
C(20)
C(19)
C(5)
O(5)
C(16)
O(6)
O(20)
H(30D)
H(30E)
O(15)
C(15)
O(16)
O(19)
Pd(3)
Pd(1)
O(30)
O(27)
Ln(1)
Ln(2)
Pd(2)
O(1)
O(23)
O(12)
C(11)
C(12)
O(2)
C(27)
O(3)
O(24)
C(1)
H(28E)
O(11)
C(23)
O(28)
C(28)
O(25)
O(21)
O(4)
C(3)
O(22)
C(2)
O(14)
C(21)
O(13)
C(24)
C(13)
C(25)
H(26D)
C(4)
C(22)
O(26)
C(26)
C(14)
+
Fig. 9. Molecular structure of the complexes [Pd(
μ
ꢀOOCMe) Ln(HOOCMe) (OH ) ] [Pd(
μ
ꢀOOCMe) Ln( ꢀ
μ
4
2
2 2
4
–
OOCMe) Pd] (Ln = Nd (7) and Ce (8)) (50% probability thermal ellipsoids).
4
In the crystal of 6b, 14 solvation H2O molecules the central LnIII atom is linked through eight bridging
acetate anions with two peripheral PdII atoms formally
belonging to two Chinese lanterns (Nd–O, 2.445(6)–
2.487(6) Å; Ce–O, 2.477(3)–2.529(3) Å).
form an intricate network of intermolecular hydrogen
bonds (O···O 2.697(3)–2.843(3) Å) involving the water
molecules coordinated to the cerium atom and the
oxygen atoms of bridging acetate anions (Fig. 8).
A considerable difference in nonbonding Pd···Ln
When the reagents were combined in
a
distances in the anion is noteworthy (Nd(1)···Pd(1)
,
Pd : Nd(Ce) ratio of 2 : 1, the basic reaction products
crystallizing directly from acetic acid were rather
3.3289(9) Å; Nd(1)···Pd(2), 3.4650(9) Å;
Ce(1)···Pd(1), 3.3399(4) Å; Ce(1)···Pd(2), 3.4895(3) Å).
This difference is likely caused by the existence of an
intermolecular hydrogen bond between the H atoms of
the MeCOOH and H2O molecules of the cation and the
oxygen atoms of the bridging acetate ligands of the anion
extraordinary cation–anion complexes [Pd(
OOCMe)4M(HOOCMe)2(OH2)2]+[Pd2M( ꢀOOCMe)8]–
(M = Nd ( ), Ce ( ). Their solvates with two
μ
ꢀ
μ
7
8
MeCOOH molecules and 1.5 H2O molecules were
obtained in 45 and 36% yield, respectively.
at the Pd(2) atom (for
O(28)···O(11), 2.580(6) Å; O(29)···O(9), 2.823(6) Å;
O(30)···O(15), 2.867(6) Å; for : O(26)···O(13),
7: O(26)···O(13), 2.654(6) Å;
The cations in complexes
5, 6) have a structure of the Pd(
nese lantern with the shortened (as compared to comꢀ
plexes and 6a and 6b) nonbonding Pd···M distance
(3.3018(9) and 3.3178(4) Å for and , respectively).
7
and
8 (Fig. 9, Tables 1,
μꢀOOCMe)4 M Chiꢀ
8
2.644(3) Å; O(28)···O(11), 2.607(3) Å; O(29)···O(9),
2.808(3) Å; O(30)···O(15), 2.828(3) Å). At the same
time, there is no noticeable elongation of the Pd(2)–O
bonds as compared with the Pd(1)–O bonds (Pd(1)–O,
1.986(6)–1.996(7) Å; Pd(2)–O, 1.988(5)–2.021(5) Å
5
7
8
The metal oxygen bond lengths of the bridging aceꢀ
tate anions are nearly the same as analogous bond
lengths in the complexes under consideration (for
Pd–O, 1.985(6)–2.009(7) Å; Nd–O, 2.384(7)–
2.438(6) Å; for : Pd–O, 1.997(3)–2.008(3) Å; Ce–
7:
for
7; Pd(1)–O, 1.990(3)–1.999(3) Å; Pd(2)–O,
1.998(2)–2.018(2) Å for
8). It is worth noting that, in
8
Pd–Ln pivalate lantern complexes (Ln = Nd, Sm, Eu)
[8], the elongation caused by hydrogen bonding was
considerable.
O, 2.431(3)–2.465(3) Å). The LnIII atom in the cation
is bonded to two oxygen atoms of the coordinated
MeCOOH molecules (Nd–O, 2.471(6), 2.499(6) Å;
Ce–O, 2.508(3), 2.537(3) Å) and the oxygen atoms of
two coordinated water molecules (Nd–O, 2.480(6),
2.481(6) Å; Ce–O, 2.528(3), 2.529(3) Å). The anion
Two neutral complexes—Au2M(μꢀOOCMe)8 (M =
Sr, Pb) obtained by the reaction of M[Au(OH)4]2 with
acetic acid [29, 30]—are known to have a structure
of the complex has a rather unique structure in which analogous to the structure of cations in
7 and 8 with
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

THE ROLE OF WATER MOLECULES IN FORMATION
371
C(6)
C(4)
C(2)
C(8)
C(18A)
C(5)
C(3)
C(7)
C(24)
C(23)
O(7)
O(9)
O(8)
C(1)
O(6)
O(12)
O(10)
C(14A)
O(5)
O(11)
C(10A)
C(16)
C(17A)
O(21A)
C(12)
Pd(3)
Pd(4)
C(13A)
O(3A)
Pd(2)
O(19)
C(9A)
O(13A)
O(27)
O(23)
Pd(1)
O(22A)
Pd(7A)
C(15)
O(28)
O(24)
C(11)
O(16)
O(2)
C(22A) O(14A)
O(26A)
C(21A)
O(18A)
O(17A)
O(4)
O(1)
C(20)
O(20)
C(19)
Ce(2A)
Pd(5A)
O(24A)
C(20A)
O(28A)
Pd(6A)
Ce(1)
Pd(6)
O(25A)
Pd(5)
Ce(2)
O(23A)
C(19A)
Pd(7)
O(2A)
O(25)
O(13)
O(20A)
C(21)
O(4A)
O(1A)
O(26)
O(22)
O(16A)
O(27A)
O(3)
O(19A)
C(15A)
Pd(2A)
O(14)
C(9)
C(22)
O(17)
O(18)
C(11A)
C(23A)
C(13)
Pd(1A)
O(7A)
Pd(4A)
C(16A)
Pd(3A)
O(9A)
C(12A)
C(10) O(21)
O(6A)
C(17)
C(14)
O(8A)
C(3A)
O(10A)
C(5A)
C(24A)
O(5A)
C(1A)
O(12A)
O(11A)
C(8A)
C(7A)
C(4A)
C(18)
C(6A)
C(2A)
Fig. 10. Molecular structure of the heptadecanuclear complex {[Pd(
O) CePd }(OH) 27H O ) (30% probability thermal ellipsoids).
μ
ꢀOOCMe) Ce(OOCMe) ] [Pd (
μ
ꢀOOCMe) ] ( ꢀ
μ
4
4 2
4
4 2
4
⋅
(9
8
4
3
2
similar nonbonding metal–metal distances (Au···Sr, squareꢀplanar environment, and the CN of the cerium
3.525 Å; Au···Pb, 3.44 Å).
atoms is eight.
An analogous reaction of two moles of
1 with a
It is worth noting that complex
9 has a rather
mole of cerium(III) acetate followed by complete
removal of the solvent and dissolution of the reaction
products in hot water yields, in addition to the aforeꢀ
mentioned complex 6b (45%), an extraordinary hepꢀ
unique skeleton of the Pd4(
ꢀOOCMe)4(O–)4 pallaꢀ
μ
dium acetate corona. As is known, almost all pallaꢀ
dium(II) carboxylates have a trinuclear structure
Pd3( ꢀOOCR)6 [31–35]. The squareꢀplanar core is
μ
tadecanuclear heterometallic complex {[Pd(
OOCMe)4Ce(OOCMe)4]2[Pd4( ꢀOOCMe)4]2(μ4ꢀO)8
CePd4}(OH)3 27H2O ( (5%).
The Ce(1) atom (Ce–O, 2.324(4)–2.339(4) Å) at
the center of molecule (Fig. 10, Tables 1, 7) is
bonded to eight oxygen atoms of two Pd4(μꢀO)4(μ
μꢀ
more typical of platinum(II) carboxylates [36–40],
but is untypical of the palladium(II) chemistry. The
only exception is the nitritoacetate complex Pd4(
μ
⋅
9)
μꢀ
OOCR)6(μꢀNO2)4 [41, 42].
9
The oxidation state of the cerium atoms deserves
special consideration. If complex were a neutral
molecule, it would contain cerium(IV) atoms; at the
same time, initial complex and isolated complexes
6a 6b, and contain cerium(III). We can assume that
ꢀ
9
OOCMe)4 moieties having a “corona” geometry (Pd···Ce,
3.3424(5)–3.3473(5) Å; Pd···Pd, 3.0569(7)–3.0905(8) Å;
Pd–μ4ꢀO, 1.990(4)–2.000(5) Å, Pd–O(OOCMe)
2.001(5)–2.029(5) Å). The palladium atoms of both
coronas are almost in the same plane (within 0.035 Å),
and two Pd4 tetragons are parallel to each other. Each
of the opposite bridging oxygen atoms of the coronas
is bonded to three palladium atoms and the central
cerium atom. The palladium atoms of the central
Pd4Ce moiety are linked by bridging acetate anions
3
,
,
8
cerium atoms are oxidized by air oxygen in the course
of reaction and product isolation. The ease of reversꢀ
ible oxidation of CeIII to CeIV has been well known
since the discovery of the Zhabotinsky reaction [43].
Noteworthy is the fact that complex
9 in the unit cell
(
V
= 29572(2) Å3) is surrounded by an extensive netꢀ
work of hydrogenꢀbonded H2O molecules, which conꢀ
with two Pd(μꢀOOCMe)4Ce Chinese lanterns
tains a large number of hardꢀtoꢀlocate H atoms. Some
(Pd···Ce, 3.3338(7) Å; Pd–O, 1987(6)–2.010(6) Å;
Ce–O, 2.471(5)–2.539(5) Å). Thus, eight oxygen of the H2O molecules can be actually OH– anions.
atoms are μ4ꢀbridges, all palladium atoms have a Based on this assumption, complex
9 is most likely a
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

372
NEFEDOV et al.
(а)
(b)
(c)
1.2
1.0
0.8
0.6
0.4
0.2
1.4
1.2
1.0
0.8
1
0.8
0.6
0.4
0.2
1
2
2
2
3
0.6
0.4
0.2
0
3
1
4
0
0
300
400
, nm
500
300
400
λ
500
600
300
400
, nm
500
, nm
λ
λ
Fig. 11. Comparison of the optical spectra of reaction solutions with the spectra of solutions of isolated heteronuclear Pd–Nd(Ce)
complexes. (a): ( ) The initial spectrum of the reaction solution (Pd : Nd = 1 : 1) at low water content ([H O] = 0.03 mol/L,
[Pd] = [Nd] = 3
1
1 + 2
2
–4
–4
×
10 mol/L, 80
solution of the complex [Pd( ꢀOOCMe) Nd(OH )(
0.03 mol/L, [ ] = 0.03 mol/L, 80
([H O] = 0.05 mol/L, [Pd] = 3.36
0
°
С); ) the spectrum of a 4.5
2HOOCMe ( ) in the same solvent ([H O] =
). (b): The final spectrum of the 1 + 3 reaction solution (Pd : Ce = 3.7 : 1) at low water content
(
2
) the final spectrum of the reaction solution; (
3
×
10 mol/L
0
0
2
μ
μ
,
η
ꢀOOCMe)]
⋅
5
4
2
2
2
5
°
С
–3
–3
–3
×
10 mol/L, [Ce] = 0.9
ꢀOOCMe) Ce(HOOCMe) (OH ) ] [Pd(
×
10 mol/L, 80
°
С); ) the spectrum of a 0.9
ꢀOOCMe) Ce( ꢀOOCMe) Pd] (7
4
(2
×
10 mol/L
) in the same solꢀ
10 mol/L solution of the complex [Pd(
) at low water content ([H O] = 0.05 mol/L, 60 С); ) the final spectrum of
reaction solution (Pd : Ce = 1 : 1) at low water content ([H O] = 0.05 mol/L, [Pd] = [Ce] = 0.9
2
0
+
–
solution of the complex [Pd(
μ
μ
μ
4
2
2 2
4
–3
vent ([H O] = 0.05 mol/L, 60
°
C
). (c): (
1
) The spectrum of a 1.0
×
μ
ꢀ
2
4
2
OOCMe) Ce(OH ) (
μ
,
η
ꢀOOCMe)] 14Н О (
⋅
6
b
°
(2
2 2
2
2
2
–3
the
1
+
3
×
10 mol/L, 60
°
С);
2
0
0
(3
) the final spectrum of the
1
+
3
reaction solution (Pd : Ce = 1 : 1) at high water content ([H O] = 11.05 mol/L, [Pd] = 0.9
) the spectrum of a 0.74
) at high water content ([H O] = 13.9 mol/L, 60 С
×
2
2
0
–3
–3
10 mol/L, 60
°С);
(
6
4
b
×
10 mol/L solution of the complex [Pd(
).
2
μ
ꢀOOCMe) Ce(OH ) (μ,η ꢀ
4 2 2
OOCMe)] 14Н О (
⋅
°
2
2
triply charged cation rather than a neutral molecule; water content in acetic acid. However, the positions
in this case, the cerium atoms have the oxidation state 3+. and intensities of absorption maxima are almost indisꢀ
tinguishable.
This assumption is supported by the fact that, using
the same procedure, we obtained red single crystals of
analogous neodymium complex 10. The unit cell about a rather complicated character of the reactions
parameters and IR spectra of complex 10 are nearly occurring in the
and systems. Most likely
identical to those of complex . Inasmuch as neodyꢀ that these reactions occur simultaneously along sevꢀ
This fact is consistent with the above assumption
1
+
2
1 + 3
9
mium(III) is not able to be oxidized by air oxygen to eral pathways and, depending of the solvent composiꢀ
NdIV, we can assume that the cerium atoms in complex tion, involve different intermediates and reaction
9
are also in the oxidation state 3+.
products with close band positions in the spectra.
Taking into account the results obtained, we can
suggest basic ways of transformation of the reagents. In
[44], it was shown by NMR that, in solutions containꢀ
ing even small amounts of water, at least one bridging
Comparison of the Optical Absorption Spectra
The optical spectra of reactions solutions of
1 + 2
and + 3 are nearly identical to the spectra of soluꢀ acetate group of molecule 1 is subjected to hydrolytic
1
tions in acetic acid of crystalline reaction products cleavage. We can assume that this process, which facilꢀ
independently synthesized under the same conditions itates the opening of the threeꢀmembered ring and forꢀ
(Fig. 11). The observed differences are most likely due mation of the PdII building block (Scheme 2), is a key
to different solvent composition, namely, different stage in the reaction system:
Me
C
Me
C
Me
Me
C
Me
Me
Me
C
C
C
O
C
O
O
O
O
O
O
O
O
Pd
O
O
O
O
O
OH2
O
O
H O
2
Pd
Pd
Pd
O
Pd
Pd
Pd
O
O
O
O
O
O
O
O
O
O
O
C
C
C
C
C
C
C
Me
Me
Me
Me
Me
Me
Me
Scheme 2.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

THE ROLE OF WATER MOLECULES IN FORMATION
373
Another component of the reaction is presumaꢀ dissociation of complex
2
or
3
in solution (Scheme 3):
bly the NdIII(CeIII) building block, which forms upon
Me
Me
Me
H
O
C
C
O
O
O
Me
O
O
O
O
H2O
O
O
O
O
O
O
Me
C
Ln
Me
C
Me
Me
C
Ln
O
Ln
O
O
O
O
O
O
OH2
C
C
O
H
C
C
Me
Me
Me
Scheme 3.
Various combinations of these building blocks can (Scheme 4). We isolated and characterized by Xꢀray
lead to a number of heterometallic complexes crystallography some of these complexes.
+
Me
Me
Me
O
O
C
C
C
O
H
H
O
O
O
O
H
O
O
H
Ln
Pd
O
C
O
O
O
Me
O
H
H
C
C
Me
Me
Me
Me
C
Me
C
Me
Me
C
Me
Me
C
C
C
C
O
L
L
O
O
O
O
O
O
O
Ln
O
O
O
O
Ln
O
O
O
O
O
O
O
Pd
+
Me
C
Pd
Ln
Pd
O
O
O
O
O
O
O
O
O
C
O
C
O
C
C
L
L
C
C
C
Me
Me
Me
Me
Me
Me
Me
–
Me
Me
Me
C
Me
C
C
C
O
O
O
O
O
O
O
O
O
Ln
Pd
Pd
O
C
O
O
C
O
O
O
O
Ln = NdIII, CeIII
C
C
L = OH2, THF, HOOCMe
Me
Scheme 4.
Me
Me
Me
Thus, our findings allow us to draw the following age of kinetically inert molecule
1. Such a “water
conclusions: First, water molecules are involved in key effect” was observed previously when we studied the
stages of the reactions and favor the hydrolytic cleavꢀ kinetics of the reaction of complex
1 with 3dꢀmetal
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

374
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ACKNOWLEDGMENTS
634, 231 (2008).
This work was supported by the Russian Foundation
for Basic Research (project nos. 09ꢀ03ꢀ00514, 09ꢀ03ꢀ
12114, and 10ꢀ03ꢀ90420), the Council for Grants of the
President of the Russian Federation for Support of Leadꢀ
ing Scientific Schools (grant no. NShꢀ65264.2010.3), and
the Presidium of the RAS (the programs “Development of
Methods of Synthesis of Chemical Substances and Design
of New Materials” and “Theoretical and Experimental
Investigation of the Chemical Bond Nature and Mechaꢀ
nisms of Chemical Reactions and Processes”).
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