Molecular and electronic structure of square planar complexes [Pd II(tbpy)(LN,OIP)]0, [PdII(tbpy)(LN,OISQ](PF 6), and [PdII(tbpy)(LN,O IBQ](PF6)(BF4)·2CH2Cl 2

Article abstract of DOI:10.1039/b614745c

Three Pd^II complexes which are members of the same electron-transfer series have been synthesized. Refluxing of the reaction mixture containing equimolar amounts of PdCl₂, 2-(2-trifluoromethyl) anilino-4,6-di-tert-butylphenol (H₂L_N,O), 4,4′-di-tert-butyl-2,2′-dipyridyl (^tbpy), and 3 equiv of triethylamine in MeOH under an argon atmosphere followed by exposure to air and addition of KPF₆ after cooling to room temperature yields reddish brown crystals of paramagnetic (S = 1/2) [Pd(LISQN,O)(^tbpy)](PF ₆) (2). Reaction of 2 with one equiv of [CoCp₂] in dry and degassed CH₂Cl₂ using anaerobic conditions gives diamagnetic [Pd(LIPN,O)(^tbpy)] (1), which is the one-electron reduced form of 2. One-electron oxidation of 2 in CH₂Cl₂ under argon with one equiv of NOBF₄ affords diamagnetic [Pd(LIBQN,O)( ^tbpy)](PF₆)(BF₄)·2CH₂Cl ₂ (3). Complexes 1, 2, and 3 constitute three members of the same electron-transfer series. They are ideally suited to distinctly distinguish the geometrical and spectroscopic features of the N,O-coordinated, closed-shell, diamagnetic o-iminophenolate (LIPN,O)^2-, the corresponding open-shell π-radical o-iminobenzosemiquinonate (LISQN,O)^1- (S_rad = 1/2), and the closed-shell o-iminobenzoquinone (LIBQN,O)⁰ forms. All complexes were characterized by X-ray crystallography (100 K), cyclic voltammetry, EPR, and UV-vis spectroscopy. Complex 2 exhibits three reversible electron transfer waves in the cyclic voltammogram. Structural characterization of complex 3 reveals an interesting strong ion pairing between the BF ₄ anion and the complex dication with a short C-F distance of 2.7 A. The Royal Society of Chemistry.

Full text of DOI:10.1039/b614745c

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www.rsc.org/dalton | Dalton Transactions
Molecular and electronic structure of square planar complexes
ISQ
[PdII(tbpy)(LNIP,O)]0, [PdII(tbpy)(L )](PF6), and
N,O
IBQ
N,O
[PdII(tbpy)(L )](PF6)(BF4)·2CH2Cl2: an o-iminophenolato
based ligand centered, three-membered redox series
Swarna-Latha Kokatam, Phalguni Chaudhuri, Thomas Weyhermu¨ller and Karl Wieghardt*
Received 10th October 2006, Accepted 9th November 2006
First published as an Advance Article on the web 28th November 2006
DOI: 10.1039/b614745c
Three PdII complexes which are members of the same electron-transfer series have been synthesized.
Refluxing of the reaction mixture containing equimolar amounts of PdCl2,
2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol (H2LN,O ), 4,4ꢀ-di-tert-butyl-2,2ꢀ-dipyridyl (tbpy),
and 3 equiv of triethylamine in MeOH under an argon atmosphere followed by exposure to air and
addition of KPF6 after cooling to room temperature yields reddish brown crystals of paramagnetic (S =
ISQ
1/2) [Pd(L )(tbpy)](PF6) (2). Reaction of 2 with one equiv of [CoCp2] in dry and degassed CH2Cl2
N,O
IP
using anaerobic conditions gives diamagnetic [Pd(L )(tbpy)] (1), which is the one-electron reduced
N,O
form of 2. One-electron oxidation of 2 in CH2Cl2 under argon with one equiv of NOBF4 affords
IBQ
diamagnetic [Pd(L )(tbpy)](PF6)(BF4)·2CH2Cl2 (3). Complexes 1, 2, and 3 constitute three members
N,O
of the same electron-transfer series. They are ideally suited to distinctly distinguish the geometrical and
spectroscopic features of the N,O-coordinated, closed-shell, diamagnetic o-iminophenolate (L )2−, the
IP
N,O
ISQ
•
1−
corresponding open-shell p-radical o-iminobenzosemiquinonate (L
)
(Srad = 1/2), and the
N,O
IBQ
closed-shell o-iminobenzoquinone (L )0 forms. All complexes were characterized by X-ray
N,O
crystallography (100 K), cyclic voltammetry, EPR, and UV-vis spectroscopy. Complex 2 exhibits three
reversible electron transfer waves in the cyclic voltammogram. Structural characterization of complex 3
reveals an interesting strong ion pairing between the BF4 anion and the complex dication with a short
˚
C–F distance of 2.7 A.
two neutral closed-shell o-iminobenzoquinone ligands has been
reported recently.10
Introduction
It is now well established1–10 that o-aminophenols are redox non-
innocent and bind to transition metal ions in four forms: (1)
In this context we have studied a series of PdII complexes where
the Pd ion is N,O-coordinated to one 2-(2-trifluoromethyl)anilino-
4,6-di-tert-butylphenol (H2LN,O )
9,10 and one N,N-coordinated 4,4ꢀ-
the paramagnetic o-iminobenzosemiquinonate(1−) monoanionic
radical ((LISQ
)
•; Srad = 1/2), (2) the diamagnetic monoanionic
1−
di-tert-butyl-2,2ꢀ-dipyridyl (tbpy); tbpy was used instead of simple
bipyridyl (bpy) to prevent stacking of molecules in the solid state.
Here, we present the syntheses, structural, and spectroscopic char-
o-aminophenolate (LAP)1−, (3) the dianionic o-iminophenolate
(LIP)2−, and (4) the neutral o-iminobenzoquinone (LIBQ)0. Note
that the o-aminophenolate(1−) anion (LAP
)
is the protonated
1−
acterizations of the diamagnetic neutral species [Pd(L )(tbpy)]
IP
N,O
form of the dianion (LIP)2−. High-resolution low-temperature X-
ray crystallography allows the assignment of the protonation and
ISQ
N,O
(1), the paramagnetic monocation [Pd(L )(tbpy)](PF6) (2), and
IBQ
N,O
the diamagnetic dication [Pd(L )(tbpy)](PF6)(BF4)·2CH2Cl2 (3),
oxidation levels of such an O,N-coordinated ligand in a given
which are members of the same electron transfer series. Complexes
complex. Average bond distances in the (LISQ
)
•, (LAP)1−, (LIP)2−,
1−
1, 2 and 3 are ideally suited to establish a comparison of the
and (LIBQ)0 forms of the ligands in transition metal complexes
have been proposed in the literature.7,10 A number of complexes of
Ni(II), Pd(II), Cu(II), Cr(III), and Co(III) containing o-aminophenol
ligand analogues in different oxidation states, namely closed-
shell o-iminophenolate and open-shell o-benzosemiquinonate p
radicals, have been isolated.2,5,7,9,10 Complexes containing closed-
shell quinone type ligands like [MII(0LINB,QO)(bpy)]2+, [MII(0LINB,QO)2]2+
have been proposed in a number of square planar complexes
from spectroelectrochemical results.2,7,9,11,12 However, only one
crystal structure, namely that of [PdII(LINB,QO)2](BF4)2 containing
structural, spectroscopic, and geometrical features of an O,N-
ISQ
coordinated monoanionic p radical (L
)
1− versus its one-electron
N,O
reduced dianion (L )2−, and its one-electron oxidized neutral
IP
N,O
IBQ
quinone (L )0. Similar neutral and monocationic complexes of
N,O
Pd with one N,O-coordinated o-aminophenolate (0L
)
ligand
IP
N,O
2−
and one N,N-coordinated bpy ligand have been reported earlier.7
The square planar, singly N,O-coordinated complexes with the
complete quinone form of ligand, on the other hand, has not
been structurally characterized previously, although the latter were
proposed on the basis of spectroscopic data.7
The present X-ray diffraction study reveals that the dication in
3 exhibits an interesting, strong ion pairing interaction with the
BF4 anion.
Max-Planck-Institut fu¨r Bioanorganische Chemie, Stiftstrasse 34-36, D-
45470, Mu¨lheim an der Ruhr, Germany
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Results and discussion
Syntheses and spectroscopic characterizations
The reaction of equimolar amounts of PdCl2, 4,4-di-tert-butyl-2,
2ꢀ-dipyridyl and 2-(2-trifluoromethyl)aniline-4,6-di-tert-butyl-
phenol in refluxing methanol in the presence of triethylamine
(∼3 equivalents) under an Ar atmosphere affords upon exposure
to air and cooling to 20 ◦C and addition of KPF6 crystals of
[PdII(tbpy)(LNIS,QO)](PF6) (2) in ∼50% yield.
Oxidation of
2 in CH2Cl2 solution with one equiva-
lent of [NO]BF4 yielded brown crystals of [PdII(tbpy)(LNIB,QO)]-
(PF6)(BF4)·2CH2Cl2 (3) in ∼56% yield whereas the reduction of
2 in CH2Cl2 with one equivalent of cobaltocene afforded the blue
neutral species [PdII(tbpy)(L )] (1) in ∼90% yield.
IP
N,O
Fig.
2
Cyclic voltammogram of 2 in CH2Cl2 solution (0.10 M
Magnetic susceptibility and 1H NMR measurements of 1
and 3 showed that these materials are diamagnetic (S = 0).
In contrast, for a solid sample of 2 temperature dependent
(20–300 K) magnetic susceptibility measurements established a
temperature independent magnetic moment of 1.72 lB (g = 1.99)
per formula unit. This indicates an S =1/2 ground state. The X-
band EPR spectrum of 2 in CH2Cl2 solution at 10 K exhibits an
isotropic signal at giso = 2.0073 without detectable Pd hyperfine
splitting. This is indicative of the presence of an organic radical
in 2 rather than a low spin PdIII ion. Fig. 1 shows the Pd(LN,O )-
fragments in 1, 2 and 3.
[N(n-Bu)4]PF6) at a glassy carbon working electrode recorded at a scan
rate of 200 mV s−1. Ferrocene was used as internal standard.
waves at E1/2 = +0.43, −0.65 and −1.99 V, respectively. From
controlled potential coulometric measurements it was established
that the first wave corresponds to a one-electron oxidation of 2
whereas the other two correspond to two successive one-electron
reductions, eqn (1).
+e
+e
[PdII(tbpy)(LNIB,QO)]2+ ≡ [PdII(tbpy)(LISQ )]+ ≡
N,O
−e
−e
1
2
E
E
(1)
+e
[PdII(tbpy)(LIP )]0 ≡ [PdII(tbpy)(LIP )]−
N,O
N,O
−e
3
E
The above cv is very similar to that reported for
[PdII(bpy)(0LNIS,QO)]PF6.7 The one-electron reduction of [PdII(t-bpy)-
IP
(L )]0 to the monoanion at −1.99 V corresponds to a ligand
N,O
centered one-electron reduction of the N,N-coordinated ligand
(tbpy) to its p-radical monoanion (tbpy)1−•. This has been reported
for similar bpy complexes of PdII and PtII.8c–d
The electronic spectra of 1, 2 and 3 in CH2Cl2 solutions at 20 ◦C
are shown in Fig. 3. These spectra are very similar to those reported
ISQ
IBQ
IP
N,O
for [PdII(bpy)(0L )], [PdII(bpy)(0LN,O)]+, and [PdII(bpy)(0LN,O)]2+
in ref. 7 as pointed out before a single N,O-coordinated p radical
ISQ
N,O
• gives rise to four intraligand charge transfer bands
1−
anion (L
)
Fig. 1 Structural formulae of the Pd(LN,O )-fragments in 1, 2 and 3.
The cyclic voltammogram of 2 shown in Fig. 2 has been recorded
at 20 ◦C in CH2Cl2 solution containing 0.10 M [N(n-Bu)4]PF6 as
supporting electrolyte at a glassy carbon working electrode. Those
of 1 and 3 have also been recorded; they are similar to that of
2 and are not shown. Ferrocene was used as internal standard,
and potentials are referenced vs. the ferrocenium/ferrocene couple
(Fc+/Fc). The cv displays three reversible one-electron transfer
Fig. 3 Electronic spectra of 1 (dotted line), 2 (solid line) and 3 (dashed
line) in CH2Cl2 solution (0.20 M [N(n-Bu)4]PF6).
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Table 1 Electronic spectra of complexes in CH2Cl2 solution at 25 ◦
C
˚
Table 2 Selected bond lengths (A) in 1, 2 and 3
Complex
kmax/nm (104 e/L mol−1 cm−1
)
1
2
3
350sh(1.0), 400sh(0.75), 708(1.08)
436(0.59), 460sh(∼0.5), 770sh(∼0.05), 850(0.07), 950sh
385(0.73), 549sh(∼0.11)
>450 nm with molar extinction coefficients of 0.5–7.0 × 103 L
mol−1 cm−1 (see Table 1).
The X-band EPR spectrum of 2 in CH2Cl2 solution at 298 K is
1
2
3
shown in Fig. 4. It displays a hyperfine split S = 1/2 signal at giso
=
2. A satisfactory simulation was obtained by using the following
parameters: a(14N) = 19.6 MHz (6.99 G), a(1H) = 13.4 MHz
(4.78 G), a(105Pd, I = 2.5, 22.2%) = 9.0 MHz (3.21 G), and a line
width of 2.0 G. These data show the iminosemiquinone character
Pd–N1
Pd–N2
Pd–N3
Pd–O
N1–C6
O–C1
N1–CPh
C1–C6
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
1.981(1)
2.042(1)
2.011(1)
1.969(1)
1.387(2)
1.353(1)
1.404(2)
1.415(2)
1.404(2)
1.413(2)
1.395(2)
1.399(2)
1.396(2)
2.021(2)
2.009(2)
1.994(2)
1.983(2)
1.360(4)
1.307(4)
1.424(4)
1.439(4)
1.422(4)
1.381(4)
1.439(4)
1.355(4)
1.422(4)
2.050(3)
2.012(3)
1.989(3)
2.024(2)
1.306(4)
1.242(4)
1.439(4)
1.499(4)
1.458(4)
1.354(5)
1.466(5)
1.345(5)
1.428(4)
•
1−
of the ligand (LISQ
)
N,O-coordinated to a diamagnetic Pd(II)
center. The spectrum is again very similar to that reported for
[PdII(bpy)(LISQ)]+.
IP
N,O
1, 2 and 3 clearly allow their identification as a dianion (L
)
2− in
ISQ
•
1−
neutral 1, a p radical monoanion (L
)
in the monocation of
2, and as a neutral o-iminobenzoquinone (L )0 in the dication
N,O
IBQ
N,O
in 3. It is revealing that the (tbpy) ligand in the three structures
have identical corresponding C–C and C–N bond lengths within
experimental error (3r). Thus, the geometrical parameters of the
(tbpy)PdII-fragments are nearly identical in the three structures
and the redox processes are predominantly localized on the o-
iminophenolate ligand. Fig. 5 displays the structure of the dication
IBQ
(top) and the ion pair {[PdII(tbpy)(LN,O)](BF4)} (bottom) in
crystals of 3. The structures of the neutral molecules in 1 and
of the monocation in crystals of 2 are similar and not shown. The
structure of 1 consists of well separated, square-planar molecules
+
Fig. 4 X-Band EPR spectrum of 2 in CH2Cl2 solution at 298 K
(conditions: frequency 9.4328 GHz, power 8.0 mW, modulation amplitude
1.0 G).
IP
of [PdII(tbpy)(L )]. The C–C, C–N and C–O bond distances
N,O
(Table 2) are clearly those of a closed shell, diamagnetic dianion
IP
N,O
(L
)
2− which renders the central metal ion a Pd(II) ion (d8) which
is coordinated to a neutral closed shell tbpy ligand.
Crystal structures
The structure of 2 consists of the monocation [PdII(tbpy) (LNIS,QO)]+
and well separated PF6− anions. The C–C, C–N, and C–O distances
of the o-iminophenolate derivative are indicative of the open-shell
From previous work we have identified the following structural
markers for the N,O-coordinated o-iminophenolate dianion,
ISQ
ISQ
•
•. The geometry of the PdII(tbpy)
IP
N,O
1−
1−
(L )2−, the o-iminosemiquinonate radical monoanion, (LN,O
)
,
p radical monoanion (L
)
N,O
IBQ
and the neutral o-iminebenzoquinone, (L )0: (a) the C–N bond
fragment is as in 1. Thus, an organic p radical monoanionic ligand
(Srad = 1/2) is N,O-coordinated to the diamagnetic fragment
[PdII(tbpy)]2+ yielding an St = 1/2 ground state.
N,O
length of the respective iminophenolate ring system decreases from
1.37 0.01 to 1.35 0.01, and finallyto 1.30 0.01with increasing
oxidation level; (b) similarly, the corresponding C–O bond length
Finally, the structure of 3 is interesting (Fig. 5). It consists of
the dication [PdII(tbpy)(LNIB,QO)]2+, BF4− and PF6− monoanions (1 : 1)
and dichloromethane solvent molecules. Fig. 5 (bottom) exhibits
the structure of the dication. The very short C–N and C–O bond
lengths indicate double bond character in both cases. In addition,
the alternating two short C–C bonds in the corresponding six-
˚
decreases from 1.35 0.01 to 1.30 0.01 to 1.24 0.01 A; and
(c) the six C–C bonds of the iminophenolate six-membered ring
IP
2−
˚
are nearly equidistant at 1.407 0.01 A in (LN,O
)
indicating the
aromatic, closed shell character of this phenyl ring. One-electron
ISQ
•
1−
oxidation to (L
˚
)
yields two alternating short C–C bonds at
N,O
∼1.36 0.01 A of partially double bond character and four longer
membered ring system are in excellent agreement with a neutral,
IBQ
˚
ones at 1.438 0.01 A. This characteristic distortion is labelled
diamagnetic o-iminoquinone ligand (L )0. Interestingly, the
N,O
IBQ
−
“quinoid-like”. In the neutral quinone form, (L )0, this distortion
dication forms unique ion pairs with the BF4 anions, namely
N,O
IBQ
+
−
is even more pronounced.
Thus, the observed C–N, C–O and C–C bond lengths summa-
rized in Table 2 for the respective o-iminophenolate derivative in
{[PdII(tbpy) (LN,O)]BF4} . The PF6 ions balance the charge; they
are well separated from the above ion pairs. As shown in Fig. 5
(bottom) in the solid state there are two structurally slightly
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ISQ
IBQ
Fig. 6 Structure of the ion pair [Pd(L )(L )](BF4) from ref. 10.
N,O
N,O
◦
argon blanketing atmosphere with stirring for 1 h at 20 C. The
solvent was then removed by evaporation in vacuo and the
resulting blue powder was redissolved in CH3OH (6 mL). A
yellow solid material, [CpCo]PF6 was filtered off. Slow evaporation
of the solvent produced blue crystals of 1 suitable for X-ray
crystallography. Yield: 0.20 g (92%). Elemental analysis: C, 63.5;
H, 6.6; N, 5.6; Pd, 14.4%. Calculated (C39H48F3N3OPd): C, 63.4;
+
H, 6.6; N, 5.7; Pd, 14.4%. ESI-MS (CH2Cl2), m/z: 737 {M} .
[PdII(tbpy)(LNIS,QO)](PF6) (2). To a solution of PdCl2 (0.18 g;
1.0 mmol) in CH3OH (20 mL) was added triethylamine (0.8 mL),
the ligand H2(LINP,O) (0.37 g; 1.0 mmol) and 4,4ꢀ-di-tert-butyl-2,2ꢀ-
dipyridyl (tbpy) (0.27 g; 1.0 mmol). The mixture was heated to
reflux under Ar for 1 h. The solution was allowed to cool to 20 ◦C
in an open vessel in the presence of air. Then KPF6 (0.8 g) dissolved
in CH3OH (10 mL) was added. After stirring for 3 h, the filtered,
reddish-brown solution was allowed to stand in an open vessel for
12 h after which time X-ray quality crystals of 2 were obtained.
Yield: 0.46 g (53%). Elemental analysis: C, 53.2; H, 5.3; N, 4.6; Pd,
12.0. Calculated (C39H48F9N3OPPd): C, 53.0; H, 5.5; N, 4.8; Pd,
Fig. 5 Structure of the dicationic complex 3 (top) (50% probability for
ellipsoids). The bottom structure represents the two forms of the ion pair
IBQ
+
{[PdII(tbpy)(LN,O)](BF4)} in 3 (see text).
−
different ion pairs present. One fluorine atom F(74) of the BF4
˚
ISQ
+
12.0. ESI-MS (CH2Cl2), m/z: 882 {Pd(tbpy)(LN,O)PF6} .
forms a short contact to the carbon atom C(1) at 2.700 A. The
resulting ion pair is present in 69%. On the other hand, in the
second ion pair (31%) fluorine atom F(71X) forms a relatively
[PdII(tbpy)(LNIB,QO)](PF6)(BF4)·2CH2Cl2 (3). To a dry, deaerated
solution of 2 (0.10 g; 0.11 mmol) in CH2Cl2 (7 mL) was
added [NO]BF4 (0.013 g; 0.11 mmol) under an Ar blanketing
atmosphere at 20 ◦C. After stirring for 2 h, a brown solution
was obtained which was filtered and topped with a layer of n-
heptane. The solvents were allowed to slowly evaporate which
gave rise to X-ray quality brown crystals of 3. Yield: 0.07 g (56%).
Elemental analysis: C, 43.9; H, 4.7; N, 3.7; Pd, 8.7. Calculated
(C41H52F13N3Cl2OBPPd): C, 43.2; H, 4.6; N, 3.7; Pd, 9.25.
˚
short contact to the palladium ion at 2.795 A. The quinone ligand
IBQ
(L )0 and the Pd(II) ion are obviously relatively electron poor
N,O
and carry partial positive charges. As has been noted before,
IBQ
paramagnetic [PdII(LNIS,QO)(L )]+ also forms an ion pair with a
N,O
−
BF4 counteranion in the solid state.10 This is shown in Fig. 6.
˚
The asymmetric F(63) · · · C contact is at 2.710 A and localizes the
ISQ
N,O
IBQ
N,O
•
1−
unpaired electron of (L
)
at this site. It is the (L ) site which
is electron poor and, consequently, forms the C · · · F contact.
X-Ray crystallographic data collection and refinement of the
structures
Experimental
Synthesis
A deep green single crystal of 1, an orange brown crystal of 2, and
a red crystal of 3 was coated with perfluoropolyether and picked
up with a glass fibers. The crystals were immediately mounted
in the nitrogen cold stream (100 K) of a Nonius Kappa-CCD
diffractometer equipped with a Mo-target rotating-anode X-ray
The ligand 2-(2-trifluoromethyl)aniline-4,6-di-tert-butylphenol,
H2(LINP,O) has been prepared as is described in ref. 9.
[PdII(tbpy)(L )] (1). To
a dry, deaerated solution of
IP
N,O
[PdII(tbpy) (LNIS,QO)](PF6) (2) (0.26 g; 0.29 mmol) in CH2Cl2 (8 mL)
source and a graphite monochromator (Mo-Ka, k = 0.71073 A).
˚
was added cobaltocene, [Cp2Co], (0.06 g; 0.295 mmol) under an
Final cell constants were obtained from least squares fits of all
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Table 3 Crystallographic data for 1, 2 and 3·2CH2Cl2
1
2
3
Chemical formula
FW
C39H48F3N3OPd
738.20
C39H48F9N3OPPd
883.17
C41H52BCl4F13N3OPPd
1139.84
Space group
P2(1)/c, No. 14
14.8500(4)
19.2194(6)
13.7915(4)
110.538(5)
3686.0(2)
4
Pbca, No. 61
17.7791(5)
20.9990(7)
21.6489(7)
90
8082.5(4)
8
100(2)
C2/c, No. 15
37.901(2)
11.5338(6)
26.740(2)
124.352(6)
9650.4(10)
8
˚
a/A
˚
b/A
˚
c/A
b/◦
˚
V/A
Z
T/K
100(2)
1.330
100(2)
1.569
q calcd/g cm−3
Refl. collected/2hmax
Unique refl./I > 2r(I)
No. of param./restr.
1.452
62 403/62.04
11 678/10 737
452/31
5.52/0.71073
0.0261/1.075
0.0603
88 473/52.0
7921/5657
499/0
5.74/0.71073
0.0417/1.037
0.0803
76 981/58.0
12 804/9741
614/94
7.26/0.71073
0.0536/1.043
0.1201
l/cm−1/k/A
˚
R1a/goodness of fitb
wR2c (I > 2r(I))
−3
˚
Residual density/e A
+0.73/−0.60
+0.68/−0.60
+1.59/−1.14
c wR2 = [ [w(Fo − Fc2)2]/ [w(Fo2)2]]1/2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a Observation criterion: I > 2r(I). R1 = ꢁFo| − |Fcꢁ/ |Fo|. b GooF = [ [w(Fo − Fc2)2]/(n − p)]1/2
.
2
2
where w = 1/r2(Fo2) + (aP)2 + bP, P = (Fo + 2Fc2)/3.
2
measured reflections. Crystallographic data of the compounds are
listed in Table 3. The Siemens ShelXTL13 software package was
used for solution and artwork of the structure, ShelXL9714 was
used for the refinement. The structures were readily solved by
direct and Patterson methods and subsequent difference Fourier
techniques. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were placed at calculated positions and refined
as riding atoms with isotropic displacement parameters. The
BF4-anion in 3 was found to be disordered and was split on
two positions in a ratio of 69 : 31. B–F and F–F distances
were restrained to be equal within errors (SADI). Equal thermal
displacement parameters were given to the corresponding parts
(EADP). The disorder of a t-butyl group (C(43)–C(46)) in 1 was
treated the same way adopting a ratio of 83 : 17.
685 nm is assigned as an inter-ligand charge transfer transition
(LLCT). The dicationic diamagnetic complex 3 with a neutral
o-iminobenzoquinone ligand has been isolated for the first time.
Identification of (LIBQ)0 has been achieved by the observation of
˚
(i) very short C–O and C–N bond lengths at 1.24 0.01 A and
˚
1.30 0.01 A, (ii) a pronounced quinone type distortion with two
=
alternating short C C and four long C–C in the aminophenolate
ring, and (iii) a quinone charge transfer bands in the UV-vis
spectrum between 350–550 nm. Thus, it is clear that the oxidation
levels of O,N-coordinated o-aminophenolate derivatives can be
established primarily from their high quality crystal structures
and electronic spectra.
Acknowledgements
CCDC reference numbers 281237–281239.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b614745c
We thank the Fonds der Chemischen Industrie for financial
support. S. K. is thankful for a stipend from the Max-Planck
Society.
Conclusions
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In summary,
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˚
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˚
˚
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