Synthesis, structure and magnetic properties of oligometallic systems derived from di- and trinuclear copper(ii) amido-oximate complexes

Article abstract of DOI:10.1039/b802822b

Three heterometallic complexes [M(H₂O)_n][Cu ₃L₂(H₂O)] (M = Mn²⁺, Co²⁺ or Ba²⁺) and one dinuclear compound (CuDien)(CuL{H₂O}) were prepared by interaction of anionic compounds Cu₃L ₂^2- or CuL^2- with the corresponding cations (H₄L = 1,9-dicyano-1,9-bis(hydroximino)-3,7-diazanonane-2,8-dione; Dien = 1,5-diamino-3-azapentane). The complexes [M(H₂O) _n][Cu₃L₂(H₂O)] have a polymeric structure, formed via oligomerization of Cu₃L₂ ^2- units and additionally, in the case of the Ba-salt, by binding of Cu₃L₂^2- units through Ba²⁺. Antiferromagnetic interactions occur in all the complexes, while for [Co(H ₂O)₆][Cu₃L₂(H₂O)] there is evidence of some ferromagnetic ordering at low temperatures. The values of J are lower in magnitude than for similar, previously reported systems, which is attributed to the electron-withdrawing effect of the ligand cyano groups. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b802822b

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis, structure and magnetic properties of oligometallic systems derived
from di- and trinuclear copper(II) amido-oximate complexes†
Sergey V. Kolotilov,a Dieter Schollmeyer,b Laurence K. Thompson,c Vladimir Golub,d Anthony W. Addisone and
Vitaly V. Pavlishchuk*a
Received 19th February 2008, Accepted 12th March 2008
First published as an Advance Article on the web 18th April 2008
DOI: 10.1039/b802822b
Three heterometallic complexes [M(H2O)n][Cu3L2(H2O)] (M = Mn2+, Co2+ or Ba2+) and one dinuclear
2−
compound (CuDien)(CuL{H2O}) were prepared by interaction of anionic compounds Cu3L2 or
CuL2− with the corresponding cations (H4L = 1,9-dicyano-1,9-bis(hydroximino)-3,7-diazanonane-
2,8-dione; Dien = 1,5-diamino-3-azapentane). The complexes [M(H2O)n][Cu3L2(H2O)] have a
2−
polymeric structure, formed via oligomerization of Cu3L2 units and additionally, in the case of the
Ba-salt, by binding of Cu3L2 units through Ba2+. Antiferromagnetic interactions occur in all the
2−
complexes, while for [Co(H2O)6][Cu3L2(H2O)] there is evidence of some ferromagnetic ordering at low
temperatures. The values of J are lower in magnitude than for similar, previously reported systems,
which is attributed to the electron-withdrawing effect of the ligand cyano groups.
influence of the “external” metal counter cation on the magnetic
properties of the system. Amido-oximate ligands were chosen due
Introduction
to their ability to form anionic coordination compounds,2 which
should favor formation of polynuclear species arising through l3-
(N,O) metal to metal bridge formation (which may allow further
oligomerization).3 Copper(II) was chosen because this ion forms
stable square-based units, which may reversibly coordinate axial
ligands; such behavior is well-suited for studies of oligomerization
through O-atoms of oximate groups.
Polynuclear complexes of 3d metals, which have been extensively
studied for several decades because of their non-trivial magnetic
properties, may be used as building blocks for more complex
2D and 3D systems.1 Directed assembly of such units allows the
construction of new compounds and materials, the properties of
which are determined by the nature of the starting blocks and
the mode of their organization. Recent examples of such systems
include porous1a–d ferromagnetic,1e,f conducting1h or ferroelectric1i
materials, made via specific organization of polynuclear multispin
particles. Such assembling of polymeric systems from polynuclear
“blocks” may open the way for creation of materials with new
properties, such as various types of magnetic ordering, as well as
for introduction of other characteristics.
In this paper we describe the synthesis, structure and magnetic
properties of new polynuclear heterometallic systems, built by
self-organization of trinuclear Cu(II) anions with 3d or 6s metal
cations as counterions, along with a dinuclear Cu(II) complex,
representative of this family of oximate-bridged coordination
compounds. The aim of the work was to create the conditions
for self-organization of Cu(II) oximate blocks and to study the
Experimental
Reagents and solvents were commercially available (Aldrich and
UkrReaChim) and were used without further purification. X-
Ray diffraction data were collected on an Enraf-Nonius CAD4
diffractometer, using the x–2h scan technique. Structures were
solved with the help of SIR-924 and refined by SHELXL-975
by full-matrix least-squares on F2. H-Atoms were treated by
a riding model. Details of structure refinement are presented
in Table 1. Not all hydrogen atoms of water molecules, both
coordinated and solvated, could be localized. IR spectra were
measured in KBr disks using a Specord M75 spectrometer;
electronic spectra were measured on a Specord M40 spectrometer
in the range 11000–30000 cm−1, and ESR spectra were obtained
on a Varian-E-12 X-band spectrometer, calibrated near g = 2
with diphenylpicrylhydrazyl. Variable-temperature magnetic data
(3–300 K) were obtained using a Quantum Design MPMS5S
SQUID magnetometer with field strengths in the range of 0.1–
1.0 T. Samples were prepared in gelatin capsules, mounted inside
straws, and then fixed to the end of the sample transport rod.
Background corrections for the sample holder assembly were
applied. Susceptibility data were corrected for diamagnetism using
Pascal’s constants6 and Co[Hg(SCN)4] was used as a calibration
standard.
aL. V. Pisarzhevskii Institute of Physical Chemistry of the National Academy
of Sciences of the Ukraine, Prospekt Nauki 31, Kiev, 03028, Ukraine. E-mail:
shchuk@svitonline.com; Fax: (38 044) 525 62 16; Tel: (38 044) 525 42 28
bUniversity of Mainz, Institute of Organic Chemistry, Duesbergweg 10-14,
55099, Mainz, Germany
cDepartment of Chemistry, Memorial University, St. John’s, NL, Canada
A1B 3X7
dInstitute of Magnetism NAS and MES of Ukraine, 36-B Vernadsky str.,
Kiev, 03142, Ukraine
eDepartment of Chemistry, Drexel University, Philadelphia, PA, 19104-2875,
USA
† CCDC reference numbers 662399–662402 for 2, 5, 3 and 4, respectively.
For crystallographic data in CIF or other electronic format see DOI:
10.1039/b802822b
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Table 1 Crystallographic data for complexes 2–5
2
3
4
5
Empirical formula
Mr
C13H14Cu2N9O10.25
611.86
C18H24Cu3MnN12O19
960.06
C18H30Cu3CoN12O19
968.10
C18H26BaCu3N12O16
994.47
Crystal size/mm
Space group
T/◦C
0.2 × 0.1 × 0.1
0.5 × 0.18 × 0.18
0.27 × 0.08 × 0.08
0.19 × 0.15 × 0.09
¯
R3
C2/c
C2/c
C2/c
298(2)
0.71069
26.551(5)
26.551(5)
19.976(5)
90.00
298(2)
298(2)
193(2)
˚
k/A
0.71069
20.315(11)
16.8866(14)
11.475(8)
90.00
113.88(2)
90.00
3599(3)
8
0.71069
20.262(4)
16.8033(9)
11.446(2)
90.00
114.3650(10)
90.00
3549.9(10)
8
0.71069
18.2664(10)
19.1141(11)
11.0179(6)
90.00
119.647(3)
90.00
3343.3(3)
4
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
90.00
120.00
12196(4)
18
3
˚
V/A
Z
l/m−1
1.635
2.182
2.324
3.131
Reflections measured
wR2
R1 [I > 2r(I)]
6759
0.2023
0.0777
5239
0.1540
0.0672
5181
0.1272
0.0678
4163
0.2043
0.0876
1,9-Dicyano-1,9-bis(oximino)-3,7-diazanonane-2,8-dione (LH4)
[{CuL(H2O)}{CuDien}]·5H2O (2)
Propane-1,3-diamine (0.74 g, 10 mmol) and ethyl cyanoacetate
(2.26 g, 20 mmol) were mixed without solvent. Within several
minutes the reaction mixture became hot and finally solidified.
The 1,9-dicyano-3,7-diazanonane-2,8-dione, which formed in es-
sentially quantitative yield, was washed with EtOH and dried
over P2O5. This compound (2.08 g, 10 mmol) was partially
dissolved/suspended in solution of EtONa (20 mmol, prepared
from 0.46 g (20 mmol) of Na) in 60 mL of absolute EtOH, and
treated with gaseous EtONO (20.5 mmol) prepared separately by
reaction of NaNO2 (1.41 g, 20.5 mmol) with an excess of H2SO4
in EtOH–water solution. After 5 h, 2 eq. of aqueous HCl were
added to the mixture, which was then filtered and concentrated by
(rotary) evaporation until yellow–orange crystals appeared. The
resulting 1,9-dicyano-1,9-bis(hydroximino)-3,7-diazanonane-2,8-
dione was filtered off and dried over P2O5. Yield 0.93 g, 35%.
Anal. (found/calc. for C9H10N6O4): C 40.6/40.6; H 3.85/3.76; N
31.6/31.6%. 1H NMR (in DMSO-d6): 1.74 (2H, central CH2), 3.37
(4H, terminal CH2), 7.90 (2 H, NH). IR, cm−1: 3370, 3120 (m(NH)
0.080 g of 1 (0.21 mmol) were dissolved in 5 mL of water, followed
by the addition of a solution prepared by reaction of 0.078 g (0.21
mmol) Cu(ClO4)2·6H2O with 0.022 g (0.21 mmol) of Dien in 5 mL
of water. The dark-blue (almost black) precipitate was filtered off,
recrystallized from a 1 : 1 DMF–CH3CN mixture and air-dried.
Yield 0.088 g (70%). Anal. (found/calc. for C13H31N9O10Cu2): C
26.2/26.0; H 5.10/5.12; N 21.3/21.0; Cu 21.0/21.2. IR, cm−1: 3250
≡
(m(OH)), 2920 (m(C–H)), 2105 (m(C N)), 1590, 1410. Electronic
spectrum (DMF solution), kmax/nm (e/L mol−1 cm−1): 514 (9.4 ×
102), 370 (sh) (2.4 × 104).
[Cu3L2(H2O)][M(H2O)n]·mH2O (3: M= Mn, n = 6, m = 3;
4, M = Co, n = 6, m = 3; 5, M = Ba, n = 5, m = 1)
0.080 g of 1 (0.21 mmol) were dissolved in 5 mL of water,
and 0.037 g of Cu(ClO4)2·6H2O (0.1 mmol) were added with
vigorous stirring. The brown solution was filtered and 0.1 g of
solid M(ClO4)2·6H2O (M = Mn or Co; about 0.3 mmol, three-
fold excess) were dissolved in the solution. After several days, the
brown crystalline precipitate which had formed was filtered off,
washed with acetonitrile and air-dried. The yield varied greatly,
from 5 to 70% (see discussion below). For 3: Anal. (found/calc. for
Cu3MnC18H32N12O18): C 22.4/22.7; H 3.34/3.37; N 17.3/17.7; Cu
19.8/20.0; Mn 6.2/5.8%; IR, cm−1: 3400 (m(OH)), 2920, 2846 (m(C–
≡
=
and m(OH)), 2960 (m(C–H)), 2110 (m(C N)), 1680, 1560 (m(C O)
=
and m(C N)), 1420.
Na2CuL·H2O (1)
0.10 g of LH4 (0.38 mmol) were dissolved in solution of 0.14 g
of Cu(ClO4)2·6H2O (0.38 mmol) in 5 mL of water, followed by
the addition of 0.15 g of Et3N (1.52 mmol). The addition of one
half of the Et3N caused formation of a bulky brown precipitate,
which rapidly dissolved on addition of the remaining Et3N.
0.25 g of NaClO4 was then dissolved in the solution, followed by
10 mL of ethanol, which caused precipitation of the complex. The
product was filtered off and air-dried. Yield 0.12 g (80%). Anal.
(found/calc. for C9H8N6O5CuNa2): C 28.0/27.9; H 2.70/2.59; N
21.6/21.7; Cu 16.5/16.4%. IR, cm−1: 3400 (m(OH)), 2920, 2840
=
=
H)), 1575 (m(C O) and m(C N)), 1373, 1175; electronic spectrum
(DMF solution), kmax/nm (e/L mol−1 cm−1): 503 (3.0·103). For
4: Anal. (found/calc. for Cu3CoC18H32N12O18): C 22.3/22.6; H
3.62/3.35; N 17.3/17.6; Cu 19.2/20.0; Co 6.1/6.2%. IR, cm−1:
=
=
3330 (m(OH)), 2920, 2840 (m(C–H)), 1575 (m(C O) and m(C N)),
1385, 1175; electronic spectrum (DMF solution), kmax/nm (e/L
mol−1 cm−1): 508 (3.0 × 103). For 5: Anal. (found/calc. for
Cu3BaC18H26N12O15): C 22.1/22.1; H 2.73/2.65; N 17.1/17.2; Cu
19.5/19.4%. IR, cm−1: 3380 (m(OH)), 2929, 2846 (m(C–H)), 1590
=
=
(m(C–H)), 1595 (m(C O) and m(C N)), 1400, 1174. Electronic
spectrum (DMF solution), kmax/nm (e/L mol−1 cm−1): 455 (sh)
(1.7 × 103).
=
=
(m(C O) and m(C N)), 1390, 1160; electronic spectrum (DMF
solution), kmax/nm (e/L mol−1 cm−1): 508 (3.0 × 103).
3008 | Dalton Trans., 2008, 3007–3014
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donor sets, the Cu atoms lying in the plane of four oximate
nitrogen atoms. In addition, each terminal Cu(II) has an axially
semicoordinated oxygen atom from the oximate of a neighboring
Results and discussion
Synthesis
˚
trimer’s CuL anion (the axial O–Cu bond length is 2.818(6) A
1,9-Dicyano-3,7-diazanonane-2,8-dione was prepared by the di-
rect reaction of 1,3-diaminopropane with 2 equivalents of ethyl
cyanoacetate, and nitrosation of this compound by ethyl nitrite
lead to the desired dioxime (H4L, Fig. 1). We note, that the
nitrosation reaction was effective only in the presence of ethoxide,
evidencing that activation of the methylene groups even by both
cyano- and amido- groups is not sufficient for direct nitrosation.7
Interaction of L with copper(II) perchlorate in 96% ethanol gave
a green solution; addition of 2 eq. of base (triethylamine, Et3N)
resulted in the precipitation of a brown gel, which rapidly dissolved
after addition of another 2 eq. of Et3N. Addition of an excess of
NaClO4 gave a brown precipitate of Na2CuL·H2O.
˚
in 3 and 2.831(6) A in 4). Thus, one of the oximate groups in
each CuL fragment interacts with three copper(II) atoms. The
central Cu(2), also pentacoordinate, is bonded to four oximate
and one water oxygen atoms. The average Cu(1)–N and Cu(2)–
O bond lengths in 3 (excluding the axial Cu(1)–O bond) are
˚
1.96(1) and 1.99(1) A, respectively, and are typical of such bonds in
Cu(II) complexes with N- and O-donor ligands. The s parameter8
for the central Cu(2)O5 chromophore is 0.67 (in both 3 and 4),
evidencing that the coordination polyhedron is close to trigonal-
bipyramidal geometry, the oximate-O’s along O(1)–Cu(2)–O(1ꢀ)
defining the pseudo-trigonal axis. As exemplified by the Cu(1)–N–
O–Cu(2) torsion angles (42.9(1) and 31.1(1)◦ in 3), the Cu2N2O2
metallocycles are not planar. Bond lengths in the M(H2O)62+ (M =
Mn2+ or Co2+) cations are typical for aqua-complexes of these
metals and show no tetragonal distortion. Other relevant distances
and separations are shown in Fig. 2(c) (almost identical for 3
and 4).
The trinuclear complexes were prepared by interaction of
Na2CuL (2 eq.) with Cu(ClO4)2 (1 eq.) in water, through addition
of M(ClO4)2 (M = Mn2+, Co2+ or Ba2+). As shown by the X-
ray structure determination (see below), the Cu2+ ion acts as
a coordination center, uniting two CuL2− blocks, to produce a
trinuclear species (CuL–Cu–LCu)2−. However, this reaction could
be performed successfully only in dilute solutions ([Na2CuL] ca.
2–5 mM), whereas attempts to perform the first step of the reaction
(generation of Cu3L22−) in more concentrated solutions resulted
in precipitation of insoluble compounds of probably polymeric
structure. These compounds can form because of the possibility
of reactants combining in unintended ratios during mixing of
reactants, or through hydrolysis of Cu2+ ions (the complex anion
CuL2− acting as a base in the latter case).
In the crystal, neighboring trinuclear anions interact through
rather long Cu–O bonds (2.818(6)–2.831(6) A in 3 and 4,
respectively, see above) and are packed in such way, that they
form infinite stacks (Fig. 2(b)). These stacks are aligned along the
c axis; the space between them is filled by M(H2O)6 cations and
˚
2+
solvate H2O molecules (Fig. 2(b)). A system of hydrogen bonds
links cations and anions.
The molecular structure of the trinuclear Cu3L2 unit in 5 is
generally similar to those in 3 and 4 (Fig. 3(a)), the only distinctive
feature is that the torsions Cu(1)–N–O–Cu(2) in 5 (48.3(1) and
33.0(1)◦) are slightly greater than in 3 and 4. The separations
between copper(II) atoms in the trinuclear units of 5 are close to
that of 3 and 4 (Cu(1)–Cu(2) 3.719(1) A, Cu(1)–Cu(1) 5.008(1)
A (cf . Fig. 2(c) and Table 2). However, there are considerable
differences between the crystal structure of the Ba-containing
complex 5 and the Mn- or Co-analogues 3 and 4 (Fig. 3b).
The Cu2L2 units in 5 are packed more closely; the length of
Cu–O bond between Cu(1) and the oximate oxygen atom of the
When three coordination positions of the otherwise central Cu2+
ion were occupied by an additional tridentate ligand, its capacity
to link two CuL units was blocked: reaction of Na2CuL with
Cu(Dien)(ClO4)2 produced dinuclear (CuL)(Cu[Dien]).
˚
˚
X-Ray molecular and crystal structures
Compounds 3 and 4 were found to be isomorphous, and bond
lengths and distances in these two compounds are very similar
(Tables 1 and 2). The trinuclear cuprate anions are built by
linking two mononuclear complexes via a central Cu(2) atom,
bound to oximato oxygen atoms (Fig. 2); Cu(2) is situated
on a local C2 axis. The terminal Cu(1) possess tetragonal N4
˚
˚
neighboring Cu2L2 unit is 2.620(5) A (vs. 2.818(6)–2.831(6) A in
ꢀ
˚
˚
3–4), the Cu(1)–Cu(1) distance is 4.396(4) A (compared to 4.45 A
in 3 and 4; exact separations are presented in Table 2) and the
Fig. 1 Synthesis of the ligand; the nitrosation processes in the two "arms" are most likely sequential.
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Fig. 2 Molecular and crystal structure of 3 (hydrogen atoms are omitted for clarity) (a), packing of molecular units in crystal cell normal to axis c
(b) and along axis c (c). Symmetry equivalent positions are the following: x, x, z; −x, y, −z + 1/2; x + 1/2, y + 1/2, z; −x + 1/2, y + 1/2, −z + 1/2;
˚
−x, −y, −z; x, −y, z − 1/2; −x + 1/2, −y + 1/2, −z; x + 1/2, −y + 1/2, z − 1/2. Selected bonds (A): Cu(1)–N(6) 1.926(5), Cu(1)–N(10) 1.934(5),
Cu(1)–N(13) 1.988(6), Cu(1)–N(2) 2.002(4), Cu(2)–O(1) 1.933(4), Cu(2)–O(5) 1.953(6), Cu(2)–O(14) 2.056(4), Mn(1)–O(2I) 2.165(6), Mn(1)–O(3I)
2.174(6), Mn(1)–O(1I) 2.184(6); selected angles (◦): N(6)–Cu(1)–N(10) 95.9(3), N(13)–Cu(1)–N(6) 178.1(2), N(13)–Cu(1)–N(10) 82.6(3), N(2)–Cu(1)–N(6)
82.7(2), N(2)–Cu(1)–N(10) 170.3(2), N(2)–Cu(1)–N(13) 98.6(2), O(1)–Cu(2)–O(5) 84.7(1), O(1)–Cu(2)–O(14) 97.8(2), O(14)–Cu(2)–O(5) 129.2(2),
O(1)–Cu(2)–O(1)ꢀ 169.3(2), O(14)–Cu(2)–O(14)ꢀ 101.5(2)
ꢀ
˚
Table 2 Selected distances (A) between metal ions in complexes 3–5
˚
˚
Cu(1)–Cu(2) separation is 3.940(4) A (compared to 4.03 A in 3
and 4). In contrast to the Mn- and Co-analogues, the Ba atom in
5 links two Cu2L2 anions through oxygen atoms of amide groups
(Fig. 3). These differences in coordination behavior between Ba2+
and the 3d metals are likely related to the ability of the larger-radius
Ba2+ ion to be heptacoordinate, each Ba additionally coordinating
five water molecules.
3 (Cu3Mn)
4 (Cu3Co)
5 (Cu3Ba)
Cu(1)–Cu(2)
Cu(1)–Cu(1)ꢀ
Cu(1)–Cu(2)ꢀ
Cu(1)–Cu(1)
Cu(2)–Cu(2)ꢀ
Cu(1)–Ma
3.711(1)
4.448(1)
4.032(1)
5.138(1)
6.347(1)
6.936(1)
7.765(1)
3.708(1)
4.465(1)
4.030(1)
5.136(1)
6.328(1)
6.898(1)
7.726(1)
3.719(1)
4.396(1)
3.940(1)
5.008(1)
6.276(1)
6.452(1)
8.226(1)
Several Cu(II) complexes with similar oximate ligands have
been reported,2b,3b,c in which oximate O-atoms form coordinative
bridges to neighbouring molecules, resulting in polymerization of
mononuclear Cu(II) complexes with oximes3c to form tetranuclear
Cu(2)–Ma
a M = Mn, Co or Ba for 3, 4 and 5, respectively.
3010 | Dalton Trans., 2008, 3007–3014
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Fig. 4 ORTEP view of 2 (hydrogen atoms are omitted for clarity). Se-
˚
lected bonds (A): Cu(1)–N(1) 1.991(6), Cu(1)–N(2) 1.990(7), Cu(1)–N(3)
1.946(5), Cu(1)–N(4) 2.076(6), Cu(1)–O(5) 2.327(4), Cu(2)–O(4) 1.956(4),
Cu(2)–N(7) 2.006(5), Cu(2)–N(8) 2.012(5), Cu(2)–N(9) 2.016(5), Cu(2)–
O(1) 2.274(6); selected angles (◦): N(3)–Cu(1)–N(2) 93.5(3), N(1)–
Cu(1)–N(2) 79.8(3), N(3)–Cu(1)–N(4) 81.2(2), N(1)–Cu(1)–O(5) 89.0(2),
N(4)–Cu(1)–O(5) 87.1(2), O(4)–Cu(2)–N(7) 90.9(2), N(7)–Cu(2)–N(8)
85.5(2), O(4)–Cu(2)–N(9) 96.5(2), N(8)–Cu(2)–N(9) 85.4(2), O(4)–
Cu(2)–O(1) 102.9(2), N(7)–Cu(2)–O(1) 99.1(2), N(8)–Cu(2)–O(1) 81.3(2),
N(9)–Cu(2)–O(1) 101.5(2)
Electronic spectra
Absorption bands in the region 455–514 nm with high e (103) were
observed in the solution electronic spectra of all the complexes (see
Experimental section). Their high intensities recommend a charge-
transfer origin for these bands. Although these have previously
been attributed to MLCT transitions,10 the strong donor ability of
the ligands, the reductive nature of oximes, the general tendency
of copper(II) to act as oxidant rather than reductant and its
attendantly high optical electronegativity leads us to favour an
LMCT assignment (such as roxime → dCu). Any Cu(II), Mn(II) or
Co(II) d–d transitions are obscured by these more intense bands.
The shoulder at 455 nm, which is observed in the spectrum of
the mononuclear complex 1 is shifted in the spectra of di- and
trinuclear 2–4 to 503–514 nm.
Fig. 3 Crystal structure of 5 (hydrogen atoms are omitted for clarity).
(a) Fragment of polymeric structure containing Cu3 unit and two
2+
adjacent Ba(H2O)5 units. Not labeled atoms bonded to Ba(1) are
oxygens, atom in trans-position to O(7) is the O(7)ꢀꢀ atom of neighboring
Cu3 unit, whereas other oxygen atoms are the ones of water. (b) Crystal
packing of 5. Arrows indicate Cu(1)–O(19)ꢀꢀ bonds, which join Cu3 units.
Symmetry equivalent positions are the following: x, y, z; − x, y, −z +
1/2; x + 1/2, y + 1/2, z; −x + 1/2, y + 1/2, −z + 1/2; −x, −y, −z;
x, −y, z − 1/2; −x + 1/2, −y + 1/2, −z; x + 1/2, −y + 1/2, z −
˚
1/2. Selected bonds (A): Cu(1)–N(12) 1.917(9), Cu(1)–N(8) 1.954(9),
Cu(1)–N(18) 1.969(9), Cu(1)–N(2) 2.031(9), Cu(2)–O(1) 1.932(6),
Cu(2)–O(20) 1.956(11), Cu(2)–O(19) 2.112(7), Ba(1)–O(7) 2.697(7),
Ba(1)–O(1W) 2.747(9), Ba(1)–(2W) 2.643(12), Ba(1)–O(3W) 2.772(11);
selected angles (◦): N(12)–Cu(1)–N(8) 96.0(4), N(12)–Cu(1)–N(18)
83.2(4), N(8)–Cu(1)–N(18) 177.8(4), N(12)–Cu(1)–N(2) 167.0(4),
N(8)–Cu(1)–N(2) 82.8(3), N(18)–Cu(1)–N(2) 97.6(4), O(1)–Cu(2)–O(1)ꢀ
169.3(4), O(1)–Cu(2)–O(20) 84.6(2), O(1)–Cu(2)–O(19) 97.6(3), O(1)–
Cu(2)–O(19)ꢀ 89.3(3), O(20)–Cu(2)–O(19) 129.8(2), O(19)–Cu(2)–O(19)ꢀ
100.5(4).
Magnetic properties
The magnetic behaviours of polycrystalline samples of the polynu-
clear complexes were measured in the temperature range 2–
300 K. For dinuclear 2, vmT decreased from 0.743 cm3 K mol−1
at 300 K to 0.006 cm3 K mol−1 at 2 K. For the Mn-salt 3, vmT
decreased from 5.01 at 300 K to 4.43 cm3 K mol−1 at 4 K and then
grew to 4.51 at 2 K. For the Co-salt 4 and the Ba-salt 5 vmT again
decreased over the whole T-range studied: from 4.48 at 300 K to
3.29 cm3 K mol−1 at 2 K in the case of 4 and from 0.899 at 300 K to
0.242 cm3 K mol−1 at 2 K in the case of 5 (Fig. 5). Keeping in mind
that the spin-only value for a g = 2.0 Cu2 system is 0.75 cm3 K
mol−1, and for Cu3, Cu3Co and Cu3Mn, 1.125, 3.0 and 5.5 cm3 K
mol−1 respectively, it is clear that the dominant interactions in 2,
3 and 5 are antiferromagnetic. The situation is not so obvious for
the Cu3Co compound (4), vide infra.
Cu2Mn2 and Cu2Ni2 complexes from CuMn and CuNi dimers,
respectively,3d as well as polymerization of Cu3 units.9
In the dinuclear complex 2 (Fig. 4) the Cu(2) of the [Cu(Dien)]2+
moiety is bound by the two oximate O-atoms from the CuL2− unit,
forming a six-membered Cu2N2O2 ring. The Dien-chelated Cu(2)
has a distorted square pyramidal donor set, with s = 0.32; the axial
position is occupied by O(1), and the longest Cu–ligand bond is
˚
to O(1) (2.274(5) A). The Cu-oximate unit’s Cu(1) is essentially
square-pyramidal (s = 0.03) with basal Cu–N bonds averaging
˚
˚
2.00(5) A and a water on the axial position (at 2.327(5) A). The
Cu2N2O2 ring in 2 is fairly planar, the Cu(1)–N-O–Cu(2) torsion
angles, at 14.5(1) and 4.8(1)◦, being about half those in 3–5. The
For the dinuclear compound 2, the magnetic behaviour was
fitted by a modified Bleaney–Bowers expression, defining J via
H = −2JS1S2,11 including temperature-independent paramag-
netism, paramagnetic impurity with S = 0.5 (q, which quantity was
estimated from vmT at 2 K as 1.8%) and a fixed g = 2, which gave
˚
Cu–Cu separation is 3.743(5) A, while the remaining structural
features are unremarkable.
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correlation between J and geometry, as noted for some other
oligonuclear oximate complexes.10,15
The decrease in vmT was not monotonic for either of 3 or 4.
Two inflections were found for 3, at 95 K and 43 K (Fig. 4); the
behavior of 4 was more complicated. However, some similarity
may be seen in the vmT vs. T curves for compounds 3 and 4.
From the structural viewpoint, at least four types of Cu–Cu
couplings should be expected for 3–5 (Fig. 5). Two of them (Ja
and Jb) occur within trinuclear Cu3L2 building blocks, whereas
two others (Jc and Jd) represent coupling to neighboring blocks;
an alternative would be to treat the compounds as alternating
infinite chains. Additional interactions may be expected between
the Cu-trimers and the 3d metals (Mn or Co). In any case, it
appears unlikely that a reliably unique set of so-derived J-values
could be obtained from susceptibility data alone, because of over-
parametrization.
The trinuclear salts 3–5 were approximated as (i) the super-
position of independent anionic (Cu2+3) and cationic (M2+) sub-
lattices, and (ii) the coupling between trinuclear units (Jc and Jd)
was treated via a molecular field (effective parameter zJ’).6,16 The
intratrimer coupling was described by an exchange Hamiltonian
for an isosceles triangle of three spins S1 = S2 = S3 = 1/2:11
H = −2Ja[(S1S2) + (S2S3)] − 2Jb(S3S1)
the exchange integrals Ja and Jb being as defined as in Fig. 5,
though it was anticipated that Jb would be small compared to Ja.
For the Cu3Ba complex 5, where there is no spin contribution
Fig. 5 (a) Definition of exchange parameters for fitting of magnetic
properties of 3–5; (b), experimental data and calculated curves for 3–5
(A, B and C, respectively, see text for the parameters).
J = −30.4(3) cm−1, tip = 0.00018(2), R2 = 1.1 × 10−3 (Fig. 6). The
angle between the mean planes N2O2 and CuO2 may be taken as a
measure of the bending of the Cu2N2O2 metallocycle, and this will
affect the coupling between the coppers. For 2, the angle between
the mean planes Cu(1)N(1)N(4)O(1)O(2) and Cu(2)O(1)O(4) is
from the cation, the best agreement was achieved with J1
=
−85(7) cm−1, g = 2.00(1), tip = 0.0003(1) and 2zJꢀ = −1.7(2) cm−1
(Fig. 5, R2 = 2.5 × 10−3). The observation that vT falls below
the S = 1/2 value of 0.375 as T approaches 0 K indicates the
need to take into account a nonzero value of zJꢀ. The fit was
insensitive to Jb: variation of Jb from 0 to +1,000 cm−1 had
little influence on R2, however, negative values of Jb were clearly
unworkable. It has been pointed out, that for Cu3 systems, the value
for a weak Jb cannot be reliably obtained from measurements
of vmT vs. T.10,17 On the other hand, for these trinuclear units,
the dominant antiferromagnetic interactions Cu(1)-Cu(2) force
the spins of the two Cu(1) atoms to be parallel, corresponding
to their ferromagnetic ordering. A similar situation was recently
described, where it was impossible to determine exact values of
the ferromagnetic exchange parameter in rhombic tetranuclear
nickel(II) complexes with dominantly antiferromagnetic couplings
because of such “spin forcing”.18
154.3◦. In CuDopnCu(phen)(CH3OH)2 ◦ the angle between cor-
2+
responding planes was found to be 153.3 , and J = −433 cm−1,12
and the related metrics for Cu(Dopn)Cu(bipy)(H2O)22+ are 162.5◦
and −674 cm−1, respectively13 (H2Dopn = 2 : 1 Schiff base of
butanedione monoxime and 1,3-diaminopropane). For dinuclear
copper(II) oximato-bridged complexes with Schiff bases prepared
from butanedione monoxime and 2-aminoalkylpyridines, the
dihedral angles between CuD4 planes (D is donor atom) vary
from ca. 180 to 128◦, and the J values lie in the range −410
to −255 cm−1.14 For dinuclear 2, J is significantly lower (in
magnitude) compared with these similar complexes. However,
the presence of electron-withdrawing substituents breaks the
For the Mn2+-salt 3, vmT was represented as the sum of vCu3 T
and a superimposed vMnT, the latter being taken to be temperature-
independent, corresponding to S = 5/2 ( vMnT = 4.375 + tip). This
model gave Ja = −130(5) cm−1, 2zJ’ = −23(1) cm−1 at fixed g =
2, with R2 = 3.4 × 10−5 (Fig. 5). The value of g was fixed to the
lowest reasonable value, because it otherwise tended to decrease
to unrealistically low values during the fitting routine. ESR
measurements of 3 in DMF solution yielded broad spectra, with
no resolution of any Cu(II) g-anisotropy or hyperfine structure
(though the resonances of the isolated Mn2+ were apparent). The
Cu-associated apparent g-values were 2.040 (293 K) and 2.046
(77 K), which correspond reasonably well to these magnetochem-
ical results.
The result, that zJ’ for the Cu3Mn salt, 3, appears to be of larger
Fig. 6 Experimental data and calculated curve for 2.
3012 | Dalton Trans., 2008, 3007–3014
magnitude than for the Ba2+ salt 5 (−23(1) cm−1 vs. −1.7(2) cm−1),
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is a little surprising, because it could be expected that interactions
between trinuclear units would be less efficient than in 5, because
of the looser packing of the trinuclear units (see X-ray structure
description). Reasonable explanations may be that in the case of 5,
(i) the contributions of all types of couplings, presented in Fig. 5,
are comparable, and the couplings Cu(1)–Cu(2) are not dominant,
or (ii) the value for zJꢀ in the Cu3Ba compound is less than in the
Cu3Mn one. This suggests that in the Mn2+ compound (where
the Cu3–Cu3 distances are longer) the larger zJꢀ is acting as the
proxy for some Mn2+–Cu3 interaction. The increase of vmT at 2 K
may be caused by ferromagnetic ordering, which may occur in
Cu–Mn systems1f (also compare with the magnetic properties of
4, vide infra). Thus, the proposed model provides a satisfactory
phenomenological fit of the Cu3–Mn system in 3, there being no
detectable interaction between the Mn2+ cation and the Cu3 anion,
at least above 4 K.
Fig. 7 Possible alignment of spins in 4 (zero-temperature approximation).
The structural features that govern the exchange parameter Ja
in such oximate-bridged trinuclear Cu(II) complexes (containing
Cu(N–O)2Cu(N–O)2Cu cores) appear indexible by the Cu(1)–
Cu(2)–Cu(3) angle (denoted as c). Strong antiferromagnetic cou-
pling amounting to complete spin pairing was found in “planar”
between O atoms coordinated to neighboring Co(II) ions is only
2+
˚
2.72 A, while the smallest distance from an O atom of Co(H2O)6
˚
to the O-atom of an amide group is 2.62 A. Such H-bonds
have been shown to transmit weak exchange interactions, for
example, in solution dimers of nitroxide radical, 1-[N-tert-butyl-
N-(oxyl)amino]-4-benzoic acid (though the overall interactions
in the solid state were antiferromagnetic).23 Similarly, there is
quite efficient coupling in Cu(II) complexes through H-bonds.24a
2+
(c = 0) complexes such as Cu3L2Lꢀ2 (H2L = dimethylglyoxime,
hereinafter H2Dmg, or diphenylglyoxime, Lꢀ = 2,2ꢀ-bipyridyl or
2+ 20
1,10-phenanthroline),19 Cu(Dmg)2{Cu(bipy)(CH3OH)}2
. This
2
2
is entirely reasonable, if unpaired spin in Cu dx
orbitals is to
−y
or H3O2 bridges24b Also, the magnetic properties of layered
−
be exchange coupled by the bridges. Buckling of the Cu2N2O2
metallocycle then renders the transmission of antiferromagnetic
exchange interactions less favourable. It may be noted that the
absolute value of Ja grows with c in the order L2Cu2Cu(Dmg)2Br+
(L = 1,4,7-trimethyl-1,4,7-triazacyclononane, Ja = −448 cm−1,
c = 152◦ 10) < Cu(CuDopn)22+ (H2Dopn = 2 : 1 Schiff base of bu-
tanedione monoxime and 1,3-diaminopropane, Ja = −290 cm−1,
c = 119◦ 9) < 3 (Ja = −130 cm−1, c = 87.6◦). However, as pointed
out by Chaudhuri at al.,10 electron-withdrawing effects of ligand
substitutents are also important, as appears to be validated by the
comparison of the J value for dinuclear compound 2 with other
dinuclear oximato-bridged copper(II) complexes, vide infra.
In the case of the Co-containing analogue 4, the situation is
complicated by the temperature-dependence of the susceptibility
−
Co(II) hydroxides Co2(OH)4−xXx·zH2O (X = CnH2n+1SO4 or
CnH2n+1CO2−) are strongly dependent on interlayer separation r, at
r even above 1 nm, without any covalent bonds between the layers25
(vT increases from 55 to 220 cm3·K mol−1 when r is increased from
˚
12.7 to 27.4 A).
Concluding remarks
Trinuclear anions, based on a diamido-dioximate, are suitable
building blocks for the generation of polymeric heterometallic
systems. Two isostructural complexes, containing infinite stacks of
trinuclear Cu3 anions and Mn(H2O)2+ or Co(H2O)2+ counterions,
2+
4
and a similar compound with a diamagnetic Ba(H2O)5 bridge,
due to spin–orbit coupling within the T1g ground state of the
octahedral cobalt(II).6,21 in the cobalt sublattice. When the pre-
vious “superimposed lattice” approach was used for this system,
reasonable values of spin–orbit coupling constant k yielded fits
of only the high-temperature part of the data (Fig. 4). The curve
shown on Fig. 4, corresponds to Ja = −110 cm−1, Jb = 0, gCu = 2,
2zJꢀ = −20 cm−1, tip = 0.002, A = 1.4 and k = −140 cm−1, where
A is a crystal field strength parameter which lies in the range from
1.5 (weak field) to 1.0 (strong field)21a
The most probable origin for the high vT of 4 at low T
is a ferromagnetic interaction involving Co2+ and Cu3 ions in
the Cu3Co system 4.22 However, we are unable to discriminate
definitively amongst the possible interactions (Cu3–Cu3, Co–Co
or Cu3–Co) which could give rise to this low-T ferromagnetic
ordering (Fig. 7). The possibility of ferromagnetic interactions
between the trinuclear Cu(II) units and Co2+ through a system of
hydrogen bonds cannot be excluded. Though the distance from
were prepared and characterized crystallographically and magne-
tochemically. Antiferromagnetic interactions dominate within the
Cu3 blocks, as well as between them in the stacks, and magnetic
data for Cu3Mn could be accounted for by this model, involving
no significant interactions between the anionic and cationic
sub-lattices. The magnetic behavior of the Cu3Co analogue,
namely, significant growth of vmT (vs. the expected values) is
consistent with additional ferromagnetic ordering in the lattice.
Exchange interactions within the trinuclear block in 3 and in the
dinuclear complex 2 are weaker than in similar previously reported
compounds, which is presumably associated with differences in the
bridging angles between the Cu(II) ions, as well as with an electron-
withdrawing effect of cyano substituents in the ligand.
Acknowledgements
˚
Co(II) to the other metal ions in 4 is rather large (5.88 A to
2+
˚
neighboring Co(II) and 6.94 A to Cu(II)), the Co(H2O)6 ions
A. W. A. thanks Drexel University for support. V. V. P. and S. V. K.
thank the L. V. Pisarzhevskii Institute for support.
take part in formation of a system of H-bonds. The distance
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11 E. Sinn, Coord. Chem. Rev., 1970, 5, 313; tip is the temperature-
independent paramagnetism; the goodness-of-fit measure is R2(vT) =
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