Spin transition in the molecular heterospin complex of Cu(hfac)2 with 4,4,5,5-tetramethyl-2-(1-methylpyrazol-5-yl)-4,5-dihydroimidazole-1-oxyl 3-oxide

Article abstract of DOI:10.1007/s11172-013-0089-y

The synthesis, structure, and magnetic properties of the products of the reaction for Cu(hfac)₂ (hfac is hexafluoroacetylacetonate) with spin-labeled nitronyl nitroxides 4,4,5,5-tetramethyl-2-(1-R-1H-pyrazol-5-yl)-3- imidazoline-1-oxyl 3-oxides L^5/R (R = Me, Et, Pr, Bu), viz., binuclear complex [Cu(hfac)₂L^5/Me]₂ and chain polymer complexes [Cu(hfac)₂L^5/R]_n, are described. The polymer heterospin chains are built according to head-to-head (R = Me, Et, Pr, Bu) and head-to-tail (R = Pr, Bu) motifs. Compound [Cu(hfac)₂L^5/Me]₂ is characterized by the ability to reveal the reversible effect of thermally induced spin transition at a temperature about 75 K (without hysteresis). In the set of heterospin Cu^II compounds with spin-labeled pyrazoles, this is the earlier unknown example of a molecular complex exhibiting a similar magnetic anomaly.

Full text of DOI:10.1007/s11172-013-0089-y

Russian Chemical Bulletin, International Edition, Vol. 62, No. 3, pp. 661—671, March, 2013
661
Spin transition in the molecular heterospin complex of Cu(hfac)2
with 4,4,5,5ꢀtetramethylꢀ2ꢀ(1ꢀmethylpyrazolꢀ5ꢀyl)ꢀ
4,5ꢀdihydroimidazoleꢀ1ꢀoxyl 3ꢀoxide*
S. V. Fokin, E. T. Kostina, E. V. Tret´yakov, G. V. Romanenko,
A. S. Bogomyakov, R. Z. Sagdeev, and V. I. Ovcharenko
International Tomography Center, Siberian Branch, Russian Academy of Sciences,
3a ul. Institutskaya, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383) 333 1399. Eꢀmail: fokin@tomo.nsc.ru
The synthesis, structure, and magnetic properties of the products of the reaction for
Cu(hfac)2 (hfac is hexafluoroacetylacetonate) with spinꢀlabeled nitronyl nitroxides 4,4,5,5ꢀ
tetramethylꢀ2ꢀ(1ꢀRꢀ1Hꢀpyrazolꢀ5ꢀyl)ꢀ3ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxides L5/R (R = Me, Et, Pr, Bu),
viz., binuclear complex [Cu(hfac)2L5/Me]2 and chain polymer complexes [Cu(hfac)2L5/R]n, are
described. The polymer heterospin chains are built according to "headꢀtoꢀhead" (R = Me, Et,
Pr, Bu) and "headꢀtoꢀtail" (R = Pr, Bu) motifs. Compound [Cu(hfac)2L5/Me]2 is characterized
by the ability to reveal the reversible effect of thermally induced spin transition at a temperature
about 75 K (without hysteresis). In the set of heterospin CuII compounds with spinꢀlabeled
pyrazoles, this is the earlier unknown example of a molecular complex exhibiting a similar
magnetic anomaly.
Key words: molecular magnets, spin transitions, copper(II) complexes, hexafluoroacetylꢀ
acetonates, nitroxyl radicals, thermomagnetic measurements, Xꢀray diffraction analysis.
"Breathing" crystals based on heterospin complexes of
CuII hexafluoroacetylacetonate, [Cu(hfac)2], with stable
nitroxyl radicals are valuable objects for the detailed study
of structural rearrangements induced by external effects.1—30
These rearrangements most substantially affect heteroꢀ
spin exchange clusters and result in the appearance of
magnetic anomalies in the curves of the effective magnetic
moment (eff) vs temperature.1—30 The study of coordinaꢀ
tion compounds Cu(hfac)2 with nitronyl nitroxide radiꢀ
cals containing a pyrazole substituent in position 2 of the
imidazoline cycle (L4/R) found a whole family of comꢀ
plexes capable of exhibiting effects similar to spinꢀcrossꢀ
over.6,10,17,19—21,29,30 They possessed a valuable property:
in the most cases, single crystals of the complexes did not
crack after passing the temperature range in which the
structural phase transition occurred along with the conjuꢀ
gated magnetic transition. Therefore, for all heterospin
complexes and related solid solutions,10,12 the structure at
different temperatures (both before and after the magnetic
transition) was determined, which presented unique posꢀ
sibility to observe the structural dynamics in these systems
in the range of phase transition.
metric nonrigidity of Cu(hfac)2 provokes a potent possiꢀ
bility of formation for a considerable number of comꢀ
pounds by the variation of the synthesis conditions: solꢀ
vent, temperature, and ratio of reagents. For example, the
reaction of Cu(hfac)2 with L4/Me gave 12 crystalline phasꢀ
es, which were structurally characterized. Of them only
two phases manifested magnetic anomalies in the eff(T)
curve.11 Therefore, not to "miss" a heterospin phase with
nontrivial magnetic properties, one should vary the synꢀ
thesis conditions and to isolate and study all products
formed in the studied synthetic system Cu(hfac)2—radiꢀ
cal—solvent. An additional complicating factor is that
crystals of two or more solid phases rather than one phase
are isolated from the mother liquor. These phases can
mechanically be separated in a favorable situation. As for
the mentioned products of the reaction of Cu(hfac)2 with
L4/Me, in several cases, single crystals of different phases
were nearly discernible in both color and habitus.11 Thereꢀ
fore, before a magnetochemical experiment, it was necesꢀ
sary to check each(!) single crystal, and only then this
crystal could be joined with crystals of the same phase.
Only 5—10 years ago, these circumstances impeded the
search for "breathing" crystals and study of their properꢀ
ties. It seems that the discovery of a similar compound
was a lucky chance and, as a consequence, a nonclassical
spin transition was detected rather rarely.9 However, to
date, when a large experience on the synthesis and magneꢀ
It is noteworthy that the search for similar compounds
requires a special approach. The matter is that the stoichioꢀ
* Dedicated to the Academician of the Russian Academy of
Sciences I. P. Beletskaya on the occasion of her birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 0660—0670, March, 2013.
1066ꢀ5285/13/6203ꢀ661 © 2013 Springer Science+Business Media, Inc.

662
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
Fokin et al.
Scheme 1
tochemical analysis of similar objects has been accumuꢀ
lated, it was revealed that this phenomenon is rather popꢀ
ular and nonclassical spin transitions are nor detected even
in the case of insignificant structural rearrangements of
the heterospin solid phase upon a polymorphous transforꢀ
mation.7,30
In this work, we describe the new complex Cu(hfac)2
with the stable nitroxyl radical possessing a spin transiꢀ
tion. The complex was observed by the study of a set of
heterospin solid phases containing spinꢀlabeled pyrazoles
L5/R. We also compared the structures and magnetic propꢀ
erties of the Cu(hfac)2 complex with isomeric ligands L4/R
and L5/R. The comparative analysis showed that the tranꢀ
sition from compounds with ligand L4/R to compounds
with ligand L5/R leads to a substantial decrease in the
plasticity of the crystals and suppression of the "breathing"
crystal effect.
R = Me (a), Et (b), Pr (c), Bu (d)
Reagents and conditions: i. (1) BuLi, THF, –90 C, then –10 C;
(2) DMF, –90 C; (3) HCl, pH = 1; (4) aqueous NaHCO3;
ii. (1) 2,3ꢀbishydroxylaminoꢀ2,3ꢀdimethylbutane sulfate H2O;
(2) NaHCO3. iii. NaIO4, CH2Cl2, H2O.
(or do not exhibit at all) effects of nonclassical spin transiꢀ
tions, because ligands L5/R have lower intramolecular
"plasticity" compared to their 4/Rꢀisomers, since a possiꢀ
ble turning angle of the pyrazole cycle relatively to the
2ꢀimidazoline cycle in L5/R is noticeably larger than in the
earlier studied ligands L4/R (see Refs 6, 10, 29, and 30).
The pairs with short distances between O atoms equal
to 3.271(3) and 3.313(2) Å can be distinguished in the
packings of L5/Me and L5/Pr, respectively (see Fig. 1). Their
experimental temperature dependences of the effective
magnetic moment are well described by the model of exꢀ
changeꢀbonded dimers (H = –2JS1S2).34 The theoretical
processing of experimental data for this model gave the
following optimum parameters: g = 2.03 and J = –36.6 K
for L5/Me (see Ref. 33) and g = 2.05 and J = –33.1 K for
L5/Pr (Fig. 2). Chains of radicals with alternating O—O
distances of 3.462(1) and 3.593(1) Å can be distinguished
in the molecular packing of L5/Et; the energy of exchange
interactions estimated by the model of exchangeꢀbonded
dimers is J  –22 K. The shortest distance between the
O atoms of the NO groups in L5/Bu is 4.553(1) Å, which
results in weak exchange interactions between paraꢀ
magnetic centers (J  –1.4 K) and, as a consequence,
an almost constant value of eff in the 10—300 K range
(see Fig. 2).
Results and Discussion
The synthesis of L5/R was carried out via the classical
scheme including the preparation of alkylpyrazoles 1a—d,
their transformation into bicyclic derivatives 2a—d, and
the oxidation of the latter to the target nitronyl nitroxides
(Scheme 1).
The structure of L5/R was confirmed by Xꢀray diffracꢀ
tion analysis. It was found that in molecules of the radicals
(Fig. 1) the N—O bond lengths range from 1.272(1) to
1.288(1) Å, which is typical of nitronyl nitroxides.31,32 In
ligand L5/R, the angles between the planes of the nitronyl
nitroxide fragment CN2O2 and pyrazole cycle change from
36.3 to 50.6, which is significantly higher than in isomerꢀ
We already mentioned that the reaction of Cu(hfac)2
with nitroxyls can afford a considerable number of heteroꢀ
spin complexes.11 This turned out valid also for the reacꢀ
tion products of Cu(hfac)2 with L5/R. Of the group of
isolated compounds, we will concentrate attention only
on the complexes with the ratio Cu(hfac)2 : L5/R = 1 : 1,
since they are most interesting for the purposes of the
present work. These products allow one to compare the
ic ligands L4/R (for L4/Me, 3.7(3) (see Ref. 33); for L4/Et
,
5.4(6)). Such a substantial increase in the intramolecular
dihedral angles in L5/R is a consequence of steric repulsion
of substituents R and N—O groups. Already at the first
stage of the work, this result suggested that coordination
compounds Cu(hfac)2 with L5/R can exhibit more rarely

Molecular magnets
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
663
3.462 Å
3.271 Å
3.593 Å
L5/Et
L5/Me
3.313 Å
4.553 Å
L5/Bu
L5/Pr
Fig. 1. Structures of molecules L5/R and the shortest intermolecular contacts NO...ON (H atoms are omitted). The parameters of
atomic shifts are given with 50% probability.
magnetic structural correlations for the complexes with
isomeric L4/R and L5/R, because all chain polymers with
L4/R exhibiting thermally induced magnetic effect had the
composition [Cu(hfac)2L4/R]n (see Refs 6, 9, 10, 17, 19,
20, 21, 29, 30).
can produce dimeric complex [Cu(hfac)2L5/Me]2 and chain
polymers [Cu(hfac)2L5/Me]n. As a rule, they are formed in
the synthesis as a mixture of crystals that can be separated
mechanically. It was found that [Cu(hfac)2L5/Me]2 is preꢀ
dominantly formed into the solid phase when using
The procedures of obtaining compounds with the ratio
Cu(hfac)2 : L5/R equal to 1 : 1 in the generalized form are
shown in Scheme 2. The reaction of Cu(hfac)2 with L5/Me
eff/
B
1.6
1.2
0.8
0.4
1
2
3
4
Scheme 2
100
200
300 T/К
Fig. 2. Plots eff(T) for L5/R at (R = Me (1), Et (2), Pr (3), and
Bu (4)). Points are experiment, and solid lines are theoretical
curves.
i. R = Me; CH2Cl2 : hexane, 3 : 1; ii. R = Pr, Bu; hexane;
iii. R = Me, Et, Pr, Bu; CH2Cl2 : hexane, <1 : 1.

664
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
Fokin et al.

eff/
B
CH2Cl2—hexane mixture with predomination of CH2Cl2,
whereas [Cu(hfac)2L5/Me]n with a minor admixture of the
dimeric complex crystallizes from a mixture with a hexane
excess. The solid phases can be obtained only with the use
of seeding crystals selected mechanically from mixtures of
the complexes.
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Product [Cu(hfac)2L5/Me]2, whose phase consists of
centrosymmetric dimeric molecules (Fig. 3), is worth speꢀ
cial mentioning. Its structure was determined at 295, 240,
120, and 30 K. Under standard conditions, the coordinaꢀ
tion modes CuNO5 are elongated octahedra with axial
distances Cu—ONO 2.354(2) Å and Cu—Ohfac 2.262(2) Å
(see Table 1). As the temperature decreases to 120 K, the
Cu—Ohfac bonds gradually shorten; with the further coolꢀ
ing to 30 K, the complex undergoes the reversible strucꢀ
tural phase transition, being a change in the Jahn—Teller
axis of the Cu bipyramid (Table 1). As a result, the ONO
atom and the Ohfac atom in the transꢀposition get in the
equatorial plane with Cu—O distances of 2.034(1) and
2.029(1) Å, respectively, and two other Ohfac atoms miꢀ
grate to the axial positions (2.279(1) and 2.320(1) Å).
The character of the dependence eff(T) typical of
[Cu(hfac)2L5/Me]2 (Fig. 4) entirely correlates with the temꢀ
100
200
300
T/К
Fig. 4. Plot eff(T) for [Cu(hfac)2L5/Me]2. Dashed lines show the
values of temperature at which the Xꢀray diffraction study was
performed.
perature dynamics of the structure. At ambient temperaꢀ
ture eff = 3.45 B, which corresponds to four nonꢀinterꢀ
acting paramagnetic centers with the spin equal to 1/2 and
the g factor equal to 2. On cooling to 120 K, eff gradualꢀ
ly decreases to 2.85 B and decreases sharply with the
further cooling. This is a consequence of the fact that at
T  120 K the coordinated ONO atoms transit from the
axial to equatorial positions (see Table 1), which results in
the appearance of a strong antiferromagnetic exchange in
the >N—•O—Cu2+ exchange clusters. This effect was deꢀ
scribed for heterospin dimers Cu(hfac)2 with metaꢀpyridylꢀ
substituted nitronyl nitroxide.1,2
Thus, compound [Cu(hfac)2L5/Me
] is characterized
2
by the capability of manifesting the reversible effect of the
thermally induced spin transition. This effect occur reproꢀ
ducibly and reversibly at temperatures about 75 K on both
heating and cooling of the polycrystalline sample of the
heterospin complex. No delay in the relaxation of the strucꢀ
ture is detected, due to which no hysteresis loop is obꢀ
served by measurements of the eff(T) dependence. Single
Fig. 3. Structure of dimeric molecule [Cu(hfac)2L5/Me]2. Hereꢀ
inafter the CF3 groups of bischelates Cu(hfac)2 and the CH3
groups of the 2ꢀimidazoline rings are omitted.*
crystals of [Cu(hfac)2L5/Me
] possess thermal plasticity,
2
which is also a distinctive feature of "breathing" crysꢀ
tals.10,29. As in the case of [Cu(hfac)2L5/Me]2, this makes
it possible to determine the structures of both highꢀ and
lowꢀtemperature phases using the same crystal. The result
obtained asserts that compounds capable manifesting the
"breathing" crystal effect can be among the heterospin
complexes with pyrazolꢀ5ꢀyl derivatives of nitroxyls.
It was also interesting to compare the magnetic strucꢀ
tural correlations for the whole series of dimers
[Cu(hfac)2L5/R]2. However, complexes of similar structure
(L5/Et, L5/Pr, and L5/Bu), including the conditions favorꢀ
able for predominant crystallization of [Cu(hfac)2L5/Me]2,
were not detected. All other isolated compounds with the
ratio Cu(hfac)2 : L5/R = 1 : 1 had the chain polymer strucꢀ
Table 1. Selected bond lengths in dimer [Cu(hfac)2L5/Me
]
2
Bond
d/Å
30 К
120 К
240 К
295 К
Cu—ONO
Cu—Ohfac
2.034(1)
2.029(1)
2.279(1)
2.320(1)
1.980(1)
2.048(2)
1.320(2)
1.282(2)
2.227(2)
2.180(4)
2.101(2)
2.120(3)
1.983(2)
2.038(2)
1.301(3)
1.281(3)
3.172(5)
2.324(2)
2.241(2)
2.006(2)
2.012(2)
1.965(2)
2.019(2)
1.288(2)
1.270(2)
3.186(3)
2.354(2)
2.262(2)
1.994(2)
2.003(2)
1.973(2)
2.030(3)
1.289(2)
1.269(2)
3.204(4)
Cu—N
N—O
ture (see Scheme 2). Complexes [Cu(hfac)2L5/R
] with
n
—•O...O•— 3.114(3)
the "headꢀtoꢀhead" chain motif (Fig. 5) was obtained for
* Figures 3, 5, and 7 are available in full color in the onꢀline version of the journal (http://www.springerlink.com).

Molecular magnets
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
665
a
b
c
d
Fig. 5. Fragments of chains with the "headꢀtoꢀhead" motif and their packing in structures [Cu(hfac)2L5/R]n (R = Me (a), Et (b), Pr (c),
and Bu (d)).
all L5/R. Two types of coordination modes alternate in the
chain: modes CuO4N2 in which the square environment
of the Cu atom in Cu(hfac)2 is supplemented to distorted
octahedral by two N atoms of the pyrazole cycles of
two bidentateꢀbridging L5/R and modes CuO6 with two
ONO atoms of the nitronyl nitroxide fragments in the axiꢀ

666
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
Fokin et al.
Table 2. Selected bond lengths (d) in complexes [Cu(hfac)2L5/R]n with the "headꢀtoꢀhead" motif of the polymer chain
Bond
d/Å
[Cu(hfac)2L5/Me
120 К
]
[Cu(hfac)2L5/(Et)
(296 К)
]
[Cu(hfac)2L5/Pr
(293 К)
]
[Cu(hfac)2L5/Bu
(240 К)
]
n
n
n
n
28 К
295 К
Cu—ONO
Cu—N
N—O
2.325(2)
2.410(2)
2.395(3)
2.557(3)
1.276(3)
1.282(3)
1.279(3)
1.268(3)
2.342(2)
2.408(2)
2.415(2)
2.586(3)
1.272(3)
1.282(3)
1.280(3)
1.271(3)
3.346(3)
2.374(2)
2.423(2)
2.450(3)
2.621(3)
1.273(3)
1.275(3)
1.279(3)
1.270(3)
3.417(3)
2.380(2)
2.390(2)
2.448(2)
2.524(2)
1.285(3)
1.277(3)
1.283(3)
1.275(3)
3.550(3)
2.402(2)
2.485(2)
2.711(3)
2.448(3)
1.288(3)
1.285(3)
1.276(3)
1.274(3)
—•O...O•— 3.281(2)
3.458(3)
>5
al positions. The latter are trispin exchange clusters
{ONCNO—Cu2+—ONCNO}. The Cu—N and Cu—ONO
bond lengths in the coordination modes are within
2.448(2)—2.621(3) and 2.374(2)—2.423(2) Å, respectiveꢀ
ly (Table 2). In [Cu(hfac)2L5/Bu]n the Cu—ONO distance
even with a correction to the Jahn—Teller effect noticeꢀ
ably exceeds the upper limit of length for this bond and
equals 2.711(3) Å (see Ref. 32). The shortest interchain
perature decreases results in a decrease in eff due to preꢀ
domination of the antiferromagnetic exchange in the solid
phases. Taking into account that the distances between
the uncoordinated ONO atoms of the adjacent chains in
[Cu(hfac)2L5/Me]n are only 3.417(3) Å at 295 K and shortꢀ
en to 3.281(2) Å on cooling to 28 K (see Table 2), it can be
assumed that in the temperature range of 30—300 K the
decrease in eff is due to the direct exchange interaction
between unpaired electrons of the paramagnetic ligands of
adjacent chains. A similar situation was observed earlier in
the complexes with tetrazolylꢀ and isoxazolylꢀsubstituted
nitronyl nitroxides.35,36 The strongest antiferromagnetic
—•O...O•— contacts were found in [Cu(hfac)2L5/Me
]
n
(3.417(3) Å) and [Cu(hfac)2LPr]n (3.458(3) Å).
The experimental dependences eff(T) for this series of
solid phases are shown in Fig. 6. In the region of high
temperatures, the values of eff for these complexes range
from 2.6 to 2.7 B, which is close to the theoretical value
(2.45 B, at g = 2.00) for the system of almost nonꢀ
interacting spins of Cu2+ ions and nitroxyl based on the
exchange interactions are manifested by [Cu(hfac)2L5/Me
]
n
and [Cu(hfac)2LPr]n in which the —•O...O•— interchain
contacts are shortest (see Fig. 6, Table 2).
Chain polymer [Cu(hfac)2L5/R
] with the "headꢀtoꢀ
n
empirical formula {Cu(hfac)2L5/R}. In [Cu(hfac)2L5/Bu
]
tail" motif (Fig. 7) were obtained only for L5/Pr and L5/Bu
.
n
the distances between the paramagnetic centers are short
and, hence, eff remains almost unchanged in the range
from 20 to 300 K and then begins to decrease. For other
complexes and especially for [Cu(hfac)2L5/Me]n, the temꢀ
In their solid phases all coordination modes are the
same. The N atoms of the pyrazole cycle and the ONO
atoms are localized in vertices of the CuO5N bipyramids.
In the complexes with LPr and LBu, the Cu—N disꢀ
tances are 2.411(4) and 2.321(3) Å, respectively, and the
Cu—ONO distances are 2.461(4) and 2.549(3) Å, respecꢀ
tively. The —•O...O•— interchain distance are long and
exceed 4.5 Å (Table 3).

eff/
B
2.75
The eff(T) dependences are similar for the solid phasꢀ
2.50
2.25
2.00
1.75
es of [Cu(hfac)2L5/Pr
] ] with the
and [Cu(hfac)2L5/Bu
n
"headꢀtoꢀtail" motif: at ambient temperature neff are 2.72
1
2
3
4
100
200
300 T/К
Fig. 6. Plots eff(T) for [Cu(hfac)2L5/R]n with the "headꢀtoꢀhead"
motif of the polymer chain (R = Me (1), Et (2), Pr (3), and
Bu (4)).
Fig. 7. Fragment of the polymer chain with the "headꢀtoꢀtail"
motif in structure [Cu(hfac)2L5/Pr]n.

Molecular magnets
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
667
Table 3. Selected bond lengths (d) in [Cu(hfac)2L5/R
with the "headꢀtoꢀtail" chain motif at 240 K
]
]
Experimental
n
n
1ꢀEthylꢀ,37 1ꢀpropylꢀ,6 and 1ꢀbutylꢀ1Hꢀpyrazoles,38 bisꢀ
(hexafluoroacetylacetonato)copper(II)39, 2,3ꢀbishydroxylaminoꢀ
2,3ꢀdimethylbutane and its sulfate salt,40 and 4,4,5,5ꢀtetramethꢀ
ylꢀ2ꢀ(1ꢀmethylꢀ1Hꢀpyrazolꢀ5ꢀyl)ꢀ4,5ꢀdihydroꢀ1Нꢀimidazoleꢀ1ꢀ
oxylꢀ3ꢀoxide33,41 were synthesized using known procedures.
Commercial reagents and solvents were used without additional
purification.
Bond
d/Å
[Cu(hfac)2L5/Pr
]
[Cu(hfac)2L5/Bu
n
Cu—ONO
Cu—N
CuON
N—O
2.461(4)
2.411(4)
147.8(3)
1.282(5)
1.261(5)
>5
2.549(3)
2.321(3)
151.1(2)
1.278(3)
1.280(3)
>5
Plates for TLC (Silica Gel 60 F254, aluminium sheets), silica
gel "0.063—0.200 mm, for column chromatography" (Merck),
and Al2O3 ("pure for chromatography," produced at the Donetsk
plant, Ukraine) were used for chromatographic procedures. The
IR spectra of samples pressed in KBr pellets were recorded on
Bruker VECTORꢀ22 spectrophotometer. Melting points were
determined on BOETIUS microheating stage. Microanalyses
were carried out at the N. N. Vorozhtsov Novosibirsk Institute of
Organic Chemistry (Siberian Branch, Russian Academy of Sciꢀ
ences) on EURO EA3000 CHNS analyzer. NMR spectra were
recorded on Bruker AVꢀ300 (300 MHz for 1Н, 75.45 MHz
—•O...O•—
and 2.64 B, respectively, which agrees with the theoretiꢀ
cal purely spin value of 2.45 B for two nonꢀinteracting
paramagnetic centers with spins of 1/2 and g = 2. On
cooling eff almost does not differ and gradually increases
below 100 K, attaining a maximum of 2.9 B at 17 K for
for 13С) and Bruker AVꢀ400 (400.13 MHz for Н; 100.61 MHz
1
[Cu(hfac)2L5/Pr
]
and at 8 K at [Cu(hfac)2L5/Bu]n. The
n
for 13С) instruments at 25—30 C. The signal from the solvent
DMSOꢀd6 was used as internal standard:  2.50,  39.52.

eff(T) dependence for [Cu(hfac)2L5/Bu]n is shown in Fig. 8
H
C
as an example. The long axial distances Cu—ONO
(2.461(4) and 2.549(3) Å) in the octahedral CuNO5 modes
are a reason for the predomination of the ferromagnetic
contribution to the exchange interactions in the >N—•O—
Cu2+ clusters in the temperature range 25—300 K (see
Refs 2, 9, 10, and 25).
Signals were assigned using the 13С NMR spectra recorded in
the Jꢀmodulation mode (noise proton decoupling, opposite
phase for signals from the C atoms with the even number of
added protons).
The magnetic susceptibility of polycrystalline samples was
measured with an MPMSXL SQUID magnetometer (Quantum
Design) in the range from 2 to 300 K in a magnetic field of
5 kOe. Paramagnetic components of magnetic susceptibility
 were determined with allowance for the diamagnetic contribuꢀ
tion estimated from Pascal´s constants. Depending on the temꢀ
perature, the effective magnetic moment was calculated using
the formula
Thus, a series of new heterospin complexes similar in
structure to the complexes from the family of "breathing"
crystals with isomeric nitroxyls L4/R was obtained by the
study of the products of the reactions of Cu(hfac)2 with
pyrazoles L5/R bearing a paramagnetic substituent in posiꢀ
tion 5 of the pyrazole cycle. It was established that, unlike
the chain polymer complexes with L4/R, the solid phases
[Cu(hfac)2L5/R]n are not characterized by structural rearꢀ
rangements similar to those obtained in "breathing" crysꢀ
tals with the temperature change. A rare example of the
molecular complex [Cu(hfac)2L5/Me]2 was found, in the
solid phase of which the reversible thermally induced tranꢀ
sition is observed for the ONO atoms from the axial to
equatorial position in the CuII—O•—N< clusters accomꢀ
panied by the replacement of weak exchange interaction
by strong antiferromagnetic one.
,
where N, k, and  are Avogadro´s number, Boltzmann conꢀ
stant, and Bohr magneton, respectively.
B
Xꢀray diffraction analysis. Reflection arrays from single crysꢀ
tals were obtained on Bruker AXS SMART APEX II diffracꢀ
tometer equipped with Helix lowꢀtemperature attachment
(Oxford Cryosystems) and on APEX DUO diffractometer
(CuꢀK radiation for [Cu(hfac)2LMe]2 at 295 K, MoꢀK radiaꢀ
tion for others; an absorption correction was applied using the
Bruker SADABS program, version 2.10). The structures were
solved by direct methods and refined by fullꢀmatrix least squares
in the anisotropic approximation for all nonꢀhydrogen atoms.
Positions of H atoms in the most part of structures were calculatꢀ
ed geometrically and refined in the riding model. All calculaꢀ
tions on structure decoding and refinement were performed usꢀ
ing the Bruker Shelxtl Version 6.14 program package. Selected
bond lengths in the studied compounds are listed in Tables 1—3.
The crystallographic characteristics and experimental details are
given in Tables 4 and 5.
eff/
B
3.0
2.7
100
200
300 T/К
2ꢀ(1ꢀEthylꢀ1Hꢀpyrazolꢀ5ꢀyl)ꢀ4,4,5,5ꢀtetramethylimidazolꢀ
idineꢀ1,3ꢀdiol (2b). A 2.5 M solution of BuLi in hexane (14 mL,
0.035 mol) was added under argon atmosphere (stirred at –90 С)
Fig. 8. Plot eff(T) for [Cu(hfac)2L5/Bu]n with the "headꢀtoꢀtail"
motif of the polymer chain.

668
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
Fokin et al.
Table 4. Crystallographic characteristics and experimental details for compounds [Cu(hfac)2LMe]2 and Cu(hfac)2LMe
Parameter
Value
Formula
M
[Cu(hfac)2LMe
1429.88
]
Cu(hfac)2LMe
714.94
2
T/K
Space group
Z
30
P21/n
2
120
P21/n
2
240
P21/n
2
295
P21/n
2
28
P1
4
120
P1
4
295
–
–
–
P1
4
a/Å
b/Å
c/Å
/deg
/deg
/deg
V/Å
10.528(2)
14.634(3)
18.653(4)
—
102.938(3)
—
2800.8(11)
1.695
0.903
10.639(3)
14.601(3)
18.786(4)
—
102.674(4)
—
2847.1(12)
1.668
0.889
10.6527(17)
14.580(2)
18.789(3)
—
102.346(11)
—
2850.7(8)
1.666
0.887
10.6980(7)
14.6423(10)
18.8181(12)
—
102.169(3)
—
2881.5(3)
1.648
2.202
13.6364(14)
14.7625(15)
15.1325(16)
64.9660(10)
80.335(2)
87.285(2)
2720.0(5)
1.746
13.7511(18)
14.833(2)
15.216(2)
64.940(2)
80.436(2)
87.077(2)
2771.8(6)
1.713
13.9588(8)
14.9820(9)
15.3531(9)
64.600(4)
80.680(4)
86.720(4)
2861.9(3)
1.659
dcalc/g cm–3
/mm–1
0.930
0.913
0.884
Ihkl
Rint
*
18444/4009
0.0300
23.39
21105/4155
0.0543
23.47
21495/6357
0.0617
27.64
35198/5060
0.1091
13366/7753
0.0900
21581/7962 23663/12226
0.0611
23.33
99.2
0.0499
28.00
95.5

max/deg
67.67
96.7
23.30
98.7
Collection com
pleteness, Ihkl
N
98.0
99.0
95.9
474
505
505
506
823
823
949
Goodnessꢀofꢀfit
R1
0.893
1.019
0.804
1.025
0.697
0.718
0.835
0.0241
0.0644
0.0257
0.0658
0.0427
0.1053
0.0498
0.1094
0.0414
0.0791
0.1065
0.0920
0.0464
0.1332
0.0486
0.1363
0.0414
0.1152
0.0493
0.1253
0.0393
0.1145
0.0461
0.1213
0.0420
0.0782
0.0878
0.0895
wR2 (I > 2 )
I
R1
wR2
* Number of measured/independent reflections.
of 1ꢀethylꢀ1Нꢀpyrazole (3.0 g, 0.031 mol) in THF (30 mL), and
then cooling was ceased. After the temperature was increased to
–10 C, the reaction mixture was again cooled to –90 С
and DMF (3.0 mL, 0.038 mol) was added. The cooling bath
was removed. The reaction mixture was stirred for 2 h, concenꢀ
trated HCl was added to pH 1, and then the mixture was
neutralized with a saturated aqueous solution of NaHCO3.
The reaction product was extracted with CH2Cl2 (5×10 mL).
The joined organic extracts were dried over Na2SO4, filtered
through silica gel layer (1×5 cm), and evaporated. The residue
(3.10 g) containing 1ꢀethylꢀ1Hꢀpyrazoleꢀ5ꢀcarbaldehyde was
stirred with 2,3ꢀbishydroxylaminoꢀ2,3ꢀdimethylbutane sulfate
hydrate (4.21 g, 0.016 mol) in water (50 mL) for 10 h. The
reaction mixture was treated with NaHCO3 until CO2 stopped
to evolve. The formed product was filtered off, washed with
water and toluene, and dried with an air flow. The obꢀ
tained product was recrystallized from a mixture of EtOAc with
heptane. The yield was 1.41 g (18%), finely crystalline white
powder. m.p. 194—195 С. IR, /cm–1: 654, 710, 784, 844, 919,
933, 1005, 1029, 1066, 1094, 1122, 1141, 1213, 1237, 1267, 1307,
1375, 1461, 2979, 3014, 3173 br. 1Н NMR (DMSOꢀd6), : 1.04,
1.08 (both s, 6 H each, C2(CH3)4); 1.34 (t, 3 H, CH2CH3,
J = 7.5 Hz); 4.21 (q, 2 H, CH2CH3, J = 7.5 Hz); 4.75 (s, 1 Н,
H(2)); 6.23 (s, 1 Н, H(3´)); 7.32 (s, 1 Н, H(5´)); 7.97 (s, 2 Н,
NOH). 13С NMR (DMSOꢀd6), : 15.7 (CH2CH3), 17.4 and
23.8 (C2(CH3)4), 43.9 (CH2), 66,4 (C2(CH3)4), 82.8 (C(2)),
105.0 (C(4´), 137.1 (C(3´)), 142.8 (C(5´)). Found (%): С, 56.4;
Н, 8.8; N, 22.1. C12H22N4O2. Calculated (%): C, 56.7; H, 8.7;
N, 22.0.
Compounds 2c and 2d were synthesized using a similar proꢀ
cedure.
4,4,5,5ꢀTetramethylꢀ2ꢀ(1ꢀpropylꢀ1Hꢀpyrazolꢀ5ꢀyl)ꢀmidazolꢀ
idineꢀ1,3ꢀdiol (2c). The yield was 22%, m.p. 159—161 С. IR,
/cm–1: 654, 703, 784, 850, 876, 921, 939, 1000, 1028, 1064,
1141, 1159, 1198, 1265, 1302, 1358, 1376, 1388, 1412, 1461,
1496, 2931, 2968, 3186 br. 1Н NMR (DMSOꢀd6), : 0.84 (t, 3 H,
CH2CH3, J = 7.5 Hz); 1.01, 1.05 (both s, 6 H each, C2(CH3)4);
1.76 (sextet, 2 H, CH2CH3, J = 7.4 Hz); 4.10 (t, 2 H, N—CH2,
J = 7.4 Hz); 4.74 (s, 1 Н, H(2)); 6.21 (d, 1 Н, H(3´), J = 1.8 Hz);
7.30 (d, 1 Н, H(5´), J = 1.8 Hz); 7.92 (s, 2 Н, NOH). 13С NMR
(DMSOꢀd6), : 11.2 (CH2CH3), 17.7 and 24.1 (C2(CH3)4), 23.7
(CH2CH3), 50.9 (N—CH2), 66.7 (C2(CH3)4), 83.2 (C(2)), 105.2
(C(4´), 137.4 (C(3´)), 143.5 (C(5´)). Found (%): С, 58.1; Н, 8.9;
N, 20.9. C13H24N4O2. Calculated (%): C, 58.2; H, 9.0; N, 21.0.
2ꢀ(1ꢀButylꢀ1Hꢀpyrazolꢀ5ꢀyl)ꢀ4,4,5,5ꢀtetramethylimidazolꢀ
idineꢀ1,3ꢀdiol (2d). The yield was 36.8%. 1Н NMR (DMSOꢀd6),
: 0.88 (t, 3 H, CH2CH3, J = 7.3 Hz); 1.01, 1.06 (both s, 6 H
each, C2(CH3)4); 1.27 (sextet, 2 H, CH2CH2CH3, J = 7.3 Hz);
1.73 (quintet, 2 H, CH2CH2CH3, J = 7.3 Hz); 4.14 (t, 2 H,
N—CH2, J = 7.25 Hz); 4.74 (s, 1 Н, H(2)); 6.21 (d, 1 Н, H(3´),
J = 1.7 Hz); 7.30 (d, 1 Н, H(5´), J = 1.6 Hz); 7.95 (s, 2 Н,
NOH). Found (%): C, 59.7; H, 9.3; N, 19.8. C14H26N4O2. Calꢀ
culated (%): С, 59.5; Н, 9.3; N, 19.8.
2ꢀ(1ꢀEthylꢀ1Hꢀpyrazolꢀ5ꢀyl)ꢀ4,4,5,5ꢀtetramethylꢀ4,5ꢀdihyꢀ
droꢀ1Hꢀimidazoleꢀ1ꢀoxyl 3ꢀoxide (L5/Et). A mixture stirred at
15 C of 2b (1.41 g, 5.6 mmol), water (30 mL), and СН2Сl2
(30 mL) was added by portions with NaIO4 (1.20 g, 5.6 mmol)
for 40 min, and then the reaction mixture was stirred for 1 h. The

Molecular magnets
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
669
Table 5. Crystallographic characteristics and experimental details for compounds Cu(hfac)2L5/Et, Cu(hfac)2L5/Pr, Cu(hfac)2L5/Bu, L5/
Et, L5/Pr, and L5/Bu
Parameter
Value
Formula
Motif
M
T/K
Space group
Z
[Cu(hfac)2L5/Et
728.97
]
Cu(hfac)2L5/Pr [Cu(hfac)2L5/Bu
"Headꢀtoꢀhead"
]
Cu(hfac)2L5/Pr [Cu(hfac)2L5/Bu
"Headꢀtoꢀtail"
]
n
LEt
—
LPr
—
265.34
LBu
—
279.36
240
P21/c
4
n
n
742.99
757.02
742.99
240
757.02
240
251.31
295
296
293
P1
240
P1
240
–
–
–
–
P1
P212121
4
P212121
4
C2/c
8
P1
4
2
2
2
a/Å
b/Å
c/Å
/deg
/deg
/deg
V/Å
14.2918(5)
15.3438(5)
15.5962(5)
62.386(2)
80.808(2)
82.670(2)
2985.99(17)
1.622
10.589(5)
11.094(5)
14.089(7)
104.42(1)
103.79(1)
97.67(1)
1523.7(12)
1.619
10.6490(9)
12.0493(9)
13.3680(10)
103.316(6)
101.108(6)
104.931(6)
1553.8(2)
1.61
15.514(2)
19.188(2)
10.355(1)
—
10.0469(8) 19.2868(10) 7.9112(5)
16.1680(13) 7.1455(3) 9.8735(7) 15.9989(9)
19.7910(16) 19.8610(10) 10.9848(11) 13.6110(6)
7.2487(4)
—
—
—
101.356(4) 111.450(5) 101.551(4)
—
—
—
—
93.751(6)
113.078(4)
—
—
3082.3(7)
1.601
0.824
3214.8(4)
1.564
0.792
2683.5(2) 712.52(10) 1546.51(14)
dcalc/g cm–3
/mm–1
1.244
0.087
1.237
0.086
1.200
0.082
0.849
0.834
0.819
Ihkl
Rint
max/deg
*
48671/13532
0.0858
16779/7127
0.0659
25371/7614
0.0882
15009/7479 27281/7543 11654/3142 15981/4675 17256/4884
0.0837
28.29
97.9
0.0469
27.95
98.4
0.0792
27.98
96.8
0.0431
31.74
96.4
0.0619
30.98
98.9

27.46
28.00
97.0
28.37
97.9
Collection comꢀ 99.0
pleteness, Ihkl
N
958
472
482
443
451
240
256
274
Goodnessꢀofꢀfit 0.752
0.886
0.807
0.729
0.844
0.839
0.694
0.857
R1
0.0402
0.0721
0.1269
0.0871
0.0436
0.1011
0.0838
0.1228
0.0474
0.1041
0.1407
0.1270
0.0503
0.0861
0.1640
0.1067
0.0409
0.0867
0.0918
0.0974
0.0439
0.0884
0.0877
0.0993
0.0455
0.1404
0.0720
0.1659
0.0452
0.0967
0.0933
0.1101
wR2 (I > 2 )
R1
wR2
I
* Number of measured/independent reflections.
organic phase was separated, and the aqueous phase was extractꢀ
ed with 10 mL of CH2Cl2. Joined organic solutions were dried
over Na2SO4, filtered through Al2O3, and evaporated. The resiꢀ
due was crystallized from hexane. The yield was 0.94 g (67%),
dark blue crystals, m.p. 143—144 С. IR, /cm–1: 651, 672, 757,
814, 869, 926, 978, 1043, 1058, 1091, 1147, 1167, 1224, 1272,
1302, 1366, 1385, 1399, 1423, 1460, 1478, 1580, 2941, 2981,
3091, 3121. Found (%): С, 57.4; Н, 7.5; N, 22.4. C12H19N4O2.
Calculated (%): C, 57.4; H, 7.6; N, 22.3.
([Cu(hfac)2L5/Me]2). A mixture of weighed samples of L5/Me
(0.0237 g, 0.1 mmol) and Cu(hfac)2 (0.0477 g, 0.1 mmol) was
dissolved in CH2Cl2 (3 mL) for 5 min, and 1 mL of hexane was
added. The reaction mixture was immediately cooled to –15 С,
and a seeding crystal of the target product was preliminarily
added. After 5 days, the dark brown crystals that formed were
filtered off, washed with cold hexane, and dried in air. The yield
was 0.056 g (80%). Found (%): C, 35.2; H, 2.6; N, 7.8; F, 32.0.
C42H38Cu2F24N8O12. Calculated (%): C, 35.3; H, 2.7; N, 7.8;
F, 31.9.
Compounds L5/Pr and L5/Br were synthesized using a similar
procedure.
Catenaꢀ{bis( ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀ(1ꢀmethylpyrazolꢀ5ꢀ
2
4,4,5,5ꢀTetramethylꢀ2ꢀ(1ꢀpropylꢀ1Hꢀpyrazolꢀ5ꢀyl)ꢀ4,5ꢀdiꢀ
hydroꢀ1Нꢀimidazoleꢀ1ꢀoxyl 3ꢀoxide (L5/Pr). The yield was 61%,
m.p. 101—102 С. IR, /cm–1: 541, 605, 673, 752, 789, 866,
888, 928, 1058, 1137, 1166, 1216, 1277, 1365, 1398, 1419, 1459,
1571, 2877, 2982. Found (%): С, 58.7; Н, 8.0; N, 21.3. C13H21N4O2.
Calculated (%): C, 58.9; H, 8.0; N, 21.1.
2ꢀ(1ꢀButylꢀ1Hꢀpyrazolꢀ5ꢀyl)ꢀ4,4,5,5ꢀtetramethylꢀ4,5ꢀdiꢀ
hydroꢀ1Нꢀimidazoleꢀ1ꢀoxyl 3ꢀoxide (L5/Bu). The yield was 67%,
m.p. 82—83 С. IR, /cm–1: 541, 610, 656, 677, 731, 760, 804,
866, 885, 926, 1045, 1065, 1134, 1162, 1212, 1264, 1330, 1364,
1383, 1399, 1420, 1453, 1476, 1575, 1686, 1765, 2345, 2876,
2934, 2957, 2995, 3104, 3127 br. Found (%): С, 60.3; Н, 8.5;
N, 20.4. C14H23N4O2. Calculated (%): C, 60.2; H, 8.3; N, 20.1.
yl)ꢀ4,5ꢀdihydroꢀ1Нꢀimidazoleꢀ3ꢀoxideꢀ1ꢀoxylꢀN,O)ꢀtetrakis(1,1,
1,5,5,5ꢀhexafluoropentaneꢀ2,4ꢀdionatoꢀO,O´)ꢀdicopper(II)}
([Cu(hfac)2L5/Me]n) ("headꢀtoꢀhead"). A mixture of weighed
samples of L5/Me (0.0400 g, 0.169 mmol) and Cu(hfac)2 (0.0805 g,
0.169 mmol) was dissolved in 3 mL of CH2Cl2, hexane (4 mL)
was added, the solution was filtered, and the filtrate was kept in
an open flask at 25 С for 15 min. Then a seeding crystal of the
target product was introduced into the solution, and the reaction
mixture was kept for 6 h at –15 С. The formed dark brown
crystals were filtered off, washed with hexane, and dried in air.
The yield was 0.077 g (65%). Found (%): C, 35.8; H, 2.9; N, 7.6;
F, 31.5. C21H19CuF12N4O6. Calculated (%): C, 35.3; H, 2.7;
N, 7.8; F, 31.9.
Bis[ ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀ(1ꢀmethylpyrazolꢀ5ꢀyl)ꢀ
Catenaꢀ{bis( ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀ(1ꢀpropylpyrazolꢀ5ꢀ
2
2
4,5ꢀdihydroꢀ1Нꢀimidazoleꢀ3ꢀoxideꢀ1ꢀoxylꢀN,O]ꢀbis(1,1,1,5,
yl)ꢀ4,5ꢀdihydroꢀ1Нꢀimidazoleꢀ3ꢀoxideꢀ1ꢀoxylꢀN,O)ꢀtetrakisꢀ
5,5ꢀhexafluoropentaneꢀ2,4ꢀdionatoꢀO,O´)dicopper(II )
(1,1,1,5,5,5ꢀhexafluoropentaneꢀ2,4ꢀdionatoꢀO,O´)dicopper(II)}

670
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
Fokin et al.
([Cu(hfac)2L5/Pr]n) ("headꢀtoꢀhead") was obtained similarly. The
yield was 90%. Found (%): C, 37.4; H, 3.1; N, 7.7; F, 31.1.
C23H23CuF12N4O6. Calculated (%): C, 37.2; H, 3.1; N, 7.6; F, 30.7.
2. F. Lanfranc de Panthou, D. Luneau, R. Musin, L. Öhrꢀ
ström, A. Grand, P. Turek, P. Rey, Inorg. Chem., 1996,
35, 3484.
Catenaꢀ{bis[ ꢀ2ꢀ(1ꢀethylpyrazolꢀ5ꢀyl)ꢀ4,4,5,5ꢀtetramethylꢀ
3. F. Iwahory, K. Inoue, H. Iwamura, Mol. Cryst. Liq. Cryst.,
1999, 334, 533.
4. A. Caneschi, P. Chiesi, L. David, F. Ferraro, D. Gatteschi,
R. Sessoli, Inorg. Chem., 1993, 32, 1445.
5. M. Baskett, P. M. Lahti, A. PaduanꢀFilho, N. F. Oliveira,
Jr., Inorg. Chem., 2005, 44, 6725.
6. V. I. Ovcharenko, S. V. Fokin, G. V. Romanenko, Yu. G.
Shvedenkov, V. N. Ikorskii, E. V. Tret´yakov, S. F. Vasiꢀ
levskii, Russ. J. Struct. Chem. (Engl. Transl.), 2002, 43, 153
[Zh. Strukt. Khim., 2002, 43, 163].
2
4,5ꢀdihydroꢀ1Нꢀimidazoleꢀ3ꢀoxideꢀ1ꢀoxylꢀN,O]ꢀtetrakisꢀ
(1,1,1,5,5,5ꢀhexafluoropentaneꢀ2,4ꢀdionatoꢀO,O´)dicopper(II)}
([Cu(hfac)2L5/Et]n) ("headꢀtoꢀhead"). A mixture of weighed samples
of Cu(hfac)2 (0.0477 g, 0.1 mmol) and L5/Et (0.0252 g, 0.1 mmol)
was dissolved in 0.7 mL of CH2Cl2. The formed brown solution
was diluted with 6 mL of hexane, and the reaction mixture was
kept at ambient temperature for 3.5 h and then cooled to –15 С.
After 24 h, the dark green crystals formed were filtered off,
washed with hexane, and dried in air. The yield was 0.061 g (85%).
Found (%): C, 36.5; H, 2.7; N, 7.6; F, 31.4. C22H21CuF12N4O6.
7. A. Okazawa, D. Hashizume, T. Ishida, J. Am. Chem. Soc.,
2010, 132, 11516.
Calculated (%): C, 36.2; H, 2.9; N, 7.7; F, 31.3. Catenaꢀ{bis[ ꢀ
2
2ꢀ(1ꢀbutylpyrazolꢀ5ꢀyl)ꢀ4,4,5,5ꢀtetramethylꢀ4,5ꢀdihydroꢀ1Нꢀimꢀ
idazoleꢀ3ꢀoxideꢀ1ꢀoxylꢀN,O]ꢀtetrakis(1,1,1,5,5,5ꢀhexafluoroꢀ
pentaneꢀ2,4ꢀdionatoꢀO,O´)dicopper(II)} ([Cu(hfac)2L5/Bu]n)
("headꢀtoꢀhead") was synthesized similarly. The yield was 60%.
Found (%): C, 38.5; H, 3.4; N, 7.3; F, 30.2. C24H25CuF12N4O6.
Calculated (%): C, 38.1; H, 3.3; N, 7.4; F, 30.1.
8. V. I. Ovcharenko, S. V. Fokin, G. V. Romanenko, V. N.
Ikorskii, E. V. Tretyakov, S. F. Vasilevsky, R. Z. Sagdeev,
Mol. Phys., 2002, 100, 1107.
9. P. Rey, V. I. Ovcharenko, in Magnetism: Molecules to Mateꢀ
rials, IV, Eds J. S. Miller, M. Drillon, WileyꢀVCH, New
York, 2003, 41.
Catenaꢀ{[ ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀ(1ꢀpropylpyrazolꢀ5ꢀyl)ꢀ
10. V. I. Ovcharenko, K. Yu. Maryunina, S. V. Fokin, E. V.
Tret´yakov, G. V. Romanenko, V. N. Ikorskii, Russ. Chem.
Bull. (Int. Ed.), 2004, 53, 2406 [Izv. Akad. Nauk, Ser. Khim.,
2004, 2304].
11. S. Fokin, V. Ovcharenko, G. Romanenko, V. Ikorskii, Inorg.
Chem., 2004, 43, 969.
12. K. Maryunina, S. Fokin, V. Ovcharenko, G. Romanenko,
V. Ikorskii, Polyhedron, 2005, 24, 2094.
13. V. I. Ovcharenko, G. V. Romanenko, K. Yu. Maryunina,
A. S. Bogomyakov, E. V. Gorelik, Inorg. Chem., 2008,
47, 9537.
2
4,5ꢀdihydroꢀ1Нꢀimidazoleꢀ3ꢀoxideꢀ1ꢀoxylꢀN,O]ꢀbis(1,1,1,5,5,5ꢀ
hexafluoropentaneꢀ2,4ꢀdionatoꢀO,O´)copper(II)} ([Cu(hfac)2L5/Pr]n)
("headꢀtoꢀtail"). A mixture of weighed samples of Cu(hfac)2
(0.0477 g, 0.1 mmol) and L5/Pr (0.0266 g, 0.1 mmol) was disꢀ
solved in 2 mL of hexane at 50 С. Then the reaction mixture
was kept in an open flask at 25 С for 40 min. The formed needleꢀ
like dark green crystals were filtered off, washed with cold hexꢀ
ane, and dried in air. The yield was 0.0676 g (90%). Found (%):
C, 37.2; H, 3.1; N, 7.7; F, 30.9. C23H23CuF12N4O6. Calculatꢀ
ed (%): C, 37.2; H, 3.1; N, 7.6; F 30.7.
Catenaꢀ{[ ꢀ2ꢀ(1ꢀbutylpyrazolꢀ5ꢀyl)ꢀ4,4,5,5ꢀtetramethylꢀ
14. M. Fedin, S. Veber, I. Gromov, V. Ovcharenko, R. Sagdeev,
A. Schweiger, E. Bagryanskaya, J. Phys. Chem. A, 2006,
110, 2315.
15. M. Fedin, S. Veber, I. Gromov, V. Ovcharenko, R. Sagdeev,
E. Bagryanskaya, J. Phys. Chem. A, 2007, 111, 4449.
16. M. Fedin, S. Veber, I. Gromov, K. Maryunina, S. Fokin,
G. Romanenko, R. Sagdeev, V. Ovcharenko, E. Bagryansꢀ
kaya, Inorg. Chem., 2007, 46, 11405.
17. S. L. Veber, M. V. Fedin, A. I. Potapov, K. Yu. Maryunina,
G. V. Romanenko, R. Z. Sagdeev, V. I. Ovcharenko,
D. Goldfarb, E. G. Bagryanskaya, J. Am. Chem. Soc., 2008,
130, 2444.
18. S. L. Veber, M. V. Fedin, G. V. Romanenko, R. Z. Sagdeev,
E. G. Bagryanskaya, V. I. Ovcharenko, Inorg. Chim. Acta,
2008, 361, 4148.
19. M. Fedin, V. Ovcharenko, E. G. Bagryanskaya, in The Treaꢀ
sures of Eureka, I: Electron Paramagnetic Resonance: From
Fundamental Research to Pioneering Applications & Zavoisky
Award, Ed. K. M. Salikhov, AXAS Publishing Ltd, Wellingꢀ
ton, New Zealand, 2009, 122.
20. M. V. Fedin, S. L. Veber, R. Z. Sagdeev, V. I. Ovcharenko,
E. G. Bagryanskaya, Russ. Chem. Bull. (Int. Ed.), 2010, 59,
1065 [Izv. Akad. Nauk, Ser. Khim., 2010, 1043].
21. M. Fedin, V. Ovcharenko, R. Sagdeev, E. Reijerse, W. Luꢀ
bitz, E. G. Bagryanskaya, Angew. Chem., Int. Ed., 2009,
47, 6897.
2
4,5ꢀdihydroꢀ1Нꢀimidazoleꢀ3ꢀoxideꢀ1ꢀoxylꢀN,O]ꢀbis(1,1,1,5,5,5ꢀ
hexafluoropentaneꢀ2,4ꢀdionatoꢀO,O´)copper(II)} ([Cu(hfac)2L5/Bu]n)
("headꢀtoꢀtail"). A mixture of weighed samples of Cu(hfac)2
(0.0477 g, 0.1 mmol) and L5/Bu (0.0280 g, 0.1 mmol) was dissolvꢀ
ed in 5 mL of hexane at 50 С. Then the reaction mixture was kept
at –15 С for 24 h. The formed crystals were filtered off, washed
with hexane, and dried in air. The yield was 0.0542 g (70%).
Found (%): C, 38.4; H, 3.4; N, 7.6; F, 29.2. C24H25CuF12N4O6.
Calculated (%): C, 38.1; H, 3.3; N, 7.4; F, 30.1.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos 11ꢀ03ꢀ12001,
12ꢀ03ꢀ00067, 11ꢀ03ꢀ00027, and 12ꢀ03ꢀ31028), the Counꢀ
cil on Grants at President of the Russian Federation (Proꢀ
gram for State Support of Leading Scientific Schools of
the Russian Federation and Young Scientists, Project
MKꢀ6497.2012.3), the Ministry of Education and Sciꢀ
ence of the Russian Federation (agreement 8436), the
Russian Academy of Sciences, and the Siberian Branch of
the Russian Academy of Sciences.
References
1. F. Lanfranc de Panthou, E. Belorizky, R. Calemczuk,
D. Luneau, C. Marcenat, E. Ressouche, P. Turek, P. Rey,
J. Am. Chem. Soc., 1995, 117, 11247.
22. Yu. A. Osip´yan, R. B. Morgunov, A. A. Baskakov, V. I. Ovꢀ
charenko, S. V. Fokin, Physics of the Solid State (Engl. Transl.),
2003, 45, 1465 [Fiz. Tverd. Tela, 2003, 45, 1396].

Molecular magnets
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
671
23. E. M. Zueva, E. R. Ryabykh, A. M. Kuznetsov, Russ. Chem.
Bull. (Int. Ed.), 2009, 58, 1654 [E. M. Zueva, E. R. Ryabykh,
A. M. Kuznetsov, Izv. Akad. Nauk, Ser. Khim., 2009, 1605].
24. A. V. Postnikov, A. V. Galakhov, S. Blügel, Phase Transiꢀ
tions, 2005, 78, 689.
Coord. Chem. (Engl. Transl.), 2001, 27, 360 [Koord. Khim.,
2001, 27, 387].
34. B. Bleaney, K. D. Bowers, Proc. Roy. Soc. A, 1952, 214, 451.
35. E. V. Tret´yakov, S. V. Fokin, G. V. Romanenko, V. N.
Ikorskii, A. V. Podoplelov, V. I. Ovcharenko, Russ. Chem.
Bull. (Int. Ed.), 2006, 55, 66 [Izv. Akad. Nauk, Ser. Khim.,
2006, 64].
25. S. Vancoillie, L. Rulнљek, F. Neese, K. Pierloot, J. Phys.
Chem. A, 2009, 113, 6149.
26. V. A. Morozov, N. N. Lukzen, V. I. Ovcharenko, J. Phys.
Chem. B, 2008, 112, 1890.
36. S. V. Fokin, S. E. Tolstikov, E. V. Tret´yakov, G. V. Romaꢀ
nenko, A. S. Bogomyakov, S. L. Veber, R. Z. Sagdeev, V. I.
Ovcharenko, Russ. Chem. Bull. (Int. Ed.), 2011, 60 [Izv. Akad.
Nauk, Ser. Khim., 2011, 2423].
37. J. D. Vaughan, G. L. Jewett, V. L. Vaughan, J. Am. Chem.
Soc., 1967, 89, 6218.
38. V. Ovcharenko, E. Fursova, G. Romanenko, I. Eremenko,
E. Tretyakov, V. Ikorskii, Inorg. Chem., 2006, 45, 5338.
39. J. A. Bertrand, R. I. Kaplan, Inorg. Chem., 1966, 5, 489.
40. V. I. Ovcharenko, S. V. Fokin, G. V. Romanenko, I. V.
Korobov, P. Rei, Russ. Chem. Bull. (Int. Ed.), 1999, 48, 1519
[Izv. Akad. Nauk, Ser. Khim., 1999, 1539].
41. S. F. Vasilevsky, E. V. Tretyakov, O. M. Usov, Y. N. Molin,
S. V. Fokin, Y. G. Shwedenkov, V. N. Ikorskii, G. V. Romaꢀ
nenko, R. Z. Sagdeev, V. I. Ovcharenko, Mendeleev Comꢀ
mun., 1998, 216.
27. V. A. Morozov, N. N. Lukzen, V. I. Ovcharenko, Russ. Chem.
Bull. (Int. Ed.), 2008, 57, 863 [V. A. Morozov, N. N. Lukzen,
V. I. Ovcharenko, Izv. Akad. Nauk, Ser. Khim., 2008, 849].
28. V. A. Morozov, N. N. Lukzen, V. I. Ovcharenko, Dokl. Phys.
Chem. (Engl. Transl.), 2010, 430, Part 2, 33 [Dokl. Akad.
Nauk, 2010, 430, 647].
29. V. I. Ovcharenko, in Stable Radicals: Fundamentals and Apꢀ
plied Aspects of OddꢀElectron Compounds, Ed. R. Hicks,
WileyꢀVCH, New York, 2010, 461.
30. G. V. Romanenko, K. Yu. Maryunina, A. S. Bogomyakov,
R. Z. Sagdeev, V. I. Ovcharenko, Inorg. Chem., 2011,
50, 6597.
31. E. V. Tret´yakov, V. I. Ovcharenko, Russ. Chem. Rev.
(Engl. Transl.), 2009, 78 [Usp. Khim., 2009, 78, 1051].
32. Cambridge Structural Database, version 5.33; Cambridge
Crystallographic Data Centre: Cambridge, UK, Nov. 2011
(last update May 2012).
33. G. V. Romanenko, S. V. Fokin, S. F. Vasilevskii, E. V.
Tret´yakov, Yu. G. Shvedenkov, V. I. Ovcharenko, Russ. J.
Received June 14, 2012;
in revised form January 28, 2013