Di- and trinuclear Pd(II) and Pt(II) complexes containing bridging 2,7-disubstituted naphthyridines

Article abstract of DOI:10.1016/S0020-1693(98)00411-3

Dinuclear complex cations of the type cis-[M₂L₂(bpy)₂]²⁺ (1, 2, M=Pd, L=onp^-, monp^-; 5, 6, M=Pt, L=onp^-, monp^-) contain μ-1κN¹:2κN⁸ bridging monoanionic naphthyridine ligands (Honp=1,8-naphthyridin-2-one, Hmonp=7-methyl-1,8-naphthyridin-2-one) in a head/tail arrangement and exhibit short MM distances in the range 2.794-2.804 A. The analogous reaction of [MCl₂(bpy)] with the dibasic 2,7-disubstituted naphthyridine H₂donp (1,8-naphthyridin-2,7-dione) in the presence of LiOH leads to the trinuclear complexes cis-[M₃(donp)₂(bpy)₃]²⁺ (3) (M=Pd) and 9 (M=Pt) with similar short MM distances (2.801-2.807 A). A head/tail arrangement is once again adopted by the μ₃-1κO²:2κN¹:3κN ⁸ bridging donp^2- dianionic ligands. Blue-green coloured 9 exhibits reversible one-electron transfer waves at E_1/2 0.65 and 1.30 V (in CH₃CN versus Ag/AgCl) accompanied by a colour change from blue-green (λ_max=725 nm) to violet (λ_max=695, 540 nm) and corresponding to oxidation to [Pt₃(donp)₂(bpy)₃]³⁺ and [Pt₃(donp)₂(bpy)₃]⁴⁺. 9 can be reduced to green coloured [Pt₃(donp)₂(bpy)₃]⁺ at E_1/2=-0.82 V. The structures of the above compounds and [Pt(mbznnp)(bpy)(H₂O)]ClO₄ (4, Hmbznnp=2-benzylamino-7-methyl-1,8-naphthyridine), [Pt(donp)(bpy)] (7) and [Pt₂Cl₂(donp)(bpy)₂] (8) were established by X-ray structural analysis.

Full text of DOI:10.1016/S0020-1693(98)00411-3

Inorganica Chimica Acta 287 (1999) 72–81
Di- and trinuclear Pd(II) and Pt(II) complexes containing bridging
2,7-disubstituted naphthyridines
Bernhard Oskui, Markus Mintert, William S. Sheldrick *
Lehrstuhl fu¨r Analytische Chemie, Ruhr-Uni6ersita¨t Bochum, Postfach 102148, D-44780 Bochum, Germany
Received 17 July 1998; accepted 9 October 1998
Abstract
Dinuclear complex cations of the type cis-[M2L2(bpy)2]2+ (1, 2, M=Pd, L=onp−, monp−; 5, 6, M=Pt, L=onp−, monp−
contain m-1kN1:2kN8 bridging monoanionic naphthyridine ligands (Honp=1,8-naphthyridin-2-one, Hmonp=7-methyl-1,8-naph-
)
˚
thyridin-2-one) in a head/tail arrangement and exhibit short M···M distances in the range 2.794–2.804 A. The analogous reaction
of [MCl2(bpy)] with the dibasic 2,7-disubstituted naphthyridine H2donp (1,8-naphthyridin-2,7-dione) in the presence of LiOH
leads to the trinuclear complexes cis-[M3(donp)2(bpy)3]2+ (3) (M=Pd) and 9 (M=Pt) with similar short M···M distances
2
1
8
(2.801–2.807 A). A head/tail arrangement is once again adopted by the m3-1kO :2kN :3kN bridging donp2− dianionic ligands.
Blue–green coloured 9 exhibits reversible one-electron transfer waves at E1/2 0.65 and 1.30 V (in CH3CN versus Ag/AgCl)
accompanied by a colour change from blue–green (lmax=725 nm) to violet (lmax=695, 540 nm) and corresponding to oxidation
to [Pt3(donp)2(bpy)3]3+ and [Pt3(donp)2(bpy)3]4+. 9 can be reduced to green coloured [Pt3(donp)2(bpy)3]+ at E1/2= −0.82 V. The
structures of the above compounds and [Pt(mbznnp)(bpy)(H2O)]ClO4 (4, Hmbznnp=2-benzylamino-7-methyl-1,8-naphthyridine),
[Pt(donp)(bpy)] (7) and [Pt2Cl2(donp)(bpy)2] (8) were established by X-ray structural analysis. © 1999 Elsevier Science S.A. All
rights reserved.
˚
Keywords: Crystal structures; Palladium complexes; Platinum complexes; Naphthyridine complexes; Polynuclear complexes
1. Introduction
P) in the 2-position provides such ligands with an
ambidentate character as exemplified by the dirho-
dium(I) complexes [Rh2(m-onp)2(CO)4] (Honp=1,8-
naphthyridin-2-one) and [Rh2Cl2(CO)2(m-dpnapy)2]
(dpnapy=2-diphenylphosphino-5,7-dimethyl-1,8-naph-
thyridine), which exhibit respectively 1kN1:2kN8 and
1kP2:2kN8 coordination modes [17,18]. Introduction of
the bulky phenyl group at the 7-position in 5-methyl-7-
phenyl-1,8-naphthyridin-2-one (Hmphonp) prevents N8
participation with the result that 1kO2:2kN1 bridging is
observed in cis-[Rh2(mphonp)2(CO)4] [16]. A trinucleat-
ing function 1kO2:2kN1:3kN8 has been established in
cis-[Rh3(m-onp)2(CO)2(cod)2]ClO4 [19] and cis-[Ru3-
(mphonp)2(CO)6] [20].
Although 1,8-naphthyridine (np) has been shown to
be capable of acting as a dinucleating ligand in both
[Rh2(np)4]Cl4 [1] and [Ni2Br2(np)4]BPh4 [2], it has more
typically been observed to function as a mono- or
bidentate ligand in mononuclear complexes such as
[CuCl2(np)2], [PtCl(np)(PEt3)2]BF4, [Cd(np)4](ClO4)2 or
[Fe(np)4](ClO4)2 [3–6]. In contrast, 2,7-disubstituted
naphthyridines such as 7-methyl-1,8-naphthyridin-2-
one (Hmonp) have been successfully employed to
bridge metal–metal bonds in dimolybdenum(II) [7,8],
diruthenium(II) [7,9–11] and dirhodium(II) complexes
[1,12–16]. The presence of a donor atom X (e.g. O, N,
An analogous 1kO2:2kN3 bridging mode is adopted
by the pyrimidine derivatives 1-methyluracil and 1-
methylthymine in dinuclear Pd(II) and Pt(II) com-
pounds [21], that have been oxidised to mixed-valence
models for palladium or platinum blues. Contrastingly,
* Corresponding author. Tel.: +49-234-7004192/4202; fax: +49-
234-7094420.
E-mail
address:
shel@anachem.ruhr-uni-bochum.de
(W.S.
Sheldrick)
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(98)00411-3

B. Oskui et al. / Inorganica Chimica Acta 287 (1999) 72–81
73
3.6; N, 9.7%. FAB-MS: m/z (%) 815 (63) [M−
2ClO4]+, 670 (56) [M−2ClO4−onp]+, 514 (100)
[M−2ClO4−onp−bpy]+, 407 (7) [M−2ClO4]2+
.
IR: 3079w, 1631m, 1603m, 1449m, 1090s, 767m, 627m,
1
560w cm−1. H NMR (D2O, d6-acetone): 6.74 (d, 2H,
H3, onp−), 7.29 (m, 4H, H5%, bpy), 7.34 (m, 2H, H6,
onp−), 7.46 (m, 4H, H3%, bpy), 7.75 (m, 4H, H4%, bpy),
7.87 (m, 4H, H2%, bpy), 8.07 (d, 2H, H4, onp−), 8.25
(dd, 2H, H5, onp−), 9.35 (dd, 2H, H7, onp−) ppm.
UV–Vis (H2O/acetone (50:50)): lmax (m (l mol−1
cm−1)) 364 (1.51×103), 354 (1.47×103), 325 (1.47×
103).
Scheme 1. The ligands Honp, Hmonp, H2donp and Hmbznnp with
the numbering scheme.
2.1.2. cis-[Pd2(monp)2(bpy)2](ClO4)2 (2)
[PdCl2(bpy)] (33.3 mg, 0.1 mmol) and Hmonp (16.0
mg, 0.1 mmol) were stirred with LiOH · H2O (4.2 mg,
0.1 mmol) in 20 ml H2O for 4 h. LiClO4 (16.2 mg, 0.15
mmol) was added to the yellow solution and the precip-
itate filtered off. The resulting yellow solid was dried in
vacuo to afford 49.0 mg of 2 (yield 94%). Single crystals
were grown by dissolving the product in a mixture of
acetone/H2O (90:10) followed by slow evaporation of
the acetone.
complexes of these Group 10 metals with naphthyridine
derivatives have, to our knowledge, with the exception
of [PtCl(np)(PEt3)2]BF4 [4] not previously been re-
ported. In the present study, we describe the prepara-
tion and structural characterisation of mono-, di- and
trinuclear complexes of the fragments (bpy)Pd(II) and
(bpy)Pt(II). The employed 2,7-disubstituted naph-
thyridine derivatives are depicted in Scheme 1.
Anal. Found: C, 40.0; H, 3.2; N, 9.6. Calc. for
C38H30Cl2N8O10Pd2 · 5H2O (M=1132.5): C, 40.3; H,
3.6; N, 9.9%. FAB-MS: m/z (%) 844 (65) [M−
2ClO4]+, 685 (63) [M−2ClO4−monp]+, 529 (100)
2. Experimental
[M−2ClO4−monp−bpy]+, 421 (6) [M−2ClO4]2+
.
Electronic spectra were recorded on a Perkin-Elmer
Lambda 15, IR spectra as KBr discs on Perkin-Elmer
1700 and 1760 spectrometers. FAB-MS were measured
on a Fisons VG Autospec with 3-nitrobenzyl alcohol as
IR: 3119w, 1637m, 1602w, 1562s, 1284w, 1130s, 855w,
1
765m cm−1. H NMR (D2O/d6-acetone (50:50)): 3.58
(s, 6H, CH3, monp−), 6.67 (d, 2H, H3, monp−),
7.09–7.28 (m, 8H, H3% H5%, bpy), 7.35 (d, 2H, H6,
monp−), 7.70 (d, 2H, H4, monp−), 7.80 (d, 2H, H5,
monp−), 7.95–8.19 (m, 8H, H2% H4%, bpy) ppm. UV–
Vis (H2O/acetone (50:50): lmax (m (l mol−1 cm−1) 369
(1.42×103), 340 (1.28×103), 327 (1.31×103).
1
the matrix, H NMR spectra on a Bruker AM 400 with
l values registered as ppm relative to the signal of the
deuterated solvent. Elemental analysis were performed
on a Carlo Erba 1106 analyser. The naphthyridine
derivatives Honp, Hmonp [22], 1,8-naphthyridin-2,7-
dione (H2donp) [23] and 2-benzylamino-7-methyl-1,8-
naphthyridine (Hmbznnp) [20] were prepared according
to literature procedures; the starting compounds
[MCl2(bpy)] (M=Pd, Pt) were synthesised [24] from
K2MCl4.
2.1.3. cis-[Pd3(donp)2(bpy)3](PF6)2 (3)
H2donp (32.4 mg, 0.2 mmol) was stirred in 40 ml
H2O with LiOH · H2O (16.8 mg, 0.4 mmol) to yield a
deep yellow solution. [PdCl2(bpy)] (100.1 mg, 0.3
mmol) was added and the yellow suspension refluxed
for 24 h. After reduction in volume, an excess of
NH4PF6 was added to the resulting solution to yield an
orange precipitate. This was filtered off, washed with
water and dried in vacuo to afford 93.7 mg (yield 67%)
of 3. Suitable crystals for an X-ray analysis were grown
by slow evaporation of an acetone/water solution of the
product.
Anal. Found: C, 40.8; H, 2.7; N, 9.2. Calc. for
C46H32F12N10O4P2Pd3 · 2H2O (M=1434.0): C, 39.5; H,
2.3; N, 10.0%. FAB-MS: m/z (%) 1399 (2) [M+H]+,
1253 (42) [M−PF6]+, 1107 (17) [M−2PF6]+, 953 (12)
[M−2PF6−bpy]+, 795 (14) [M−2PF6−2bpy]+, 638
(10) [Pd3(donp)2]+, 530 (17) [Pd2(donp)(bpy)]+, 423
(100) [Pd(donp)(bpy)+H]+. IR: 3117m, 3088m, 1626s,
2.1. Preparation of the complexes 1–9
2.1.1. cis-[Pd2(onp)2(bpy)2](ClO4)2 (1)
[PdCl2(bpy)] (33.3 mg, 0.1 mmol), Honp (14.6 mg,
0.1 mmol) and LiOH · H2O (4.2 mg, 0.1 mmol) were
stirred for 3 h in 20 ml H2O. LiClO4 (16.2 mg, 0.15
mmol) was added to the yellow solution and the result-
ing yellow precipitate filtered off. The solid was subse-
quently dried in vacuo to afford 29.9 mg of 1 (yield
59%). The product was dissolved in a mixture of ace-
tone and H2O (90:10) to afford suitable crystals for
X-ray analysis by slow evaporation of acetone.
Anal. Found: C, 36.7; H, 2.9; N, 9.5. Calc. for
C36H26Cl2N8O10Pd2 · 7H2O (M=1014.4): C, 37.3; H,

74
B. Oskui et al. / Inorganica Chimica Acta 287 (1999) 72–81
1603s, 1558s, 1524s, 1500s, 1471m, 841vs, 766s. 1H
NMR (d6-DMSO): 6.27 (d, 2H, H6), 6.57 (d, 2H, H3),
7.00 (m, 2H, bpy), 7.17 (m, 2H, bpy), 7.35 (d, 2H, bpy),
7.46 (m, 2H, bpy), 7 59 (d, 2H, bpy), 7.70 (d, 4H, bpy),
7.80 (4H, d, bpy), 7.86 (2H, d, bpy), 7.91 (m, 2H, bpy),
8.05 (m, 2H, bpy), 8.09 (d, 4H, bpy), 8.15 (d, 2H, bpy)
ppm. UV–Vis (DMSO): lmax (m (l mol−1 cm−1)) 411
(0.78×103), 360 (2.57×103, sh), 344 (3.24×103), 325
(3.58×103), 305 (4.65×103), 258 (4.31×103).
2.1.6. cis-[Pt2(monp)2(bpy)2](ClO4)2 (6)
[PtCl2(bpy)] (42.2 mg, 0.1 mmol), Hmonp (16.0 mg,
0.1 mmol) and LiOH · H2O (4.2 mg, 0.1 mmol) were
combined in 20 ml H2O and the yellow suspension
stirred at reflux for 1 h. After cooling LiClO4 (16.0
mg, 0.15 mmol) was added to the red solution and
the resulting precipitate filtered off and dried in vacuo
to afford 57.9 mg of 6 (yield 95%). The product was
dissolved in a mixture of acetone/H2O (95:5) to
provide crystals for X-ray analysis by slow evapora-
tion.
2.1.4. [Pt(mbznnp)(bpy)(H2O)](ClO4) (4)
[PtCl2(bpy)] (42.2 mg, 0.1 mmol), Hmbznnp (25.0
mg, 0.1 mmol) and LiOH · H2O (4.2 mg, 0.1 mmol)
were refluxed in 20 ml H2O for 1 h. After cooling
LiClO4 (16.1 mg, 0.15 mmol) was added to the solution
and the resulting yellow precipitate filtered off and
dried in vacuo to afford 62.4 mg of 4 (yield 87%).
Crystals for an X-ray analysis were grown by dissolving
the product in an acetone/H2O (95:5) mixture followed
by slow evaporation of the acetone.
Anal. Found: C, 34.9; H, 2.6; N, 8.4. Calc. for
C38H30Cl2N8O8Pt2 (M=1219.8): C, 35.8; H, 2.8; N,
8.8%. FAB-MS: m/z (%) 1020 (100) [M−2ClO4]+,
861 (33) [M−2ClO4−monp]+, 510 (62) [M−
2ClO4]2+. IR: 3088w, 1641s, 1607w, 1567s, 1452m,
1
1270w, 1089s, 766m cm−1. H NMR (D2O/d6-acetone
(50:50): 2.41 (s, 6H, CH3, monp−), 6.63 (d, 4H, H3,
monp−), 7.00 (d, 2H, H6, monp−), 7.19–7.45 (m,
8H, H3% H6%, bpy), 7.79 (d, 2H, H5, monp−), 7.90
(d, 2H, H5, monp−), 8.02–8.35 (m, 8H, H2%, H4%,
bpy) ppm. UV–Vis (H2O/acetone (50:50)): lmax (m (l
mol−1 cm−1)) 518 (0.62×103), 361 (1.53×103), 352
(1.48×103), 327 (1.66×103).
Anal. Found: C, 40.2; H, 3.7; N, 8.7. Calc. for
C26H24ClN5O5Pt (M=717.0): C, 40.5; H, 3.9; N, 9.1%.
FAB-MS: m/z (%) 618 (23) [M−ClO4]+, 600 (100)
[M−ClO4−H2O]+, 369 (6) [M−ClO4−mbznnp]+.
IR: 3084w, 1632m, 1551s, 1452m, 1415m, 1311w, 1089s,
1
767m, 625m cm−1. H NMR (D2O/d6-acetone): 3.11 (s,
2.1.7. [Pt(donp)(bpy)] (7)
3H, CH3, mbznnp−), 4.95 (d, 2H, CH2, mbznnp−),
6.63 (d, 1H, H3, mbznnp−), 6.77 (d, 1H, H6,
mbznnp−), 6.80–7.02 (m, 4H, H3% H5%, bpy), 7.22 (m,
5H, C6H5, mbznnp−), 7.35 (d, 1H, H4, mbznnp−),
7.96 (d, 1H, H5, mbznnp−), 8.14–8.42 (m, 4H, H2%,
H4%, bpy) ppm. UV–Vis (H2O/acetone (50:50)): lmax (m
(l mol−1 cm−1)) 362 (1.23×103), 321 (0.85×103), 313
(0.76×103).
[PtCl2(bpy)] (84.4 mg, 0.2 mmol) was refluxed in 20
ml H2O with LiOH · H2O (16.8 mg, 0.4 mmol). After
cooling Ag2SO4 (62.4 mg, 0.2 mmol) was added to the
yellow solution and the precipitated AgCl filtered off.
Addition of H2donp (32.4 mg, 0.2 mmol) followed by
stirring at reflux for 4 h led to the precipitation of a
yellow–brown solid. This was filtered off, washed sub-
sequently with H2O, acetone and CH2Cl2 and dried in
vacuo to afford 30.7 mg of (7) (yield 30%). Crystals for
the X-ray analysis were grown by slow gas diffusion of
isopropanol into a 3-nitrobenzyl alcohol solution of the
product.
2.1.5. cis-[Pt2(onp)2(bpy)2](PF6)2 (5)
[PtCl2(bpy)] (42.2 mg, 0.1 mmol), Honp (14.6 mg, 0.1
mmol) and LiOH · H2O (4.2 mg, 0.1 mmol) were com-
bined in 20 ml H2O and the resulting yellow mixture
refluxed for 1 h to afford a red solution. This was
evaporated to dryness and the residue was taken up in
20 ml MeOH. NH4PF6 (17.0 mg, 0.1 mmol) was added
and the red precipitate filtered off and dried in vacuo to
afford 60.9 mg of 5 (yield 95%). Crystals for X-ray
analysis were grown by gas diffusion of diethyl ether
into a DMF solution of the product.
Anal. Found: C, 39.9; H, 2.7; N, 10.2; Calc. for
C18H12N4O2Pt2 · 3H2O (M=565.4): C, 40.8; H, 2.7;
N, 10.6%. FAB-MS: m/z (%) 512 (100) [M]+, 350
(15) [M−donp]+. IR: 3403s, 3170vs, 2917m, 2822m,
1636vs, 1510s, 1371s, 1143m, 936w, 893m, 840m,
.
785m, 717w, 661w, 499m cm−1 1H NMR (d6-
DMSO): 5.71 (d, 2H, H3, H6, donp2−), 7.70 (d, 2H,
H4, H5, donp2−), 8.35 (ddd, 2H, H3, H9, bpy), 8.35
(ddd, 2H, H4, H10, bpy), 8.49 (dd, 2H, H5, H11,
bpy), 11.24 (dd, 2H, H2, H8, bpy) ppm. UV–Vis
(DMSO): lmax (m (l mol−1 cm−1)) 423 (0.74×103),
400 (0.73×103), 361 (8.33×103), 345 (6.52×103),
326 (8.41×103).
Anal. Found: C, 33.0; H, 2.9; N, 9.0. Calc. for
C36H26F12N8O2P2Pt2 (M=1282.7): C, 33.7; H, 2.0; N,
8.7%. FAB-MS: m/z (%) 1137 (68) [M−PF6]+, 992
(25) [M−2PF6]+, 846 (6) [M−2PF6−onp]+, 690 (12)
[M−2PF6−onp−bpy]+, 496 (100) [M−2PF6]2+
.
IR: 3081w, 1634s, 1607m, 1553s, 1435m, 1141s, 1088s,
1
768m cm−1. H NMR (d6-acetone): 6.51–8.53 overlap-
2.1.8. [Pt2Cl2(donp)(bpy)2] (8)
ping proton multiplets. UV–Vis (acetone): lmax (m (l
mol−1 cm−1)) 485 (0.75×103), 357 (1.87×103), 326
(1.98×103).
[PtCl2(bpy)] (84.4 mg, 0.2 mmol), H2donp (16.2 mg,
0.1 mmol) and LiOH · H2O (8.4 mg, 0.2 mmol) were
stirred at reflux in 20 ml H2O for 4 h leading to a

B. Oskui et al. / Inorganica Chimica Acta 287 (1999) 72–81
75
green–blue solution and a red–orange precipitate. The
2.2. X-ray structural analyses
solid was filtered off, washed subsequently with H2O,
acetone and CH2Cl2 and dried in vacuo to afford 21.55
mg of 8 (yield 23%). Crystals for the X-ray analysis
were grown by slow gas diffusion of isopropanol into a
3-nitrobenzyl alcohol solution of the product.
Units of all constants were obtained for crystals of
1–9 from least-squares fits to setting of 25 reflections
centred on a Siemens P4 diffractometer. Intensity data
were collected on the four-circle diffractometer at
varied scan rates in the v mode for Mo Ka radiation
Anal. Found: C, 41.7; H, 3.0; N, 9.0; Calc. for
C28H20Cl2N6O2Pt2 · 3C7H7NO3 (M=1393.0): C, 42.2,
H, 3.0, N, 9.0%. FAB-MS: m/z (%) 934 (39) [M]+, 898
(4) [M−Cl]+, 705 (3) [M−bpy−Cl]+, 512 (100) [Pt-
(donp)(bpy)]+, 350 (4) [Pt(bpy)]+. IR: 3087m, 1623m,
1596m, 1543s, 1471m, 1451m, 1431s, 1366m, 1140m,
˚
(l=0.71073 A). Semi-empirical absorption corrections
(c scans) were applied to the registered intensities. The
structures were solved by standard heavy atom methods
and refined by full-matrix least-squares, for 1, 2, 4–6
against F with the SHELXTL program system, for 3, 7–9
against F2 with SHELXL-93 [25]. Rw=[ꢀw(Fo−Fc)2/
839m, 765s, 722w, 473m cm−1 1H NMR (DMSO):
.
5.83 (d, 2H, H3, H6, donp2−), 7.27 (d, 2H, H4, H5,
donp2−), 7.39 (m, 2H, bpy), 7.68 (m, 2H, bpy), 7.98 (d,
2H, bpy), 8.07 (d, 2H, bpy), 8.15 (m, 2H, bpy), 8.23 (m,
2H, bpy), 8.47 (d, 2H, bpy), 8.86 (d, 2H, bpy) ppm.
UV–Vis (DMSO): lmax (m (l mol−1 cm−1)) 590 (0.13×
103), 540 (0.18×103), 442 (0.34×103), 393(sh) (3.55×
103), 370 (3.24×103), 354 (3.28×103), 320 (3.67×103),
258 (5.93×103).
ꢀwFo ] for the former system, wR2=[ꢀw(Fo −Fc ) /
2 1/2
2
2 2
2 2 1/2
ꢀw(Fo ) ] for SHELXL-93. The crystal lattices of 1–4
and 6 contain solvate water molecules, 5 crystallises
together with diethyl ether, 7–9 together with the em-
ployed solvent 3-nitrobenzyl alcohol. Crystal and refin-
ement data for 1–9 are summarised in Tables 1 and 2
(for details of supplementary material, see Section 4).
2.1.9. cis-[Pt3(donp)2(bpy)3](PF6)2 (9)
3. Discussion
H2donp (32 mg, 0.2 mmol) and LiOH · H2O (16.8
mg, 0.4 mmol) were stirred in 40 ml H2O. Addition of
[PtCl2(bpy)] (126.7 mg, 0.3 mmol) to the dark yellow
solution followed by refluxing for 3 days led to a
green–blue solution and a red–orange precipitate. This
was filtered off, the filtrate evaporated to dryness and
the resulting residue extracted with CH3NO2. The sol-
vent was subsequently removed in vacuo and the result-
ing solid taken up in H2O. Addition of excess of
NH4PF6 led to a green–blue precipitate, that was
filtered off, washed with cold H2O and dried in vacuo
to afford 99.4 mg of 9 (yield 60%). Crystals for the
X-ray analysis were grown by slow gas diffusion of
isopropanol into a 3-nitrobenzyl alcohol solution of the
product.
All four dimeric complex cations of the type cis-
[M2L2(bpy)2]2+ (1, 2, M=Pd, L=onp−, monp−; 5, 6,
M=Pt, L=onp−, monp−) exhibit the m-1kN1:2kN8
coordination mode with head/tail positioning of their
bridging naphthyridine ligands. This binding pattern,
which was also previously established for [Ru2(monp)4]
[7], should be electronically favoured for M42+ cores
with occupied antibonding orbitals (e.g. Ru42+, Rh24+
)
as it will enhance the interaction between the d* orbital
of the dimetal core and the p* molecular orbitals of the
bridging aromatic anions [9]. In contrast, the bridging
monp− ligands in [Mo2(monp)4] display
a
m2-
1kN1:2kO2 coordination mode [7].
Figs. 1 and 2 depict the structures of the cations in
cis-[Pd2(onp)2(bpy)2](ClO4)2 (1) and cis-[Pd2(monp)2-
(bpy)2](ClO4)2 (2), which are analogous to those of
their Pt(II) counterparts 5 and 6. The Pd···Pd and
Pt···Pt intramolecular distances in these dinuclear spe-
Anal. Found: C, 35.1; H, 2.3; N, 8.2. Calc. for
C46H32F12N10O4P2Pt3 · C7H7NO3 · H2O (M=1773.2):
C, 34.7; H, 2.3; N, 8.4%. FAB-MS: m/z (%) 1666 (6)
[M]+, 1519 (59) [M−PF6]+, 1374 (60) [M−2PF6]+,
1218 (4) [M−bpy−2PF6]+, 1056 (15) [Pt3(donp)-
(bpy)2]+, 907 (14) [Pt3(donp)2]+, 861 (17) [Pt2(donp)-
˚
cies lie in the narrow range 2.794–2.804 A and are
markedly shorter than values previously reported for
analogous 1-methylthyminato (1-Met) and 1-methyl-
(bpy)2]+, 687 (71) [M−2PF6]2+
, 512 (100) [Pt-
(donp)(bpy)]+. IR: 3117w, 3085w, 1635m, 1607m,
1558s, 1528s, 1471m, 1454m, 1407m, 1366m, 1140m,
uracilato (1-MeU) bridged complexes (2.841–2.974 A)
˚
[26–30]. Metal coordination leads to a widening of
the N1···N8 bite distance of the bridging naphthyridine
ligands onp− and monp−. This may be gauged by
comparing the relevant N1···N8 distance in the free
1
842s, 766m, 558m, 493w cm−1. H NMR (d6-DMSO):
6.31 (d, 2H, H6, donp2−), 6.68 (d, 2H, H3, donp2−),
7.04 (m, 2H, bpy), 7.22 (m, 2H, bpy), 7.41 (m, 2H,
bpy), 7.64 (d, 2H, H4, donp2−), 7.76 (d, 4H, H5,
donp2−, bpy), 7.88 (m, 2H, bpy), 8.10 (m, 4H, bpy),
8.19 (d, 2H, bpy), 8.26 (d, 2H, bpy) ppm. UV–Vis
(DMSO): lmax (m (l mol−1 cm−1)) 725 (0.44×103), 606
(0.29×103), 368 (4.19×103), 357 (4.36×103), 324(sh)
(3.45×103), 309 (4.18×103), 258 (5.6×103).
˚
˚
ligand Hmonp (2.293(6) A [31]) with those average
values of 2.39 and 2.36 A in 2 and 6, respectively.
Interestingly the N1–M1···M2 angle is consistently
smaller (79.4–81.8°) than N8–M2···M1 (84.1–86.3°) in
all four dinuclear species. As the Pd(II) and Pt(II)
atoms are not significantly displaced from the least-

76
B. Oskui et al. / Inorganica Chimica Acta 287 (1999) 72–81
Table 1
Crystal and refinement data for 1, 2 and 4–6
Compound
1 · 4H2O
2 · 5H2O
4 · 2.5H2O
5 · (C2H5)2O
6 · 4H2O
Space group
P2/c
C2/c
C2/c
C2/c
C2/c
˚
a (A)
10.914(2)
13.216(3)
14.860(3)
103.25(3)
2086.3(7)
2
22.813(5)
13.934(3)
14.249(3)
110.01(3)
4256(2)
4
22.362(4)
11.303(2)
23.549(5)
96.10(3)
5919(2)
8
21.849(4)
14.761(3)
13.665(3)
102.49(3)
4303(1)
4
23.080(8)
14.008(5)
14.219(5)
110.81(5)
4297(2)
4
˚
b (A)
˚
c (A)
i (°)
V (A )
3
˚
Z
M
1086.4
1.729
1132.5
1.767
762.1
1.710
1356.9
2.095
1291.8
1.997
Dcalc (g cm−3
)
Crystal size (mm)
0.60×0.32×0.34
1.07
0.60×0.08×0.04
1.05
0.42×0.26×0.21
4.88
0.58×0.24×0.06
6.67
0.66×0.48×0.10
6.71
v (mm−1
)
Scan type
2q max (°)
v
45
v
45
v
45
v
45
v
55
Independent reflections
Reflections observed
Rejection criterion
Refined parameters
R
2.681
1835
IB1.5s(I)
224
0.077
2467
1885
IB1.5s(I)
195
0.081
3834
2267
IB2s(I)
323
0.042
2773
1799
IB2s(I)
286
0.067
5250
3361
IB2s(I)
258
0.047
Rw
0.077
0.96/−0.89
0.081
0.95/−0.82
0.042
0.93/−0.51
0.068
0.84/−0.73
0.047
1.61/−1.12
−3
˚
Max./min. Dz (e A
)
Table 2
Crystal and refinement data for 3 and 6–9
Compound
3 · 2H2O
7 · 3C7H7NO3
8 · 3C7H7NO3
9 · C7H7NO3 · H2O
(
(
Space group
P21/n
15.697(3)
17.412(4)
19.312(4)
90
105.61(3)
90
5084(2)
4
P1
P21/c
P1
˚
a (A)
6.961(1)
20.212(4)
21.335(4)
61.96(3)
84.00(3)
82.54(3)
2623.7(8)
2
11.258(3)
27.657(5)
16.005(2)
90
103.54(2)
90
13.597(3)
14.563(3)
14.565(3)
96.99(3)
91.37(3)
98.70(3)
2827(1)
2
˚
b (A)
˚
c (A)
h (°)
i (°)
k (°)
3
˚
V (A )
4845(2)
4
Z
M
1430.0
1.868
1473.2
1.865
1388.0
1.903
1830.1
2.150
Dcalc (g cm−3
)
Crystal size (mm)
0.48×0.42×0.36
1.22
0.80×0.23×0.15
5.41
0.80×0.20×0.16
5.95
0.48×0.42×0.32
7.57
v (mm−1
)
Scan type
2q max (°)
v
47.5
v
50
v
48.5
v
46
Independent reflections
Refined parameters
R [I\2s(I)]
wR2
7534
490
0.053
0.114
8796
766
0.049
0.124
7591
674
0.055
0.137
7662
817
0.037
0.100
−3
˚
Max./min. Dz (e A
)
0.75/−0.57
2.42/−2.32
1.84/−1.71
0.86/−0.78
squares planes of their coordination spheres, the nar-
row N1···N8 bite distances of the bridging naph-
thyridine ligands cause the square-planar MN4 units to
tilt away from one another at dihedral angles in the
range 18.1–20.5°. Steric interaction between C(171)
and O(12)% (Fig. 2) in the monp− complexes 2 and 6
leads to a pronounced rotation of the naphthyridine
and 2,2%-bipyridyl ligands relative to one another
about the M1···M2 axis. Torsion angles N1–M1···M2–
N8 of 23.8 and 22.1° in 2 and 6 contrast with values
of only 1.7 and 10.4° in 1 and 5.
It is apparent in the dinuclear complexes that the
observed pronounced tilting of the M(bpy) planes is
necessary to reduce steric interactions between compo-
nent atoms of adjacent bpy ligands. This poses the
question as to whether 1,8-naphthyridin-2-ones could
be capable of coordinating three such M(bpy) frag-
ments in a 1kO2:2kN1:3kN8 bridging mode. We were

B. Oskui et al. / Inorganica Chimica Acta 287 (1999) 72–81
77
9 in Fig. 3. Employment of a dibasic naphthyridine
ligand was essential for both Group 10 metals in order
to reduce the overall cation charge to +2 as in the
dinuclear species discussed above. Both the M···M dis-
˚
˚
tances (3, 2.801(1), 2.804(1) A; 9, 2.801(1), 2.807(1) A)
and dihedral angles between neighbouring square-pla-
nar M coordination spheres (3, 22.3, 22.8°; 9, 22.0,
24.0°) in the trinuclear species are similar to those in
the dipalladium and diplatinum complexes, thereby in-
dicating that steric effects, in particular interactions
between neighbouring bipyridyl ligands, must indeed be
responsible for the observed molecular geometries (Fig.
4). As observed in the dimeric complexes 2 and 6,
tilting of the metal coordination planes is accompanied
by a marked twisting of the donp2− and bpy ligand
sites relative to the M1···M2 and M2···M3 vectors in 3
and 9. The relevant torsion angles average to 17.4° in 3
and 18.7° in 9, whose M3 chains exhibit respective
nearly linear M1···M2···M3 angles of 169.7(1) (3) and
167.4(1)° (9).
To the best of our knowledge, 3 and 9 represent the
first reported examples of (effectively) linear tripalla-
dium and triplatinum complexes of the type cis-
[(ML%2)3(m3-L)2] (L%=bpy/2, en/2, NH3, NR3).
However, trimetallic heteronuclear complexes of the
type cis-[L%Pt(m-L)2M(m-L)2PtL%]X2 (M=Pd; L%=en/
Fig. 1. Molecular structure of cis-[Pd2(onp)2(bpy)2]2+ in 1.
2
2
2, NH3; L=1-MeU; 1-MeT, X=NO3−, ClO4− or M=
Ni, Cu; L%=NH3; L=NHCOCH3−; X=NO3−, ClO4−)
˚
are known [32]. The Pt···Pd distances of 2.839(1) A in
the 1-methyluracilato bridged complex cis-[(NH3)2Pt(1-
MeU)2Pd(1-MeU)2Pt(NH3)2](ClO4)2 are however con-
siderably longer than in 3 and 9 and point to the
increased bite range of the 1-methyluracilato ligands in
comparison to the more rigid naphthyridine skeleton of
donp2−. It is also instructive to compare the optical
and electrochemical properties of 9 with those of plat-
inum blues with their likewise linear chains of Pt atoms
[33], whose typical oxidation states lie in the range
2.25–2.75. Interestingly, distances between adjacent
platinum atoms in Pt(II) model complexes have, in
general, been found to be significantly longer than
˚
those of 2.801(1) and 2.807(1) A recorded for the
triplatinum(II) complex 9, e.g. the tetrameric com-
pound [{(NH3)4Pt2(C5H4NO)2}2](NO3)4 (C5H4NO=a-
˚
pyridonate) exhibits a Pt···Pt separation of 2.88 A in its
a-pyridinato dimeric sub-units, that are linked through
hydrogen bonds to provide a central Pt···Pt interaction
of 3.13 A [33]. The analogous Pt···Pt distances in the
Fig. 2. Molecular structure of cis-[Pd2(monp)2(bpy)2]2+ in 2.
˚
oxidation product [{(NH3)4Pt2(C5H4ON)2}2](NO3)5
with its average Pt oxidation state of 2.25, are 2.779
and 2.885 A [34], i.e. the shorter distance for a bonding
Pt–Pt interaction in this complex is similar to the
formally nonbonding Pt···Pt distances found in 9. In
the potential range 0 to +1.6 V versus Ag/AgCl, 9
shows one-electron transfer waves at E1/2 0.65 and 1.30
V, respectively, corresponding to oxidation to
successful in achieving this goal by refluxing an
aqueous solution of [MCl2(bpy)] with H2donp and
LiOH in a molar 3:2:4 ratio. Both trinuclear complexes,
cis-[Pd3(donp)2(bpy)3](PF6)2 (3) and cis-[Pt3(donp)2-
(bpy)3](PF6)2 (9), which are also formed in good yield at
a 1:1:2 ratio, once again exhibit a head/tail arrangement
of their bridging heteroaromatic ligands as depicted for
˚

78
B. Oskui et al. / Inorganica Chimica Acta 287 (1999) 72–81
Fig. 3. Molecular structure of cis-[Pt3(donp)2(bpy)3]2+ in 9.
[Pt3(donp)2(bpy3]3+ and [Pt3(donp)2(bpy)3]4+ (see Fig.
5). 9 can be reduced to [Pt3(donp)2(bpy)3]+ at E1/2
=− 0.82 V. At the employed scan speed of 0.1 V s−1
characteristic values of IpA/IpC and DEp for a reversible
system are obtained. A localised oxidation scheme of
the following type can be tentatively formulated,
mation mechanism may well be involved. This hypothe-
sis is supported by the isolation of a precipitate of the
red–orange poorly soluble compound [Pt2Cl2(donp)-
(bpy)2] (8) as an intermediate product on the route to 9.
Its yield may be increased to 23% by employing a 2:1:2
molar ratio of [PtCl2(bpy)], H2donp and LiOH and
[PtIIPtIPtII] green
−0.82 V +e−8−e−
[PtIIPtIIPtII] blue–green, lmax=725 nm
+0.65 V +e−8−e−
[PtIIIPtIIPtII] blue–violet, lmax=710 nm, 555 nm
+1.30 V +e−8−e−
[PtIIIPtIIPtIII] violet, lmax=695 nm, 540 nm
although, of course, delocalisation is possible. Oxida-
tion is accompanied by a shift in the main absorption
maximum in the visible range to lower wavelengths and
the appearance of a second maximum for the tri- and
tetracations.
In view of the head/tail m-1kN1:2kN8 coordination in
the dimeric species [M2L2(bpy)2]2+ (1, 2, 5, 6), which
could provide intermediate products on the reaction
pathway to trinuclear complexes [M3L2(bpy)3]n+, the
head/tail positioning of the donp2− ligands in 3 and 9
is, at first sight, somewhat surprising. However, the
failure to isolate dinuclear complexes of the type
[M2(donp)2(bpy)2], even at optimised molar ratios of
the starting materials, indicates that an alternative for-
Fig. 4. A view of the cis-[Pt3(donp)2(bpy)3]2+ dication of 9 perpen-
dicular to its central PdN4 coordination plane.

B. Oskui et al. / Inorganica Chimica Acta 287 (1999) 72–81
79
the N(11)–Pt(1)–Pt(2)–N(81) torsion angle of 33.2(4)°.
It is apparent that further reaction of 8 to the trinu-
clear complex 9 must involve a relative reorganisation
of the Pt(1) and Pt(2) coordination spheres. An interest-
ing insight into possible reaction mechanisms is pro-
vided by the monomer [Pt(donp)(bpy)] (7), which can
be isolated in 30% yield as a yellow–brown precipitate
when [Pt(bpy)(H2O)2]2+ is employed as a starting mate-
1
rial instead of [PtCl2(bpy)]. A H NMR study of the
resulting blue–green mother liquor confirmed the pres-
ence of 9 and possibly two further products in solution.
The asymmetric unit of the triclinic crystal lattice of 7
contains two independent molecules, whose structures
are illustrated in Fig. 7. As is to be expected, the Pt–N1
and Pt–N3 bonds are somewhat longer than in the
dinuclear and trinuclear complexes discussed in this
Fig. 5. Cyclic voltammogram of 9 (CH3CN; 0.1 M (n-Bu4N)PF6) at
a glassy-carbon electrode (scan speed 0.1 V s−1); Ag/AgCl reference
electrode.
˚
work and lie between 2.040 and 2.082 A.
Associated narrow N1–Pt–N8 angles of 63.2(3) and
63.8(3)° are observed for the four-membered chelate
rings of the independent molecules, which stack into
respective a- and b-chains depicted in Fig. 8. Whereas
alternating shorter and longer Pt···Pt interactions (3.39,
restricting the reaction time to 4 h. As depicted in Fig.
6, the remaining chloride ligands are sited on opposite
sides of the plane of the bridging naphthyridine deriva-
tive donp2−
, an arrangement that minimises in-
˚
3.89 A) are apparent for the zigzag a chain with its
Pt···Pt···Pt angles of 145.9°, neighbouring Pt···Pt dis-
tramolecular contacts. In the presence of only one
1kN1:2kN8 coordinated donp2−, the platinum atoms
are able to increase their distance from an average
value of 2.804(2) in 9 to 3.045(1) in 8, a structural
alteration that is accompanied by a characteristic
colour change from green–blue to orange–red. The
tilting of the Pt coordination planes is also associated
with a remarkable relative rotation of the PtClN3 units
about the Pt(1)···Pt(2) vector, as can be gauged from
tances in the more linear b chain are closely similar
˚
(3.47, 3.51 A, angles Pt···Pt···Pt 172.0°).
Introduction of the bulky benzyl side chain in the
naphthyridine derivative 2-benzylamino-7-methyl-1,8-
naphthyridine (Hmbznnp) prevents dimer formation
and facilitates the isolation of the monomer [Pt(m-
bznnp)(bpy)(H2O)]ClO4 (4) with monodentate kN8 co-
Fig. 7. Molecular structures of the first of the two independent
molecules of [Pt(donp)(bpy)] (7) in the asymmetric unit of its crystal
lattice.
Fig. 6. Molecular structure of [Pt2Cl2(donp)(bpy)2] (8).

80
B. Oskui et al. / Inorganica Chimica Acta 287 (1999) 72–81
Table 3
M···M distances in di- and trinuclear complex cations
˚
Nuclearity M···M (A) Colour
Complex
no.
M
L
1
2
3
5
6
8
9
Pd
Pd
Pd
Pt
Pt
Pt
onp
2
2
3
2
2
2
3
2.804(2)
2.794(6)
2.803(2)a
2.802(2)
2.796(2)
3.045(1)
2.804(2)a
yellow
yellow
orange
red
red
orange–red
green–blue
monp
donp
onp
monp
donp
donp
Pt
a Average values.
pathway to trinuclear products. Although intermediate
m-1kN1:2kN8 (n=0) or m-1kN1:2kO2 (n=2) dinuclear
complexes of the type [M2L2(bpy)2]n+ could not be
isolated for the bridging ligand 1,8-naphthyridin-2,7-
one it seems probable that such species must also be
involved.
Our present work clearly demonstrates that 2,7-di-
substituted naphthyridines are capable of bridging two
or three (bpy)M(II) fragments (M=Pd, Pt), thereby
forcing the Group 10 metals to adopt the closest M···M
˚
distances (2.794–2.807 A) previously observed for the
Fig. 8. Stacking of the independent molecules of 7 into a and b
chains in the solid state.
oxidation state +2 (see Table 3). It is also reasonable
to assume that oxidation of [Pt3(donp)2(bpy)3]2+ (9) by
one-electron steps at +0.65 and +1.30
V to
ordination (Fig. 9). The aromatic bpy and benzyl ring
systems exhibit an interplanar angle of only 14.1° and
apparently strive towards coplanarity. Isolation of the
complexes 4 and 7 suggests that mononuclear species
may well be involved in the initial phase of the reaction
[Pt3(donp)2(bpy)3]4+ will lead to even closer Pt–Pt
interactions, as indicated by the associated colour
change from blue–green to violet. Work is now in
progress to isolate and structurally characterise such
unique tetracations of this type with their average
platinum oxidation state of 2.667.
A blue shift is, however, also apparent on going from
[Pt2Cl2(donp)(bpy)2] (8) with its relatively long Pt···Pt
˚
distance of 3.045(1) A to the other dinuclear complexes
studied in this work (M(II)···M(II) distances of 2.794–
˚
2.804 A). It may, therefore, be speculated that the close
proximity of the Group 10 metals and an associated
possible significant overlap between p* and/or d* or-
bitals of the dimetal core and p* molecular orbitals of
the bridging naphthyridine ligands could lead to an
M(II)–M(II) interaction in the di- and trinuclear com-
plexes discussed in this work (with the exception of 8),
which might well be of weakly bonding character and
not nonbonding as would formally be expected for
Pd(II) and Pt(II). The blue–green colour of cis-
[Pt3(donp)2(bpy)3]2+ (9) is in accordance with such
considerations.
4. Supplementary material
Fig. 9. Molecular structure of the [Pt(mbznnp)(bpy)(H2O)]+ cation
of 4.
Crystallographic data (excluding structure factors)
for the structures reported in this paper have been

B. Oskui et al. / Inorganica Chimica Acta 287 (1999) 72–81
81
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+44(0)1223/336-033, e-mail: deposit@chemcrys.cam.
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