Synthesis and characterization of nickel-, palladium- and platinum(II) complexes of three o,o′-dihydroxydiarylazo dyes: Determination of the coordination geometry of this comprehensive series of tridentate diaryl dye complexes by combining results from NMR and X-ray experiments with theoretical ab initio calculations

Article abstract of DOI:10.1016/j.ica.2006.05.027

The syntheses of the square-planar platinum(II) complexes [Pt(L)(tba)] (L = 5,5′-dichloro-2,2′-dihydroxyazobenzenate (dhab), (5-chloro-2-hydroxyphenylazo)-3-oxo-N-phenylbutanamidate (hpab) or (5-chloro-2-hydroxyphenylazo)-2-naphtholate (hpan) and (tba) = tributylamine) is reported, together with those of the complete set of analogous complexes [M(L)(py)] (M = nickel(II), palladium(II), platinum(II) and (py) = pyridine). The coordinating nitrogen has been assigned to the azo-nitrogen attached to the 5-chloro-2-hydroxyphenyl substituent in both [Ni(hpab)(py)] and [Pt(hpan)(tba)] by single crystal X-ray diffraction methods. It has been established that complexes with different group 10 metals are iso-structural by isomorphology of the crystals as determined by X-ray powder diffraction studies on the complexes containing pyridine in the fourth coordination site. Furthermore, we present a method to determine the coordination geometry by comparison of calculated ¹³C chemical shifts for possible coordination modes optimized by ab initio methods with experimentally measured ¹³C chemical shifts.

Full text of DOI:10.1016/j.ica.2006.05.027

Inorganica Chimica Acta 359 (2006) 4493–4502
www.elsevier.com/locate/ica
Synthesis and characterization of nickel-, palladium- and
platinum(II) complexes of three o,o0-dihydroxydiarylazo dyes:
Determination of the coordination geometry of
this comprehensive series of tridentate diaryl dye complexes
by combining results from NMR and X-ray experiments
with theoretical ab initio calculations
a
a
a,
a
Jens Abildgaard , Poul Erik Hansen , Jens Josephsen *, Bjarke K.V. Hansen ,
Henning Osholm Sørensen b,1, Sine Larsen
b,2
a
Department of Life Sciences and Chemistry, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark
Centre for Crystallographic Studies, Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark
b
Received 4 May 2006; accepted 27 May 2006
Available online 7 June 2006
Abstract
The syntheses of the square-planar platinum(II) complexes [Pt(L)(tba)] (L = 5,50-dichloro-2,20-dihydroxyazobenzenate (dhab), (5-
chloro-2-hydroxyphenylazo)-3-oxo-N-phenylbutanamidate (hpab) or (5-chloro-2-hydroxyphenylazo)-2-naphtholate (hpan) and
(tba) = tributylamine) is reported, together with those of the complete set of analogous complexes [M(L)(py)] (M = nickel(II), palla-
dium(II), platinum(II) and (py) = pyridine).
The coordinating nitrogen has been assigned to the azo-nitrogen attached to the 5-chloro-2-hydroxyphenyl substituent in both [Ni(h-
pab)(py)] and [Pt(hpan)(tba)] by single crystal X-ray diffraction methods. It has been established that complexes with different group 10
metals are iso-structural by isomorphology of the crystals as determined by X-ray powder diffraction studies on the complexes containing
pyridine in the fourth coordination site.
Furthermore, we present a method to determine the coordination geometry by comparison of calculated 13C chemical shifts for pos-
sible coordination modes optimized by ab initio methods with experimentally measured 13C chemical shifts.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: o,o0-dihydroxydiarylazo dye complexes; Group 10 metals; X-ray crystal structures; ab initio; NMR
1. Introduction
gens is coordinated to the central metal atom in the com-
mercially important tridentate diarylazo dye complexes,
and that a different coordinating nitrogen affects the col-
ouring properties, several attempts have been made to find
methods for assignment of the ligating azo-nitrogen in
unsymmetrically substituted o,o0-dihydroxydiarylazo-com-
plexes (Na–Nb-isomerism), and to describe the factors
determining this type of isomerism.
Since it was firmly established by single crystal X-ray
crystallography [1–3] that only one of the two azo-nitro-
*
Corresponding author. Tel.: +45 4674 2415; fax: +45 4674 3011.
E-mail address: phjens@ruc.dk (J. Josephsen).
Present address: Centre for Fundamental Research: Metal Structures
1
in Four Dimensions, Risø National Laboratory, P.O. Box 49, DK-4000
Roskilde, Denmark.
Very few unambiguous coordinating nitrogen assign-
ments have been made, which should be compared to the
2
Present address: ESRF, BP 220, F-38043 Grenoble Cedex, France.
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.05.027

4494
J. Abildgaard et al. / Inorganica Chimica Acta 359 (2006) 4493–4502
large number of complexes reported [1,4–16]. In order to
overcome the solubility problem and facilitate the full
assignment [17] of the 13C-spectra by heteronuclear NMR
correlation techniques, a number of soluble square planar
platinum complexes have been designed and synthesized.
Mono anionic octahedral chromium(III)- and cobalt
(III) complexes with two o,o0-dihydroxy-diarylazo ligands
would be expected to exist in six different isomers, one
meridional and five facial [2,18]. It has been found [19–
21] that the type of isomer formed is determined by the
resulting angular strain of the chelate rings. It is generally
stated that tridentate diarylazo ligands, which form one
five-membered and one six-membered chelate ring with
the central metal atom, coordinate in the meridional mode,
while tridentate diaryl-azo ligands forming two annelated
six-membered chelate rings form facially coordinated com-
plexes. The evidence for this assumption is largely the num-
ber of isomers formed and separated by chromatography.
The present study describes square planar complexes
of three tridentate o,o0-dihydroxydiarylazo ligands with
nickel, palladium and platinum, thus avoiding the ambigu-
ities of coordination geometry and enabling studies of Na–
Nb-isomerism.
Analogous nickel(II), palladium(II) and platinum(II)
complexes with pyridine in the fourth coordination site
should be isostructural, if they exhibit the same Na–Nb-
isomerism. Isostructural complexes may form isomorphous
crystals [22], and accordingly the three series of analogous
complexes (each series containing three complexes with dif-
ferent metal ion but identical diazo ligand) were studied
using X-ray powder diffraction.
o,o0-Dihydroxydiarylazo compounds may exist as tau-
tomers. Hintermaier et al. [15] discuss the possibility that
a ‘‘keto-hydrazone’’ coordination plays a role in a Pd com-
plex of an azonaphthalene derivative, a question which has
been addressed.
2-naphthol, hydrochloric acid (37%), ammonia (25%),
chloroform, pentane and silica gel 60 F254 TLC plates were
from Merck, Germany. Pyridine, dimethylsulfoxide and
tributylamine were from Fluka AG, Switzerland. Deion-
ized water (cond. <2 lS/cm) was used without further
purification.
2.2. Preparations
2.2.1. 5,50-Dichloro-2,20-Dihydroxyazobenzene (dhabH2)
dhabH2 was made by a coupling reduction in a freshly
prepared 5-chloro-2-hydroxyphenyldiazonium-copper(I)
complex according to the method of Freeman et al. [35]
using 14.5 g (0.10 mol) of 5-chloro-2-hydroxyaniline for
the diazonium mixture. Purification was achieved through
treating a solution of the product and sodium methanolate
in methanol with activated carbon after which precipita-
tion was accomplished by neutralization with aqueous
hydrochloric acid. Yield of the pure compound (6.9 g,
49%). (Anal. Calc. for C12H8Cl2N2O2: C, 50.91; H, 2.85;
N, 9.89. Found: C, 51.12; H, 2.87; N, 9.79%).
2.2.2. 2-(5-Chloro-2-hydroxyphenylhydrazo)-3-oxo-N-
phenylbutanamide (hpabH2)
hpabH2 was prepared by diazonium coupling of the
in situ prepared 5-chloro-2-hydroxyphenyldiazoniumchlo-
ride to 8.85 g (0.05 mol) of acetoacetic anilide in alkaline
aqueous solution [36] using 7.23 g (0.05 mol) of 5-chloro-
2-hydroxyaniline for the diazonium mixture. Recrystallisa-
tion from ethanol (6.7 g, 77%). (Anal. Calc. for C16-
H14ClN3O3: C, 57.93; H, 4.25; N, 12.69. Found: C, 57.88;
H, 4.19; N, 12.65%.)
2.2.3. 2-(5-Chloro-2-hydroxyphenylazo)-2-naphthol
(hpanH2)
hpanH2 was prepared by diazonium coupling of the
in situ prepared 5-chloro-2-hydroxyphenylazonium-chlo-
ride to 7.16 g (0.05 mol) of 2-naphthol in alkaline aqueous
solution [37] using 7.23 g (0.05 mol) of 5-chloro-2-hydrox-
yaniline for the diazonium mixture. Purification as for
dhabH2 (9.2 g, 62%). (Anal. Calc. for C16H11ClN2O2: C,
64.33; H, 3.71; N, 9.38. Found: C, 64.14; H, 3.73; N,
9.32%.)
Ab initio DFT calculations [23–26] may be used both to
obtain realistic structures [27–30] and NMR chemical shifts
[28,29,31–34]. 13C chemical shifts have previously been sug-
gested as a way of determining which nitrogen is ligating
[17]. In order to support this conclusion, further ab initio
calculated and experimental 13C chemical shifts have been
compared for [Ni(hpab)py], the structure of which has been
determined by X-ray crystallography and also calculated
correctly.
2.2.4. (5,50-Dichloro-2,20-dihydroxyazobenzenate)-
pyridinenickel(II) ([Ni(dhab)(py)])
2. Experimental
[Ni(dhab)(py)] was prepared by the dropwise addition of
a solution of 0.71 g (3.0 mmol) of hexaaquanickel chloride
in 15 ml dimethylsulfoxide and 5 ml pyridine to a boiling
solution of 0.85 g (3.0 mmol) of dhabH2 and sodium meth-
anolate (from 0.2 g (8.7 mmol) of sodium) in 100 ml meth-
anol. After 1 h reflux the suspension was cooled at room
temperature, and the reddish precipitate was filtered off,
washed with water and ethanol and dried at 100 ꢁC. The
product was recrystallized from hot pyridine and precipita-
tion of the red crystals was completed by slow addition of
twice the volume of water at room temperature. (.92 g,
2.1. Materials
All chemicals were of reagent grade and were used as
received unless otherwise stated. Potassium tetrachloropla-
tinate and palladium(II) chloride were obtained from
Johnson Matthey, England. Hexaaquanickel(II) chloride,
sodium nitrite, sodium carbonate, sodium hydroxide,
hydroxylammonium chloride, copper(II) sulfate pentahy-
drate, 5-chloro-2-hydroxyaniline, acetoacetic acid anilide,

J. Abildgaard et al. / Inorganica Chimica Acta 359 (2006) 4493–4502
4495
75%). (Anal. Calc. for C17H11Cl2N3O2Ni: C, 48.74; H, 2.65;
N, 10.03. Found: C, 48.84; H, 2.64; N, 9.93%.)
methanolate (from 0.2 g (8.7 mmol) of sodium) in 100 ml
methanol. After 1 h of reflux, the reaction mixture was
allowed to cool and the yellow precipitate filtered off,
washed with water and ethanol and dried at 100 ꢁC. The
product was recrystallised by dissolving it in 50 ml of hot
pyridine, which was filtered and allowed to cool down to
room temperature, followed by the slow addition of
50 ml of ethanol. (0.31 g, 35%). (Anal. Calc. for
C17H11Cl2N3O2Pt: C, 36.77; H, 2.00; N, 7.57. Found: C,
36.86; H, 1.99; N, 7.54%.)
2.2.5. ([5-Chloro-2-hydroxyphenylazo]-3-oxo-N-
phenylbutanamidate)pyridinenickel(II) ([Ni(hpab)(py)])
[Ni(hpab)(py)] was prepared as described for [Ni(d-
hab)(py)] using 0.99 g (3.0 mmol) of hpabH2 giving yellow
crystals (.88 g, 65%). (Anal. Calc. for C21H17ClN4O3Ni: C,
53.95; H, 3.66; N, 11.98. Found: C, 53.99; H, 3.59; N,
11.96%.)
2.2.6. ([5-Chloro-2-hydroxy-phenylazo]-2-naphtholate)-
pyridinenickel(II) ([Ni(hpan)(py)])
2.2.11. ([5-Chloro-2-hydroxyphenylazo]-3-oxo-N-phenyl-
butanamidate)pyridineplatinum(II) ([Pt(hpab)(py)])
[Pt(hpab)(py)] was prepared as described for
[Pt(dhab)(py)] using 0.50 g (1.5 mmol)of hpabH2 giving
yellow crystals (0.39 g, 45%). (Anal. Calc. for C21H17-
ClN4O3Pt: C, 41.76; H, 2.84; N, 9.28. Found: C, 41.72;
H, 2.72; N, 9.01%.)
[Ni(hpan)(py)] was prepared as described for [Ni(d-
hab)(py)] using 0.90 g (3.0 mmol) of hpanH2 giving red
crystals. (1.01 g, 75%) (Anal. Calc. for C21H14ClN3O2Ni:
C, 58.05; H, 3.25; N, 9.67. Found: C, 58.11; H, 3.15; N,
9.57%.)
2.2.7. (5,50-Dichloro-2,20-dihydroxy-azobenzenate)-
pyridinepalladium(II) ([Pd(dhab)(py)])
2.2.12. ([5-Chloro-2-hydroxyphenylazo]-2-naphtholate)-
pyridineplatinum(II) ([Pt(hpan)(py)])
[Pd(dhab)(py)] was prepared by dropwise addition of a
solution of 0.27 g (1.5 mmol) of palladium chloride in
25 ml of dimethylsulfoxide to a stirred refluxing solution
of 0.43 g (1.5 mmol) of dhabH2 and sodium methanolate
(from 0.2 g (8.7 mmol) of sodium) in 100 ml methanol.
After 1 h the addition of 5 ml pyridine caused precipita-
tion, and the reaction mixture was allowed to cool down
to room temperature. The precipitate was filtered off,
washed with water and ethanol and dried at 100 ꢁC.
Recrystallisation from pyridine using twice the volume of
ethanol for complete precipitation gave orange crystals
(.57 g, 80%). (Anal. Calc. for C17H11Cl2N3O2Pd: C, 43.76;
H, 2.38; N, 9.01. Found: C, 43.68; H, 2.34; N, 8.81%.)
[Pt(hpan)(py)] was prepared as described for
[Pt(dhab)(py)] using 0.45 g (1.5 mmol) of hpanH2 giving
red crystals (0.69 g, 80%). (Anal. Calc. for C21H14ClN3-
O2Pt: C, 44.18; H, 2.47; N, 7.36. Found: C, 44.14; H,
2.45; N, 7.27%.)
2.2.13. (5,50-Dichloro-2,20-dihydroxyazobenzenate)-
tributylamineplatinum(II) ([Pt(dhab)(tba)])
[Pt(dhab)(tba)] was prepared by treating 0.83 g
(2.0 mmol) of potassium tetrachloroplatinate with 1 ml of
dimethylsulfoxide at 100 ꢁC for about 15 min to complete
the colour change to yellow. To the suspension was added
a solution of 0.56 g (2.0 mmol) of (dhab)H2 and 0.42 g
(4.0 mmol) of sodium carbonate in 15 ml methanol, and
the mixture was refluxed for 30 min. The reaction mixture
was allowed to cool, the yellow precipitate filtered off,
washed with water and dried at 100 ꢁC. The precipitate
was treated with 10 ml of tributylamine at 150 ꢁC for 6 h
after which a deep red solution had formed. The solution
was allowed to cool, 40 ml of acetone was added and a
red precipitate was obtained by slow addition of 25 ml of
0.5 M hydrochloric-acid to the stirred solution. For purifi-
cation the precipitate was dissolved in 40 ml of acetone, the
solution filtered; slow addition of 10 ml of water resulted in
the formation of red crystals which was filtered off, washed
with water, and dried at 100 ꢁC (0.44 g, 35%). (Anal. Calc.
for C24H33Cl2N3O2Pt: C, 43.57; H, 5.03; N, 6.35. Found:
C, 43.61; H, 4.92; N, 6.30%.)
2.2.8. ([5-Chloro-2-hydroxy-phenylazo]-3-oxo-N-phenyl-
butanamidate)pyridinepalladium(II) ([Pd(hpab)(py)])
[Pd(hpab)(py)] was prepared as described for
[Pd(dhab)(py)] using 0.50 g (1.5 mmol) of hpabH2 giving
yellow crystals (0.71 g, 90%) of. (Anal. Calc. for
C21H17ClN4O3Pd: C, 48.95; H, 3.33; N, 10.87. Found: C,
49.02; H, 3.18; N, 10.79%.)
2.2.9. ([5-Chloro-2-hydroxyphenylazo]-2-naphtholate)-
pyridinepalladium(II) ([Pd(hpan)(py)])
[Pd(hpan)(py)] was prepared as described for
[Pd(dhab)(py)] using 0.45 g (1.5 mmol) of (hpan)H2 giving
orange crystals (0.60 g, 80%) of. (Anal. Calc. for
C21H14ClN3O2Pd: C, 52.31; H, 2.93; N, 8.71. Found: C,
52.12; H, 2.92; N, 8.56%.)
2.2.10. (5,50-Dichloro-2,20-dihydroxyazobenzenate)-
pyridineplatinum(II) ([Pt(dhab)(py)])
[Pt(dhab)(py)] was prepared by dropwise addition of a
solution of 0.62 g (1.5 mmol) of potassium tetrachloropla-
tinate in 25 ml dimethylsulfoxide to a stirred refluxing solu-
tion of 0.43 g of (1.5 mmol) dhabH2 and sodium
2.2.14. ([5-Chloro-2-hydroxyphenylazo]-3-oxo-N-
phenylbutanamidate)tributylamineplatinum(II)
([Pt(hpab)(tba)])
[Pt(hpab)(tba)] was prepared as described for
[Pt(dhab)(tba)] using 0.66 g (2.0 mmol) of hpabH2
giving yellow crystals (0.31 g, 20%). (Anal. Calc. for

4496
J. Abildgaard et al. / Inorganica Chimica Acta 359 (2006) 4493–4502
C28H39ClN4O3Pt: C, 47.36; H, 5.53; N, 7.89. Found: C,
47.29; H, 5.51; N, 7.85%.)
the Laue symmetry of the diffraction pattern and the sys-
tematically absent reflections were P21/n for [Ni(hpab)(py)]
and C2/c for [Pt(hpan)(tba)]. Weissenberg photographs
revealed the same space groups at room temperature.
The structures were solved with the program SHELXS97
[40] , [Ni(hpab)(py)] by direct methods and [Pt(hpan)(tba)]
by the Patterson method. The structures were refined by
full-matrix least-squares on F2 using SHELXL97 [41] with
anisotropic temperature parameters for all non-hydrogen
atoms, except for C303, C313, C403, and C413 in
[Pt(hpan)(tba)], which were refined with isotropic displace-
ment parameters due to structural disorder of tba. The
population of the two conformations of one of the butyl
groups is refined to be 0.55(2) and 0.45(2), respectively.
The ADP’s of the ligating oxygens, O1 and O2, in
[Pt(hpan)(tba)] were restrained to be close to isotropic.
Hydrogen atoms could be located in the difference Fourier
map and their positions were refined without constraints in
the structure of [Ni(hpab)(py)]. In [Pt(hpan)(tba)], the
hydrogen atom positions were constrained to follow the
connected atom. The isotropic displacement parameters
of the hydrogen atoms were constrained to 1.2 (1.5 for
methyl groups) times Ueq of the parent atom in both struc-
tures. Further details about the data collections and refine-
ments are presented in Table 1.
2.2.15. ([5-Chloro-2-hydroxyphenylazo]-2-naphtholate)-
tributylamineplatinum(II) ([Pt(hpan)(tba)])
[Pt(hpan)(tba)] was prepared by dissolving 1.25 g
(3.0 mmol) of potassium tetrachloroplatinate in 10 ml of
dimethylsulfoxide at 100 ꢁC resulting in a yellow suspen-
sion. This mixture was added drop by drop to a stirred
solution of 0.90 g (3.0 mmol) of hpanH2 and 0.64 g
(6.0 mmol) of sodium carbonate in 25 ml of dimethylsulf-
oxide. After 1 h at 110 ꢁC, the stirred solution was cooled
and 70 ml of water was added slowly. The resulting red
precipitate was filtered off and washed with water, metha-
nol and dried at 100 ꢁC (1.67 g, 98% based on
[Pt(hpan)(DMSO)]). A fraction of this compound was used
for the synthesis of [Pt(hpan)(tba)]. Another fraction was
recrystallized from toluene from which red crystals were
obtained by cooling at ꢀ20 ꢁC for 12 h. (Anal. Calc. for
C18H15ClN2O3SPt: C, 37.93; H, 2.65; N, 4.92. Found: C,
38.29; H, 2.64; N, 4.64%.)
1.14 g (2.0 mmol) of [Pt(hpan)(DMSO)] was treated
with 10 ml of tributylamine for 1 h at 150 ꢁC after which
most of the solvent had evaporated. 40 ml of hot acetone
was added to the suspension and the red complex was pre-
cipitated from the cooled and stirred solution by slow addi-
tion of 25 ml of 1.0 M hydrochloric acid. For purification
the precipitate was dissolved in 125 ml of hot acetone,
the solution was filtered and after cooling the slow addition
of 20 ml of water resulted in the precipitation of red crys-
tals which were filtered off, washed with water, and dried
at 100 ꢁC (.83 g, 61%). (Anal. Calc. for C28H36ClN3O2Pt:
C, 49.66; H, 5.36 N, 6.21. Found: C, 49.61; H, 5.38; N,
6.03%.)
2.4. X-ray powder-diffraction analyses
Crystals of [MLpy] (M = Ni, Pd, and Pt, L = dhab,
hpab, and hpan, cf. Table 2) were obtained from pyridine
solutions of the complexes by slow vapour phase diffusion
of the precipitating liquid (water or ethanol) at room
temperature over several weeks, rather than by dropwise
2.3. Single crystal X-ray diffraction analyses
Table 1
Crystallographic data and structure refinement results for [Ni(hpab)(py)]
and [Pt(hpan)(tba)]
Deep red plate-like crystals suitable for structure deter-
mination of [Ni(hpab)(py)] were grown from a filtered solu-
tion of 9.4 mg of [Ni(hpab)(py)] in a 3.0 ml of pentane/
chloroform mixture (1:9) in a test tube. The tube was
placed in a sealed 1000 ml container together with 20 ml
of pentane at room temperature for 2 days. Crystals of
[Pt(hpan)(tba)] were grown from a filtered solution of
25 mg [Pt(hpan)(tba)] in 3 ml of chloroform in a test tube,
covered with thin film of polyethylene through which the
solvent gradually diffused over 7 days.
Formula
Mr
NiC21H17ClN4O3
467.54
PtC28H36ClN3O2
677.14
Crystal system
Space group
T (K)
monoclinic
P21/n
monoclinic
C2/c
122.4(5)
6.941(3)
14.031(3)
20.148(3)
90.88(2)
1962.0(10)
4
122.4(5)
24.113(7)
11.041(2)
20.812(6)
102.71(2)
5405(2)
8
˚
a (A)
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z
Data were collected with an Enraf-Nonius CAD-4 dif-
fractometer using graphite monochromated Mo Ka radia-
tion on crystals cooled to 122.4(5) K. The unit cell
parameters were determined from 18 reflections
(17.92ꢁ < h < 22.34ꢁ) for [Ni(hpab)(py)] and 22 reflections
(18.73ꢁ < h < 21.22ꢁ) for [Pt(hpan)(tba)]. The data were
corrected for background, polarisation and Lorentz effects
with the DREAR program suite [38]. Corrections for absorp-
tion were performed using numerical Gaussian integration
[39]. The space groups were determined from an analysis of
˚
k (A)
0.71073
1.157
0.34 · 0.15 · 0.07
30
0.719, 0.942
6517
5691
0.0255
5691/0/322
0.0432
0.71073
5.320
0.30 · 0.28 · 0.04
25
0.272, 0.752
8488
4752
0.0591
4752/12/317
0.0667
l, (Mo Ka) (mmꢀ1
Crystal size (mm3)
Hmax (ꢁ)
)
Tmin, Tmax
Measured reflections
Independent reflections
Rint
Data/restraints/parameters
R(F2) [F2 > r(F2)]
wR(F2)
0.0907
0.1068

J. Abildgaard et al. / Inorganica Chimica Acta 359 (2006) 4493–4502
4497
Table 2
Isomorphous complex crystals
[Ni(dhab)(py)]
[Ni(dhab)(py)]/[Pd(dhab)(py)] (1:1)
[Ni(hpab)(py)]
[Ni(hpab)(py)]/[Pd(hpab)(py)] (1:1)
[Pd(dhab)(py)]
[Ni(hpan)(py)]
[Pd(hpab)(py)]
[Pt(hpab)(py)]
[Pd(hpan)(py)]
[Pt(hpan)(py)]
[Pt(dhab)(py)]
Complexes, in columns, established to be isomorphous by identical powder diffraction patterns, but with some intensity differences between the individual
lines in the photographs.
addition, cf. the recrystallisation procedures for the
pyridine containing complexes described above.
hybrid functional B3PW91 [25,26] and the basis set 6-
31G(d) for all atoms except Ni for which 6-311G(d) was
used. The use of the latter basis set for all atoms was also
tested, but this did not give rise to any improvement in the
prediction of the molecular geometries (cf. Table S1).
Calculations with the functional BPW91 B3PW91 [25,26]
were also performed, but these were found to give a slightly
poorer prediction of the 13C chemical shifts. Chemical
shifts were calculated using the GIAO method [43,44].
Calculations of the complexes [Ni(hpab)(py)] and [Ni
(hpan)(py)] were performed with both Na and Nb as ligat-
ing atom, but due to a symmetric ligand in [Ni(dhab)(py)]
only one calculation was necessary. In order to determine
the predominant species, the structure and NMR shifts
were calculated for all tautomers and relevant rotamers
of the protonated ligands.
X-ray powder-diffraction photographs were taken in a
50 mm radius Guinier-camera. The complexes were finely
ground in an agate mortar, mixed with xylol and silicon
˚
as internal reference (a = 5.41959 A at 293 K [42]) and
fixed on a piece of tape on the rotating sample-holder.
The X-ray films were exposed for several hours to Cu Ka
radiation. Analysis of possible isomorphology of the com-
plex crystals was simply established by visual inspection, as
the photographs showed many very weak reflections of
which some might be unobservable and this could lead to
wrong assignments.
2.5. Co-crystallization of dhab complexes
Co-crystals were obtained by mixing filtered solutions of
equimolar amounts of the two complexes (i.e. 5.0 mg
(12 lmol) of [Ni(dhab)(py)] and 5.6 mg of (12 lmol)
[Pd(dhab)(py)]) in 30 ml of 1:9 pentane/chloroform mix-
ture in a test tube. The tube was placed in a sealed con-
tainer with 30 ml pentane for several days. In the
resulting clusters of small thread-like crystal only one
external shape could be detected by polarization micros-
copy. The complex mixture migrated as two equal-sized
spots, with identical retention as the pure complexes, in
pyridine/chloroform (1:9) on silica gel TLC-plates,
completely vapor phase equilibrated with the solvent. The
co-crystals had 1H NMR spectra in deutero-chloroform
identical with a 1:1 mixture of the two complexes.
3. Results and discussion
3.1. Stability and coordination geometry
The nickel complexes, giving sharp and well resolved 1H
NMR spectra, are obviously square planar in CDCl3 solu-
tion in agreement with a low-spin d8 nickel(II) electron
configuration. In DMSO-d6 solution, this is not true since
the signals shift to low field and are broad with no fine
structure at all. Unlike the more robust palladium and plat-
inum analogues, the nickel complexes are changed in the
presence of 1 M hydrochloric or nitric acid.
3.2. Crystal structures
2.6. Co-crystallization of hpab complexes
The crystal structure of both [Ni(hpab)(py)] and
[Pt(hpan)(tba)] shown in Figs. 1 and 2 (as ORTEPII draw-
ings [45]) unequivocally establishes these complexes to be
Na-isomers, the nitrogen atom being attached to the 5-
chloro-2-hydroxyphenyl substituent. The coordinating
nitrogen (Na) lies exactly in the plane described by the
metal atom, the second azo-nitrogen (Nb) and the aromatic
carbon atom bound to the coordinating nitrogen (C1), and
indeed all the atoms composing the two annelated 5- and
6-membered chelate rings are planar, and have very similar
dimensions in the two complexes. The distances between
Co-crystals of the nickel and palladium complexes of
ligand hpab were obtained and analysed with TLC and
NMR in the same way as with the dhap complexes
described above using 23.4 mg (50 lmol) of [Ni
(hpab)(py)] and 25.8 mg (50 lmol) of [Pd(hpab)(py)] in
6 ml of a 1:9 pentane/chloroform mixture and using
12 ml of pentane for diffusion. The resulting needle-
formed crystals were 3–5 mm long with the dark colour
of the nickel complex.
˚
2.7. Computational methodology
the azo nitrogens of 1.286(2) A and 1.278(8) in [Ni(h-
pab)(py)] and [Pt(hpan)(tba)], respectively, strongly suggest
that the azo-bond in ligand dianions should be described as
having a high degree of double bond character (Table 3).
Ab initio DFT calculations were performed with the
GAUSSIAN98 and 03 program packages [23,24] using the

4498
J. Abildgaard et al. / Inorganica Chimica Acta 359 (2006) 4493–4502
and the two planar dianionic ligands coordinate through
the nitrogen which is attached to the 2-hydroxy-4-nitro-
phenyl substituent, i.e. in the Na-mode.
In [Ni(hpab)(py)], the distances Ni–N1 and Ni–N4
(Table 3) are typical for low-spin complexes (cf. the
˚
Ni–N of 1.87 A in bisdimethylglyoximatonickel [46]),
whereas in trans-dichlorotetrakis(pyridine)nickel(II) [47] it
˚
is 2.00 A and in bis[2-{2-(phenylamido)phenyl}azopyri-
˚
dine]nickel(II) [48] they are 1.99–2.10 A.
The pyridine ring of the Ni complex is twisted 38.9ꢁ out
of the coordination plane defined by the planar tridentate
ligand and the nickel atom. In other d10 systems a large
twist is also found. For example, in trans-[Pdpy2Cl2], the
two pyridines are twisted about 20ꢁ relative to each other,
and 48ꢁ and 68ꢁ relative to the coordination plane [49]. In
the similar copper(II)-systems (cf. Table 3), the twist is
rather small [16].
Fig. 1. ORTEPII drawing [44] showing structure and labelling of
[Ni(hpab)(py)]. The ellipsoids are drawn at the 50% probability level.
The X-ray powder diffraction photographs of the com-
plexes show that they can be divided in five isomorphic
groups for which diffraction lines at identical 2h angles
but with significant relative intensity differences are in
agreement with varying diffractive power and absorption
by the different group 10 metals. The comparisons clearly
show that the platinum and palladium complex crystals
with the same ligand are isomorphous, and in the case of
the (hpan) complexes all three, nickel, palladium and plat-
inum-(L)-pyridine, complexes are isomorphous (Table 2).
Hence, we conclude that these complexes are isostructural.
The fact that the nickel and palladium complexes of both
dhab and hpab co-crystallise maintaining the nickel
complex morphology strongly suggests that they are iso-
structural as well. Such a change in crystal form when
co-crystallised with an isostructural, analogous complex
has been shown in other series of complexes [22].
3.3. Theoretical calculations
Structures of the [Ni(hpab)(py)], [Ni(hpan)(py)] and
[Ni(dhab)(py)] have been calculated using DFT with the
B3PW91 functional and 6-31G(d)/6-311G(d) basis sets
[24–26]. Calculations both with the a and b nitrogen atoms
as ligating atoms were performed. The structure of [Ni(h-
pab)(py)] with coordination to the Na has been compared
with the one determined by X-ray crystallography (Table
1). The calculated structure of [Ni(hpab)(py)] is in good
agreement with that determined by X-ray crystallography
with most bond distances and angles deviating less than 2
standard uncertainties (Table 3). Structures of the two
other complexes, [Ni(hpan)(py)] and [Ni(dhab) (py)], have
also been calculated and show very similar structures to
that of [Ni(hpab)(py)] (Table 3). [Ni(hpan)(py)] is a naph-
thalene derivative, but shows very little tendency to ‘‘hyd-
roazone’’ complexation contrary to the suggestion by
Hintermaier et al. [15] for [Pd(1-(2-hydroxy-4-nitropheny-
lazo)-2-naphthol)(PPh3).
Fig. 2. ORTEPII drawing [44] showing the structure and labelling of
[Pt(hpan)(tba)]. The ellipsoids are drawn at the 50% probability level.
These structural features are in good agreement with the
previously published structures of the Pd and Cu
complexes [15,16] (see Table 3) and the chromium(III)-
complexes of 2,20-dihydroxyazobenzene and (2-hydroxy-
4-nitrophenylazo)-2-naphthol [2,3]. The pyridinium salt
of the latter chromium complex is the meridional isomer,
13C chemical shifts have been calculated using the opti-
mised structures just mentioned and the calculated nuclear

J. Abildgaard et al. / Inorganica Chimica Acta 359 (2006) 4493–4502
4499
Table 3
Selected bond distances (A) and angles(ꢁ)
˚
Me = Ni, Pt
[Ni(hpab)-
(py)]a
[Ni(hpab)-
(py)]b
[Ni(hpan)-
(py)]b
[Ni(dhab)-
(py)]
[Pt(hpan)-
(tba)]a
[Cu(DAB)-
(py)]ac
Cu(py)-
(azophenolate)a,d
[Pd(DAB)PPh3]a,e
b,g
Me–N1
Me–N4/3
Me–O1
1.8319(18)
1.9301(18)
1.8518(16)
1.8423(15)
87.50(7)
92.70(7)
90.50(7)
89.31(7)
1.286(2)
1.412(3)
1.331(3)
1.278(3)
1.345(3)
1.456(3)
1.405(3)
1.8305
1.9277
1.8229
1.8352
87.7
93.1
89.1
90.2
1.2736
1.4103
1.3211
1.2765
1.3492
1.4527
1.4093
1.8321
1.9351
1.8301
1.8066
87.6
93.9
89.3
89.3
1.2749
1.4047
1.3147
1.2960
1.3549
1.4259
1.4119
1.8381
1.9351
1.8320
1.8079
87.4
94.5
89.1
89.0
1.2716
1.4037
1.3124
1.2996
1.3656
1.4331
1.4115
1.946(6)
2.121(6)
2.004(6)
1.974(5)
83.5(2)
94.6(2)
95.2(2)
86.8(2)
1.278(8)
1.406(9)
1.342(9)
1.309(8)
1.387(9)
1.413(10)
1.404(10)
1.946(6)
2.040(4)
1.933(5)
1.880(5)
82.9 (2)
94.3(2)
1.923(6)
2.007(6)
1.905(4)
1.867(4)
84.5(2)
1.999(5)
2.298(3) Phosphf
2.011(4)
1.969(4)
83.7(2)
Me–O2
N1–Me–O1
N1–Me–O2
N4/3–Me–O1
N4/3–Me–O2
N1–N2
N1–C1
O1–C2
O2–C7/8
N2–C8/7
C7–C8
93.0(2)
92.3(2)
93.2(2)
91.0(2)
91.58(16) Phosphf
92.68(13) Phosphf
1.212(8)
1.249(9)
1.464(8)
1.300(8)
1.316(8)
1.429(10)
1.398(10)
1.408(10)
1.263(8)
1.405(8)
1.331(9)
1.309(8)
1.390(9)
1.44(10)
1.400(9)
1.474(9)
1.333(9)
1.321(7)
1.410(8)
1.407(9)
1.388(11)
C1–C2
a
X-ray data.
b
B3PW91/6-31G(d)/6-311G(d) DFT data (see text).
Taken from Ref. [16].
Taken from Ref. [14].
Taken from Ref. [15].
Distance to phosphorous.
c
d
e
f
g
Numbering as given in structure:
shielding (r) and experimental chemical shifts (d) are
correlated.
Bagno et al. [50]. Therefore, for non-halogen bonded car-
bon nuclei, the calculation of 13C chemical shifts can be
performed by density functional methods employing the
functional B3PW91 together with the 6-31G(d)/6-311G(d)
basis set that reflect those determined experimentally.
These calculations confirm the assignments made earlier
by Abildgaard et al. [17] and hence contradict to the
assumptions made by Hintermaier et al. [15] for a series
of Pd, Pt, Ni and Rh complexes as they assume that the
chemical shifts of C16 (ortho-position of five-membered
ring) are at lower frequency than that of C6 of the other
phenyl ring. From the experimental data [17], it can be seen
that the chemical shifts of the Ni, Pd and Pt complexes are
very similar. The values obtained by the calculation of a Ni
complex can therefore be extrapolated to other complexes
of similar coordination.
For the [Ni(hpab)(py)] structure (see Fig. 1), a reason-
able correlation with experimental results rcalc = ꢀ0.942
*
d
exp + 190.88 ppm; R2 = 0.996 was obtained (for a com-
parison of experimental and calculated values, see Table
4). For the corresponding complex with Ni coordination
to the Nb atom, a significant poorer R2 = 0.951 was
obtained. Including only the aromatic carbons the discrim-
ination is even better, R2 = 0.995 for the a-coordination
and only 0.870 for b-coordination. In case of the [Ni(hpan)
(py)] complex the, picture is even clearer : rcalc
=
ꢀ0.942
d
exp + 190.88 R2 = 0.971, whereas for b-coordi-
*
nation, R2 = 0.67. The [Ni(dhab) (py)] complex gives very
exp + 184.23 R2 = 0.973.
similar results: rcalc = ꢀ0.900
d
*
The discrimination between coordination to the a and the
b nitrogen atoms is thus very good. The above given corre-
lations are slightly improved if the data for the chlorine
substituted carbons are excluded. The shortcomings found
here in the prediction of 13C chemical shifts for halogen-
bonded carbon nuclei have recently been pointed out by
To establish the method further, 13C chemical shifts of
the hpanH2, hpabH2 and dhabH2 have been calculated
including both tautomers and rotamers (see Fig. 3).
For hpabH2, for which three different tautomers can be
envisaged, the hydrazo-form resulting in the 5-chlorophenyl

4500
J. Abildgaard et al. / Inorganica Chimica Acta 359 (2006) 4493–4502
Table 4
Calculated and measured [17] 13C chemical shifts in ppm
Atom
[Ni(hpab)(py)]
Measured
[Ni(hpan)(py)]
Measured
[Ni(dhab)(py)]
Calculated N-a
Calculated N-b
Calculated N-a
Calculated N-b
Measured
Calculateda
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
147.7
161.4
116.0
127.5
120.4
114.8
153.6
121.7
197.9
26.6
149.1
161.0
117.0
128.1
126.5
114.9
153.3
122.1
197.5
26.5
141.3
145.5
122.0
129.9
127.0
130.0
166.7
127.7
187.9
34.3
147.8
163.0
117.3
129.8
121.0
116.1
132.5
150.7
124.5
138.6
127.8
124.5
127.8
122.6
132.5
127.8
149.9
124.5
138.6
149.1
162.7
117.5
130.2
127.5
116.1
134.2
151.7
123.5
134.6
127.8
122.8
127.4
122.6
132.3
125.1
152.2
123.1
136.7
149.5
163.1
118.0
130.7
128.1
116.6
134.5
152.2
124.0
135.1
128.3
123.3
127.9
123.1
132.8
125.6
152.6
123.6
137.1
146.9
164.5
117.9
129.4
121.5
116.6
140.5
149.2
121.9
132.6
122.2
131.7
148.0
164.1
116.2
131.0
126.6
115.0
140.1
149.2
120.8
131.2
126.3
130.3
136.7
122.5
128.8
124.2
136.8
118.7
127.6
122.2
138.0
118.3
128.1
121.8
C10(C15/C17/C13)
C20(C16/C18/C14)
C30(C17/C19/C15)
a
150.1
125.3
138.7
152.6
123.2
136.8
152.7
123.8
137.5
149.8
124.5
138.8
151.7
121.5
136.0
There is no a-b isomerism with this symmetrical ligand.
ring becoming quinoid was not found to contribute at all.
A weighting of the two remaining ones in the ratio
Cl
Cl
H
O
H
O
O
H
O
H
N
H
H
H
(hydrazo/azo) 0.71:0.29 leads to
a
correlation:
1
N
H
N
H
exp + 186.8 ppm; R2 = 0.98. For hpanH2
2
2
rcalc = ꢀ0.92
d
H
*
1
H
N
H
H
a similar picture was found. For dhabH2, it emerged that
H
H
H
only the rotamer in Fig. 3d contributes leading to a corre-
Cl
Cl
a
d
exp + 208.6 ppm; R2 = 0.92. This
*
indicates that dhabH2 is not forming an intramolecular
b
lation: rcalc = ꢀ1.068
H
Cl
H
O
H
hydrogen bond in DMSO.
In order to see how coordination of the ligand affects the
13C chemical shifts, we have compared theoretically pre-
H
O
H
H
O
H
Cl
N
H
N
H
H
N
H
N
H
O
Cl
H
H
Table 5
H
Cl
H
Calculated nuclear shieldings r in ppm
H
d
c
Atom
[Ni(hpab)(py)]
[Ni(hpan)(py)]
[Ni(dhab)(py)]
Cl
Cl
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
50.4
39.2
80.7
70.2
71.8
82.7
46.4
75.9
4.8
65.9
62.0
79.0
70.6
75.8
50.4
37.6
80.2
68.3
70.8
81.5
64.5
48.0
74.6
64.2
70.5
75.2
70.9
75.4
66.3
73.1
47.5
74.9
62.2
51.0
36.5
79.7
66.3
70.3
80.7
58.1
49.9
75.5
66.1
70.6
66.9
H
O
H
Cl
H
Cl
N
H
N
H
H
N
1
H
N
2
H
H
H
O
H
H
H
O
O
H
H
f
e
Cl
H
O
Cl
H
O
H
Cl
H
H
Cl
H
N
H
N
H
H
N
H
N
H
H
H
O
H
H
O
H
g
C10(C15/C17/C13)
C20(C16/C18/C14)
C30(C17/C19/C15)
47.1
74.9
62.0
47.6
74.8
61.9
h
Fig. 3. Tautomers/rotamers of dhabH2 (calculated nuclear shieldings and
energies are given in Table 6). Numbering for c–h as in a.

J. Abildgaard et al. / Inorganica Chimica Acta 359 (2006) 4493–4502
4501
Table 6
ben Hansen for the elemental analyses, Dr. Peter Andersen
for the powder-diffraction photographs and advice on their
interpretation and Mr. Flemming Hansen for help with the
crystallographic experiments.
Calculated nuclear shieldingsa r in ppm and energies for tautomers and
rotamers of dhabH2 (cf. Fig. 3)
a
b
c
d
e
f
g
h
C1
C2
C3
C4
C5
C6
C7
C8
74.1
48.2
78.3
68.7
66.9
78.0
66.2
24.1
70.5
59.5
66.4
68.7
20
57.7
55.8
81.5
68.2
66.6
59.2
57.7
55.8
81.5
68.2
66.6
59.2
58.2
45.2
82.3
65.9
65.1
81.2
58.2
45.2
82.3
65.9
65.1
81.2
81
60.5
48.0
82.6
66.3
64.3
81.2
60.8
46.9
78.6
64.1
68.1
63.8
32
59.6
41.9
81.4
62.7
66.0
84.4
58.8
54.5
81.4
67.8
65.4
60.4
55
60.6
46.2
80.5
64.1
64.8
81.1
61.2
48.1
79.1
63.5
66.8
63.4
25
57.6
45.1
82.1
66.1
65.3
83.5
58.7
54.8
81.5
67.9
66.6
59.5
96
46.1
78.3
64.4
67.3
66.8
64.2
46.1
78.3
64.4
67.3
66.8
0
Appendix A. Supplementary material
X-ray crystallographic data, in files of the CIF format,
for the structures of Figs. 1 and 2 have been deposited with
the Cambridge Crystallographic Data Centre, CCDC ref-
erence Nos. 268776 and 268777. Copies of the data can
be obtained free of charge, on application to The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, fax:
+44 1223 336 033, email: deposit@ccdc.cam.uk or on the
web: http://www.ccdc.cam.ac.uk. Calculated structural
data are also available. Supplementary data associated
with this article can be found, in the online version, at
doi:10.1016/j.ica.2006.05.027.
C9
C10
C11
C12
Calculated
energiesb
a
105
B3PW91/6-31G(d).
In kJ molꢀ1 relative to rotamer a.
b
dicted nuclear shieldings for dhabH2 in the co-ordination-
like mode (i.e. with oxygens to the same side as the diazo
group and a hydrogen-bond forming a six-membered ring,
cf. Figs. 3e, g and Table 6) with those calculated for the
[Ni(dhab)(py)] complex (cf. Table 5). The calculated data
show that the complex formation leads to a large difference
in the nuclear shieldings of carbons 2 and 8. The same is
true though to a slightly lesser extent for carbon atoms 1
and 7 (Table 6). For the remaining nuclei, the changes in
chemical shifts upon coordination are only moderate.
The chemical shifts are therefore very distinct in discrimi-
nating the carbon nuclei of the five- and the six-membered
coordination rings.
References
[1] H. Jaggi, Helv. Chim. Acta 51 (1968) 580.
[2] R. Greib, A. Niggli, Helv. Chim. Acta 48 (1965) 317.
[3] R. Greib, Inaugural-Dissertation, Universita¨t Zurich, 1967.
¨
[4] E. Steiner, C. Mayer, G. Schetty, Helv. Chim. Acta 59 (1976) 364.
[5] A. Lycka, J. Jirman, A. Cee, Magn. Res. Chem. 28 (1990) 408.
[6] G. Schetty, Helv. Chim. Acta 53 (1970) 1437.
[7] G. Schetty, E. Steiner, Helv. Chim. Acta 55 (1972) 1509.
[8] G. Schetty, E. Steiner, Helv. Chim. Acta 57 (1974) 2149.
[9] G. Schetty, Helv. Chim. Acta 45 (1962) 809, and 1026.
[10] G. Schetty, Helv. Chim. Acta 45 (1962) 1095.
[11] F. Beffa, P. Lienhard, E. Steiner, C. Mayer, G. Schetty, Helv. Chim.
Acta 46 (1963) 1369.
[12] C. Wittwer, Helv. Chim. Acta 51 (1968) 1691.
[13] E. Steiner, G. Schetty, Helv. Chim. Acta 56 (1973) 368.
[14] G. Speier, J. Csihony, A.M. Whalen, C.G. Pierpont, Inorg. Chem. 35
(1996) 3519.
4. Conclusions
[15] F. Hintermaier, F. Kuhlwein, C. Robl, W. Beck, Z. Anorg. Allg.
¨
Nine new nickel-, palladium- and platinum(II) com-
plexes of three o,o0-dihydroxydiarylazo dyes have been
synthesized.
Chem. 621 (1995) 829.
[16] H. Adams, R.M. Bucknall, D.E. Fenton, M. Garcia, J. Oakes,
Polyhedron 17 (1998) 4169.
[17] J. Abildgaard, P.E. Hansen, J. Josephsen, A. Lycka, Inorg. Chem. 33
(1994) 5271.
[18] G. Schetty, W. Kuster, Helv. Chim. Acta 44 (1961) 2193.
[19] G. Schetty, Helv. Chim. Acta 46 (1963) 1132.
The X-ray structure determinations of both [Ni
(hpab)(py)] and [Pt(hpan)(tba)] unambiguously showed
that Na is the coordinating atom in both cases. Further,
analogous Ni, Pd and Pt complexes are isostructural since
the X-ray powder diffraction patterns show the crystals to
be isomorphous. The calculated structure and the calcu-
lated 13C chemical shifts correspond well to the X-ray
structure and the measured 13C chemical shifts in solution
showing that the structure is the same in the solid and in
solution. It has also been shown that the structure of the
complexes can be determined based on a comparison of
experimentally measured 13C chemical shifts of the com-
pound with 13C chemical shifts calculated for the possible
structures.
[20] G. Schetty, Chimia 18 (1964) 244.
[21] S.J. Higgins, Coordin. Chem. Rev. 152 (1962) 175.
[22] P. Andersen, J. Josephsen, Acta Chem. Scand. 25 (1971) 3255.
[23] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery Jr., R.E.
Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels,
K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M.
Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford,
J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma,
D.K. Malick, .A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.
Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R. Gomper, D.J. Fox, T.
Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, C. Gonzalez,
M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong,
J.L. Andres, C. Gonzalez, M.E.S.F. Head-Gordon, GAUSSIAN98,
Revision A.7, Gaussian Inc., Pittsburgh, PA, 1998.
Acknowledgements
[24] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C.
Burant, J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B.
The authors thank the following colleagues from the
H.C. Ørsted Institute, University of Copenhagen: Mr. Pre-

4502
J. Abildgaard et al. / Inorganica Chimica Acta 359 (2006) 4493–4502
Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H.
[35] D.C. Freeman, C.E. White, J. Org. Chem. 21 (1956) 379.
[36] Y. Yagi, Bull. Chem. Soc. Jpn. 36 (1963) 492.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene,
X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, C. Adamo, J.
Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin,
R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma,
G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S.
Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D.
Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G.
Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T.
Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challa-
combe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C.
Gonzalez, J.A. Pople, GAUSSIAN 03, Revision B.03, Gaussian Inc.,
Pittsburgh, PA, 2003.
[37] K.H. Schudehutte, Methoden zur herstellung und umwandlung von
¨
¨
diarylazo verbindungen, in: Houben-Weyls (Ed.), Methoden der
Organishe Chemie, 10, Georg Thieme Verlag, Stuttgart, 1965, p. 219
(Part 3).
[38] R.H. Blessing, Cryst. Rev. 1 (1987) 3.
[39] G.M. DeTitta, J. Appl. Crystallogr. 18 (1985) 75.
[40] G.M. Sheldrick, Acta Crystallogr. A46 (1990) 467.
[41] G.M. Sheldrick, SHELXL97, Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.
[42] International tables for X-ray-crystallography, The International
Union of X-ray Crystallography, III, The Kynoch Press, Birming-
ham, England, 1962.
[43] R. Dithfield, Mol. Phys. 27 (1974) 789.
[25] D. Becke, Phys. Rev. A 38 (1988) 3098.
[26] P. Perdew, Y. Wang, Phys. Rev. B 45 (1992) 1324.
[44] K. Wolinski, J.F. Hilton, P. Pulay, J. Am. Chem. Soc. 112 (1990)
8251.
[27] S. Niu, M.B. Hall, Chem. Rev. 100 (2000) 353.
[28] J. Abildgaard, S. Bolvig, P.E. Hansen, J. Am. Chem. Soc. 120 (1998)
[45] C.K. Johnson, ORTEPII. Report ORNL-5138. Oak Ridge National
Laboratory, Tennessee, USA, 1976..
9063.
[46] S. Yamashita, Y. Yanase, T. Yamaguchi, H. Wakita, Bull. Chem.
Soc. Jpn. 62 (1989) 2902.
[29] A. Kno¨dler, W. Kaim, V.K. Jain, S. Zalis, J. Organomet. Chem. 655
(2002) 218.
[47] M.A. Porai-Koshits, A.S. Antsishkina, Dokl. Akad. Nauk. SSSR 92
(1953) 333.
[30] A. Ishii, H. Oshida, J. Nakayama, Bull. Chem. Soc. Jpn. 75 (2002)
319.
[48] A. Saha, P. Majumda, S-M. Peng, S. Goswami, Eur. J. Inorg. Chem.
(2000) 2631.
[49] P.B. Viossat, G. Nguyen-Huy, F. Robert, Acta Crystallogr. C 49
(1993) 84.
[31] S.S. Kidambi, D.K. Lee, A. Ramamoorthy, Inorg. Chem. 42 (2003)
3142.
[32] M. Buhl, M. Kaupp, O.L. Malkina, V.G. Malkin, J. Comput. Chem.
¨
20 (1999) 91.
[50] A. Bagno, F. Rastrelli, G. Saielli, J. Phys. Chem. A 107 (2003)
9964.
[33] S. Vasques, J. Chem. Soc., Perkin Trans. 2 (2002) 2100.
[34] T. Helgaker, M. Jaszunski, H. Ruud, Chem. Rev. 99 (1999) 293.