4,4′-bipyridine-N-monoxide. A hybrid ligand for building networks using a combination of metal-ligand and hydrogen-bonding interactions

Article abstract of DOI:10.1039/b703456c

The ligand 4,4′-bipyridine-N-monoxide, (BIPYMO) coordinates through the pyridine N-donor to Pt(ii) and Pd(ii) to form square planar [ML ₄]²⁺ complexes and to Cu(ii) and Zn(ii) to form octahedral trans-[M(H₂O)₂L₄]²⁺ complexes. Single crystal X-ray structures show that these individual building blocks are organized via hydrogen bonding through the external N-oxide O-atoms to form 2D and 3D networks. The Royal Society of Chemistry.

Full text of DOI:10.1039/b703456c

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PAPER
www.rsc.org/dalton | Dalton Transactions
ꢀ
4
,4 -Bipyridine-N-monoxide. A hybrid ligand for building networks using a
combination of metal–ligand and hydrogen-bonding interactions†‡
Dennis J. Hoffart, Nicolle C. Habermehl and Stephen J. Loeb*
Received 7th March 2007, Accepted 4th May 2007
First published as an Advance Article on the web 6th June 2007
DOI: 10.1039/b703456c
ꢀ
The ligand 4,4 -bipyridine-N-monoxide, (BIPYMO) coordinates through the pyridine N-donor to
2
+
Pt(II) and Pd(II) to form square planar [ML
4
]
complexes and to Cu(II) and Zn(II) to form octahedral
complexes. Single crystal X-ray structures show that these individual building
blocks are organized via hydrogen bonding through the external N-oxide O-atoms to form 2D and
D networks.
2
+
trans-[M(H
2
O)
2
4
L ]
3
Table 1 A search of the Cambridge Crystallographic Database (CCD),
provided the statistics shown for these ligands acting as a bridge between
two transition metal centres (February 2007)
Introduction
The design of coordination polymers via metal–ligand self-
1–7
assembly has burgeoned in recent years. Although many cre-
atively designed ligands now exist for bridging together metal
Donor atoms
N,N
O,O
N,O
8
ions, there are still some very simple ligands that remain totally
Bridging ligand
ꢀ
unexplored. One of the most ubiquitous linkers, 4,4 -bipyridine
˚
(
BIPY) provides a perfectly linear, ∼10 A, bridge between d-block
transition metal centres and has been used to construct numerous
-, 2- and 3D coordination networks. Only recently however, have
9
1
Schroeder, Champness and others begun to study the bis(N-oxide)
derivative of BIPY (i.e. BIPYDO) as a suitable bridging ligand for
10–13
BIPY
BIPYDO
BIPYMO
more oxophilic metals such as lanthanides.
Indeed, a search
of the Cambridge Crystallographic Database indicated that 372
CCD entries
372
14
0
structures with BIPY bridging two metals have been reported as
14
compared to only 14 for BIPYDO; Table 1.
forming a 2D square network with alternating metal–ligand (ML)
and hydrogen-bonding (HB) nodes as depicted in Fig. 1.
In a similar vein, we have been interested in the design of
transition metal complexes that can act as building blocks to form
networks utilising second-sphere interactions such as hydrogen-
15
bonding. As such, we noted during our database search that the
mono-N-oxide of BIPY (i.e. BIPYMO) has never, to the best of
our knowledge, been investigated as a ligand; there were no entries
14
in the CCD.
BIPYMO could act as a ligand for d-block transition metals
through the pyridine N-donor or for lanthanide ions through
the N-oxide donor. In each case, the resulting complex would
contain external donors (pyridine or pyridine-N-oxide) that could
be involved in hydrogen bonding in the second-sphere. Although
complexes of BIPY and especially BIPYDO, are known to be
11
involved in various modes of hydrogen-bonding and p-stacking,
it was of interest to see whether the hybrid ligand BIPYMO
could utilise such secondary interactions by design. For example,
n+
a square planar [M(BIPYMO)
4
]
complex would be capable of
Fig.
1
A
cartoon depicting how
a
square planar complex
n+
[
M(BIPYMO)
4
]
(dark spheres and bold bonds) could be organized
into a 2D square network via hydrogen-bonding. The letters M represent
metal–ligand coordination nodes, the spheres hydrogen-bonding nodes
and the connecting lines the ligand BIPYMO.
Department of Chemistry and Biochemistry, University of Windsor, Wind-
sor, Ontario, Canada. E-mail: loeb@uwindsor.ca; Fax: +1-519-973-7098;
Tel: +1-519-253-3000
This article describes our initial investigations into the synthesis
of late-transition metal complexes containing the hybrid N,O-
donor ligand BIPYMO. The intent was to create relatively inert,
homoleptic complexes containing multiple BIPYMO ligands
coordinated through the pyridine nitrogen atoms, thus leaving the
†
CCDC reference numbers 639375–639378. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b703456c
Electronic supplementary information (ESI) available: Figures showing
1) the core and (2) the detailed H-bonding of the Pd(II) structure. See
DOI: 10.1039/b703456c
‡
(
2
870 | Dalton Trans., 2007, 2870–2875
This journal is © The Royal Society of Chemistry 2007

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pyridine-N-oxide oxygen donors on the periphery of the complex
available for further interactions as described above. In particular,
it was of interest to construct these complexes to allow for the
self-assembly of networked structures via hydrogen-bonding.
Results and discussion
Synthesis and characterization of BIPYMO
ꢀ
The mono-N-oxide of 4,4 -bipyridine, BIPYMO, is readily pre-
pared on a multigram scale at room temperature in CHCl using
3
16
meta-chloroperoxybenzoic acid (MCPBA) as the oxidant. The
mild reaction conditions are important in order to minimize
production of the dioxide; a moderate isolated yield of 55% was
1
achieved. BIPYMO is only soluble in polar solvents; the H NMR
spectrum in D
2
O was straightforward showing four doublets in the
Fig. 2 A ball-and-stick representation of the X-ray structure of the
2+
aromatic region (d 8.52 (a), 8.32 (d), 7.80 (c), 7.60 (b) ppm) due to
the four sets of different pyridyl protons (see Scheme 1).
complex cation [Pt(BIPYMO)
4
]
with numbering scheme; numbering of
carbon atoms is sequential around each ring. Triflate anions, solvents of
crystallization and H-atoms are omitted for clarity.
hydrogen-bonding of the N-oxide oxygen atoms to both a-
pyridinium and MeCN solvent hydrogen atoms constitutes the
second-sphere hydrogen-bonding node. Fig 3 centres on a single
hydrogen-bonding node (circle) and shows how these complexes
come together in a single plane to form the 2D network. The
˚
closest Pt · · · Pt distance measures 17.6 A. The repeating square
˚
tile (shown as dotted lines) has a side length of ∼26 A. These 2D
nets are layered such that the ML and HB nodes are directly over
each other in an offset pattern which alternates from layer to layer.
3
Scheme 1 Preparation of BIPYMO. (i) MCPBA 1.5 equiv. in CHCl , r.
t. for 17 d. Recrystallized from EtOAc–MeOH. Numbering scheme (a–d)
1
for H NMR assignments is shown for BIPYMO.
Square planar complexes as building blocks
The reaction of one equivalent of [PtCl
equivalents of AgOTf and four equivalents of BIPYMO in dry
MeCN gave the homoleptic complex [Pt(BIPYMO) ] [OTf] in
7% yield as an off-white solid. The H NMR spectrum of
2
(EtCN) ] with two
2
4
2
1
8
2
+
[
Pt(BIPYMO)
4
]
in DMF-d also showed four doublets in the
7
aromatic region (d 9.39 (a), 8.41 (d), 8.25 (b), 8.05 (c) ppm)
demonstrating that all the BIPYMO ligands are equivalent and
HR-ESI-MS confirmed the ML
4
stoichiometry showing a well-
resolved peak for [M–2OTf] at m/z 441.6111 (calcd 441.6097).
X-Ray quality crystals with the formula {[Pt(BIPYMO)
OTf] (H O)} were grown by slow evaporation of an
·(MeCN)
MeCN solution of the complex. Fig. 2 shows the structure of the
2
+
4
]
[
2
2
2
2
+
square planar cation [Pt(BIPYMO)
4
] . The Pt–N distances range
˚
from 2.03(2) to 2.08(2) A and the N–Pt–N angles from 88.1(7) to
9
◦
◦
1.0(7) for cis disposed ligands and are 176.7(8) and 178.3(7)
for the trans positioned ligands. The pyridine donor rings are
arranged in a propeller-like fashion around the square plane of
the complex. The angles of the four pyridine ligands relative to the
square plane of the complex range from 49.4 to 58.8 . While each
of the pyridine-N-oxide ligand rings is approximately coplanar
Fig. 3 The in-plane packing diagram shows how the square planar
◦
2+
[
Pt(BIPYMO)
4
]
complex cations are arranged in a 2D network by
hydrogen-bonding; shown inside the circle. One complex cation, two OTf
anions and two MeCN molecules (one H-bonded) are shown (dark) along
to the attached pyridine ring; dihedral angles range from 16.5 to
◦
2
9.3 . None of these metric parameters are unusual.
with three symmetry related complex cations (light). The closest Pt · · · Pt
2
+
The individual [Pt(BIPYMO)
4
]
cations are arranged in a
distance is 17.6 A˚ . A square tile is defined by the dotted lines shown; each
2
D network very similar to that envisaged in Fig. 1. C–H · · · O
side has a length of ∼26 A˚ .
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An analogous reaction involving four equivalents of BIPYMO
and Pd(II) starting materials produced, after recrystallization from
of the H-bond accepting water molecules. This was done by
positioning them at the axial positions of an octahedral metal ion
while maintaining the square planar arrangement of the BIPYMO
ligands.
a H
[Pd(BIPYMO)
2
O–MeCN mixture, crystalline material with the formula
)][BF [OTf] O)10}. The basic structure of
·(H
{
4
4
]
2
2
2
the individual complex cations is essentially the same as that
observed for the Pt(II) complex (see ESI‡ for a picture of the
Pd(II) core analogous to Fig. 2). Although the networks are almost
identical, the presence of water during the crystal growth for this
compound yields a slightly different 2D network. Fig. 4 shows
that in this compound, clusters of water molecules define slightly
larger second-sphere, HB nodes which results in a more spread out
To this end, we reacted [Cu(MeCN)
4
][PF ] with four equiv-
6
alents of BIPYMO in MeCN solution under mild oxidiz-
ing conditions. X-Ray quality, blue crystals with the formula
{[Cu(H
oration of an MeCN solution of the complex. An analogous exper-
iment using [Zn(H O) ][OTf] gave crystalline material from a so-
lution of MeNO O) (BIPYMO) ][OTf]
2
O)
2
(BIPYMO)
4
][PF
6
]
2
·(H
2
O)
4
} were grown by slow evap-
2
6
2
2
with formula {[Zn(H
2
2
4
2
}.
2
D array than was found for the Pt(II) structure. This results in a
repeating tile that is slightly rectangular (shown as dotted lines)
The Zn(II) complex is isomorphous with the Cu(II) one having
identical cations but with triflate ions positioned in the space
˚
with side lengths of ∼24 and ∼28 A. The 2D nets are again layered
occupied by the combination of PF
molecules in the Cu(II) complex.
Fig. 5 shows the structure of the trans-[Cu(H
6
anions and solvent water
such that the ML and HB nodes are directly over each other in an
offset pattern which alternates from layer to layer (see ESI).‡
2
+
2
O)
2
(BIPYMO) ]
4
building block which has four BIPYMO ligands in the square
plane and two water molecules in the axial positions of a Cu(II)
octahedron. The four BIPYMO ligands are crystallographically
equivalent; the Cu atom and the two water molecules are at sites
with imposed fourfold symmetry. The unique Cu–N1 distance is
˚
2
2
.046(4) A and the two Cu–water distances are 2.383(12) and
˚
.282(11) A for Cu–Ow1 and Cu–Ow2 respectively. The N1–
Cu–N1 angles are 90.00(5) for cis disposed BIPYMO ligands
and 179.7(4) for the trans positioned ligands. The Ow1–Cu–Ow2
angle is crystallographically imposed at 180 . The two PF anions
ꢀ
◦
◦
◦
−
6
and two water molecules were disordered in the cavities between
cations.
Fig. 4 An in-plane packing diagram shows how the square planar
2+
[
Pd(BIPYMO)
4
]
complex cations are arranged in a 2D network by
hydrogen-bonding with clusters of water molecules; one of these clusters is
shown inside the circle. A slightly rectangular tile is defined by the dotted
Fig. 5 A ball-and-stick representation of the X-ray structure of the
2+
complex cation trans-[Cu(H
2
O)
2
(BIPYMO)
4
]
with numbering scheme;
lines shown; the sides have sides of ∼24 A˚ (width) and ∼28 A˚ (height).
numbering of carbon atoms is sequential around each ring. PF
solvents of crystallization and H-atoms are omitted for clarity.
6
anions,
The closest Pd · · · Pd distance is 17.5 A˚ . There are three cations and 30
water molecules in the asymmetric unit. The three unique complex cations,
one OTf anion and 10 water molecules are shown (dark) along with one
symmetry related complex cation (light). A complete hydrogen-bonding
array can be found in the ESI.‡
Much like the Pd(II) and Pt(II) complexes, the pyridine donor
rings are arranged in a propeller-like fashion in a square plane
around the Cu centre. In this complex, the angle of the unique
◦
pyridine ligand relative to the square plane of the complex is 44.8 .
While the angle between the pyridine-N-oxide and pyridine ligand
rings is 28.6 . There are no unusual metric parameters.
Octahedral complexes as building blocks
◦
2
+
The two square planar [M(BIPYMO)
4
]
(M = Pd, Pt) building
As was designed, the axial water molecules along with lig-
and pyridine-N-oxide ortho-protons provide a hydrogen-bond
accepting node for formation of a much more compact and well
organized 2D square network. Fig. 6 shows the hydrogen-bonded
node (circle) which is centred on a bound axial water molecule
from an adjacent layer. The repeating tile (dotted lines) is a perfect
blocks demonstrate clearly that self-assembly of hydrogen-bonded
networks can be accomplished in the presence of a small, mobile,
hydrogen-bond acceptor such as water or a similar solvent. Since
we have established 2D networks are favoured for a square
arrangement of BIPYMO ligands, it was of interest to see if a
more ordered array could be prepared by fixing the positions
˚
square ∼24 A on a side. By virtue of a bound water molecule
2
872 | Dalton Trans., 2007, 2870–2875
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Fig. 7 A ball-and-stick representation of the X-ray structure of
2+
[
Cu(BIPYMO)
4
(H
2
O)
2
]
showing how the axial water molecules on a
single Cu atom hydrogen-bond to four different pyridine N-oxide oxygen
atoms from the layers directly above and below to form a closely packed
alternating HB–ML–HB layered pattern. Note: the H-atoms on the bound
water molecules are half-occupancy and disordered as a result of the
four-fold axis through Ow1–Cu1–Ow2.
was found when the H-bond donor components (water) were
bound directly to the metal centre.
Fig.
6
An in-plane packing diagram shows how the octahedral
Future work will be focused on discerning (1) what other types
of hydrogen-bond acceptors are suitable for formation of these
hybrid ML–HB networks and (2) whether a simple ligand such as
BIPYMO can be used to link the type of transition metal building
blocks described herein directly to lanthanide or other oxophilic
metal ions to generate multi-metallic networks.
2+
trans-[Cu(BIPYMO)
4
(H
2
O)
2
]
cations are arranged in a 2D network
by intermolecular hydrogen-bonding between BIPYMO and axial water
molecules shown inside the circle. One complex cation and one water
molecule (H-bonded) are shown (dark) along with three symmetry related
complex cations (light). Each cation has crystallographically imposed
four-fold symmetry.
acting as the HB node, the 2D nets are layered exactly with the
ML and HB nodes aligned along the crystallographic 4-fold axis
of the lattice.
Experimental
ꢀ
4
,4 -Bipyridine and meta-chloroperoxybenzoic acid (MCPBA)
The design of a single building block that contains both the
donor (BIPYMO) and acceptor (water) components allows for
the possibility of self-association. The water molecules are no
longer flexible but positioned exactly above and below the metal
ion as a consequence of occupying the axial positions of the
octahedral complex cation. This enforces the alignment of the
donor and acceptor groups producing an alternating ML–HB–
ML–HB pattern between layers that is rigid and well defined.
Fig 7 shows a close-up view of the combination of metal–ligand
and hydrogen-bonding interactions which constitute the driving
forces that allow individual building blocks to come together in
this well ordered 3-dimensional network.
were purchased from Aldrich Chemicals and were used as received.
All metal salts were purchased from Aldrich Chemicals and were
used as received. All deuterated solvents were purchased from
Cambridge Isotope Laboratories. All solvents were purchased
from EM Science. H NMR spectra were recorded on a Br u¨ ker
Avance 500 instrument locked to the deuterated solvent at
1
5
00.1 MHz respectively. All peak positions are listed in ppm
relative to TMS.
Preparation of BIPYMO
BIPYMO was prepared by a variation of the literature
16
ꢀ
method. To a solution of 4 4-bipyridine (10.0 g, 64.0 mmol)
in CHCl (200 mL) was added a solution of 57–86% meta-
chloroperoxybenzoic acid (MCPBA) (12.9 g, 64.0 mmol) in CHCl
(500 mL) and the solution stirred for 3 d at room temperature.
Four more portions of MCPBA (2.0 g, 9.9 mmol), each in CHCl
3
Conclusions
3
It has been clearly demonstrated that the hybrid N,O-ligand
BIPYMO can form simple transition metal complexes by dona-
tion through the pyridine N-atom. This coordination geometry
positions the N-oxide O-donor atoms of BIPYMO on the
periphery of the molecule and allows for their participation in a
hydrogen-bonding scheme by acting as a hydrogen-bond donor
group. When the BIPYMO ligands are organized in a square
planar arrangement, H-bonding allows formation of a 2D square
network. The exact nature of the network depends on the type
of hydrogen-bond acceptor used. A loose network was observed
when mobile solvent molecules (water and MeCN solvates) were
the H-bond acceptors while a more tightly packed rigid network
3
(150 mL), were then added every 24 h. After stirring for a total
of 17 d, the crude mixture was filtered and the solvent removed in
vacuo. The resulting brown solid was extracted with hot water (3 ×
200 mL) to give a mixture of BIPYMO and BIPYDO. The water
was removed to give a light tan coloured solid which was further
extracted with a mixture of EtOAc and MeOH (9 : 1) (3 × 50 mL)
1
to yield pure BIPYMO. Yield 6.0 g (55%). H NMR (D
2
O): d
(ppm) 8.52 (d, 2H, J = 6.1 Hz, ortho-N), 8.32 (d, 2H, J = 7.1 Hz,
ortho-N–O), 7.80 (d, 2H, J = 7.1 Hz, meta-N), 7.60 (d, 2H, J =
6.1 Hz, meta-N–O).
This journal is © The Royal Society of Chemistry 2007
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Table 2 X-Ray crystallographic data collection, solution and refinement parameters for complexes of BIPYMO with Pt(II), Pd(II), Cu(II) and Zn(II)
Compound
[Pt(BIPYMO)
4
][OTf]
2
{[Pd(BIPYMO)
4
]
3
[BF
4
]
2
[OTf]
4
[Cu(H
2
O)
2
(BIPYMO)
4
][PF
6
]
2
[Zn(H
2
O)
2
4 2
(BIPYMO) ][OTf]
Formula
C
46
H
40
F
6
N
10
O
11PtS
2
C
41.33
H
42
B
0.67
F
6.67
N
8
O
18PdS1.33
C
40
H
39CuF12
N
8
O
7.5
P
2
C H F N O S Zn
1088.28
42 36 6 8 12 2
M/g mol−
1
1282.09
Monoclinic
P2 /n (14)
17.559(4)
14.088(4)
19.738(5)
90
94.894(4)
90
4 865(2)
4
1187.28
Triclinic
P1 (2)
20.624(2)
21.311(2)
22.366(2)
63.191(2)
64.445(2)
82.821(2)
7 885.5(12)
6
173.0(5)
1.544
1105.27
Tetragonal
P4nc (104)
17.183(8)
17.183(8)
8.128(6)
90
90
90
2 400(2)
2
173.0(5)
1.530
Crystal system
Tetragonal
P4nc (104)
17.347(4)
17.347(4)
8.061(4)
90
¯
Space group
1
a/A˚
b/A˚
c/A˚
◦
a/
b/
◦
90
90
◦
c /
V/A˚
Z
3
2 425.7(13)
2
173.0(5)
1.490
Temperature/K
173.0(5)
1.750
3.065
−
3
d
calc/g cm
−
1
l(Mo–Ka)/mm
0.507
0.625
0.683
Ratio min./max. trans. 0.1448
0.8637
27 687
20 300
0.0413
0.0797
0.1040
0.2219
0.2481
0.8572
2113
1777
0.0693
0.0676
0.0831
0.1599
0.1719
0.549499
2141
1939
0.0997
0.1060
0.1052
0.2657
0.2704
Measured reflections
Unique data [I > 2rI]
R(int)
5092
3240
0.1838
0.0998
0.1524
0.2123
0.2369
R1 [I > 2rI]
R1 [all data]
wR2 [I > 2rI]
wR2 [all data]
Max./min. peak/e A˚ −
3
2.483/−1.654
2.440/−1.217
2080/167
1.023
0.587/−0.269
0.707/−0.636
Variables/restraints
Goodness-of-fit
442/37
208/145
200/68
1.074
1.165
1.183
1
Preparation of [Pt(BIPYMO)
4
][OTf]
2
and were isolated by filtration. Yield (12.2 mg) 58%. H NMR
O): Only resonances due to the free ligand were observed.
(
D
2
[
PtCl (EtCN) ] (7.5 mg, 0.02 mmol), AgOTf (10.3 mg 0.04 mmol)
2
2
and BIPYMO (17.8 mg, 0.08 mmol) were combined in MeCN
◦
X-Ray crystallography†
(
2 mL). After warming the solution for 16 h at 60 C, the
precipitated AgCl(s) was filtered and the solvent removed to give
All crystals were frozen in paratone oil inside a cryoloop to prevent
loss of solvent. Reflection data were integrated from frame data ob-
tained from full hemisphere scans on a Br u¨ ker Apex diffractometer
1
an off-white solid. Yield (18.0 mg) 76%. H NMR (DMF-d
ppm) 9.39 (d, 2H, J = 7.0 Hz, ortho-N), 8.41 (d, 2H, J = 7.5 Hz,
ortho-N–O), 8.25 (d, 2H, J = 7.5 Hz, meta-N), 8.05 (d, 2H, J =
.0 Hz, meta-N–O).
7
): d
(
˚
with a CCD area detector with MoKa radiation (k = 0.71073 A).
7
Diffraction data and unit cell parameters were consistent with the
assigned space groups; see Table 2. The structures were solved
by direct methods, completed by subsequent Fourier syntheses
Preparation of {[Pd(BIPYMO)
4
]
3
[BF
4
]
2
[OTf]
4
}
2
and refined with full-matrix least-squares methods against |F |
[
Pd(MeCN) ][BF (9.7 mg, 0.02 mmol), [Gd][OTf]
4
4
]
2
3
(13.2 mg
data. All non-hydrogen atoms were refined anisotropically except
for the carbon atoms in the Pt(II) complex. All hydrogen atoms
0
.02 mmol) and BIPYMO (15.0 mg, 0.08 mmol) were combined
in H O (1 mL). Large colourless blocks of the mixed anion, Pd(II)
2
were calculated and treated as idealised contributions. In the
complex formed upon slow concentration of the solution. Yield
−
Cu(II) compound, the cavities are occupied by disordered PF
6
1
(
6
2
22.4 mg) 83%. H NMR (DMF-d
7
): d (ppm) 9.28 (d, 2H, J =
.9 Hz, ortho-N), 8.40 (d, 2H, J = 7.4 Hz, ortho-N–O), 8.24 (d,
H, J = 7.4 Hz, meta-N), 8.02 (d, 2H, J = 6.9 Hz, meta-N–O).
anions and two partial occupancy water molecules, while in
the isomorphous Zn compound the cavities are occupied by
disordered triflate anions but no solvent was located. Scattering
factors and anomalous dispersion coefficients were contained
Preparation of trans-[Cu(H
2
O)
2
(BIPYMO)
4
][PF
6
]
2
17
in the SHELXTL 5.03 software package. All crystallographic
18
figures were prepared using the graphics program DIAMOND.
[
Cu(MeCN)
4
][PF
6
] (22.3 mg, 0.06 mmol) was combined with four
O (1 mL) and
equivalents of BIPYMO (41.2 mg, 0.24 mmol) in H
2
heated until the solution turned a deep blue colour. Large blue
crystals were observed to form upon cooling to room temperature.
Yield (29.6 mg) 46%.
Acknowledgements
SJL thanks the NSERC of Canada for financial support of this
work through a Discovery Grant.
Preparation of trans-[Zn(H
2
O)
2
(BIPYMO)
4
][OTf]
2
Notes and references
[
0
Zn(H
.08 mmol) were combined in MeNO
stirred for 12 h. After standing for 48 h, colourless crystals formed
2
O)
6
][OTf]
2
(9.4 mg, 0.02 mmol) and BIPYMO (17.8 mg,
2
(2 mL) and the solution
1
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2
874 | Dalton Trans., 2007, 2870–2875
This journal is © The Royal Society of Chemistry 2007

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3
M. Ruben, Angew. Chem., Int. Ed., 2005, 44, 1594.
J.-C. Dai, Z.-Y. Fu and X.-T. Wu, Encyclopedia of Nanoscience and
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14 The CCD entries reported in Table 1 are restricted to those for which
the ligands are bridging between two metal centres. Searches on BIPY
and BIPYDO as ligands in general gave a higher number of hits but
there were still zero hits for BIPYMO.
15 D. A. Beauchamp and S. J. Loeb, Chem.–Eur. J., 2002, 8, 5084.
16 BIPYMO has only been reported as a synthetic intermediate for the
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substitution. See: H. Brunner, R. St o¨ riko and F. Rominger, Eur. J. Inorg.
Chem., 1998, 6, 771.
17 G. M. Sheldrick, SHELXTL 5.03 Program Library, Br u¨ ker Analytical
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This journal is © The Royal Society of Chemistry 2007
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