Monitoring the formation of coordination complexes using electrospray mass spectrometry

Article abstract of DOI:10.1002/asia.200900007

cis,trans-1,3,5-Triaminocyclohexane (trans-tach) has been shown to be an excellent ligand in the synthesis of discrete complexes, molecular clusters, and infinite architectures. Herein, we report the Schiff-base derivitization of trans-tach to form cis,tr

Full text of DOI:10.1002/asia.200900007

DOI: 10.1002/asia.200900007
Monitoring the Formation of Coordination Complexes Using Electrospray
Mass Spectrometry
Jennifer S. Mathieson, Geoffrey J. T. Cooper, Alexandra L. Pickering, Marco Keller,
De-Liang Long, Graham N. Newton, and Leroy Cronin*[a]
Abstract: cis,trans-1,3,5-Triaminocyclohexane (trans-tach) has been shown to be an
excellent ligand in the synthesis of discrete complexes, molecular clusters, and in-
finite architectures. Herein, we report the Schiff-base derivitization of trans-tach to
form cis,trans-1,3,5-tris (pyridine-2-carboxaldimino) cyclohexane (ttop), and the
complexation of this ligand with copper(II) salts. The complexation reaction leads
to the crystallization of transition-metal complexes with nuclearities of 1, 2, and 4,
and the formation of the complexes can be followed stepwise, in real time, using
electrospray mass spectrometry.
Keywords: coordination modes
ligand design · mass spectrometry ·
·
Schiff bases
chemistry
·
supramolecular
Introduction
for supramolecular architectures[13] because of their ability
to bind to multiple transition metals and to stabilize struc-
tures through noncoordinative interactions.[14] The design of
a ligand, that is, the geometrical arrangement of the binding
sites and the structural flexibility of the backbone, has great
importance in the metal-binding ability of the ligand.[15–16]
Ideally, to engineer polynuclear coordination clusters,
multiple discrete binding sites and a degree of structural ri-
gidity is required. In this respect, the inclusion of a cyclo-
hexane backbone in a ligand can satisfy both of these de-
mands. For instance, in previous studies we have shown that
the complexation of cis,trans-1,3,5-triaminocyclohexane
(trans-tach) yielded a range of interesting complexes includ-
ing polynuclear clusters,[17] coordination networks,[18] and
one-dimensional chain complexes.[19] Herein, we not only
report an extension to these studies, but also start to follow
the complexation reactions using mass spectrometry. cis,-
The control of transition-metal architectures is an area of
great interest to chemists because of the vast potential for
the design of functional compounds,[1–2] as well as expanding
the understanding of the fundamental processes that under-
pin the formation of the complexes,[3–4] and large self-assem-
bled structures based upon smaller building blocks.[5–6] Of
course the development of optical,[7] porous,[8] catalytic,[9]
and magnetic materials[10] based upon such complexes is of
vital importance and interest, but understanding the assem-
bly of larger cluster structures remains a great challenge,
and arguably limits our ability to produce systems with radi-
cally new properties.[11] One route to address these problems
has been to design ligands that will help create a new struc-
ture type with well-defined physical properties, and almost
invariably the need to produce crystalline material for single
crystal diffraction studies has been mandatory.[12] Indeed,
much research has been focused on the use of ligand-design
principles to develop polydentate ligands as building blocks
trans-1,3,5-Tris(pyridine-2-carboxaldimino)
cyclohexane
(ttop) was chosen for this work since we understand the
complexation chemistry of this ligand system (see
Scheme 1).
In this study, we have chosen to employ mass spectrome-
try to monitor the complexation process, in conjunction with
a well-understood ligand system, to see if we can monitor
the overall complexation process. Indeed, electrospray ioni-
sation mass spectrometry (ESI-MS) has been shown to be a
potent tool in the analysis of such labile coordination com-
plexes.[20–23] Herein, we report our investigations into the co-
ordination chemistry of the ligand ttop and its behavior
when coordinated with copper(II) chloride. Using both stan-
[a] J. S. Mathieson, Dr. G. J. T. Cooper, A. L. Pickering, M. Keller,
Dr. D.-L. Long, G. N. Newton, Prof. L. Cronin
WestCHEM, Department of Chemistry
The University of Glasgow
Glasgow G12 8QQ (UK)
Fax : (+44)141-330-4888
E-mail: L.Cronin@chem.gla.ac.uk
Homepage: www.chem.gla.ac.uk/staff/lee
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.200900007.
Chem. Asian J. 2009, 4, 681 – 687
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Structural Analysis
In total, in this paper we present five new crystal structures
(2–6) (see Figure 1), and the structural data is summarized
in Table 1. For complex 2, a stoichiometry of 1:2 CuIICl2/ttop
Scheme 1. Reaction scheme describing the formation of cis,trans-1,3,5-
tris(pyridine-2-carboxaldimino) cyclohexane (ttop, L1) from trans-tach
Figure 1. Crystal structure of [Cu(L1)Cl]ClACTHNURGTNEG(UN CH3OH)2 2 showing only the
tetradentate coordination site being filled; Crystal structure of
[Cu2(L1)Cl4]CH3OH 3 showing both the tetradentate and bidentate coor-
and pyridine2-carboxaldehyde in methanol, which yields
Schiff-base ligands.
a range of
dination sites being filled; Crystal structure of [Cu(L2)Cl
showing the hydrolyzed ligand, in which the trans-pyridyl arm has been
cleaved; Crystal structure of [Cu2(L3)2A(NO3)2](NO3) 5 showing two hy-
ACHTUGNRETN(NUGN H2O)]Cl2 4
G
ACHTUNGTRENNUNG
dard crystallographic techniques and ESI-MS, the study
aims to investigate the complex formation, and probe if we
can control the assembly of the architecture with bulk reac-
tion parameters (e.g., stoichiometry) with the particular aim
of monitoring the assembly of multinuclear cluster species
in solution.
drolyzed ligands complexed with two metals. The two axial pyridine
groups are twisted in relation to each other and the equatorial trans pyri-
dine arm has been cleaved off to allow the nitrogen from the trans arm
to coordinate to the adjacent copper(II) center; Crystal structure of
{[Cu2(L1)Cl3]Cl}2 6 showing the two ligand-four metal center complex.
The two ligands are held together by two bridging chlorides coordinating
to the bidentate copper(II) centers. (Grey corresponds to carbon atoms;
dark blue to nitrogen atoms; light blue to copper; green to chloride) (hy-
drogen atoms, counterions, and noncoordinated solvent molecules are ex-
cluded for clarity).
Results and Discussion
Ligand Design
The ligand designed for this investigation was produced by
the reaction of trans-tach with pyridine-2-carboxaldehyde to
give the ligand, ttop (C24H24N6) (L1), the trans hydrolyzed
ttop (C18H21N5) (L2), and the mono cis hydrolyzed ttop (L3)
(see Scheme 1). These ligands are highly labile and can flip
from a bisequatorial monoaxial to a bisaxial monoequatorial
conformation arising from the ring-flip ability of the cyclo-
hexane backbone. The energetically favored conformer, in
which the ligand takes on the ring-flipped ꢁclosedꢂ confor-
mation, is maintained in each of the presented complexes 2–
yields the mononuclear complex [Cu(L1)Cl]ClACHTNUGTRNEG(UN CH3OH)2 (2)
(see Figure 2), with the imine double bonds substituted in
the sterically favored E-conformation. The copper(II) ion is
coordinated within the tetradentate binding site in a distort-
ed square-pyramidal geometry by basal coordination to each
of the four nitrogen atoms of the cis-imidyl pyridyl moieties.
À
The Cu1 N bond lengths for the imine groups are 1.997(2)
À
and 2.019(2) ꢃ, with the bond lengths for the pyridyl Cu1
N being 2.099(2) and 2.035(2) ꢃ, which lie within expected
ranges,[24–26] and an apical coordination of one chloride ion
with a bond length of 2.4198(7) ꢃ. The chloride ligand is
oriented above the cyclohexane ring with the copper(II) ion
also oriented towards the center of the molecule at an angle
of 166.5(8)8, placing the copper(II) over the cyclohexane
ring. The bidentate binding site is not involved in the coor-
dination of a metal center. The nitrogen atoms of the imine
group and pyridyl group are oriented anti with respect to
each other to minimise electronic repulsion between the
lone pair on each nitrogen. The trans-imidyl pyridine arm is
twisted with respect to the cyclohexane ring at an angle of
60.0(1)8.
6: [Cu(L1)Cl]Cl
ACHTUNGTRENNUNG
[Cu(L2)Cl(H2O)]Cl2 (4), [Cu2(L3)
N
N
ACHTUNGTRENNUNG
{[Cu2(L1)Cl3]Cl}2 (6). As such, this favored conformation of
L1 gives rise to two coordination sites, an axial tetradentate
site, constructed from the nitrogen atoms on both the pyri-
dine groups and the associated imine groups, and an equato-
rial bidentate coordination site, formed from the two nitro-
gen atoms from the trans arm of ttop. As expected, the axial
tetradentate coordination site is the most favored site for
metal ion coordination, and is filled first.
682
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Chem. Asian J. 2009, 4, 681 – 687

Monitoring the Formation of Coordination Complexes
Table 1. Crystal structure data for compounds 2–6.
2
3
4
5
6
Empirical formula
Fw
Crystal system
a [ꢃ]
b [ꢃ]
c [ꢃ]
a [8]
b [8]
g [8]
C26H32N6O2CuCl2
595.02
C25H28N6OCu2Cl4
697.41
Monoclinic
9.1119(4)
8.8875(8)
17.8313(7)
90
98.715(8)
90
Pc
1412.2(2)
2
1.624
1.915
150(2)
6892
CuC18H28N5O3Cl3
532.34
C36H42N14Cu2O12
1086.04
Monoclinic
11.8957(3)
26.6195(8)
15.8896(3)
90
110.442(1)
90
P21/n
4714.7(2)
4
1.530
0.985
150(2)
C26H32N6Cu2Cl4O2
729.46
Triclinic
7.5983(2)
11.5797(5)
16.5969(7)
73.601(4)
89.339(3)
84.940(3)
P-1
1395.3(1)
2
1.416
1.002
150(2)
Triclinic
7.4342(5)
11.5628(6)
14.1665(8)
95.409(3)
94.561(3)
106.415(3)
P-1
1155.7(2)
2
1.530
1.321
150(2)
Triclinic
9.7929(3)
12.8175(5)
13.9117(7)
88.942(2)
78.430(2)
69.323(2)
P-1
1597.9(1)
2
1.516
1.699
150(2)
Space group
V [ꢃ3]
Z value
1calcd [gcmÀ3
]
m [mmÀ1
T [K]
]
No. of Reflections Collected
No. of Unique Reflections
No. parameters
9129
4474
338
14110
4218
289
30755
8258
645
21121
5623
370
4393
345
R
(I>2s(I))
0.0275
0.0611
0.0288
0.0474
0.0490
0.0914
0.0751
0.1770
0.0659
0.1666
wR2 (all data)
If the stoichiometry is changed to 1:1 CuIICl2/ttop, then
the complex [Cu2(L1)Cl4]CH3OH 3 (see Figure 2) can be
formed. From 3, it can be seen that both binding sites have
been filled by copper(II) centers. One copper(II) ion is coor-
dinated in the tetradentate binding site in a distorted
square-pyramidal geometry by a basal coordination to each
of the four nitrogen donors, with a chloride ligand occupying
the apical binding site oriented away from the cyclohexane
2.6590(11) ꢃ with the Cu OH2 bond length being
2.407(3) ꢃ.
À
If the stoichiometry and counterion are changed to 1:1
CuII
(NO3)]ACHTNUGTRENNUNG
ACHTUNGTRENNUNG
G
coordinated at the hydrolyzed cis amine and the cis imidyl
pyridyl arm of the first ligand, and the trans imidyl pyridyl
arm from the second ligand. The octahedral coordination
À
À
ring. The Cu1 N bond lengths for the imine groups of the
sphere is completed by an axial nitrate group. The Cu1 N
cis arms are 1.998(2) and 1.980(2) ꢃ, and 2.081(2) and
2.026(2) ꢃ for the pyridyl nitrogen to copper(II) bond
lengths. The apical coordination of one chloride ligand
bond distances are 1.999(5) ꢃ and 2.279(5) ꢃ for the imine
groups, 2.023(5) ꢃ and 2.045(5) ꢃ for the pyridyl nitrogens,
and 2.035(5) ꢃ for the amine group. Cu2 has a distorted oc-
À
À
(Cu1 Cl bond length=2.429(8) ꢃ) completes the square-
tahedral coordination geometry with the Cu2 N bond dis-
pyramidal coordination sphere. The bidentate site of the
trans arm binds a second copper(II) ion, which is coordinat-
ed, in square-pyramidal geometry,by the imidyl and pyridyl
tances for the imine groups being 2.333(5) ꢃ, 2.010(5) ꢃ,
2.054(5) ꢃ, and 2.034(5) ꢃ for the pyridyl nitrogens,
2.014(5) ꢃ for the amine group, and 2.827(5) ꢃ for the ni-
trate ion. Cu2 also exhibits long range axial coordination to
the neighboring nitrate of the nearest ligand, forming a
À
nitrogen atoms, with bond lengths of Cu Nimidyl =2.026(2) ꢃ
and Cu Npyridyl =2.074(2) ꢃ. The final three coordination
À
À
sites are occupied by chloride anions, with binding distances
of 2.282(8), 2.273(8), and 2.562(8) ꢃ. The trans-imidyl pyrid-
yl arm is oriented perpendicular to the two axial pyridine
rings, as with the mononuclear complex 2, and is twisted
with respect to the cyclohexane ring at an angle of 66.1(2)8.
Complex 2 reacted with 4,4’-bipyridine resulting in the
chain-like structure. The Cu2 ONO2 bond length is
2.635(5) ꢃ, this bond length lying within the range previous-
ly reported for highly distorted octahedrons.[27]
If the stoichiometry is changed to 2:1 CuIICl2/ttop, a two
ligand-four metal center complex {[Cu2(L1)Cl3]Cl}2 6 (see
Figure 2) is formed. Both coordination sites on each ligand
are complexed to copper(II) ions in a square-pyramidal ge-
ometry. As with the mononuclear and dinuclear complexes
2 and 3, respectively, the tetradentate binding site coordi-
nates Cu1 by its four nitrogen atoms available upon ring-flip
of the cyclohexane ring (Cu1 N imine groups=1.996(2) and
2.004(6) ꢃ, Cu1 N pyridyl=2.036(6) and 2.069(5) ꢃ). The
coordination sphere of Cu1 is completed by one chloride
ligand, which like 3, is pointing away from the cyclohexane
formation of a monoligand complex [Cu(L2)ClACTHNUTRGNE(UNG H2O)]Cl2 4
(see Figure 2). The trans arm is hydrolyzed and protonated
preventing coordination, but increasing the donor ability of
the amino group to form hydrogen-bonded interactions with
the chloride counterions. The tetradentate pocket, formed
by the cis arms of the ring-flipped cyclohexane backbone,
coordinates to one copper(II) ion with the octahedral geom-
etry being completed by one chloride ion and one water
À
À
À
À
molecule. The Cu N bond lengths for the imine groups are
1.9991(3) ꢃ and 2.022(3) ꢃ, and 2.066(3) ꢃ and 2.030(3) ꢃ
ring (Cu1 Cl=2.427(2) ꢃ). The bidentate binding site coor-
dinates a second copper(II) with its two nitrogen atoms
À
À
À
for the pyridyl nitrogens. The Cu Cl bond length is
(Cu2 Nimine =2.046(6) ꢃ, Cu2 Npyridyl =2.045(6) ꢃ), along
Chem. Asian J. 2009, 4, 681 – 687
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683

L. Cronin et al.
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Mass Spectrometry
ESI-MS studies were used to observe the stepwise construc-
tion of 2–6 (see Figure 2). From the electrospray measure-
ments, it can be seen that the labile ttop ligand can complex
with the copper(II) chloride firstly to form the mononuclear
complex [Cu(L1)Cl]+, while the change of the stoichiometry
gives the higher nuclearity complexes. The ability to observe
the formation of the complexes from low to higher nucleari-
ty probably arises from the most favorable site (the tetra-
dentate binding site) being filled first, and therefore allow-
ing control over the nuclearity of the complex. Ttop in
methanol (10À5 m) gave the ESI-MS spectrum A (ESI-MS of
[L1H]+, m/z=397.2); half an equivalent of copper(II) chlo-
ride to one equivalent of L1 produced spectrum B (ESI-MS
of [Cu(L1)Cl]+, m/z=494.1); one equivalent of copper(II)
chloride reacted with one equivalent of L1 produced spec-
trum C (ESI-MS of [Cu2(L1)Cl3]+, m/z=629.0); one equiva-
lent of 4,4ꢀ-bipyridine reacted with one equivalent of com-
plex 2 and gave spectrum D (ESI-MS of [Cu(L2)Cl]+, m/z=
405.1); one equivalent of copper(II) nitrate reacted with one
equivalent of L1 producing complex 5 and gave spectrum E
(ESI-MS of [Cu2(L3)2ACHTNURTGENUNG
(NO3)3]+, m/z=928.2); two equiva-
lents of copper(II) chloride with one equivalent of L1 pro-
duced spectrum F (ESI-MS of [Cu4(L1)2Cl7]+, m/z=1294.9).
From the spectra produced, it can be seen that the stoichi-
ometry of the reactant used in the reaction is the predomi-
nant factor in the formation of the complex. The copper(II)
chloride salt reacts to give complexes 2–4 and 6 with the ni-
trate salt producing the hydrolyzed dimer 5 (Scheme 2).
In-situ Mass Spectrometry
The combination of pre-diluted reactants in-situ was investi-
gated using ESI-MS to allow the kinetically favored product
to be observed and analysed. To create such experimental
conditions, a tee-piece was used to enable the input and sub-
sequent mixing of the reactants (see Figure 3). Initially,
input A was L1 in methanol (10À5 m) and input B was a
blank control containing only methanol. This reaction mix-
ture resulted in a spectrum with a predominant peak at
397 m/z being L1. Replacing the blank with 0.5 equivalents,
1 equivalent, and 2 equivalents of copper(II) chloride pro-
duced spectra b) to d), respectively. The spectra produced
show the kinetic product formed with each equivalent
(Figure 4): 0.5 equivalents of copper(II) chloride gave the
Figure 2. A) ESI-MS measurement of [L1H]+ (1); B) ESI-MS measure-
ment of [Cu(L1)Cl]+ 2; C) ESI-MS measurement of [Cu2(L1)Cl3]+ 3;
D) ESI-MS measurement of [Cu(L2)Cl]+ 4; E) ESI-MS measurement of
[Cu2(L3)2ACHTUNGTRENNUNG
(NO3)3]+ 5; F) ESI-MS measurement of [Cu4(L1)2Cl7]+ 6.
(Black spectrum=experimental measurement; grey spectrum=predicted
measurement).
À
with one terminal chloride ligand (Cu2 Cl=2.256(2) ꢃ) and
two bridging chloride ligands (Cu2 Cl=2.284(18) and
species [Cu(L2)ACTHNGUTERNNUG
(H2O)4(OH)]+; the predominant species
À
À
2.651(2) ꢃ). The Cu2 Cu2* distance of 3.497 ꢃ lies within
with 1 equivalent of copper(II) chloride being [Cu(L1)Cl]+;
2 equivalents of copper(II) chloride produces a spectrum
showing the species [Cu2(L1)Cl3]+.
The use of a tee-piece allows a combination of dilute re-
actants to be observed directly after mixing. By using the
most simple of building blocks, clusters were formed almost
instantaneously, providing further evidence of the coordina-
tion self-assembly processes occuring in ttop CuII systems. It
is interesting to note that the stoichiometry used to produce
the thermodynamic products is different to that used to pro-
the reported range of m2-chloride bridged copper(II)
dimers.[28–30] A number of different divalent 1st row transition
metals can also be coordinated to the L1, L2, and L3 li-
gands. Cobalt(II) and zinc(II) can be coordinated (with both
chloride and nitrate counter ions as with copper(II)) to give
the isostructural complexes of those found in copper(II) sys-
tems.[31]
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Chem. Asian J. 2009, 4, 681 – 687

Monitoring the Formation of Coordination Complexes
duce the same complex when
using in-situ mass spectrometry.
Conclusions
The labile ligand ttop has the
ability to form a range of coor-
dination complexes when com-
bined with copper(II) salts. This
coordination reaction can be
followed in real time using ESI-
MS.[34] Control over the stoichi-
ometry and reaction conditions
allows the formation of com-
plexes with different metal to
ligand ratios. As both cobalt(II)
and zinc(II) can be coordinated
to the ttop ligand, it is hoped to
continue the work to include
cobalt
(III),
nickel(II),
and
iron(II) using both the chloride
and nitrate salts. Further, by
using metals that can be
ꢁswitchedꢂ between relatively
labile and inert kinetic forms
(e.g., cobalt II/III), the use of
in-situ mass spectrometry to
Scheme 2. Summary of complexes (2–6) obtained from ttop (L1) under different stoichiometries and reaction
conditions.
monitor the assembly of very large systems using a variety
of control parameters (stoichiometry, REDOX reagent, con-
centration, range, and rigidity of ligands) will become possi-
ble.
Figure 3. Schematic of tee-piece (mixer) combining two inputs to ESI-
MS. The distance d is variable, but for these experiments was set at 5 cm.
The mixer had no dead volume and the tubing had a diameter, d, of
0.9 mm. Inputs were set to a rate of approximately 100 mLhÀ1, and thus, a
combined input of approximately 200 mLhÀ1 was obtained.
Experimental Section
All reagents were used as received from commercial sources, without fur-
ther purification. The ligand cis,trans-1,3,5-triaminocyclohexane was syn-
thesized according to literature methods.[32] 1H and 13C NMR spectra
were recorded at room temperature (RT) unless otherwise stated, on a
Bruker DRX-500 and DPX-400 spectrometer in CH3Cl. Infra-red spec-
tral analyses were performed on a JASCO 410 spectrophotometer, using
a KBr disc and a Shimadzu FTIR 8400S; peaks are quoted in wavenum-
bers (cmÀ1) and their relative intensity are reported as follows: s=strong,
m=medium, w=weak. UV/Vis spectroscopy was performed on Shimad-
zu UV-310PC UV/Vis/NIR scanning spectrophotometer. Microanalyses
were performed on a CE-440 elemental analyzer. Mass spectra were ob-
tained using a Bruker MicrOTOF-Q in ESI positive ion mode. X-ray dif-
fraction was performed using an Oxford Diffraction Gemini Ultra with a
CrysAlis CCD detector [l MoKa =0.71073 ꢃ)]. Crystal data for com-
pounds 2–6 is presented in Table 1. Structure refinements were per-
formed using the SHELXS-97[33] by WinGX[35] software package.
CCDC 714504,
CCDC 714505,
CCDC 714506,
CCDC 714507,
CCDC 714508 contain the supplementary crystallographic data for this
paper for compounds 2–6 respectively. These data can be obtained free
of charge from The Cambridge Crystallographic Data Center at
www.ccdc.cam.ac.uk/data_request/cif.
Figure 4. ESI-MS measurement of a) Input A: L1 in methanol (10À5 m),
Input B: methanol, predominant species [L1H]+, m/z=397; b) Input A:
L1 in methanol (10À5 m), Input B: 0.5 equivalents copper(II) chloride,
predominant species [Cu(L2)ACHTNUGRTNEUNG
(H2O)4(OH)]+, m/z=419; c) Input A: L1 in
Syntheses
methanol (10À5 m), Input B: 1 equivalent copper(II) chloride, predomi-
nant species [Cu(L1)Cl]+, m/z=494; d) Input A: L1 in methanol
(10À5 m), Input B: 2 equivalents copper(II) chloride, predominant species
[Cu2(L1)Cl3]+, m/z=629.
cis,trans-1,3,5-Tris(pyridine-2-carboxaldimino) cyclohexane (L1) 1: Pyri-
dine-2-carboxaldehyde (2.38 g, 23.18 mmol) was added to a methanolic
solution (100 mL) of cis,trans-1,3,5-triaminocyclohexane (1 g, 7.85 mmol)
Chem. Asian J. 2009, 4, 681 – 687
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685

L. Cronin et al.
FULL PAPERS
and triethylamine (2.38 g, 23.55 mmol) and refluxed for 24 h under nitro-
gen. The solvent was removed under vacuum, the resulting brown prod-
uct (2.24 g, 5.64 mmol, 72%) being taken off in dichloromethane
(150 mL), and washed with water (3ꢄ50 mL). The organic layer was
dried over magnesium sulfate and the dichloromethane removed in
vacuo. M.p.: 758C; IR (Golden Gate): n˜ =3059 (w), 2928 (m), 2858 (m),
1643 (s), 1585 (s), 1566 (s), 1466 (s), 1435 (s), 1373 (m), 1319 (w), 1288
(w), 1227 (w), 1134 (m), 1080 (m), 1042 (m), 1018 (w), 991 (s), 972 (s),
volume to approximately 5 mL. Crystallization by diffusion of ether re-
sulted in dark green crystals (278.1 mg, 0.209 mmol, 83%). IR (Golden
Gate): n˜ =3435 (m), 2037 (m), 2951 (m), 2925 (m), 1643 (s), 1597 (s),
1567 (m), 1479 (m), 1444 (s), 1398 (w), 1381 (w), 1323 (w), 1302 (s), 1269
(w), 1227 (s), 1159 (w), 1132 (s), 1105 (m), 1049 (m), 1014 (m), 980 (s),
935 (w), 881 (m), 768 (s), 742(m), 696 (w), 642 (s) cmÀ1; elemental analy-
sis: calcd (%) for Cu2C24H24N6Cl4: C 43.32, H 3.64, N 12.63; found:
C 42.33, H 3.48, N 12.17.
860 (s), 772 (s), 741 (s), 664 (m), 650 (m), 617 (s), 562 (m), 517 (s) cmÀ1
;
ESI-MS Experimental and Analyses
1H NMR (400 MHz, CDCl3): d=8.56 (d, 1H, J 4.9 Hz), 8.55 (d, 2H, J
5.0 Hz), 8.40 (s, 2H), 8.38 (s, 1H), 8.02 (d, 1H, J 8.0 Hz), 7.90 (d, 2H, J
8.0 Hz), 7.68 (d, 1H, J 8.0, 7.5 Hz), 7.62 (td, 2H, J 8.0, 7.5 Hz), 7.23 (ddd,
1H, J 6.5, 6.0 Hz), 7.12 (ddd, 2H, J 6.5, 6.0 Hz), 4.11 (pt, 2H, J 11.3 Hz),
3.97 (brs, 1H), 2.07 (m, 3H), 1.95 (brd, 1H, J 12.5 Hz), 1.80 ppm (brd,
2H, J 12.5 Hz); 13C NMR (75 MHz, CDCl3): d=159.16 (CH2), 158.83
(CH), 153.38 (C), 153.33 (C), 147.95 (CH), 147.84 (CH), 135.00 (CH),
123.20 (CH), 123.10 (CH), 119.99 (CH), 119.75 (CH) 63.48 (CH), 61.68
(CH), 39.90 (CH2), 38.68 ppm (CH2); MS (ESI): m/z (%): 419 [M+Na]+;
elemental analysis: calcd (%) for C24H24N6: C 72.70, H 6.10, N 21.20;
found: C 72.53, H 6.31, N 20.90.
All MS data were collected using a Q-trap, time-of-flight MS (MicrO-
TOF-Q MS) instrument supplied by Bruker Daltonics Ltd. A cryospray
source, also supplied by Bruker Ltd., was used to collect data under the
conditions specified below. The detector was a time-of-flight, microchan-
nelplate detector, and all data were processed using the Bruker Daltonics
Data Analysis 3.4 software, while simulated isotope patterns were investi-
gated using Bruker Isotope Pattern software and Molecular Weight Cal-
culator 6.45. The following parameters were consistent for all CSI-MS
scans given below. The calibration solution used was Agilent ES tuning
mix solution, Recorder No. G2421A, enabling calibration between
À100 m/z and 3000 m/z. This solution was diluted 60:1 with acetonitrile.
Samples were introduced into the MS by direct injection at 180 mLhÀ1
having been diluted to 10À5 m in methanol. The drying nitrogen gas tem-
perature was at 1808C. The ion polarity for all MS scans recorded was
positive, with the voltage of the capillary tip set at 4500 V, end plate
offset at À500 V, funnel 1RF at 300 Vpp, and funnel 2RF at 400 Vpp.
All theoretical peak assignments were determined by comparison of the
experimentally determined isotopic patterns for each peak, with simulat-
ed isotopic patterns. For relatively small complexes, such as the ttop com-
plexes, the isotopic pattern is quite distinct, and comparison between ex-
perimental and simulated patterns is more meaningful (see Figure 2)
than in the case of larger fragments, in which the isotopic pattern takes
on a Gaussian shape, and it cannot be said with certainty that the sug-
gested peak is unequivocally correct.
[Cu(L1)Cl]Cl
ACHTUNGTRENNUNG
0.25 mmol) was added to
a
0.23 mmol) in methanol (5 mL). The solution changed from a pale yellow
color to dark green. The solution was stirred for 30 min and reduced in
volume to approximately 5 mL. Crystallization by diffusion of ether re-
sulted in dark green crystals (20 mg, 0.034 mmol, 13%). IR (KBr): n˜ =
3433 (s), 2928 (w), 2356 (w), 1644 (m), 1602 (m), 1385 (s), 1309 (m), 1242
(s), 1135 (m), 978 (w), 867 (w) cmÀ1; elemental analysis: calcd (%) for
C24H24Cl2CuN6: C 54.29, H 4.56, N 15.83; found: C 53.18, H 4.63, N 15.54.
A
A
methanolic solution (20 mL) of L1 (100 mg,
solution of copper(II) chloride (34 mg,
a
0.25 mmol) in methanol (5 mL). The solution changed from a pale yellow
color to dark green. The solution was stirred for 30 min and reduced in
volume to approximately 5 mL. Crystallization by diffusion of ether re-
sulted in dark green crystals (133.9 mg, 0.192 mmol, 76%). IR (KBr): n˜ =
3430 (s), 2926 (w), 2065 (w), 1638 (s), 1598 (s), 1478 (m), 1446 (m), 1384
(m), 1305 (m), 1271 (w), 1226 (m), 1158 (w), 1132 (m),1048 (w), 1019
(w), 992 (w),926 (w), 874 (w), 775 (m) cmÀ1; elemental analysis: calcd
(%) for Cu2C24H24N6Cl4: C 43.32, H 3.64, N 12.63; found: C 40.78, H 3.98,
N 11.19.
Acknowledgements
[Cu(L2)
0.041 mmol) was added to
0.041 mmol) in methanol (5 mL).
ACHTUNGTRENNUNG
The authors wish to thank the EPSRC and the University of Glasgow for
funding this research.
a
A
formed immediately. Methanol was added until the volume was 75 mL
and the solution was refluxed for 30 min. After evaporation of methanol
to a volume of approximately 5 mL, filtration through cotton wool af-
forded a clear brown solution. Crystallization by diffusion with ether re-
sulted in brown-green crystals (5.1 mg, 0.0095 mmol, 23%). IR (KBr):
n˜ =3424 (s), 2857 (w), 2057 (w), 1639 (s), 1598 (s), 1479 (w), 1444 (w),
1383 (m), 1303 (w), 1269 (w), 1227 (w), 1157 (m), 1132 (w), 1101 (w),
1047 (w), 1019 (w), 882 (m), 776 (m) cmÀ1; elemental analysis: calcd (%)
for CuC18H28N5O3Cl3: C 40.611, H 5.301, N 13.156; found: C 40.61,
H 4.46, N 12.33.
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Received: January 7, 2009
Published online: April 9, 2009
Chem. Asian J. 2009, 4, 681 – 687
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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