Photoactive trans ammine/amine diazido platinum(IV) complexes

Article abstract of DOI:10.1016/j.ica.2008.02.039

The synthesis and characterisation of eight new octahedral Pt^IV complexes of the type trans,trans,trans-[Pt(N₃)₂(OH)₂(NH₃)(Am)] where Am = methylamine (2), ethylamine (4), thiazole (6), 2-picoline (8)

Full text of DOI:10.1016/j.ica.2008.02.039

Available online at www.sciencedirect.com
Inorganica Chimica Acta 362 (2009) 811–819
www.elsevier.com/locate/ica
Photoactive trans ammine/amine diazido platinum(IV) complexes
Fiona S. Mackay a, Stephen A. Moggach a, Anna Collins a, Simon Parsons a,
Peter J. Sadler a,b,
*
a School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK
b Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
Received 30 January 2008; accepted 18 February 2008
Available online 4 March 2008
Dedicated to Professor Bernhard Lippert.
Abstract
The synthesis and characterisation of eight new octahedral PtIV complexes of the type trans,trans,trans-[Pt(N3)2(OH)2(NH3)(Am)]
where Am = methylamine (2), ethylamine (4), thiazole (6), 2-picoline (8), 3-picoline (10), 4-picoline (12), cyclohexylamine (14), and quin-
oline (16) are reported, including the X-ray crystal structures of complexes 2, 8, and 14 as well as that of two of the precursor PtII com-
plexes (trans-[Pt(N3)2(NH3)(methylamine)] (1) and trans-[Pt(N3)2(NH3)(cyclohexylamine)] (13)). Irradiation with UVA light rapidly
induces loss in intensity of the azide-to-PtIV charge-transfer bands and gives rise to photoreduction of platinum. These complexes have
potential for use as photoactivated anticancer agents.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Platinum; Azide; Photochemistry; Crystal structure; Anticancer
1. Introduction
can exhibit cancer cell cytotoxicity upon photoactivation
[5], with the potential to be much more potent than clini-
cally-used cisplatin under conditions of short treatment
times [6]. Moreover their mechanisms of cytotoxicity
appear to be novel [7]. The work reported here is part of
our investigation into the effect of variations in the amine
ligand in trans diazido dihydroxo mixed-ammine/amine
PtIV complexes on photoactivation. The synthesis and
characterisation of eight new complexes is described
(Fig. 1).
Square-planar platinum(II) diam(m)ine complexes such
as cisplatin and carboplatin are successful anticancer
drugs. However their use is sometimes accompanied by
side-effects and by the development of cellular resistance.
We are studying relatively inert PtIV complexes which
might be non-toxic and capable of activation specifically
in cancer cells by the use of (laser) light [1]. Suitable com-
plexes contain intense ligand-to-metal charge-transfer
bands. Iodo PtIV complexes were early candidates [2] but
these proved to be too readily reduced by glutathione [3],
the abundant intracellular tripeptide containing a thiol
group. Our recent work [4] has shown that PtIV diazido
complexes are much more stable towards reduction by glu-
tathione and interestingly that both cis and trans complexes
2. Experimental
2.1. Materials and instrumentation
Silver nitrate, methylamine (40% solution, MeNH2),
ethylamine (70% solution, EtNH2), thiazole (tz), 2-picoline
(2-pic), 3-picoline (3-pic), 4-picoline (4-pic), cyclohexyl-
amine (cha), acetone-d6, D2O and the platinum standard
solution for ICP-OES were purchased from Aldrich.
NaN3 and HCl (37%) were from Fisher. K2[PtCl4] from
*
Corresponding author. Address: Department of Chemistry, University
of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK. Tel.: +44 24
76523818; fax: +44 24 76523819.
E-mail address: p.j.sadler@warwick.ac.uk (P.J. Sadler).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.02.039

812
F.S. Mackay et al. / Inorganica Chimica Acta 362 (2009) 811–819
Spectrometer (Optima 5300 DV) calibrated with standard
solutions (0.1–100 ppm).
H2
N
H2
N
OH
Pt
OH
Pt
N3
N3
The ultraviolet light source used for photochemical
studies was a UV lamp (2 ꢀ 15 W tubes, model VL-
215 L; Merck Eurolab, Poole, UK) which operates at
365 nm. Samples were irradiated at a distance of 10 cm
from the lamp, where the power is 1.5 mW/cm2, this power
delivers a dose of 10 J/cm2 over 2 h.
N3
NH3
N3
NH3
OH
OH
2
4
S
OH
Pt
OH
Pt
N
2.2. Syntheses
N3
N
N3
H3C
Caution. No problems were encountered during this
work, however heavy metal azides are known to be shock
sensitive detonators, therefore it is essential that all plati-
num azide compounds are handled with care.
N3
NH3
N3
NH3
OH
OH
6
8
H3C
2.2.1. trans-[Pt(N3)2(NH3)(methylamine)] (1)
trans-[PtCl2(NH3)(methylamine)] (75.9 mg, 0.242 mmol)
was suspended in H2O (25 mL) and AgNO3 (1.95 mol e-
quiv., 80.1 mg) added. The reaction was stirred in the dark
at 333 K for 24 h then filtered with an inorganic membrane
filter (Whatman, Anotop 10, 0.02 lm). NaN3 (0.968 mmol,
63.0 mg) was added and the yellow solution was stirred for
4 h, then reduced to dryness. Ice-cold H2O was added and
the product filtered, washed with ethanol and diethyl ether
then dried under vacuum. Crystals suitable for X-ray crys-
tal structure determination were grown from H2O at
277 K. Yield: 77.6%. 1H NMR (acetone-d6): d 4.20 (s,
OH
Pt
OH
Pt
H3C
N
N3
N
N3
N3
NH3
N3
NH3
OH
OH
12
10
H2
N
OH
Pt
OH
Pt
N
N3
N3
1
NH2, 2H), 3.70 (s, NH3, 3H), 2.45 (t, CH3, J(CH3–NH2)
6.5 Hz, 3H).
N3
NH3
N3
NH3
OH
OH
14
16
2.2.2. trans,trans,trans-[Pt(N3)2(OH)2(NH3)
(methylamine)] (2)
Fig. 1. Structures of some of the complexes synthesized in this study.
trans-[Pt(N3)2(NH3)(methylamine)] (59.8 mg, 0.183
mmol) was suspended in H2O (20 mL) and H2O2
(0.732 mmol, 0.083 mL) added. After stirring in the dark at
298 K for 1 h the solvent was removed. Ethanol was added
to precipitate the product which was filtered, washed spar-
ingly with ice cold water, ethanol and diethyl ether then dried
under vacuum. Crystals suitable for X-ray structure determi-
Alfa Aesar, NH4Cl from BDH and H2O2 from Sigma.
trans-[PtCl2(NH3)(methylamine)], trans-[PtCl2(NH3)(ethyl-
amine)] and trans-[PtCl2(NH3)(cyclohexylamine)] were pre-
pared by the literature method [8].
NMR spectra were recorded at 298 K on a Bruker
DMX500 spectrometer (1H: 500.13 MHz). Samples were
prepared in acetone-d6 or 90% H2O/10% D2O with 1H
chemical shifts referenced internally to dioxane (d
3.764 ppm). All data were processed with XWIN-NMR soft-
ware (Version 3.6, Bruker, UK Ltd.).
1
nation were grown from water at 298 K. Yield: 81.3%. H
NMR (90% H2O/10% D2O): d 2.36 (septet, CH3, 3H).
ESI-MS: obs. 362.1 m/z, calc. for [PtCN8O2H11]+ 362.2
m/z. UV–Vis: kmax = 286 nm (e = 19,384 Mꢁ1 cmꢁ1).
Positive ion electrospray mass spectrometry (ESI-MS)
was performed on a Platform II Mass Spectrometer (Micro-
mass, Manchester, UK). The capillary voltage was 3.5 V,
and the cone voltage typically varied between 5 and 30 V.
All samples were prepared in water. Data was acquired
and processed with MASS LYNX software (Version 2.5).
UV–Vis electronic absorption spectra were recorded on
a Varian Cary 300 UV–Vis spectrophotometer in 1 cm
path-length cuvettes. All spectra were recorded in water
and referenced to solvent alone. Data were processed with
Microcal Origin 5.0.
2.2.3. trans-[Pt(N3)2(NH3)(ethylamine)] (3)
trans-[Pt(N3)2(NH3)(ethylamine)] was prepared by the
1
same method as complex 1. Yield: 80.3%. H NMR (ace-
tone-d6):
d
4.20 (s, 14NH2, 2H), 3.70 (d, 15NH3,
1J(15N–1H) 60.0 Hz, 3H), 2.77 (sextet, CH2, 2H), 1.32 (t,
1
CH3, J(CH2-CH3) 6.0 Hz, 3H).
2.2.4. trans,trans,trans-[Pt(N3)2(OH)2(NH3)
(ethylamine)] (4)
trans,trans,trans-[Pt(N3)2(OH)2(NH3)(ethylamine)] was
prepared by the same method as complex 2. Yield:
72.7%. ESI-MS: obs. 375.9 m/z, calc. for [PtC2N8O2H13]+
The platinum content of aqueous solutions was deter-
mined by ICP-OES with a Perkin Elmer Optimal Emission

F.S. Mackay et al. / Inorganica Chimica Acta 362 (2009) 811–819
813
1
376.2 m/z. UV–Vis: kmax = 285 nm (16,516 Mꢁ1 cmꢁ1). H
2.2.9. trans-[Pt(N3)2(NH3)(2-picoline)] (7)
NMR (90% H2O/10% D2O): 5.71 (s, NH2, 2H), 2.89 (sex-
tet, CH2, 2H), 1.33 (t, CH3, J(CH2-CH3) 7.3 Hz, 3H).
trans-[PtCl2(NH3)(2-picoline)] (87.3 mg, 0.232 mmol)
was suspended in H2O (50 mL) and DMF (0.5 mL).
AgNO3 (1.95 mol equiv., 76.9 mg) was added and the reac-
tion stirred in the dark at 333 K for 24 h. All the solvent
was removed and the solid redissolved in H2O (50 mL).
NaN3 (0.928 mmol, 60.3 mg) was added and the solution
stirred for 4 h, the volume was then reduced to 3 mL and
the bright yellow solid filtered, washed with water, ethanol
and diethyl ether and dried under vacuum. Yield: 90.0%.
1H NMR (acetone-d6): d 8.95 (d, H-6, 1J 5.9 Hz, 1H),
1
2.2.5. trans-[PtCl2(NH3)(thiazole)]
Cisplatin (81.8 mg, 0.273 mmol) was suspended in H2O
(2 mL) and thiazole (tz, 0.819 mmol, 0.058 mL) added.
The reaction was stirred at 343 K for 2 h, brought to reflux,
then cooled. HCl (3.276 mmol, 0.273 mL) was added and
the solution stirred at 378 K for 6 h. After cooling to room
temperature the product was further precipitated by cool-
ing on ice, then filtered, washed with water, ethanol and
1
2
7.89 (td, H-4, J 7.7 Hz, J 1.7 Hz, 1H), 7.59 (d, H-3, 1H)
1
1
diethyl ether and dried under vacuum. Yield: 77.3%. H
7.42 (t, H-5, 1H), 3.74 (s, NH3, J(15N–1H) 72.0 Hz, 3H),
2
2
NMR (acetone-d6: d 9.53 (dd, H-2, J2,4 0.9 Hz, J2,5
3.20(s, CH3, 3H).
1
2.4 Hz, 1H), 8.29 (dd, H-4, J4,5 3.7 Hz, 1H), 7.81 (dd,
H-5, 1H), 3.81 (s, NH3, 3H).
2.2.10. trans,trans,trans-[Pt(N3)2(OH)2(NH3)
(2-picoline)] (8)
2.2.6. trans-[Pt(N3)2(NH3)(thiazole)] (5)
trans-[Pt(N3)2(NH3)(thiazole)] was prepared by the
same method as complex 1 except the reaction was stirred
trans,trans,trans-[Pt(N3)2(OH)2(NH3)(2-picoline)] was
prepared by the same method as complex 6. Crystals suit-
able for X-ray structure determination were grown from
H2O at 277 K. Yield: 73.4%. ESI-MS: obs. 446.6 m/z, calc.
for [PtC6N8O2H12Na]+ 446.2 m/z. UV–Vis: kmax = 292 nm
(17,888 Mꢁ1 cmꢁ1), 276 nm (sh, 14,500 Mꢁ1 cmꢁ1). 1H
1
for 24 h after adding NaN3. Yield: 77.4%. H NMR (ace-
2
2
tone-d6): d 9.42 (dd, H-2, J2,4 0.9 Hz, J2,5 2.4 Hz, 1H),
1
8.12 (dd, H-4, J4,5 3.7 Hz, 1H), 7.95 (dd, H-5, 1H), 4.07
1
(s, NH3, 3H).
NMR (90% H2O/10% D2O): d 8.66 (d, H-6, J 6.4 Hz,
1
1H), 8.04 (td, H-4, J 7.7 Hz, 1H), 7.54 (d, H-3, 1H) 7.51
2.2.7. trans,trans,trans-[Pt(N3)2(OH)2(NH3)(thiazole)]
(6)
(t, H-5, 1H), 3.06 (d, CH3, 3H).
trans-[Pt(N3)2(NH3)(thiazole)] (31.7 mg, 0.083 mmol)
was suspended in H2O (200 mL) and H2O2 (30%,
0.332 mmol, 0.034 mL) added. After stirring in the dark
at room temperature for 24 h, the volume was reduced to
15 mL and filtered. All solvent was then removed and ace-
tone added to precipitate the product. The yellow solid was
collected by filtration, washed sparingly with ice-cold
water, ethanol and diethyl ether, and dried under vacuum.
Yield: 71.2%. ESI-MS: obs. 415.9 m/z, calc. for
2.2.11. trans-[Pt(N3)2(NH3)(3-picoline)] (9)
trans-[PtCl2(NH3)(3-picoline)] and trans-[Pt(N3)2(NH3)-
(3-picoline)] were prepared by the same method as the anal-
ogous 2-picoline complexes 9 and 10. Yield: 73.2%. 1H
1
NMR (acetone-d6): d 8.59 (s, H-2, 1H), 8.57 (d, H-6, J5,6
1
5.9 Hz, 1H), 7.88 (d, H-4, J4,5 7.9 Hz, 1H), 7.46 (dd, H-
5, 1H), 3.95 (s, NH3, 3H), 2.42 (s, CH3, 3H).
2.2.12. trans,trans,trans-[Pt(N3)2(OH)2(NH3)
(3-picoline)] (10)
[PtC3N8O2H9S]+ 416.3 m/z. UV–Vis:
(15,234 Mꢁ1 cmꢁ1), 236 nm (8,630 Mꢁ1 cmꢁ1). 1H NMR
kmax = 289 nm
trans,trans,trans-[Pt(N3)2(OH)2(NH3)(3-picoline)] was
prepared by the same method as complex 6. Yield:
81.4%. ESI-MS: obs. 424.0 m/z, calc. for [PtC6N8O2H13]+
424.2 m/z. UV–Vis: kmax = 289 nm (13,575 Mꢁ1 cmꢁ1).
1H NMR (90% H2O/10% D2O): d 8.53 (s, H-2, 1H), 8.51
2
2
(90% H2O/10% D2O): d 9.51 (dd, H-2, J2,4 1.0 Hz, J2,5
1
2.4 Hz, 1H), 8.24 (dd, H-4, J4,5 3.6 Hz, 1H), 8.04 (dd,
H-5, 1H).
1
2.2.8. trans-[PtCl2(NH3)(2-picoline)]
(d, H-6, 1H), 8.07 (d, H-4, J4,5 7.9 Hz, 1H), 7.65 (dd,
Cisplatin (0.103 g, 0.343 mmol) was suspended in H2O
(1 mL) and 2-picoline (1.372 mmol, 0.1277 g) added. The
reaction was stirred at 348 K for 2.5 h and then refluxed
for 30 min. The solvent was removed and HCl (2.7 M,
1.5 mL) added. The solution was stirred at 378 K for 5 h
then cooled to 277 K for 24 h and filtered. The filtrate
was returned to heat at 378 K for a further 6 h and then
cooled to 277 K and filtered again. The two batches of yel-
low solid were combined and washed with water, ethanol
and diethyl ether and dried under vacuum. Yield: 68.5%.
1H NMR (acetone-d6): d 8.80 (d, H-6, 1J 5.7 Hz, 1H),
H-5, 1H), 2.50 (s, CH3, 3H).
2.2.13. trans-[Pt(N3)2(NH3)(4-picoline)] (11)
trans-[PtCl2(NH3)(4-picoline)] and trans-[Pt(N3)2(NH3)-
(4-picoline)] were prepared by the same method as the anal-
ogous 2-picoline complexes 9 and 10. Yield: 84.2%. 1H
NMR (acetone-d6): d 8.57 (d, H-2, H-6, J(2,6ꢁ3,5) 6.6 Hz,
2H), 7.41 (d, H-3, H-5, 2H), 3.94 (s, NH3, 3H), 2.46 (s,
CH3, 3H).
1
2.2.14. trans,trans,trans-[Pt(N3)2(OH)2(NH3)
(4-picoline)] (12)
trans,trans,trans-[Pt(N3)2(OH)2(NH3)(4-picoline)] was
prepared by the same method as complex 6. Yield:
1
2
1
7.78 (td, H-4, J 7.7 Hz, J 1.5 Hz, 1H), 7.43 (d, H-3, J
1
7.7 Hz, 1H), 7.27 (t, H-5, 1H), 3.68 (s, NH3, J(15N–1H)
72.0 Hz, 1H), 3.13(s, CH3, 3H).

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F.S. Mackay et al. / Inorganica Chimica Acta 362 (2009) 811–819
3
3
68.2%. ESI-MS: obs. 424.0 m/z, calc. for [PtC6N8O2H13]+
9.43 (dd, H2, J2,3 5.3 Hz, 1H), 8.65 (d, H4, J3,4 8.1 Hz,
1
3
3
424.2 m/z. UV–Vis: kmax = 289 nm (14318 Mꢁ1 cmꢁ1). H
1H), 8.14 (d, H5, J5,6 8.3 Hz, 1H), 8.07 (dd, H7, J6,7
6.8 Hz, 1H), 7.81 (dd, H6, 1H), 7.73 (dd, H3, 1H), 3.91
(br s, NH3, 3H).
NMR (90% H2O/10% D2O): d 8.51 (d, H-2, H-6,
1J(2,6ꢁ3,5) 6.8 Hz, 2H), 7.60 (d, H-3, H-5, 2H), 2.58 (s,
CH3, 3H).
2.2.19. trans,trans,trans-
[Pt(N3)2(OH)2(NH3)(quinoline)] (16)
2.2.15. trans-[Pt(N3)2(NH3)(cyclohexylamine)] (13)
trans-[PtCl2(NH3)(cyclohexylamine)] (7.97 mg, 0.021
mmol) dissolved in DMF (2 mL) was added to a solution
of NaN3 (0.044 mmol, 2.87 mg) in methanol. After stirring
at 298 K for 2 d the volume was reduced and crystals suit-
able for X-ray structure determination were grown at
298 K. 1H NMR (acetone-d6): d 4.18 (s, NH2), 3.75 (s,
NH3), 2.35 (m, H-1, 1H), 1.76 (m, H-2a,5a, 2H), 1.61 (d,
H-3a,5a, 2H), 1.33 (t, H4a, 1H), 1.16 (m, H-2b,3b,5b,6b,
4H), 0.88 (m, H-4b, 1H). a are equatorial, b are axial
hydrogens.
trans-[Pt(N3)2(NH3)(quinoline)] (12.9 mg, 0.03 mmol)
was placed in H2O (30 mL) and H2O2 (40 mol equiv.,
124 lL) added. After stirring at 323 K for 5 h, the yellow
solution was filtered through an inorganic membrane filter
(Whatman, Anotop 10, 0.02 lm) and then the solvent
removed. Acetone was added, the solid was collected by
filtration and washed with water, ethanol and ether and
dried under vacuum. Yield: 68.8%. 1H NMR (D2O): d
3
3
9.82 (d, H8, J7,8 8.8 Hz, 1H), 9.43 (dd, H2, J2,3 5.3 Hz,
3
3
1H), 8.65 (d, H4, J3,4 8.1 Hz, 1H), 8.14 (d, H5, J5,6
3
8.3 Hz, 1H), 8.07 (dd, H7, J6,7 6.8 Hz, 1H), 7.81 (dd,
2.2.16. trans,trans,trans-[Pt(N3)2(OH)2(NH3)
(cyclohexylamine)] (14)
H6, 1H), 7.73 (dd, H3, 1H), 3.91 (br s, NH3, 3H). ESI-
MS: [M+Na]+ 482.14 m/z. UV–Vis: 233 nm, 294 nm,
316 nm (sh).
trans-[Pt(N3)2(NH3)(cyclohexylamine)] (5.0 mg, 0.013
mmol) was suspended in H2O (2 mL) and H2O2
(0.500 mmol, 51 lL) was added. After stirring at 298 K
for 12 h the volume was reduced and crystals suitable for
X-ray structure determination were grown at 277 K. ESI-
MS: obs. 452.1 m/z, calc. for [PtC6N8O2H18Na]+ 452.2
2.3. X-ray structure determination
Diffraction data were collected with Mo Ka radiation
˚
(k = 0.71073 A) on a Bruker Smart Apex CCD diffractom-
1
m/z. H NMR (90% H2O/10% D2O): 2.94 (m, H-1, 1H),
eter equipped with an Oxford Cryosystems low-tempera-
ture device operating at 150 K. Data were corrected for
absorption using the program SADABS [9].
The crystal structures of 1, 8, and 13 were solved by
Patterson methods (DIRDIF [10]), and 2 and 14 by direct
methods (SHELXS [11] or SIR92 [12]). All structures were
refined against F2 using SHELXL [13] or CRYSTALS [14], and
the H-atoms placed in geometrically calculated positions.
NH3 and CH3 groups in 1, 8, and 13 were treated as rotat-
ing rigid groups.
In 8, the 2-picoline ligand is disordered by a 180° rota-
tion about the Pt–N bond. Similarity restraints were
applied to the geometry of the two part-weight components
of the disorder. The occupancies were refined. Only full-
occupancy atoms were refined with anisotropic displace-
ment parameters.
Analysis of the poorly-fitting data [15] showed that the
crystal of 14 was twinned via a twofold rotation about
[100], the twin law being expressed by the matrix
2.14 (m, H-2a,5a, 2H), 1.76 (d, H-3a,5a, 2H), 1.63 (t,
H4a, 1H), 1.35 (m, H-2b,3b,5b,6b, 4H), 1.18 (m, H-4b,
1H). a are equatorial, b are axial hydrogens.
2.2.17. trans-[PtCl2(NH3)(quinoline)]
Cisplatin (48.0 mg, 0.16 mmol) was suspended in H2O
(2 mL) and quinoline added (0.32 mmol, 37.8 lL). After
stirring at 378 K for 1 h a pale yellow solution was pres-
ent and no precipitate appeared on cooling. HCl
(1.92 mmol, 0.16 mL) was added and the solution stirred
at 378 K for 5 h, 368 K for 12 h and then 378 K again
for 5 h. The reaction was cooled on ice for 1 h and filtered
to collect the yellow solid which was washed with water,
ethanol and ether and dried under vacuum. Yield:
64.6%. 1H NMR (acetone-d6): d 9.80 (d, H8, J7,8
3
3
8.8 Hz, 1H), 9.29 (dd, H2, J2,3 5.3 Hz, 1H), 8.55 (d, H4,
3
3J3,4 8.1 Hz, 1H), 8.06 (d, H5, J5,6 8.3 Hz, 1H), 7.96
3
(dd, H7, J6,7 6.8 Hz, 1H), 7.74 (dd, H6, 1H), 7.59 (dd,
H3, 1H), 3.86 (br s, NH3, 3H).
0
1
1
0
0
0
B
@
C
A
0:758 ꢁ1
0:878
:
2.2.18. trans-[Pt(N3)2(NH3)(quinoline)] (15)
trans-[PtCl2(NH3)(quinoline)] (30.6 mg, 0.0743 mmol)
and AgNO3 (25.1 mg, 0.148 mmol) were stirred in H2O
(30 mL) and DMF (0.3 mL) at 333 K for 12 h. The AgCl
precipitate was filtered off with an inorganic membrane fil-
ter (Whatman, Anotop 10, 0.02 lm) and NaN3 (48.3 mg,
0.743 mmol) added. After stirring at 298 K for 12 h the
pale yellow was collected by filtration, washed with water,
ethanol and ether and dried under vacuum. Yield: 81.7%.
0
ꢁ1
The twin scale factor refined to 0.5482(13).
3. Results and discussion
Eight novel PtIV diazido complexes, with general struc-
ture trans,trans,trans-[Pt(N3)2(OH)2(NH3)(Am)], have been
synthesised and fully characterised.
1H NMR (acetone-d6): d 9.82 (d, H8, J7,8 8.8 Hz, 1H),
3

F.S. Mackay et al. / Inorganica Chimica Acta 362 (2009) 811–819
815
3.1. Synthesis and characterisation
nitrate method, and therefore this reaction was carried out
by direct substitution in DMF/methanol instead.
The PtII dichloro complexes (trans-[PtCl2(NH3)(Am)],
Am = MeNH2, EtNH2, tz, 2-pic, 3-pic, 4-pic, cha and
quin) were all prepared from cisplatin by replacing the
chloride ligands with the appropriate Am ligand followed
by addition of HCl. Due to the trans effect, the chlorides
bind to platinum in a trans position. Conversion of the
chloride ligands to azides was generally carried out by
removing the chlorides with silver nitrate, and then adding
azide in the form of sodium azide, except for complex 13,
the reasons for this are discussed later. Hydroxyl ligands
were added to the PtII diazido complexes in the axial posi-
tion by oxidation of aqueous solutions with hydrogen
peroxide.
trans,trans,trans-[Pt(N3)2(OH)2(NH3)(MeNH2)] (2) and
trans,trans,trans-[Pt(N3)2(OH)2(NH3)(EtNH2)] (4) were
both prepared in high yields by the same method. Their
electronic absorbance spectra closely resemble that of
trans,trans,trans-[Pt(N3)2(OH)2(NH3)2] [5]; the kmax for all
three complexes is 285–286 nm. The aqueous solubilities
of 2 and 4 are significantly increased by the incorporation
of the methylamine and ethylamine ligands.
3.2. X-ray crystal structures
The X-ray crystal structures of two PtII azide complexes
(trans-[Pt(N3)2(NH3)(MeNH2)] (1) and trans-[Pt(N3)2-
(NH3)(cha)] (13)) were determined. ORTEP structures are
depicted in Fig. 2 and crystal structure data can be found
in Table 1. The X-ray structure of trans-[PtCl2(MeNH2)2]
has been published [18], the bond lengths did not differ sig-
nificantly from those of transplatin [19], and these
am(m)ine bond lengths are also very similar to those of
trans-[Pt(N3)2(NH3)(MeNH2)] (1) (Table 2). The geometry
of 1 is square-planar and the angles are all very close to 90°.
The azide bond lengths compare very well with other plat-
inum azide compounds (PtII and PtIV) [5,20]. The Pt–N(a)–
N(b) angles agreed well with the other PtII complexes, but
were found to be significantly larger than those of the PtIV
compounds (2, 8, and 14, Table 5, Fig. 3). This same differ-
ence is seen for the cis-diazido PtII and PtIV structures [20].
The synthesis of trans-[PtCl2(NH3)(tz)] has been
described previously [16], however the method described
here produced high yields of pure product without the need
for recrystallisation. It was necessary to carry out the oxi-
dation of trans-[Pt(N3)2(NH3)(tz)] (5) in a large volume of
water, this is due to its aqueous insolubility. The kmax of
trans,trans,trans-[Pt(N3)2(OH)2(NH3)(tz)] (6) is shifted
slightly towards the visible region, and a separate absor-
bance due to the internal transitions of the thiazole ring
can be seen at 236 nm. The X-ray crystal structures of
trans-[PtCl2(tz)2] and trans[PtCl2(NH3)(tz)] have been
determined by Farrell et al. [16,17]. In both cases platinum
is bound to the nitrogen atom of thiazole. Although PtII is
a soft metal centre and is known to have a high affinity for
sulphur donors, calculations on the electronic structure of
thiazole have shown that the net charge of the thioether-
type sulphur is positive [17]. The negative charge resides
on the nitrogen and it is therefore a much better donor
to platinum. For this reason it is assumed that trans,trans,
trans-[Pt(N3)2(OH)2(NH3)(tz)] also has thiazole bound
through the nitrogen.
trans-[PtCl2(NH3)(2-pic)] was prepared from cisplatin in
a similar way to trans-[PtCl2(NH3)(tz)]. The silver nitrate
step was carried out with a small amount of DMF added
to help solubilise the hydrophobic PtII dichlorido species.
In the electronic absorption spectrum, the LMCT
(N3 ? Pt) band of trans,trans,trans-[Pt(N3)2(OH)2(NH3)-
(2-pic)] is at 292 nm, which is at a longer wavelength than
any of the other PtIV azide compounds synthesised.
Problems were encountered during the synthesis of trans-
[PtCl2(NH3)(cha)] and oxidation to PtIV was often observed.
1
PtIV–NH protons were detected by H NMR spectroscopy
Fig. 2. X-ray crystal structures of PtII complexes (a) trans-
[Pt(N3)2(NH3)(MeNH2)] (1) and (b) trans-[Pt(N3)2(NH3)(cha)] (13) (50%
probability ellipsoids).
in acetone-d6. Oxidation also occurred during conversion
of the chloride ligands to azide ligands by the usual silver

816
F.S. Mackay et al. / Inorganica Chimica Acta 362 (2009) 811–819
Table 1
Table 3
Crystal structure data for the PtII diazido complexes trans-
[Pt(N3)2(NH3)(MeNH2)] (1) and trans-[Pt(N3)2(NH3)(cha)] (13)
Crystal structure data for the PtIV diazido complexes trans,trans,trans-
[Pt(N3)2(OH)2(NH3)(MeNH2)] (2), trans,trans,trans-[Pt(N3)2(OH)2(NH3)-
(2-pic)] (8) and trans,trans,trans-[Pt(N3)2(OH)2(NH3)(cha)] (14)
1
13
2
8
14
Empirical formula
Formula weight
Crystal size (mm)
Crystal system
Space group
CH8N8Pt
327.24
0.28 ꢀ 0.16 ꢀ 0.10
monoclinic
P21/c
13.4380(2)
7.65630(10)
6.99530(10)
90
96.7290(10)
90
C6H16N8Pt
395.36
0.39 ꢀ 0.37 ꢀ 0.22
monoclinic
P21/n
6.12230(10)
21.9394(5)
8.1404(2)
90
98.8660(10)
90
Empirical
formula
Formula
weight
Crystal size
(mm)
CH10N8O2Pt
C6H12N8O2Pt
C6H18N8O2Pt
361.23
423.33
429.35
˚
a (A)
0.35 ꢀ 0.11 ꢀ 0.10 0.52 ꢀ 0.28 ꢀ 0.12 0.24 ꢀ 0.14 ꢀ 0.12
˚
b (A)
˚
c (A)
Crystal
system
triclinic
monoclinic
triclinic
a (°)
b (°)
c (°)
Z
ꢀ
ꢀ
Space group P1
I2/a
P1
˚
a (A)
5.0127(2)
12.9666(2)
7.8790(1)
21.5367(4)
90
92.898(1)
90
5.5050(2)
13.3500(4)
17.8930(6)
75.307(2)
82.238(2)
81.007(2)
4
˚
4
4
b (A)
5.6360(2)
14.5362(5)
86.981(2)
82.408(2)
82.706(2)
2
Dcalc (mg/m3)
3.041
19.572
592
3.05 to 30.35
13043
2.431
12.972
744
1.86 to 43.18
18880
c (A)
˚
l (mmꢁ1
F(000)
)
a (°)
b (°)
c (°)
Z
h Range (°)
Reflections collected
8
Independent reflections
Volume (A )
Conventional R
wR2
2117
714.756(17)
0.0197
6296
1080.35(4)
0.0329
Dcalc
2.973
2.559
2.281
3
˚
(mg/m3)
l (mmꢁ1
F(000)
)
17.367
332
12.778
1584
11.232
816
0.0503
0.0710
h Range (°)
Reflections
collected
2.829 to 30.461
11081
2.75 to 29.98
15237
1.590 to 30.494
7070
Independent 3950
reflections
Volume (A ) 403.51(3)
3171
7070
Table 2
˚
Selected bond lengths (A), and bond angles (°) for trans-
[Pt(N3)2(NH3)(MeNH2)] (1) and trans-[Pt(N3)2(NH3)(cha)] (13)
3
˚
2197.46(6)
0.0191
1250.07(7)
0.0355
Conventional 0.0291
1
13
R
wR2
0.0738
0.0467
0.0817
Pt–N(13)
Pt–N(14)
2.030(2) Pt–N(13)
2.027(2) Pt–N(12)
2.039(3)
2.041(3)
1.197(4)
1.150(4)
1.203(4)
1.146(5)
2.052(3)
2.056(2)
121.1(2)
175.7(3)
121.0(2)
174.7(3)
95.69(10)
84.99(11)
94.52(11)
84.80(11)
179.49(11)
178.42(10)
115.74(17)
175.4
N(13)–N(23)
N(23)–N(33)
N(14)–N(24)
N(24)–N(34)
Pt–N(11)
1.204(3) N(13)–N(23)
1.152(3) N(23)–N(33)
1.202(3) N(12)–N(22)
1.155(3) N(22)–N(32)
2.050(2) Pt–N(1)
2.051(2) Pt–N(11)
124.48(19) Pt–N(13)–N(23)
173.80(3)
122.48(19) Pt–N(12)–N(22)
174.5(3)
177.55(9)
178.95(9)
90.80(10) N(1)–Pt–N(13)
91.61(11) N(13)–Pt–(11)
88.10(10) N(12)–Pt–N(13)
89.51(10) N(11)–Pt–N(1)
119.67(18) Pt–N(11)–C(21)
Table 4
˚
H-bonding distances (A) and angles (°) of complex 13
D–H
d(D–H)
d(Hꢂ ꢂ ꢂA)
\DHA
d(Dꢂ ꢂ ꢂA)
A
Pt–N(12)
N1–H
N1–H
N1–H
N11–H
N11–H
0.910
0.910
0.910
0.920
0.920
2.289
2.542
2.200
2.598
2.419
150.44
133.98
162.45
156.11
141.81
3.113
3.241
3.079
3.459
3.193
N12a
N32b
N33c
N12d
N33e
Pt–N(13)–N(23)
N(13)–N(23)–N(33)
Pt–N(14)–N(24)
N(14)–N(24)–N(34)
N(11)–Pt–N(12)
N(13)–Pt–N(14)
N(11)–Pt–N(14)
N(14)–Pt–N(12)
N(12)–Pt–N(13)
N(13)–Pt–N(11)
Pt–N(12)–C(22)
N(13)–Pt–N(14)–
N(24)
N(13)–N(23)–N(33)
N(12)–N(22)–N(32)
N(11)–Pt–N(12)
N(12)–Pt–N(1)
Symmetry operations: (a) ꢁx + 1, ꢁy, ꢁz + 1; (b) x, y, z ꢁ 1; (c) ꢁx, ꢁy,
ꢁz; (d) x ꢁ 1, y, z; (e) x, y, z + 1.
distorted from square-planar, the angle between the cyclo-
hexylamine ring and the azide ligand which is orientated
towards it (N(12)–N(22)–N(32)) is >95° (Table 2). This dis-
tortion is not seen for trans-[PtCl2(NH3)(cha)] where the
angles are all 90 1° [21]. The complex is still relatively
planar around the platinum centre with angles very close
to 180°. The molecules form hydrogen-bonded chains, with
interactions occurring between the am(m)ine hydrogens
and azide nitrogens (Table 4); similar hydrogen bonds are
found in the analogous chloride compound trans-
[PtCl2(NH3)(cha)] [21].
ꢁ44.2
N(13)–Pt–N(14)–
N(24)
N(14)–Pt–N(13)–
N(23)
N(14)–Pt–N(13)–
N(23)
ꢁ149.1
ꢁ2.97
The smaller Pt–N(a)–N(b) angle for PtIV complexes could
be a result of intramolecular hydrogen bonding between
the axial hydroxide hydrogen and the azide ligand. There
is intermolecular hydrogen bonding in complex 1 between
the am(m)ine hydrogens and the azide nitrogens.
The azide bond lengths and angles of trans-
[Pt(N3)2(NH3)(cha)] (13) also compare well with other plat-
inum azide structures [20]. However the geometry of 13 is
trans,trans,trans-[Pt(N3)2(OH)2(NH3)(2-pic)] (8) crystal-
lised in an monoclinic crystal system with the space group
I2/a (Table 3). The structure is shown in Fig. 3. The azide
bond lengths and angles are very similar to the other PtIV

F.S. Mackay et al. / Inorganica Chimica Acta 362 (2009) 811–819
817
azide compounds (Table 5) [5,6]. The Pt–N(2-pic) bond
gen-bonded to produce ‘‘slabs” of molecules bound either
˚
length is significantly longer (2.092(5) A) than that of Pt–
side of the hydrophobic picolines. The centroid–centroid
˚
˚
N(py) in compound 4 (2.059(4) A), which is presumably
separation of the p – p stacked picoline rings is 3.355 A with
due to steric hindrance caused by the methyl group of 2-pic-
oline. In the crystal structure of trans-[PtIICl2(NH3)(2-pic)],
the methyl group lies over the square-plane above the plat-
inum atom [22,23]. The 2-picoline ligand is disordered by a
180° rotation about the Pt–N bond. The system is hydro-
a dihedral angle of 0.00(27)°.
trans,trans,trans-[Pt(N3)2(OH)2(NH3)(cha)] (14) crystal-
ꢀ
lised in a triclinic crystal system with the space group P1
(Table 3), as did complex 2. The structure of 14 is shown
in Fig. 3. The azide bond lengths and angles are very
Table 5
˚
Bond lengths (A) and angles (°) of azide ligands in trans,trans,trans-[Pt(N3)2(OH)2(NH3)(MeNH2)] (2), trans,trans,trans-[Pt(N3)2(OH)2(NH3)(2-pic)] (8)
and trans,trans,trans-[Pt(N3)2(OH)2(NH3)(cha)] (14, 140)
2
8
14
140
Pt–N(a1)
Pt–N(a2)
N(a1)–N(b1)
N(b1)–N(c1)
N(a2)–N(b2)
N(b2)–N(c2)
2.055(3)
2.048(3)
1.228(4)
1.149(4)
1.229(4)
1.133(5)
2.054(2)
2.051(2)
1.212(4)
1.158(4)
1.222(4)
1.141(4)
2.041(7)
2.032(7)
1.224(10)
1.139(11)
1.194(11)
1.148(11)
2.028(7)
2.053(7)
1.190(10)
1.149(11)
1.213(10)
1.142(10)
Pt–N(a1)–N(b1)
N(a1)–N(b1)–N(c1)
Pt–N(a2)–N(b2)
N(a2)–N(b2)–N(c2)
N(a1)–Pt–N(a2)–N(b2)
N(a2)–Pt–N(a1)–N(b1)
115.2(2)
115.7(2)
114.9(5)
123.5(6)
175.5(3)
117.2(2)
174.8(4)
175.3(3)
115.3(2)
175.0(3)
175.6(9)
119.0(6)
174.0(9)
174.0(9)
116.5(6)
174.5(9)
104.2
ꢁ131.23
ꢁ114.5
ꢁ119.4
ꢁ91.44
164.4
ꢁ91.2
127.0
Fig. 3. X-ray crystal structures of PtIV complexes (a) trans,trans,trans-[Pt(N3)2(OH)2(NH3)(MeNH2)] (2), (b) trans,trans,trans-[Pt(N3)2(OH)2(NH3)(2-pic)]
(8), and (c) trans,trans,trans-[Pt(N3)2(OH)2(NH3)(cha)] (14) (50% probability ellipsoids).

818
F.S. Mackay et al. / Inorganica Chimica Acta 362 (2009) 811–819
1.0
0.8
0.6
0.4
0.2
0.0
1.0
OH
H2
N
OH
Pt
NH2
N3
N3
0.8
0.6
0.4
0.2
0.0
Pt
N3
NH3
N3
NH3
OH
OH
2
4
200
300
400
500
600
200
300
400
500
600
Wavelength (nm)
Wavelength (nm)
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
S
OH
N
OH
N3
N
N3
Pt
Pt
H3C
N3
NH3
N3
NH3
OH
OH
6
8
200
300
400
500
600
200
300
400
500
600
Wavelength (nm)
Wavelength (nm)
1.0
0.8
1.2
1.0
0.8
0.6
0.4
0.2
0.0
H3C
OH
H3C
OH
N
N3
N
N3
0.6
0.4
Pt
OH
Pt
N3
NH3
N3
NH3
OH
0.2
0.0
10
12
200
300
400
500
600
200
300
400
500
600
Wavelength (nm)
Wavelength (nm)
1.0
0.8
0.6
0.4
1.0
0.8
0.6
0.4
0.2
0.0
H2
OH
OH
N
N3
N
N3
Pt
Pt
N3
NH3
N3
NH3
OH
OH
0.2
0.0
16
14
200
300
400
500
600
200
300
400
500
600
Wavelength (nm)
Wavelength (nm)
Fig. 4. Effect of UVA irradiation on the electronic absorption spectra of 50–80 lM aqueous solutions of complexes 2, 4, 6, 8, 10, 12, 14, and 16 showing
the decrease in intensity of the azide-to-PtIV charge-transfer band after 0, 1, 5, 15, 30, and 60 min.
similar to the other PtIV azide compounds. The X-ray struc-
ture of trans,cis,cis-[Pt(OAc)2Cl2(NH3)(cha)] (JM216) has
been determined; it crystallised in a monoclinic crystal sys-
tem with space group P21/a [24]. The cyclohexylamine bond
lengths and angles of complex 14 compare well with those of
JM216, as do the Pt–am(m)ine bond lengths. The geometry
of 14 is nearly octahedral with the cyclohexylamine ring
adopting a chair conformation. Complex 14 crystallised

F.S. Mackay et al. / Inorganica Chimica Acta 362 (2009) 811–819
819
with four molecules in the unit cell, two of which were
different. Intermolecular hydrogen bonding between the
ammonia, hydroxide and azide ligands is present, as for
complexes 2 and 8. An NH2 hydrogen and the equatorial
ring hydrogen attached to C2 are also involved in intramo-
lecular hydrogen bonding to the azide ligands.
plexes 1, 2, 8, 13, and 14. These data can be obtained free
of charge from The Cambridge Crystallographic Data Cen-
tre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the
online version, at doi:10.1016/j.ica.2008.02.039.
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3.3. Photochemistry
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´
´
´
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aromatic systems.
These complexes all react extremely rapidly upon expo-
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Appendix A. Supplementary material
[26] F.S. Mackay, Ph.D. Thesis, University of Edinburgh, 2006.
CCDC 675566, 675570, 675567, 675568, and 675569
contain the supplementary crystallographic data for com-