metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
bronchodilator, and both oxopurines are also used as cardiac
stimulants or muscle relaxants. Pt complexes of these
oxopurines may be worthy of additional attention because of
the potential antitumour activity of such complexes (Bloe-
mink & Reedijk, 1996; Whitehead & Lippard, 1996). Here, we
report the synthesis and structure of two molecular plati-
num(II) complexes involving triphenylphosphine and the
anions of theophylline (TP) and theobromine (TB) as ligands,
respectively, namely cis-[Pt(TP )2(PPh3)2], (I), and cis-
[PtCl(TB )(PPh3)2]Á0.5EtOH, (II).
ISSN 0108-2701
Platinum complexes of oxopurines:
cis-bis(theophyllinato-N7)bis-
(triphenylphosphine)platinum(II) and
cis-chloro(theobrominato-N1)bis-
(triphenylphosphine)platinum(II)
ethanol hemisolvate
 Â
Erich Dubler, Helmut W. Schmalle,* Frederic Arod and
Alain Schneider
Institute of Inorganic Chemistry, University of Zurich, Winterthurerstrasse 190,
È
CH-8057 Zurich, Switzerland
È
Correspondence e-mail: schmalle@aci.unizh.ch
In metal complexes synthesized in non-alkaline media,
theophylline binds as a neutral ligand, whereas complexes
crystallized from alkaline solutions show the presence of
theophyllinate anions (Madarasz et al., 2000), usually depro-
tonated at N7, the atom where the H atom is located in the
crystal structure of neutral theophylline (Ebisuzaki et al.,
1997), and single-crystal data for many metal complexes prove
that theophylline moieties are normally bonded to the metal
centre through N7 (Madarasz et al., 2000). There are, however,
some rare examples of other coordination modes of unsub-
stituted theophylline or theophyllinate anions. N7 coordina-
tion including a balanced metal±O6 chelation has been found
in a titanium cyclopentadienyl complex, with a TiÐO6
Received 13 September 2001
Accepted 28 November 2001
Online 23 January 2002
The syntheses and structures of two mixed-ligand complexes
of platinum(II) with deprotonated oxopurine bases and
triphenylphosphine are reported, namely the theophyllin-
ate complex cis-bis(1,2,3,6-tetrahydro-1,3-dimethylpurine-2,6-
dionato-ꢀN7)bis(triphenylphosphine-ꢀP)platinum(II), [Pt(C7-
H7N4O2)2(C18H15P)2], (I), and the theobrominate complex
cis-chloro(1,2,3,6-tetrahydro-3,7-dimethylpurine-2,6-dionato-
ꢀN1)bis(triphenylphosphine-ꢀP)platinum(II) ethanol hemi-
solvate, [PtCl(C7H7N4O2)(C18H15P)2]Á0.5C2H5OH, (II). In
(I), the coordination geometry of Pt is square planar, formed
by the two coordinating N atoms of the theophyllinate anions
in a cis arrangement and two P atoms from the triphenyl-
phosphine groups. In (II), there are two crystallographically
independent molecules. They both exhibit a square-planar
coordination geometry around Pt involving one Cl atom, the
coordinating N atom of the theobrominate anion and two P
atoms from the triphenylphosphine groups. The two triphenyl-
phosphine groups are arranged in a cis con®guration in both
structures. The heterocyclic rings are rotated with respect to
the coordination plane of the metal by 82.99 (8) and 88.09 (8)ꢀ
in complex (I), and by 85.91 (16) and 88.14 (18)ꢀ in complex
(II). Both structures are stabilized by intramolecular stacking
interactions involving the purine rings and the phenyl rings of
adjacent triphenylphosphine moieties.
Ê
distance of 2.28 A (Cozak et al., 1986), whereas some weak
N7/O6-chelating interactions have been established, for
example, in copper(II) complexes, with a CuÐO6 distance of
Ê
Ê
2.92 A (Szalda et al., 1976) or 3.34 A (Kistenmacher et al.,
1978; Madarasz et al., 2000). N9 coordination of theophyllinate
anions, in spite of steric hindrance by the neighbouring methyl
group at N3, has been established in a dimeric rhodium(II)
complex (Aoki
theophylline also bonds through N9 in a chloroplatinum(II)
complex (Grif®th Amma, 1979). N7/N9 bridging
& Yamazaki, 1980), whereas neutral
&
theophyllinate anions, including a weak PtÐO6 interaction of
Ê
2.34 A, have been observed in a hexameric trimethylplatinum
complex (Lorberth et al., 1988). Finally, in a mixed-ligand PdII
complex, theophyllinate anions are linked to the metal
through C8 (Romerosa et al., 1997).
The molecular structure of (I) is shown in Fig. 1. Two
theophyllinate monoanions coordinate to PtII via the N7
atoms. Compound (I) exhibits a slightly distorted square-
planar coordination geometry around Pt, with two N7-coor-
Comment
Transition metal complexes of nucleobase derivatives may
serve as models for the coordination of metals to nucleic acids.
The methylated oxopurines theophylline and theobromine are
of additional interest in view of their pharmacological prop-
erties. Theophylline exhibits anti-asthmatic effects, theo-
bromine is in current clinical use as a vasodilator and a
Ê
dinating theophyllinate anions [PtÐN71 2.069 (3) A and PtÐ
Ê
N72 2.071 (3) A] and two P atoms from the triphenyl-
Ê
phosphine groups [PtÐP1 2.2792 (11) A and PtÐP2
Ê
2.2685 (11) A] in a cis arrangement (Fig. 1). Weak CÐHÁ Á ÁO
Acta Cryst. (2002). C58, m111±m115
DOI: 10.1107/S0108270101020364
# 2002 International Union of Crystallography m111