Molecular squares, rectangles and infinite helical chains utilising the simple 'corner' ligand 4-(2-pyridyl)-pyrimidine

Article abstract of DOI:10.1039/b206989j

The ligand 4-(2-pyridyl)-pyrimidine forms multinuclear Ag(I) complexes by a combination of chelating and bridging coordination modes; molecular shape (square or rectangle) and degree of aggregation depend on the anion used.

Full text of DOI:10.1039/b206989j

Molecular squares, rectangles and infinite helical chains utilising the
simple ‘corner’ ligand 4-(2-pyridyl)-pyrimidine
Derek A. Beauchamp and Stephen J. Loeb*
Department of Chemistry & Biochemistry, University of Windsor, Windsor, ON, Canada N9B 3P4.
E-mail: loeb@uwindsor.ca; Fax: 519 973 7098; Tel: 519 253 3000
Received (in Cambridge, UK) 17th July 2002, Accepted 12th September 2002
First published as an Advance Article on the web 26th September 2002
The ligand 4-(2-pyridyl)-pyrimidine forms multinuclear
Ag( ) complexes by a combination of chelating and bridging
coordination modes; molecular shape (square or rectangle)
and degree of aggregation depend on the anion used.
complex to be the square tetramer {[2][BF
head-to-tail aggregation of four corner residues requires that the
Ag( ) ions each bond to 1 in a pseudo-trigonal planar geometry
with respect to the N-donors of 1. The tetra-cationic unit is
4 4
]} ; Fig. 2(A). The
I
I
7
2
essentially planar and forms alternating layers with the BF
4
Sophisticated polydentate nitrogen ligands based on pyridine,
pyrazine, pyrimidine and pyradizine units have become the
scaffold of choice for designing and assembling novel metal–
anions as shown in Fig. 2(B). The asymmetric trigonal
geometry and layered structure are stabilized by interactions
2
between the large flat cation and non-coordinating BF
4
anions;
1
ligand architectures. Interestingly, a very simple ligand that has
closest contact is 2.86 Å between Ag(2) and F(2).
been essentially ignored is 4-(2-pyridyl)-pyrimidine, 1. To date,
A compound with the same 1+1 ligand to metal ratio and
basic tetrameric formula was formed when AgCF SO was
reacted with 1 in MeNO . The X-ray structure showed this
complex to be the rectangular isomer {[3][CF SO ]} ; Fig.
3(A). The head-to-head plus tail-to-tail aggregation requires
that the Ag( ) ions adopt different coordination geometries.
2
only the free ligand, 1, and [Ru(bipy)
2
(L)][PF
6
]
2
where L =
3
3
2
-methyl-4-(2-pyridyl)-pyrimidine, have been characterised by
2
3
X-ray crystallography. A few structural reports have appeared
3
3
4
on complexes of the symmetrical ligands 4,4A-bipyrimidine and
2,2A-dimethyl-4,4A-bipyrimidine, but the symmetrical nature of
I
these species makes direct comparson to the coordination
Ag(1) is bonded in a distorted square planar geometry to the
chelating sites of two different ligands while Ag(2) adopts a
linear geometry by coordinating to the bridging N-donors from
chemistry of 1 peripheral.4
,5
As shown below (Fig. 1), 1 has two sites for metal–ligand
interaction; a simple chelating site analogous to 2,2A-bipyridyl
and an exo N-donor site for bridging. Since these two sites are
oriented ~ 90° to each other, we reasoned that this ligand could
be used to assemble simple molecular polygons. There are, of
course, two very simple planar polygons that can be generated
using four ML units with 90° corners; a square and a rectangle.
Which of these is formed depends upon whether the building
blocks are arranged head-to-tail (square) or head-to-head
4
+
two different molecules of 1. The cationic unit in [3] is also
4+ 7
flat but not as planar as the cation in [2] . As is shown in Fig.
3(B), the rectangular tetrameric cations also form alternating
2
layers with the CF
3
SO
3
anions. The greater distortion from
). It is
planarity is a result of the tetrahedral distortion about Ag(
I
(
rectangle). What might dictate the formation of either of these
molecular motifs is difficult to predict and may be quite
subtle.
4
-(2-Pyridyl)-pyrimidine, 1, was prepared in 90% yield using
2
the published method. 2-[3-(N,N-dimethylamino)-1-oxoprop-
-en-1-yl]pyridine, prepared from 2-acetylpyridine and N,N-
2
dimethylformamidine dimethylacetate, was reacted with 3
equivalents of formamidine and 3 equiv. of sodium ethoxide. As
a way of initially probing the coordination preferences of 1, we
reacted equivalent amounts of the Ag(
AgCF SO or AgNO and 1 in a non-coordinating solvent,
MeNO . In each case, X-ray quality crystals were grown from
4
I) salts AgBF ,
3
3
3
6
2
the reaction mixture and the solid state structure determined.†
A complex with a 1+1 metal to ligand ratio was formed from
the reaction of 1 with AgBF . The X-ray structure showed this
4
Fig. 2 Ball-and-stick representations of the X-ray structure of the cationic
square [2]4 . There is a crystallographic inversion centre at the centre of the
+
2
square. Colour key: pyridine ring, red, pyrimidine ring, blue, BF
4
anions,
yellow. Top view (A) shows the cationic tetramer with a basic numbering
scheme. Bottom view (B) shows an edge-on view with four closest anions
of the intervening layers. Selected distances (Å) and angles (°):
Ag(1)…Ag(1)A 9.83, Ag(2)…Ag(2)A 7.84, Ag(1)…Ag(2) 6.39,
Ag(1)…Ag(2)A 6.18, Ag(1)–N(1) 2.270(8), Ag(1)–N(2) 2.356(7), Ag(1)–
N(6)A 2.184(7), Ag(2)–N(3) 2.141(8), Ag(2)–N(4) 2.372(8), Ag(2)–N(5)
2.276(7), N(1)–Ag(1)–N(2) 71.8(3), N(1)–Ag(1)–N(6)A 150.8(3), N(2)–
Ag(1)–N(6)A 135.3(3), N(3)–Ag(2)–N(4) 126.8(3), N(3)–Ag(2)–N(5)
160.8(3), N(4)–Ag(2)–N(5) 70.8(3).
Fig. 1 The ~ 90° angle ‘corner’ provided by 1 could produce either a
molecular square complex (left) via head-to-tail aggregation or a molecular
rectangle complex (right) from head-to-head aggregation.
2
484
CHEM. COMMUN., 2002, 2484–2485
This journal is © The Royal Society of Chemistry 2002

Fig. 3 Ball–and–stick representations of the X–ray structure of the cationic
4+ 9
rectangle [3] . There is a crystallographic inversion centre at the centre of
the rectangle. Top view (A) shows the cationic tetramer with a basic
numbering scheme. Bottom view (B) shows an edge-on view with four
closest anions of the intervening layers. Selected distances (Å) and angles
+
Fig. 4 An illustration (left) of [Ag(1)] units linked head-to-tail into a 1D
polymer. A ball-and-stick representation (right) of the X–ray structure of the
n+
1
D helical polymer {[4]}
n
Selected distances (Å) and angles (°):
(°): Ag(1)…Ag(1)A 11.22, Ag(2)…Ag(2)A 5.87, Ag(1)…Ag(2) 6.34,
Ag(1)…Ag(1)A 6.02, Ag(1)–N(1) 2.347(3), Ag(1)–N(2) 2.204(3), Ag(1)–
N(3) 2.374(3), Ag(1)–O(1) 2.468(3), Ag(1)–O(2) 2.810(3), N(1)–Ag(1)–
N(2)A 134.4(1), N(1)–Ag(1)–N(3) 70.0(1), N(2)A–Ag(1)–N(3), 126.6(1)
N(1)–Ag(1)–O(1) 90.4(1), N(2)A–Ag(1)–O(1) 129.4(1), N(3)–Ag(1)–O(1)
4.8(1), N(1)–Ag(1)–O(2) 110.3(1), N(2)A–Ag(1)–O(2) 89.7(1), N(3)–
Ag(1)–O(2) 130.5(1), O(1)–Ag(1)–O(2) 46.3(1).
Ag(1)…Ag(2)A 6.33, Ag(1)–N(2) 2.423(5), Ag(1)–N(3) 2.335(5), Ag(1)–
N(5) 2.378(5), Ag(1)–N(6) 2.413(5), Ag(2)–N(1) 2.203(5), Ag(2)–N(4)
2
.206(5), N(2)–Ag(1)–N(3) 69.5(2), N(2)–Ag(1)–N(5) 110.5(2), N(2)–
Ag(1)–N(6) 154.2(2), N(3)–Ag(1)–N(5) 174.9(2), N(3)–Ag(1)–N(6)
08.7(2), N(5)–Ag(1)–N(6) 69.0(2), N(1)–Ag(2)–N(4)A 171.7(2).
8
1
not possible to form a strictly square planar [M(2,2A-bipy)
2
]n+
(
2402 reflections, I > 2sI), R
= 1.134. {[3][CF SO ]} : C40
P-1, a = 10.127(1), b = 10.453(1), c = 13.504(2) Å, a = 81.403(2), b =
2
= 0.2352, wR
2
= 0.2396, (all data), GoF(F2)
4 12 12 12 4
F N O S , M = 1656.5, triclinic,
complex without some degree of tetrahedral distortion even
8
3
3
4
H28Ag
when the metal ion strongly prefers this geometry. The linear
two-coordinate geometry at Ag(2) defines the short side of the
3
7
1
wR
2.533(2), g = 89.410(2)°, U = 1347.3(3) Å , T = 293(2) K, Z = 1, m =
rectangle. This Ag…Ag distance is spanned by bridging
2
1
.699 mm , 5794 independent reflections (Rint = 0.0091). R
1
= 0.0486,
= 0.1422,
2
CF
3
SO
3
anions and is probably the reason why a rectangle is
1
= 0.0539, (3834 reflections, I > 2sI), R
2
= 0.1365, wR
AgN
2
preferred with this anion; contacts are Ag(2)…O(6) 2.57,
2
(all data), GoF(F ) = 1.068. {[4][NO
]}
3 n
C
9
H
7
4 3
O , M = 327.1,
Ag(1)…O(2) 2.83, Ag(2)…O(4) 2.59 Å.
1
monoclinic, P2 /n, a = 5.432(2), b = 10.860(5), c = 18.009(8) Å, b =
2
2) with
3
21
Since two different anions (BF
4
and CF
3
SO
3
98.486(6)°, U = 1050.7(8) Å , T = 289(2) K, Z = 4, m = 1.920 mm
4381 independent reflections (Rint = 0.0200). R = 0.0279, wR = 0.0299,
1490 reflections, I > 2sI), R = 0.0741, wR = 0.0764 (all data), GoF(F )
1.085. Data were collected on a Bruker APEX CCD instrument and
,
different shapes and arguably (slightly) different coordinating
abilities gave two very different shaped aggregates it was of
interest to examine the effect of using a coordinating oxyanion
such as nitrate. A compound with a 1+1 metal to ligand ratio was
1
1
2
(
=
2
2
solutions performed using the SHELXTL 5.03 Program Library, Bruker
Analytical Instrument Division, Madison, WI, USA, 1997. CCDC numbers
1
prepared from AgNO
the X-ray structure revealed that for AgNO
formed was a linear 1D helical coordination polymer
[4][NO ]} . Each molecule of ligand 1 propagates an [ML]
chain by alternately chelating and bridging to two different
3
and 1 in MeNO
2
. As shown in Fig. 4(B),
91503, 191504, 191505. See http://www.rsc.org/suppdata/cc/b2/
3
the complex
b206989j/ for crystallographic data in CIF or other electronic format.
{
3
n
n
1 G. H. Swiegers and T. J. Malefetes, Chem. Rev., 2000, 100, 3483.
2 E. Bejan, H. Aït-Haddou, J.-C. Daran and G. G. A. Balavoine, Synthesis,
1996, 1012.
Ag(
Ag(
I
) ions. The remainder of the coordination sphere of each
) ion is occupied by 2 O atoms from a nitrate ion. This
3
H. Aït-Haddou, E. Bejan, J.-C. Daran, G. G. A. Balavoine, F. Berruyer-
Penaud, L. Bonazzola, H. Smaoui-Chaabouni and E. Amouyal, J. Chem.
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C. Janiak, L. Uehlin, H-P. Wu, P. Klüfers, H. Piotrowski and T. G.
Scharmann, J. Chem. Soc., Dalton Trans., 1999, 3121.
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Dusausoy, N. Bouhmaida, N. E. Ghermani and Y. Dusausoy, Inorg.
Chem., 1995, 34, 5205.
I
infinite 1D motif is, of course, one of two alternate ways of
linking 90° corners; the head-to-tail version as illustrated in Fig.
4
5
4
(A).
We thank the Natural Sciences and Engineering Research
Council of Canada for financial support of this research.
6
7
M. Schröder, Coord. Chem. Rev., 2001, 222, 1555.
The mean deviation from a least-squares plane that included all of the
Notes and references
† 1
to assign structure. Only crystalline material was isolated and data crystals
selected randomly from the bulk. Crystal data, {[2][BF ]}
28Ag 12, M = 1407.4, triclinic, P-1, a = 7.841(2), b =
.214(2), c 17.007(3) Å, a 102.984(3), b 94.837(3), g
01.366(3)°, U = 1163.1(4) Å , T = 289(2) K, Z = 1, m = 1.768 mm
067 independent reflections (Rint = 0.0179). R = 0.0712, wR = 0.0724,
H NMR spectra (VT, MeNO
-d
) showed no features that could be used
non-H atoms of the cation was; 0.0927 Å for square [2] and 0.2887 Å
4+
2
3
for rectangle [3]4
+
.
4
4
:
8 A. Hazell, O. Simonson and O. Wernberg, Acta Crystallogr. Sect. C:
Cryst. Struct. Commun., 1986, C42, 1707.
9 Ball-and-stick diagrams were prepared using DIAMOND – Visual
Crystal Structure Information System CRYSTAL IMPACT, Postfach
1251, D-53002 Bonn.
36
C H
4 4 16
B F N
9
1
4
=
=
=
=
,
3
21
1
1
CHEM. COMMUN., 2002, 2484–2485
2485