N,N′-bis(substituted-phenyl)oxamides and their dinuclear pentacoordinate nickel(II) complexes

Article abstract of DOI:10.1016/j.jorganchem.2008.03.001

The preparation, spectroscopic characterization and magnetic study of N,N′-bis(substituted-phenyl)oxamidate-bridged nickel(II) dinuclear complexes of formula {[Ni(N₃-mc)]₂(μ-CONC₆H₄-X)}(PF₆)₂

Full text of DOI:10.1016/j.jorganchem.2008.03.001

Journal of Organometallic Chemistry 693 (2008) 2009–2016
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
N,N0-bis(substituted-phenyl)oxamides and their dinuclear pentacoordinate
nickel(II) complexes
a
a
b
b
M. Dolores Santana a, , Gabriel García , Consuelo Vicente-Hernández , Luís García , José Pérez ,
*
Teófilo Rojo c, Luís Lezama c
a Departamento de Química Inorgánica, Universidad de Murcia, 30071 Murcia, Spain
b Departamento de Ingeniería Minera, Geológica y Cartográfica, Universidad Politécnica de Cartagena, 30203 Cartagena, Spain
c
´
´
Departamento de Quımica Inorgánica, Facultad de Ciencia y Tecnologıa, Universidad del País Vasco, E-48080 Bilbao, Spain
a r t i c l e i n f o
a b s t r a c t
The preparation, spectroscopic characterization and magnetic study of N,N0-bis(substituted-
phenyl)oxamidate-bridged nickel(II) dinuclear complexes of formula {[Ni(N3-mc)]2(l-CONC6H4-X)}
(PF6)2 (N3-mc = 2,4,4-trimethyl-1,5,9-triazacyclo-dodec-1-ene (Me3-N3-mc) or 2,4,4,9-tetramethyl-
1,5,9-triazacyclododec-1-ene (Me4-N3-mc), X = 2-Cl, 4-Cl, 2-OCH3, 4-OCH3) are reported. These paramag-
netic nickel(II) complexes have been characterized by both one- and two-dimensional (COSY) 1H NMR
techniques. The COSY spectrum of 5 has allowed to achieve the assignment of the phenyl protons of
the N,N0-diphenyloxamidate. The crystal structures of [Ni(Me3-N3-mc)(l-CONC6H4-4-Cl)]2(PF6)2 (6),
[Ni(Me3-N3-mc)(l-CONC6H4-4-OMe)]2(PF6)2 (8) and [Ni(Me4-N3-mc)(l-CONC6H4-2-Cl)]2(PF6)2 (9) have
been determined and their magnetic properties have been studied. The value of magnetic coupling
between the two nickel(II) ions across the oxamidate bridge [J = ꢀ 37.6 (6), ꢀ39.9 (8) and ꢀ39.7 cmꢀ1
(9)] is sensitive to the distortion of the coordination sphere of the metal ions and the topology of the
molecular bridge.
Article history:
Received 16 January 2008
Received in revised form 25 February 2008
Accepted 1 March 2008
Available online 7 March 2008
Keywords:
Nickel
Macrocyclic ligands
N,O ligands
NMR spectroscopy
Magnetic properties
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
cerning these complexes [6] in contrast to the relevant magneto-
chemical role played by the corresponding copper(II) complexes
Symmetrically N,N0-disubstituted oxamidate derivatives have
been thoroughly investigated both in aqueous solution and in
the solid state [1]. The great variety of N,N0-substituents make
them very suitable ligands in the design of homo- and heterome-
tallic species [2] and have played an important role in the devel-
opment of molecular magnetism [3]. One of the most appealing
aspects of this type of ligands is the remarkable efficiency that
they exhibit to mediate strong antiferromagnetic interactions be-
tween paramagnetic centres when acting as bridges [2b,2e,2f,2g].
Moreover, paramagnetic mononuclear copper(II) complexes have
been used as chelating bricks to synthesize polymetallic systems
exhibiting predictable magnetic properties and irregular spin-
state structures [4,5]. In the case of oxamidate-containing mono-
nuclear nickel(II) complexes are obtained square planar diamag-
netic species due to the coordination of strong-field amide N
atoms. This fact explains the scarcity of magnetic studies con-
[1,6,7]. In all reported cases, nickel(II) was in an octahedral geom-
etry [8,9] or in heterodinuclear nickel(II)–copper(II) complexes
[10] containing pentacoordinate nickel(II). In
a recent paper
[11], we reported the structure, spectroscopic and magnetic
behaviour of dinuclear oxamidate-bridged nickel(II) complexes,
in which the two nickel(II) atoms are in a pentacoordinate
environment and we discussed the role of the distortion of the
coordination sphere of the metal ion and the pendant organic
groups on the bridging ligand in the magnetic interaction. In this
paper, we have further explored these factors by studying a
new family of N,N0-disubstituted-oxamidate-bridged nickel(II)
complexes since the prediction of the magnetic behavior for
new dinuclear compounds is not perfect, mainly due to the subtle
interplay between different factors determining the magnetic
properties [12]. In the context mentioned above new N,N0-bis-
(substituted-phenyl)oxamides have been prepared and their
dinuclear nickel(II) complexes {[Ni(N3-mc)]2(l-oxamidate)}(PF6)2
characterized by X-ray crystallography and spectroscopic and
magnetic studies.
* Corresponding author. Tel.: +34 968 367458; fax: +34 968 364148.
E-mail address: dsl@um.es (M.D. Santana).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.03.001

2010
M.D. Santana et al. / Journal of Organometallic Chemistry 693 (2008) 2009–2016
(CONC6H4-4-OMe)2 (4). M.p. = 184–185 °C. ESIMS: m/z = 300
[M]. IR (nujol): mmax = 3286 (NH), 1652, 1534 (CO), 822 (C@C–H)
cmꢀ1 1H NMR (300 MHz, CDCl3, 20 °C): d = 9.236 (s; 2H, NH),
2. Experimental
2.1. General methods
.
7.572 (d, J = 8.7 Hz; 4H, 2,6-H), 6.910 (d, J = 8.7 Hz; 4H, 3,5-H),
3.804 (s; 6H, 4-OCH3) ppm.
The C, H, and N analyses were carried out with a microanalyzer
LECO model CHNS-932. Conductance measurements were per-
formed with a CRISON 525 conductimeter (in acetone solution,
c ꢁ 10ꢀ3 mol Lꢀ1). The UV/Vis spectra (in acetone) were recorded
on a UNICAM 520 spectrophotometer for 300–800 nm range. Infra-
red spectra were recorded on a Perkin-Elmer 16F PC FT-IR spectro-
photometer using Nujol mulls between polyethylene sheets. The
1H NMR spectra of (CD3)2CO solutions were recorded on a Bruker
AV-300 or a Bruker AV-400 spectrometer. Chemical shifts (in
ppm) are reported with respected to the residual solvent signal.
The 1H COSY spectrum were recorded on the Bruker 200 MHz spec-
trometer at 0 °C in (CD3)2CO solutions using 256 individual FID’s
with 4096 scans each and the mixing time was 30 ms. Experimen-
tal parameters were varied to obtain best resolution and the sig-
nal-to-noise. Electrospray ionization mass spectra were measured
with an Agilent VL mass spectrometer. Magnetic susceptibilities
of powdered samples were measured between 5 and 300 K with
a Quantum Design MPMS-7 SQUID magnetometer in an external
field of 0.1 T. The experimental susceptibilities were corrected for
the diamagnetism of the sample-holders and the constituent
atoms (Pascal tables) and for the temperature-independent para-
2.2.2. Synthesis of the complexes [Ni(N3-mc)(l-CONC6H4-X)]2(PF6)2
(X = 2-Cl, 4-Cl, 2-OCH3, 4-OCH3)
To a suspension of [Ni(N3-mc)(l-OH)]2(PF6)2 (0.116 mmol) in
acetone (25 mL) X-C6H4HNCOCONHC6H4-X (0.116 mmol) was
added. The mixture was stirred at room temperature for 24 h. Ace-
tone was evaporated under reduced pressure until ca. 5 mL, and
the addition of diethyl ether (15 mL) resulted in the formation of
a light blue-violet solid which was filtered off, washed with diethyl
ether and air-dried.
2.2.2.1. [Ni(Me3-N3-mc)(l-CONC6H4-2-Cl)]2(PF6)2 (5). Yield: 0.124 g
(94%). Anal. Calc. for C38H58Cl2F12N8Ni2O2P2: C, 40.1; H, 5.1; N,
9.9. Found: C, 40.1; H, 5.2; N, 9.7%. ES-MS: m/z (%) = 991 (100)
[M]+, 845 (45) [M]2+. KM: 257 S cm2molꢀ1. UV/Vis (acetone) kmax
(e): 594 nm (130 Mꢀ1 cmꢀ1), 366 (491). IR (nujol): mmax = 3278,
3255 (N–Hmc), 1656 (C@Nmc), 1602 (C–Ooxamidate), 1578 (C–Coxamidate
)
cmꢀ1. 1H NMR (300 MHz, (CD3)2CO, 20 °C): d = 268.2 (Ha), 178.5 (d,
Ha), 140.2 (d, Ha), 118.0 (d, Ha), 83.8 (Ha), 50.7 (Ha), 40.5 (4-Me,
3H), 26.5 (d, Ha), 18.7 (Ha),15.8 (m, 4-Me, 3H),15.4 (3-H),14.7 (5-
H), ꢀ3.5 (6-H), ꢀ4.4 (m, 4-H) ꢀ9.6 (Hb), ꢀ10.4 (d, Hb), ꢀ12.6 (d,
2-Me, 3H), ꢀ18.4 (Hb), ꢀ20.7 (Hb), ꢀ24.6 (m, Hb), ꢀ26.7 (d, Hb)
ppm.
magnetism estimated to be 100 ꢂ 10ꢀ6 cm3 molꢀ1
.
2.2. Syntheses
All chemicals were of reagent grade and were used without fur-
ther purification. Solvents were dried and distilled by general
methods before use. The complexes [Ni(N3-mc)(l-OH)]2(PF6)2
(N3-mc = Me3-N3-mc or Me4-N3-mc) were prepared by the previ-
ously described procedures [13,14].
2.2.2.2. [Ni(Me3-N3-mc)(l-CONC6H4-4-Cl)]2(PF6)2 (6). Yield: 0.120 g
(89%). Anal. Calc. for C38H58Cl2F12N8Ni2O2P2: C, 40.1; H, 5.1; N, 9.9.
Found: C, 39.9; H, 5.2; N, 9.8%. ES-MS: m/z (%) = 991 (100) [M]+.
KM: 220 S cm2 molꢀ1
.
UV/Vis (acetone) kmax (e): 591 nm
(130 Mꢀ1 cmꢀ1), 369 (681). IR (nujol): mmax = 3292, 3256 (N–Hmc),
1656 (C@Nmc), 1598 (C–Ooxamidate), 1578 (C–Coxamidate) cmꢀ1 1H
.
NMR (300 MHz, (CD3)2CO, 20 °C): d = 261.7 (Ha), 168.3 (Ha),
137.1 (d, Ha), 115.4 (m, Ha), 78.9 (Ha), 48.8 (d, Ha), 39.0 (d, 4-Me,
3H), 25.9 (Ha), 17.9 (Ha), 15.5 (m, 4-Me, 3H), 15.3 (3,5-H, 2H),
ꢀ3.6 (2,6-H, 2H), ꢀ9.4 (m, 2Hb), ꢀ12.8 (d, 2-Me, 3H), ꢀ18.5 (Hb),
ꢀ20.9 (Hb), ꢀ24.6 (Hb), ꢀ27.9 (d, Hb) ppm.
2.2.1. Ligands preparations
The ligands N,N0-bis(substituted-phenyl)oxamides were
synthesized by the following experimental procedure [15]: oxa-
lyldichloride (10 mmol) in anhydrous tetrahydrofuran (25 mL)
was added dropwise to an anhydrous tetrahydrofuran solution
(50 mL) of the appropriate aniline X-C6H4-NH2 (X = 2-Cl, 4-Cl,
2-OCH3, 4-OCH3) (20 mmol) and triethylamine (2 mmol) cooled
in an ice bath. The resulting suspension was stirred at room tem-
perature for 24 h. The white precipitate was filtered and the tetra-
hydrofuran solution was partially evaporated under reduced
pressure and a white precipitate was obtained. It was filtered off,
washed with diethylether and dried in vacuo.
2.2.2.3. [Ni(Me3-N3-mc)(l-CONC6H4-2-OMe)]2(PF6)2
(7). Yield:
0.123 g (94%). Anal. Calc. for C40H64F12N8Ni2O4P2: C, 42.6; H, 5.7;
N, 9.9. Found: C, 42.4; H, 5.6; N, 9.8%. ES-MS: m/z (%) = 981 (100)
[M]+, 835 (11) [M]2+. KM: 272 S cm2 molꢀ1. UV/Vis (acetone) kmax
(e): 590 nm (100 Mꢀ1 cmꢀ1), 367 (480). IR (nujol): mmax = 3290,
3260 (N–Hmc), 1660 (C@Nmc), 1608 (C–Ooxamidate), 1584 (C–Coxamidate
)
cmꢀ1 1H NMR (400 MHz, (CD3)2CO, 25 °C): d = 240.0 (Ha), 172.2
.
(CONC6H4-2-Cl)2 (1). M.p. = 203–204 °C. ESIMS: m/z = 308
[M], 273 [MꢀCl]. IR (nujol): mmax = 3312 (NH), 1676, 1520 (CO),
(Ha), 89.5 (Ha), 83.7 (Ha), 77.6 (Ha), 47.3 (4-Me, 3H), 33.6 (Ha),
25.0 (Ha), 21.3 (Ha), 19.1 (m, 4-Me, 3H), 15.4 (m, 3,5-H), 4.8 (2-
OMe, 3H), ꢀ4.8 (m, 4-H), ꢀ5.3 (6-H), ꢀ7.2 (Hb), ꢀ10.9 (Hb),
ꢀ11.5 (d, 2-Me, 3H), ꢀ12.6 (Hb), ꢀ19.5 (Hb), ꢀ24.5 (Hb), ꢀ25.6 (Hb).
1048 (Ph–Cl), 754 (C@C–H) cmꢀ1 1H NMR (300 MHz, CDCl3,
.
20 °C): d = 9.900 (s; 2H, NH), 8.437 (dd; J = 7.9 Hz, J = 1.5 Hz;
2H, 6-H), 7.326 (td; J = 7.9 Hz, J = 1.5 Hz; 2H, 5-H), 7.423 (dd;
J = 7.8 Hz, J = 1.5 Hz; 2H, 3-H), 7.127 (td; J = 7.8 Hz, J = 1.5 Hz;
2H, 4-H) ppm.
2.2.2.4. [Ni(Me3-N3-mc)(l-CONC6H4-4-OMe)]2(PF6)2
(8). Yield:
0.118 g (90%). Anal. Calc. for C40H64F12N8Ni2O4P2: C, 42.6; H, 5.7;
N, 9.9. Found: C, 42.4; H, 5.6; N, 9.8%. ES-MS: m/z (%) = 983 (100)
[M]+, 836 (10) [M]2+. KM: 276 S cm2molꢀ1. UV/Vis (acetone) kmax
(e): 588 nm (130 Mꢀ1 cmꢀ1). IR(nujol): mmax = 3288, 3250 (N–
(CONC6H4-4-Cl)2 (2). M.p. = 279–280 °C. ESIMS: m/z = 308 [M].
IR (nujol): mmax = 3296 (NH), 1660, 1514 (CO), 1092 (Ph–Cl), 830
(C@C–H) cmꢀ1 1H NMR (300 MHz, CDCl3, 20 °C): d = 9.286 (s;
.
2H, NH), 7.608 (AB, J = 8.85 Hz; 4H, 2,6-H), 7.354 (AB, J = 8.85 Hz;
H
mc), 1658 (C@Nmc), 1608 (C–Ooxamidate), 1584 (C–Coxamidate
)
4H, 3,5-H) ppm.
cmꢀ1 1H NMR (400 MHz, (CD3)2CO, 25 °C): d = 248.3 (Ha), 160.3
.
(CONC6H4-2-OMe)2 (3). M.p. = 220–221 °C. ESIMS: m/z = 300
[M]. IR (nujol): mmax = 3354 (NH), 1682, 1526 (CO), 756 (C@C–H)
(Ha), 132.7 (d, Ha), 108.3 (d, Ha), 76.7 (Ha), 49.6 (d, Ha), 40.3 (4-
Me, 3H), 25.5 (Ha), 18.0 (Ha), 14.8 (4-Me, 3H), 14.1 (3,5-H, 2H),
5.9 (4-OMe, 3H), ꢀ3.3 (2,6-H, 2H), ꢀ9.2 (d, Hb), ꢀ10.1 (d, Hb),
ꢀ11.7 (m, 2-Me, 3H), ꢀ17.7 (Hb), ꢀ20.3 (Hb), ꢀ23.9 (Hb), ꢀ25.9
(Hb) ppm.
cmꢀ1 1H NMR (300 MHz, CDCl3, 20 °C): d = 9.950 (s; 2H, NH),
.
8.375 (d, J = 7.5 Hz; 2H, 6-H), 6.998 (t, J = 7.5 Hz; 2H, 5-H), 6.925
(d, J = 7.5 Hz; 2H, 3-H), 7.131 (t, J = 7.5 Hz; 2H, 4-H), 3.920 (s; 6H,
2-OCH3) ppm.

M.D. Santana et al. / Journal of Organometallic Chemistry 693 (2008) 2009–2016
2011
Table 1
2.2.2.5. [Ni(Me4-N3-mc)(l-CONC6H4-2-Cl)]2(PF6)2 (9). Yield: 0.119 g
Crystallographic data for complexes 6, 8 and 9
(91%). Anal. Calc. for C40H62Cl2F12N8Ni2O2P2: C, 41.2; H, 5.4; N,
9.6. Found: C, 41.0; H, 5.4; N, 9.5%. ES-MS: m/z (%) = 1019 (69)
[M]+, 875 (54) [M]2+. KM: 269 S cm2molꢀ1. UV/Vis (acetone) kmax
(e): 613 nm (140 Mꢀ1 cmꢀ1), 377 (501). IR (nujol): mmax = 3262
Complex
6
8
9
Formula
M
T (K)
C
38H58Cl2F12N8Ni2O2P2 C40H64F12N8Ni2O4P2 C40H62Cl2F12N8Ni2O2P2
1137.18
100(2)
1128.35
100(2)
1165.24
100(2)
0.71073
(N–Hmc), 1650 (C@Nmc), 1600 (C–Ooxamidate), 1578 (C–Coxamidate
)
cmꢀ1 1H NMR (300 MHz, (CD3)2CO, 20 °C): d = 251.5 (Ha), 165.1
.
Wavelength 0.71073
(Å)
0.71073
(m, Ha), 120.0 (Ha), 112.6 (Ha), 103.7 (d, Ha), 99.1 (d, 9-Me, 3H),
75.3 (m, Ha), 40.5 (4-Me, 3H), 36.8 (m, Ha), 25.8 (Ha), 18.0 (m, 4-
Me, 3H), 14.9 (m, 3,5-H, 2H), ꢀ2.1 (d, 6-H), ꢀ2.6 (m, 4-H), ꢀ10.2
(Hb), ꢀ10.9 (Hb), ꢀ12.9 (2-Me, 3H), ꢀ14.8 (Hb), ꢀ16.0 (Hb), ꢀ24.1
(Hb), ꢀ25.5 (Hb) ppm.
Crystal
system
Space group Pcab
Orthorhombic
Orthorhombic
Monoclinic
Pbca
P21/c
a (Å)
b (Å)
c (Å)
a (°)
b (°)
c (°)
V (Å3)
Z
12.7060(8)
13.3751(8)
27.5048(16)
90
90
90
4674.3(5)
4
13.3116(10)
13.7772(11)
26.045(2)
90
90
90
10.1932(7)
18.8848(14)
13.6223(10)
90
108.490 (1)
90
2486.9(3)
2
1.556
2.2.2.6. [Ni(Me4-N3-mc)(l-CONC6H4-4-Cl)]2(PF6)2
(10). Yield:
0.118 g (90%). Anal. Calc. for C40H62Cl2F12N8Ni2O2P2: C, 41.2; H,
5.4; N, 9.6. Found: C, 41.0; H, 5.4; N, 9.5%. ES-MS: m/z (%) = 1019
(100) [M]+, 873 (32) [M]2+. KM: 275 S cm2molꢀ1. UV/Vis (acetone)
kmax (e): 618 nm (140 Mꢀ1 cmꢀ1), 375 (541). IR (nujol): mmax = 3266
4776.5(6)
4
Dcalc
1.616
1.569
(Mg/m3)
l (mmꢀ1
)
1.081
0.952
1.018
28495
(N–Hmc), 1660 (C@Nmc), 1634 (C–Ooxamidate), 1598 (C–Coxamidate
)
Reflections
collected
51410
52814
cmꢀ1 1H NMR (300 MHz, (CD3)2CO, 20 °C): d = 258.0 (Ha), 165.1
.
(d, Ha), 146.3 (Ha), 127.6 (Ha), 107.8 (d, Ha), 100.0 (d, Ha), 88.0
(9-Me, 3H), 73.5 (d, Ha), 66.2 (Ha), 34.6 (4-Me, 3H), 15.4 (d, 4-
Me, 3H), 14.4 (3,5-H, 2H), ꢀ4.6 (2,6-H, 2H), ꢀ8.0 (Hb), ꢀ9.8 (2-
Me, 3H), ꢀ13.6 (2Hb), ꢀ14.8 (Hb), ꢀ16.1 (Hb), ꢀ20.6 (2Hb) ppm.
Independent 5554 [0.1416]
reflections
5664 [0.0556]
5754 [0.0457]
[Rint
]
Goodness-of- 1.247
1.080
1.047
fit on F2
Final R
R1 = 0.0951
R1 = 0.0758
R1 = 0.0951
indices
2.2.2.7. [Ni(Me4-N3-mc)(l-CONC6H4-2-OMe)]2(PF6)2 (11). Yield:
0.117 g (90%). Anal. Calc. for C42H68F12N8Ni2O4P2: C, 43.6; H, 5.9;
N, 9.7. Found: C, 43.4; H, 5.9; N, 9.6%. ES-MS: m/z (%) = 1011
(100) [M]+, 863 (51) [M]2+. KM: 287 S cm2molꢀ1. UV/Vis (acetone)
kmax (e): 621 nm (120 Mꢀ1 cmꢀ1), 374(440). IR (nujol): mmax = 3264
[I > 2r(I)]a,b
R indices
wR2 = 0.1970
R1 = 0.1166
wR2 = 0.1870
R1 = 0.0964
wR2 = 0.2036
2.722 and ꢀ0.448
wR2 = 0.2429
R1 = 0.1104
wR2 = 0.2546
2.052 and ꢀ1.535
(all data) wR2 = 0.2108
Maximum/
1.035 and ꢀ0.964
minimum
Dq (e Åꢀ3
)
(N–Hmc), 1656 (C@Nmc), 1606 (C–Ooxamidate), 1582 (C–Coxamidate
)
cmꢀ1 1H NMR (300 MHz, (CD3)2CO, 20 °C): d = 309.5 (Ha), 278.5
.
P
P
a
R1
=
kFoj ꢀ jFck/ jFoj for reflections with I > 2rI.
P
P
2
2
1=2
wR2 ¼ f ½wðF2o ꢀ Fc2Þ ꢃ= ½wðF2oÞ ꢃg
for all reflections; wꢀ1 = r2(F2) + (aP)2
+
b
(Ha), 247.9 (Ha), 157.6 (Ha), 105.0 (Ha), 94.1 (9-Me, 3H), 55.9
(Ha), 45.4 (Ha), 36.6 (4-Me, 3H), 24.9 (Ha), 19.0 (m, 4-Me, 3H),
14.5 (m, 3,5-H, 2H), 5.5 (2-OMe, 3H), ꢀ2.9 (4-H), ꢀ4.4 (6-H),
ꢀ8.8 (Hb), ꢀ11.4 (Hb), ꢀ11.7 (Hb), ꢀ13.2 (2-Me, 3H), ꢀ14.4 (Hb),
ꢀ20.0 (Hb), ꢀ23.2 (Hb) ppm.
bP, in which P ¼ ð2F2c þ Fo2Þ=3 and a and b are constants set by the program.
3. Results and discussion
3.1. Synthesis and spectroscopic characterization
2.2.2.8. [Ni(Me4-N3-mc)(l-CONC6H4-4-OMe)]2(PF6)2 (12). Yield:
0.120 g (92%). Anal. Calc. for C42H68F12N8Ni2O4P2: C, 43.6; H, 5.9;
N, 9.7. Found: C, 43.4; H, 5.8; N, 9.5%. ES-MS: m/z (%) = 1011 (97)
[M]+. KM: 257 S cm2 molꢀ1. UV/Vis (acetone) kmax (e): 602 nm
(170 Mꢀ1 cmꢀ1). IR (nujol): mmax = 3262 (N–Hmc), 1654 (C@Nmc),
The N,N0-bis(substituted-phenyl)oxamides were synthesized by
treating oxalyldichloride with the corresponding aniline(X-C6H4-
NH2) in THF and Et3N at 0 °C for 24 h (Scheme 1). These oxamides
behave as weak acids towards the dinuclear hydroxo-complexes
[Ni(N3-mc)(l-OH)]2(PF6)2 (N3-mc = 2,4,4-trimethyl-1,5,9-triazacy-
clo-dodec-1-ene (Me3-N3-mc) or 2,4,4,9-tetramethyl-1,5,9-triaza-
cyclododec-1-ene (Me4-N3-mc)), these hydroxo complexes have
been used as precursors in the synthesis of mono- [19] and
dinuclear [20] pentacoordinate nickel(II) complexes in different
coordination environments. The oxamidate complexes of pentaco-
ordinate nickel(II) were obtained from reaction mixtures of [Ni(N3-
mc)(l-OH)]2(PF6)2 and N,N0-bis(substituted-phenyl)oxamides (1:1
molar ratio) in acetone. The isolated complexes are sketched in
Scheme 2.
1606 (C–Ooxamidate), 1582 (C–Coxamidate) cmꢀ1 1H NMR (300 MHz,
.
(CD3)2CO, 20 °C): d = 244.8 (Ha), 155.9 (Ha), 127.9 (Ha), 120.5
(Ha), 103.1 (d, Ha), 95.5 (9-Me, 3H), 74.5 (d, Ha), 59.2 (Ha), 38.0
(4-Me, 3H), 26.2 (Ha), 14.6 (m, 4-Me, 3H), 14.2 (m, 3,5-H, 2H),
6.2 (4-OMe, 3H), ꢀ4.2 (2,6-H, 2H), ꢀ8.9 (Hb), ꢀ10.2 (2Hb), ꢀ12.9
(2-Me, 3H), ꢀ17.6 (Hb), ꢀ20.6 (Hb), ꢀ23.4 (Hb) ppm.
2.3. Crystallographic data collection and structure determination
Crystals of 6, 8 and 9 suitable for a diffraction study were pre-
pared by slow diffusion of diethyl ether into their acetonitrile solu-
tion. Diffraction data were measured on a Bruker SMART APEX
using Mo Ka radiation (k = 0.71073 Å). Crystallographic data are
summarised in Table 1. The diffraction frames were integrated
using the SAINT package [16] and corrected for absorption with SAD-
ABS [17]. The raw intensity data were converted (including correc-
tions for Lorentz and polarization effects) to structure amplitudes
and their esd using the SAINT program. The structures were solved
by direct methods [18] and refined [18] by full-matrix least-
squares techniques using anisotropic thermal parameters for
non-hydrogen atoms. Hydrogen atoms were set at calculated
positions.
X
X
NH
O
Cl
O
O
NEt3
THF
+ 2
NH2
C
C
C
C
Cl
O
HN
X = 2-Cl (1), 4-Cl (2), 2-OCH3 (3), 4-OCH3 (4)
X
Scheme 1.

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M.D. Santana et al. / Journal of Organometallic Chemistry 693 (2008) 2009–2016
When the oxamides are deprotonated both oxygen and nitrogen
H
O
R
N
2+
Me
Me
are coordinated to nickel ions with an effective p-delocalization in
the NCO fragments. The anion oxamidate acts as a nickel–nickel
bound ligand. The IR spectra of all the dinuclear complexes are
similar: the signals attributable to N3-mc ligands and two strong
characteristic bands due to the PFꢀ6 anion appear at normal fre-
quencies [19]. The m(C–O) stretching frequencies of the oxamidate
groups at ꢄ1600 cmꢀ1 are consistent with the presence of a bridg-
ing oxamidate ligand in 5–12 [11].
Me
Ni
Ni
N
N
O
H
N
H
N
H
Me
Me
N
Me
R
X
+
The 1H NMR spectra for complexes 5–12 show the resonance
line pattern observed for the N3-macrocycle ligands that has been
assigned on the basis of previous studies of nickel macrocyclic
complexes [20]. The spectra of derivatives 5–12 are similar to that
of the previously reported oxamidate complexes [11] in both sig-
nals and magnitudes of contact shifts, but some striking differences
are evident upon their inspection (see Fig. 1); thus some signals re-
lated to a given proton occur as doubled signal. The magnitude of
contact shift differences for some a-CH protons and for 4-Me and
2-Me groups implies that these differences arise from distinct con-
figurations. The intrinsically dissimilar forms are possibly further
differentiated by a lack of free rotation of the phenyl groups about
the C–N bond [21]; even so the presence of conformers in solution
has been observed also by Curtis et al. [13] and Dei et al. [22] in
other complexes containing this Ni(II) [12]aneN3-macrocycle
moiety and has been attributed to the two possible reciprocal
chiralities of nitrogen atoms. The isotropically shifted 1H NMR sig-
nals observed for the phenyl group of N,N0-bis(substituted-
phenyl)oxamidates can be initially assigned by inspection of their
peak areas. Definitive assignment of these signals comes from two-
dimensional NMR techniques. A magnitude COSY spectrum of 5
was recorded at 0 °C and shows cross-signals between resonances
at 15.8, 15.2, ꢀ3.8 and ꢀ4.9 ppm (Fig. 2). These signals can be as-
signed to the phenyl 3-H, 5-H, 6-H and 4-H protons, respectively.
The shift direction alternation of the N-phenyl protons is character-
istic when the p-contact shift is dominant, therefore the unpaired
electrons could polarize the net spin density in the dp orbitals
[23].
NH
O
- 2 H2O
C
C
O
HN
X
X
2+
N
O
R
N
Me
Me
C
C
Me
Ni
Ni
N
N
N
N
H
H
Me
Me
O
N
N
Me
R
X
R
X
Complex
H
2-Cl
4-Cl
(5)
(6)
2-OCH3 (7)
4-OCH3 (8)
CH3 2-Cl
4-Cl
(9)
(10)
2-OCH3 (11)
4-OCH3 (12)
Scheme 2.
Fig. 1. 1H NMR spectra of 8 in (CD3)2CO solution at room temperature.

M.D. Santana et al. / Journal of Organometallic Chemistry 693 (2008) 2009–2016
2013
Fig. 4. ORTEP plot of the cation of [Ni(Me3-N3-mc)(l-CONC6H4-4-OMe)]2(PF6)2 (8).
Fig. 2. 1H COSY spectrum of 5 obtained at 200 MHz at 0 °C in (CD3)2CO solution.
This map was collected with a 30 ms mixing time, 256 t1 values (4096 scans each)
using 1 K data points in F2 dimension, only the region relevant to assign resonances
is shown in the top trace.
3.2. Structural investigations
The complexes 6 and 8 crystallize in an orthorhombic space
group, Pcab and Pbca, respectively, and the compound 9 crystallizes
in the monoclinic space group P21/c. The structure of the three
compounds consist of non-coordinated PFꢀ6 ions and a {[Ni(N3-
mc)]2(l-oxamidate)}2+ dinuclear cations, Figs. 3–5. The oxamidate
ions join two adjacent coordination polyhedra with its nitrogen
and oxygen atoms occupying in both polyhedra two cis positions
and the N3-mc ligands act as a facially coordinated tridentate li-
gand. The complexes lie on a crystallographic inversion center.
The coordination geometry around each nickel ion can be regarded
as a distorted square pyramid; the equatorial plane is built by the
O1 and N4 atoms from the oxamidate group and N1 and N2 nitro-
gen atoms from the N3-macrocycle, whereas the apical position is
Fig. 5. ORTEP plot of the cation of [Ni(Me4-N3-mc)(l-CONC6H4-2-Cl)]2(PF6)2 (9).
occupied by a N3 atom from N3-mc. The values of the Ni–N bond
lengths are in the range 2.034–2.089 Å and are comparable with
those reported for complexes of pentacoordinate nickel(II) contain-
ing N3-macrocycle [19]. The Ni–Ooxamidate and Ni–Noxamidate bond
distances are a little longer than those observed in dinuclear Ni(II)
complexes containing oxamides with square pyramidal environ-
ment for Ni(II) [11]. The Ni atom is 0.291(2) (6), 0.267(2) (8) and
0.348(3) (9) Å out of the basal plane defined by N1, N2, N4 and
O1 toward the axial nitrogen, respectively. The dihedral angles be-
tween the basal and the bridging ligand mean planes are
13.83(15)° (6), 12.39(16)° (8) and 16.04(29)° (9), respectively.
The nickel–nickel separations through the oxamidate bridges are
5.474(1), 5.463(1) and 5.467(1) Å for complexes 6, 8 and 9, respec-
tively, these distances are longer than the reported for dinuclear
Ni–Ni complexes with the bridging-oxamidate ligands [1,6,8,9];
whereas the shortest intermolecular Niꢅ ꢅ ꢅNi separations are
9.056(1) (6), 9.452(1) (8) and 9.432(2) (9) Å, respectively. The
geometry of pentacoordinate complexes can be described by a
structural index parameter s [24] such that s = (b ꢀ a)/60°, where
b and a are the two largest angles (b > a). Thus, the geometric
parameter s is applicable to pentacoordinate structures as an index
of the degree of trigonality, between s = 1 for trigonal bipyramid
(TBP) (b ꢀ a = 60 °) and s = 0 for square pyramid (SP) (b ꢀ a = 0 °).
Complexes 8 and 9 have s values of 0.37 and 0.38, respectively
Fig. 3. ORTEP plot of the cation of [Ni(Me3-N3-mc)(l-CONC6H4-4-Cl)]2(PF6)2 (6).

2014
M.D. Santana et al. / Journal of Organometallic Chemistry 693 (2008) 2009–2016
indicating a moderated distortion from perfect SP. However, com-
plex 6 has a s value of 0.52 and the environment around nickel
atom is intermediate between square pyramidal and trigonal bipy-
ramidal. Moreover, the angles between the plane of the substituent
at the bridging nitrogen atom and the plane of the bridging ligand
are 57.47(18)° for 6, 67.51(14)° for 8 and 68.72(23)° for 9, respec-
tively. All of these structural factors influence the magnitude of the
exchange coupling constant, these facts are studied in the next
section.
3.3. Magnetic properties
The thermal evolution of the magnetic molar susceptibility (vm)
and the vmT product for compounds 6, 8 and 9 are shown in Fig. 6.
For the three compounds, the susceptibility values increase with
decreasing temperature until a broad maximum about 50 K. The
curves drop to relative minima at 12 K (6), 9.5 K (8) and 6.5 K
(9), at which vm values exponentially increases upon further cool-
ing. At room temperature vmT is about 2.1 cm3 K molꢀ1 for 6, 8 and
9, which agrees well with the value expected for two uncoupled
S = 1 ions with g values slightly greater than 2. Upon cooling, the
vmT magnitude continuously decreases and it tends to zero at very
low temperatures indicating the occurrence of one S = 0 ground
state. On the other hand, Curie–Weiss behaviour is not well de-
fined even at room temperature. Both the continuous decrease in
the magnetic effective moment and the maximum observed in
the thermal variation of the molar susceptibility clearly indicate
the existence of relatively strong antiferromagnetic interactions
between two Ni(II) ions. The low temperature increase of vm can
be explained by considering the presence of a small amount of
monomeric Ni(II) ions in the polycrystalline powder sample. From
these considerations the experimental susceptibility data can be
0.02
2
0.01
1
a
0
0.01
0
0
2
χ
m
T/cm
-1
mol
3
3
Koml
1
/cm
m
χ
-1
b
0
2
0.01
1
0
c
0
0
50
100
150
200
250
300
T / K
Fig. 6. Thermal variation of vm and vmT for compounds 6 (a), 8 (b) and 9 (c). The
solid lines correspond to the best fits obtained with Eq. (1).

M.D. Santana et al. / Journal of Organometallic Chemistry 693 (2008) 2009–2016
2015
fitted by using the expression for a dinuclear S = 1 unit (H = ꢀ JS1S2)
modified to take into account the contribution of isolated Ni(II)
ions:
substitution in the bridging ligand. The first conclusion that can be
derived from Table 2 is that the replacement of the oxamidate
hydrogen by a bulkier group causes a decrease in the antiferromag-
netic interactions. It is probably due to the important increase of
the distortion of the coordination sphere of the metal ion (s is only
0.12 for the unsusbtituted compound). This result agrees well with
a DFT study previously reported showing that stronger antiferro-
magnetic interactions must be expected for nickel(II) ions in
square pyramidal than in trigonal bipyramidal environments
[11]. However, it appears that this is not the only factor with influ-
ence on the exchange parameter. In this way, the calculated J value
is slightly larger for compound 6 than for the phenyl derivative de-
spite its greater s distortion factor. Considering the structural data
recorded in Table 2 this anomalous behaviour can be ascribed to
the topology of the bridging ligand. Thus the phenyl compound
has the larger asymmetry between the N–C and C–O distances in
the oxamidate bridge indicating a poor p-delocalization and there-
fore a less effective exchange pathway. In summary, both the ste-
reochemistry of the metal ion and the topology of the bridging
ligand play a relevant role on the magnetic properties, whereas
the substitution on the N-phenyl group has less influence. How-
ever, the magnitudes of contact shifts, due to both p-spin delocal-
ization and spin polarization effects, increase as result of the
delocalization of the lone pair throughout the aromatic group
and it is reflected in a smaller spin density at the donor atom
and so in weaker antiferromagnetic coupling.
2Ng2b2
1 þ 5 expð2xÞ
kT 3 þ 5 expð2xÞ þ expðꢀxÞ
4Ng2b2
3kT
vm ¼ ð1 ꢀ qÞ
þ q
ð1Þ
where x = J/kT, J is the intradimeric exchange parameter, q the pro-
portion of paramagnetic contribution, of which the susceptibility is
assumed to follow Curie’s law, and N, b and k have their usual
meanings. The same isotropic g value has been used for the dimeric
and monomeric entities in order minimize the number of adjustable
parameters. Least-squares fit of the susceptibility data through
Eq. (1) leads to J = ꢀ 37.6 cmꢀ1
,
g = 2.17, q = 0.046 and R =
1.6 ꢂ 10ꢀ3 for 6, J = ꢀ 39.9 cmꢀ1
, g = 2.23, q = 0.022 and R =
1.0 ꢂ 10ꢀ3 for 8, and J = ꢀ 39.4 cmꢀ1
, g = 2.22, q = 0.008 and
R = 2.3 ꢂ 10ꢀ3 for 9, respectively. R is the minimized agreement fac-
ꢀ
ꢁ
P
P
2
2
tor defined as R ¼
vemxp ꢀ vcmalc
=
½vemxpꢃ . As can be seen in Fig. 6,
the theoretical curves reproduce very well the main features of the
experimental data.
On the other hand, all the compounds are completely EPR silent
from 4.2 K to 300 K. This behaviour is in concordance with the
presence of a Ni(II) single-ion zero-field splitting parameter, D, of
5–10 cmꢀ1 and negative in sign, i.e. the Ms = 0 state lying below
the Ms = 1 doublet [25]. However, in the precedent calculations
we have not considered the zero-field splitting of the 3A2 ground
state, because this contribution on the magnetic behaviour of di-
mers with strong antiferromagnetic interactions (ꢀJ > 20 cmꢀ1) is
usually negligible [26]. In fact, the experimental data have been
also fitted by the classical Ginsberg equation [27] modified to take
into account the magnetic contribution of Ni(II) ions with ZFS. The
agreement R factors are slightly lowers than those obtained with
Eq. (1), but the J values remain practically unchanged. The calcu-
lated D values are at ꢀ7.6 cmꢀ1 6, ꢀ11.1 cmꢀ1 8 and ꢀ8.3 cmꢀ1
9, but a strong correlation is observed between D and q and there-
fore we have little confidence on the accuracy of those values.
Usually, mononuclear oxamidate-containing nickel(II) com-
plexes are diamagnetic square planar species due to the coordina-
tion of the strong field-amide nitrogen atoms [2g,8,28]. However,
paramagnetic pentacoordinate Ni(II)-oxamidate complexes can
be prepared blocking partially the coordination sphere of the nick-
el(II) ion by a polydentate ligand prior to its complexation with the
oxamidate ligand. The macrocyclic ligands Me3-N3-mc and Me4-
N3-mc allow us to illustrate this strategy and the N,N0-substituted
oxamides which can introduce some angular strain when bound to
the nickel atom. The nickel atom in complexes 5–12 is paramag-
netic and five-coordinate with a stereochemistry intermediate be-
tween square pyramidal and trigonal bipyramidal: the three
nitrogen atoms from the macrocycle and two oxamidate atoms
(N,O) form a distorted five-coordinate environment around the
nickel atom. It seems that these macrocyclic ligands are specially
suited to induce a unusual five-coordinate surrounding around
the nickel(II) ion. The structures of the complexes 6, 8 and 9 of
the present work reinforce this observation. The environment of
each nickel(II) ion in the case of complexes 8 and 9 are square pyr-
amid fairly distorted while the substitution 4-chloro in the N-phe-
Acknowledgement
We thank the Fundación Séneca, CARM, Spain (Projects 00484/
PI/04 and 03010/PI/05) for financial support.
Appendix A. Supplementary material
CCDC 663968 , 663969 and 663970 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.03.001.
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