Copper(ii) assembling with bis(2-pyridylcarbonyl)amidate and N,N′-2,2-phenylenebis(oxamate)

Article abstract of DOI:10.1039/c3dt32949f

We herein present the synthesis and X-ray structures of five copper(ii) complexes of formulae [Cu(bpca)(CF₃SO₃)(H ₂O)]·H₂O (1), [Cu(bpca)(Phpr)(H₂O)] ·3/2H₂O (2), {[Cu(bpca)]₂[Cu(opba)(H ₂O)]}·H₂O (3), {[Cu(bpca)]₂(H ₂opba)}₂·6H₂O (4) and [Cu(bpca)(EtH ₂opba)]_n (5), where bpca = bis(2-pyridylcarbonyl)amidate, Phpr = 3-phenylpropionate, CF₃SO₃^- = triflate (anion of the trifluoromethanesulphonic acid), H₄opba = N,N′-1,2-phenylenebis(oxamic acid), and EtH₃opba = monoethyl ester derivative of the H₄opba. 1 and 2 are mononuclear copper(ii) complexes where the copper atom is five-coordinate in distorted square pyramidal surroundings with a tridentate bpca and a water molecule (1)/carboxylate oxygen (2) building the basal plane and a triflate oxygen (1)/water molecule (2) filling the apical position. 3 is a neutral tricopper(ii) complex where the [Cu(opba)(H₂O)]^2- unit acts as a bis-bidentate ligand toward two peripheral [Cu(bpca)]⁺ fragments. The three crystallographically independent copper(ii) ions in 3 are five-coordinate with two nitrogen and two oxygen atoms (inner copper atom)/three bpca-nitrogen and an oxamate oxygen (outer copper atom) building the basal plane plus a water molecule (inner copper)/an oxamate oxygen (outer copper) in the apical position (inner copper atom) of somewhat distorted square pyramidal surroundings. 4 is a centrosymmetric tetracopper(ii) compound where four [Cu(bpca)]⁺ fragments are assembled by two H₂opba^2- groups adopting an unusual bidentate/bis-monodentate bridging mode. The two crystallographically independent copper(ii) ions in 4 are also five-coordinate having the three bpca-nitrogens in basal positions, the other two sites of the distorted square pyramid being filled by two oxygens of either a bidentate oxamate (at one copper centre) or two bis-monodentate oxamates (at the other copper atom). 5 is a zigzag chain of [Cu(bpca)(H₂O)]⁺ units which are connected through the EtH₂opba^- ligand adopting a bidentate/monodentate bridging mode across the monodeprotonated oxamate group. Each copper(ii) ion in 5 is six-coordinate in an elongated octahedral CuN ₃O₃ chromophore. The magnetic properties of 3-5 were investigated in the temperature range 1.9-300 K. 3 exhibits an intermediate intramolecular antiferromagnetic interaction [J = -65.8(2) cm^-1 with the Hamiltonian H = -J(S_Cu1·S _Cu2 + S_Cu2·S _Cu3)] which leads to a low-lying spin doublet at low temperatures. A weak antiferromagnetic coupling between the inner copper(ii) ions occurs in 4 [J = -2.36(2) cm^-1, H = -JS₁· S₂)] and a very small intrachain antiferromagnetic interaction is observed in 5 [J = -0.17(1) cm^-1 with H = -J∑_iS _i·S_i+1]. These values are analyzed by means of simple orbital symmetry considerations and compared with those previously reported for parent systems.

Full text of DOI:10.1039/c3dt32949f

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Copper(II) assembling with bis(2-pyridylcarbonyl)-
amidate and N,N’-2,2-phenylenebis(oxamate)†
Cite this: Dalton Trans., 2013, 42, 5778
Tatiana R. G. Simões,a Raquel V. Mambrini,a Daniella O. Reis,a Maria V. Marinho,b
Marcos A. Ribeiro,a,c Carlos B. Pinheiro,c Jesús Ferrando-Soria,b Mariadel Déniz,d
Catalina Ruiz-Pérez,d Danielle Cangussu,e Humberto O. Stumpf,*a Francesc Lloretb
and Miguel Julve*b
We herein present the synthesis and X-ray structures of five copper(II) complexes of formulae [Cu(bpca)-
(CF3SO3)(H2O)]·H2O (1), [Cu(bpca)(Phpr)(H2O)]·3/2H2O (2), {[Cu(bpca)]2[Cu(opba)(H2O)]}·H2O (3), {[Cu-
(bpca)]2(H2opba)}2·6H2O (4) and [Cu(bpca)(EtH2opba)]n (5), where bpca = bis(2-pyridylcarbonyl)amidate,
−
Phpr = 3-phenylpropionate, CF3SO3 = triflate (anion of the trifluoromethanesulphonic acid), H4opba =
N,N’-1,2-phenylenebis(oxamic acid), and EtH3opba = monoethyl ester derivative of the H4opba. 1 and 2
are mononuclear copper(II) complexes where the copper atom is five-coordinate in distorted square pyra-
midal surroundings with a tridentate bpca and a water molecule (1)/carboxylate oxygen (2) building the
basal plane and a triflate oxygen (1)/water molecule (2) filling the apical position. 3 is a neutral tricopper(II)
complex where the [Cu(opba)(H2O)]2− unit acts as a bis-bidentate ligand toward two peripheral [Cu-
(bpca)]+ fragments. The three crystallographically independent copper(II) ions in 3 are five-coordinate
with two nitrogen and two oxygen atoms (inner copper atom)/three bpca-nitrogen and an oxamate
oxygen (outer copper atom) building the basal plane plus a water molecule (inner copper)/an oxamate
oxygen (outer copper) in the apical position (inner copper atom) of somewhat distorted square pyrami-
dal surroundings. 4 is a centrosymmetric tetracopper(II) compound where four [Cu(bpca)]+ fragments are
assembled by two H2opba2− groups adopting an unusual bidentate/bis-monodentate bridging mode.
The two crystallographically independent copper(II) ions in 4 are also five-coordinate having the three
bpca-nitrogens in basal positions, the other two sites of the distorted square pyramid being filled by two
oxygens of either a bidentate oxamate (at one copper centre) or two bis-monodentate oxamates (at the
other copper atom). 5 is a zigzag chain of [Cu(bpca)(H2O)]+ units which are connected through the
EtH2opba− ligand adopting a bidentate/monodentate bridging mode across the monodeprotonated
oxamate group. Each copper(II) ion in 5 is six-coordinate in an elongated octahedral CuN3O3 chromo-
phore. The magnetic properties of 3–5 were investigated in the temperature range 1.9–300 K. 3 exhibits
an intermediate intramolecular antiferromagnetic interaction [J = −65.8(2) cm−1 with the Hamiltonian
H = −J(SCu ·SCu + SCu ·SCu )] which leads to a low-lying spin doublet at low temperatures. A weak anti-
1
2
2
3
Received 8th December 2012,
Accepted 10th February 2013
ferromagnetic coupling between the inner copper(II) ions occurs in 4 [J = −2.36(2) cm−1, H = −J S1·S2)]
and a very small intrachain antiferromagnetic interaction is observed in 5 [J = −0.17(1) cm−1 with
H = −J∑i Si·Si+1]. These values are analyzed by means of simple orbital symmetry considerations and
compared with those previously reported for parent systems.
DOI: 10.1039/c3dt32949f
www.rsc.org/dalton
aDepartamento de Química, ICEX, Universidade Federal de Minas Gerais, Av. Antônio
Carlos 6627, Belo Horizonte-MG, 31270-901, Brazil. E-mail: stumpf@ufmg.br
bDepartament de Química Inorgànica/Instituto de Ciencia Molecular, Facultat de
Química de la Universitat de València, C/Catedrático José Beltrán 2, 46980-Paterna
(València), Spain. E-mail: miguel.julve@uv.es
dLaboratorio de Rayos X y Materiales Moleculares, Departamento de Física
Fundamental II, Facultad de Física de la Universidad de La Laguna, Avda. Astrofísico
Francisco Sánchez s/n, 38204 La Laguna, Tenerife, Spain
eInstituto de Química, Universidade Federal de Goias, Campus Samambaia, Goiânia-
GO, 74001-970, Brazil
cDepartamento de Física, ICEX, Universidade Federal de Minas Gerais, av. Antônio
Carlos 6627, Belo Horizonte-MG, 31270-901, Brazil
†CCDC 909388 (1), 909389 (2), 909390 (3), 909391 (4) and 909392 (5). For crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c3dt32949f
5778 | Dalton Trans., 2013, 42, 5778–5795
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of the coordinated water molecules by better donor atoms have
made possible their use as Lewis bases against potential
Introduction
Substituted s-triazines such as tris(2-pyridyl)-1,3,5-triazine mono- or polyatomic bridges (organic linkers) and preformed
(tpyt) and tris(2-pyrimidyl)-1,3,5-triazine (tpymt) undergo complexes acting as donors in order to prepare homo-7–9 and
copper(II)-assisted hydrolysis under mild conditions yielding heteropolymetallic compounds.10,11 The isolation of the
the [bis(2-pyridylcarbonyl)amido]copper(II) ([Cu(bpca)]+) and Hbpca monoprotic acid12 conducted for the preparation
2-pyridylformamide fragments in the case of tpyt and [bis(2-pyri- of mononuclear compounds such as [M(bpca)x](m−x)+ (M = 3d
midylcarbonyl)amido]copper(II) ([Cu(bpcam)]+) and 2-pyrimi- metal ion).12–15 Their use as ligands has afforded hetero-
dylformamide when using tpymt (see Scheme 1).1 dinuclear complexes,16 homo- and heterotrinuclear com-
Interestingly, these fragments could be characterized by single pounds,12a,14b,17,18 chains15,17b,19,20 as well as honeycomb
crystal X-ray diffraction occurring as ligands in the same layered materials17b,21 whose magnetic properties have been
copper(II) complex or apart from each other in two different investigated, some of them being examples of single molecule
copper(II) species, the composition of the products being mon- magnets (SMMs)16,18 and single chain magnets (SCMs).19
itored by modifying the starting triazine : Cu(II) molar ratio.2
Having in mind the good coordinating properties of the
According to kinetic and thermodynamic data,3,4 this oxamato-containing complexes and the remarkable ability of
hydrolytic reaction could take place through a nucleophilic the oxamato to mediate strong magnetic interactions,22 we
attack at the triazine ring by the OH− or H2O and geometrical explored the possibility of preparing polynuclear [Cu(bpca)]+/
constraints have been pointed out to be highly significant on oxamate polynuclear compounds by using preformed oxamate-
the basis of the structural data obtained for the mononuclear containing complexes as ligands towards the [Cu(bpca)]+ unit.
species [Cu(bpcam)(H2O)3]NO3·2H2O and [Cu(bpca)(H2O)2]- Our first results through this approach are presented herein
NO3·2H2O.1b,2b Although first-row transition metal ions other and they concern the synthesis and X-ray structures of the
than Cu(II) have been unable to cause this hydrolytic reaction, compounds [Cu(bpca)(CF3SO3)(H2O)]·H2O (1), [Cu(bpca)(Phpr)-
the heavier Rh(III)/Rh(II) ions have been demonstrated to be (H2O)]·3/2H2O (2), {[Cu(bpca)]2[Cu(opba)(H2O)]}·H2O (3), {[Cu-
able to hydrolyze tpyt affording the same fragments.5 In this (bpca)]2(H2opba)}2·6H2O (4) and [Cu(bpca)(EtH2opba)]n (5)
latter case, the authors suggest that an electron-withdrawing [Phpr = 3-phenylpropionate, H4opba = N,N′-1,2-phenylenebis-
effect of the metal ion, rather than the angular strain, would (oxamic acid) and EtH3opba = monoethyl ester derivative of
be responsible for the metal-promoted hydrolysis of the tpyt. the H4opba molecule] together with the variable-temperature
Theoretical molecular orbital calculations of M(tpyt) [M = Ru(II), magnetic study of 3–5.
Cu(II) and Rh(III)] support that the main hydrolytic effect is the
electron-withdrawing effect of the metal ions.6
The stability of the [Cu(bpca)(H2O)2]+ and [Cu(bpcam)-
Experimental
Materials
(H2O)3]+ species in solution together with the easy replacement
Tpyt, copper(II) triflate and 3-phenylpropionic acid were
purchased from commercial sources and they were used
without further purification. (Bu4N)2[Cu(opba)], Me4N[Mn-
(opba)(H2O)2] and the Et2H2opba proligand [Bu4N+ = tetra-
n-butylammonium, Me4N+
= tetramethylammonium and
Et2H2opba = diethyl ester derivative of H4opba] were prepared
according to procedures reported elsewhere.23–25 Elemental
analyses (C, H, N) were performed with a Perkin Elmer 2400
analyzer and the copper contents were determined by means
of a Hitachi-Z8200 spectrophotometer.
Preparation of the complexes
[Cu(bpca)(CF3SO3)(H2O)]·H2O (1). The addition of solid tpyt
(0.156 g, 0.49 mmol) to a warm (50 °C) aqueous solution
(30 cm3) of copper(II) triflate (0.534 g, 1.48 mmol) led to a blue
solution that was heated at 70 °C for half an hour under con-
tinuous stirring. The resulting dark blue solution was filtered
and allowed to evaporate in a hood at room temperature. X-ray
quality crystals of 1 as deep blue squares were obtained after a
few days. They were collected on a filter paper, washed with a
small amount of cold water (10 °C) and dried in the open air.
Yield is ca. 70%. The 3 : 1 Cu(II) : tpyt molar ratio used in
the synthesis of 1 avoids the formation of the heteroleptic
Scheme 1
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[Cu(bpca)(NC5H4CONH2)]CF3SO3 complex which is the only Physical techniques
product when a 1 : 1 Cu(II) : tpyt molar ratio is used.2b Anal.
Calcd for C13H12CuF3N3O7S (1): C, 32.89; H, 2.53; N, 8.85; Cu,
13.38. Found: C, 32.65; H, 2.48; N, 8.67; Cu, 13.28%.
Infrared spectra were recorded with Bruker IF S55 (1 and 2)
and Perkin-Elmer FTIR (3–5) spectrometers as KBr pellets in
the 4000–400 cm−1 region. The magnetic susceptibility
measurements were carried out on polycrystalline samples of
3–5 in the temperature range 1.9–295 K with a Quantum
Design SQUID susceptometer and using applied magnetic
fields of 0.1 T (T ≥ 100 K) and 0.025 T (T < 100 K). The
complex (NH4)2Mn(SO4)2·6H2O was used as a susceptibility
standard. Diamagnetic corrections of the constituent atoms
were calculated from Pascal’s constants26 and found to be
−372 × 10−6 (3), −627 × 10−6 (4) and −337 × 10−6 cm3 mol−1 (5)
per three (3), four (4) and one (5) mole of copper(II) ions.
Experimental susceptibilities were also corrected for the temp-
erature-independent paramagnetism of [60 × 10−6 cm3 mol−1
per Cu(II)] and the magnetization of the sample holder.
[Cu(bpca)(Phpr)(H2O)]·3/2H2O (2). Solid sodium hydroxide
was added to an aqueous solution (20 cm3) of 3-phenylpropio-
nic acid (0.042 g, 0.28 mmol) under continuous stirring until
pH ca. 9.0. This solution was poured into another aqueous
solution (10 cm3) of 1 (0.133 g, 0.28 mmol) with stirring and
gentle warming (60 °C) for half an hour. Slow evaporation of
the resulting solution under ambient conditions afforded deep
blue hexagons of 2 which were suitable for X-ray diffraction.
They were collected on a filter paper, washed with a small
amount of cold water (10 °C) and dried in the open air. Yield
is ca. 50%. Calcd for C21H22CuF3N3O6.5 (2): C, 52.14; H, 4.55;
N, 8.68; Cu, 13.13. Found: C, 52.03; H, 4.41; N, 8.53; Cu,
13.05%.
{[Cu(bpca)]2[Cu(opba)(H2O)]}·H2O (3). Compound
obtained as a blue polycrystalline powder in a practically
3 was
Crystallography
quantitative yield by mixing concentrated aqueous solutions of X-ray data for 1 and 2 were collected on an Agilent Supernova
1 (0.095 g, 0.20 mmol) and (Bu4N)2[Cu(opba)] (0.080 g, X-ray source at 293(2) K with mirror monochromated Cu radi-
0.10 mmol). Blue needles of 3 suitable for X-ray diffraction ation (λ = 1.5418 Å) whereas those for 3–5 were performed
were grown by slow diffusion in an H-shaped tube (h = 10 cm; using an Oxford-Diffraction GEMINI diffractometer by using
w = 4 cm; d = 1 cm) of aqueous solutions of the complex 1 at graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at
one arm and the (Bu4N)2[Cu(opba)] species at the other one. 293 (3), 260 (4) and 120 K (5). Accurate cell dimensions and
The crystals were collected, washed with a small amount of orientation matrices were determined by least-squares refine-
cold water (10 °C) and air dried. Calcd for C34H24Cu3N8O12 (3): ment of the reflections obtained by θ − χ scans for 1–5. The
C, 44.05; H, 2.59; N, 12.08; Cu, 20.56. Found: C, 43.95; H, 2.48; data for 1–5 were indexed and scaled with the CrysalisPro
N, 11.96; Cu, 20.44%.
program.27 Analytical absorption corrections of the diffracted
{[Cu(bpca)]2(H2opba)}2·6H2O (4). An aqueous solution intensities based on a multifaceted crystal model using Crysa-
(85 cm3) of 1 (0.095 g, 0.20 mmol) was poured into an aqueous lisPro27 were applied in 1–5. The indexes of the data collection
solution (12 cm3) of Me4N[Mn(opba)(H2O)2] (0.124 g, were −12 ≤ h ≤ 18, −9 ≤ k ≤ 9, −15 ≤ l ≤ 17 (1), −33 ≤ h ≤ 34,
0.27 mmol) under continuous stirring. The resulting blue solu- −12 ≤ k ≤ 12, −24 ≤ l ≤ 19 (2), −14 ≤ h ≤ 14, −16 ≤ k ≤ 16,
tion was allowed to evaporate at 20 °C. X-ray quality crystals −17 ≤ l ≤ 17 (3), −12 ≤ h ≤ 12, −14 ≤ k ≤ 14, −22 ≤ l ≤ 22 (4)
of 4 as blue needles were grown after 20 days. Yield is ca. 11%. and −17 ≤ h ≤ 16, −12 ≤ k ≤ 12, −24 ≤ l ≤ 24 (5). Of the 3296
This compound was obtained in a practically quantitative yield (1), 4151 (2), 6982 (3), 7869 (4) and 5254 (5) measured indepen-
by reacting H2opba2− (generated in situ) and 1 in water: solid dent reflections in the θ range 3.99–71.83° (1), 4.32–73.50° (2),
hydroxide (0.040 g, 1.0 mmol) dissolved in a minimum 3.0–26.4 (3), 2.7–27.5° (4) and 3.1–27.5° (5), 2873 (1), 3955 (2),
amount of water was added to a suspension of Et2H2opba 5451 (3), 6221 (4) and 4722 (5) were considered as observed
(0.154 g, 0.5 mmol) in 10 cm3 of a 9 : 1 water–ethanol (v/v) [I ≥ 2σ(I)]. The crystal structure of 1 was solved by using the
mixture; the mixture was stirred at 60 °C for 5 min. Then, a SIR92 software,28 while those of 2–5 were solved by direct
warm aqueous solution (20 cm3) of 1 (0.474 g, 1.0 mmol) was methods using the SHELX-97 package.29 The structures of 1–5
added under continuous stirring. Compound 4 separates were refined by a full-matrix least-squares technique on F2
as
C68H56Cu4N16O26 (4): C, 46.22; H, 3.17; N, 12.68; Cu, 14.39. ware package.30 All non-hydrogen atoms in 1–5 were refined
Found: C, 46.01; H, 3.09; N, 12.39; Cu, 14.10%. anisotropically. The crystallization water molecule O(3W) in 2
a
blue polycrystalline solid on standing. Calcd for using the SHELX-97 programs29 included in the WINGX soft-
[Cu(bpca)(EtH2opba)]n (5). An aqueous solution (50 cm3) of is in a special position and the free water molecule O(12W) in
1 (0.266 g, 0.56 mmol) was added dropwise to an acetone solu- 3 was found to be disordered in two positions and partial
tion (10 cm3) of Et2H2opba (0.088 g, 0.56 mmol) and the occupancy factors of 0.5 [O(2W1)] and 0.5 [O(2W2)] were
resulting blue solution (pH ca. 3.7) was filtered and allowed to assigned. The hydrogen atoms of the organic ligands in 1–5
evaporate under ambient conditions. Plate-like blue plates of 5 were placed in calculated positions and refined with a riding
were grown after seven days. They were collected by filtration, model. However, those of the coordinated (1–5) and free
washed with a small amount of cold water (10 °C) and air (1 and 2) water molecules were located from Fourier differ-
dried. Yield is ca. 34%. Calcd for C24H19CuN5O8 (5): C, 50.68; ences although their hydrogen isotropic displacement has
H, 3.34; N, 12.31; Cu, 11.17. Found: C, 50.45; H, 3.25; N, 12.23; been constrained to their respective oxygen atom. The final
Cu, 11.02%.
geometrical calculations were carried out with PARST,31
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whereas the graphical manipulations were performed with the concerned the νas(COO) and νs(COO) appear at 1570s and
DIAMOND32 and ORTEP33 programs. The crystal data and 1392m cm−1 respectively, the value of Δ being 178 cm−1 [Δ =
structure refinements of 1–5 are listed in Table 1. Selected νas(COO) − νs(COO)]. These last values suggest a chelating
bond lengths and angles and hydrogen bonds are given in coordination of the carboxylate group having in mind that the
Tables 2 (1), 3 (2), 4 (3) 5 (4) and 6 (5).
νas(COO) and νs(COO) for the phenylpropionate as Na+ salt are
1556 and 1354 cm−1, respectively [Δ = 202 cm−1].41,42
The use of the [Cu(opba)]2− unit as a ligand towards the
[Cu(bpca)]+ in aqueous solution yields compound 3 as a poly-
crystalline blue solid. Single crystals of this complex were
grown by slow diffusion in an H-shape tube. The broad absorp-
tion centered at ca. 3400 cm−1 [ν(OH)] and the strong peak at
1717 cm−1 [ν(CO)imide] in the i.r. spectrum of 3 are due to the
presence of water molecules and the [Cu(bpca)]+ fragment,
respectively. Interestingly, the pattern of peaks in the
1700–1600 cm−1 region from the i.r. spectrum of the mono-
nuclear (Bu4N)2[Cu(opba)] complex [1676sh, 1648s and 1614s
cm−1] is simplified to only one strong peak at 1619 cm−1 with
a shoulder at 1600 cm−1 in the i.r. spectrum of 3. These fea-
tures are consistent with the different coordination mode of
the carbonyl groups of the opba ligand in 3 (bridging bis-
bidentate) versus that in the mononuclear complex (bidentate).
The reaction of stoichiometric amounts of 1 and Me4N[Mn-
(opba)(H2O)2] in aqueous solution afforded a small amount
of single crystals of 4 where four [Cu(bpca)]+ fragments
are assembled through two H2opba2− ligands. The partial
decomposition of the [Mn(opba)(H2O)2]+ species in aqueous
solution (after the mixture of the starting chemicals in the
preparation of 4, the pH of the resulting solution was 5.6)
accounts for the formation of single crystals of 4 in a low yield.
Anyway, this compound was obtained as a blue polycrystalline
solid in a good yield by the reaction of stoichiometric amounts
of 1 and H2opba2− (generated in situ) in a water–ethanol
mixture. The i.r. spectrum of 4 exhibits a strong and broad
Results and discussion
Synthesis and IR characterization
The copper(II)-promoted hydrolysis of tpyt in aqueous solution
affords the [Cu(bpca)]+ fragment (see Scheme 1) which is
isolated as the mononuclear compounds 1 and 2 where the
positive charge has been neutralized by the trifluoromethane-
sulphonate (1) and 3-phenylpropionate (2). The strong peak at
1717 (1) and 1708 cm−1 (2) in the infrared spectra of these
complexes, which corresponds to an imide group, is diagnostic
of the presence of the bpca ligand in them.1,2,34 Another
common feature in the i.r. spectra of 1 and 2 is the occurrence
of a strong and broad absorption in the high-frequency region
[continuous absorption in the range 3600–3250 cm−1 with
maxima centered at ca. 3435 (1) and 3450 cm−1 (2)] which is
indicative of the presence of hydrogen bonded coordinated/
free water molecules.35,36 Evidence for unidentate sulphonate
coordination of the triflate group (C3v symmetry) in 1 is pro-
vided by the set of peaks due to this anion:37–39 two SO3
stretching modes at 1282s and 1254s cm−1 [ν4(E)], an SO3
deformation mode at 520m cm−1 [ν5(E)] plus three absorptions
at 1032s [ν1(A1)], 800w [ν2(A1)] and 650s cm−1 [ν3(A1)] to be
−
compared with the set of peaks for the ionic CF3SO3 as the
Na+ salt [stretching vibrations of the SO3 at 1280 and
1240 cm−1 and the CF3 stretching modes at 1175 and
1035 cm−1].40 As far as the 3-phenylpropionate group in 2 is
Table 1 Summary of the crystal data and refinement details for 1–5
Compound
1
2
3
4
5
Formula
Fw
C13H12CuF3N3O7S
474.86
C21H22CuN3O6.5
483.95
C34H24Cu3N8O12
927.23
C68H56Cu4N16O26
1767.49
C24H19N5O8
568.98
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
C2/c
Triclinic
P(1)
Triclinic
P(1)
Monoclinic
P21/c
ˉ
ˉ
a/Å
b/Å
c/Å
α/°
14.6006(3)
8.0694(2)
14.7344(3)
90.0
98.067(2)
90.0
28.5694(7)
10.23660(10)
20.1856(5)
90.0
134.242(4)
90.0
11.6502(3)
13.4289(4)
13.6461(5)
61.971(3)
65.206(3)
80.022(3)
1710.05(11)
2
9.4297(4)
11.2189(9)
17.0787(13)
75.037(7)
80.294(5)
89.324(5)
1719.6(2)
1
13.2927(3)
9.66889(15)
18.7558(4)
90.0
107.619(2)
90.00
β/°
γ/°
V/Å3
1718.80(7)
4
4229.2(3)
8
2297.52(8)
4
Z
λ/Å
1.54184
1.835
1.54184
1.867
0.71073
1.797
0.71073
1.707
0.71073
1.645
ρ/g cm−3
T/K
293(2)
3.667
253
1.033
0.037, 0.100
0.042, 0.106
0.27, −0.43
293(2)
1.867
288
1.044
0.036, 0.099
0.037, 0.101
0.38, −0.46
293(2)
19.1
544
1.06
0.027, 0.075
0.037, 0.077
0.78, −0.47
260(1)
13.2
531
1.02
0.039, 0.084
0.057, 0.091
0.63, −0.47
120(1)
10.1
350
1.04
0.027, 0.068
0.031, 0.071
0.43, −0.42
μ(Mo-Kα)/cm−1
No. parameters
Goodness-of-fit on F2
R,a wRb [I > 2σ(I)]
R,a wRb (all data)
Largest diffraction peak and hole/e A−3
a R = ∑||Fo| − |Fc||/∑|Fo|. b wR = [∑(|Fo|2 − |Fc|2)2/∑|Fo|2]1/2
.
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Table 2 Selected bond distances (Å) and angles (°) for 1a
Copper(II) environment
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(3)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(3)
N(1)–Cu(1)–O(1W)
N(1)–Cu(1)–O(3)
N(2)–Cu(1)–N(3)
Bpca ligand
2.002(3)
1.931(2)
2.001(2)
82.32(9)
163.33(8)
95.50(8)
99.37(8)
82.20(8)
Cu(1)–O(1W)
Cu(1)–O(3)
1.971(2)
2.297(2)
N(2)–Cu(1)–O(1W)
N(2)–Cu(1)–O(3)
N(3)–Cu(1)–O(1W)
N(3)–Cu(1)–O(1W)
O(1W)–Cu(1)–O(3)
172.14(8)
102.08(8)
99.01(8)
99.01(8)
85.71(8)
N(2)–C(6)
C(6)–O(1)
C(5)–C(6)
C(4)–C(5)
C(3)–C(4)
C(2)–C(3)
C(1)–C(2)
C(1)–N(1)
1.359(3)
1.219(3)
1.508(4)
1.374(4)
1.382(5)
1.373(5)
1.383(4)
1.324(4)
1.352(3)
128.9(3)
111.1(2)
120.0(2)
122.3(2)
115.8(2)
121.8(3)
112.66(17)
119.2(2)
128.02(18)
121.7(3)
119.4(3)
118.9(3)
118.9(3)
117.60(17)
124.9(2)
N(2)–C(7)
C(7)–O(2)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
C(10)–C(11)
C(11)–C(12)
C(12)–N(3)
1.370(3)
1.214(3)
1.500(3)
1.373(4)
1.385(4)
1.366(5)
1.384(4)
1.334(3)
1.352(3)
128.3(2)
111.09(19)
120.6(2)
121.8(2)
115.9(2)
122.3(2)
112.97(15)
118.7(2)
128.09(17)
121.6(3)
119.6(3)
119.3(3)
118.5(3)
117.49(16)
N(1)–C(5)
N(3)–C(8)
N(2)–C(6)–O(1)
N(2)–C(6)–C(5)
O(1)–C(6)–C(5)
C(6)–C(5)–C(4)
C(6)–C(5)–N(1)
C(4)–C(5)–N(1)
C(5)–N(1)–Cu(1)
C(5)–N(1)–C(1)
C(1)–N(1)–Cu(1)
N(1)–C(1)–C(2)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
Cu(1)–N(2)–C(6)
C(6)–N(2)–C(7)
Hydrogen bondsb,c
D–H⋯A
N(2)–C(7)–O(2)
N(2)–C(7)–C(8)
O(2)–C(7)–C(8)
C(7)–C(8)–C(9)
C(7)–C(8)–N(3)
C(9)–C(8)–N(3)
C(8)–N(3)–Cu(1)
C(8)–N(3)–C(12)
C(12)–N(3)–Cu(1)
N(3)–C(12)–C(11)
C(12)–C(11)–C(10)
C(11)–C(10)–C(9)
C(10)–C(9)–C(8)
Cu(1)–N(2)–C(7)
D–H (Å)
0.87(2)
0.87(2)
0.88(2)
0.90(2)
H⋯A (Å)
2.00(2)
1.84(2)
2.13(2)
2.00(2)
D⋯A (Å)
2.777(3)
2.696(3)
2.761(3)
2.815(3)
D–H⋯A (°)
149.50(13)
170.90(14)
127.80(14)
149.6(2)
O(1W)–H(1WA)⋯O(2Wa1)
O(1W)–H(1WB)⋯O(2W)
O(2W)–H(2WB)⋯O(2b1)
O(2W)–H(2WB)⋯O(1b1)
a Estimated standard deviations in the last significant digits are given in parentheses. b D and A stand for donor and acceptor, respectively.
c Symmetry code: (a1) = −x + 3/2, y − 1/2, −z + 1/2; (b1) = x − 1/2, −y + 1/2, z − 1/2.
absorption in the range 3600–3100 cm−1 due to the OH Description of the structures
stretching of the water molecules that masks the observation
of the expected N–H amide of the H2opba2− ligand around
[Cu(bpca)(CF3SO3)(H2O)]·H2O (1). The structure of 1 con-
3200 cm−1. As for the preceding compounds, the peak at sists of neutral [Cu(bpca)(H2O)(CF3SO3)] mononuclear units
1711s,sh supports the presence of the [Cu(bpca)]+ fragment in and crystallization water molecules (Fig. 1) which are inter-
4. Finally, four medium intensity peaks at 1690, 1660, 1640 linked by hydrogen bonds involving all the water molecules
and 1608 cm−1 are tentatively attributed to amide and carboxy- and the carbonyl-oxygens (see the end of Table 2) and π–π type
late stretching vibration of the H2opba2− group.
interactions between the pyridyl rings of the bpca ligands.
The partial hydrolysis of the Et2H2opba proligand (the pH These weak intermolecular interactions lead to a supramole-
of the initial mixture of 1 and Et2H2opba is ca. 3.8) which is cular two-dimensional structure growing in the diagonal of the
assisted by the subsequent coordination of its resulting mono- ac plane (Fig. 2). Additional weak π–π type stacking inter-
hydrogenoxamate arm to the [Cu(bpca)]+ unit would account actions between pyridyl rings of pairs of bpca ligands [N(1)C(1)-
for the formation of 5. The i.r. spectra of 5 also exhibit the C(2)C(3)C(4)C(5)/N(3c1)C(8c1)C(9c1)C(10c1)C(11c1)C(12c1) with
strong absorption at 1710 cm−1 characteristic of the ν(CO)imide a centroid–centroid distance of 3.769(2) Å; symmetry oper-
vibration from the bpca ligand. The presence of a medium ation: (c1) = −x + 2, −y, −z + 1] contribute to the stabilization
intensity peak at 3164 cm−1 [ν(N–H)amide] together with the set of the resulting supramolecular layered structure. The shorter
of peaks at 1738m, 1665m, 1643s and 1615m cm−1 [ν(COO)ester intermolecular copper–copper separation in 1 is 4.6006(4)
and ν(CO)amide] supports the occurrence in 5 of the monoethyl [Cu(1)⋯Cu(1c1)].
ester derivative EtH2opba−. All these spectroscopic features for
Each copper(II) ion in 1 is five-coordinate in a somewhat
1–5 were confirmed by their X-ray structures (see below).
distorted square pyramidal CuN3O2 environment, the value of
5782 | Dalton Trans., 2013, 42, 5778–5795
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Table 3 Selected bond distances (Å) and angles (°) for 2a
Copper(II) environment
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(3)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(3)
N(1)–Cu(1)–O(3)
N(1)–Cu(1)–O(1W)
N(2)–Cu(1)–N(3)
Bpca ligand
2.012(2)
1.9391(13)
2.007(2)
81.64(6)
163.10(6)
97.05(6)
90.60(6)
81.63(6)
Cu(1)–O(3)
Cu(1)–O(1W)
Cu(1)–O(4)
N(2)–Cu(1)–O(3)
N(2)–Cu(1)–O(1W)
N(3)–Cu(1)–O(3)
N(3)–Cu(1)–O(1W)
O(3)–Cu(1)–O(1W)
1.9365(13)
2.365(2)
2.852(2)
175.22(6)
90.88(6)
99.44(7)
92.01(6)
93.73(6)
N(2)–C(6)
C(6)–O(1)
1.360(2)
1.215(2)
N(2)–C(7)
C(7)–O(2)
1.360(2)
1.215(2)
C(5)–C(6)
C(4)–C(5)
1.511(2)
1.375(3)
C(7)–C(8)
C(8)–C(9)
1.508(2)
1.370(3)
C(3)–C(4)
C(2)–C(3)
1.389(3)
1.368(3)
C(9)–C(10)
C(10)–C(11)
1.384(3)
1.376(3)
C(1)–C(2)
C(1)–N(1)
1.378(3)
1.337(2)
C(11)–C(12)
C(12)–N(3)
1.371(3)
1.338(2)
N(1)–C(5)
1.339(2)
N(3)–C(8)
1.344(2)
N(2)–C(6)–O(1)
N(2)–C(6)–C(5)
O(1)–C(6)–C(5)
C(6)–C(5)–C(4)
C(6)–C(5)–N(1)
C(4)–C(5)–N(1)
C(5)–N(1)–Cu(1)
C(5)–N(1)–C(1)
C(1)–N(1)–Cu(1)
N(1)–C(1)–C(2)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
Cu(1)–N(2)–C(6)
C(6)–N(2)–C(7)
Hydrogen bondsb,c
D–H⋯A
128.61(16)
111.00(14)
120.38(16)
121.74(17)
115.84(15)
122.41(17)
113.37(11)
118.67(16)
127.80(13)
122.07(19)
119.13(19)
119.27(19)
118.42(19)
117.79(11)
124.12(14)
N(2)–C(7)–O(2)
N(2)–C(7)–C(8)
O(2)–C(7)–C(8)
C(7)–C(8)–C(9)
C(7)–C(8)–N(3)
C(9)–C(8)–N(3)
C(8)–N(3)–Cu(1)
C(8)–N(3)–C(12)
C(12)–N(3)–Cu(1)
N(3)–C(12)–C(11)
C(12)–C(11)–C(10)
C(11)–C(10)–C(9)
C(10)–C(9)–C(8)
Cu(1)–N(2)–C(7)
128.13(17)
111.07(14)
120.80(16)
122.00(16)
115.62(15)
122.38(17)
113.53(12)
118.21(16)
128.15(13)
122.59(19)
118.93(19)
119.0(2)
118.86(19)
117.92(11)
D–H (Å)
0.87(2)
0.87(2)
0.89(2)
0.87(3)
0.89(2)
H⋯A (Å)
2.55(3)
2.40(2)
1.94(2)
2.39(2)
2.09(2)
D⋯A (Å)
2.872(4)
2.873(2)
2.808(2)
3.065(3)
2.885(2)
D–H⋯A (°)
102.71(14)
114.00(13)
164.80(15)
134.56(13)
149.35(4)
O(1W)–H(1WB)⋯O(1a2)
O(1W)–H(1WB)⋯O(2Wb2)
O(2W)–H(2WA)⋯O(4)
O(2W)–H(2WB)⋯O(2c2)
O(3W)–H(3WA)⋯O(3d2)
a Estimated standard deviations in the last significant digits are given in parentheses. b D and A stand for donor and acceptor, respectively.
c Symmetry code: (a2) = −x, −y, −z + 2; (b2) = x − 1/2, −y + 1/2, z − 1/2; (c2) = −x + 1/2, y + 1/2, −z + 5/2; (d2) = −x, y, −z + 3/2.
the trigonality parameter τ being 0.2 (τ = 0 and 1 for square complexes (1.5–8.6°).1,2,7b–d,8–11,15 The bonding parameters of
−
pyramidal and trigonal bipyramidal surroundings, respecti- the CF3SO3 ligand are similar to those found in other com-
vely).43 The basal positions are occupied by the three bpca- plexes and it adopts
a staggered-ethane conformation
nitrogen atoms and a water molecule whereas the apical site is about the S–C bond and the O–S–O angles are greater than the
filled by a sulphonate-oxygen atom from the triflate group. The C–S–O ones. The S(1)–O(3) bond length [1.440(2) Å] is
Cu–N bond distances [1.931(2)–2.002(3) Å] are close to those somewhat longer than those involving the terminally bound
reported for previous structural reports concerning [bis(2-aryl- oxygen atoms [mean value 1.429(2) Å] because of the mono-
carbonyl)amido]copper(II) complexes1,2,7b–d,8–11,15 and the dentate coordination through O(3) to the copper(II) ion.
remaining basal Cu–Ow bond length [1.971(2) Å] is shorter
[Cu(bpca)(Phpr)(H2O)]·3/2H2O (2). The structure of 2 is
than the apical Cu–Otriflate interaction [2.297(2) Å]. The copper(II) made up of discrete neutral [Cu(bpca)(Phpr)(H2O)] units and
ion is shifted by 0.0114(3) Å from the mean basal plane water of crystallization (Fig. 3) which are interlinked by van der
towards the apical site. The reduced bite of the two fused five- Waals forces and hydrogen bonds (see the end of Table 3)
membered chelate rings subtended at the copper(II) ion by the leading to
tridentate bpca ligand accounts for significant departure of (Fig. 4).
a supramolecular three-dimensional network
the values of the angles N(1)–Cu(1)–N(2) [82.32(9)°] and N(2)–
Cu(1)–N(3) [82.20(8)°] from the ideal value of 90°.
Each copper(II) ion in 2 exhibits a somewhat distorted
square pyramidal CuN3O2 chromophore (τ = 0.20) comprising
The two pyridylcarbonyl halves of the bpca ligand form a a tridentate bpca ligand [values of the Cu–N bond lengths in
dihedral angle of 3.38(6)°, a value which is in the range of the range 1.9391(13)–2.012(2) Å], a carboxylate-oxygen atom
those reported for other [bis(2-arylcarbonyl)amido]copper(II) [Cu(1)–O(3) = 1.9365 Å] forming the equatorial plane and a
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Table 4 Selected bond distances (Å) and angles (°) for 3a
Copper(II) environments
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(1)–O(4)
Cu(1)–O(3)
Cu(2)–N(4)
Cu(2)–N(5)
1.9956(19)
1.9163(17)
2.0111(19)
1.9683(14)
2.3277(15)
1.9221(16)
1.9177(16)
1.9846(15)
82.54(8)
Cu(2)–O(6)
Cu(2)–O(1W)
Cu(3)–N(6)
Cu(3)–N(7)
Cu(3)–N(8)
Cu(3)–O(7)
Cu(3)–O(8)
1.9766(14)
2.425(2)
2.0129(17)
1.9293(17)
1.9894(17)
1.9553(14)
2.3201(14)
Cu(2)–O(5)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(3)
N(1)–Cu(1)–O(3)
N(1)–Cu(1)–O(4)
N(2)–Cu(1)–N(3)
N(2)–Cu(1)–O(3)
N(2)–Cu(1)–O(4)
N(3)–Cu(1)–O(3)
N(3)–Cu(1)–O(4)
O(3)–Cu(1)–O(4)
N(4)–Cu(2)–N(5)
N(4)–Cu(2)–O(5)
N(4)–Cu(2)–O(6)
N(4)–Cu(2)–O1W)
N(5)–Cu(2)–O(6)
N,N′-Phenylenebis(oxamate) ligand
C(13)–O(3)
N(5)–Cu(2)–O(5)
N(5)–Cu(2)–O(1W)
O(5)–Cu(2)–O(6)
O(5)–Cu(2)–O(1W)
O(6)–Cu(2)–O(1W)
N(6)–Cu(3)–N(7)
N(6)–Cu(3)–N(8)
N(6)–Cu(3)–O(7)
N(6)–Cu(3)–O(8)
N(7)–Cu(3)–N(8)
N(7)–Cu(3)–O(7)
N(7)–Cu(3)–O(8)
N(8)–Cu(3)–O(7)
N(8)–Cu3)–O(8)
O(7)–Cu(3)–O(8)
165.65(7)
96.35(7)
107.77(6)
91.41(7)
90.07(7)
81.99(8)
163.48(7)
96.16(7)
92.47(6)
82.51(8)
173.86(7)
106.89(6)
98.66(7)
97.46(6)
78.99(x)
162.39(7)
94.19(7)
99.71(7)
82.40(8)
108.52(7)
172.86(7)
99.21(6)
94.21(7)
78.17(5)
82.99(7)
83.76(6)
164.46(7)
100.24(7)
84.34(6)
1.240(2)
C(17)–C(18)
1.382(3)
C(13)–O(5)
C(13)–C(14)
1.266(3)
1.552(3)
C(18)–C(19)
C(19)–C(20)
1.381(3)
1.396(3)
C(14)–O(4)
C(14)–N(4)
1.266(2)
1.293(2)
N(5)–C(20)
C(21)–N(5)
1.397(3)
1.315(2)
N(4)–C(15)
C(15)–C(16)
1.408(3)
1.381(3)
C(21)–O(8)
C(21)–C(22)
1.244(2)
1.556(3)
C(15)–C(20)
C(16)–C(17)
1.417(3)
1.337(2)
C(22)–O(6)
C(22)–O(7)
1.253(2)
1.255(2)
C(13)–O(3)–Cu(1)
C(14)–O(4)–Cu(1)
O(3)–C(13)–O(5)
O(3)–C(13)–C(14)
O(5)–C(13)–C(14)
C(13)–O(5)–Cu(2)
C(13)–C(14)–O(4)
C(13)–C(14)–N(4)
O(4)–C(14)–N(4)
C(14)–N(4)–Cu(2)
C(14)–N(4)–C(15)
C(15)–N(4)–Cu(2)
N(4)–C(15)–C(16)
N(4)–C(15)–C(20)
C(16)–C(15)–C(20)
C(15)–C(16)–C(17)
C(16)–C(17)–C(18)
Hydrogen bondsb,c
D–H⋯A
106.87(13)
116.28(13)
125.98(19)
116.92(18)
117.09(18)
111.39(13)
118.79(17)
111.74(17)
129.45(19)
115.51(14)
129.84(17)
114.64(13)
126.25(18)
113.45(17)
120.27(18)
119.44(19)
120.8(2)
C(17)–C(18)–C(19)
C(18)–C(19)–C(20)
C(19)–C(20)–N(5)
C(19)–C(20)–C(15)
N(5)–C(20)–C(15)
C(20)–N(5)–Cu(2)
C(20)–N(5)–C(21)
C(21)–N(5)–Cu(2)
N(5)–C(21)–O(8)
N(5)–C(21)–C(22)
O(8)–C(21)–C(22)
C(21)–O(8)–Cu(3)
C(21)–C(22)–O(6)
C(21)–C(22)–O(7)
O(6)–C(22)–O(7)
C(22)–O(6)–Cu(2)
C(22)–O(7)–Cu(3)
120.4(2)
119.94(19)
126.96(18)
119.10(19)
113.92(17)
114.99(12)
129.61(17)
115.37(13)
131.20(19)
109.69(17)
119.12(17)
104.19(12)
119.23(18)
117.17(17)
123.60(18)
110.31(13)
116.11(12)
D–H (Å)
0.89(2)
0.91(2)
0.891(10)
0.891(10)
H⋯A (Å)
2.06(4)
2.12(6)
2.071(12)
2.02(2)
D⋯A (Å)
2.885(6)
2.773(6)
2.945(2)
2.867(19)
D–H⋯A (°)
154(7)
128(6)
167(3)
159(3)
O(2W2)–H(222)⋯O(5a3)
O(2W2)–H(221)⋯O(9b3)
O(1W)–H(1W1)⋯O(3a3)
O(1W)–H(2W1)⋯O(2W2)
a Estimated standard deviations in the last significant digits are given in parentheses. b D and A stand for donor and acceptor, respectively.
c Symmetry code: (a3) = −x + 2, −y + 1, −z; (b3) = −x + 2, −y, −z + 1.
water molecule [Cu(1)–O(1W) = 2.365(2) Å] in the apical posi- Cu(1)–N(3) and N(1)–Cu(1)–N(3), respectively]. The rigidity of
tion. In fact, although the copper(II) ion in 2 can be con- the tridentate bpca ligand is at the origin of these deviations.
sidered as basically five-coordinate, the O(4) carboxylate- The copper atom is displaced by 0.0071(3) Å from the mean
oxygen atom is occupying a sixth coordinating position at a basal plane toward O(1W).
distance of 2.852(2) Å. As in 1, some of the angles subtended
No unusual bonds lengths and angles are observed in the
at the ligating atoms are far from the ideal 90 and 180° bpca ligand and the dihedral angle between its two pyridyl-
[81.64(6), 81.63(6) and 163.10(6)° for N(1)–Cu(1)–N(2), N(2)– carbonyl halves is 6.63(8)°. The C(14)C(13)(O3)O(4) set of
5784 | Dalton Trans., 2013, 42, 5778–5795
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Table 5 Selected bond distances (Å) and angles (°) for 4a
Copper(II) environments
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(1)–O(3)
Cu(1)–O(3a4)
1.994(2)
1.9053(19)
1.996(2)
1.9271(16)
2.6692(19)
82.66(8)
164.61(8)
97.06(8)
93.60(7)
82.58(8)
176.44(9)
99.28(8)
97.95(8)
93.05(7)
77.19(7)
Cu(2)–N(6)
Cu(2)–N(7)
Cu(2)–N(8)
Cu(2)–O(7)
1.990(2)
1.9253(18)
2.007(2)
1.9300(16)
2.2386(17)
82.26(8)
160.99(8)
97.07(8)
95.79(7)
82.01(8)
177.46(8)
102.41(7)
98.17(8)
97.96(7)
80.09(6)
Cu(2)–O(8)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(3)
N(1)–Cu(1)–O(3)
N(1)–Cu(1)–O(3a4)
N(2)–Cu(1)–N(3)
N(2)–Cu(1)–O(3)
N(2)–Cu(1)–O(3a4)
N(3)–Cu(1)–O(3)
N(3)–Cu(1)–O(3a4)
O(3)–Cu(1)–O(3a4)
Hydrogen bondsb,c
D–H⋯A
N(5)–H(5)⋯O(9b4)
N(5)–H(5)⋯O(10b4)
N(4)–H(4)⋯O(9b4)
O(1W)–H(11A)⋯O(4c4)
O(2W)–H(12A)⋯O(2d4)
O(2W)–H(12B)⋯O(1)
O(3W)–H(13B)⋯O(6e4)
O(3W)–H(13A)⋯O(4b4)
O(3W)–H(13B)⋯O(7e4)
N(6)–Cu(2)–N(7)
N(6)–Cu(2)–N(8)
N(6)–Cu(2)–O(7)
N(6)–Cu(2)–O(8)
N(7)–Cu(2)–N(8)
N(7)–Cu(2)–O(7)
N(7)–Cu(2)–O(8)
N(8)–Cu(2)–O(7)
N(8)–Cu(2)–O(8)
O(7)–Cu(2)–O(8)
D–H (Å)
0.86
0.86
H⋯A (Å)
2.29
2.26
D⋯A (Å)
3.026(3)
2.877(3)
2.990(3)
2.890(4)
2.858(3)
2.875(3)
3.046(4)
3.045(4)
3.162(3)
D–H⋯A (°)
144.3
128.6
164.6
87(3)
165(3)
141(3)
140(3)
134(2)
143(3)
0.86
2.15
0.856(18)
0.850(18)
0.850(18)
0.819(13)
0.815(13)
0.819(13)
2.80(4)
2.03(2)
2.17(3)
2.376(19)
2.419(18)
2.47(2)
a Estimated standard deviations in the last significant digits are given in parentheses. b D and A stand for donor and acceptor, respectively.
c Symmetry code: (b4) = 1 + x, +y, +z; (c4) = 1 − x, 1 − y, 1 − z; (d4) = 2 − x, 1 − y, 1 − z; (e4) = 1 − x, −y, 2 − z; (e4) = 1 − x, −y, 2 − z;
atoms from the Phpr ligand are planar and the different C–O trinuclear entity acting as a bis-bidentate ligand towards two
values [1.284(2) and 1.220(2) Å for C(13)–O(3) and C(13)–O(4), peripheral [Cu(bpca)]+ fragments. Centrosymmetric bis-trinuc-
respectively] are consistent with its equatorial and pseudo- lear motifs result by hydrogen bonds involving the coordinated
axial coordination through O(3) and O(4) atoms, respectively. A water molecule [O(1W)] and one oxamate-oxygen [O(3a3)], the
supramolecular one-dimensional arrangement of the mono- disordered water molecule O(2W) contributing also to the
nuclear copper(II) units involving the coordinated water mole- stabilization of this supramolecular assembling by additional
cule O(1W), the crystallization water molecule O(2W) and the hydrogen bonds (see Fig. 6 and the end of Table 4).
carboxylate-oxygen O(4) [O(1W)⋯O(2Wb2) = 2.873(2) Å and
The central copper(II) ion [Cu(2)] in 3 is five-coordinate in
O(2W)⋯O(4) = 2.808(2) Å] is observed in the crystal packing of distorted square pyramidal surroundings with τ = 0.02. Two
2 (see Fig. 4a). These chains are interlinked through an deprotonated amidate-nitrogens and two carboxylate-oxygen
additional hydrogen bond between the coordinated water atoms from the opba ligand build the basal plane and a water
molecule [O(1W)] and the bpca carbonyl-oxygen O(1) [O(1W)⋯ molecule [O(1W)] fills the apical position. The average Cu(2)–N
O(1a2) = 2.872(4) Å] affording layered motifs, which are in turn and Cu(2)–O bond lengths in the basal plane [1.919(2) and
connected through another hydrogen bond between the free 1.981(2) Å, respectively] agree with those previously reported
water molecule O(3W) and the carboxylate-oxygen O(3d2) for the [Cu(opba)]2− unit in other structurally characterized tri-
[O(3W)⋯O(3d2) = 2.885(2) Å] to afford a supramolecular three- copper(II) compounds where this entity adopts the bis-chelat-
dimensional structure (see Fig. 4b). Finally, weak π–π type ing coordination mode,44 the shorter value for the copper–
interactions between the phenyl ring of the Phpr ligand and nitrogen interaction being due to the stronger basicity of the
the pyridyl-bpca rings [values of the angle between the normal amidate-nitrogen compared to that of the carboxylate-
to the phenyl-Phpr and centroid pyridyl-bpca rings of 21.82(6) oxygen.45 Cu(2) is shifted by 0.1385(9) Å from the mean basal
and 18.35(6)° and centroid–centroid distances of 3.9401(3) and plane towards O(1W). The geometrical constraints caused by
3.7825(3) Å] contribute to the stabilization of the supramole- the occurrence of the three fused five-membered chelate rings
cular arrangement of 2.
The shorter intermolecular copper–copper separation in 2 severe distortion of the ideal basal square at the copper
is 6.6474(6) Å [Cu(1)⋯Cu(1d2)]. environment: an opening of the less constrained O(5)–Cu(2)–
subtended by the opba ligand at the Cu(2) account for the
{[Cu(bpca)]2[Cu(opba)(H2O)]}·H2O (3). The structure of 3 O(6) angle [107.77(6)°] whereas the bite angles at the 5–5–5
consists of the neutral tricopper(II) unit of formula {[Cu- fused chelate rings are smaller than 90° [82.99(7), 83.76(6) and
(bpca)]2[Cu(opba)(H2O)]} and a crystallization water molecule 84.34(6)° for N(4)–Cu(2)–N(5), N(4)–Cu(2)–O(5) and N(4)–
[O(2W)] (Fig. 5), the inner [Cu(opba)(H2O)]2− unit from each Cu(2)–O(6), respectively].
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Table 6 Selected bond distances (Å) and angles (°) for 5a,b
Copper environment
Cu(1)–N(3)
Cu(1)–N(4)
Cu(1)–N(5)
N(3)–Cu(1)–N(4)
N(3)–Cu(1)–N(5)
N(3)–Cu(1)–O(5)
N(3)–Cu(1)–O(4)
N(3)–Cu(1)–O(6a5)
N(4)–Cu(1)–N(5)
N(4)–Cu(1)–O(5)
N(4)–Cu(1)–O(4)
EtH2opba− ligand
C(23)–C(24)
1.9937(13)
1.9438(13)
1.9987(13)
87.71(5)
162.71(5)
96.82(5)
90.41(5)
86.29(5)
82.61(5)
174.13(5)
98.69(5)
Cu(1)–O(5)
Cu(1)–(O4)
Cu(1)–O(6a5)
N(4)–Cu(1)–O(6a5)
N(5)–Cu(1)–O(5)
N(5)–Cu(1)–O(4)
N(5)–Cu(1)–O(6a5)
O(5)–Cu(1)–O(4)
O(5)–Cu(1)–O(6a5)
O(4)–Cu(1)–O(6a5)
1.9583(11)
2.4649(11)
2.4255(11)
95.28(5)
98.71(5)
100.79
86.02(5)
75.46(4)
90.52(4)
165.13(4)
1.448(3)
C(6)–C(7)
1.384(2)
C(23)–O(2)
C(1)–O(2)
1.470(2)
1.322(2)
C(7)–C(8)
C(8)–C(9)
1.386(2)
1.387(2)
C(1)–O(1)
C(1)–C(2)
C(2)–O(3)
C(2)–N(1)
1.198(2)
1.544(2)
1.215(2)
1.349(2)
C(9)–C(10)
C(10)–N(2)
N(2)–C(4)
C(4)–O(4)
1.388(2)
1.4302(19)
1.3375(19)
1.2351(18)
1.556(2)
C(5)–N(1)
1.418(2)
C(3)–C/4)
C(5)–C(10)
C(5)–C(6)
1.402(2)
1.397(2)
C(3)–O(5)
C(3)–O(6)
1.2720(18)
1.2275(18)
120.38(15)
119.51(16)
120.80(15)
119.64(14)
121.34(14)
125.27(14)
127.18(16)
111.23(14)
121.56(15)
110.00(14)
123.71(15)
126.29(16)
116.01(14)
106.38(15)
C(3)–O(5)–Cu(1)
C(3)–O(6)–Cu(1b5)
O(5)–C(3)–O(6)
O(5)–C(3)–C(4)
O(6)–C(3)–C(4)
C(3)–C(4)–O(4)
C(3)–C(4)–N(2)
O(4)–C(4)–N(2)
C(4)–N(2)–C(10)
N(2)–C(10)–C(5)
N(2)–C(10)–C(9)
C(9)–C(10)–C(5)
C(10)–C(5)–C(6)
C(5)–C(6)–C(7)
Hydrogen bondsc
D–H⋯A
122.52(9)
128.35(10)
127.27(14)
115.19(13)
117.53(13)
120.78(13)
113.68(12)
125.52(14)
126.96(13)
123.78(14)
116.39(13)
119.78(14)
118.97(15)
120.54(15)
C(6)–C(7)–C(8)
C(7)–C(8)–C(9)
C(8)–C(9)–C(10)
C(10)–C(5)–N(1)
C(6)–C(5)–N(1)
C(5)–N(1)–C(2)
N(1)–C(2)–O(3)
N(1)–C(2)–C(1)
O(3)–C(2)–C(1)
C(2)–C(1)–O(2)
C(2)–C(1)–O(1)
O(1)–C(1)–O(2)
C(1)–O(2)–C(23)
O(2)–C(23)–C(24)
D–H (Å)
H⋯A (Å)
2.32(3)
2.014(19)
2.012(17)
D⋯A (Å)
D–H⋯A (°)
107(2)
142(3)
N(1)–H(1)⋯O(1)
N(1)–H(1)⋯O(4)
N(2)–H(2)⋯O(8a5)
0.887(10)
0.887(10)
0.891(10)
2.7114(19)
2.7704(17)
2.8149(17)
149(3)
a Estimated standard deviations in the last significant digits are given in parentheses. b D and A stand for donor and acceptor, respectively.
c Symmetry code: (a5) = x, y + 1, z.
The terminal copper(II) ions [Cu(1) and Cu(3)] are also five-
The central [Cu(2)(opba)]2− moiety is quite flat indicating a
coordinate in distorted square pyramidal surroundings with π-conjugating system extended to the CuN2O2 chromophore.
τ = 0.17 [Cu(1) and Cu(3)]. The basal positions at each peri- Within a trinuclear unit the dihedral angles between the
pheral copper(II) ion are occupied by the three bpca-nitrogen central Cu(2) and the terminal Cu(1) and Cu(3) basal planes
atoms [N(1), N(2) and N(3) at Cu(1) and N(6), N(7) and N(8) at are 83.98(6) and 78.24(5)°, respectively. The values of the intra-
Cu(3)] and one outer carboxylate-oxygen [O(7) at Cu(3)] and an molecular copper–copper separation are 5.3492(4) [Cu(1)-
oxamate-oxygen [O(4) at Cu(1)] from the [Cu(2)(opba)] frag- ⋯Cu(2)] and 5.2507(4) Å [Cu(2)⋯Cu(3)], whereas that of the
ment whereas the apical position is filled by the remaining shortest intermolecular metal–metal distance is 5.3936(5) Å
oxamate- [O(8) at Cu(3)] and carboxylate-oxygen [O(3) at Cu(1)] [Cu(3)⋯Cu(3c3); symmetry code: (c3) = −x + 3, −y, −z + 1].
atoms of such a fragment. The supramolecular bis-trinuclear
{[Cu(bpca)]2(H2opba)}2·6H2O (4). The crystal structure of 4
assembling through the O(1W)⋯O(3a3) and its symmetry- consists of centrosymmetric, neutral {[Cu(bpca)]2(H2opba)}2
related pair (see Fig. 6) is most likely responsible for the axial tetrameric units and crystallization water molecules (Fig. 7).
coordination of O(3) towards Cu(1) versus the equatorial one of Within each tetracopper(II) unit, the dideprotonated H2opba2−
O(7) towards Cu(3). The pattern of the Cu–Nbpca bond lengths entity acts as a bridging ligand adopting simultaneously
[the Cu–Nimido bond being shorter than the two Cu–Npyridyl bidentate [through the oxamate O(7) and O(8) oxygen atoms
ones] is as observed in 1 and 2. Cu(1) and Cu(3) are shifted by towards Cu(2)] and bis-monodentate [through the carboxylate-
0.1419(0) and 0.1068(8) Å respectively, from the mean basal oxamate O(3) towards Cu(1) and Cu(1a4)] coordination modes,
plane towards the apical position.
whereas the bpca exhibits the usual tridentate coordination at
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Fig. 1 ORTEP view of complex 1 with the atom numbering scheme. The
thermal ellipsoids are drawn at the 50% probability level.
Fig. 3 ORTEP view of complex 2 with the atom numbering scheme. The
thermal ellipsoids are drawn at the 50% probability level.
Fig. 2 (a) View of fragments of the supramolecular chain growing in the [101]
direction. (b) View of the supramolecular two-dimensional structure of
extending in the (101) plane. The hydrogen bonds are drawn as dashed lines.
1
Fig. 4 (a) Details of the hydrogen bonding pattern in 2 leading to a supra-
molecular three-dimensional arrangement. (b) A view of the packing in 2 down
the crystallographic b axis. The hydrogen bonds are drawn as dashed lines.
each copper(II) ion. An extensive network of hydrogen bonds
involving all the water molecules and the two N–H amide
groups as donors and the carbonyl-oxygens from the bpca
ligands plus three of the four carboxylate-oxygen atoms from
the two oxamate groups as acceptors lead to a supramolecular
two-dimensional structure (see the end of Table 5 and
Fig. 8). π–π type interactions between the planes defined by N
(6)C(27)C(26)C(25)C(24)C(13) and N(3c3)C(8c3)C(9c3)C-(10c3)C-
(11c3)C(12c3) also occur [symmetry operation: (c3) = 1 + x, +y, +z].
The distance of each aromatic ring centroid is 3.6181(4) Å. The
least-square planes defined by aromatic rings are 6.6(2)° from
each other showing the formation of π⋯π interaction.
Two crystallographically independent copper(II) ions [Cu(1)
and Cu(2)] occur in 4. They are both five-coordinate in dis-
torted square pyramidal CuN3O2 surroundings with values of
the trigonality parameter of 0.20 [Cu(1)] and 0.27 [Cu(2)]. The
bpca-nitrogen atoms [N(1), N(2) and N(3) at Cu(1) and N(6),
N(7) and N(8) at Cu(2)] and the carboxylate(oxamate)-oxygens
from an opba2− ligand [O(3) at Cu(1) and O(7) at Cu(2)] build
the basal plane whereas the apical position is occupied by
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Fig. 5 ORTEP view of complex 3 with the atom numbering scheme. The
thermal ellipsoids are drawn at the 50% probability level.
Fig. 7 (a) ORTEP view of the crystallographically independent unit of 4 with
the atom numbering scheme. The thermal ellipsoids are drawn at the 50%
probability level and the hydrogen atoms are omitted for clarity. (b) Perspective
view of the tetranuclear motif of 4.
Fig. 6 View of the supramolecular bis-trinuclear assembling in 3. The hydrogen
bonds are represented as dashed lines and the hydrogen atoms are omitted for
clarity.
either one carbonyl-oxygen from this bis-oxamate ligand [O(8)
at Cu(2)] or a carboxylate(oxamate)-oxygen atom from a sym-
metry-related opba2− ligand [O(3a4) at Cu(1)]. The Cu–Nbpca
bond lengths vary in the ranges 1.9053(19)–1.9996(2) and
1.9253(18)–2.007(2) Å around Cu(1) and Cu(2) respectively,
values which agree with those observed in 1–3. The values of
the basal copper to carboxylate(oxamate) bond distance in 4
[1.9271(16) and 1.9300(16) Å] are very close to the equatorial
copper to carboxylate(3-phenylpropionate) in 2 [Cu(1)–O(3) =
1.9365(13) Å]. Whereas Cu(1) lies in the basal plane defined by
the N(1)N(2)N(3)O(3) set of atoms, Cu(2) is shifted by 0.1106 Å
from its mean basal plane towards the apical O(8) atom.
The phenyl ring of the H2opba2− ligand and one of its two
oxamate arms [O(3)C(13)O(4)C(14)N(4)O(5)] are quasi-planar
and their mean planes form a dihedral angle of 17.0(1)°.
However, the other oxamate fragment [N(5)C(21)O(8)C(22)O(6)-
O(7)] exhibits a significant twisting, the value of the dihedral
angle between the planes of the carboxylate and amide groups
Fig. 8 View of the assembling of the tetranuclear units of
4 along two
different directions. The hydrogen bonds are drawn as dashed lines and the
being 71.06(8)°. This structural flexibility of the H2opba2− hydrogen atoms are omitted for clarity.
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Fig. 10 View of the packing in 5 showing interchain π–π type interactions.
[C(5d5)C(6d5)C(7d5)C(8d5)C(9d5)C(10d5)] with
a
centroid–
centroid distance of 3.8730 Å [symmetry code: (d5) = 1 − x,
2 − y, 1 − z] (see Fig. 10). An additional π–π stacking interaction
arises from pyridyl rings of pairs of bpca ligand [N(5)C(18)-
C(19)C(20)C(21)C(22)/N(5e5)C(18e5)C(19e5)C(20e5)C(21e5)C(22e5)]
with a centroid–centroid distance of 3.8225 Å [symmetry code:
(e5) = 2 − x, 1 − y, 1 − z].
The crystallographically independent copper(II) ion is six-
coordinate in a somewhat distorted elongated octahedral
CuN3O3 environment. Three equatorial positions at each
copper(II) ion are occupied by the N(3), N(4) and N(5) nitrogen
atoms from the tridentate bpca ligand whereas the remaining
equatorial site and one of the axial positions are filled by the
O(5) carboxylate- and the O(4) carbonyl-oxygen atoms respecti-
vely, from the monodeprotonated oxamate group of the
EtH2opba− monoester derivative. The other axial position is
occupied by the O(6a5) carboxylate-oxygen from a symmetry-
related EtH2opba− ligand. The copper atom is shifted by only
0.0220(6) Å from the mean equatorial plane towards the axial
O(4) atom. The Cu–Nbpca [values in the range [1.9438(13)–
1.9987(13) Å] and Cu–Oeq [Cu(1)–O(5) = 1.9583(11) Å] bond
lengths agree with those reported for the above structures.
The monodeprotonated oxamate group in 5 exhibits a
bidentate/outer monodentate bridging mode, the N(2) amide-
nitrogen being not involved in the coordination given its low
basicity. This non-coordination of the amide nitrogen is also
observed in the two monoprotonated oxamate groups in the
structure of compound 4, the difference being that these act as
bidentate (one of them) and bridging bis-monodentate (the
other one) in 4. The bpca ligand and the bridging monoproto-
nated oxamate group are practically planar [max. deviation
from the mean planes being 0.2963(16) Å at the C(13) atom
and −0.1452(10) Å at the O(5) atom, respectively]. The values of
the dihedral angle between the bridging monoprotonated
oxamate [O(5)O(4)O(6)C(4)C(3)N(2)] and the mean equatorial
planes of two adjacent copper(II) ions [O(5)N(5)N(4)N(3)]
within each chain are 86.28(3) and 89.99(3)°. The intrachain
Fig. 9 (a) ORTEP view of the crystallographically independent unit of 5 with
the atom numbering scheme. The thermal ellipsoids are drawn at the 50%
probability level. (b) View of a fragment of the neutral chain of 5 running paral-
lel to the crystallographic b axis (hydrogen bonds are drawn as dashed lines and
the hydrogen atoms are omitted for clarity).
ligand in 4 compared to the planarity of its fully deprotonated
opba4− form in 3 is due to the different coordination modes
that they exhibit which are related to their different protona-
tion degrees. The low basicity of the amide-nitrogen atoms of
the H2opba2− ligand accounts for the coordination to the
[Cu(bpca)]+ fragments through its carboxylate-oxygen atoms.
The two crystallographically independent bpca ligands are
practically planar [max. deviation from the mean plane being
0.1207(27) Å at the C(32) atom]. The intramolecular copper–
copper distances amount to 3.6220(7) Å [Cu(1)⋯Cu(1a4)] and
10.2014(9) Å [Cu(1)⋯Cu(2)] whereas the shortest intermole-
cular metal–metal separation is 4.8312(7) Å [Cu(2)⋯Cu(2f4);
symmetry code: (f4) = −x − 1, −y, −z + 2].
[Cu(bpca)(EtH2opba)]n (5). The crystal structure of 5 is
made up of neutral zigzag chains of copper(II) ions where the
[Cu(bpca)] units are connected through the EtH2opba− ligand
which adopts a bidentate/outer monodentate bridging mode
(Fig. 9). Intra- and interchain hydrogen bonds involving N–H
and opba/bpca carbonyl-oxygens are observed (see the end of
Table 6 and Fig. 9b). There are two types of π⋯π interactions
that contribute to stabilize the structure of 5 leading to a
supramolecular two-dimensional structure. One of them is
between phenyl rings of EtH2opba [C(5)C(6)C(7)C(8)C(9)C(10)]/
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○
Fig. 11 χMT versus T plot for compound 3: ( ) experimental; (–) best-fit curve
through eqn. (2) (see text).
Scheme 2 Relative orientations of magnetic orbitals for the oxamato bridges.
copper–copper separation is 5.5356(2) Å [Cu(1)–Cu(1b5); sym-
metry code: (b5) = 2 − x, −0.5 + y, 1.5 − z], a value which is
smaller than the shortest interchain metal–metal separation
[7.9459(4) Å for Cu(1)⋯Cu(1c5); symmetry code: (c5) = 2 − x,
1 − y, 1 − z].
with
A ¼ f1 þ exp½ꢀJ=kTꢂ þ 10 exp½J=2kTꢂg
and
B ¼ f1 þ exp½ꢀJ=kTꢂ þ 2 exp½J=2kTꢂg
where g is the average Landé factor for the three copper(II) ions
and it has been assumed that J12 = J23 = J. The quasi negligible
deviation of the Curie law behaviour for a spin doublet in the
very low temperature range, which can be seen in Fig. 11,
accounts for the lack of magnetic coupling between peripheral
copper(II) ions in 3. Excellent agreement between calculated
and experimental magnetic data has been obtained with
the parameters J = −65.8(2) cm−1, g = 2.08(1) cm−1 and R =
2.1 × 10−5 (R is the agreement factor defined as ∑i[(χMT)obs(i)
− (χMT)calcd(i)]2/∑i[(χMT)obs(i)]2).
Two families of oxamato-bridged trinuclear copper(II) com-
plexes have been magneto-structurally characterized: one with
bidentate diamines as capping ligands and the other one with
tridentate triamines as blocking ligands. Both families exhibit
intramolecular antiferromagnetic couplings, but they are
much larger in the former one [−J values in the ranges
330–380 cm−1 (diamines) and 84–196 cm−1 (triamines)].44,46–48
The type of interacting magnetic orbitals [that is the molecular
orbital which describes the unpaired electron on each copper(II)
ion] and their relative orientation account for these two
extreme situations. In the case where a bidentate diamine acts
as the terminal ligand, the peripheral copper(II) ions exhibit a
square pyramidal surrounding. The involved magnetic orbitals
are of the dx2−y2 type and they are localized in the basal plane
(see Scheme 2a). The good σ in-plane overlap between the peri-
pheral magnetic orbitals and the central one through the
OCN and OCO arms of the two oxamato bridges is responsible
for the strong antiferromagnetic coupling observed (−J values
Magnetic properties of 3–5
The magnetic properties of 3 in the form of the χMT versus T
plot [χM is the magnetic susceptibility per three copper(II) ions]
are shown in Fig. 11. At room temperature, χMT is equal to
1.03 cm3 mol−1 K, a value which is smaller than that expected
for three magnetically isolated copper(II) ions (χMT = 1.20 cm3
mol−1 K with gCu = 2.09). Upon cooling, χMT continuously
decreases to reach a plateau in the temperature range 20–6.0 K
with χMT = 0.406 cm3 mol−1 K, a value which is as expected for
a spin doublet state with g = 2.08. Finally, χMT exhibits a very
small decrease in the very low temperature range attaining a
value of 0.395 cm3 mol−1 K at 1.9 K. These features are indica-
tive of a relatively strong intramolecular antiferromagnetic
interaction leading to a low lying spin doublet, the incipient
decrease of χMT at very low temperatures being due to an extre-
mely weak intermolecular magnetic interaction.
The spin Hamiltonian appropriate to describe the magnetic
properties of the tricopper(II) unit of 1 is given by eqn (1)
H ¼ ꢀJ12 SCu ꢁ SCu ꢀ J23 SCu ꢁ SCu
ð1Þ
1
2
2
3
where J12 and J23 denote the exchange coupling parameters
between the central and peripheral copper(II) ions. The
expression for the magnetic susceptibility deduced from this
Hamiltonian is given by eqn (2)
χM ¼ ðNg 2β2=4kTÞ ½A=Bꢂ
ð2Þ
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Scheme 3 Equatorial–axial pathway through the parallel dx2−y2 magnetic
orbitals.
the Curie law for two magnetically non-interacting spin
doublets. N, β, g and k have their usual meaning and J is the
magnetic coupling between the inner copper(II) ions [Cu(1)
and Cu(1a4)]. A common g factor has been assumed for the
two crystallographically independent Cu(1) and Cu(2) centers.
Best-fit parameters are: J = −2.36(2) cm−1, g = 2.08(1) and R =
1.7 × 10−6 (R is the agreement factor defined as ∑i[(χMT)obs(i)
− (χMT)calcd(i)]2/∑i[(χMT)obs(i)]2).
○
Fig. 12 χMT versus T plot for compound 4: ( ) experimental; (–) best-fit curve
through eqn. (3) (see text).
The weak intramolecular antiferromagnetic coupling
between the symmetry-related Cu(1) and Cu(1a4) centers in 4
can be understood by simple orbital symmetry considerations.
The unpaired electron on each copper(II) ion is of the dx2−y2
type with the x and y axes being roughly defined by the short
equatorial bonds [mainly located on the N(1)N(2)N(3)O(3) (at
Cu(1)) and N(1a4)N(2a4)N(3a4)O(3a4) (at Cu(1a4)) basal planes].
These magnetic orbitals are parallel to each other and they are
connected in an equatorial–axial pathway by a double oxo-
carboxylate bridge (see Scheme 3), the poor overlap between
them allows the prediction of a weak antiferromagnetic inter-
action which could be ferromagnetic in the case of accidental
orthogonality. Well known magneto-structural examples of
this out-of-plane exchange pathway have been observed in
other di-μ-chloro,50 di-μ-oximato,51 di-μ-1,1-azido/cyanato52
and di-μ-oxo-carboxylato bridged dicopper(II) units (see
Table 7), the sign and magnitude of the magnetic coupling
depending mainly on the value of the bond angle at the
bridgehead atom (θ) and the basal to apical Cu–X bond length
(Rax). The values of these parameters for 4 [102.81(7)° and
2.6692(19) Å, respectively] are at the origin of the weak antiferro-
of ca. 330–380 cm−1). Subtle structural factors such as the devi-
ation of the coplanarity of the three basal planes or the shift of
the copper(II) ion from the basal plane are at the origin of
small changes of the value of the antiferromagnetic coupling
in this family. Concerning the second family, the magnetic
orbital at each peripheral copper(II) ion can be described by dz2
(Scheme 2b) or dx2−y2 (Scheme 2c) type magnetic orbitals or by
an intermediate situation. In the two cases, the overlap is
reduced (σ pathway through the OCN arm of each oxamato
bridge) and then, the antiferromagnetic coupling is decreased,
the weakening of the magnetic coupling being greater for the
case of Scheme 2c, as discussed in a previous contribu-
tion.46c,49 The situation in 3 corresponds to Scheme 2c and the
value of the observed magnetic coupling (J = −65.8 cm−1
)
is close to the lowest value previously reported for this family
[J = −84 cm−1 for the compound {[Cu(terpy)]2Cu(pba)}(ClO4)2
with terpy = 2,2′:6′,2″-terpyridine and H4pba = N,N′-1,3-propyl-
enebis(oxamic acid)].46c
The magnetic properties of 4 in the form of the χMT versus
T plot [χM is the magnetic susceptibility per four copper(II)
ions] are shown in Fig. 12. At room temperature, χMT is
1.63 cm−1 mol−1 K, a value which is as expected for four mag-
netically isolated spin doublets (χMT = 1.65 cm3 mol−1 K with
gCu = 2.1). Upon cooling, this value remains constant until
magnetic coupling (J = −2.36(2) cm−1
) observed in this
compound.
The magnetic properties of compound 5 in the form of the
χMT versus T plot [χM is the magnetic susceptibility per copper(II)
ion] are shown in Fig. 13. χMT at room temperature is equal
to 0.405 cm3 mol−1 K, a value which is as expected for a
magnetically isolated spin doublet. Upon cooling, this value
remains constant until ca. 40 K and then decreases smoothly
to 0.377 cm3 mol−1 K at 1.9 K. The occurrence of a weak intra-
chain antiferromagnetic interaction accounts for this slight
decrease of the χMT product at low temperature.
ca. 60 K and then, it decreases smoothly to 1.22 cm3 mol−1
K
at 1.9 K. This behaviour agrees with an overall weak antiferro-
magnetic interaction.
Following the tetranuclear structure of 4, its magnetic data
were treated through eqn (3)
χM ¼ ð2Nβ2g 2=kTÞ½3 þ expðꢀJ=kTÞꢂꢀ1 þ Nβ2g 2=2kT
ð3Þ
Bearing in mind that the structure of 5 is made up of a
zigzag chain of copper(II) ions bridged by a monodeprotonated
oxamate group exhibiting the bidentate/outer monodentate
coordination mode, its magnetic data were analyzed through
where the first term is the Bleaney–Bowers expression for a
coupled binuclear copper(II) species and the second term is
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Table 7 Selected magneto-structural data for double μ-oxo carboxylate-bridged copper(II) complexes
Compounda
Rax/Å
θ/°
96.3(5)
96.1(1)
96.9(2)
98.1(3)
98.3(5)
J/cm−1
Ref.
{[CuL1(MeCO2)]2}
2.665(4)
2.577(2)
2.512(5)
2.498(8)
2.495(6)
2.446(2)
2.651(1)
2.37(1)
2.490(1)
2.331(4)
2.443(2)
2.669(2)
−1.84
53
53
54, 55
55
56
{[CuL2(MeCO2)]2}
−1.51
{[CuL3(MeCO2)]2}
−1.33
{[CuL4(MeCO2)]2·2H2O}n
{[CuL5(MeCO2)]2·2MeOH}n
{[CuL6(MeCO2)]2}·H2O·2EtOH
−1.54 (−2.26)b
−1.50 (−7.88)b
+0.63c
95.7(1)
57
102.6(1)
107.0(59
95.34(5)
102.2(2)
97.38(7)
102.81(7)
{[Cu(PhCONHCH2CO2)(H2O)2]2}·2H2O
{[CuL7(MeCO2)]2}
{[Cu(tzq)2(HCO2)]2(μ-HCO2)2}·4H2O
{[Cu(H2O)3][Cu(Phmal)2]}n
−2.15
58, 59
60
61
62
−0.25
−0.52
+1.95d
−2.36(2)
{[Cu(bpca)]2(H2opba)}2·6H2O
This work
a HL1 = N-(5-Bromosalicylidene)-N-methylpropane-1,3-diamine, HL2 = N-methyl-N′-(5-nitrosalicylidene)propane-1,3-diamine, HL3 = N-methyl-N′-
salicylidenepropane-1,3-diamine, HL4 = N-(5-methoxysalicylidene)-N′-methylpropane-1,3-diamine, HL5 = N,N′-[bis(2-o-hydroxybenzylideneamino)-
ethyl]ethane-1,2-diamine, HL6 = N-(2-hydroxy-1,1-dimethylethyl)-salicyleneamine, HL7 = 7-amino-4-methyl-5-azahept-3-en-2-onate and H2Phmal =
phenylmalonic acid. b Magnetic analysis through an alternating chain model. c This is the only compound whose Cu2O2 core is non-
centrosymmetric. d This value is zj and it has derived from a molecular mean field term.
fit parameters through eqn. (4) are: J = −0.17(1) cm−1, g = 2.08
and R = 3.2 × 10−5 (R is the agreement factor defined as
∑i[(χMT)obs(i) − (χMT)calcd(i)]2/∑i[(χMT)obs(i)]2).
The intrachain magnetic coupling in 5 is very weak. This
can be understood having in mind the equatorial–axial
exchange pathway involved through the monodeprotonated
oxamate ligand that adopts the bidentate/outer monodentate
coordination mode. Just focusing on the Cu(1)–O(5)–C(3)–O(6)–
Cu(1a5) skeleton, one can see that the carboxylate bridge exhi-
bits the anti–syn conformation (equatorial–axial), a pathway
which is well known to mediate very weak ferro- or antiferro-
magnetic interactions.64 Anyway, we would like to outline
that to our mind, 5 is the first structurally characterized
example where the monodeprotonated oxamate group acts as
a bridge.
○
Fig. 13 χMT versus T plot for compound 5: ( ) experimental; (–) best-fit curve
Conclusions
through eqn. (4) (see text).
In this work we report on the synthesis and structural charac-
terization of five copper(II) complexes on the basis of rational
design and serendipity: two mononuclear (1 and 2) bpca-based
compounds, a trinuclear (3) containing two building blocks
[Cu(bpca)]+ and [Cu(opba)]2−, a tetranuclear (4) with H2opba2−
bridging [Cu(bpca)]+ units, and an unusual zigzag chain (5).
The magnetic studies of the polynuclear compounds (3–5)
show antiferromagnetic couplings dependent on the opba
bridging mode. For 3, that presents the [Cu(opba)(H2O)]2− unit
the theoretical expression proposed by Hall63a for a uniform
chain of local spins S = 1/2 [eqn. (4)]
χM ¼ ðNβ2g 2=kTÞ½A=Bꢂ
ð4Þ
with
and
A ¼ 0:25 þ 0:14995x þ 0:30094x2
acting as
a bis-bidentate ligand toward two peripheral
[Cu(bpca)]+ fragments, relatively strong intramolecular anti-
ferromagnetic interaction leads to a low lying spin doublet,
although the J value found [J = −65.8(2) cm−1] is an intermedi-
B ¼ 1 þ 1:9862x þ 0:68854x2 þ 6:0626x2
the Hamiltonian being H = −J∑i Si·Si+1 and x = |J|/kT. This ate in relation to the family of compounds with diamines as
expression was derived from the numerical results from terminal ligands (−J values in the ranges 330–380 cm−1). The
Bonner and Fisher63b and it has been widely used for the treat- weak intramolecular antiferromagnetic coupling [J = −2.36(2)
ment of the magnetic data of uniform copper(II) chains. Best- cm−1] in 4 can be understood by simple orbital symmetry
5792 | Dalton Trans., 2013, 42, 5778–5795
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considerations. The magnetic dx2−y2 orbitals on each copper(II)
are parallel and present poor overlap between them due to the
equatorial–axial connection through the double oxo-carb-
oxylate bridge promoted by the H2opba2− ligand. It is worthy
of note that besides this bis-monodentate coordination mode,
H2opba2− acts simultaneously as a bidentate ligand in 4. The
present work has also demonstrated that the opba ligand can
still provide us with more bridging modes in spite of the
numerous compounds described in the literature with these
building blocks and derivatives. In fact, within the 5 zigzag
chain the monodeprotonated EtH2opba− oxamato group acts
as a bidentate/monodentate bridge connecting unconventional
six-coordinate copper(II) of [Cu(bpca)(H2O)]+ units. The mag-
netic properties for 5 reveal an isolated spin doublet behaviour
[the χMT value almost constant at 0.405 cm3 mol−1 K] with
weak intrachain antiferromagnetic interaction [χMT decreases
smoothly below 40 K; J = −0.17(1) cm−1] as a consequence of
the equatorial–axial [anti–syn conformation] exchange pathway
involved through the monodeprotonated oxamate ligand.
Finally, for all the complexes herein described, theoretically a
further application as building blocks is possible since they
present free coordination sites (principally the carbonyl-
oxygens of bpca or opba ligands), even when considering the
inherent difficulty of the solubility decrease with increasing
nuclearity.
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Acknowledgements
The authors thank the Conselho Nacional de Desenvolvimento
Cientifico e Tecnológico (CNPq), the Fundação de Amparo à
Pesquisa do estado da Minas Gerais (FAPEMIG), the Coordena-
ção de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
and the Ministerio Español de Ciencia e Innovación (Projects
CTQ2010-15364, MAT2010-19681 and Consolider-Ingenio
CSD2006-00015) for financial support. One of us,
H. O. Stumpf, acknowledges the University of Valencia for a
Visiting Professorship.
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