Coordination alternatives in dinuclear bis(pyridin-2-ylalkyl)- benzylaminecopper(II) complexes with OH-, RO-, F -, or Cl- bridges: Experimental structures and DFT preferences

Article abstract of DOI:10.1002/ejic.200700637

The compounds [L¹Cu(μ-OH)₂CuL¹] (ClO₄)₂ (1), [L²Cu(μ-OH)₂CuL ²](ClO₄)₂ (2), [L³Cu(μ-OH) ₂CuL³](ClO₄)₂ (3), [L ³Cu-(μ-OMe)₂CuL³](ClO₄) ₂ (4), [L₃Cu(μ-F)₂CuL³](BF ₄)₂ (5), [L⁴Cu-(μ-Cl)₂CuL ⁴](ClO₄)₂ (6), and [Cu(μ-L⁵) ₂Cu](ClO₄)₂ (7), where L¹ = bis(pyridin-2-ylmethyl)benzylamine, L² = (6-methyl-pyridin-2- ylmethyl)(pyridin-2-ylmethyl)benzylamine, L³ = bis(6-methylpyridin-2- ylmethyl)benzylamine, L⁴ = (pyridin-2-ylethyl)(pyridin-2-ylmethyl) benzylamine, and L⁵ = (6-oxidomethylpyridin-2-ylmethyl)(6- methylpyridin-2-yl-methyl)benzylamine, were structurally characterized and studied by low-temperature EPR spectroscopy. The formation of compound 5 involved fluoride abstraction from BF₄^- and that of 7 involved O₂-assisted C-H (methyl) activation/monooxygenation of L³. Whereas the dications of 1-4 and 7 possess a square-pyramidal configuration at the copper(II) centers with hydroxide or alkoxide bridges in equatorial positions, the dications of 5 and 6 exhibit equatorial/axial arrangements for the bridging halide ions. In the dication of 5, the tridentate ligand binds in a meridional fashion and includes two adjacent five-membered chelate rings. Such a situation has been observed previously only with chloride, alkoxide, or aqua bridges. In contrast to the syn configuration of the dication of 2, the dications of complexes 1, 3, 4, and 7 adopt an anti configuration with respect to the binding of Lⁿ. The dications of 1, 2, and 7 have the pyridinyl or 6-methyl-pyridinyl groups in the axial position, whereas those of 3 and 4 feature the tertiary amine N atom at that site. DFT calculations of various configurations of the dications of 1-6 reproduce the experimentally observed structural alternatives in complexes 1-4, but they do not predict the axial/equatorial structure of 5 as the lowest-energy configuration. The systematic overestimation of repulsive forces and thus of distances by DFT may result in an underestimation of the π-π interaction between the largely coplanar mer-L³ ligands separated by about 3.6 A in 5, which probably affects its structure. By incorporating these and previous results, the syn versus anti, equatorial/equatorial versus equatorial/axial, and axial pyridine versus axial amine structural alternatives are discussed. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700637

FULL PAPER
DOI: 10.1002/ejic.200700637
Coordination Alternatives in Dinuclear Bis(pyridin-2-ylalkyl)-
benzylaminecopper(II) Complexes with OH–, RO–, F–, or Cl– Bridges:
Experimental Structures and DFT Preferences
Jorge Manzur,*[a] Andrés Vega,*[b] Ana María García,[a] Carolina Acuña,[a]
Monika Sieger,[c] Biprajit Sarkar,[c] Mark Niemeyer,[c] Falk Lissner,[c] Thomas Schleid,[c]
and Wolfgang Kaim*[c]
Keywords: Copper / EPR spectroscopy / Isomerism / N ligands / Structure
The compounds [L1Cu(μ-OH)2CuL1](ClO4)2 (1), [L2Cu(μ-
OH)2CuL2](ClO4)2 (2), [L3Cu(μ-OH)2CuL3](ClO4)2 (3), [L3Cu-
(μ-OMe)2CuL3](ClO4)2 (4), [L3Cu(μ-F)2CuL3](BF4)2 (5), [L4Cu-
(μ-Cl)2CuL4](ClO4)2 (6), and [Cu(μ-L5)2Cu](ClO4)2 (7), where
L1 = bis(pyridin-2-ylmethyl)benzylamine, L2 = (6-methyl-
oxide, or aqua bridges. In contrast to the syn configuration
of the dication of 2, the dications of complexes 1, 3, 4, and 7
adopt an anti configuration with respect to the binding of Ln.
The dications of 1, 2, and 7 have the pyridinyl or 6-methyl-
pyridinyl groups in the axial position, whereas those of 3 and
4 feature the tertiary amine N atom at that site. DFT calcula-
tions of various configurations of the dications of 1–6 repro-
duce the experimentally observed structural alternatives in
pyridin-2-ylmethyl)(pyridin-2-ylmethyl)benzylamine, L3
bis(6-methylpyridin-2-ylmethyl)benzylamine, L4 = (pyridin-
2-ylethyl)(pyridin-2-ylmethyl)benzylamine, and
L5
=
=
(6-oxidomethylpyridin-2-ylmethyl)(6-methylpyridin-2-yl- complexes 1–4, but they do not predict the axial/equatorial
methyl)benzylamine, were structurally characterized and
studied by low-temperature EPR spectroscopy. The formation
of compound 5 involved fluoride abstraction from BF4 and
structure of 5 as the lowest-energy configuration. The sys-
tematic overestimation of repulsive forces and thus of dis-
tances by DFT may result in an underestimation of the π-π
interaction between the largely coplanar mer-L3 ligands sep-
arated by about 3.6 Å in 5, which probably affects its struc-
ture. By incorporating these and previous results, the syn ver-
sus anti, equatorial/equatorial versus equatorial/axial, and
axial pyridine versus axial amine structural alternatives are
discussed.
–
that of 7 involved O2-assisted C–H (methyl) activation/
monooxygenation of L3. Whereas the dications of 1–4 and 7
possess a square-pyramidal configuration at the copper(II)
centers with hydroxide or alkoxide bridges in equatorial po-
sitions, the dications of 5 and 6 exhibit equatorial/axial ar-
rangements for the bridging halide ions. In the dication of 5,
the tridentate ligand binds in a meridional fashion and in-
cludes two adjacent five-membered chelate rings. Such a sit-
uation has been observed previously only with chloride, alk-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
tions of CuI with O2 have found interest in synthesis be-
cause of their potential use in the hydroxylation of aromatic
and other organic compounds.[9] In O2 transport proteins[10]
and oxygenation or oxidoreductase enzymes,[11,12] however,
the formation of bis(hydroxido)dicopper(II) products is
usually avoided to ensure reversibility. Among the most
widely used copper coligands in this context are the triden-
tate bis(pyridin-2-ylalkyl)amines,[2,3,6,7a] which can be modi-
fied in terms of their steric bulk, electronic effects, and alkyl
chain lengths, which thus allows tridentate coordination in
both facial[2a,2b,13] and meridional fashions.[2b–2d] In con-
trast, the equally popular[6] tris(pyrazolyl)borate,[4] tris(pyr-
azolyl)methane,[7b] and triazacyclononane ligands[5] are re-
stricted to facial coordination.
Introduction
Bis(hydroxido)-bridged dicopper(II) complexes are
among the most typical products from reactions between
copper(I) compounds and molecular oxygen.[1–8] The reac-
[a] Universidad de Chile, Facultad de Ciencias Físicas y Matemát-
icas, Departamento de Ciencia de los Materiales,
Casilla 2777, Santiago, Chile
Fax: +56-2-699-4119
E-mail: jmanzur@dqb.uchile.cl
[b] Universidad Nacional Andres Bello, Facultad de Ecología y Re-
cursos Naturales, Departamento de Ciencias Químicas,
República 275, Santiago, Chile
Fax: +56-2-6618269
E-mail: andresvega@unab.cl
[c] Institut für Anorganische Chemie, Universität Stuttgart,
Pfaffenwaldring 55, 70550 Stuttgart, Germany
Fax: +49-711-685-64165
The formation of copper(II) [or copper(III)][6] species af-
ter the interaction of O2 and CuI is accompanied by the
typical structural peculiarities of the d9 (or d8) configura-
tion, that is, the tendency to form approximately square-
E-mail: kaim@iac.uni-stuttgart.de
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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Coordination of Bis(pyridin-2-ylalkyl)benzylaminecopper(II) Complexes
pyramidal structures with significantly different equatorial kinds of structural alternatives are established: the axial li-
(e) and axial (a) binding sites.[6] Because tridentate chelating gands may be arranged in an anti or syn orientation relative
ligands restrict rapid interconversion, there are clear struc- to the Cu(μ-X)2Cu plane (Scheme 1b),[7a] and the unsym-
tural alternatives for doubly bridged dicopper(II) systems, metrical tridentate bis(pyridin-2-ylalkyl)amine ligands may
viz., the e/e or e/a situations (Scheme 1a). Whereas the e/e bind with the pyridine or the amine N atoms in the axial
conformation typically shows a rather symmetrical bridging position (Scheme 1c).[2a]
arrangement with CuII–OH distances of about
In this contribution we describe seven additional exam-
1.93 Å,[2a,2b,3–5,7a,13] the much longer axial bonds extend to ples of these kinds of [LnCu(μ-X)2CuLn]2+ complexes,
2.25–2.30 Å for the few e/a examples described so which may shed light on the structural alternatives delin-
far.[2b–2d,14] These isolated examples were formulated as eated above. Of the compounds [L1Cu(μ-OH)2CuL1]-
containing six-membered chelate rings with relaxed N–Cu– (ClO4)2 (1), [L2Cu(μ-OH)2CuL2](ClO4)2 (2), [L3Cu(μ-OH)2-
N bite angles of about 90°.[2b–2d] Examples with smaller CuL3](ClO4)2 (3), [L3Cu(μ-OMe)2CuL3](ClO4)2 (4),
chelate rings were restricted to chlorido-, alkoxido-, and [L3Cu(μ-F)2CuL3](BF4)2 (5), [L4Cu(μ-Cl)2CuL4](ClO4)2 (6)
aqua-bridged species.[7a,15]
and [Cu(μ-L5)2Cu](ClO4)2 (7), where L1 = bis(pyridin-2-yl-
In a detailed analysis of the original assertion of a bis(hy- methyl)benzylamine, L2 = (6-methylpyridin-2-ylmethyl)-
droxido)-bridged dicopper(II) complex with an e/a arrange- (pyridin-2-ylmethyl)benzylamine, L3 = bis(6-methylpyridin-
[2b]
ment,
Lee and Holm showed[14] that bridging by two 2-ylmethyl)benzylamine, L4 = (pyridin-2-ylethyl)(pyridin-2-
–
fluoride ions abstracted from PF6 Ϫ perhaps by a Cu/O2/ ylmethyl)benzylamine, and L5 = (6-oxidomethylpyridin-2-
H2O-assisted process Ϫ may instead account for the ob- ylmethyl)(6-methylpyridin-2-ylmethyl)benzylamine, com-
served configuration. In addition, these authors reported plexes 1–3 and 7 were obtained from treatment of in situ
the formation of small amounts of a dicopper(II) complex generated copper(I) precursors [LnCu(LЈ)]+ with air (LЈ:
doubly bridged by a tetradentate anionic monooxygenated solvent). The ligands except for L5 were described in the
ligand generated by the activation of benzylic CH2.[14]
literature,[7a,17] as were some of the copper(I) precursors.[17]
For the more common[16] [LnCu(μ-X)2CuLn]2+ systems An additional copper(I) compound, [L3Cu(PPh3)]-
with e/e configurations of the bridging ligands, two further (BF4), is described here for comparison with the recently
Scheme 1.
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J. Manzur, A. Vega, W. Kaim et al.
FULL PAPER
reported [L3CuLЈ](BF4) species, where LЈ = CH3CN or corresponding copper salt. In the absence of an available
CO.[17] Whereas the oligomethylene chain length in the li- halide ion for bridging, a secondary reaction may occur that
gands controls the chelate ring sizes,[18] the 6-methyl substi- presumably involves the metal-assisted monooxygenation of
tution at the pyridin-2-yl ring has been reported to decrease a partially activated C–H bond. These reactions proceed
its donor ability and slow down the reaction rate due to in low yields.[14] However, whereas Lee and Holm found a
steric repulsion.[17] Within the L1, L2, and L3 ligand series, product with a monooxygenated benzylic CH2 group from
substitution at the pyridin-2-yl rings was increased while a pyridyl–amine linkage,[14] we observed the monooxygen-
the five-membered chelate rings were maintained, which ation of a CH3 group in the α position of the pyridine. The
thus resulted in a largely planar ligand geometry relative to resulting complex 7 thus contains two anionic, tetradentate
some previously studied systems.[2b,2d] In the course of these (6-oxidomethylpyridin-2-ylmethyl)(6-methylpyridin-2-ylme-
studies we not only encountered the well-established[14,19] thyl)benzylamine bridges. CH activation by Cu/O2 is cur-
fluoride abstraction from BF4– to yield an unusual structure rently studied in the context of synthetic transformations[9]
for 5, we also observed small amounts of dimeric product and within attempts to elucidate the mechanisms of corre-
complex 7, which contained a tetradentate anionic mono- sponding enzymes,[20] that is, tyrosinases,[21] for aromatic
oxygenated ligand L5, from the reaction involving L3. In CH groups and dopamine β monoxygenase or peptidylgly-
contrast to a previous observation,[14] however, the attack cine α-hydroxylating monooxygenase (PHM) for nonaro-
had not occurred at the connecting benzylic methylene matic CH groups.[22] These reactions may proceed via
functionality, but at the α-methyl group of the pyridine ring. mononuclear (CuII-superoxido)[23] or dinuclear (CuII-per-
Such CH activation by Cu/O2 resembles enzymatic pro- oxido)[6,9e] precursor intermediates to yield the reactive cop-
cesses[14,20] and is studied in the context of synthetic trans- per–oxyl (O·–) species that effects the necessary H abstrac-
formations;[9] an alkylperoxidocopper(II) complex resulting tion before rebound.[24]
from the attack on an α-picolyl methyl group was reported
recently.[9e]
To investigate the metal–metal interaction (coupling) and
Structure Description
the possible dissociation of the dinuclear complexes in solu-
tion,[2b] we studied compounds 1–6 by EPR spectroscopy.
The crystallographic data of the systems studied by X-
The dications of compounds 1–6 were subjected to DFT ray diffraction are summarized in Tables 5 and 6.
calculations of various coordination alternatives in order to Despite the poor data quality, the structure results (bond
confirm their configurational preferences and to under- lengths and angles; Tables 1 and 2) for [L3Cu(PPh3)](BF4)
stand the stereochemically relevant factors involved.
indicate that the corresponding complex cation possesses an
intermediate structure between those of [L3Cu(CH3CN)]+
and [L3Cu(CO)]+.[17] This reflects the moderately lower π-
acceptor ability of PPh3 relative to that of CO. The overall
structure of this complex (Figure 1) remains that of a highly
distorted tetrahedron,[17] which can be alternatively de-
scribed as a trigonal pyramid with the more weakly bonded
amine N atom at the apex.
Among the bis(hydroxido)-bridged dicopper(II) com-
plexes with nearly square-pyramidal configurations
(τϽ0.20),[25] compounds 1–3 (Figures 2, 3, and 4; Table 1)
exhibit the familiar e/e configuration[2a,2b,3–5,7a] for the
rather symmetrically bonded hydroxide bridges. However,
whereas 1 and 3 show anti-positioned axial (6-methyl)pyr-
idin-2-yl ligands, the 6-methylpyridin-2-yl axial ligands in 2
Results and Discussion
Synthesis
Bis(hydroxido)-bridged dicopper(II) complexes 1–3 were
typically obtained as final products from reactions between
in situ generated copper(I) complexes of the ligands after
exposure to atmospheric conditions [Equation (1)]. One CuI
compound, [L3Cu(PPh3)](BF4), was isolated for NMR
spectroscopic analysis and structural characterization (cf.
below).
4 LnCu+ + O2 + 2 H2O Ǟ 2 [LnCu(μ-OH)2CuLn]2+
(1)
The lability of the bis(hydroxido)-bridged dicopper(II) were found in a syn configuration and face each other with
complexes in certain solvents allowed simple conversion of the smallest distance between the methyl-substituted ring
3 into bis(methoxido)-bridged 4 containing the [L3Cu(μ- C6Ј and C6ЈЈ carbon atoms measuring 3.57 Å (Figure 3).
OMe)2CuL3]2+ dication. The use of the [Cu(CH3CN)4]- The least-squares planes defined by the apical rings (N1Ј,
(BF4) precursor led to bis(fluorido)-bridged 5 by well-estab- C2Ј, C3Ј, C4Ј, C5Ј, C6Ј and N1ЈЈ, C2ЈЈ, C3ЈЈ, C4ЈЈ, C5ЈЈ,
lished[14,19] F– abstraction from tetrafluoroborate, where the C6ЈЈ) are not completely parallel; they adopt a small dihe-
remaining BF3 can act as a Lewis acidic partner for amines. dral angle of 4.2(1)°. The distances between the centroids of
–
This reactivity has been observed even with PF6 , a suppos- each ring and the neighboring planes are 3.44 and 3.50 Å,
edly more inert anion.[14] Both the unambiguous crystallo- respectively.
graphic signature of F– versus OH– and the much more pro-
The preference of the sterically more demanding 6-meth-
nounced asymmetry of the central four-membered ring is ylpyridin-2-yl group for the axial position is not unexpec-
typical for bis(fluorido)- versus bis(hydroxido)-bridged di- ted, and the tendency of unactivated pyridines to adopt this
copper(II) complexes (cf. below).[14] Otherwise, halide- position has been reconfirmed recently.[2a] However, with
bridged complexes such as 6 can be obtained by using the strong donor substituents such as OR or NR2 in the para
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Coordination of Bis(pyridin-2-ylalkyl)benzylaminecopper(II) Complexes
Table 1. Selected bond lengths [Å] and angles [°] for compounds 1·CH3COCH3, 2·H2O, and 3.
1[a]
2[b]
3[c]
Cu–O1
Cu–O1A
Cu–N1
Cu–N2
Cu–N3
Cu–CuA
N1–Cu–N2
N1–Cu–N3
N2–Cu–N3
N1–Cu–O1
N2–Cu–O1
N3–Cu–O1
N3–Cu–O1A
N2–Cu–O1A
N1–Cu–O1A
O1–Cu–O1A
Cu–O1–CuA
1.921(4)
1.947(4)
1.983(5)
2.058(4)
2.280(5)
2.922(1)
83.4(2)
101.4(2)
77.3(2)
97.6(2)
176.2(2)
106.0(2)
93.7(2)
96.2(2)
164.4(2)
81.9(2)
CuЈ–O1Ј
1.952(5)
1.948(5)
1.919(4)
1.960(5)
2.279(7)
2.332(6)
83.6(3)
CuЈ–N2Ј
CuЈЈ–N2ЈЈ
Cui–N3i
CuЈЈ–N3ЈЈ
CuЈ–CuЈЈ
2.054(6)
2.043(5)
2.013(6)
1.993(6)
2.955(1)
Cu–O1A
Cu–O1
Cu–N1
Cu–N2
Cu–N3
Cu–CuA
N1–Cu–N2
N1–Cu–N3
N2–Cu–N3
N1–Cu–O1
N2–Cu–O1
N3–Cu–O1
N3–Cu–O1A
N2–Cu–O1A
N1–Cu–O1A
O1–Cu–O1A
Cu–O1–CuA
1.891(11)
1.905(12)
2.041(12)
2.288(13)
2.018(11)
3.009(3)
79.6(5)
100.1(5)
77.6(5)
93.2(5)
107.9(5)
166.4(5)
91.3(5)
120.3(6)
159.0(5)
75.1(6)
CuЈ–O1ЈЈ
CuЈЈ–O1Ј
CuЈЈ–O1ЈЈ
CuЈ–N1Ј
CuЈЈ–N1ЈЈ
N3Ј–CuЈ–N2Ј
N1ЈЈ–CuЈЈ–O1ЈЈ 94.8(2)
N3ЈЈ–CuЈЈ–O1Ј 97.9(2)
N3ЈЈ–CuЈЈ–O1ЈЈ 167.2(2)
N2ЈЈ–CuЈЈ–O1Ј 173.8(2)
N2ЈЈ–CuЈЈ–O1ЈЈ 95.5(2)
N3ЈЈ–CuЈЈ–N2ЈЈ 84.4(2)
N3Ј–CuЈ–N1Ј
N3ЈЈ–CuЈЈ–N1ЈЈ 97.6(2)
N2Ј–CuЈ–N1Ј
76.0(3)
96.8(3)
N2ЈЈ–CuЈЈ–N1ЈЈ 76.0(2)
N1Ј–CuЈ–O1Ј
N1Ј–CuЈ–O1ЈЈ
CuЈ–O1Ј–CuЈЈ
98.1(2)
111.2(3)
99.5(2)
N3Ј–CuЈ–O1Ј
N3Ј–CuЈ–O1ЈЈ
N2Ј–CuЈ–O1Ј
N2Ј–CuЈ–O1ЈЈ
N1ЈЈ–CuЈЈ–O1Ј
164.1(2)
99.3(2)
94.6(2)
171.6(3)
109.2(2)
CuЈ–O1ЈЈ–CuЈЈ 98.2(2)
O1Ј–CuЈ–O1ЈЈ
O1Ј–CuЈЈ–O1ЈЈ 80.9(2)
80.4(2)
98.1(2)
104.9(6)
[a] A: –x, –y + 2, –z. [b] The symbols Ј and ЈЈ refer to two crystallographically nonequivalent molecule halves. [c] A: 0.5 – x,1.5 – y,1 – z.
Table 2. Selected bond lengths [Å] and angles [°] for compounds 4–7.
4[a]
5[b]
6[c]
7[d]
Cu–O1A
Cu–O1
Cu–N1
Cu–N2
Cu–N3
Cu–CuA
N1–Cu–N2
N1–Cu–N3
N2–Cu–N3
N1–Cu–O1
N2–Cu–O1
N3–Cu–O1
N3–Cu–O1A
N2–Cu–O1A
N1–Cu–O1A
O1–Cu–O1A
Cu–O1–CuA
1.930(2)
1.933(2)
2.040(2)
2.254(2)
2.019(2)
3.0520(7)
80.61(9)
98.11(9)
78.45(9)
94.47(9)
105.44(9)
167.31(9)
91.69(9)
107.91(9)
168.22(9)
75.62(8)
104.38(8)
Cu–F1
Cu–F1A
Cu–N1
Cu–N2
Cu–N3
Cu–CuA
N1–Cu–N2
N1–Cu–N3
N2–Cu–N3
N1–Cu–F1
N2–Cu–F1
N3–Cu–F1
1.878(1)
2.268(1)
2.016(2)
2.011(2)
2.031(2)
3.134(1)
84.12(7)
163.79(7)
81.90(7)
97.02(6)
169.10(6)
98.27(6)
Cu–N1
Cu–N2
Cu–N3
Cu–Cl1
Cu–Cl1A
Cu–CuA
N1–Cu–N2
N1–Cu–N3
N2–Cu–N3
N1–Cu–Cl1
N2–Cu–Cl1
N3–Cu–Cl1
N1–Cu–Cl1A
N2–Cu–Cl1A
N3–Cu–Cl1A
Cu–Cl1–CuA
1.994(4)
2.088(4)
2.008(4)
2.298(1)
2.791(1)
3.714(1)
90.7(2)
172.0(2)
81.3(2)
93.5(1)
166.3(1)
94.5(1)
95.3(1)
105.9(1)
85.8(1)
93.2(1)
Cu–O1A
Cu–O1
Cu–N1
Cu–N2
Cu–N3
Cu–CuA
N1–Cu–N2
N1–Cu–N3
N2–Cu–N3
N1–Cu–O1
N2–Cu–O1
N3–Cu–O1
N3–Cu–O1A
N2–Cu–O1A
N1–Cu–O1A
O1–Cu–O1A
Cu–O1–CuA
1.948(3)
1.962(3)
2.186(4)
2.102(3)
1.923(3)
2.9067(10)
80.42(13)
114.15(15)
81.75(14)
112.90(13)
162.24(13)
81.98(13)
144.81(14)
105.63(12)
101.03(13)
83.95(12)
96.05(12)
F1–Cu–F1A
Cu–F1–CuA
82.26(5)
97.74(5)
Cl1–Cu–Cl1A 86.8(1)
[a] A: –x, 2 – y, –z. [b] A: 1 – x, 1 – y, 1 – z. [c] A: 1 – x, 1 – y, 1 – z. [d] A: 2 – x, –y, 1 – z.
Figure 1. Molecular structure of the cation in the crystal of
[L3Cu(PPh3)](BF4). Selected bond lengths [Å] and angles [°]: Cu–
P 2.178(4), Cu–N1 2.007(11), Cu–N2 2.202(10), Cu–N3 2.074(10);
P–Cu–N1 129.1(3), P–Cu–N2 119.2(3), P–Cu–N3 116.9(3), N1– Figure 2. Molecular structure of the dication in the crystal of
Cu–N2 80.9(4), N1–Cu–N3 112.8(4), N2–Cu–N3 78.0(4).
[L1Cu(μ-OH)2CuL1](ClO4)2·2Me2CO (1).
Eur. J. Inorg. Chem. 2007, 5500–5510
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J. Manzur, A. Vega, W. Kaim et al.
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Figure 3. Molecular structure of the dication in the crystal of
Figure 5. Molecular structure of the dication in the crystal of
[L2Cu(μ-OH)2CuL2](ClO4)2·H2O (2).
[L3Cu(μ-OMe)2CuL3](ClO4)2 (4).
6, [L4Cu(μ-Cl)2CuL4](ClO4)2, described here shows that the
same kind of structure is obtained after lengthening either
one of the alkyl chains that connects the amine N atom or
the pyridin-2-yl moiety from CH2 to CH2CH2 (Figure 6,
Table 2).
Figure 4. Molecular structure of the dication in the crystal of
[L3Cu(μ-OH)2CuL3](ClO4)2 (3).
position, the pyridines may prefer the equatorial coordina-
tion, leaving the axial binding site for the trialkylamine N
atom.[2a] The syn configuration for 2 is reminiscent of that
of a 6-trifluoromethyl-substituted analogue,[7a] which sug-
gests that there is an attractive interaction.
Figure 6. Molecular structure of the dication in the crystal of
[L4Cu(μ-Cl)2CuL4](ClO4)2 (6).
The related hydroxido- and methoxido-bridged struc-
tures 3 and 4 (Figures 4 and 5, respectively) are very similar
In contrast to μ-Cl–, μ-OR–, and μ-OH2, the smaller μ-
in their anti configurations, which are almost superimpos- OH– bridges typically favor the e/e configuration in dinu-
able. The Cu–O distances are a bit shorter for 3 [1.891(2), clear [(η3-L)Cu(μ-OH)2Cu(η3-L)]2+ complexes. The triden-
1.905(2) Å] than for 4 [1.930(2), 1.933(2) Å]. The methoxy tate ligands will then coordinate in a facial mode. This rule
carbon atoms of the OMe groups lie at opposite sides of is not only confirmed by the revision of the initially as-
the central Cu2O2 plane in 4 and are almost coplanar. The signed hydroxido-bridged complex with the e/a configura-
C–O vector defines an angle of only 7.9° with the plane.
tion[2b] to a fluorido-bridged species,[14] but it is also cor-
As pointed out before,[2d] bis(chlorido)-bridged dicop- roborated by the examples presented here, viz., an e/e con-
per(II) complexes can readily adopt the e/a arrangement for figuration for 3 and 4 but an e/a configuration for fluorido-
the bridges with long axial Cu–Cl distances of about 2.8 Å. bridged 5 (Figure 7). Nevertheless, the latter is surprising
A
previous study of [L1Cu(μ-Cl)2CuL1](ClO4)2 (8) because meridional binding of tridentate ligands such as L3
showed[7a] that this also holds when two five-membered is less favorable due to the necessity to form two adjacent
chelate rings are formed in the LnCu moiety. Compound five-membered chelate rings (Table 2).
5504
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Eur. J. Inorg. Chem. 2007, 5500–5510

Coordination of Bis(pyridin-2-ylalkyl)benzylaminecopper(II) Complexes
by its preferred central position in mer-L3. In contrast, the
difference between the short equatorial Cu–F bond length
and the typically[14] long axial Cu–F distance is almost
0.4 Å. The molecular dication of 5 has inversion symmetry
(Figure 7), and the central Cu2F2 ring approaches a rectan-
gular geometry because the bond lengths differ widely but
the Cu–F1–CuA and F1–Cu–F1A angles [97.74(5) and
82.26(5)°, respectively] do not strongly deviate from 90°.
Measuring 3.134(1) Å, the Cu–CuA distance is longer than
the corresponding distances in the e/e-configured hydroxido
Table 3. Relative energies (most stable isomer = 0 kcalmol–1) calcu-
lated for the different coordination alternatives of compounds 1–6,
8, and [L2Cu(μ-OMe)2CuL2]2+ [a]
.
Compound Bridge
Orientation Axial
ligand
Relative energy
[kcalmol–1
]
number
configuration
Figure 7. Molecular structure of the dication in the crystal of
[L3Cu(μ-F)2CuL3](BF4)2·2CH2Cl2 (5).
1
e/e
e/e
e/e
e/e
e/a
anti
anti
syn
syn
syn
Pyridine-N
0.1
0
0.9
2.8
16.7
Amine-N
Pyridine-N
Amine-N
OH
According to the five-membered chelate ring situation,
the N–Cu–N angles in 5 have decreased to about 83° and
the trans-N1–Cu–N3 angle to 163.79(7)°. Measuring
169.10(6)°, the other trans-N2–Cu–F1 angle is distinctly
more linear, as is the N1–Cu–N3 angle for the mer-coordi-
nated L4 in compound 6, which measures 172.0(2)°. All
Cu–N bond lengths in 5 lie around 2.02 Å; the typically
weaker bonding to the amine N atom is compensated for
2
3
4
e/e
e/e
e/e
e/e
e/a
anti
anti
syn
syn
syn
Pyridine-N
Amine-N
Pyridine-N
Amine-N
OH
0.3
2.1
0.1
0
17.9
e/e
e/e
e/e
e/e
e/a
anti
anti
syn
syn
syn
Pyridine-N
Amine-N
Pyridine-N
Amine-N
OH
9.5
0
9.7
0.3
23.8
e/e
e/e
e/e
e/e
e/a
anti
anti
syn
syn
syn
Pyridine-N
Amine-N
Pyridine-N
Amine-N
OMe
12.5
0
15.2
1.0
2.4
[L2Cu(μ-
MeO)2]
[CuL2]2+
e/e
e/e
e/e
e/e
e/a
anti
anti
syn
syn
syn
Pyridine-N
Amine-N
Pyridine-N
Amine-N
OMe
3.6
0
4.2
5.9
19.7
Scheme 2.
5
6
8
e/e
e/e
e/e
e/e
e/a
anti
anti
syn
syn
syn
Pyridine-N
Amine-N
Pyridine-N
Amine-N
F
0
0.1
0.8
1.1
6.3
e/e
e/e
e/e
e/e
e/a
anti
anti
syn
syn
syn
Pyridine-N
Amine-N
Pyridine-N
Amine-N
Cl
10.6
8.0
9.8
47.5
0
e/e
e/e
e/e
e/e
e/a
anti
anti
syn
syn
syn
Pyridine-N
Amine-N
Pyridine-N
Amine-N
Cl
1.7
7.8
0.9
9.2
0
[a] e/e: equatorial/equatorial; e/a: equatorial/axial; in bold: experi-
mentally observed geometry.
Figure 8. Molecular structure in the crystal of [Cu(μ-L5)2Cu] (7).
Eur. J. Inorg. Chem. 2007, 5500–5510
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J. Manzur, A. Vega, W. Kaim et al.
FULL PAPER
derivatives 1–3 (Ͻ3.01 Å), but much smaller than those in was computed to be 0.723 eV less stable than the anti-e/e
the chlorido-bridged 6 [3.714(1) Å] and 8 [3.566(1) Å],[7a] pyridyl isomer. Interestingly, the anti-e/e pyridyl configura-
and that reported for a complex involving nonplanar, six- tion is preserved when complex 2 is crystallized as an aqua
membered chelate rings (3.271 Å).[2d] In fact, the virtually solvate instead of the acetone solvate described in the text,
planar L3CuII moieties in 5 are arranged in a parallely where the packing interactions must be completely dif-
stacked structure (dihedral angle of 4.5°) with partially ferent.
overlapping pyridyl-ring π systems and oppositely oriented
Replacement of one α-hydrogen atom on one of the pyr-
methyl groups. The interplanar distance of about 3.6 Å (vs. idyl groups of L1 by a methyl group leads to L2. The dicat-
3.35 Å in graphite) indicates a π–π interaction that probably ion of 2, [L2Cu(μ-OH)2CuL2]2+, crystallizes in the syn-e/e
induces and stabilizes[2b] the structure. π–π interactions have pyridyl geometry (with perchlorate counteranions); this was
been implicated before in similar complexes,[2b] and rela- also observed for the trifluoromethyl derivative of L2.[7a]
tively long interplanar distances are typical for nitrogen- DFT calculations for 2 show that the energy of the syn-e/e
containing aromatic molecules.[26] The aromatic rings of the pyridyl isomer lies just 0.002 eV above that of the most
benzyl substituents in 5 also overlap with the pyridyl rings stable syn-e/e amine alternative. The anti configurations are
(dihedral angle of 21.4°) with interplanar distances (e.g. a bit higher in energy, whereas the energy of the e/a isomer
3.068 Å for N1–C21) that allow such π–π interactions. In lies about 0.7 eV above that of the most stable isomer. The
total, a π–π–π arrangement (pyridyl, pyridyl, benzyl) results observed structure may result from CX3···ring interactions
that is reminiscent of a recently described dicopper(I) com- that could occur in the syn configuration between the sub-
plex involving phenylphosphane and bipyrimidine π sys- stituted pyridine rings. The replacement of the other α-hy-
tems.[27]
drogen atom by a methyl group to give [L3Cu(μ-OH)2-
Complex 7 in which the L3 ligand has undergone CuL3]2+ (dication of 3) has a strong effect on the relative
monooxygenation at a picolyl methyl group and then de- energies. In this complex, the anti-e/e amine configuration
protonation to yield tetradentate anionic L5 (Scheme 2) is computed to be the most stable isomer, and this result
shows the familiar anti configuration of the e/e arrange- coincides with the X-ray determined structure for the per-
ment, with the nonmonooxygenated 6-methylpyridyl group chlorate salt.
in the axial position (Figure 8). Because of the restriction
Changing the hydroxy bridge into a methoxy one leads
by tetrachelation, the square planar configuration is slightly to [L2Cu(μ-OMe)2CuL2]2+[7a] and [L3Cu(μ-OMe)2CuL3]2+
more distorted (τ = 0.28) than in the other cases (τϽ0.20). (dication of 4), where again the anti-e/e amine form is calcu-
Table 3 summarizes the experimentally observed coordina- lated to be the most stable isomer, and this is confirmed by
tion situations, and the following discussion is concerned the X-ray diffraction results. Moreover, the computed en-
with the possible predictability of such structural prefer- ergy differences between the most stable isomer and the
ences.
others are now larger, which suggests that the incorporation
of a methyl group on the bridge produces enhanced repul-
sion.
The complexes [L3Cu(μ-F)2CuL3]2+ (dication of 5),
[L4Cu(μ-Cl)2CuL4]2+ (dication of 6), and [L1Cu(μ-Cl)2-
DFT Calculations for the [LnCu(μ-X)2CuLn]2+ Dications
The variety of structural alternatives for these complexes CuL1]2+ (dication of 8) were studied to test the effect of
(Scheme 1, Table 3) and their realization under different halide bridges. Their experimental structures correspond to
conditions have prompted us to undertake a DFT calcula- the e/a isomer. The most stable isomer computed for the
tion study to rationalize the experimental results and to ex- dication of 5 is the anti-e/e pyridyl form. Although this re-
plore the predictive potential of the method. Table 3 sum- sult does not fit the experimental observations (e/a isomer),
marizes the energies calculated for the different stereoiso- the difference in energy of this isomer relative to the most
mers, and the DFT-calculated structure parameters are stable one at 0.275 eV is noticeably diminished in compari-
found in Table S1 (Supporting Information).
son to the hydroxy or methoxy analogues, where the energy
As can be expected just by considering steric hindrance, differences between the e/e and e/a configurations are of the
dicopper(II) complexes sharing an edge of the two square- order of 1 eV. The computational results for the dications
based pyramids favor the anti arrangement for the apical of 6 and 8 show that the most stable isomers possess e/a
ligands. For the dication of 1, [L1Cu(μ-OH)2CuL1]2+, the configurations, which is in agreement with the experimental
anti-e/e structure with pyridine or amine nitrogen atoms in results.
the apical position should be expected. The X-ray structure
In conclusion, the DFT method makes a clear distinction
shows a pyridyl anti-e/e geometry for this complex (as a between the e/e and e/a configurations. Although the calcu-
perchlorate salt). DFT results predict this isomer to be lated energy differences are not very large in the case of
0.006 eV higher in energy than the most stable anti-e/e some syn- and anti-e/e isomers, the DFT method has cor-
amine configuration. Both these isomers are practically of rectly reproduced the experimentally favored complex con-
the same energy, so packing could play an important role figurations except in the case of the dication of 5 where
in determining the observed crystal structure. The syn-e/e additional, highly distance-dependent π–π interactions are
isomers for the complex are 0.041 and 0.121 eV higher in obviously underestimated[26,27] because of the systematic
energy that the most stable configuration. The e/a isomer overestimation of distances.
5506
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Eur. J. Inorg. Chem. 2007, 5500–5510

Coordination of Bis(pyridin-2-ylalkyl)benzylaminecopper(II) Complexes
EPR Spectroscopy
orbit coupling contributions from Cl– are held responsible
for these differences.
The EPR method is suited to study intramolecular spin–
spin interactions of copper(II) ions in dinuclear complexes
and to investigate their possible dissociation into mononu-
clear species in solution.[2b] We therefore studied the com-
pounds by this method in the solid state and in frozen solu-
tions at 110 K (Figure 9, Table 4).
Conclusions
During this study of [LnCu(μ-X)2CuLn)]2+ complex di-
cations, we encountered a remarkable structural variety
(Table 3). Nevertheless, DFT calculations were able to con-
firm the preferred configuration of most of these structures
by their computed relative energies except in the case of the
F–-bridged complex 5, where the systematic overestimation
of repulsive forces and thus of distances led to wrong pre-
dictions as a result of underestimated π–π interactions.
Whereas some effects such as the preference of the more
weakly basic halide ligands for the axial position are easily
rationalized, the differences between the anti and syn orien-
tations or the preferred N donor for the axial position are
not readily obvious. Karlin and coworkers noted that “such
structural differences or variations may need to be consid-
ered to explain certain aspects of […] reactivity pat-
terns”,[2a] and therefore, a detailed computational approach
may provide increased efficiency in the design and develop-
ment of ligands for broader interest such as in metal/O2-
induced CH activation;[9] an example encountered acciden-
tally is presented here as doubly monooxygenated complex
Figure 9. EPR signal of compound [L4Cu(μ-Cl)2CuL4](ClO4)2 (6)
with half-field component (insert).
Table 4. EPR parameters of complexes in CH2Cl2/CH3CN (x/y) at
110 K.
7.
Complex (x/y)
gʈ
gЌ
gav
Aʈ[a]
1
3
4
5
6
8
2/1
4/1
4/1
1/0
4/1
5/1
2.10[b]
4.10[b,c]
2.120
Experimental Section
2.260
2.270
2.270
2.050
2.057
2.056
15.0
14.6
15.6
Instrumentation: EPR spectra in the X band were recorded with a
Bruker System EMX. 1H NMR spectra were recorded in CDCl3
with a Bruker AMX-300 NMR spectrometer. IR spectra were ob-
tained with a Bruker Vector 22 instrument.
4.27[b–d]
2.128
4.26[b–d]
2.127
Syntheses of Ligands: The ligands L1 = bis(pyridin-2-ylmethyl)ben-
4.21[b–d]
2.075
2.206
4.91[c]
2.224
4.86[c]
2.040
17.6
8.3[c]
17.7
8.7[c]
zylamine, L2 = (6-methylpyridin-2-ylmethyl)(pyridin-2-ylmethyl)-
4.21[c]
2.015
4.44[c]
2.085
benzylamine, L3
= bis(6-methylpyridin-2-ylmethyl)benzylamine,
and L4 = (pyridin-2-ylethyl)(pyridin-2-ylmethyl)benzylamine were
prepared according to the literature[7a,17] by reaction of the appro-
priate secondary amine with benzyl bromide in CH3CN as the sol-
vent.
4.16[c,e]
4.39[c]
[a] In mT. [b] Unresolved signal. [c] Half-field signal. [d] Weak sig-
nal. [e] AЌ = 2.0 mT.
Synthesis of Copper Complexes
The complexes show typical[2] EPR signals for CuII(μ-X)2-
CuII cores in both cases with the spectra in frozen solutions
being better resolved (Figure 9). Under both sets of condi-
tions we could observe half-field transitions for certain
compounds, especially for the halide-bridged species pos-
sessing a pronounced asymmetry of the Cu(μ-X)Cu core
and possible triplet ground states.[7a] The fact that both so-
lid samples and frozen solutions exhibit the half-field sig-
nals for the triplet excited states suggests that the dinuclear
arrangement remains largely intact in the chosen CH2Cl2/
CH3CN solvent mixtures. Preliminary UV/Vis spectro-
scopic experiments have shown that association and ligand
Caution: Perchlorate complexes are potentially explosive and should
be handled with care.
[L3Cu(PPh3)](BF4): To a solution of L3 (55 mg, 0.173 mmol) in
CH2Cl2 (10 mL) was added [Cu(CH3CN)3(PPh3)]BF4 (83 mg,
0.155 mmol). The mixture was stirred at room temperature over-
night. After reducing the solvent 3 mL, a bright yellow product
precipitated in 79% yield (89 mg) by adding hexane/toluene (1:1).
Crystals were obtained by recrystallization from CH2Cl2 at –20 °C.
Single crystals were covered with a layer of viscous hydrocarbon
oil (Paratone N, Exxon), attached to a glass fiber, and instantly
placed in a low-temperature N2 stream. 1H NMR (300 MHz,
CD3CN): δ = 2.62 (s, 6 H), 3.56 (s, 2 H), 3.67 (AB-m, 4 H), 7.08
substitution equilibria can occur in media such as alcohols. (br., 2 H), 7.21–7.33 (m, 15 H), 7.37–7.54 (m, 7 H), 7.80 (pt, J =
7.7 Hz, 2 H) ppm. C39H38BCuF4N3P (730.07): calcd. C 64.16, H
5.25, N 5.76; found C 63.92, H 5.93, N 5.12.
[L3Cu(CH3CN)](BF4): To a solution of L3 (100 mg, 0.315 mmol)
The differences between the complexes are rather small ex-
cept for the somewhat higher Aʈ (63,65Cu) and lower g val-
ues for the chloride-bridged species 6 and 8 (Table 4). The
increased copper–halide covalency and the higher spin- in CH2Cl2 (10 mL) was added [Cu(CH3CN)4]BF4 (100 mg,
Eur. J. Inorg. Chem. 2007, 5500–5510
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J. Manzur, A. Vega, W. Kaim et al.
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0.318 mmol). The mixture was stirred for 2 h at room temperature.
After reducing the solvent to 2 mL and adding hexane a partially
crystalline and highly air-sensitive precipitate was obtained and
for X-ray studies were obtained by slow evaporation of the solvent.
Yield: 448 mg (45%). IR (KBr pellet): ν = 3560 (sharp, shoulder),
˜
–
3500 (br., OH), 1610, 1579, 1469, 1441 (sharp, py), 1095 (vs, ClO4 )
dried. Yield: 69 mg (43%). 1H NMR (300 MHz, CD3CN): δ = 2.71 cm–1. C42H48Cl2Cu2N6O10 (994.9): calcd. C 50.7, H 4.9, N 8.5, Cu
(s, 6 H), 3.81 (AB-m, 4 H), 3.93 (s, 2 H), 7.11 (d, J = 8 Hz, 2 H), 12.8; found C 52.1; H 4.8; N 8.2; Cu 13.1.
[L3Cu(μ-OMe)2CuL3](ClO4)2 (4): This compound was obtained by
7.25–7.40 (m, 7 H), 7.68 (pt, J = 7.7 Hz, 2 H) ppm.
[L1Cu(μ-OH)2CuL1](ClO4)2·2CH3COCH3 (1·2CH3COCH3): To a
suspension of [Cu(CH3CN)4](ClO4) (654 mg, 2 mmol) in acetone
(10 mL) was added an acetone solution of the ligand (579 mg,
2 mmol) under an atmosphere of nitrogen. The mixture was stirred
for 30 min to give a yellow solution, and then the flask was opened
to the atmosphere. The solution turned blue, and the solid product
separated with time. Crystals suitable for X-ray diffraction studies
were obtained by recrystallization from boiling acetone. Yield:
recrystallization of compound 3 in boiling methanol. IR (KBr pel-
let): ν = 1609, 1578, 1468, 1441 (sharp, py), 1090 (vs, ClO ) cm–1.
–
˜
4
C44H52Cl2Cu2N6O10 (1022.9): calcd. C 51.6, H 5.1, N 8.2, Cu 12.4;
found C 50.8, H 5.0, N 7.9, Cu 12.6.
[L3Cu(μ-F)2CuL3](BF4)2·2CH2Cl2 (5·2CH2Cl2): To
a
cooled
(–20 °C) solution of [L3Cu(CH3CN)]BF4 (89 mg, 0.175 mmol) in
CH2Cl2 (5 mL) was added O2-saturated CH2Cl2 solution (5 mL).
The initially bright-yellow solution turned deep green spontane-
ously. The mixture was stirred for 1 h at –20 °C. Removal of the
solvent gave a deep green residue that was recrystallized from
CH2Cl2 at –10 °C to afford a green product. Yield: 30 mg (36%).
C44H50B2Cl4Cu2F10N6 (1143.42): calcd. C 47.68, H 4.69, N 8.20;
found C 45.71, H 4.64, N 8.67.
697 mg (66%). IR (KBr pellet): ν = 3570 (sharp, shoulder), 3450
˜
–
(br., OH), 1604, 1574, 1481, 1444 (sharp, py), 1100 (vs, ClO4 )
cm–1.C44H52Cl2Cu2N6O12 (1054.9): calcd. C 50.1, H 5.0, N 8.0, Cu
12.0; found C 48.8, H 4.9, N 8.1, Cu 12.3.
[L2Cu(μ-OH)2CuL2](ClO4)2·H2O (2·H2O): To a suspension of
[Cu(CH3CN)4](ClO4) (654 mg, 2 mmol) in CH2Cl2 (10 mL) was
added a dichloromethane solution of the ligand (607 mg, 2 mmol)
under an atmosphere of nitrogen. The mixture was stirred for
30 min after which the flask was opened to the atmosphere. After
several hours a blue solid separated. Recrystallization from boiling
ethanol gave crystals suitable for X-ray diffraction studies. Yield:
[L4Cu(μ-Cl)2CuL4](ClO4)2 (6): This complex was obtained by the
reaction of a 1:1 mixture of copper(II) perchlorate hexahydrate
(370 mg) and anhydrous copper(II) chloride (135 mg) with the L4
ligand in methanol. Recrystallization from boiling methanol af-
forded crystals suitable for X-ray diffraction. Yield: 442 mg (44%).
IR (KBr pellet): ν = 1610, 1570, 1485, 1448 (sharp, py), 1100 (vs,
˜
–
ClO4 ) cm–1. C40H42Cl4Cu2N6O8 (1003.7): calcd. C 47.8, H 4.2, N
460 mg (45%). IR (KBr pellet): ν = 3600 (sharp, shoulder), 3500
˜
–
(br., OH), 1603, 1577, 1473, 1458 (sharp, py), 1100 (vs, ClO4 ) cm–1.
8.4, Cu 12.7; found C 47.1, H 4.0, N 8.3, Cu 12.5.
[Cu(μ-L5)2Cu](ClO4)2 (7): Evaporation of the residual solution re-
sulting from the synthesis of compound 3 gave a blue-green syrup
that was dissolved in acetonitrile. Slow evaporation of this solution
gave a small amount of green crystals identified as compound 7 by
X-ray diffraction.
C40H46Cl2Cu2N6O11 (1020.9): calcd. C 48.8, H 4.7, N 8.5, Cu 12.9;
found C 48.2, H 4.6, N 8.5, Cu 13.4.
[L3Cu(μ-OH)2CuL3](ClO4)2 (3): To a suspension of [Cu(CH3CN)4]-
(ClO4) (654 mg, 2 mmol) in CH2Cl2 (10 mL) was added a dichloro-
methane solution of the ligand (635 mg, 2 mmol) under an atmo-
sphere of nitrogen. The mixture was stirred for 30 min after which
the flask was opened to the atmosphere. Blue crystals of 3 suitable
X-ray Data Collection and Refinement Details: Single crystals of the
compounds were glued to the tip of glass capillaries and then
Table 5. Crystallographic and refinement details for compounds [L3Cu(PPh3)](BF4), 1·2CH3COCH3, 2·H2O, and 3.
[L3Cu(PPh3)](BF4)
1·2CH3OCH3
2·H2O
3
Formula
Fw
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C39H38BCuF4N3P
730.04
monoclinic
P21/c
16.225(7)
9.925(4)
23.327(9)
90
105.79(1)
90
C44H52Cl2Cu2N6O12
1054.91
C40H46Cl2Cu2N6O11
984.82
orthorhombic
P212121
12.1372(7)
16.777(1)
22.710(1)
90
90
90
4624.2(5)
4
C42H48Cl2Cu2N6O10
994.85
monoclinic
C2/c
18.979(5)
8.7256(18)
27.449(6)
90
104.854(8)
90
triclinic
¯
P1
10.530(1)
11.019(1)
11.390(1)
67.289(2)
87.113(2)
86.747(2)
1216.6(3)
1
α [°]
β [°]
γ [°]
Volume [Å3]
Z
3615(3)
4
4393.7(17)
4
F(000)
1512
1.341
0.5ϫ0.05ϫ0.01
173
546
1.440
0.45ϫ0.13ϫ0.05
293
2028
1.413
0.50ϫ0.34ϫ0.16
293
2072
1.519
0.38ϫ0.18ϫ0.02
293
Dcalcd. [gcm–3]
Crystal size [mm]
T [K]
2θ range
μ [mm–1]
Index ranges
3.15 to 27.04
0.701
–19ՅhՅ20
–10ՅkՅ12
–27ՅlՅ26
3.88 to 50.20
1.049
–12ՅhՅ12
–13ՅkՅ13
–13ՅlՅ13
4272
3.02 to 50.16
1.097
–14ՅhՅ14
–20ՅkՅ19
–26ՅlՅ27
8211
1.53 to 25.04
1.156
–22ՅhՅ22
–10ՅkՅ10
–32ՅlՅ32
3887
No. reflections collected 4214
No. reflections observed 2355
2737
0.0738, 0.1676
0.665, –0.552
6010
0.0728, 0.1926
0.852, –0.743
2768
0.1625, 0.3581
1.043, –1.531
[a]
R, Rw
0.1184, 0.2100
0.530, –0.548
Final difference [eÅ–3]
[a] R = Σ||Fo| – |Fc||/Σ|Fo|. Rw = [Σw(|Fo| – |Fc|)2/Σw(Fo)2]1/2, where w = 1/σ2(Fo). λ(Mo-Kα) = 0.71073 Å.
5508
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Eur. J. Inorg. Chem. 2007, 5500–5510

Coordination of Bis(pyridin-2-ylalkyl)benzylaminecopper(II) Complexes
Table 6. Crystallographic and refinement details for compounds 4, 5·2CH2Cl2, 6, and 7.
4
5·2CH2Cl2
6
7
Formula
Fw
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C44H52Cl2Cu2N6O10
1022.92
monoclinic
P21/n
10.8139(11)
16.8512(18)
13.4087(14)
90
C44H50B2Cl4Cu2F10N6
1141.83
monoclinic
P21/n
11.9814(3)
13.4624(3)
15.7738(4)
90
C40H42Cl4Cu2N6O8
1003.70
monoclinic
P21/c
9.1595(8)
17.762(2)
12.557(1)
90
C42H44Cl2Cu2N6O10
990.83
monoclinic
P21/n
10.4493(11)
17.0095(18)
12.8309(13)
90
α [°]
β [°]
γ [°]
109.745(2)
90
2299.8(4)
2
112.168(1)
90
2356.22(10)
4
91.305(2)
90
2042.5(3)
2
109.945(2)
90
2143.7(4)
2
Volume [Å3]
Z
F(000)
1060
1.477
0.30ϫ0.20ϫ0.17
293
1168
1.614
0.46ϫ0.2ϫ0.06
293
1028
1.632
0.27ϫ0.24ϫ0.12
293
1020
1.535
0.42 ϫ0.20ϫ0.07
293
Dcalcd. [gcm–3]
Crystal size [mm]
T [K]
2θ range
μ [mm–1]
Index ranges
2.02 to 25.10
1.104
–12ՅhՅ12
–20ՅkՅ20
–15ՅlՅ15
3.88 to 28.28
1.21
–15ՅhՅ15
–17ՅkՅ17
–20ՅlՅ19
5784
3.98 to 50.16
1.365
–10ՅhՅ10
–21ՅkՅ21
–14ՅlՅ14
3610
2.07 to 25.07
1.182
–12ՅhՅ12
–20ՅkՅ20
–15ՅlՅ15
3808
No. reflections collected 4087
No. reflections observed 3323
4850
0.0375, 0.0805
0.487, –0.477
2557
0.0593, 0.1452
0.817, –0.487
2661
0.0573, 0.1498
0.566, –0.285
[a]
R, Rw
0.0438, 0.1067
0.633, –0.209
Final difference [eÅ–3]
[a] R = Σ||Fo| – |Fc||/Σ|Fo|. Rw = [Σw(|Fo| – |Fc|)2/Σw(Fo)2]1/2, where w = 1/σ2(Fo). λ(Mo-Kα) = 0.71073 Å.
mounted on either a Bruker SMART-APEX[28a] (1–4, 6, 7), or a
Bruker-Nonius Kappa CCD diffractometer [{L3Cu(PPh3)}(BF4)
and 5]. Intensity data for 1–4, 6, and 7 were collected by using 10 s
by frame (except for 4 where 30 s was used), separated by 0.3°.
Data integration and cell refinement was made by using
SAINTPLUS.[28b] The structures were solved by direct methods
with the use of XS and XL in SHELXTL,[28c] or the program sys-
tem SHELXL-97 in connection with absorption correction.[28d]
Anisotropic thermal parameters were included for all non-hydrogen
atoms. H atoms were placed geometrically and refined by using a
riding model, including free rotation of methyl groups and variable
isotropic displacement parameters. Final R values and important
bond parameters are listed in Tables 1, 2, 5, and 6.
C, 1s. Geometry optimization and single point calculations were
done for [Cu2L2X2]2+ by considering a unrestricted singlet state
involving Ci or C2 symmetry as constraints for anti and syn models,
respectively.
CCDC-647370 to -647377 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Supporting Information (see footnote on the first page of this arti-
cle): Selected DFT optimized distances and angles for model com-
plexes 1–6, 8, and [L2Cu(μ-MeO)2CuL2]2+, bond lengths and
angles for [L3Cu(PPh3)](BF4).
Analysis of the raw data for complex 3 clearly suggested that the
crystal had two identifiable components, related by a 180° rotation
around Ͻ–1,–2,0Ͼ. Data reduction using both components shows
one major component (mean I/σ = 2.0) and a minor one (mean
I/σ = 0.5). A rather small amount of reflections (≈5%) corresponds
to overlapped data. Structure solution and structure refinement
were finally performed considering just the major component.
Acknowledgments
This work was performed within the Collaborative Research Centre
SFB 706 (Selective Catalytic Oxidations Using Molecular Oxygen;
Stuttgart) and funded by the German Research Foundation, the
Fonds der Chemischen Industrie (FCI) and by FONDECYT (pro-
ject No. 1050484).
During the last stages of refinement some disorder of the perchlo-
rate anions for complexes 1, 2, 3, 4, and 6 was obvious. This was
modeled by using partially occupied positions, which were first re-
fined and then held constant for the final refinement.
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