Bimetallic copper(II) and zinc(II) complexes of acyclic Schiff base ligands derived from amino acids

Article abstract of DOI:10.1016/j.ica.2010.08.043

The acyclic Schiff-base ligands (2-(OH)-5-(R³)C ₆H₂-1,3-(HCNC(R¹)(R²)CO ₂H), derived from the dialdehyde 2-hydroxy-5-R-1,3- benzenedicarboxaldehyde (R = Me or t-Bu) and two equivalents of the amino acids glycine, 2,2-diphenylglycine or phenylalanine, have been reacted with the metal acetates M(OAc)₂ (M = Cu, Zn) in the presence of triethylamine, affording the complexes [HNEt₃][M₂(CH₃CO ₂)₂(2-(O)-5-(t-Bu)C₆H₂-1,3- (HCNC(R¹)(R²)CO₂)₂] (M = Cu, R ¹ = R² = C₆H₅, R³ = Me (1); M = Zn, R¹ = R² = H, R³ = t-Bu (2); M = Zn, R¹ = R² = C₆H₅, R³ = t-Bu (3); M = Zn, R¹ = H, R² = CH₂C ₆H₅, R³ = t-Bu (4)) in good yields. The crystal structures of 1·MeCN, 2·112MeOH, 3·2MeOH, and 4·3MeOH have been determined.

Full text of DOI:10.1016/j.ica.2010.08.043

Inorganica Chimica Acta 365 (2011) 96–102
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Bimetallic copper(II) and zinc(II) complexes of acyclic Schiff base ligands
derived from amino acids
b
b
Abdessamad Arbaoui a, Carl Redshaw a, , Noelia M. Sanchez-Ballester , Mark R.J. Elsegood ,
⇑
David L. Hughes a
a Energy Materials Laboratory, School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK
b Chemistry Department, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK
a r t i c l e i n f o
a b s t r a c t
The acyclic Schiff-base ligands (2-(OH)-5-(R3)C6H2-1,3-(HC@NC(R1)(R2)CO2H), derived from the dialde-
hyde 2-hydroxy-5-R-1,3-benzenedicarboxaldehyde (R = Me or t-Bu) and two equivalents of the amino
acids glycine, 2,2-diphenylglycine or phenylalanine, have been reacted with the metal acetates
M(OAc)2 (M = Cu, Zn) in the presence of triethylamine, affording the complexes [HNEt3][M2(CH3CO2)2-
(2-(O)-5-(t-Bu)C6H2-1,3-(HC@NC(R1)(R2)CO2)2] (M = Cu, R1 = R2 = C6H5, R3 = Me (1); M = Zn, R1 = R2 = H,
Article history:
Received 15 June 2010
Received in revised form 15 August 2010
Accepted 21 August 2010
Available online 22 September 2010
R
3 = t-Bu (2); M = Zn, R1 = R2 = C6H5, R3 = t-Bu (3); M = Zn, R1 = H, R2 = CH2C6H5, R3 = t-Bu (4)) in good
Keywords:
Copper
Zinc
yields. The crystal structures of 1ꢀMeCN, 2ꢀ1 21 MeOH, 3ꢀ2MeOH, and 4ꢀ3MeOH have been determined.
Ó 2010 Elsevier B.V. All rights reserved.
Schiff-base
Amino acids
Crystal structures
e-Caprolactone
1. Introduction
employed for the synthesis of a number of new macrocyclic Schiff
base ligand systems [13], we decided to employ a template strategy
There is currently much academic and industrial interest in bio-
compatible catalytic systems for the ring opening polymerisation
of lactides and lactone [1–8]. Recently, Hillmyer and Tolman drew
an interesting analogy between the coordination/insertion mecha-
nism in lactone polymerisation and the mechanism of hydrolysis
by some metalloenzymes [9]. In a commonly accepted mechanism
pathway, one of the two or more metals in the active site of the en-
zyme coordinates a water molecule enhancing its nucleophilic
ability by lowering its pKa and generating a metal bound hydroxide
species; while another metal coordinates to the substrate render-
ing it more electrophilic and more susceptible to nucleophilic at-
tack. Considering this, Hillmyer and Tolman studied lactone
polymerisation catalysts containing a Zn–O–Zn motif as metallo-
enzyme mimics, with the intention of promoting potential cooper-
ative effects between metal centres [9–12].
which led to the one-pot synthesis of complexes 1–4 (Scheme 1).
2. Results and discussion
2.1. Copper
The reaction of the dialdehyde 2-hydroxy-5-methyl-1,3-ben-
zenedicarboxaldehyde with the amino acid 2,2-diphenylglycine
and copper diacetate in the presence of triethylamine in refluxing
methanol afforded the green complex [HNEt3][Cu2(CH3CO2)2-
(2-(O)-5-(Me)C6H2-1,3-(HC@NC(Ph2CO2)2] in high yield (ca. 64%).
Crystals suitable for a single crystal X-ray diffraction study were
grown from a saturated acetonitrile solution on prolonged standing
at 0 °C. The crystal structure of 1 is shown in Fig. 1 with selected
bond lengths and angles given in the caption. Crystallographic data
are given in Table 1. The asymmetric unit comprises two cation/an-
ion pairs and two acetonitrile lattice solvent molecules. The cation
hydrogen bonds to the anion via N–Hꢀ ꢀ ꢀO(carboxylate) interactions
that are bifurcated in one case and mono-furcated in the other. One
cation is disordered such that it forms H-bonds to one anion or the
other.
With this in mind, we have decided to investigate the synthesis
and catalytic behaviour of zinc complexes supported by acyclic
Schiff base ligands. Using a phenolate residue as the central motif
of our ligand framework, we hoped to promote the formation of
the desired Zn–O–Zn motif. After failing to prepare this ligand
framework in a template-free fashion, a strategy that was recently
The copper metal centres in complex 1 are five coordinate and
adopt a distorted square-based pyramidal geometry (Reedijk crite-
ria s = 0.4 for Cu(1) and Cu(2)) [14] with O(6) and O(9) at the apex
⇑
Corresponding author.
E-mail address: carl.redshaw@uea.ac.uk (C. Redshaw).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.08.043

A. Arbaoui et al. / Inorganica Chimica Acta 365 (2011) 96–102
97
R3
HNEt3
R3
R1
R2
NH2
O
R1
R1
O
O
N
O
N
R2
R2
M
M
HO
O
O
OH
O
O
O
O
O
O
Scheme 1. Synthesis of complexes 1 (M = Cu, R1 = R2 = C6H5, R3 = Me), 2 (M = Zn, R1 = R2 = H, R3 = t-Bu), 3 (M = Zn, R1 = R2 = C6H5, R3 = t-Bu) and 4 (M = Zn, R1 = H,
R2 = CH2C6H5, R3 = t-Bu). Conditions: M(OAc)2 (2 equivalents wrt the dialdehyde), triethylamine (5 equivalents wrt the dialdehyde), methanol or ethanol, reflux 12 h.
Fig. 1. Crystal structure of one of two cation/anions pairs in the asymmetric unit of 1ꢀ2MeCN. The solvent of crystallisation is omitted for clarity. Selected bond lengths and
angles (Å, °): Cu(1)–O(1) 1.934(6), Cu(1)–N(1) 1.960(8), Cu(1)–O(3) 1.978(6), Cu(1)–O(6) 2.125(6), Cu(1)–O(8) 1.918(7), Cu(2)–O(3) 1.977(6), Cu(2)–N(2) 1.926(8), Cu(2)–O(4)
1.943(7), Cu(2)–O(7) 1.905(7), Cu(2)–O(9) 2.191(7), Cu(1)–O(3)–Cu(2) 112.2(3), O(3)–Cu(1)–O(1) 173.8(3), O(7)–Cu(2)–N(2) 150.1, O(8)–Cu(1)–N(1) 149.5(3), O(3)–Cu(2)–
O(4) 173.4(3), H(5)ꢀ ꢀ ꢀO(4) 2.11, N(5)–H(5)ꢀ ꢀ ꢀO(4) 143, H(5)ꢀ ꢀ ꢀO(5) 2.15, N(5)–H(5)ꢀ ꢀ ꢀO(5) 154.
for Cu(1) and Cu(2), respectively. Cu(1) and Cu(2) lie ca. 0.274 and
0.245 Å respectively above the mean planes defined by N(1), O(1),
O(3) and O(8) for Cu(1) and N(2), O(3), O(4) and O(7) for Cu(2). The
copper centres are bridged through a Cu–O–Cu bond and through
two acetate moieties.
for single crystal X-ray diffraction studies were grown from satu-
rated methanol solutions at ꢁ25 °C. Crystals of 2ꢀ1 12 MeOH and
4ꢀ3MeOH were small and required the use of synchrotron radiation
[15,16].
The X-ray crystal structure of complexes 2 and 3 and that of the
anion of 4 are presented in Figs. 2–4, respectively, with selected
bond lengths and angles given in the captions. Crystallographic
data are collated in Table 1.
2.2. Zinc
The reaction of the dialdehyde 2-hydroxy-5-tert-butyl-1,3-
benzenedicarboxaldehyde with the amino acids glycine, 2,2-
diphenylglycine or phenylalanine, and zinc diacetate in the presence
of triethylamine in refluxing ethanol or methanol readily afforded
the complexes [HNEt3][Zn2(CH3CO2)2(2-(O)-5-(t-Bu)C6H2-1,3-
(HC@NC(R1)(R2)CO2)2] (R1 = R2 = H (2); R1 = R2 = C6H5 (3); R1 = H,
R2 = CH2C6H5 (4)) in excellent yields (75%, 93% and 96%, respec-
tively). Crystals of 2ꢀ1 12 MeOH, 3ꢀ2MeOH, and 4ꢀ3MeOH suitable
Crystals of complex 2ꢀ1 12 MeOH formed as small, thin needles
and the resulting diffraction was weak even at the synchrotron.
The cations and methanol molecules were subject to substantial
disorder and the structure refinement was good enough only for
a confirmation of the connectivity. The asymmetric unit comprises
two cation/anion pairs and three methanol molecules. As in the
case of 1, the cations hydrogen bond to the anions via N–Hꢀ ꢀ ꢀO(car-
boxylate) interactions. The two zinc ions Zn(1) and Zn(2) adopt a

98
A. Arbaoui et al. / Inorganica Chimica Acta 365 (2011) 96–102
Table 1
Crystallographic data for 1ꢀMeCN, 2ꢀ1 12 MeOH, 3ꢀ2MeOH, and 4ꢀ3MeOH.
2ꢀ1 12 MeOH
Compound
1ꢀMeCN
3ꢀ2(CH3OH)
4ꢀ3(CH3OH)
[C20H21Zn2N2O9][C6H16N]ꢀ1 12 CH4O
Formula
[C41H33Cu2N2O9][C6H16N]ꢀC2H3N
968.03
[C44H39N2O9Zn2][C6H16N]ꢀ2(CH4O) [C32H35N2O9Zn2][C6H16N]ꢀ3(CH4O)
Formula weight
(g/mol)
714.39
1036.79
930.76
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
Triclinic
P1
Monoclinic
P21
Monoclinic
P21/c
Triclinic
P1
ꢀ
ꢀ
10.459(5)
15.366(7)
28.666(13)
96.789(6)
92.233(6)
104.282(6)
4422(4)
4
14.176(9)
14.524(9)
17.073(10)
90
105.501(8)
90
10.3992(2)
16.2391(3)
29.9788(6)
90
96.676(2)
90
11.516(4)
12.909(5)
16.327(6)
87.411(4)
70.978(3)
72.015(3)
2178.5(13)
2
a
(°)
b (°)
c
(°)
V (Å3)
3397(4)
4
5028.30(17)
4
Z
Temperature (K)
Wavelength (Å)
Calculated density
160(2)
0.71073
1.454
150(2)
0.6939
1.401
140(1)
0.71073
1.370
150(2)
0.7848
1.419
(g cmꢁ3
)
Absorption
coefficient
1.025
1.472
1.016
1.165
(mmꢁ1
)
Transmission
factors;
0.960, 0.762
0.985, 0.683
0.771, 0.615
0.966, 0.854
maximum,
minimum
Crystal size (mm)
h(maximum) (°)
Reflections
0.28 ꢂ 0.10 ꢂ 0.04
22.5
25 409
0.28 ꢂ 0.03 ꢂ 0.01
22.5
21 390
0.53 ꢂ 0.35 ꢂ 0.27
29.0
72 107
0.14 ꢂ 0.08 ꢂ 0.03
25.0
11 424
measured
Unique reflections
Reflections with
F
11 558
5275
9421
6485
13 277
9155
5643
3215
2 > 2 (F2)
r
Rint
Number of
parameters
R1 [F2 > 2 (F2)]
0.1223
1203
0.0626
728
0.0595
709
0.0521
430
r
0.0722
0.0880
0.0403
0.0660
wR2 (all data)
0.1838
0.2499
0.1008
0.1866
Goodness-of-fit
Largest difference
peak and hole
0.983
0.674 and ꢁ0.739
1.036
0.945 and ꢁ0.714
0.992
0.599 and ꢁ0.497
0.936
0.554 and ꢁ0.360
(e Åꢁ3
)
trigonal bipyramidal geometry with the phenolic oxygen (O(3))
and the oxygen from the glycine residue (O(1) and O(4), respec-
tively) occupying the axial positions.
In the structure of 3ꢀ2MeOH the asymmetric unit comprises one
anion, one disordered cation and two methanol molecules of crys-
tallisation, one of which is also disordered. The cation and anion
hydrogen bond as seen for the previous two examples, while the
two methanol molecules hydrogen bond to each other and one
hydrogen bonds to the anion.
The asymmetric unit of 4ꢀ3MeOH comprises one cation, one an-
ion and probably three MeOH of crystallisation. The cation and
methanol molecules were so badly disordered they were modelled
with the Platon Squeeze procedure [17] as areas of diffuse electron
density. However, during the development of the structural model
it was clear that the cation and anion formed a hydrogen bonded
interaction in tune with those of the other compounds reported
here.
geometry is closer to a distorted square base pyramid (s = 0.4) with
O(9) at the apex. In each complex, the two zinc centres are bridged
through a Zn–O–Zn bond and through two acetate moieties thus
forming a distorted eight membered ring in a boat conformation.
Each zinc centre is also bound to the imino nitrogen and an oxygen
atom from the amino acid residue.
The Zn–Ophenolate bond lengths range from 2.0619(15) to
2.100(5) Å and are similar to those found in related dinuclear zinc
complexes supported by phenolate ligands (1.997(3)–2.112(4) Å).
The Zn–O–Zn angles (101.39(6) (3) and 100.8(2)° (4)) are also com-
parable to those found in related dinuclear complexes (100.92(7)
and 101.19(15)°) [6,18].
2.3. e-Caprolactone polymerisation
As mentioned for the iron complexes studied by Gibson [3] and
ourselves [19], the initiating metal alkoxide (obtained via alkoxy/
carboxylate exchange), obtained by mixing complexes 1–4 with
benzyl alcohol, may exhibit enhanced nucleophilicity due to the
anionic nature of the metal complex [20]. Complexes 1–4 were
For complex 4, the zinc centres are five coordinate and their
geometry is best described as trigonal bipyramidal (Reedijk criteria
s
= 0.7 for Zn(1) and Zn(2)) [14] with the phenolic oxygen and the
oxygen from the amino acid residue occupying the axial positions.
In the case of Zn(1) in complex 3, the geometry adopted by the ion
is intermediate between trigonal bipyramidal and square base
pyramidal as demonstrated by the calculated Reedijk criteria
(s = 0.5). In the case of Zn(2) in complex 3, the hydrogen bond be-
tween the triethyl ammonium cation and the carboxylic oxygen
therefore screened for the ring opening polymerisation of e-capro-
lactone in toluene at room temperature and at 80 °C and in the
presence of benzyl alcohol. In all cases however, only traces of
polymers were isolated. Due to these disappointing results, no fur-
ther investigation of the potential of these complexes for ring
opening polymerisation was attempted.
somehow perturbs the geometry around the zinc centre: the

A. Arbaoui et al. / Inorganica Chimica Acta 365 (2011) 96–102
99
Fig. 2. Crystal structure of one of two cation/anion pairs in the asymmetric unit of 2ꢀ1 12 MeOH. The solvent of crystallisation is omitted for clarity.
In conclusion, four copper and zinc di-nuclear complexes sup-
ported by acyclic Schiff base ligands were synthesised and struc-
turally characterised. Surprisingly, these anionic complexes were
3.2. Synthesis of [HNEt3][Cu2(CH3CO2)2(2-(O)-5-(Me)C6H2-1,3-
(HC@NCPh2CO2)2] (1)
found to be inactive for the ring opening polymerisation of
rolactone in the presence of benzyl alcohol.
e
-cap-
A solution of 2,2-diphenyl glycine (0.42 g, 1.8 mmol), copper
diacetate (0.37 g, 2.0 mmol) and 2-hydroxy-5-methyl-1,3-benzen-
edicarboxaldehyde (0.15 g, 0.92 mmol) in methanol (30 mL) was
stirred at room temperature for 30 min. Triethylamine (0.28 mL,
2.0 mmol) was then added and the solution brought to reflux for
12 h. The solvent was then removed in vacuo and the residue
extracted in hot acetonitrile. Recrystallisation from a saturated
acetonitrile solution afforded 1 as green needles. Yield: 0.54 g,
64%; m.p. > 350 °C; elemental analysis calculated for C47H49Cu2-
N3O9: C, 60.90; H, 5.33; N, 4.53. Found: C, 60.68; H, 5.62; N,
4.61%. IR (nujol mull, KBr): 1662(w), 1623(m), 1569(w),
1539(w), 1303(w), 1259(w), 1169(m), 1073(w), 1026(m),
972(m), 815(s), 768(w), 738(s), 698(m), 665(w) cmꢁ1; MS (MAL-
DI): m/z 822.2 [MꢁHꢁHNEt3].
3. Experimental
3.1. General
All manipulations, unless otherwise stated, were carried out un-
der an atmosphere of dry nitrogen using conventional Schlenk and
cannula techniques or in a conventional nitrogen-filled glove box.
Hexane, diethyl ether and tetrahydrofuran were refluxed over
sodium and benzophenone. Toluene, octane and methanol were
refluxed over sodium. Dichloromethane and acetonitrile were
refluxed over calcium hydride. All solvents were distilled and
degassed prior to use. Dry methanol or ethanol was stored over
activated 4 Å molecular sieves.
e-Caprolactone was dried over cal-
3.3. Synthesis of [HNEt3][Zn2(CH3CO2)2(2-(O)-5-(t-Bu)C6H2-1,3-
cium hydride, vacuum distilled and degassed prior to use. IR spec-
tra (nujol mulls, KBr windows) were recorded on a Nicolet Avatar
360 FT IR spectrometer; ATR spectra were recorded on a Spectrum
BX FT IR system equipped with an ATR probe. 1H NMR spectra were
recorded at room temperature on a Varian VXR 400 S spectrometer
at 400 MHz and a Gemini 300 NMR spectrometer or a Bruker
Advance DPX-300 spectrometer at 300 MHz. The 1H NMR spectra
were calibrated against the residual portio impurity of the deuter-
ated solvent. Elemental analyses were performed by the elemental
analysis service at the London Metropolitan University. All other
chemicals were obtained commercially from Aldrich and used
without further purification.
(HC@NCH2CO2)2] (2)
A solution of glycine (79 mg, 1.1 mmol), zinc diacetate (196 mg,
1.1 mmol) and 2-hydroxy-5-tert-butyl-1,3-benzenedicarboxalde-
hyde (95 mg, 0.46 mmol) in methanol (50 mL) was stirred at room
temperature for 30 min. Triethylamine (0.35 mL, 2.5 mmol) was
then added and the solution brought to reflux for 12 h. Yield:
230 mg, 75%; m.p. > 350 °C; elemental analysis calculated for
C26H39N3O9Zn2: C, 46.72; H, 5.88; N, 6.29. Found: C, 46.81; H,
5.93; N, 6.21%; IR (nujol mull, KBr): 1653(s), 1587(s), 1297(w),
1261(w), 1228(w), 1157(w), 1076(m), 1020(m), 893(w), 807(w),
777(m), 734(m), 668(m), 618(w), 589(w) cmꢁ1 1H NMR (C6D6,
;

100
A. Arbaoui et al. / Inorganica Chimica Acta 365 (2011) 96–102
Fig. 3. X-ray crystal structure of complex 3 showing the atom numbering scheme. Hydrogen atoms except those involved in H-bonding, and minor disorder components have
been omitted for clarity. Selected bond lengths and angles (Å, °): Zn(1)–O(3) 2.0696(15), Zn(1)–N(1) 2.0501(17), Zn(1)–O(1) 2.0268(16), Zn(1)–O(6) 1.9707(18), Zn(1)–O(8)
1.9858(17), Zn(2)–O(3) 2.0623(15), Zn(2)–N(2) 2.0517(18), Zn(2)–O(4) 2.0475(15), Zn(2)–O(7) 1.9746(18), Zn(2)–O(9) 1.9721(17), Zn(1)–O(3)–Zn(2) 101.39(6), O(1)–Zn(1)–
O(3) 164.91(6), O(8)–Zn(1)–N(1) 136.49(7), O(3)–Zn(2)–O(4) 160.13(7), O(7)–Zn(2)–N(2) 138.62(9), H(3)ꢀ ꢀ ꢀO(4) 1.92, N(3)–H(3)ꢀ ꢀ ꢀO(4) 155, H(11)ꢀ ꢀ ꢀO(10) 1.94, O(11)–
H(11)ꢀ ꢀ ꢀO(10) 173, H(10)ꢀ ꢀ ꢀO(2) 1.74, O(10)–H(10)ꢀ ꢀ ꢀO(2) 164.
400 MHz) d 8.38 (s, 2H, CH@N), 7.37 (s, 2H, C6H2), 4,25 (s, 4H, N–
CH2), 3.11 (q, 6H, J = 7.3 Hz, HN(CH2CH3)3), 2.04 (s, 6H, CH3CO2),
3.5. Synthesis of [HNEt3][Zn2(CH3CO2)2(2-(O)-5-(t-Bu)C6H2-1,3-
(HC@NCHCH2PhCO2)2] (4)
1.31 (t, 9H, J = 7.3 Hz, HN(CH2CH3)3), 1.29 (s, 9H, C(CH3)3) ppm;
+ +
MS (ES+): m/z 102.2 [HNEt3
]
567.0 [MꢁHNEt3+2H]+ 668.1
A solution of phenylalanine (0.80 g, 4.8 mmol), zinc diacetate
(0.98 g, 5.3 mmol) and 2-hydroxy-5-tert-butyl-1,3-benzenedicar-
boxaldehyde (0.50 g, 2.4 mmol) in methanol (50 mL) was stirred
at room temperature for 30 min. Triethylamine (1.7 mL, 12 mmol)
was then added and the solution brought to reflux for 4 h. The sol-
vent volume was reduced to 3 mL. After prolonged standing at
ꢁ25 °C, 4 was isolated as yellow crystals. Yield: 1.98 g, 96%; m.p.:
[M+H]+; (ES-): m/z 567.0 [MꢁHNEt3]ꢁ.
3.4. Synthesis of [HNEt3][Zn2(CH3CO2)2(2-(O)-5-(t-Bu)C6H2-1,3-
(HC@NCPh2CO2)2] (3)
252 °C; elemental analysis calculated for
C40H51N3O9Zn2: C,
A solution of 2,2-diphenyl glycine (1.10 g, 4.8 mmol), zinc diac-
etate (0.98 g, 5.3 mmol) and 2-hydroxy-5-tert-butyl-1,3-benzen-
edicarboxaldehyde (0.50 g, 2.4 mmol) in methanol (50 mL) was
stirred at room temperature for 30 min. Triethylamine (1.7 mL,
12 mmol) was then added and the solution brought to reflux for
12 h. The solvent volume was reduced to 3 mL. After prolonged
standing at room temperature, 3 was isolated as yellow crystals.
Yield: 2.20 g, 93%; m.p.: 192 °C; elemental analysis calculated for
56.61; H, 6.06; N, 4.95. Found: C, 56.72; H, 5.96; N, 4.90. IR (nujol
mull, KBr): 2724(m), 2663(w), 1629(w), 1588(w), 1260(m),
1169(w), 1084(w), 1021(s), 805(m), 700(w), 665(w) cmꢁ1 1H
;
NMR (C6D6, 400 MHz) d 7.41 (s, 2H, CH@N), 6.89-6.72 (m, 10H,
C6H5), 6.42(br s, 2H, Ar-H), 3.92 (d, 2H, J = 10.8 Hz, CH2C6H5), 3.77
(d, 2H, J = 12.8 Hz, CH2C6H5), 3.49 (m, 1H, C@N–CH), 3.03 (m, 1H,
C@N–CH), 2.85 (m, 6H, HNCH2CH3þ), 2.17 (br s, 6H, CH3CO2),
1.35 (s, 9H, C(CH3)3), 1.04 (m, 9H, HNCH2CH3þ) ppm; MS (ES-):
m/z 747.1 [MꢁHNEt3þ]ꢁ.
C
50H55N3O9Zn2: C, 61.74; H, 5.70; N, 4.32. Found: C, 61.65; H,
5.61; N, 4.25%. IR (nujol mull, KBr): 2719(w), 2660(w), 1661(m),
1643(m), 1608(m), 1587(w), 1340(w), 1261(m), 1159(w),
1097(m), 1024(m), 800(s) cmꢁ1
;
1H NMR (C6D6, 400 MHz) d 7.99
3.6. X-ray crystallography
(s, 2H, N@CH), 7.20–7.77 (m, 20H, C6H5), 7.07 (s, 2H, C6H2), 2.62
(m, 6H, HN+CH2CH3), 2.01 (s, 6H, CH3CO2), 0.93 (t, J = 6.5 Hz, 9H,
HN+CH2CH3), 0.88 (s, 9H, C(CH3)3) ppm; MS (ES-): m/z 870.3
[MꢁHNEt3+]-, (ES+): m/z 102.1 [HNEt3+].
Diffraction data were collected using CCD diffractometers with
sealed tube sources for 1ꢀMeCN [21] and 3ꢀ2MeOH [22], and with
synchrotron radiation for 2ꢀ1 12 MeOH, and 4ꢀ3MeOH [21].

A. Arbaoui et al. / Inorganica Chimica Acta 365 (2011) 96–102
101
Fig. 4. X-ray crystal structure of the anion of complex 4 showing the atom numbering scheme. Hydrogen atoms, the cation and three methanol solvent molecules have been
omitted for clarity. Selected bond lengths and angles (Å, °): Zn(1)–O(1) 2.100(5), Zn(1)–N(1) 2.012(7), Zn(1)–O(2) 2.087(6), Zn(1)–O(6) 1.969(6), Zn(1)–O(8) 1.975(7), Zn(2)–
O(1) 2.100(5), Zn(2)–N(2) 2.027(6), Zn(2)–O(4) 2.076(5), Zn(2)–O(7) 1.967(5), Zn(2)–O(9) 1.988(7), Zn(1)–O(1)–Zn(2) 100.8(2), O(1)–Zn(1)–O(2) 165.6(2), O(8)–Zn(1)–N(1)
124.8(3), O(1)–Zn(2)–O(4) 168.0(2), O(7)–Zn(2)–N(2) 127.2(2).
Narrow-frame exposures were employed. Cell parameters were re-
fined from all strong reflections in each data set. Intensities were
corrected semi-empirically for absorption, based on symmetry-
equivalent and repeated reflections. The structures were solved
by direct methods and refined by full-matrix-least squares on F2
values for all unique data [23,24]. All non-hydrogen atoms were re-
fined anisotropically. H atoms were included in a riding model
with Uiso set to be 1.2 times (1.5 times for methyl-H) Ueq for the
carrier atom. Further details are presented in Table 1. In 1ꢀMeCN
one of the cations is disordered over two sets of positions with
some atoms common, major component 52.4(11)%. The data for
2ꢀ1 12 MeOH were rather weak and hampered by the needle crystal
habit. Both cations and parts of the anions suffered from unre-
solved disorder while the highly disordered methanol molecules
were modelled as areas of diffuse electron density by the Platon
Squeeze procedure [17]. In 3ꢀ2MeOH twofold disorder was mod-
elled in the methyl group C(42) (major component 62.5(18)%), all
of the ethyl groups in the cation (major component 76.0(4)%)
and the methanol molecule, O(10)/C(51) (major component:
84.7(9)%). In each case the point atom disorder was modelled using
restraints on geometry and anisotropic displacement parameters.
In 4ꢀ3MeOH the cation and the methanol of crystallization were
badly disordered and modelled as diffuse regions of electron
density [17].
Acknowledgements
The EPSRC is thanked for financial support and the award of
beam time at Daresbury Laboratory (Stations 9.8 and 16.2 SMX).
Drs. Simon J. Teat, Simon J. Coles, John E. Warren and Pierre J. Riz-
kallah are thanked for technical support at Daresbury Laboratory.
The EPSRC Mass Spectrometry Service (Swansea, UK) is thanked
for data collection.
Appendix A. Supplementary material
CCDC 767782–767785 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. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2010.08.043.
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