Crystal structures of cis-diiododiammine platinum and trans-diazidodiammine platinum

Article abstract of DOI:10.1134/S0022476617080315

Platinum(II) complexes cis-[Pt(NH₃)₂I₂] (1) and trans-[Pt(NH₃)₂(N₃)2] (2) are structurally characterized separately for the first time. The crystallographic data are as follows: for 1, a = 7.0065(6) ?, b = 6.8714(6) ?, c = 7.4106(8) ?, β = 108.432(7)°, space group P2₁/m, Z = 2, ρ_calc = 4.739 g/cm³; for 2, a = 8.1337(5) ?, b = 11.5821(7) ?, c = 6.9705(5) ?, β = 107.256(2)°, space group P2₁/c, Z = 4, ρ_calc = 3.318 g/cm³. Platinum atoms have a square planar environment; the main structure-forming factor is the presence of intermolecular hydrogen bonds forming chain motifs in the structure of 1 and a threedimensional framework in the structure of 2.

Full text of DOI:10.1134/S0022476617080315

Journal of Structural Chemistry. Vol. 58, No. 8, pp. 1689-1692, 2017.
Original Russian Text © 2017 D. B. Vasilchenko, A. V. Zadesenets, I. A. Baidina, D. A. Piryazev, G. V. Romanenko.
CRYSTAL STRUCTURES OF CIS-DIIODODIAMMINE
PLATINUM AND TRANS-DIAZIDODIAMMINE PLATINUM
1,2 1,2
D. B. Vasilchenko , A. V. Zadesenets ,
UDC 546.97:546.59:547.821.2:548.736
1 1
I. A. Baidina , D. A. Piryazev ,
3
and G. V. Romanenko
Platinum(II) complexes cis-[Pt(NH
3
2 2
) I ] (1) and trans-[Pt(NH
3 2
) (N
3 2
) ] (2) are structurally characterized
separately for the first time. The crystallographic data are as follows: for 1, a = 7.0065(6) Å,
3
b = 6.8714(6) Å, c = 7.4106(8) Å, β = 108.432(7)°, space group P2
1
/m, Z = 2, ρcalc = 4.739 g/cm ; for 2,
/c, Z = 4,
calc = 3.318 g/cm . Platinum atoms have a square planar environment; the main structure-forming factor is
a = 8.1337(5) Å, b = 11.5821(7) Å, c = 6.9705(5) Å, β = 107.256(2)°, space group P2
1
3
ρ
the presence of intermolecular hydrogen bonds forming chain motifs in the structure of 1 and a three-
dimensional framework in the structure of 2.
DOI: 10.1134/S0022476617080315
Keywords: platinum, iodide, azide, ammonia.
Nowadays, oncotherapy with drugs based on platinum complexes develops exponentially due to the introduction of
new methods based on the generation of the active component directly in diseased tissues using visible, UV, or IR irradiation
[1, 2]. This approach (photodynamic therapy) includes the use of photosensitive platinum(IV) complexes (exhibiting low
toxicity), which, when introduced into the zone of infection, are converted under irradiation into platinum(II) complexes
acting as active components [3]. The greatest attention of researchers is attracted to azido and iodido complexes of platinum,
which additionally contain ammonia (or amine) and oxoligands (carboxylates, hydroxide) [4, 5]. The synthesis of such
complexes traditionally includes the following three stages: 1) the preparation of a diazido or diiodido complex of
platinum(II); 2) oxidation of the prepared platinum(II) complex to a corresponding dihydroxo derivative using hydrogen
peroxide; 3) modification of N and O ligands. Due to a speedy progress of this direction, the structures of not all intermediate
platinum(II) compounds and target platinum(IV) compounds were studied in the solid phase, although such data are
extremely useful for both identification of compounds during the synthesis process, and also analysis of the drug activity in
order to create predictive models of their effect. The present paper describes the synthesis of two platinum(II) compounds of
3 2 2 3 2 3 2
the diammine series (cis-[Pt(NH ) I ] and trans-[Pt(NH ) (N ) ]), the precursors of drugs for photodynamic therapy. Single
crystals of these compounds were grown, and their structures were studied by XRD.
Experimental. Hexachloroplatinic acid (Joint Stock Company “The Gulidov Krasnoyarsk Non-Ferrous Metals
Plant”) was used as an initial chemical agent for the synthesis of the compounds. Complex 1 was synthesized according to the
procedures published in [6], and single crystals were grown by the isopiestic technique from of its solution in DMFA with
1
Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia;
2
3
vasilchenko@niic.nsc.ru. Novosibirsk National Research State University, Russia. International Tomography Center,
Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia. Translated from Zhurnal Strukturnoi Khimii, Vol. 58,
No. 8, pp. 1739-1742, November-December, 2017. Original article submitted January 19, 2017.
0022-4766/17/5808-1689 © 2017 by Pleiades Publishing, Ltd.
1689

water at room temperature within two days. Complex 2 was synthesized according to the procedure described below.
A stoichiometric amount of KI dissolved in the minimum volume of water was added to a [Pt(NH ](NO solution
] precipitate was
solution (0.947 g, 5.6 mmol) in 15 ml of water was poured in portions
] (1.354 g, 2.80 mmol) in water on a steam bath (40°С). A KN solution
1.30 g, 16.0 mmol, fivefold excess) was added to the solution obtained after the separation of the AgI precipitate and
3
)
4
3 2
)
3 2 2
(prepared according to the previously described procedure [7]) in 10 ml of water. The trans-[Pt(NH ) I
filtered off, washed with alcohol and ether. An AgNO
3
within 30 min to a suspension of trans-[Pt(NH
) I
3 2 2
3
(
2+
containing trans-[Pt(NH ) (H O) ] . In 15 min the yellow solution was filtered on the membrane filter (PTFE, 0.45 µm)
3
2
2
2
3 2 4
from trace amounts of suspended AgN . The solution was evaporated in a vacuum desiccator over H SO in darkness. In two
days, yellow needle-shaped crystals of 2 formed. The yield was 70%. The purity of the compounds was proved by the
elemental analysis (N, H, Pt) and IR spectroscopy.
Single crystal X-ray diffraction analysis. The experimental data for the crystal structure refinement were collected
on an automated four-circle Bruker-Nonius X8 Apex diffractometer equipped with a two-dimensional CCD detector (MoK
α
radiation, graphite monochromator). The structures were solved by the direct method and refined in the anisotropic (isotropic
for H) approximation; hydrogen atoms were placed geometrically with a riding model. All the calculations were carried out
using the SHELX-97software package [8]. The absorption correction was applied empirically using the SADABS program
[9]. The crystallographic characteristics of the compounds studied and the parameters of the experiment are listed in Table 1.
TABLE 1. Crystallographic Characteristics of the Compounds and Parameters of the Diffraction Experiment
Compound
Formula
M, g/mol
Т, K
1
2
H
6 2
I N
2
Pt
6 8
H N Pt
482.96
296(2)
313.22
150(2)
λ, Å
0.71073
Monoclinic
0.71073
Monoclinic
Crystal system
Space group
a, b, c, Å
β, deg
P2
1
/m
1
P2 /c
7.0065(6), 6.8714(6), 7.4106(8)
8.1337(5), 11.5821(7), 6.9705(5)
108.432(7)
338.48(6)
2
107.256(2)
627.10(7)
4
3
V, Å
Z
3
ρcalc, g/cm
4.739
3.318
–1
Adsorption coefficient, mm
Crystal size, mm
29.723
22.300
0.11×0.08×0.06
3.06-28.27
0.16×0.14×0.08
3.52-30.92
θ range for data collection, deg.
Index ranges h, k, l
–9 ≤ h ≤ 9, –9 ≤ k ≤ 9,
–10 ≤ h ≤ 10, –12 ≤ k ≤ 16,
–9 ≤ l ≤ 7
–
8 ≤ l ≤ 9
Number of measured / independent reflections
Completeness to θ = 25.00°,%
3131 / 888 [R(int) = 0.1091]
98.8
6744 / 1774 [R(int) = 0.0275]
99.7
Max and min transmission
0.2686 and 0.1385
Full-matrix least-squares on F
888 / 0 / 34
0.2685 and 0.1247
2
2
Refinement method
Full-matrix least-squares on F
Number of reflections / restrains / parameters
1774 / 0 / 84
1.120
2
S-factor on F
1.146
R-factor [I > 2σ(I)]
R1 = 0.0520; wR2 = 0.1340
R1 = 0.0604; wR2 = 0.1393
3.757 and –3.405
432506
R1 = 0.0197; wR2 = 0.0374
R1 = 0.0226; wR2 = 0.0381
1.037 and –1.251
432507
R-factor (all data)
3
Δρmax, Δρmin, e/Å
CSD no.
1690

The additional crystallographic data are available at the Inorganic Crystal Structure Database, FIZ Karlsruhe (https://icsd.fiz-
karlsruhe.de): CSD no. 432506 (1) and no. 432507 (2).
Results and discussion. Compounds 1 and 2 crystallize in monoclinic cells that include two and four structural units
respectively. The general views of cis-[Pt(NH
main geometric parameters, which characterize the coordination cores, are listed in Table 2. The central platinum atom has
a square planar environment in both compounds, but in cis-[Pt(NH ], all atoms of the {PtN } core lie in the same plane,
while in the structure of trans-[Pt(NH (N ], a slight tetragonal distortion is observed: the deviation from the median plane
of the {PtN } core is 0.01 Å for the N1, N2 atoms, and –0.005 Å for the N3A, N4A atoms.
In complex 2, the Pt–NH and Pt–N bond lengths are close to the values given in the literature for its cis-isomer [4];
3 2 2 3 2 3 2
) I ] and trans-[Pt(NH ) (N ) ] molecules are shown in Figs. 1 and 2, and the
) I
3 2 2
2 2
I
)
3 2
3 2
)
4
3
3
azide ligands have an asymmetric angular (angle N–N–N = 176°) structure; the N–N bond located closer to the platinum
atom is slightly longer than the terminal one (1.22 Å and 1.14 Å respectively). It should be noted that in compound 1 the
Pt–NH
geometric characteristics of the cis-[Pt(NH
in the structures of cis-[Pt(NH ]⋅nDMA (DMA = dimethylacetamide) solvates [10]. The presence of the iodide ion in the
trans-position relative to ammonia does not lead to any noticeable changes in the Pt–N bond lengths in the cis-[Pt(NH ) I ]
3
bond lengths are nearly the same as those in 2; h, there is no pronounced trans effect in the given structural data. The
3 2 2
) I ] molecules in the structure of compound 1 are nearly the same as those found
3 2 2
) I
3
2 2
3 2 2
complex in comparison with the previously found Pt–N bond lengths in cis-[Pt(NH ) Cl ] (1.95 Å, 2.05 Å) and cis-
Fig. 1. Chain of cis-[Pt(NH ) I ] molecules linked by
3 2 2
hydrogen bonds (dashed lines) in the structure of 1. The
central structural unit is drawn with the atomic
numbering scheme.
Fig. 2. Chain of trans-[Pt(NH ) (N ) ] molecules linked by hydrogen
3 2 3 2
bonds (dashed lines) in the structure of 2. The central structural unit
is drawn with the atomic numbering scheme.
TABLE 2. Main Bond Lengths and Angles of the {PtN
2 2 2 2
I } Coordination core in the Crystal Structure of 1 and {PtN N } in
the Crystal Structure of 2
Parameter
Value
Parameter
Value
Parameter
Value
2 2
{PtN N }
Parameter
Value
{
PtN
2 2
I }
Pt–N1
Pt–N2
Pt–I2
Pt–I1
2.04(2) Å
2.07(2) Å
2.590(2) Å
2.598(1) Å
N1–Pt–N2
N1–Pt–I2
N2–Pt–I2
N1–Pt–I1
N2–Pt–I1
I2–Pt–I1
88.7(8)°
89.8(6)°
178.5(5)°
178.0(6)°
89.3(5)°
92.19(5)°
Pt1–N4A
Pt1–N3A
2.031(3) Å
2.043(3) Å
2.050(3) Å
2.054(3) Å
179.7(1)°
92.9(1)°
N3A–Pt1–N2
N4A–Pt1–N1
N3A–Pt1–N1
N2–Pt1–N1
87.0(1)°
86.9(1)°
93.2(1)°
179.4(1)°
120.5(2)°
119.8(3)°
Pt1–N2
Pt1–N1
N4A–Pt1–N3A
N4A–Pt1–N2
N3B–N3A–Pt1
N4B–N4A–Pt1
1691

[Pt(NH
3 2 2 2
) (NO ) ] (2.039 Å, 2.052 Å) [11, 12]. A disorder of hydrogen atoms of ammonia ligands over two positions with
equal relative occupancy is observed in the structure of 1.
3–
–
The formation of weak hydrogen bonds between anionic ligands (NO , I ) and ammonia molecules of the
neighboring complex particles is observed in the structures of both compounds. This leads to the formation of pronounced
chain motifs in the structures (Figs. 1 and 2) with the following characteristic distances: I1…N2 3.783 Å, I2…N1 3.750 Å
(for 1), and N1…N4C 3.124 Å, N2…N3C 3.115 Å (for 2). In the case of the azido complex, the atoms bonded to the central
ion (N3A, N4A) are involved in the system of hydrogen bonds, together with the terminal nitrogen atoms (N3C, N4C) of the
−
NO ion, thus a three-dimensional hydrogen bond network is formed.
3
The presence of sufficiently short Pt…Pt contacts (3.37 Å for cis-[Pt(NH
between these atoms was previously described for cis-[Pt(NH Cl ] and the related compounds [11]. In the structures
studied, the Pt–Pt interaction, probably, does not play any structure- forming role (d(Pt…Pt) ≥ 3.5 Å); in the case of
compound 1 (Pt…Pt 3.97 Å), this is hindered by a large van der Waals radius of iodide ions, similar to [Pt(bpy)I ] (3.63 Å)
3 2 2
) Cl ]) that indicate the interaction
)
3 2
2
2
[
13], and the steric hindrance in complex 2 (Pt…Pt 3.50 Å) is due to extended azide ligands involved in the system of
hydrogen bonds, too.
The work was supported by the Russian Science Foundation (grant No. 15-13-10012).
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