Copper(II) complex of a tridentate N-donor ligand with unexpected Cu-H interaction

Article abstract of DOI:10.1016/j.inoche.2005.11.008

The new pyridine-amine ligand, meophdpa (bis(dipyridylmethyl)-4- methoxyaniline) was synthesised and reacted with copper(II) perchlorate. The X-ray crystal structure of the resulting complex revealed a monomeric copper(II) site, with the copper bound to the three ligand nitrogens in a relatively unusual meridional fashion, as well as a chloride and a water molecule. The sixth coordination site was, unexpectedly, occupied by a phenyl ring hydrogen atom.

Full text of DOI:10.1016/j.inoche.2005.11.008

Inorganic Chemistry Communications 9 (2006) 231–234
www.elsevier.com/locate/inoche
Copper(II) complex of a tridentate N-donor ligand with unexpected
Cu–H interaction
a
b
c,
a
Bernadette S. Creaven , Mary F. Mahon , John McGinley *, Ann-Marie Moore
a
Department of Applied Science and Advanced Smart Materials Research Centre, Institute of Technology, Tallaght, Dublin 24, Ireland
b
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, England, United Kingdom
c
Department of Chemistry, National University of Ireland Maynooth, Maynooth, Co. Kildare, Ireland
Received 19 October 2005; accepted 13 November 2005
Available online 20 December 2005
Abstract
The new pyridine–amine ligand, meophdpa (bis(dipyridylmethyl)-4-methoxyaniline) was synthesised and reacted with copper(II) per-
chlorate. The X-ray crystal structure of the resulting complex revealed a monomeric copper(II) site, with the copper bound to the three
ligand nitrogens in a relatively unusual meridional fashion, as well as a chloride and a water molecule. The sixth coordination site was,
unexpectedly, occupied by a phenyl ring hydrogen atom.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Tridentate pyridine–amine ligand; Synthesis; Copper(II) complex; X-ray crystal structure
The design and construction of supramolecular architec-
tures has been a rapidly developing area in the past number
of years [1]. Indeed, the last decade has witnessed a surge of
interest in the discovery of simple building blocks capable
of forming specific molecular arrays under certain chemical
conditions [2]. For bio-inorganic model complexes, the
design and synthesis of the ligand is perhaps the most
important step in the modelling process. Control of the
number and type of coordinating atoms is key to achieving
metal complexes that mimics the coordination sphere and
reactivity of metal-containing enzymes.
As part of our continuing research, we have previously
reported upper and lower rim functionalised calix[4]arenes,
capable of binding transition metal and alkali metal salts
[3]. One such calix[4]arene contained picolyl groups [3a].
In extending this theme, we targeted the design of ‘‘pre-
ligands’’, capable of having two or three donor atoms
present, with a view to attaching these to the lower rim
of the calix[4]arene and thereby forming di-or tri-nuclear
metal complexes. The compounds chosen as pre-ligands
were derivatives of bis(2-pyridylmethyl)amine (dpa) and
are shown in Fig. 1. The related analogue of the ligands
(R@H in Fig. 1, phdpa) has been previously reported by
McKenzie et al. [4]. This paper reports the attempted syn-
thesis of these pre-ligands and an X-ray crystallographi-
cally characterised copper(II) derivative containing one of
them.
Ligands meophdpa1 and hophdpa were, respectively,
prepared by nucleophilic substitution of (2-chloro-
methyl)pyridine with 4-methoxyaniline or 4-aminophenol
in a water–dichloromethane system, in a manner analogous
to that previously described [4]. While the ligand meop-
1
Meophdpa.HCl: %yield = 78.5%; Found: C, 60.79%, H, 6.24% N,
11.10%; Calc. for C19H21Cl2N3O: C, 60.32%, H, 5.60% N, 11.11%; dH
(300 MHz, CDCl3): 8.71 (d, 2H, J = 6.8 Hz, py-H6), 8.01 (t, 2H,
J = 6.8 Hz, py-H4), 7.69 (d, 2H, J = 6.8 Hz, py-H3), 7.51 (t, 2H,
J = 6.8 Hz, py-H5), 6.79–6.73 (m, 4H, Ph-H), 5.01 (s, 2H, CH2), 3.99 (s,
3H, OMe); dH (300 MHz, d6-DMSO): 8.93 (d, 2H, J = 6.8 Hz, py-H6),
8.24 (t, 2H, J = 6.8 Hz, py-H4), 7.81 (d, 2H, J = 6.8 Hz, py-H3), 7.68 (t,
2H, J = 6.8 Hz, py-H5), 6.72 (d, 2H, J = 6.8 Hz, o-Ph-H), 6.50 (d, 2H,
J = 6.8 Hz, m-Ph-H), 5.05 (s, 2H, CH2), 3.58 (s, 3H, OMe); dC (300 MHz,
CDCl3): 156.7, 153.6, 145.4, 141.3, 140.7, 124.0, 123.8, 116.6, 115.0, 56.4,
55.5; ESMS: m/z 306.4, (meophdpa + H); C19H19N3O requires 305.37.
*
Corresponding author. Tel.: +353 1 708 4615; fax: +353 1 708 3815.
E-mail address: john.mcginley@nuim.ie (J. McGinley).
1387-7003/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.11.008

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B.S. Creaven et al. / Inorganic Chemistry Communications 9 (2006) 231–234
R
OMe
H
H
N
N
N
N
N
N
Fig. 3. Alternative structure of meophdpa showing potential interaction
between pyridyl nitrogens and phenyl ring.
Fig. 1. Ligands chosen for synthesis; meophdpa, R@OMe; hophdpa,
R@OH.
The crystal structure of [Cu(meophdpa)Cl(H2O)](ClO4) Æ
H2O, 1, is shown in Fig. 4 [5]. Selected bond lengths (A)
˚
and angles (°) are given in Table 1. The copper atom is
bonded to the three nitrogens of the meophdpa ligand, a
chloride and a water molecule in a distorted square-pyra-
midal arrangement. The water molecule is also hydrogen
bonded to a second water molecule and that molecule is
in turn hydrogen bonded to the perchlorate anion. Further-
more, the proton on C18 of the phenyl ring is located at a
HO
N
N
H
Fig. 2. Ligand obtained from reaction of 4-aminophenol with (2-
chloromethyl)pyridine.
˚
distance of 2.417 (A) from the copper atom, which is less
than the sum of the Van der Waals radii for these two
atoms and hence must be considered as a reasonably strong
interaction [6]. Thus, a pseudo-octahedral geometry is
observed for the central metal. No other interactions about
the copper are observed, which is interesting, since copper–
chloride bridging might have been expected. However, the
position of the phenyl ring precludes such bridging interac-
tions on steric grounds.
hdpa was obtained as a solid in good yield, the second syn-
thesis of hophdpa only gave a monosubstituted aniline,
hophmpa, as shown in Fig. 2. Complexation studies of this
ligand will be reported elsewhere. The ligand meophdpa
was isolated as the di-hydrochloride salt, as confirmed by
the elemental analysis. No attempt to remove the HCl from
the ligand was undertaken prior to complexation reactions.
The 1H NMR spectrum of meophdpa was obtained in both
CDCl3 and d6-DMSO. The spectra exhibited the same sig-
nal distribution with the exception of the phenyl protons,
which appeared as a multiplet in the CDCl3 but as two dis-
tinct doublets in the case of the d6-DMSO spectrum. This
suggests that, in the DMSO solution, there was an interac-
tion of the pyridyl nitrogens with the ortho-hydrogens of
the phenyl ring (see Fig. 3). McKenzie et al. [4] report a
similar pattern in the phdpa compound but make no com-
ment on this possible interaction.
The reaction of the ligand, meophdpa.2HCl, with cop-
per(II) perchlorate hexahydrate in methanol in a 2:1 ratio,
resulted in the formation of a metal complex. [Caution!
Although no problems were encountered in the preparation
of the perchlorate salts, suitable care should be taken when
handling such potentially hazardous compounds.] Elemental
analysis for the complex2 suggested the presence of a 1:1
metal–ligand complex, instead of the anticipated 1:2 stoi-
chiometry generally observed for complexes of ligands of
this general type [4,7,8]. The product was isolated as blue
crystals from a suitable sample was selected for an X-ray
structure determination.
2
[Cu(meophdpa)Cl(H2O)2](ClO4): %yield = 91.5%; Found: C, 48.24%,
Fig. 4. X-ray crystal structure of [Cu(meophdpa)Cl(H2O)](ClO4) Æ H2O, 1.
Ellipsoids are represented at the 30% probability level.
H, 5.24% N, 9.10%; Calc. for C19H23Cl2N3O7: C, 47.91%, H, 4.87% N,
8.82%.

B.S. Creaven et al. / Inorganic Chemistry Communications 9 (2006) 231–234
233
Table 1
Selected bond distances (A) and angles (°) for 1
˚
Cu(1)–N(3)
Cu(1)–N(2)
Cu(1)–Cl(1)
Cl(2)–O(1)
Cl(2)–O(3)
O(7)–C(19)
N(2)–C(7)
1.989(2)
2.078(2)
2.2539(7)
1.428(2)
1.449(3)
1.433(4)
1.491(3)
Cu(1)–N(1)
Cu(1)–O(5)
Cl(2)–O(2)
Cl(2)–O(4)
O(7)–C(16)
N(2)–C(6)
1.994(2)
2.234(2)
1.395(3)
1.433(2)
1.360(3)
1.490(3)
N(3)–Cu(1)–N(1)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–O(5)
N(3)–Cu(1)–Cl(1)
N(2)–Cu(1)–Cl(1)
C(16)–O(7)–C(19)
C(1)–N(1)–Cu(1)
C(13)–N(2)–C(6)
C(6)–N(2)–C(7)
C(6)–N(2)–Cu(1)
C(8)–N(3)–C(12)
C(12)–N(3)–Cu(1)
163.83(9)
81.94(9)
88.45(8)
96.99(7)
150.04(6)
116.9(2)
126.01(18)
111.7(2)
112.8(2)
105.93(15)
119.3(2)
126.19(19)
N(3)–Cu(1)–N(2)
N(3)–Cu(1)–O(5)
N(2)–Cu(1)–O(5)
N(1)–Cu(1)–Cl(1)
O(5)–Cu(1)–Cl(1)
C(1)–N(1)–C(5)
C(5)–N(1)–Cu(1)
C(13)–N(2)–C(7)
C(13)–N(2)–Cu(1)
C(7)–N(2)–Cu(1)
C(8)–N(3)–Cu(1)
N(1)–C(1)–C(2)
82.01(9)
93.84(9)
105.30(9)
97.91(7)
104.64(7)
119.3(2)
114.62(17)
111.7(2)
109.67(15)
104.62(15)
114.44(18)
121.8(3)
The three nitrogen atoms of the meophdpa ligand exhi-
bit a meridional type of coordination at copper, whereas
structures of complexes containing these ligand types show
almost exclusively facial coordination of the ligands [4,8].
This coordination type observed here is unusual for struc-
tures of complexes containing bis(picolyl)amine and N-
substituted bis(picolyl)amine, with only two previous
examples reported for copper(II) complexes [7]. The struc-
ture of Cu(phdpa)Cl2 [7b], which relates directly to that of
1, consists of discrete copper(II) neutral complexes with the
metal atom being five-coordinated to three nitrogens from
the terdentate phdpa species and two chloride ions. One of
the pyridine nitrogens therein is involved in an intramolec-
ular hydrogen bond with one of the aniline protons, an
interaction replaced by a H–Cu interaction in 1. The
pseudo-planar nature of the nitrogen donor atoms in 1
forces the phenyl ring attached to N(2) to be positioned
in a manner that maintains the expected bond angle of
106.98° as found in ammonia. There are two water mole-
cules present in the lattice; one of which is ligated to the
copper and hydrogen bonded to the second water mole-
cule, while this second water molecule is further hydrogen
bonded to the perchlorate anion. The copper–Owater bond
Fig. 5. Packing diagram for 1, showing hydrogen-bonding interactions in
the lattice.
the motif consists of a monomeric copper(II) site, with
the copper bound to the three nitrogens of the ligand in
a relatively unusual meridional fashion, as well as a chlo-
ride and a water molecule. The sixth coordination site is
occupied by a Cu–H bond of the phenyl ring. The pack-
ing diagram of the structure reveals extensive hydrogen-
bonding.
Appendix A. Supplementary data
Crystallographic data for the structural analysis on
[Cu(meophdpa)Cl(H2O)2](ClO4) have been deposited with
the Cambridge Crystallographic Data Centre, CCDC No.
286615. Copies of this information may be obtained free
of charge from deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.inoche.2005.11.008.
˚
distance of 2.234(2) (A), while being longer than that pre-
viously reported for [Cu2(tpbd)(H2O)4](S2O6)2 [7] at
2.170(5) (A), where tpbd = N,N,N0,N0-tetrakis(2-pyr-
˚
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In summary, a new pyridine–amine ligand (meophdpa)
has been synthesised and characterised. This ligand was
reacted with copper(II) perchlorate and the resulting com-
plex analysed. The X-ray crystal structure revealed that
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˚
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