First-row transition metal bis(amidinate) complexes; planar four-Coordination of FeII enforced by sterically demanding aryl substituents

Article abstract of DOI:10.1002/ejic.200500094

The sterically hindered benzamidinate ligand [PhC(NAr)₂] ^- (Ar = 2,6-iPr₂C⁶H₃) has been employed to prepare bis(amidinate) complexes [{PhC(NAr)₂} ₂M] of the divalent first-row tr

Full text of DOI:10.1002/ejic.200500094

FULL PAPER
First-Row Transition Metal Bis(amidinate) Complexes; Planar Four-
Coordination of FeII Enforced by Sterically Demanding Aryl Substituents
Christian A. Nijhuis,[a] Erica Jellema,[a] Timo J. J. Sciarone,[a] Auke Meetsma,[a]
Peter H. M. Budzelaar,[b] and Bart Hessen*[a]
Keywords: Transition metals / Solid-state structures / Ligand effects / Amidinate / Density functional calculations
The sterically hindered benzamidinate ligand [PhC(NAr)2]–
(Ar = 2,6-iPr2C6H3) has been employed to prepare bis(amid-
inate) complexes [{PhC(NAr)2}2M] of the divalent first-row
transition metals Cr–Ni (1–5). For Cr (planar), Mn and Co
(tetrahedral) the observed structures follow the electronic
preference for the metal ion in its highest spin multiplicity,
as determined by DFT calculations. Remarkably, the Fe de-
rivative adopts a distorted planar structure while retaining
the high-spin (S = 2) configuration. This rare combination is
due to reduced interligand steric interactions in the planar
vs. the tetrahedral structure, combined with a relatively small
electronic preference of FeII for the tetrahedral environment.
Thus, the simple bidentate ligand N,NЈ-diarylbenzamidinate
provides a convenient means to make this unusual species
accessible for further study.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
chelation), while small substituents lead to a more parallel
orientation of the lone pairs (enabling bridging).[34,35]
The substituents on the amidinate nitrogen atoms can be
used to tune the steric demand of the ligand, influencing the
coordination geometry of the metal centre in bis(amidinate)
complexes with chelating amidinate ligands. Thus, Winter
et al. have demonstrated that an increase in steric demand
of the alkyl substituent R in [{MeC(NR2)}2Cr] from R =
iPr to tBu results in a change from square-planar to tetrahe-
dral coordination of the high-spin CrII centre.[36] For R =
tBu, interligand steric interactions apparently become
dominant over an electronic preference for square-planar
coordination.[37]
Introduction
Amidinate anions, with general formula [RЈNC(R)-
NRЈЈ]–, have been employed widely as ligands in transition
metal and in main group chemistry.[1,2] Their steric and
electronic properties are readily modified through variation
of the substituents on the carbon and nitrogen atoms, and
they have been employed as ancillary ligands in various
catalytic conversions, e.g. oligomerisation[3,4] or polymeris-
ation[5–20] of olefins or of cyclic esters.[21,22] Due to the geo-
metric constraints of the NCN ligand backbone, amidinates
have small N–M–N bite angles (typically 63–65°). They
have a rich coordination geometry in which both chelating
and bridging coordination modes can be achieved. The lat-
ter has allowed the synthesis of a range of dinuclear com-
plexes with short metal–metal separations.[23–34] The bal-
ance between chelating and bridging coordination is criti-
cally governed by the substitution pattern of the amidinate
ligand. Steric interactions between the substituents on the
carbon and nitrogen atoms influence the orientation of the
nitrogen lone pairs. Large substituents on the carbon atom
induce a convergent orientation of the lone pairs (favouring
The steric hindrance imparted by alkyl substituents on
the amidinate nitrogen atoms has its main effect in the
NMN coordination plane. To effect steric shielding above
and below this coordination plane, two approaches are pos-
sible. Introduction of a terphenyl substituent on the amidin-
ate backbone carbon atom provides such shielding (as
shown by Arnold et al. in complexes of LiI, MgII, AlIII
,
YIII and a series of first-row transition metals),[38–43] but
relatively remote from the metal–ligand bonds. Another ap-
proach is the use of ortho-disubstituted aryl groups on the
[a] Dutch Polymer Institute, Center for Catalytic Olefin Polymeri-
sation, Stratingh Institute for Chemistry and Chemical Engi- nitrogen atoms. By virtue of the perpendicular orientation
neering, University of Groningen,
of the aryl moieties with respect to the NCN backbone (es-
Nijenborgh 4, 9747 AG Groningen, Netherlands
pecially when relatively large substituents on the carbon
atom are used), the ortho substituents provide steric protec-
tion to the sites above and below the coordination plane.
The 2,6-(diisopropyl)phenyl group (Ar = 2,6-iPr2C6H3) has
proven to be very efficient in this respect, and has been
used successfully in the development of late transition metal
olefin polymerisation catalysts with neutral diimine li-
Fax: +31-50-363-4315
E-mail: hessen@chem.rug.nl
[b] Dutch Polymer Institute, Institute for Molecules and Materials,
Metal-Organic Chemistry, Radboud University Nijmegen,
P. O. Box 9010, 6500 GL Nijmegen, Netherlands
Fax: +31-24-355-3450
E-mail: p.budzelaar@science.ru.nl
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2005, 2089–2099
DOI: 10.1002/ejic.200500094
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C. A. Nijhuis, E. Jellema, T. J. J. Sciarone, A. Meetsma, P. H. M. Budzelaar, B. Hessen
FULL PAPER
gands[44–47] and in the synthesis of low-coordinate, electron-
deficient metal complexes stabilised by β-diketiminates.[48]
With amidinate ligands, these substituents have been used
only sparingly thus far. The amidines [RC(NAr)2]H (R =
CH3, 4-MeC6H4, 4-MeOC6H4) were synthesised by Boeré
et al., who also reported some initial studies of their Mo0
coordination chemistry.[49] The amidinates [tBuC(NAr)2]–,
[4-MeC6H4C(NAr)2]– and [PhC(NAr)2]– have been used as
ligands for AlIII [50] NiII,[7] group 3 and lanthanide met-
,
als.[9,20,22] Due to the positioning of the steric hindrance of
these ligands, interesting interligand steric interactions may
be anticipated when two of these ligands are attached to
(relatively small) first-row transition metals.
Scheme 1.
Bis(amidinate) complexes of the divalent first-row transi-
tion metal ions have been found to adopt either a (dis-
torted) tetrahedral or a (distorted) square-planar geometry.
The former is observed for bis(amidinates) complexes of
MnII–CoII,[41,51–54] while for bis(amidinate) complexes of
CrII and NiII both types of geometry have been found to
occur.[34,36,41,55–58] In this paper we describe the synthesis
and characterisation of the bis(benzamidinate) complexes
[{PhC(NAr)2}M] (M = Cr–Ni, Ar = 2,6-iPr2C6H3, Fig-
ure 1). Interligand interactions between the sterically de-
The complexes were characterised by elemental analysis,
X-ray diffraction, 1H NMR and IR spectroscopy and solid-
state variable-temperature magnetic susceptibility measure-
ments.
Molecular Structures
The molecular structures of the bis(amidinate) complexes
manding amidinate ligands are found to enforce a distorted were determined by single-crystal X-ray diffraction. Geo-
square-planar geometry onto high-spin FeII, which is excep- metric parameters for the structures displayed in Figure 2
tional for this ion when bound to two bidentate ligands.
are given in Table 1.
All structures show symmetric, chelating coordination of
the amidinate ligands with the aryl and phenyl substituents
making angles of 61–86° (Ar) and 23–51° (Ph) with the N–
M–N coordination planes. The C–N bonds in the amidinate
backbones do not differ significantly in length and the ni-
trogen atoms deviate only slightly from planarity (ΣЄN
=
354–360°), suggesting full electron delocalisation in the
NCN framework. The bite angle of the ligand is restricted
to 64–69° by the geometry of the amidinate backbone.
The Mn and Co complexes 2 and 4 are best described as
distorted tetrahedral, in which the NMN coordination pla-
nes of the two amidinate ligands are inclined at 74.18(15)°
(Mn) and 69.5(4)° (Co), respectively. The average bite
angles in the Mn complex (63.59°) are ca. 2° smaller than
those in the Co analogue (66.3°) reflecting the smaller ionic
radius of the latter metal ion.[59] Consistently, the M–N dis-
tances in the MnII complex are ca. 0.1 Å longer than in the
and CoII derivative.
Figure 1. N,NЈ-Bis(2,6-diisopropylphenyl)benzamidinate
Results and Discussion
Synthesis
The Cr and Ni complexes 1 and 5 show a distorted
planar arrangement of the four coordinating nitrogen
The bis(amidinate) complexes [{PhC(NAr)2}2M] [M = atoms. For bis(amidinate) derivatives of CrII, this coordina-
Cr (1), Mn (2), Fe (3), Co (4)] were obtained by reaction of tion geometry is commonly observed,[34,36,57] but planar co-
the anhydrous metal chlorides with the lithium amidinate ordination in NiII bis(amidinates) is less common, the only
Li[PhC(NAr)2] (Scheme 1). The latter was generated in situ example being the complex [{PhC(NXyl)(NSiMe3)}2Ni]
by deprotonation of the amidine by nBuLi in THF. The (Xyl = 2,6-Me2C6H3) reported recently by Lee et al.[56] The
products were isolated by extraction with hexanes or pen- amidinate NMN coordination planes are inclined at
tane and crystallisation from the same solvents, affording 7.73(10)° (Cr) and 4.13(13)° (Ni), respectively. The average
the air-sensitive, crystalline bis(amidinate) complexes in 48 bite angles in the Cr complex are approximately 4° smaller
(2) to 91% (3) isolated yield. The Ni complex [{PhC- than in the Ni complex, consistent with the smaller ionic
(NAr)2}2Ni] (5) was prepared from the lithium amidinate radius for square planar NiII.[59] The same trend is observed
and [(DME)NiBr2]. This complex was obtained in 47% in the M–N bond lengths, which are significantly shorter
yield after crystallisation from toluene.
for the Ni derivative.
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First-Row Transition Metal Bis(amidinate) Complexes
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Figure 2. Molecular structures of complexes [{PhC(NAr)2}2M] (1–5) (50% ellipsoids). Hydrogen atoms and cocrystallised solvent mole-
cules have been omitted for clarity.
Surprisingly, the Fe complex 3 is also found to adopt a are exclusively tetrahedral. Planar structures for FeII are
distorted-planar coordination geometry. The angle between commonly found with (macrocyclic) tetradentate donor li-
the two NMN coordination planes of 12.37(8)° is slightly gands, which are preorganised for this geometry.[60,61] Ex-
larger than for the Cr and Ni analogues, but still warrants a amples include salen [salen = N,NЈ-ethylenebis(salicylidene-
description of 3 as a distorted planar structure. The planar imine)],[62] calix[4]arene,[63] porphyrins,[64,65] phthalocyan-
coordination geometry in 3 is in sharp contrast to the other ines[66–69] and a number of macrocyclic bis(β-diiminato) li-
homoleptic bis(amidinate) complexes of FeII,[51–54] which gands.[70–73] Planar coordination of FeII by two bidentate
Eur. J. Inorg. Chem. 2005, 2089–2099
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C. A. Nijhuis, E. Jellema, T. J. J. Sciarone, A. Meetsma, P. H. M. Budzelaar, B. Hessen
Table 1. Selected bond lengths and angles for bis(amidinate) complexes [{PhC(NAr)2}2M].
FULL PAPER
Distances [Å]
Cr (1)
Mn (2)
Fe (3)
Co (4)
Ni (5)[a]
M–N1
M–N2
M–N3
M–N4
N1–C1
N2–C1
N3–C32
N4–C32
2.0577(16)
2.0546(18)
2.0575(16)
2.0583(18)
1.340(3)
1.344(2)
1.343(3)
2.111(3)
2.118(3)
2.101(3)
2.123(3)
1.343(4)
1.336(4)
1.340(4)
1.323(4)
2.0662(14)
2.0532(16)
2.0639(12)
2.0528(16)
1.335(2)
1.338(2)
1.336(2)
1.989(7)
2.029(6)
1.998(7)
2.012(6)
1.317(10)
1.342(12)
1.322(9)
1.346(11)
1.918(2)
1.9288(18)
1.918(2)
1.9288(18)
1.344(3)
1.338(3)
1.344(3)
1.338(3)
1.345(2)
1.338(2)
Angles(°)
N1–M–N2
N1–M–N3
N1–M–N4
N2–M–N3
N2–M–N4
N3–M–N4
M–N1–C1
M–N1–C8
C1–N1–C8
M–N2–C1
M–N2–C20
C1–N2–C20
M–N3–C32
M–N3–C39
C32–N3–C39
M–N4–C32
M–N4–C51
C32–N4–C51
N1–C1–N2
N1–C1–C2
N2–C1–C2
N3–C32–N4
N3–C32–C33
N4–C32–C33
64.87(7)
177.08(6)
115.70(7)
114.71(7)
174.69(6)
65.00(7)
63.55(9)
133.73(10)
125.83(10)
132.3(1)
152.41(10)
63.63(9)
92.00(19)
140.4(2)
123.2(3)
91.92(19)
141.3(2)
124.7(3)
91.55(18)
143.2(2)
121.5(3)
91.08(19)
143.6(2)
123.7(3)
112.5(3)
122.4(3)
125.2(3)
113.5(3)
122.6(3)
123.8(3)
65.06(6)
174.93(5)
114.72(6)
116.11(5)
171.86(5)
64.90(5)
91.25(10)
142.12(12)
124.56(15)
91.75(11)
141.81(11)
124.49(15)
91.59(9)
142.69(11)
124.50(13)
92.03(11)
140.03(11)
125.18(15)
111.93(15)
124.08(14)
123.99(16)
111.42(14)
124.51(14)
124.06(15)
66.2(3)
140.4(3)
129.3(3)
123.7(3)
146.8(2)
66.4(3)
68.63(8)
177.12(8)
111.42(8)
111.42(8)
178.29(9)
68.63(8)
91.88(15)
138.35(16)
124.0(2)
91.57(14)
139.36(18)
124.5(2)
91.88(15)
138.35(16)
124.0(2)
91.57(14)
139.36(18)
124.5(2)
107.9(2)
125.7(2)
126.4(2)
107.9(2)
125.7(2)
126.4(2)
92.25(11)
141.74(14)
123.99(17)
92.27(13)
138.69(13)
124.91(17)
92.20(11)
140.60(14)
124.11(17)
92.09(13)
141.20(13)
123.91(17)
110.52(17)
124.97(17)
124.49(19)
110.69(17)
124.66(17)
124.64(18)
92.4(6)
140.2(5)
124.7(7)
89.9(4)
142.9(6)
123.9(6)
92.0(5)
137.6(5)
124.8(7)
90.7(4)
143.1(6)
124.8(6)
111.2(7)
124.5(8)
124.3(7)
110.7(7)
124.8(8)
124.4(7)
[a] For ease of comparison, the atoms of the Ni complex (5) have been labelled here in analogous fashion to that in the other complexes,
in spite of its crystallographic C2 symmetry (N1_a Ǟ N3, N2_a Ǟ N4, C1_a Ǟ C32 etc.).
ligands is exceptional, although some bis(dithiolato)FeII di- a departure from the Curie–Weiss law is seen at elevated
anions have been structurally characterised as distorted temperatures. This behaviour indicates the presence of a
square-planar.[74,75]
temperature-independent paramagnetism (TIP) contri-
A prominent feature of the complexes with the planar bution, which is not unusual for tetrahedral CoII.[76] Over
structure, 1, 3 and 5, is that the Ar substituents are all tilted the temperature range of 25–175 K, the susceptibility of 4
relative to the coordination plane to minimise interligand can be described by Curie–Weiss behaviour with θ = –5.6 K.
repulsion by interlocking the iPr substituents. This imparts
to these compounds an approximate D2 symmetry. It is seen
by NMR spectroscopy that this behaviour is also present in
solution (vide infra).
Magnetic Properties
Except for the diamagnetic Ni derivative 5, all the bis-
(amidinate) derivatives reported here are paramagnetic.
Variable-temperature magnetic susceptibility measurements
were performed on crystalline samples of 1–4. In view of
the low symmetry of the complexes, d-orbital degeneracy is
expected to be largely removed, thus quenching most or-
Figure 3. Temperature dependence of reciprocal susceptibility for
bital contributions to the ground state. Normal Curie–
1 (diamonds), 2 (squares), 3 (triangles) and 4 (circles). Solid lines
Weiss behaviour is therefore anticipated. Indeed, plots of
represent best fits to Curie–Weiss law.
χ–1 vs. T in the range 25–300 K (Figure 3) show good linear
correlation for the Cr, Mn and Fe complexes with θ =
The room temperature magnetic moments of the com-
–2.3, –1.3 and 2.5 K, respectively. For the Co derivative 4 plexes 1 (4.7 μB), 2 (5.9 μB), 3 (5.4 μB) and 4 (5.1 μB) are
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First-Row Transition Metal Bis(amidinate) Complexes
FULL PAPER
indicative of maximum spin multiplicity for all four com- overlap of resonances. In contrast, the Fe and Co bis(amid-
pounds. The observed magnetic moments for 1, 3 and 4 inate) complexes display spectra that consist mainly of well-
deviate noticeably from the spin only values [4.90 μB for S separated, broad singlets. The chemical shifts in the 1H
= 2 (Cr and Fe) or 3.87 μB for S = 3/2 (Co)], but are well NMR spectrum of the Fe complex 3 span a range from ca.
within the ranges usually observed for high-spin d4, d6 and +60 to –30 ppm, displaying 11 lines. For the Co complex 4,
d7 metals.[77]
twelve lines are observed from ca. +120 ppm to –140 ppm.
The high spin (S = 2) ground state of planar bis(amidin- Full interpretation of these spectra is complicated, but the
ate) 3 contrasts with the more usual observation of an inter- number of resonances indicates that the solution structures
mediate spin state (S = 1) for FeII complexes with this ge- have symmetries lower than D2h (3) and D2d (4). This
ometry,[60,61] and is more common for tetrahedral FeII.[37,78] strongly suggests that also for the Fe and the Co derivatives
The planar FeII complexes of N4 macrocycles and dithiol- the sterically demanding aryl substituents cause restricted
ates all exhibit intermediate spin states,[64,66–75] with the motion of the aryl rings in solution.
planar, but high-spin, salen[62] and calix[4]arene[63] com-
plexes of FeII constituting the only exceptions.
Calculations
1H NMR Spectroscopy
DFT calculations were used to obtain more insight into
the factors that determine the coordination geometry of
The room-temperature 1H NMR spectrum of the dia-
these complexes. In order to separate electronic from steric
magnetic Ni complex 5 in [D6]benzene shows two septuplets
contributions, calculations were performed on the model
for the isopropyl methine protons and four doublets for the
complexes [{HC(NH)2}2M] containing an unsubstituted
isopropyl methyl protons. This is consistent with the ap-
proximate D2 symmetry observed in the solid state in which
the aromatic rings are tilted with respect to the N4Ni coor-
dination plane. This inclination establishes a propeller-like
formamidinate ligand. The system was studied at the
B3LYP/SV level using the GAMESS-UK program,[81] using
the spin-restricted (S = 0) or spin-unrestricted (S Ͼ 0) for-
malism; see Exp. Sect. for details. For every metal, both
arrangement of the six aromatic rings, thus imparting a
planar and perpendicular geometries were optimised (con-
screw-sense to the molecule. Apparently, libration of the
strained to D2h and D2d symmetry, respectively); the spin
aryl groups, inverting the screw sense through a D2h-sym-
states assumed for these calculations were the ones found
metric transition state (Figure 4), is slow on the NMR time
scale at ambient temperature. Warming a solution of 5 in
experimentally for the fully substituted system. In Table 2,
the geometries calculated to be most stable for the model
[D8]toluene results in gradual broadening of the isopropyl
system are compared to those observed experimentally. The
resonances, but coalescence is not yet reached at 110 °C.
energy differences between the calculated perpendicular and
Nevertheless, slow chemical exchange of the two isopropyl
methine and the two sets of methyl signals is confirmed by
planar geometries are included.
positive cross-peaks in the EXSY 2D-spectrum.
Table 2. Relative energies of tetrahedral vs. planar geometries of
[{HC(NH)2}2M] by DFT calculations.
X-ray
[{PhC(NAr)2}2M]
S
B3LYP/SV
[{HC(NH)2}2M]
ΔEtet.–plan
[kJ·mol–1]
Cr
Mn
Fe
Co
Ni
planar
tetrahedral
planar
tetrahedral
planar
2
5/2
2
3/2
0
planar
100
tetrahedral
tetrahedral
tetrahedral
planar
–27.3
–10.1
–23.2
[a]
–
[a] No reasonable orbital occupation for perpendicular S = 0 struc-
ture.
Figure 4. Epimerisation process in [{PhC(NAr)2}2Ni] (5).
The rate constant for the interconversion of the enantio-
For the model complexes, most of the geometries pre-
mers k = 2.25(38) s–1 at 338 K was obtained by plotting the dicted on electronic grounds match the experimental ones,
extent of exchange vs. the mixing time.[79] The free energy except for Fe (Table 2). However, the calculated energy dif-
of activation ΔG‡338 = 80.9(4) kJ·mol–1 was calculated from ference between the two geometries is significantly smaller
the rate constant k.[80]
for Fe than for either Mn or Co. These results for the model
In contrast to the Ni complex, the paramagnetic bis- system indicate that the observed geometries are deter-
(amidinates) 1–4 exhibit broad, shifted lines in their 1H mined mainly by the intrinsic electronic preference of the
NMR spectra in [D6]benzene. The Cr complex 1 shows metal. For the special case of Fe, where this preference is
resonances in the region +20 to –10 ppm. Severe overlap calculated to be small, steric factors probably dominate;
of the resonances renders the spectrum uninformative. The these seem to favour the planar structure due to a more
resonances of the Mn derivative 2 appear in the same spec- efficient reduction of interligand repulsion by tilting of the
tral region, with even more line-broadening and inherent aryl substituents.
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Decrease of Ligand Size
Table 3. Selected interatomic distances and angles for
[{Ph(NAr)(NXyl)}2Fe] (6).
To see whether a slight decrease in ligand steric demand
could already cause a reversion of the FeII bis(amidinate)
structure to distorted tetrahedral, the asymmetric amidinate
ligand [PhC(NAr)(NXyl)]– (Ar = 2,6-iPr2C6H3, Xyl = 2,6-
Me2C6H3) was prepared. Reaction of FeCl2 with 2 equiv.
of the amidinate lithium salt resulted in formation of cis-
[{PhC(NAr)(NXyl)}2Fe] (6, Scheme 2) that was character-
ised by single-crystal X-ray diffraction.
Distances [Å]
Fe–N1
Fe–N2
2.0639(10)
2.0697(10)
N1–C13
N2–C13
1.3408(14)
1.3280(14)
Angles [°]
N1–Fe–N2
64.82(4)
125.51(4)
105.97(4)
167.58(4)
140.02(8)
91.40(7)
Fe–N2–C13
Fe–N2–C20
C13–N2–C20
N1–C13–N2
N1–C13–C14
N2–C13–C14
91.51(7)
140.27(8)
127.25(10)
112.23(10)
123.71(10)
124.06(10)
N1–Fe–N1_a
N2–Fe–N2_a
N1–Fe–N2_a
Fe–N1–C1
Fe–N1–C13
C1–N1–C13
123.22(9)
Conclusions
The coordination geometry of the bis(amidinate) com-
plexes of the divalent first-row transition metal ions is gov-
erned by a subtle balance between electronic and steric fac-
tors. This balance can be tipped by variation of the substit-
Scheme 2.
The molecular structure of 6 is shown in Figure 5 and uents on the amidinate nitrogen atoms. It was shown by
selected bond angles and bond lengths are listed in Table 3. Winter et al. that substituents with steric demand in the
It is seen that even with this smaller, asymmetric ligand, the amidinate plane (tBu) can force an ion with an electronic
complex still adopts a distorted square-planar geometry. preference for a planar geometry (CrII) to adopt a tetrahe-
Remarkably, the two 2,6-iPr2C6H3 groups are located on dral structure.[36] The work presented here shows that sub-
the same side of the molecule, with their iPr substituents stituents with steric demand above and below the amidinate
interlocking in a similar fashion as observed in complex 3. plane (2,6-iPr2C6H3) can force an ion with a mild prefer-
The NFeN coordination planes in 6 are inclined at an angle ence for a tetrahedral geometry (FeII) to adopt a planar
of 14.21(6)°, which is only about 2° larger than in 3. The one. Apparently, in this geometry the interligand steric in-
room-temperature magnetic moment of 6 is 5.6 μB, indica- teractions can be more effectively diminished by tilting the
tive of high-spin FeII. Despite the difference in steric de- aryl rings to allow interlocking of the iPr substituents.
mand of the substituents, the two Fe–N distances in 6 are
These substituted amidinate ligands provide a simple way
essentially equal, but the interligand N–Fe–N angle is no- to generate rare high-spin (S = 2) FeII complexes with a
ticeably larger on the side with the Ar substituents planar geometry. It should be interesting to study the reac-
[125.51(4)o] than on the side with the Xyl substituents tivity of these species (especially towards oxygen transfer
[105.97(4)°]. As is the case in the other complexes, the NAr agents) and compare that with the more extensively studied
nitrogen atom deviates slightly from planarity (ΣЄN1
=
reactivity of planar intermediate spin (S = 1) FeII systems
354.64°), whereas the NXyl nitrogen atom is close to per- such as porphyrin and phthalocyanin complexes.
fectly planar (ΣЄN2 = 359.03°).
Experimental Section
General Remarks: All manipulations involving air-sensitive com-
pounds were carried out under nitrogen using standard Schlenk
and drybox techniques. Diethyl ether and THF (99.9% Aldrich)
were percolated through a column of Al2O3 and stored under nitro-
gen. Toluene, hexane and pentane (99.9% Aldrich) were percolated
through a column packed with molecular sieves (4 Å) (90 wt-%)
and Al2O3 (10 wt-%) and stored under nitrogen. Benzene was dis-
tilled from Na/K alloy. Deuterated solvents (Aldrich) were dried
with Na/K alloy and vacuum-transferred before use. Magnetic
susceptibility measurements were performed with a Quantum De-
sign MPMS-7 SQuID magnetometer of the department of Solid
State Chemistry at the University of Groningen. NMR spectra
were recorded with Varian Inova 500, VXR 300 and Gemini 200
instruments. IR spectra were recorded with a Mattson 4020 Galaxy
FT–IR spectrometer. Elemental analyses were performed by the
Microanalytical Department at the University of Groningen or by
Mikroanalytisches Laboratorium H. Kolbe, Mülheim an der Ruhr,
Figure 5. Molecular structure of [{PhC(NAr)(NXyl)}Fe] (6) (50%
ellipsoids). Hydrogen atoms and cocrystallised benzene molecule
have been omitted for clarity.
2094
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2005, 2089–2099

First-Row Transition Metal Bis(amidinate) Complexes
FULL PAPER
Germany. Anhydrous FeCl2 and CoCl2 and [(DME)NiBr2][84]
were prepared according to published procedures. All other chemi-
cals were commercially available products, which were used without
further purification.
of all volatiles in vacuo. The residue was repeatedly extracted with
pentane (10 mL, unless mentioned otherwise) until the extracts
were colourless. The extract was concentrated and cooled to afford
the crystalline bis(amidinate) complex, which was isolated by fil-
tration and dried in vacuo.
[82]
[83]
N-(2,6-Diisopropylphenyl)benzanilide: Benzoyl chloride (39 mL,
0.33 mol) was added to a vigorously stirred mixture of 10% aque-
ous NaOH (240 mL) and 2,6-diisopropylaniline (57.0 mL, 0.30
mol). After 60 min, the solid was collected on a glass filter and
washed several times with water, and once with ethanol. The pro-
duct was dried in vacuo and isolated as a white powder. Yield:
57.6 g (0.19 mol, 65%). 1H NMR (200 MHz, [D1]chloroform, room
temp.): δ = 7.92 (d, J = 6.6 Hz, 2 H, ArH), 7.58–7.05 (m, 8 H,
ArH), 3.15 (sept, J = 6.8 Hz, 2 H, iPr-CH), 1.22 (d, J = 6.8 Hz, 6
[{PhC(NAr)2}2Cr] (1): The general procedure was applied using
0.76 g [PhC(NAr)2]H (1.7 mmol) and 0.11 g CrCl2 (0.86 mmol).
The reaction was stirred for 15 h at room temperature. Extraction
and crystallisation were carried out using hexanes. The product was
obtained as red crystals. Yield: 0.48 g (0.52 mmol, 61%). 1H NMR
(300 MHz, [D6]benzene, room temp.) by deconvolution: δ (Δν ) =
½
15.3 (194), 14.4 (239), 7.0 (140), 5.0 (939), 2.5 (250), 0.9 (5396),
–7.6 (205) ppm (Hz); integral ratio 2:2:2:23:1:20:1. C62H78CrN4
(931.32): calcd. C 79.96, H 8.44, N 6.02; found C 79.31, H 8.49, N
5.95.
H, iPr-CH ) ppm. IR (KBr): ν = 3302 cm–1 (m), 3293 (m), 3270
˜
3
(m), 2956 (m), 2923 (s), 2854 (m), 1640 (s), 1580 (w), 1515 (m),
1486 (m), 1463 (m), 1453 (m), 1380 (w), 1361 (w), 1291 (w) cm–1.
[{PhC(NAr)2}2Mn] (2): The general procedure was applied for li-
gand deprotonation using 1.0 g amidine (2.3 mmol). MnCl2
(143 mg, 1.1 mmol) was added as a solid to the Li[PhC(NAr)2]
solution. The reaction mixture was stirred for 2 h at room tempera-
ture, during which no significant colour change was observed. Off-
white crystals were obtained from pentane at –25 °C. Yield: 0.51 g
(0.54 mmol, 48%). H NMR (300 MHz, [D6]benzene, room temp.)
by deconvolution: δ (Δν ) = 15.1 (2761), 14.1 (566), 6.2 (1465), 3.5
(230), –4.2 (784) ppm (Hz); integral ratio 1:2:11:1:6. C62H78MnN4
(934.27): calcd. C 79.71, H 8.42, N 6.00; found C 79.97, H 8.48, N
5.89.
N-(2,6-Diisopropylphenyl)benzimidoyl Chloride: A mixture of N-
(2,6-diisopropylphenyl)benzanilide (57.6 g, 0.19 mol) and thionyl
chloride (43.1 mL, 0.58 mol) was refluxed for 1 h. The remainder
was distilled using a Kugelrohr apparatus (oven 200 °C, 0.02 Torr),
to give the imidoyl chloride as a yellow, slowly solidifying oil. Yield:
51.3 g (0.17 mol, 90%). 1H NMR (300 MHz, [D1]chloroform, room
temp.): δ = 8.26 (d, J = 5.2 Hz, 2 H, ArH), 7.61–7.50 (m, 3 H,
ArH), 7.24 (s, 3 H, ArH), 2.88 (sept, J = 4.4 Hz, 2 H, iPr-CH),
1.27 (d, J = 4.4 Hz, 6 H, iPr-CH3), 1.21 (d, J = 4.4 Hz, 6 H, iPr-
1
½
CH ) ppm. IR (KBr): ν = 2959 (s), 2926 (s), 1665 (s), 1582 (w),
˜
3
1462 (m), 1451 (m), 1167 (m), 398 (m), 797 (w), 760 (m), 986 (m)
[{PhC(NAr)2}2Fe] (3): The general procedure was applied. The reac-
tion mixture was stirred for 2 h at room temperature, during which
the solution turned dark green. Extraction was performed with
hexanes. The product was isolated as dark green crystals after
recrystallisation from hexanes. Yield: 0.98 g (1.0 mmol, 91%). 1H
cm–1.
N,NЈ-Bis(2,6-diisopropylphenyl)benzamidine and N-(2,6-Diisopro-
pylphenyl)-NЈ-(2,6-dimethylphenyl)benzamidine: The amidines were
prepared from N-(2,6-diisopropylphenyl)benzimidoyl chloride and
the appropriate aniline according to a previously reported pro-
cedure.[9] Yield and characterisation data for N,NЈ-bis(2,6-diisopro-
pylphenyl)benzamidine have been published.[9] Data for N-(2,6-di-
isopropylphenyl)-NЈ-(2,6-dimethylphenyl)benzamidine (obtained
as a mixture of isomers): Yield: 7.4 g (19 mmol, 84%). 1H NMR
(300 MHz, [D1]chloroform, room temp.): δ = 7.53–6.70 (m, 11 H,
ArH), 5.78, 5.75 (2×s overlapping, 1 H, NH), 3.62–3.11 (4× sept
overlapping, 2 H, iPr-CH), 2.42, 2.17, 2.10 (3×s overlapping, 6
H, Xyl-CH3), 1.42, 1.30, 1.07, 0.97 (4×d, J = 6.6 Hz, 12 H, iPr-
CH3) ppm. 13C NMR (75 MHz, [D1]chloroform, room temp.): δ =
154.0, 153.5 (NCN), 145.8, 144.9, 143.4, 139.2, 137.1, 135.4, 134.6,
134.4, 134.0 (ArCipso), 129.3, 129.2 (ArCH), 128.8 (ArCipso), 128.6,
128.4, 128.0, 127.6, 127.5, 126.9, 126.3, 123.5, 123.3, 122.9 (ArCH),
28.4, 28.1 (iPr-CH), 24.4, 24.3, 22.8, 21.9 (iPr-CH3), 18.9, 17.6
NMR (300 MHz, [D6]benzene, room temp.): δ = (Δν integral) =
½,
57.4 (952, 4 H), 31.9 (74.6, 4 H), 22.2 (74.5, 4 H), 16.8 (61.0, 4 H),
14.8 (158, 12 H), 6.23 (140, 4 H), 3.80 (126, 12 H), –2.05 (54.5, 2
H), –5.19 (89.7, 12 H), –6.18 (64.5, 4 H), –29.2 (274, 12 H) ppm
(Hz); one of two expected iPr-CH resonances not observed, poss-
ibly due to extreme line-broadening. C62H78FeN4 (935.18): calcd.
C 79.63, H 8.41, N 5.99; found C 79.44, H 8.47, N 6.05.
[{PhC(NAr)2}2Co] (4): The general procedure was applied, but in
this case no colour change was observed after stirring at room tem-
perature for 30 min. Upon warming the suspension at 50 °C for
30 min, a colour change from green to dark red was observed. The
Co complex was obtained as red crystals after recrystallisation of
the crude product from hexanes. Yield: 0.70 g (0.74 mmol, 65%).
1H NMR (500 MHz, [D6]benzene, room temp.): δ (Δν½, integral) =
115 (697), 60.9 (140, 4 H), 45.3 (1994), 35.0 (80.9, 2 H), 24.8 (110,
12 H), 21.2 (129, 4 H), 2.77 (119, 4 H), –19.0 (86.6, 4 H), –69.6
(1007), –73.2 (431, 12 H), –84.0 (85.8, 12 H), –138 (2461) ppm (Hz);
integration of resonances at δ = 115, 45.3, –69.6 and –138 ppm
inaccurate due to extreme broadness. C62H78CoN4 (938.26): calcd.
C 79.37, H 8.38, N 5.97; found C 78.60, H 8.42, N 5.88.
(Xyl-CH ) ppm. IR (KBr): ν = 3424 (w, NH), 3354 (m, NH), 3058
˜
3
(m), 2942 (s), 2915 (s), 1642 (s), 1614 (s), 1588 (s), 1574 (s), 1494
(m), 1435 (s), 1355 (s), 1326 (m), 1301 (w), 1273 (w), 1255 (w), 1220
(w), 1192 (m), 1179 (m), 1162 (w), 1109 (w), 1099 (w), 1077 (w),
1060 (w), 1043 (w), 1026 (w), 923 (w), 898 (w), 835 (w), 806 (w),
775 (s), 742 (w), 697 (s), 616 (w), 600 (w), 577 (w), 543 (w), 516
(w), 507 (w), 487 (w) cm–1. HRMS (EI): calcd. for C27H32N2:
384.2565; found: 384.2571.
[{PhC(NAr)2}2Ni] (5): The general procedure was applied using
0.53 g (1.2 mmol) [PhC(NAr)2]H and [(DME)NiBr2] (0.19 g,
Complexes [{PhC(NAr)2}2M] (1–5). General Procedure: [PhC- 0.6 mmol) as Ni source. The reaction mixture was stirred under
(NAr)2]H (1.0 g, 2.3 mmol) was dissolved in THF (10 mL). nBuLi reflux conditions for 66 h. The crude product was recrystallised
(2.5 m in hexanes, 0.91 mL, 2.3 mmol) was added and the solution
was stirred for 30 min. The solution of Li[PhC(NAr)2] thus ob-
tained was added dropwise to a suspension of MCl2 (1.1 mmol) in
THF (10 mL). The mixture was stirred under the conditions men-
tioned below for the various derivatives. After the reaction, the sol-
vent was pumped off and the residue was freed of any residual
THF by suspending it in pentane (10 mL) and subsequent removal
from toluene and the resulting red crystals were washed with di-
ethyl ether. Yield: 0.26 g (0.30 mmol, 47%). H NMR (300 MHz,
1
[D6]benzene, room temp.): δ = 6.87–7.03 (m, 12 H), 6.41–6.64 (m,
10 H), 4.24 (sept, J = 7.0 Hz, 4 H), 3.13 (sept, J = 7.0 Hz, 4 H),
2.31 (d, J = 7.0 Hz, 12 H), 1.55 (d, J = 7.0 Hz, 12 H), 0.60 (d, J =
7.0 Hz, 12 H), 0.49 (d, J = 7.0 Hz, 12 H) ppm. 13C NMR (75 MHz,
[D6]benzene, room temp.): δ = 175.1 (NCN), 144.5, 143.3, 141.5
Eur. J. Inorg. Chem. 2005, 2089–2099
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2095

C. A. Nijhuis, E. Jellema, T. J. J. Sciarone, A. Meetsma, P. H. M. Budzelaar, B. Hessen
(3×ipso-C), 130.8, 130.4 (ipso-C), 129.6, 126.8, 125.7, 124.9, 123.6, full three-circle goniometer). The diffractometer was equipped with
FULL PAPER
29.4, 28.5 (2× iPr-CH), 24.4, 24.0, 22.3, 21.4 (4×iPr-CH3) ppm.
C62H78N4Ni (938.04): calcd. C 79.38, H 8.38, N 5.97; found C
79.37, H 8.29, N 5.88.
a 4 K CCD detector set 60.0 mm from the crystal. The crystals
were cooled using the Bruker KRYOFLEX low-temperature device.
Intensity measurements were performed using graphite-monochro-
mated Mo-Kα radiation from a sealed ceramic diffraction tube
(SIEMENS). Generator settings were 50 kV/40 mA. SMART[87]
was used for preliminary determination of the unit cell constants
and data collection control. The intensities of reflections of a hemi-
sphere were collected by a combination of 3 sets of exposures
(frames). Each set had a different φ angle for the crystal and each
exposure covered a range of 0.3° in ω. A total of 1800 frames were
collected with an exposure time of 20.0 s (1, 2, 5) or 10.0 s (3, 4, 6)
per frame. Data integration and global cell refinement was per-
formed with the program SAINT.[87] The final unit cell was ob-
tained from the xyz centroids of 5709 (1), 3348 (2), 6534 (3), 4586
(4), 5447 (5), 9843 (6) reflections after integration. Intensity data
were corrected for Lorentz and polarisation effects, scale variation,
for decay and absorption: a multi-scan absorption correction was
applied, based on the intensities of symmetry-related reflections
measured at different angular settings (SADABS),[88] and reduced
to Fo2. The program suite SHELXTL was used for space group
determination (XPREP).[87] The unit cells[89] were identified as mo-
noclinic; reduced cell calculations did not indicate any higher met-
ric lattice symmetry.[90] For 4, The |E| distribution statistics were
ambiguous about a centrosymmetric/non-centrosymmetric space
group.[91] The space groups were derived from the systematic ex-
tinctions. Examination of the final atomic coordinates of the struc-
ture did not yield extra symmetry elements.[92] The structures of 1,
2, 4, 5 and 6 were solved by Patterson methods and extension of the
model was accomplished by direct methods applied to difference
structure factors using the program DIRDIF.[93] For 3, the struc-
ture was solved by direct methods with SIR-97.[94,95] The positional
and anisotropic displacement parameters for the non-hydrogen
atoms were refined. The unit cell of 2 contains a molecule of hexane
solvent of which one end is highly disordered. One of the C atoms
(C68) was described as occupying two positions with separately
refined site occupancy factors. The s.o.f. of the major fraction re-
fined to a value of 0.625(13). Refinement for 4 was complicated by
a twinning problem. After introducing a twin matrix as detected
by PLATON ([–1 0 0 0 –1 0 0.99 0 1], 180° rotation about the c*
axis), with scale factors for the fractional contributions of the vari-
ous twin components, the structure refined smoothly. The s.o.f. of
the major fraction of the component of the twin model refined to
a value of 0.629(3). All hydrogen atoms of 1, 2, 5 and 6 (except
those belonging to the disordered hexane solvent molecule in 2)
were located from a subsequent difference Fourier synthesis, and
their coordinates and isotropic displacement parameters were re-
fined. For 3, Fourier synthesis resulted in the location of most of
the hydrogen atoms. The remaining hydrogen atoms in 3 and all
hydrogen atoms in 4 were included in the final refinement riding
on their carrier atoms with their positions calculated by using sp2
or sp3 hybridisation at the C atom as appropriate with Uiso = c ×
Uequiv of their parent atom, where c = 1.2 for the non-methyl hydro-
gen atoms and c = 1.5 for the methyl hydrogen atoms and where
values Uequiv are related to the atoms to which the H atoms are
bonded. The methyl groups were refined as rigid groups, which
were allowed to rotate freely. Neutral atom scattering factors and
anomalous dispersion corrections were taken from International
Tables for Crystallography.[96] All refinement calculations and
graphics were performed with the program packages SHELXL[97]
(least-square refinements) and PLATON[98,99] (calculation of geo-
metric data and ORTEP illustrations). No classic hydrogen bonds,
no missed symmetry (MISSYM), but potential solvent-accessible
[{PhC(NAr)(NXyl)}2Fe] (6): LiCH2SiMe3 (0.13 g, 1.4 mmol) was
added to a stirred solution of N-(2,6-diisopropylphenyl)-NЈ-(2,6-
dimethylphenyl)benzamidine (0.53 g, 1.4 mmol) in 15 mL 1%
THF/C6H6 at room temperature. After 15 min, FeCl2 (0.09 g,
0.7 mmol) was added to the yellow solution. The colour of the
mixture changed from yellow to green. The reaction mixture was
stirred for 2 h after which the solvents were removed in vacuo. Re-
sidual THF was removed by suspending the residue in pentane that
was subsequently pumped off. The solid was extracted with ben-
zene (40 mL) until the extracts were colourless. The crude product
was recrystallised from hot benzene, affording 6·C6H6 as green
crystals. Yield: 0.32 mg (0.4 mmol, 50%).1H NMR (300 MHz, [D6]
benzene, room temp.): δ = (Δν , integral): 26.07 (25, 4 H), 25.15
½
(25, 4 H), 16.55 (18, 4 H), 11.79 (235, 12 H), 4.02 (74, 4 H), 0.46
(43, 12 H), –2.57 (19, 2 H), –5.48 (183, 12 H), –7.24 (22, 2 H), –
9.24 (22, 2 H) ppm (Hz). C54H62FeN4·C6H6 (901.07): calcd. C 80.0,
H 7.6, N 6.2; found C 79.6, H 7.8, N 6.3.
1
Determination of k and ΔG‡ for Epimerisation of 5: H 2D EXSY
spectra (500 MHz, [D8]toluene, 338 K) were obtained using the
NOESY sequence (d1–90°–d2–90°–τ–90°–FID) with an extra gradi-
ent during the mixing time τ. The spectral width was 8000 Hz. Mix-
ing times of 0.2, 0.3, 0.4 and 0.5 s were used. The relaxation delay
d1 was 1 s and the increment for the evolution time d2 was 98 μs.
Peak volumes of the isopropyl methine resonances (δ = 4.24 and
3.13 ppm) and their cross-peaks were determined by means of the
Gaussian method in the integration program Sparky.[85] The ratio
of the peak volumes of the cross-peaks and the diagonal peaks (Ix/
Id) was plotted vs. mixing time τ. The rate constants k for the ex-
change process was determined by fitting the data to the equa-
tion[79]
The free energy of activation ΔG‡ at 338 K was calculated by sub-
stitution of k338 according to the relation[80]
Magnetic Measurements: Data were collected on crystalline sam-
ples (ca. 25 mg) from 300 to 5 K at a field of 1000 G. Measured
magnetic susceptibilities are corrected for diamagnetism using Pas-
cal’s constants.[86] Effective magnetic moments are calculated as
X-ray Crystallographic Study: Single crystals suitable for X-ray dif-
fraction were obtained by recrystallisation from pentane (1), hex-
anes (2, 3), benzene (4, 6) or diethyl ether (5). Some crystals were
found to contain cocrystallised solvent molecules (2·n-hexane,
4·2C6H6 and 6.C6H6). The crystals were mounted on top of a glass
fibre, by using inert-atmosphere handling techniques, and aligned
on a Bruker87 SMART APEX CCD diffractometer (Platform with
2096
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 2089–2099

First-Row Transition Metal Bis(amidinate) Complexes
FULL PAPER
area [voids of 325.2 (1), 78.7 (2), 372.6 (3), 111.2 (4) and 296.4
(5) Å3/unit cell] were detected by procedures implemented in
PLATON.[98,99] Crystallographic data for 1–6 and details of the
-247628 contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
refinement are listed in Table 4 and Table 5. CCDC-247623 to data_request/cif.
Table 4. Crystal, collection and refinement data for complexes 1–3.
1
2
3
Empirical formula
Formula mass
Crystal dimensions [mm]
Colour, habit
Crystal system
Space group (no.)[96]
a [Å]
b [Å]
c [Å]
β [°]
C62H78N4Cr
931.32
C62H78MnN4·C6H14
1020.44
C62H78FeN4
935.18
0.37×0.13×0.034
red, platelet
monoclinic
P21/c (#14)
23.795(1)
10.3509(4)
25.189(1)
115.714(1)
4
5589.7(4)
1.107
2.18–26.37
0.71073 (Mo-Kα)
100(1)
0.22×0.16×0.14
pale yellow, block
monoclinic
P21/c (#14)
11.9048(5)
24.826(1)
20.7161(8)
96.035(1)
4
6088.7(4)
1.113
2.14–26.37
0.71073 (Mo-Kα)
110(1)
0.40 × 0.40×0.08
green, platelet
monoclinic
P21/c (#14)
23.846(1)
10.3346(6)
25.211(1)
115.898(1)
4
5589.0(5)
1.111
2.37–29.80
0.71073 (Mo-Kα)
105(1)
Z
V [Å3]
ρcalcd. [g/cm3]
θ range [°]
λ [Å]
T [K]
Data collect. time [h]
No. of measured reflections
No. of unique reflections
μ [cm–1]
13.0
43872
11424
2.45
13.6
48623
12423
2.59
983
0.0797, 0.0
0.0642
0.1719
–0.44, 0.56(6)
0.993
8.9
43919
14931
3.1
No. of parameters
Weighting scheme a, b[a]
R(F) for Fo Ն 4σ(Fo)[b]
wR(F2)[c]
916
913
0.0559, 0.7843
0.0483
0.1213
–0.27, 0.33(6)
1.017
0.0842, 1.6145
0.0519
0.1454
–0.38, 2.38(7)
1.024
Residual electron density [e Å–3]
GoF[d]
2
2
2 2
[a] w = 1/[σ2(Fo22) + (aP)2 + bP], P = [max(Fo2,0) + 2Fc ]/3. [b] R(F) = Σ(||Fo| – |Fc||)/|Fo|. [c] wR(F2) = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2. [d]
2 2
½
GoF = {Σ[w(Fo – Fc ) ]/(n – p)} , n = # refl., p = # param. refined.
Table 5. Crystal, collection and refinement data for complexes 4–6.
4
5
6
Empirical formula
Formula mass
Crystal dimensions [mm]
Colour, habit
Crystal system
Space group (no.)[96]
a [Å]
b [Å]
c [Å]
β [°]
C62H78CoN4·2C6H6
1049.49
C62H78N4Ni
938.02
C54H62FeN4·C6H6
901.08
0.24×0.19×0.12
red/brown, block
monoclinic
P21/c (#14)
18.028(5)
18.145(5)
20.797(6)
113.146(5)
4
6255(3)
1.162
2.22–22.21
0.71073 (Mo-Kα)
110(2)
0.19×0.13×0.07
red, block
monoclinic
C2/c (#15)
23.052(2)
10.6550(8)
24.402(2)
113.667(1)
4
5489.5(8)
1.135
2.47–28.60
0.71073 (Mo-Kα)
100(1)
0.55×0.42×0.21
green, block
monoclinic
C2/c (#15)
8.9541(3)
24.3880(9)
23.5938(9)
99.936(1)
4
5075.0(3)
1.179
2.42–28.28
0.71073 (Mo-Kα)
100(1)
Z
V [Å3]
ρcalcd. [g/cm3]
θ range [°]
λ [Å]
T [K]
Data collect. time [h]
No. of measured reflections
No. of unique reflections
μ [cm–1]
8.0
53509
7864
3.19
13.0
21358
5575
3.94
459
0.0304, 5.30
0.0490
0.1041
–0.24, 0.43(6)
1.005
8.0
23145
6269
3.39
430
0.0565, 1.690
0.0359
0.0973
–0.25, 0.41(5)
1.083
No. of parameters
Weighting scheme a, b[a]
R(F) for Fo Ն 4σ(Fo)[b]
wR(F2)[c]
730
0.0016, 46.8803
0.0938
0.2390
–0.19, 0.24(4)
0.957
Residual electron density [e/Å–3]
GoF[d]
[a] w = 1/[σ2(Fo2) + (aP)2 + bP], P = [max(Fo2,0) + 2Fc ]/3. [b] R(F) = Σ(||Fo| – |Fc||)/Σ|Fo|. [c] wR(F2) = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
2
2
2 2
2
2 2
½
[d] GoF = {Σ[w(Fo – Fc ) ]/(n – p)} , n = # refl., p = # param. refined.
Eur. J. Inorg. Chem. 2005, 2089–2099
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2097

C. A. Nijhuis, E. Jellema, T. J. J. Sciarone, A. Meetsma, P. H. M. Budzelaar, B. Hessen
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Received: January 28, 2005
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