Synthesis, characterisation and speciation studies of heterobimetallic pyridinehydroxamate-bridged Pt(II)/M(II) complexes (M = Cu, Ni, Zn). Crystal structure of a novel heterobimetallic 3-pyridinehydroxamate-bridged Pt(II)/Cu(II) wave-like coordination polymer

Article abstract of DOI:10.1039/b501105a

The reaction of cis-[Pt(NH₃)₂(3-pyhaH) ₂]²⁺ (3-pyhaH = 3-pyridinehydroxamic acid) and cis-[Pt(NH₃)₂(4-pyhaH)₂]²⁺ (4-pyhaH = 4-pyridinehydroxamic acid) with Cu(II), Ni(II) or Zn(II) in aqueous solution affords novel heterobimetallic pyridinehydroxamate-bridged complexes, {cis-[Pt(NH₃)₂(μ-3-pyha)M(μ-3-pyha)]·SO ₄·xH₂O}_n and {cis-[Pt(NH ₃)₂-(μ-4-pyha)M(μ-4-pyha)]·SO ₄·xH₂O}_n respectively. The crystal and molecular structure of one of these, {cis-[Pt-(NH₃) ₂(μ-3-pyha)Cu(μ-3-pyha)]SO₄·8H ₂O}_n 3a, has been determined and was found to be a novel heterobimetallic wave-like coordination polymer, the structure of which contains interlinked pyridinehydroxamate-bridged repeating units of Pt(II) and Cu(II) ions in slightly distorted square-planar N₄ and O₄ coordination environments respectively and extensive hydrogen-bonding through the Pt ammines and the deprotonated hydroxamate O and via the O of the SO ₄^2- counterions and the H(N) of the hydroxamate moiety. Spectrophotometric and speciation studies on the other heterobimetallic systems confirm that very similar species are being formed in solution and based on elemental analysis and spectroscopic results analogous complexes are formed in the solid-state. In this paper, we report the first examples of coordination polymers incorporating both Pt(II)/Cu(II), Pt(II)/Ni(II) and Pt(II)/Zn(II) and containing pyridinehydroxamic acids as bridging scaffolds. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b501105a

View Online / Journal Homepage / Table of Contents for this issue
F U L L P A P E R
Synthesis, characterisation and speciation studies of heterobimetallic
pyridinehydroxamate-bridged Pt(II)/M(II) complexes (M = Cu, Ni,
Zn). Crystal structure of a novel heterobimetallic
3-pyridinehydroxamate-bridged Pt(II)/Cu(II) wave-like
coordination polymer†
Clodagh Mulcahy,a Fedor M. Dolgushin,b Krystyna A. Krot,a Darren Griffitha and
Celine J. Marmion*a
a Centre for Synthesis & Chemical Biology, Department of Pharmaceutical & Medicinal
Chemistry, Royal College of Surgeons in Ireland, 123 St. Stephens Green, Dublin 2, Ireland.
E-mail: cmarmion@rcsi.ie; Fax: 353 1 402 2168; Tel: 353 1 402 2161
b X-Ray Structural Centre, General and Technical Chemistry Division, Academy of Sciences of
Russia, Vavilov Str. 28, Moscow, B-334, 117813, Russia
Received 24th January 2005, Accepted 15th April 2005
First published as an Advance Article on the web 4th May 2005
The reaction of cis-[Pt(NH3)2(3-pyhaH)2]2+ (3-pyhaH = 3-pyridinehydroxamic acid) and cis-[Pt(NH3)2(4-pyhaH)2]2+
(4-pyhaH = 4-pyridinehydroxamic acid) with Cu(II), Ni(II) or Zn(II) in aqueous solution affords novel heterobimetal-
lic pyridinehydroxamate-bridged complexes, {cis-[Pt(NH3)2(l-3-pyha)M(l-3-pyha)]·SO4·xH2O}n and {cis-[Pt(NH3)2-
(l-4-pyha)M(l-4-pyha)]·SO4·xH2O} respectively. The crystal and molecular structure of one of these, {cis-[Pt-
(NH3)2(l-3-pyha)Cu(l-3-pyha)]SO4·n8H2O}n 3a, has been determined and was found to be a novel heterobimetallic
wave-like coordination polymer, the structure of which contains interlinked pyridinehydroxamate-bridged repeating
units of Pt(II) and Cu(II) ions in slightly distorted square-planar N4 and O4 coordination environments respectively
and extensive hydrogen-bonding through the Pt ammines and the deprotonated hydroxamate O and via the O of the
2−
SO4 counterions and the H(N) of the hydroxamate moiety. Spectrophotometric and speciation studies on the other
heterobimetallic systems confirm that very similar species are being formed in solution and based on elemental
analysis and spectroscopic results analogous complexes are formed in the solid-state. In this paper, we report the first
examples of coordination polymers incorporating both Pt(II)/Cu(II), Pt(II)/Ni(II) and Pt(II)/Zn(II) and containing
pyridinehydroxamic acids as bridging scaffolds.
surprisingly they have never been utilised as building blocks in
Introduction
the rational design of coordination polymers. Hydroxamic acids
In recent years, there has been an exponential growth in the
are also involved in numerous biological processes including
level of research activity surrounding the rational design and
metal-ion transport and inhibition of metalloenzymes such
synthesis of molecular architectures from both a structural
as matrix metalloproteinases, ureases, lipoxygenases, cyclooxy-
and topological viewpoint as well as exploiting their potential
genases and peptide deformylases.8,11,12 Hydroxamic acids also
as functional materials in relation to host–guest chemistry,
represent a wide spectrum of bioactive compounds having
electrical conductivity, magnetism, ion exchange and catalysis.
hypotensive, anti-cancer, anti-malarial, anti-tuberculosis and
The diverse range of metal coordination geometries, as well
anti-fungal properties and have been identified as key the-
as the ability to fine-tune ligands in terms of size, shape and
rapeutic agents targeting cardiovascular diseases, HIV,
functionality have culminated in structural motifs1 such as
Alzheimer’s disease and metal-poisoning.8 The versatile biolog-
grids,2 boxes,2 cylinders,2 helicates2 and coordination polymers,3
ical activity of hydroxamic acids is due to their strong metal-
extended structures comprising metal centres joined by bridging,
chelating ability and possibly their NO-releasing properties.13 To
multi-functional ligands. The self-assembly of coordination
the best of our knowledge, there have been no reports to date of
polymeric chains using template counterions, although reported
either organometallic or coordination polymers incorporating
for a variety of metal ions including Cu(I)/Cu(II),4 Zn(II)3
both Pt(II) and Cu(II), Ni(II) or Zn(II), nor any containing
and Ag(I),5 is hitherto relatively unexplored in relation to Pt
hydroxamic acids as building blocks. With this in mind, we
chemistry. In fact there are only two recent reports in the
soughttocreate a novel class of 2Dnetworkpolymers specifically
literature, both by Lang et al., of Pt(II)/Ag(I) and Pt(II)/Cu(I)
containing Pt(II) and M(II) where M = Cu, Ni or Zn and utilising
coordination polymers and in both cases, an alkynyl ligand
hydroxamic acids as scaffolds.
bridges the two metal ions where coordination is via a r-C–Pt
Our initial strategy focussed on the design of a hydrox-
bond and a p-C–M bond (M = Cu(I) or Ag(I)).6,7
amic acid-containing ligand with two coordination sites jux-
Furthermore, although hydroxamic acids, a remarkable fam-
taposed in such a fashion that they cannot both coordinate
ily of bioligands8 of general formula RCONRꢀOH, have been
to the same metal ion. While 2-pyridinehydroxamic acid (2-
pyhaH) was recently shown to coordinate to Pt(II) forming a
extensively employed as scaffolds in metallacrown chemistry,9,10
novel dinuclear Pt(II) hydroximate complex, [{cis-Pt(NH3)2}2(l-
2-pyhaH−1)](ClO4)2·H2O with the diammine Pt(II) moieties
† Electronic supplementary information (ESI) available: Species distri-
bridged via the doubly deprotonated pyridinehydroximate lig-
and, with (N,N) chelation to one Pt and (O,O) to the other,14
we hypothesised that 3- or 4-pyridinehydroxamic acid (3- or 4-
pyhaH) could be utilised as bridging scaffolds in the design of
bution for the L : Zn(II) system where L is cis-[Pt(NH3)2(3-pyhaH)2]2+
,
pH 4–11; Titration curve for the L : Zn(II) system where L =
cis-[Pt(NH3)2(3-pyhaH)2]2+. See http://www.rsc.org/suppdata/dt/b5/
b501105a/
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 1 9 9 3 – 1 9 9 8
1 9 9 3
©

View Online
coordination polymers because they could coordinate Pt(II) in
a monodentate fashion via the pyridine nitrogen, leaving the
hydroxamic acid moiety free to coordinate to a separate metal
ion, Fig. 1.
used instead of methylnicotinate. Yield: 55%. (Found: C, 51.94;
H, 4.29; N, 20.12. C6H6N2O2 requires C, 52.17; H, 4.38; N,
20.28%); dH (d6-DMSO) 11.60 (s, 1H, OH), 9.37 (sb, 1H, NH),
3
3
8.70 (d, J 5.6 Hz, 2H, H2/6), 7.68 (d, J 6.0 Hz, 2H, H3/5);
mmax/cm−1 (KBr disc) 3186vs, 3061s, 2999s, 2850b, 1642vs, 1608s,
1551s, 1531s, 1321s, 1164s, 1009s 906s, 850vs, 688vs, 639vs.
cis-[Pt(NH3)2(3-pyhaH)2](BPh4)2·4H2O, 1. Iodoplatin (cis-
Pt(NH3)2I2) (0.40 g, 0.83 mmol) was stirred with AgNO3
(0.27 g, 1.60 mmol) in deionised water (10 cm3) at 40 ◦C in
darkness for 24 h. The AgI precipitate was filtered off and
3-pyridinehydroxamic acid, 3-pyhaH (0.27 g, 1.98 mmol) in
deionised water (10 cm3) was added to the filtrate. This reaction
solution was stirred at room temperature for 24 h. NaBPh4
(0.58 g, 2.1 mmol) was added and the resulting yellow precipitate
was filtered and dried over P2O5. The solid was subsequently
recrystallised from an aqueous/methanol solution, filtered and
dried over P2O5. Yield: 0.72 g, 0.59 mmol, 71%. (Found: C,
59.83; H, 5.28; N, 6.66. PtC60H66N6O8B2 requires C, 59.27; H,
5.47; N, 6.91%; dH (d6-DMSO): 11.61 (s, 2H, OH), 9.49 (s, 2H,
NH), 9.10 (s, 2H, H2), 8.65 (d, 2H, H4), 8.22 (d, 2H, H6), 7.50 (m,
2H, H5), 7.17 (s, 8H, phenyl H), 7.05 (t, 8H, phenyl H), 6.97 (t,
4H, phenyl H), 4.08 (s, 6H, NH3); mmax/cm−1 (KBr disc) 3253vs,
2879s, 1650vs, 1612s, 1558s, 750vs, 706vs.
Fig. 1 Pt(II)/M(II) pyridinehydroxamate moiety (M = Cu, Ni, Zn).
Herein we report the synthesis and characterisation of
the first examples to date of Pt(II)/M(II) heterobimetallic
pyridinehydroxamate-bridged coordination polymers of general
formula {cis-[Pt(NH3)2(l-pyha)M(l-pyha)]SO4·xH2O}n, where
M = Cu(II), Ni(II) or Zn(II) and pyha is 3- or 4-pyridine-
hydroxamate. The crystal structure of {cis-[Pt(NH3)2(l-3-
pyha)Cu(l-3-pyha)]SO4·8H2O}n, is also described. Speciation
and spectroscopic studies of related systems are also reported.
cis-[Pt(NH3)2(4-pyhaH)2](BPh4)2·4H2O, 2. This was syn-
thesised by the same method as cis-[Pt(NH3)2(3-pyhaH)2]-
(BPh4)2·4H2O but using 4-pyhaH in place of 3-pyhaH. Yield:
69%. (Found: C, 59.83; H, 5.28; N, 6.66. PtC60H66N6O8B2
requires C, 59.27; H, 5.47; N, 6.91%); dH (d6-DMSO) 11.72 (s,
2H, OH), 9.57 (s, 2H, NH), 8.82 (d, 2H, H2/6), 7.70 (d, 2H,
H3/5), 7.10 (s, 8H, phenyl H), 6.78 (t, 8H, phenyl H), 6.64 (t,
4H, phenyl H), 4.71 (s, 6H, NH3); mmax/cm−1 (KBr disc) 3251vs,
2872s, 1661vs, 1614s, 1553s, 751vs, 705vs.
Experimental
Materials and methods
All reagents, deuterated solvents and metal salts were purchased
from Sigma Aldrich and used without further purification.
Iodoplatin was synthesised by a previously reported literature
method.15 IR spectra were recorded on KBr discs on a Mattson
Genesis II CSI FTIR spectrometer in the 4000–400 cm−1 region.
UV-Vis spectra wereperformed on aHelios aThermo Spectronic
Spectrophotometer in a quartz cell. C, H, N, Cu, Ni and
Zn elemental analysis were peformed at the Microanalytical
laboratories, University College Dublin, Ireland. 1H NMR
spectra were recorded on a Bruker Advance DPX 400 FT
spectrometer at the Department of Chemistry, Trinity College
Dublin, Ireland. The residual undeuterated DMSO signal was
used as an internal reference at 2.505 ppm. ESR spectra were
recorded on a Varian E9 X-band spectrometer at a temperature
of 158 K. Variable-temperature magnetic measurements were
carried out on polycrystalline samples using a Faraday type mag-
netometer (Oxford Instruments), equipped with a continuous-
flow cryostat, and an electromagnet operating at a magnetic field
of 0.8 T. Diamagnetic corrections were estimated from Pascal
constants.
Preparation of heterobimetallic pyridinehydroxamate-bridged
Pt(II)/M(II) complexes
{cis-[Pt(NH3)2(l-3-pyha)Cu(l-3-pyha)]SO4·2H2O}n, 3. After
stirring for 24 h at 40 ◦C in darkness, an aqueous suspension
(15 cm3) of cis-Pt(NH3)2I2 (0.26 g, 0.55 mmol) and AgNO3
(0.18 g, 1.09 mmol) generated cis-[Pt(NH3)2(H2O)2](NO3)2
(0.55 mmol) which was subsequently reacted in situ with 3-
pyhaH (0.15 g, 1.1 mmol) and, upon stirring at 40 ◦C for
24 h, yielded cis-[Pt(NH3)2(3-pyhaH)2](NO3)2 (0.55 mmol).
CuSO4·5H2O (0.14 g, 0.55 mmol) was added to this solution and,
upon adjusting the pH to 5.5 using 5% NaOH solution, a grass-
green solid precipitated which was filtered, washed with cold
water and dried over P2O5. Single crystals suitable for an X-ray
diffraction study were obtained from the filtrate, after standing
at room temperature for two days, 3a (0.17 g, 218 mmol, 40%).
(Found C, 21.07; H, 2.66; N, 12.46; Cu, 9.81. PtCuC12H18N6O9S
requires C, 21.16; H, 2.66; N, 12.34; Cu, 9.33%); mmax/cm−1 (KBr
disc) 3434vs, 3228s, 3114s, 2929s, 1619vs, 1610s, 1570m, 1523s,
1384vs, 1116vs, 1054m, 931m, 846m, 618s. The IR spectra of the
grass-green precipitate and 3a were identical.
Syntheses
3-Pyridinehydroxamic acid (3-pyhaH). Hydroxylamine hy-
drochloride (5.07 g, 72 mmol) was added to sodium hydroxide
(5.83 g, 146 mmol) in deionised water (37 cm3). The resulting
solution was added dropwise to methylnicotinate (5.00 g,
36 mmol) in methanol (55 cm3). The solution was stirred at
room temperature for 72 h, after which the solution was acidified
to pH 5.5 using 5% HCl. The solvent was removed in vacuo
yielding a yellow solid. Methanol (60 cm3) was added and
sodium chloride was filtered. The solvent was removed in vacuo
yielding a light pink solid, which was recrystallised from water
(3.00 g, 22 mmol, 66%). (Found: C, 51.98; H, 4.24; N, 20.14.
C6H6N2O2 requires C, 52.17; H, 4.38; N, 20.28%); dH (d6-DMSO)
11.41 (s, 1H, OH), 9.24 (sb, 1H, NH), 8.90 (d, 4J 2.00 Hz,
The following heterobimetallic pyridinehydroxamate-bridged
complexes were synthesised by the method described for 3 above.
{cis-[Pt(NH3)2(l-3-pyha)Ni(l-3-pyha)]SO4·4H2O}n, 4. Pale
green solid. Yield 38%. (Found C, 20.85; H, 2.89; N, 12.21; Ni,
8.64. PtNiC12H20N6O10S requires C, 20.76; H, 2.90; N, 12.11;
Ni, 8.46%); mmax/cm−1 (KBr disc) 3399vs, 3212vs 1620vs, 1539m,
1477m, 1384s, 1357s, 1223m, 1201m, 1166m, 1107s, 927s, 822m,
734m, 697s, 616s.
1H, H2), 8.70 (dd, J 5.04 Hz, J 1.52 Hz, 1H, H4), 8.10 (dt,
3J 8.00 Hz, 4J 2.00 Hz, 1H, H6) 7.51 (dd, 3J 8.04 Hz, 4J 5.04 Hz,
1H, H5); mmax/cm−1 (KBr disc) 3196vs, 2950m, 2802s, 1660vs,
1643vs, 1594s, 1557s, 1496s, 1422s, 1306m, 1025vs, 713vs, 646vs.
3
4
{cis-[Pt(NH3)2(l-3-pyha)Zn(l-3-pyha)]SO4·8H2O}n, 5. Yel-
low solid. Yield 53%. (Found C, 19.45; H, 2.96; N, 11.73; Zn,
8.41. PtZnC12H24N6O12S requires C, 19.56; H, 3.28; N, 11.40;
Zn, 8.87%); mmax/cm−1 (KBr disc) 3401vs, 3199s, 1620vs, 1601s,
1546s, 1476m, 1451m, 1384vs, 1356s, 1223m, 1168s, 1110s, 1054s,
929s, 964m, 697s, 618s.
4-Pyridinehydroxamic acid (4-pyhaH). This was prepared by
the same method as for 3-pyhaH except ethylisonicotinate was
1 9 9 4
D a l t o n T r a n s . , 2 0 0 5 , 1 9 9 3 – 1 9 9 8

View Online
Table 1 Crystallographic data for 3a
{cis-[Pt(NH3)2(l-4-pyha)Cu(l-4-pyha)]SO4·4H2O}n, 6. Grass-
green solid. Yield 42%. (Found C, 19.86; H, 2.60; N, 12.03; Cu,
9.32. PtCuC12H20N6O10S requires C, 20.62; H, 2.88; N, 12.02;
Cu, 9.09%); mmax/cm−1 (KBr disc) 3433vs, 3227s, 3108s, 1620s,
1570m, 1522m, 1384s, 1116vs, 931w, 846w, 726w, 619s.
Compound
3a
Chemical formula
Formula weight
Crystal system
Space group
C12H32CuN6O16PtS
807.13
Triclinic
P-1
8.268(2)
10.003(2)
17.156(4)
80.524(5)
81.164(5)
72.404(5)
1325.9(5)
2
{cis-[Pt(NH3)2(l-4-pyha)Ni(l-4-pyha)]SO4·4H2O}n, 7. Pale
green solid. Yield 53%. (Found C 19.45; H 2.76; N 12.73; Ni
7.91. PtNiC12H20N6O10S requires C, 20.76; H, 2.90; N, 12.11;
Ni, 8.46%); mmax/cm−1 (KBr disc) 3401vs, 3199s, 1620vs, 1546s,
1451m, 1384vs, 1357s, 1223m, 1168s, 1110s, 1054s, 930s, 962m,
696s, 622s. Expect: C, 20.76; H, 2.90; N, 12.11; Ni, 8.46
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
{cis-[Pt(NH3)2(l-4-pyha)Zn(l-4-pyha)]SO4·4H2O}n, 8. Yel-
low solid. Yield 67%. (Found C, 20.65; H, 2.60; N, 12.17; Zn,
9.27. PtZnC12H20N8O10S requires C, 20.56; H, 2.88; N, 11.99;
Zn, 9.33%); mmax/cm−1 (KBr disc) 3400s, 3368s, 3231vs, 3090s,
1626m, 1602s, 1529m, 1429w, 1384vs, 1335m, 1317m, 1162m,
1054m, 923m, 847w, 723w, 619w.
˚
V/A
Z
D
calc/Mg m−3
2.022
6.231
120(2)
0.20
l(Mo–Ka)/mm−1
T/K
Crystal Size max/mm
Mid/mm
0.10
0.05
Min/mm
Potentiometric and spectrophotometric studies
2hmax
52.2
0.318/0.694
0.0943
0.0737, 0.1517
0. 1402, 0.1736
9679
Min/Max trans. factor
All measurements were carried out using solutions of
0.1 mol dm−3 ionic strength (KNO3) at 25 0.1 ◦C. Carbonate-
free KOH solutions of known concentrations (ca. 0.2 mol dm−3)
standardised with potassium hydrogen phthalate,16 were used
as titrant. The pH-metric titrations were carried out on a
Molspin pH meter and titration controller with Thermo Russell
CMAW711 combined electrode and Hamilton syringe autobu-
rette; data were analysed using HYPERQUAD.17 The electrode
Rint
R1, wR2 [I>2r(I)]a
R1, wR2 (all data)
Reflections: Collected
Independent
Observed
5093
2777
a R1 = RꢁFo| − |Fcꢁ/R|Fo|, wR2 = [Rw(Fo − Fc2)2/Rw(Fo2)2]1/2
.
2
system was calibrated by the method of Irving et al.18 (pKw
=
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) with estimated
standard deviations for 3a
13.831) so that the pH-meter readings could be converted into
hydrogen ion concentration. The pKa values of the platinum
pyridinehydroxamic acids and the stability constants of the
Pt(II)/M(II) pyridinehydroxamic acid systems, where M =
Cu, Ni, Zn, were determined by titrating solutions (∼2.0 ×
10−3 mol dm−3) in HNO3 (5.0 × 10−3 mol dm−3) with a KOH
solution of known concentration (0.1977 mol dm−3).
Pt(1)–N(5)
Pt(1)–N(3)
Pt(1)–N(6)
Pt(1)–N(1)
2.007(10)
2.004(11)
2.017(12)
2.046(14)
O(1)–Cu(1)–O(1)#1
O(1)–Cu(1)–O(2)
O(1)#1–Cu(1)–O(2)
O(1)–Cu(1)–O(2)#1
O(1)#1–Cu(1)–O(2)#1
O(2)–Cu(1)–O(2)#1
180.000(2)
84.2(5)
95.8(5)
95.8(5)
84.2(5)
Cu(1)–O(1)
Cu(1)–O(2)
Cu(2)–O(3)
Cu(2)–O(4)
1.908(10)
1.933(12)
1.882(12)
1.924(12)
180.000(1)
Crystallographic measurements on 3a
O(3)#2–Cu(2)–O(3)
O(3)#2–Cu(2)–O(4)#2
O(3)–Cu(2)–O(4)#2
O(3)–Cu(2)–O(4)
O(3)–Cu(2)–O(4)
O(4)#2–Cu(2)–O(4)
180.000(2)
86.1(5)
93.9(5)
93.9(5)
86.1(5)
Crystal data and experimental details for 3a are summarised in
Table 1. Crystal analysis was determined on a Bruker SMART
1000 CCD diffractometer at 120(2) K using monochromated
N(5)–Pt(1)–N(3) 176.3(5)
N(5)–Pt(1)–N(6)
N(3)–Pt(1)–N(6)
N(5)–Pt(1)–N(1)
N(3)–Pt(1)–N(1)
90.9(5)
91.9(6)
90.3(5)
86.8(6)
˚
Mo–Ka radiation, (k = 0.71073 A) and the φ–x scan method.
180.000(2)
The structure was solved by direct methods and refined by full-
matrix least-squares against F2 in the anisotropic approximation
for all non-hydrogen atoms, using SHELXTL-97 package.19
The hydrogen atoms in 3a were placed geometrically and were
included in the structure factor calculations in the riding motion
approximation. Hydrogen atoms in the solvate molecules of wa-
ter were not localised. The atomic numbering scheme and atom
connectivity for 3a are shown in Fig. 2 and a selection of bond
lengths and angles are gathered together in Table 2. The crystals
were small and were found to have low diffraction ability which
is reflected in the relatively high R factor. The high anisotropy
of ellipsoids is most probably due to the twinning of the crystal.
Although substantial effort went into resolving the twinning
components, we were not successful in finding either a twinned
or disordered model which would have provided a more ac-
curate and consistent description of the structure. Therefore we
returned to the original anisotropic refinement, which, according
to our opinion, still gives the best possible approximation of the
structure. Even though one should admit that the ellipsoids in
this case may not reflect the actual thermal displacements, the
overall general connectivity and ballpark geometry in fact do
not raise any doubts in this structure of the first example of a
heterobimetallic wave-like coordination polymer incorporating
repeating units of Pt(II) and Cu(II) ions interlinked via 3-pyha.
CCDC reference number 246167 (3a).
N(6)–Pt(1)–N(1) 178.1(5)
Fig. 2 Molecular structure and atomic labelling scheme of the wave-like
coordination polymer, 3a, with solvent molecules omitted for clarity.
Electron spin resonance spectroscopy
X-Band ESR spectra were recorded at 158 K using a Varian E-9
spectrometer. A 3.965 mM solution of 3, pH = 6.5 in 50 : 50
water : ethanediol was prepared to ensure good glass formation
See http://www.rsc.org/suppdata/dt/b5/b501105a/ for cry-
stallographic data in CIF or other electronic format.
D a l t o n T r a n s . , 2 0 0 5 , 1 9 9 3 – 1 9 9 8
1 9 9 5

View Online
when frozen. A modulation amplitude of 20 G and a microwave
power of 5 mW were used.
Results and discussion
Syntheses of 3- and 4-pyridinehydroxamic acids
3- and 4-pyridinehydroxamic acids were synthesised from the
corresponding methyl or ethyl esters in high yield and purity.
They were characterised by elemental analysis, IR and 1H NMR
spectroscopy. Their IR spectra contained strong bands at 2802,
3196 and 1660 cm−1 for 3-pyhaH and 2850, 3186 and 1642 cm−1
for 4-pyhaH which may be assigned to m(OH), m(NH) and
=
m(C O) respectively. These values concur with those previously
1
reported in the literature.20 The H NMR spectra of 3- and 4-
pyhaH show N–H and O–H resonances at ca. 9.3 ppm and
ca. 11.5 ppm, respectively, both of which are concentration-
dependent due to intermolecular hydrogen bonding at high
concentrations. In addition, for 3-pyhaH, four main resonances
at 8.90, 8.70, 8.10 and 7.51 ppm are observed and correspond to
the four protons of the meta-substituted pyridine. In contrast, for
4-pyhaH, 2 main resonances at 8.70 and 7.68 ppm are observed
for the 4 protons of the para-substituted pyridine ring.
Syntheses of 1 and 2
cis-[Pt(NH3)2(3-pyhaH)2](BPh4)2·4H2O, 1 and cis-[Pt(NH3)2(4-
pyhaH)2](BPh4)2·4H2O, 2 were synthesised in high yield and
purity and were charactersied by elemental analysis, IR and 1H
NMR spectrsocopy. Their IR and 1H NMR data are similar to
those of the corresponding free ligands exhibiting the expected
shifts indicative of coordination to the metal ion and are
consistent with the free nature of the hydroxamic acid moiety.
The cis-configurations of both complexes were confirmed by
the classic Kurnakov test.21 Complexes 1 and 2 served as
scaffolds for the subsequent formation of the heterobimetallic
pyridinehydroxamate-bridged Pt(II)/M(II) coordination poly-
mers 3–8, where M = Cu, Ni or Zn.
Syntheses of 3–8
Reaction of an aqueous solution of cis-[Pt(NH3)2(3-pyhaH)2]2+
or cis-[Pt(NH3)2(4-pyhaH)2]2+ with M(II) salts where M is Cu, Ni
or Zn in a 1 : 1 ratio at pH 5.5 resulted in deprotonation of the hy-
droxamic acid moieties, complexation of the metal cation, M(II),
and precipitation of heterobimetallic pyridinehydroxamate-
bridged Pt(II)/M(II) coordination polymers, Scheme 1. Sat-
isfactory elemental analysis and IR data for all complexes
were obtained. For complexes 3–8, O,O-coordination of the
hydroxamate moiety resulted in a significant lowering of the
Scheme 1 Preparation of the Pt precursors and complexes 3–8
where M(II) = Cu, Ni or Zn.
2−
hydroxamate O and via the O of the SO4 counterions and the
H(N) of the hydroxamate moiety as can be seen in the corrugated
layered structure, Fig. 3 (a). In addition to the aforementioned
hydrogen bonding interactions, the polymeric arrangement is
further stabilised by p–p stacking between polymeric chains,
Fig. 3 (b). The distance between mean planes of neigbouring
−1
−1
=
=
m(C O) to ca. 1620 cm (cf. m(C O) is at 1660 cm and
1642 cm−1 for 3-pyhaH and 4-pyhaH, respectively).
˚
3-pyha fragments is 3.3 A and the shortest interatomic distances
˚
lie in the range of 3.28–3.47 A. The use of 3-pyha as the bridging
Crystal structure of 3a
ligand and hence absence of random chain lengths undoubtedly
provides structural regularity and reduced flexibility.
Of the complexes 3–8 synthesised, only crystals of {cis-[Pt-
(NH3)2(l-3-pyha)Cu(l-3-pyha)]SO4·8H2O}n, 3a, materialised
which were suitable for an X-ray diffraction study. The
structure, shown to be {cis-[Pt(NH3)2(l-3-pyha)Cu(l-3-
pyha)]SO4·8H2O}n, 3a, is the first example of a heterobimetallic
wave-like coordination polymer incorporating repeating units of
Pt(II) and Cu(II) ions interlinked via 3-pyha. It was refined in the
triclinic P-1 space group with an asymmetric unit consisting
of two formula units. The Pt(II) and Cu(II) ions, separated
Formation constants and species distribution curves
Speciation and spectroscopic studies were also carried out on L
(cis-[Pt(NH3)2(3-pyhaH)2]2+) or L1 (cis-[Pt(NH3)2(4-pyhaH)2]2+)
with M(II) where M is Cu, Ni or Zn salts and confirm the
presence of Pt(II)/M(II) species analogous to those found in
the solid state in 3–8 above.
The protonation constants of the novel Pt(II) complexes
and the overall stability constants for the heterobimetallic
systems were calculated from the potentiometric data. Both
cis-[Pt(NH3)2(3-pyhaH)2]2+, L, and cis-[Pt(NH3)2(4-pyhaH)2]2+,
L1, release two protons from the hydroxamate moieties upon
titration with KOH, Table 3. The pKa values differ by one
logarithmic unit probably due to intermolecular hydrogen-
bonding.
˚
˚
by a distance of 7.905 A (for Pt(1) · · · Cu(1)) and 7.939 A
(for Pt(1) · · · Cu(2)), are in distorted square-planar N4 and O4
coordination environments, respectively, with a N5–Pt–N6 angle
of 90.9(5)◦ and a N3–Pt–N1 angle of 86.8(6)◦ and an O–Cu–
O (internal hydroxamate) angle of 84.2(5) and 86.1(5)◦ and an
O–Cu–O (external hydroxamate) angle of 95.8(5) and 93.9(5)◦.
Self-assembly of the polymeric chains is achieved by inter-chain
hydrogen bonds through the Pt ammines and the deprotonated
1 9 9 6
D a l t o n T r a n s . , 2 0 0 5 , 1 9 9 3 – 1 9 9 8

View Online
Fig. 4 Titration curves for L : M(II) systems where L = cis-[Pt(NH3)2-
(3-pyhaH)2]2+ and M = Cu, Ni.
Fig. 3 (a) Cation–anion corrugated layer of 3a. Chains in layer are
bonded by weak hydrogen bonds (N5–H5B · · · O1 and N6–H6A · · · O3).
(b) Fragment of crystal packing along a axis. Layers are parallel to
(0 1 1) crystal plane. Solvate molecules of water (8 independent
molecules, omitted for clarity) are located between layers.
Speciation studies confirm the presence of 1 : 1 L : Cu and
L1 : Cu species analogous to those found in the solid-state in
complexes 3 and 6, respectively. Upon coordination of Cu to
L/L1, consecutive deprotonations of the hydroxamate NHs are
observed with increasing pH (Table 3, Fig. 5, for Zn, see ESI†).
This is the first investigation to date using speciation studies
involving Pt(II)/M(II) heterobimetallic systems. L forms slightly
more stable heterobimetallic complexes than those formed by L1
and, although this difference is only very slight, it is observed in
every case. We speculate that this may be due to the increased
difference in the distance of the pyridine N from the hydroxamate
moiety in 4-pyhaH resulting in a slightly diminished electron-
donating effect.
Table 3 Stability constants (log b values, which refer to the equilibrium
pM + qL + rH ↔ MpLqHr) of the proton, Cu(II), Ni(II) and Zn(II)
heterobimetallic complexes of L and L1 where L is cis-[Pt(NH3)2(3-
pyhaH)2]2+ and L1 is cis-[Pt(NH3)2(4-pyhaH)2]2+ at 25 ◦C (I = 0.1 M
KNO3)
Species
MpLqHr log b value
LH
0 1 1
0 1 2
0 1 1
0 1 2
7.66(0.004)
14.29(0.003)
7.35(0.008)
13.65(0.007)
L H2
L1H
L1H2
Cu2+
Ni2+
Zn2+
ML2H2
M2L2H
1 2 2
2 2 1
26.26(0.01)
23.85(0.01)
14.98 (0.01)
8.52 (0.01)
1.07 (0.01)
−7.51(0.02)
M2L2H−1 2 2 −1
M2L2H−2 2 2 −2
M2L2H−3 2 2 −3
M2L2H−4 2 2 −4
MLH
ML
1 1 1
1 1 0
10.64(0.04)
4.50(0.01)
10.57(0.03)
4.46(0.01)
MLH−1
M2LH−3
1 1 −1
2 1 −3
1 2 2
−4.52(0.01)
−4.49(0.03)
−19.05(0.03) −17.00(0.02)
ML1 H2
25.41(0.01)
23.45(0.02)
13.05 (0.02)
7.67 (0.02)
1.27 (0.02)
2
M2L1 H
2 2 1
2
M2L1 H−1 2 2 −1
2
M2L1 H−2 2 2 −2
2
M2L1 H−3 2 2 −3
2
ML1H
1 1 1
1 1 0
10.58(0.04)
4.24(0.02)
−19.32 (0.03) −16.90(0.03)
10.47(0.03)
4.12(0.01)
Fig. 5 Species distribution for the L : Cu(II) where L is cis-[Pt(NH3)2-
(3-pyhaH)2]2+, pH 2–11, [Cu(II)] = 1 mM, [L] = 2 mM.
ML1
M2L1H−3 2 1 −3
In addition, an ESR spectrum was obtained for a 3.965 mM
solution of 3 in 50 : 50 water : ethanediol, pH = 6.5 where
there is a 50 : 50 mixture of [Cu2L2H−1]3+ and [Cu2L2H−2]2+.
We found gꢁ = 2.262 and Aꢁ = 190 × 10−4 cm−1, both of
which, as expected, lie between those previously observed for
Titration curves of L and L1 with Cu show significant shifts
both for L : Cu and L1 : Cu in the ratios of 2 : 1 and 1 : 1
suggesting the formation of heterobimetallic complexes, Fig. 4.
The titration curves for the L : Ni and L1 : Ni systems, Fig. 4,
in contrast, indicate complexation of either one or two Ni ions
per L or L1 and were practically identical to those obtained for
the L : Zn and L1 : Zn systems (see ESI†).
acetohydroximato Cu(II) complexes [CuA2H−1]− (where gꢁ
=
2.258 and Aꢁ = 192 × 10−4 cm−1)22 and [CuA2H−2]2− (where
gꢁ = 2.219 and Aꢁ = 207 × 10−4 cm−1)22 (A is acetohydroxamic
D a l t o n T r a n s . , 2 0 0 5 , 1 9 9 3 – 1 9 9 8
1 9 9 7

View Online
acid). The above results are also in good agreement with
other previously published ESR results for Cu-hydroximato
species.22,23 The condition gꢁ > g⊥ > 2.0023 (where we found
g⊥ = 2.053) shows the ground state to be dx2–y2. In addition,
the ratio of gꢁ/Aꢁ is 119 cm, consistent with values expected
for Cu(II) chelated to a square planar array of ligands.24 The
spectrum of the solid polymeric material, 3, appears to be
similar (g = 2.051), although with a poorly resolved parallel
component that spans the same field range as that observed in the
frozen glass. These observations are consistent with the observed
distorted square-planar geometry in the solid structure, while
comparison with the ESR parameters of the frozen glass shows
the species in solution to be similarly coordinated. Assuming
that the broad, unresolved parallel feature of the spectrum of
the solid represents a similar g value to that in the frozen glass,
we may apply the criterion25 G > 4 as a condition of insignificant
exchange coupling between the paramagnetic Cu(II) centres,
where G = (gꢁ − 2)/(g⊥− 2). This is further substantiated by
magnetic measurements on 3 where the magnetic moment of 3
is 1.78 BM at 280 K and 1.95 BM at 80 K, essentially remaining
unchanged with temperature, confirming the above ESR data.
Speciation studies further confirm the presence of 1 : 1 L :
Ni, L1 : Ni, L : Zn and L1 : Zn species analogous to those
found in the solid-state in complexes 4, 7, 5 and 8 respectively.
In addition, both Pt derivatives, L and L1, are able to bind up to
two metal ions per Pt for Ni(II) and Zn(II) forming the species
LM2H−3 and L1M2H−3, respectively, where the metal ions are
(O,O)-coordinated by two hydroxamate moieties, Fig. 6. These
complexes were not observed for Cu.
construction of these novel polymeric structures. Speciation and
spectroscopic studies of related systems are also reported. The
crystal structure of one of the above polymers, {cis-[Pt(NH3)2(l-
3-pyha)Cu(l-3-pyha)]SO4·8H2O}n, the first example to date of
a Pt(II)/Cu(II) heterobimetallic pyridinehydroxamate-bridged
wave-like coordination polymer, is also reported. The presence
of peripheral hydrogen-bonding substituents on the hydroxamic
2−
acid moiety, the Pt-ammines and the SO4 counterions un-
doubtedly play a critical role in the assembly and topology of
the resulting polymer.
Acknowledgements
We thank Charles J. Harding for his invaluable help and
expertise with the ESR spectroscopic data and magnetic mea-
surements and Vijaya Velagapudi for her helpful assistance
(RCSI Summer Studentship). We also gratefully acknowledge
The Research Committee of the Royal College of Surgeons in
Ireland, Enterprise Ireland, EU COST D20, Dun-Laoghaire
Rathdown County Council, EU (ICA2-CT-2000-10052) and the
Programme for Research in Third Level Institutions (PRTLI),
administered by the HEA for funding.
References
1 J. L. Atwood, J. E. D. Davies, D. D. MacNicol, F. Vogtle and J.-M.
Lehn, Comprehensive Supramolecular Chemistry, vol. 9, Pergamon,
Oxford, 1996; J.-M. Lehn, Supramolecular Chemistry, Concepts and
Perspectives, VCH, Weinheim, Germany, 1995.
2 O. Costisor and W. Linert, Rev. Inorg. Chem., 2003, 23(4), 289.
3 A. Erxleben, Coord. Chem. Rev., 2003, 246, 203.
4 S. A. Barnett and N. R. Champness, Coord. Chem. Rev., 2003, 246(1–
2), 145.
5 A. N. Khlobystov, A. J. Blake, N. R. Champness, D. A. Lemenovskii,
A. G. Majouga, N. V. Zyk and M. Schro¨der, Coord. Chem. Rev., 2001,
222(1), 155.
6 H. Lang, A. del Villar, B. Walfort and G. Rheinwald, J. Organomet.
Chem., 2004, 689, 1464.
7 H. Lang, A. d. Villar and B. Walfort, Inorg. Chem. Commun., 2004,
7, 694.
8 C. J. Marmion, D. Griffith and K. B. Nolan, Eur. J. Inorg. Chem.,
2004, 3003–3016 and references therein.
9 B. R. Gibney and V. L. Pecoraro, in Inorganic Syntheses, vol. 33,
McGraw-Hill Book Company, Inc., New York, 2002, pp. 70-74; V. L.
Pecoraro, A. J. Stemmler, B. R. Gibney, J. J. Bodwin, H. Wang,
J. W. Kampf and A. Barwinski, in Prog. Inorg. Chem., vol. 45, ed.
K. Karlin, Pergamon Press, 1996, pp. 83-177.
10 A. J. Stemmler, J. W. Kampf, M. L. Kirk, B. H. Atasi and V. L.
Pecoraro, Inorg. Chem., 1999, 38, 2807.
11 E. M. Muri, M. J. Nieto, R. D. Sindelar and J. S. Williamson, Curr.
Med. Chem., 2002, 9, 1631–1653.
12 B. Lou and K. Yang, Mini Rev. Med. Chem., 2003, 3, 609–620.
13 C. J. Marmion, T. Murphy, J. R. Docherty and K. B. Nolan, Chem.
Commun., 2000, 1153–1154.
14 D. Griffith, K. L. Lyssenko, P. Jensen, P. E. Kruger and C. J.
Marmion, Dalton Trans., 2005, 956–961.
15 S. C. Dhara, Indian J. Chem., 1970, 8, 193.
16 G. Gran, Acta Chem. Scand., 1950, 4, 599.
17 A. Sabatini, A. Vacca and P. Gans, Coord. Chem. Rev., 1992, 120,
389–405.
Fig. 6 Species distribution for the L : Ni(II) where L is cis-[Pt(NH3)2-
(3-pyhaH)2]2+, pH 2–11, [Ni(II)] = 1 mM, [L] = 1 mM.
Furthermore, spectrophotometric studies carried out on the
L : Cu and L1 : Cu systems are consistent with the potentiometry
data described earlier where, at higher pH, deprotonation of the
hydroximate NH’s are observed (for L : Cu, pH = 4.3, kmax
765 nm, eav = 30 mol−1 cm−1; pH = 5.7, kmax = 645 nm, eav
130 mol−1 cm−1 and for L1 : Cu, pH = 4.4, kmax = 755 nm, eav
=
=
=
37.5 mol−1cm−1; pH = 4.8, kmax = 650 nm, eav = 108 mol−1cm−1).
18 H. Irving, M. G. Miles and L. D. Pettit, Anal. Chim. Acta, 1967, 38,
475.
We also recorded spectra for the L : Ni system (pH = 6.5, kmax
=
=
19 G. M. Sheldrick, SHELXTL-97, Programme for Solution and Refine-
ment of Crystal Structure, Bruker-AXS, Madison, WI, USA, 1997.
20 D. A. Brown, R. A. Coogan, N. J. Fitzpatrick, W. K. Glass, D. E.
Abukshima, L. Shiels, M. Ahlgren, K. Smolander, T. T. Pakkanen,
T. A. Pakkanen and M. Perakyla, J. Chem. Soc., Perkin Trans., 1996,
2, 2673.
21 J. Arpalahti and B. Lippert, Inorg. Chim. Acta, 1987, 138, 171–173.
22 E. Farkas, E. Kozma, M. Petho, K. M. Herlihy and G. Micera,
Polyhedron, 1998, 17, 3331–3342.
660 nm, eav = 8.75 mol−1cm−1; pH = 8.2, kmax = 660 nm, eav
13.5 mol−1cm−1, pH = 10.3, kmax = 660 nm, eav = 22.5 mol−1cm−1)
and for the L1 : Ni system (pH = 6.5, kmax = 670 nm, eav
=
6.75 mol−1cm−1; pH = 8.2, kmax = 670 nm, eav = 37.5 mol−1cm−1.
Precipitation occurred at higher pH at 2 mM concentration).
Conclusions
23 E. Farkas, H. Csoka, G. Micera and A. Dessi, J. Inorg. Biochem.,
1997, 65, 281–286.
In summary, we report the synthesis and characterisation of
novel Pt(II)/M(II) pyridinehydroxamate-bridged coordination
polymers where M is Cu, Ni or Zn, and where 3- or 4-pyha
have proven themselves to be versatile building-blocks for the
24 U. Sakagushi and A. W. Addison, J. Chem. Soc., Dalton Trans., 1979,
600.
25 B. J. Hathaway and D. E. Billing, Coord. Chem. Rev., 1970, 5, 143.
1 9 9 8
D a l t o n T r a n s . , 2 0 0 5 , 1 9 9 3 – 1 9 9 8