Phosphinocarboxylic acids as building blocks in organometallic crystal engineering. Self-organisation of one-dimensional photoluminescent cyclometallated platinum(II) polymeric structures

Article abstract of DOI:10.1039/a805593i

Diphenylphosphinopropanoic acid (Ppa) is utilised for the self-organisation of a luminescent organoplatinum polymeric material, the crystal structure of which features intermolecular hydrogen bonding and π-stacking interactions.

Full text of DOI:10.1039/a805593i

Phosphinocarboxylic acids as building blocks in organometallic crystal
engineering. Self-organisation of one-dimensional photoluminescent
cyclometallated platinum(II) polymeric structures
Man-Chung Tse, Kung-Kai Cheung, Michael C.-W. Chan and Chi-Ming Che*
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong. E-mail: cmche@hkucc.hku.hk
Received (in Cambridge, UK) 20th July 1998, Accepted 15th August 1998
Diphenylphosphinopropanoic acid (Ppa) is utilised for the
self-organisation of a luminescent organoplatinum poly-
meric material, the crystal structure of which features
intermolecular hydrogen bonding and p-stacking inter-
actions.
Treatment of Pt(L)Cl [HL = 4-(p-tolyl)-6-phenyl-2,2A-
bipyridine]7 with Ppa in CH3CN–H2O (1 : 1 v/v) at room
temperature in the presence of excess NH4PF6 yielded
[Pt(L)(Ppa)]PF6 1 as an orange crystalline solid in 75% yield.†
Absorption bands at 1709 and 3448 cm21 in the IR spectrum are
assigned to n(CO) and n(OH) respectively of the Ppa ligand,
while 195Pt satellites (JPtP 3943 Hz) are observed in the 31P
NMR spectrum.
The structure of 1 has been determined by X-ray crystallog-
raphy (Fig. 1).‡ The tridentate cyclometallated ligand L and the
phosphine are arranged in a distorted square-planar geometry
about the platinum atom. The platinum–nitrogen bond length
trans to the phenyl group [Pt(1)–N(1) 2.128(8) Å] is noticeably
longer than that trans to the phosphine ligand [Pt(1)–N(2)
2.018(8) Å]; this is consistent with the greater trans influence
exerted by the phenyl substituent. The crystal packing in 1 [Fig.
1(b)] reveals hydrogen bonding between two carboxylic acids in
adjacent molecules, with clear directionality and short inter-
molecular contacts [2.65(1) Å] between successive oxygen
atoms (O–H···ONC). p-Stacking between the aromatic planes of
L (mean 3.68 Å) is more distant than that in [Pt(6-phenyl-2,2A-
bipyridine)(PPh3)]ClO4 (mean 3.35 Å), although an identical
‘head–tail’ orientation of the overlapping ligands is evident in
both structures.7 Infinite one-dimensional polymeric zig-zag
chains linked by alternating hydrogen-bonding and p–p
Tertiary phosphines are versatile ligands in coordination and
organometallic chemistry, but functional groups which are
capable of complementary hydrogen bonding, such as car-
boxylic acids,1 are rarely incorporated.2 Molecular self-assem-
bly employing hydrogen bonding has generated considerable
interest in the domain of supramolecular chemistry and
molecular recognition.3 From an organometallic perspective,4,5
the resultant materials have potential applications in non-linear
optics, conductivity and ferromagnetism. The use of p–p
stacking interactions in crystal engineering has also been
prominent.6 Their importance is further emphasised by their
manifestation, in tandem with hydrogen bonding, in the
structures of biological molecules such as DNA and proteins.
Our earlier work on cyclometallated-(6-phenyl-2,2A-bipyridine)
platinum(II) complexes revealed favourable p–p interactions in
solid and solution states.7 Herein, we describe the employment
of diphenylphosphinopropanoic acid8 (Ppa) as a building block
in the supramolecular assembly of an organometallic polymer
directed by p-stacking and hydrogen-bonding interactions.
Fig. 1 (a) Perspective view of cation in 1 [40% thermal ellipsoids, all hydrogens are omitted including H(1) attached to O(1)]. Selected bond distances (Å)
and angles (°): Pt(1)–P(1) 2.249(3), Pt(1)–N(1) 2.128(8), Pt(1)–N(2) 2.018(8), Pt(1)–C(31) 2.03(1), O(1)–C(3) 1.31(1), O(2)–C(3) 1.21(1), N(1)–Pt(1)–N(2)
76.7(3), N(1)–Pt(1)–C(31) 158.0(4), N(2)–Pt(1)–C(31) 82.1(4), P(1)–Pt(1)–N(2) 172.7(2), O(1)–C(3)–O(2) 124(1). (b) Crystal packing in 1, showing infinite
polymeric zig-zag chains linked by alternating hydrogen-bonding and p–p interactions (anion and all hydrogens are omitted for clarity).
Chem. Commun., 1998, 2295–2296
2295

phosphinocarboxylic acids as versatile building blocks in
transition metal-based crystal engineering.
We acknowledge support from The University of Hong Kong
(for a Post-doctoral Fellowship to M. C.-W. C.), the Hong Kong
Research Grants Council, and the Croucher Foundation of Hong
Kong.
Notes and references
† Satisfactory elemental analysis has been obtained. Selected data for 1: 1H
NMR (CD3CN): 2.44 (s, 3, PhMe), 2.87–3.22 (m, 4, PC2H4), 6.64–8.33 (m,
24, aryl H); 31P NMR (CD3CN): 18.75 (JPtP 3943 Hz); IR (KBr, cm21):
1709 n(CO), 3448 n(OH).
¯
‡ Crystal data for 1: {[C38H32N2O2PtP]PF6}, M = 919.71, triclinic, P1 (No.
2), a = 9.715(2), b = 20.479(8), c = 9.245(2) Å, a = 101.76(3), b =
95.01(2), g = 88.46(3)°, V = 1794(1) Å3, Z = 2, Dc = 1.703 g cm23
,
m(Mo-Ka) = 40.53 cm21, F(000) = 904, T = 301 K. A yellow crystal of
dimensions 0.15 3 0.10 3 0.25 mm was used. A total of 4688 independent
reflections were measured on a Rigaku AFC7R diffractometer with graphite
monochromatized Mo-Ka radiation (l = 0.71073 Å) using w–2q scans.
The structure was solved by Patterson methods and all 51 non-H atoms were
refined anisotropically. The H(1) atom bonded to O(1) was located in the
difference Fourier map. Convergence for 463 variable parameters by least-
squares refinement on F with w = 4Fo2/[s2(I) + (0.024Fo2)2] for 3954
absorption-corrected (min, max transmission 0.596, 1.000) reflections with
I > 3s(I) was reached at R = 0.044 and wR = 0.058. CCDC 182/1015.
Fig. 2 UV–VIS absorption (a, in CH3CN ) and solid-state emission (b, Eex
350 nm) spectra of 1 at room temperature.
1 A. Bader and E. Lindner, Coord. Chem. Rev., 1991, 108, 27.
2 J. M. Forward, Z. Assefa, R. J. Staples and J. P. Fackler Jr., Inorg.
Chem., 1996, 35, 16.
3 (a) J.-M. Lehn, Angew. Chem., Int. Ed. Engl., 1990, 29, 1304; (b) A. D.
Burrows, C. W. Chan, M. M. Chowdhry, J. E. McGrady and D. M. P.
Mingos, Chem. Soc. Rev., 1995, 24, 329; (c) G. M. Whitesides, E. E.
Simanek, J. P. Mathias, C. T. Seto, D. N. Chin, M. Mammen and D. M.
Gordon, Acc. Chem. Res., 1995, 28, 37; (d) G. R. Desiraju, Angew.
Chem., Int. Ed. Engl., 1995, 34, 2311.
4 (a) D. Braga, F. Grepioni and G. R. Desiraju, Chem. Rev., 1998, 98,
1375; (b) D. Braga and F. Grepioni, Chem. Commun., 1996, 571.
5 (a) S. L. James, G. Verspui, A. L. Spek and G. van Koten, Chem.
Commun., 1996, 1309; (b) P. J. Davies, N. Veldman, D. M. Grove, A. L.
Spek, B. T. G. Lutz and G. van Koten, Angew. Chem., Int. Ed. Engl.,
1996, 35, 1959.
6 (a) O. Ermer, Adv. Mater., 1991, 3, 608; (b) L. Carlucci, G. Ciani, D. M.
Proserpio and A. Sironi, J. Chem. Soc., Chem. Commun., 1994, 2755;
(c) K. A. Hirsch, S. R. Wilson and J. S. Moore, Chem. Eur. J., 1997, 3,
765 and references therein.
7 T. C. Cheung, K. K. Cheung, S. M. Peng and C. M. Che, J. Chem. Soc.,
Dalton Trans., 1996, 1645.
8 K. Issleib and G. Thomas, Chem. Ber., 1960, 93, 803.
9 M. Munakata, L. P. Wu, M. Yamamoto, T. Kuroda-Sowa and M.
Maekawa, J. Am. Chem. Soc., 1996, 118, 3117. For organic analogues,
see: (a) A. P. Bisson, F. J. Carver, C. A. Hunter and J. P. Waltho, J. Am.
Chem. Soc., 1994, 116, 10292; (b) F. D. Lewis, J. S. Yang and C. L.
Stern, J. Am. Chem. Soc., 1996, 118, 12029; (c) P. R. Ashton, A. N.
Collins, M. C. T. Fyfe, P. T. Glink, S. Menzer, J. F. Stoddart and D. J.
Williams, Angew. Chem., Int. Ed. Engl., 1997, 36, 59. For a structure
with alternating auriophilic and hydrogen bonding, see: W. Schneider,
A. Bauer and H. Schmidbaur, Organometallics, 1996, 15, 5445.
10 (a) V. H. Houlding and V. M. Miskowski, Coord. Chem. Rev., 1991,
111, 145; (b) C. W. Chan, T. F. Lai, C. M. Che and S. M. Peng, J. Am.
Chem. Soc., 1993, 115, 11245.
interactions are therefore created. This combination of supra-
molecular synthons is rarely encountered in coordination
compounds.9
The absorption spectrum of 1 [Fig. 2(a)] contains a broad
low-energy absorption at 430 nm (emax 1560 dm3 mol21 cm21
)
which is tentatively assigned, like analogous cyclometallated
platinum(II) derivatives,10 to a metal-to-ligand charge transfer
(MLCT) transition, namely (5d)Pt?p*(L). Complex 1 exhibits
luminescence in solution and in the solid state. Emission at 542
nm in CH3CN solution at room temperature is similarly ascribed
3
to MLCT. The solid-state emission is red-shifted to 568 nm
with a shoulder at 604 nm [Fig. 2(b)] and is at a higher energy
than the metal–metal-to-ligand charge transfer (MMLCT)
emission (630 nm) of [Pt2(6-phenyl-2,2A-bipyridine)2(m-
dppm)]2+ which exhibits close intramolecular Pt–Pt contacts
[3.270(1) Å].7 The emission is therefore proposed to originate
from 3MLCT accompanied by partial excimeric character.
Similar shifts in emission energy have recently been found for
transmetallated gold(III) complexes.11 A blue shift to 528 nm
with well-resolved vibronic structure is observed in the frozen
state, where the vibrational spacing of 1240 cm21 is comparable
to the skeletal stretching of the free ligand L.
Finally, it is pertinent to note that ligation of diphen-
ylphosphinopropanoic acid does not necessitate the formation
of complexes with complementary hydrogen bonding in the
solid state. The molecular structure of the silver( ) dimer
I
[(PPh3)(Ppa)Ag]2(m-Cl)2 2, synthesised from the reaction of
[AgCl(PPh3)]4 with Ppa, is comprised of bulky peripheral
phenyl groups and no hydrogen bonding is apparent.12 This
situation is expected for complexes with congested geometry
where possible hydrogen-bonding motifs are segregated and
such interactions are precluded. Our future work will exploit
11 K. H. Wong, K. K. Cheung, M. C. W. Chan and C. M. Che,
Organometallics, 1998, 17, 3505.
12 M. C. Tse, K. K. Cheung and C. M. Che, unpublished results.
Communication 8/05593I
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Chem Commun., 1998