2-Anilinopyridinate of Cu(I) and adducts of 2-anilinopyridine and metal acetates. Crystal structure of Cu2(μ-OAc)4(PhNHpy)2

Article abstract of DOI:10.1016/S0277-5387(01)01015-4

The adducts of M(OAc)₂·nH₂O (M = Cu, Co, Ni, Zn) with 2-anilinopyridine, M(OAc)₂(PhNHpy), have been synthesized and characterized. The X-ray crystal structure of Cu₂(μ-OAc)₄(PhNHpy)₂ shows the dimer structure of Cu₂(μ-OAc)₄(H₂O)₂ with the PhNHpy ligand in the axial positions of the water molecules. It is antiferromagnetic (2J = - 286 cm ^{- 1}). Signals of the triplet state are observed in its EPR spectrum and the zero field splitting parameter (D = 0.33 cm ^{- 1}) has been calculated. The electronic spectra and the strong antiferromagnetism of the cobalt (2J = - 324 cm ^{- 1}) and nickel (2J = - 382 cm ^{- 1}) compounds allow to propose also a dimeric structure for them. By excess of ligand, in the anionic form, the Cu(I) compound Cu(PhNpy) was obtained for which a dinuclear structure with a lineal coordination in Cu(I) is proposed.

Full text of DOI:10.1016/S0277-5387(01)01015-4

Polyhedron 21 (2002) 457–464
www.elsevier.com/locate/poly
2-Anilinopyridinate of Cu(I) and adducts of 2-anilinopyridine and
metal acetates.
Crystal structure of Cu2(m-OAc)4(PhNHpy)2
Jose´ M. Seco a, Mar´ıa J. Gonza´lez Garmendia a,*, Elena Pinilla b,c, Mar´ıa R. Torres b
a Grupo de Qu´ımica Inorga´nica, Facultad de Ciencias Qu´ımicas, Uni6ersidad del Pa´ıs Vasco, UPV/EHU, Apartado 1072,
E-20080 San Sebastian, Spain
b Laboratorio de Difraccio´n de Rayos-X, Facultad de Ciencias Qu´ımicas, Uni6ersidad Complutense, E-28040 Madrid, Spain
c Departamento de Qu´ımica Inorga´nica, Facultad de Ciencias Qu´ımicas, Uni6ersidad Complutense, E-28040 Madrid, Spain
Received 17 July 2001; accepted 6 December 2001
Abstract
The adducts of M(OAc)2·nH2O (M=Cu, Co, Ni, Zn) with 2-anilinopyridine, M(OAc)2(PhNHpy), have been synthesized and
characterized. The X-ray crystal structure of Cu2(m-OAc)4(PhNHpy)2 shows the dimer structure of Cu2(m-OAc)4(H2O)2 with the
PhNHpy ligand in the axial positions of the water molecules. It is antiferromagnetic (2J= −286 cm−1). Signals of the triplet
state are observed in its EPR spectrum and the zero field splitting parameter (D=0.33 cm−1) has been calculated. The electronic
spectra and the strong antiferromagnetism of the cobalt (2J= −324 cm−1) and nickel (2J= −382 cm−1) compounds allow to
propose also a dimeric structure for them. By excess of ligand, in the anionic form, the Cu(I) compound Cu(PhNpy) was obtained
for which a dinuclear structure with a lineal coordination in Cu(I) is proposed. © 2002 Elsevier Science Ltd. All rights reserved.
Keywords: 2-Anilinopyridine; Crystal structures; Antiferromagnetic dimers; Dinuclear acetates; Copper(I)
ture. Among the carboxylate complexes of Co(II) and
Ni(II) the dimer structures as that of [Cu2(m-OAc)4L2]
are infrequent. The X-ray diffraction has confirmed this
structure in [M2(m-O2CPh)4(quin)2], for quin=quino-
line and M=Co(II) [8] and Ni(II) [9]. These complexes
are antiferromagnetic, unlike other compounds with the
same components but different structure, as
[Co3(O2CPh)6(quin)2] [10].
In Zn(OAc)2·2H2O two bidentate acetate anions and
two water molecules are coordinated to the zinc atom
[11]. The hydrogen bonds are established in a bidimen-
sional net.
The 2-anilinopyridine, (N-phenyl-2-pyridinamine,
PhNHpy), is an asymmetrical ligand, with two nitrogen
atoms in the 1,3 positions, which can coordinate as
monodentate or bidentate. As monodentate ligand the
coordination is established through the pyridinic nitro-
gen and as anionic bidentate through both nitrogen
atoms [12,13]. In previous papers we reported the reac-
tion between [Cu2(NN)2(m-OH)2]X2·nH2O, where
NN=2,2%-bipyridyl or 1,10-phenanthroline and X−=
1. Introduction
The dinuclear copper(II) acetate dihydrate [Cu2(m-
OAc)4(H2O)2], with four bridging acetate groups and
the water molecules in the axial positions, is one of the
most studied dinuclear compounds of Cu(II) in the
structural and magnetic aspects [1,2]. Also the adducts
[Cu2(m-OAc)4L2] and [Cu2(m-O2CR)4L2] with different
ligands in the axial positions [3–6].
The hydrated acetates of cobalt(II) and nickel(II),
M(OAc)2·4H2O, are monomers and isostructurals [7].
The acetate groups are monodentate and two of them
are coordinated to each metal atom. The octahedral
coordination is completed by four water molecules.
Intermolecular hydrogen bonds between non-coordi-
nated oxygen atoms of the acetate groups and hydro-
gen atoms of water are involved in a tridimensional net.
They have normal magnetic moments at room tempera-
* Corresponding author. Tel.: +34-943-018208; fax: +34-943-
212236.
E-mail address: qppgogam@sq.ehu.es (M.J. Gonza´lez Garmendia).
0277-5387/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)01015-4

458
J.M. Seco et al. / Polyhedron 21 (2002) 457–464
PF6− or CLO4−, and PhNHpy. For X−=PF6− [14]
each PhNHpy molecule is coordinated to a copper
atom through the pyridinic nitrogen and the hydrogen
bonded to the anilinic nitrogen is involved in an hydro-
gen bond with the oxygen atom of a bridging OH
group. When X−=ClO4− [15] the ligand interacts with
the medium (methanol) and a methylene group is in-
serted between the anilinic nitrogen atom and the
bridging oxygen. The corresponding magneto–struc-
tural correlations were established for the resulting
dinuclear complexes.
In this paper we describe the interaction between
PhNHpy and the M(OAc)2·nH2O acetates (M=Cu,
Co, Ni, Zn). The scope of substitution of AcO− by the
anionic ligand PhNpy− was unsuccessful and the Cu(I)
compound CuPhNpy was obtained. The other adducts
of PhNHpy, M(OAc)2(PhNHpy) were obtained. Crys-
tal structure of Cu(II) compound has been determined.
Electronic spectra and magnetic and EPR results are
C, 51.2; H, 4.6; Cu, 18.0; N, 8.0%. Soluble in dimethyl-
formamide, C6H5NO2, nitromethane and partially solu-
ble in CHCl3 and MeOH.
2.1.3. M(OAc)2(PhNHpy), M=Co (3), Ni (4), Zn (5)
These complexes were synthesized according to the
method described by Brookes and Martin [17] for the
reaction of NiOAc with azaindole. A solution of
PhNHpy (0.68 g, 4 mmol) in MeOH (10 ml) was added
to a solution of M(OAc)2·nH2O (2 mmol) in MeOH (40
ml). The solution was stirred during 5 min and was
concentrated to dryness in the rotavapor. The product
was of colour garnet for Co, green for Ni and white for
Zn. It was dissolved in C6H5CH3 and heated at 100 °C
during 45 min (30 min for the Zn compound). The
precipitate formed was filtered off, washed with
C6H5CH3 and dried by air suction.
Compound 3: Dark green powder. Yield: 79%. m.p.
(dec.) 215 °C. Anal. Found: C, 51.8; H, 4.4; N, 8.5.
Calc. for C15H16CoN2O4: C, 51.9; H, 4.6; N, 8.1%.
Soluble in C6H5NO2. Soluble in dimethylformamide,
MeOH, EtOH and C3H6O with colour change from
green to garnet. Partially soluble in CHCl3.
also described and allow to make
proposition.
a structural
2. Experimental
Compound 4: Light green powder. Yield: 60%. m.p.
(dec.) 209 °C. Anal. Found: C, 51.2; H, 4.5; N, 78.3;
Ni, 17.3. Calc. for C15H16N2NiO4: C, 51.9; H, 4.6; N,
8.1; Ni, 16.7%. Soluble in dimethylformamide and
C6H5NO2 and partially soluble in MeOH, EtOH and
CHCl3.
Compound 5: White powder. Yield: 87%. m.p. (dec.)
172 °C. Anal. Found: C, 50.5; H, 4.4; N, 7.6; Zn, 18.7.
Calc. for C15H16N2O4Zn: C, 50.9; H, 4.6; N, 7.9; Zn,
18.4%. Soluble in dimethylformamide, C6H5NO2,
MeOH and CHCl3 (partially).
2.1. Synthesis
The anionic form of PhNHpy was prepared, in situ.
The ligand was dissolved in the minimal volume of
absolute EtOH and metallic Na, in stoichiometric pro-
portion, was added. The mixture was allowed to stand
15 min before using it [16].
2.1.1. Cu(PhNpy) (1)
A solution of anionic PhNHpy (5 mmol) in absolute
EtOH (10 ml) was added to
a
solution of
2.2. Measurements
Cu(OAc)2·H2O (1 mmol) in MeOH (30 ml). The mix-
ture was refluxed for 3 h and cooled at room tempera-
ture (r.t.). A yellow precipitate was formed. It was
filtered off, washed with MeOH and dried by air
suction.
Yield: 83%. m.p. (dec.) 262 °C. Anal. Found: C,
56.6; H, 3.9; Cu, 27.6; N, 11.9. Calc. for C11H9CuN2: C,
56.8; H, 3.9; Cu, 27.3; N, 12.0%. Soluble in C6H6 and
CH2Cl2 under nitrogen and slightly soluble in
dimethylformamide.
C, H and N were analysed in a Perkin–Elmer 240C
Elemental Analyser. Copper, Ni and Zn were measured
with an Atomic Absorption Spectrophotometer
Perkin–Elmer 2380, u=324.8, 232.0 and 213.9 nm,
respectively. Melting points were measured on an Elec-
trothermal 9300. Conductivity measurements were
made using a Metrhom E518 conductometer. IR spec-
tra were recorded on a Nicolet FT-IR 510 spectrometer
in the range 4000–400 cm−1 using KBr pellets and on
a Nicolet 740 in 650–50 cm−1 range using nujol on a
polyethylene film. Mass spectrum was obtained on an
VG Autospec instrument with the liquid secondary ion
mass spectra technique (LSISM), using nitrobenzyl al-
cohol as matrix with the addition of trifluoroacetic
acid. Cs+ cations at 30 Kv were used. Electronic spec-
2.1.2. Cu(OAc)2(PhNHpy) (2)
A solution of PhNHpy (0.34 g, 2 mmol) in THF (10
ml) was added to Cu(OAc)2·H2O (0.20 g, 1 mmol) in
THF (40 ml). The solution was stirred during 2 h and
a precipitate was formed. The blue green precipitate
was filtered off, washed with THF and dried in vacuo
over CaCO3.
tra were recorded on
spectrophotometer.
a Shimadzu UV-265 FW
Yield: 80%. m.p. (dec.) 262 °C. Anal. Found: C,
51.7; H, 4.5; Cu, 17.9; N, 7.7. Calc. for C15H16CuN2O4:
Magnetic measurements were carried out with a mag-
netometer Manics DSM-8 or a SQUID MPMSXL of

J.M. Seco et al. / Polyhedron 21 (2002) 457–464
459
,
0.71073 A), operating in the ꢀ and € scanning mode. A
summary of the crystallographic data, conditions used
for the data collection and some refinement data are
listed in Table 1.
Quantum Design. Diamagnetic corrections have been
applied [2]. The EPR spectra were recorded on a
Bruker ESP 300 spectrometer with a Bruker ER 035 M
gaussmeter, and HP 5325B frequency counter.
Data were collected over and hemisphere of the
reciprocal space by combination of the three exposure
sets. Each exposure of 20 s covered 0.3 in ꢀ. The first
50 frames were collected at the end of the data collec-
tion to monitor crystal decay. No appreciable drop in
the intensities of standard reflections was observed.
The structure was solved by Patterson (Cu atoms)
and conventional Fourier techniques and refined by
full-matrix least-squares on F2 [18]. All atoms were
refined anisotropically. Hydrogen atoms were included
in calculated positions and refined riding on the respec-
tive carbon atoms, with some exceptions. H(2) has been
located in a Fourier synthesis, included and riding on a
N bonded atom.
2.3. Crystal structure determination
Prismatic single crystals of C30H32Cu2N4O8 (2) were
grown by layering MeOH solution of copper(II) acetate
dihydrate, MeOH and ether solution of 2-anilinopy-
ridine. The X-ray diffraction data were collected, at 296
K, on a Bruker Smart CCD diffractometer, with
graphite-monochromated Mo Ka radiation (u=
Table 1
Crystallographic and structure refinement data for [Cu2(m-
O2CCH3)4(PhNHpy)2] (2)
Empirical formula
Formula weight
Temperature (K)
C30H32Cu2N4O8
703.68
296(2)
3. Results and discussion
,
Wavelength (A)
0.71073
Crystal system
Space group
Unit cell dimensions
monoclinic
P21/n
3.1. Characterization
,
a (A)
11.3622(12)
7.5900(8)
17.9726(19)
101.093(2)
1521.0(3)
2
The molar conductivity values for 1 in dimethylfor-
mamide and for 2–5 in methanol correspond to non-
ionic compounds. The most significant band in the IR
spectra is that assigned to the stretching w(NꢀH) at
approximately 3300 cm−1. In compound 1 this band is
not observed. This result confirms the presence of the
anion PhNpy−. In compounds 2–5 this band appears
between 3274 and 3312 cm−1, indicating the neutral
form of the ligand.
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
Dcalc (g cm−3
)
1.536
1.455
Absorption coefficient, v
(mm−1
F (000)
Crystal size (mm)
)
724
0.20×0.20×0.40
q Range for data collection (°) 1.96–23.29
In Table 2 are registered the mass spectra results for
the Cu(I) compound. They agree with the dimeric struc-
ture of 1. The most intense signals are those of LH+1,
CuL+1 and CuLLH+1, which can be generated in
the matrix, from the dimer Cu2L2. The spectrum ex-
hibits some signals for a mass higher than that of the
dimer, but of very low intensity (B1%). The corre-
sponding cations can be due to molecular associations.
The electronic spectrum of 1 shows the ligand band
at 280 nm and no d“d transition bands. The yellow
colour is due to charge transfer. The compound is
diamagnetic.
Index ranges
Reflections collected
Independent reflections
Completeness to q=23.29° (%) 99.6
Absorption correction
Refinement method
(−12, −8, −19) to (11, 7, 19)
6446
2188 (Rint=0.0448)
None
full-matrix least-squares on F2
Data/restraints/parameters
Final R indices [I\2|(I)]
R indices (all data)
2188/0/209
R1=0.0365 (obs. 1545)
wR2=0.0893
0.904
Goodness-of-fit on F2
Maximum residual (e−3
)
0.39
R1=S(ꢀFoꢀ−ꢀFcꢀ)/SꢀFoꢀ; wR2={S[w(Fo2−Fc2)2]/S[w(Fo2)2]}1/2
.
According to the coordination possibilities of the
ligand and the ligand–metal ratio, the compound 1
may present a dimeric or a linear chain structure
(Scheme 1). In both cases the Cu(I) cation adopts a
linear coordination and the ligand, in the anionic form,
acts as bridging bidentate through pyridine and aniline
nitrogen atoms. The dimeric structure has been found
Table 2
Mass spectra results for Cu(PhNpy) (1), (L=PhNpy)
m/z
Ion
Relative intensity (%)
465
403
233
171
78
Cu2L2+1
CuLLH+1
CuL+1
LH+1
3
42
75
100
13
8
in
[Cu2(form)2]
[20] and [Cu2(hpp)2] (hppp=1,3,4,6,7,8-hexahydro-2H-
[Cu2(dab)2]
(dab=diazoaminobenzene)
[19],
py+1
(form=N,N%-di-p-tolylformamidinato)
63
Cu+1

460
J.M. Seco et al. / Polyhedron 21 (2002) 457–464
four acetate groups are bridging the two copper atoms
and a PhNHpy neutral ligand occupies the axial posi-
tion of each copper atom, coordinated to them through
the pyridine nitrogen atom. Fig. 2 shows an ORTEP
view of the dimer geometry with 35% probability ellip-
soids that includes the atom labelling. The hydrogen
atoms have been omitted for clarity, only H(2) involved
in an hydrogen bond is included. Selected interatomic
distances and angles are listed in Table 3.
Scheme 1. Dimer and linear chain disposition for Cu(PhNpy) (1).
Each copper atom has a distorted square-planar
pyramidal coordination, with four oxygen atoms in a
,
plane, at an average distance of 1.971(3) A; the fifth
coordination position is occupied by the pyridine nitro-
,
gen, N(1), of a ligand molecule at 2.186(3) A. The
copper atom rises from the basal plane to the apical
,
N(1) atom by 0.209(0.001) A. The Cu···Cu separation is
,
2.6479(9) A. The hydrogen atom, H(2), bonded to the
anilinic nitrogen, N(2), is involved in an hydrogen bond
to the oxygen, O(1), of an acetate group. Only two of
the four acetate groups are involved in hydrogen bond.
The results are similar to those found for [Cu2(m-
OAc)4(H2O)2] [2] and other complexes, as the polymeric
adduct of copper(II) acetate with 2-amonipyrimidine
[22]. Hydrogen bonds of PhNHpy have been before
described [12,14].
Fig. 1. Proposed structure for Cu(PhNpy) (1).
pyrimido[1,2-a]pyrimidinate) [21a]. In all three cases an
eight members ring is formed, with a short Cu···Cu
,
distance (2.45–2.50 A) attributed to a combination of
,
strong CuꢀN bonding (1.86–1.94 A) and very short bite
distance for the ligands. In the ligand PhNpy− the
relative position of the coordinating nitrogen atoms is
the same that in the reported complexes and a similar
dimeric structure is proposed (Fig. 1). The chain struc-
ture will be hindered by the steric effects between
pyridine and phenyl groups of neighbouring ligands.
The same dimeric structure has been proposed for
[Cu2(MeNpy)2] [21b].
3.3. Electronic spectra
The dimethylformamide solution and diffuse reflec-
tance spectral data are summarized in Table 4. The
p“p* band on the ligand, at 274 nm, which in the
reflectance spectra presents a broad absorption in the
360–190 nm range, is reproduced in all the complexes.
For [Cu2(m-OAc)4(PhNHpy)2] in solution, the three
expected bands are observed: (a) 700 nm for the d“d
transitions; (b) 360 nm, characteristic of copper acetate
dimer structure and which is not observed in analogue
monomers; and (c) 300 nm for charge transfer [23,24].
3.2. Crystal structure of [Cu2(v-OOCCH3)4(PhNHpy)2]
(2)
Compound 2 consists of centrosymmetric dinuclear
units, similar to other copper acetate derivates, in which
Fig. 2. ORTEP view of [Cu2(m-OAc)4(PhNHpy)2] (2).

J.M. Seco et al. / Polyhedron 21 (2002) 457–464
461
Table 3
[25]. The spectrum is similar to those described for the
dimer [Co2(m-O2CPh)4(quin)2] [10]. The transition
4A2“4E (4T2g) can be of lower energy than the limit of
the spectrophotometer (900 nm). The bands at 730, 585
,
Selected interatomic distances (A) and angles (°) for [Cu2(m-
OOCCH3)4(PhNHpy)2] (2)
Interatomic distances
4
4
Cu(1)ꢀO(2)
Cu(1)ꢀO(4)
Cu(1)ꢀO(3)
Cu(1)ꢀO(1)
Cu(1)ꢀN(1)
Cu(1)···Cu(1)*
O(1)ꢀC(1)
N(1)ꢀC(5)
N(1)ꢀC(9)
C(1)ꢀC(2)
1.969(3)
1.964(3)
1.976(3)
1.974(3)
2.186(3)
2.6479(9)
1.268(5)
1.349(5)
1.344(5)
1.499(6)
1.252(5)
1.385(5)
1.417(5)
1.505(6)
1.400(5)
1.371(6)
1.385(6)
1.359(6)
1.383(6)
1.392(6)
1.391(6)
1.376(6)
1.373(6)
1.376(6)
and 440 nm are assigned to the transition to B1, E
4
(4T1g) and A2 (4T1g), respectively. The shoulders at 530
and 370 nm may be due to transitions to levels of the
2
2G and F free ion terms, respectively.
The reflectance spectrum of the nickel compound 4 is
similar to those of [Ni2(m-O2CPh)4(quin)2] [9]. Scheme 3
shows the splitting of the T(Oh) levels for a d8 ion, in a
square-pyramidal symmetry (C46). The transitions to
3E[3T2g(F)], 3B2[3T2g(F)], and 3A2[3T1g(F)] are of low
O(2)ꢀC(3)
3
energy. The band at 690 nm is assigned to the B1“
N(2)ꢀC(5)
N(2)ꢀC(10)
C(3)ꢀC(4)
C(5)ꢀC(6)
C(6)ꢀC(7)
C(7)ꢀC(8)
C(8)ꢀC(9)
C(10)ꢀC(11)
C(10)ꢀC(15)
C(11)ꢀC(12)
C(12)ꢀC(13)
C(13)ꢀC(14)
C(14)ꢀC(15)
3E[3T1g(F)] transition and the band at 410 nm to the
3
3
3
non-resolved transitions to A2 and E levels of T1g(P).
The solution spectrum is similar. The shoulder at 740
nm can be assigned to the spin forbidden A2g“1Eg
3
transition, which frequently is observed near the 3A2g“
3T1g(F) transition when Dq/B is close to one. In this
3
case, the assumption of 687 and 400 nm as the A2g“
3T1g(F) and A2g“3T1g(P) transitions, respectively, al-
3
lows to estimate the values Dq=830 cm−1 and
B=850 cm−1 (Dq/B=0.98). The absorption at 300
nm is assigned to charge transfer between metal and
acetates.
Bond angles
O(2)ꢀCu(1)ꢀO(4)
O(2)ꢀCu(1)ꢀO(3)
O(4)ꢀCu(1)ꢀO(3)
O(2)ꢀCu(1)ꢀO(1)
O(4)ꢀCu(1)ꢀO(1)
O(3)ꢀCu(1)ꢀO(1)
O(2)ꢀCu(1)ꢀN(1)
O(4)ꢀCu(1)ꢀN(1)
O(3)ꢀCu(1)ꢀN(1)
O(1)ꢀCu(1)ꢀN(1)
O(2)ꢀCu(1)ꢀCu(1)*
O(4)ꢀCu(1)ꢀCu(1)*
O(3)ꢀCu(1)ꢀCu(1)*
O(1)ꢀCu(1)ꢀCu(1)*
167.6(1)
89.4(1)
90.0(1)
88.4(1)
89.5(1)
168.0(1)
98.4(1)
94.0(1)
95.7(1)
96.3(1)
84.24(8)
83.38(8)
83.97(8)
84.03(8)
For the zinc compound 5 only the ligand band and
the charge transfer between metal and acetates are
observed.
3.4. Magnetic results
Compounds of Cu(I), (1), and Zn(II), (5), are dia-
magnetic. Other three compounds 2, 3 and 4 are
antiferromagnetic.
The plots of MT versus temperature (T) for com-
pound 2 are shown in Fig. 3. The data, between 14 and
300 K, were fitted to the Bleaney–Bowers equation for
a dimer with S1=S2=1/2, modified by the inclusion of
the fraction of monomeric impurity [26]:
Hydrogen bond
N(2)ꢀH(2)
H(2)···O(1)
N(2)···O(1)
N(2)ꢀH(2)ꢀO(1)
0.95
1.99
2.912(4)
162.7
M=[Cex(1−z)/(1+3ex)]+Cz/4+Na
where C=Ng2i2/kT, x=2J/kT, z is the fraction of
monomeric impurity and Na is the temperature inde-
pendent paramagnetism (TIP). The results of the best
fit for g=2.16 (EPR result) and Na=60×10−6 cm3
mol−1 are collected in Table 5. The 2J value, indicating
a significant antiferromagnetic intradimer interaction, is
similar to the values found in other adducts of copper
acetate [27,28].
For Co(II) (3) and Ni(II) (4) complexes, a strong
antiferromagnetic effect is observed. The magnetic mo-
ment decreases with decreasing temperature, from 3.03
(287 K) to 0.75 MB (4 K) for 3 and from 2.16 (293 K)
to 1.24 MB (14 K) for 4. This effect is still stronger
than the found in other dimeric carboxylate complexes
Symmetry transformations used to generate equivalent atoms: *,
−x+2, −y+2, −z.
The cobalt compound 3 changes colour from green
(solid) to pink (solution). The solution spectrum may
be explained in basis to an octahedral coordination.
4
The absorption at 540 nm is assigned to the T1g(F)“
4T1g(P) transition. Of the three possible transitions for a
4
4
d7 high spin state: T1g(F)“4T2g(F), T1g(F)“4A2g(F)
and T1g(F)“4T1g(P), the first is of low energy and can
4
be not observed and the second is a transition of two
electrons (Scheme 2).
The diffuse reflectance spectrum corresponds to a d7
high spin ion in a square-pyramidal (C46) environment

462
J.M. Seco et al. / Polyhedron 21 (2002) 457–464
Table 4
Electronic spectral data
Compound
umax (nm), in dimethylformamide
mmax (l mol−1 cm−1
)
u (nm), diffuse reflectance
360–190
PhNHpy
274
25 900
2
700
360
300
275
193
810
10 030
26 600
725
380
310–190
3
4
540
310
275
39
(sh)
24 000
730
585
530(sh)
440
370(sh)
360–190
274
740
687
400
310
274
(sh)
50
230
9440
24 000
690
410
310–190
5
310
272
8000
19 860
380–190
sh, shoulder.
of Co(II) and Ni(II) [9,10,29]. These results are inter-
preted in basis to a dimeric structure, with an in-
tramolecular interaction between the cations through
the bridging acetate groups. The plots of MT versus T
(Fig. 4) have been fitted using the application of the
Van Vleck equation to each case [30]. These are, with
C=Ng2i2/kT, x=2J/kT and z=fraction of
monomeric impurity, for cobalt(II) dimer (S1=S2=3/
2):
M=C[ex+5e3x+14e6x](1−z)/[1+3ex+5e3x+7e6x]
+5Cz/4+Na
for nickel(II) dimer (S1=S2=1):
M=C[ex+5e3x](1−z)/[1+3ex+5e3x]+2Cz/3+Na
The results of these fittings in the range 50–300 K,
with Na=60×10−6 and 100×10−6, for 3 and 4,
respectively, are summarized in Table 5.
The magnetic behaviour below 50 K may be compli-
cated by zero field splitting effects, especially in nickel
compound, and other possible intermolecular interac-
tions. The lack of knowledge of the crystal structure
prevents us to make a more accurate interpretation.
The conjunction of electronic spectra and magnetic
results lets suppose a dimeric structure for the com-
pounds 3 and 4, [M2(m-OAc)4(PhNHpy)2], similar to
one of Cu(II) compound.
3.5. EPR spectra
The powder EPR spectra of 2 in Q band, at room
temperature, shows the typical signals of the triplet
state (S=1) for D"0 and E:0 (Fig. 5). The spectra
were interpreted according to the Wasserman, Snyder
and Yager equations [31,32], based on the Hamiltonian
Scheme 2. Level splitting for d7, high spin configuration, in C46
symmetry.

J.M. Seco et al. / Polyhedron 21 (2002) 457–464
463
H=gHSi+D[Sz2−2/3]+E[Sx2−Sy2], with D"0 y
E=0. For DM= 91:
Hꢀꢀ=(ge/gꢀꢀ)(Ho−D%)
HÞ1=(ge/gÞ)[Ho(Ho−D%)]1/2
HÞ2=(ge/gÞ)[Ho(Ho+D%)]1/2
For DM= 92:
H
H
min=(ge/gmin)[(Ho2/4)−(D%2/3)]1/2
dq=(ge/gav)[Ho2−D%2/3]1/2
Ho=hw/gei; D%=D/gei
From the experimental values: Hmin=4896; Hꢀꢀ=7262;
HÞ1=9755; HÞ2=13 317 and Hdq=11 035 G, the fol-
lowing parameters have been calculated: gꢀꢀ=2.33;
gÞ=2.07; gav=2.16 and D=0.33 cm−1. These results
agree with the results found for analogue compounds
[23,28].
Scheme 3. Level splitting for d8 configuration in C46 symmetry.
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 167019 for compound 2.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Fig. 3. Plot of T versus T for 2.
Fig. 4. Temperature dependence of T for 3 (ꢀ) and 4 (").
Table 5
Magnetic results
Compound
g
2J (cm−1
)
z
Ra
2
3
4
2.12
4.27
2.78
−286 b
−324 c
−382 d
0.0083
0.020
0.119
7.85×10−5
2.46×10−4
4.45×10−4
a R=S(Tiexp−Tical)2/S(Tiexp)2.
b Calculated from M=[Cex(1−z)/(1+3ex)]+Cz/4+Na.
c Calculated from M=C[ex+5e3x+14e6x] (1−z)/[1+3ex+5e3x
7e6x]+5Cz/4+Na.
+
d Calculated from M=C[ex+5e3x] (1−z)/[1+3ex+5e3x]+2Cz/
Fig. 5. EPR Q band spectrum of powdered [Cu2(m-OAc)4(PhNHpy)2]
(2), at room temperature.
3+Na.

464
J.M. Seco et al. / Polyhedron 21 (2002) 457–464
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mail: deposit@ccdc.cam.ac.uk or www: http://www.
ccdc.cam.ac.uk).
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This work was supported by the ‘Diputacio´n Foral
de Gipuzkoa’.
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