Binary zinc-oligophosphate complexes

Article abstract of DOI:10.1016/S0020-1693(99)00614-3

Diorganodiphosphates (DPP^2-), triorganodiphosphates (TPP^-), a diorganotriphosphate (DPPP^3-), and a triorganomethylenediphosphonate (TPCP^-) were reacted with zinc perchlorate to form the complex compounds Zn(DPP), Zn(TPP)₂, Zn₃(DPPP)₂, and Zn(TPCP)₂. Spectroscopic investigations and the solubility properties allow to assign Zn(DPP) and Zn₃(DPPP)₂ as coordination polymers, while Zn(TPP)₂ and Zn(TPCP)₂ are molecular complexes. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00614-3

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Inorganica Chimica Acta 300–302 (2000) 531–536
Binary zinc-oligophosphate complexes
A. Mu¨ller-Hartmann, H. Vahrenkamp *
Institut fu¨r Anorganische und Analytische Chemie der Uni6ersita¨t Freiburg, Albertstr. 21, D-79104 Freiburg, Germany
Received 15 November 1999; accepted 18 November 1999
Abstract
Diorganodiphosphates (DPP2−), triorganodiphosphates (TPP−), a diorganotriphosphate (DPPP3−), and a triorgano-
methylenediphosphonate (TPCP−) were reacted with zinc perchlorate to form the complex compounds Zn(DPP), Zn(TPP)2,
Zn3(DPPP)2, and Zn(TPCP)2. Spectroscopic investigations and the solubility properties allow to assign Zn(DPP) and Zn3(DPPP)2
as coordination polymers, while Zn(TPP)2 and Zn(TPCP)2 are molecular complexes. © 2000 Elsevier Science S.A. All rights
reserved.
Keywords: Zinc complexes; Diphosphate; Triphosphate; Spectra
We are interested in the biorelevant coordination
chemistry of zinc and thus feel attracted also to sys-
tems containing zinc-bound oligophosphates. The ear-
liest results in this field were the isolation and
spectroscopic characterization of Zn3(ADP)2 and
Zn2(ATP) [12]. Besides a number of zinc-pyrophos-
phate species [11] the structures of a triphosphate [13]
and a cyclotetraphosphate [14] were determined, fol-
lowed by the structures of zinc complexes with
H2ATP2− [15] and HATP3− [16] ligands. No zinc
enzyme containing metal-bound oligophosphate has
been structurally characterized yet. We have already
reported the cleavage of tetraorgano-diphosphates by
ZnꢀOH complexes which are inorganic models of zinc
enzymes [17].
We have now initiated a study of zinc-oligophos-
phate complexes, trying to contribute to an under-
standing of the binding and activation of biological
oligophosphates by zinc. We are using organic
oligophosphates instead of ATP, ADP or TPP, in or-
der to simplify the systems and to reduce the func-
tionality at the phosphate units. On the side of the
zinc ion we control the number of available coordina-
tion sites by using chelate ligands of varying haptic-
ity. This paper describes the simplest systems studied,
i.e. the binary compounds containing only zinc and
oligophosphate.
1. Introduction
All enzymes transferring phosphate units from
oligophosphates, e.g. ATPases, kinases, pyrophos-
phates, need metal ions for their function [1–5].
These are typically magnesium and calcium, but quite
often zinc is also essential or can take the role of the
former [6]. It suggests itself that during enzymatic ac-
tion the oligophosphate unit which has to be inter-
converted is coordinated to the metal ion or ions in
the active center. Support for this assumption comes
from structure determinations of such enzymes con-
taining metal-bound thiamine pyrophosphate (TPP)
[7,8], ADP [9], or inorganic pyrophosphate [10].
The coordination chemistry associated with these
phenomena, i.e. the study of metal-oligophosphate in-
teractions, has attracted attention earlier on. The
structural chemistry of metal oligophosphates is well
developed [11], and interactions between metal ions
and nucleotides or their constituents in solution have
been studied extensively [4], with heavy emphasis on
the omnipresent ATP.
* Corresponding author. Tel.: +49-761-203 6120; fax: +49-761-
203 6001.
E-mail address: vahrenka@uni-freiburg.de (H. Vahrenkamp)
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00614 -3

532
A. Mu¨ller-Hartmann, H. Vahrenkamp / Inorganica Chimica Acta 300–302 (2000) 531–536
2. Results and discussion
2.2. Zinc complexes
When the three diorganodiphosphates 1a–1c were
treated with zinc perchlorate in boiling methanol or
ethanol, they yielded the 1:1 complexes 2a–2c upon
cooling. 2a–2c are soluble at room temperature (r.t.)
only in very polar solvents like DMSO, but could be
recrystallized from the hot alcohols.
2.1. Anionic oligophosphates
The oligophosphates were chosen such that they bear
not more than one negative charge per phosphorus
atom. As a rule, but not throughout, aromatic sub-
stituents were used. Synthetic availability and, in the
end, purity of the resulting products dictated the choice
of the starting materials.
The simplest reagents were the diorganodiphosphates
1a–1c. The preparation of 1c from tetrabenzyl py-
rophosphate by hydrolysis using NaI in acetone has
been described before [18]. 1a and 1b are new. They
were obtained in analogy to the described procedure
[19] by condensation between the organophosphoric
acid and the organo(n-butylcarbamoyl)phosphate.
Zn[ROꢀPO2ꢀOꢀPO2ꢀOR]
2a: R=p-tolyl
2b: R=p-tert-butylphenyl
2c: R=benzyl
1:2 complexes of much better solubility were ob-
tained when the triorganodiphosphates 1d and 1e were
reacted with zinc perchlorate. The resulting species 2d
and 2e are soluble in ethyl acetate, and 2e was suscepti-
ble to FAB mass spectrometry from solution.
M2[ROꢀPO2ꢀOꢀPO2ꢀOR]
1a: M=Li, R=p-tolyl
Zn[(RO)2POꢀOꢀPO2ꢀOR]2
2d: R=benzyl
1b: M=Li, R=p-tert-butylphenyl
1c: M=Na, R=benzyl
2e: R=p-bromobenzyl
In order to use ligands with an even lower charge,
two triorganodiphosphates were employed. The two
benzyl derivatives 1d and 1e [18] resulted from the
corresponding tetraorganopyrophosphates by hydroly-
sis like 1c, using NaI in acetone.
The formation and solubility properties of the
diorganotriphosphate complex 2f, resulting from 1f and
zinc perchlorate in water, resemble those of the
diorganodiphosphate complexes 2a–2c. 2f has a good
solubility only in water, in which the NMR data,
however (see below) correspond to those of the free
ligand 1f.
Na[(RO)2POꢀOꢀPO2ꢀOR]
1d: R=benzyl
Zn3[ROꢀPO2ꢀOꢀPO2ꢀOꢀPO2ꢀOR]2
2f: R=p-tolyl
1e: R=p-bromobenzyl
As a representative of the triphosphates the new
bis(p-tolyl) ester 1f was chosen which is accessible by
condensation between POCl3 and two equivalents of
p-tolylphosphoric acid. Finally a monoanionic methyl-
enediphosphonate was employed: the triethyl ester 1g
[20] resulted from the commercially available tetraester
by hydrolysis with NaOH.
The methylenediphosphonate 1g turned out to be
most easily hydrolyzed in the presence of zinc salts. The
preparation of its zinc complex 2g in methanol there-
fore required strictly anhydrous conditions, but still the
product could not be obtained analytically pure. 2g is
soluble in most organic solvents, even in hydrocarbons.
Zn[(RO)2POꢀCH2ꢀPO2ꢀOR]2
2g: R=ethyl
Na3[ROꢀPO2ꢀOꢀPO2ꢀOꢀPO2ꢀOR]
1f: R=p-tolyl
Na[(RO)2POꢀCH2ꢀPO2ꢀOR]
1g: R=ethyl
2.3. Product identifications
Although most of the products 2 were obtained as
crystalline materials, none of them was suitable for
X-ray diffraction. Hence indirect evidence had to be
used for structural assignments. The simplest one is the
solubility of the compounds: only the derivatives of the
monoanionic triorganodiphosphates, 2d, 2e, and 2g, are
soluble in nonpolar organic solvents thereby pointing
to their molecular nature. For 2e and 2g it was shown
by mass spectrometry that they are monomolecular.
Of the organophosphates described here only the tri-
organodiphosphates are easily susceptible to hydrolytic
cleavage into the monophosphates in the presence of
water, even more so in the presence of divalent metal
ions. They therefore were handled accordingly. It was
observed, however, for all oligophosphates 1a–g that in
some cases their reactions with zinc salts produced
hydrolysis products in the reaction mixtures.

A. Mu¨ller-Hartmann, H. Vahrenkamp / Inorganica Chimica Acta 300–302 (2000) 531–536
533
The low solubility of all other complexes, which are
derived from dianionic oligophosphates, indicates that
they are oligonuclear or polymeric.
NMR resonances shift to more positive l values while
the 31P NMR resonances shift to more negative l
values upon coordination. In all cases the expected
multiplet patterns are observed, proving the identity of
the coordinated oligophosphates.
NMR data of all complexes could be obtained from
solutions in DMSO. It must be assumed that the poly-
mers break up in this solvent and that the molecular
complexes are partly dissociated. However, in all cases
the spectra of the free ligands and of the complexes
The IR spectra of oligophosphates are well investi-
gated [21], and some data for their zinc complexes have
been published [22,23]. The observations for the or-
ganic oligophosphates 1 and their complexes 2 are in
accord with these findings, cf. Table 2. The spectra are
dominated by intense bands due to PꢀO functions in
the 950–1300 cm−1 range. The two most intense of
these can be assigned to the terminal PꢀO units as given
in the table. As discussed previously [21–23], unam-
biguous assignments like the assignment for the
(RO)2PꢁO units in d, e, and g or for the symmetrical
and antisymmetrical stretch of the ROꢀPO2 units in all
ligands and complexes, cannot be made and superposi-
tions of the bands for the various PꢀO functions,
especially in the triphosphate derivatives f, must be
assumed. Nevertheless a consistent picture emerges
from the comparison of the data. In all but one cases
the highest frequency PꢀO band is shifted significantly
to lower frequencies while the position of the other
band varies irregularly and only by small amounts. In
all cases the PꢀOꢀP band loses so much intensity upon
coordination that it can no longer be assigned among
other bands of equally low intensity. This, in accor-
dance with the literature data [21–23], allows the con-
clusion that two neighbouring phosphate units of all
seven phosphate ligands are coordinated to zinc in the
solid state compounds, and it does not rule out the
possibility that more than two oxygen atoms of each
oligophosphate are coordinated.
1
differ slightly. Table 1 lists the data. As a rule the H
Table 1
NMR data (in DMSO-d6, data given as l [ppm]/J [Hz])
No. 1H NMR
31P NMR
1a
2a
1b
2b
1c
2c
1d
2d
1d
2d
1e
2e
1e
2e
1f
6.98m (C6H4), 2.21 (CH3)
7.02m (C6H4), 2.23 (CH3)
7.05m, 7.18m (C6H4), 1.25 (t-Bu)
7.05m, 7.25m (C6H4), 1.25 (t-Bu)
7.29m (C6H5), 4.79m (CH2)
−15.2
−17.6
−15.5
−17.5
−8.5
−11.8
−10.7/22.4
−11.4/28.9
−11.4/22.4
−12.2/18.9
−10.6/21.1
−11.1/19.0
−11.0/21.1
−11.8/19.0
−23.2t,
7.31m (C6H5), 4.90m (CH2)
(P(OR)2): 7.32m (C6H5), 5.03/7.6
(P(OR)2): 7.30m (C6H5), 5.06/8.0
(PꢀOR): 7.32m (C6H5), 4.83/7.8
(PꢀOR): 7.30m (C6H5), 4.89/8.0
(P(OR)2): 7.35m (C6H5), 5.00/7.6
(P(OR)2): 7.28m (C6H5), 5.03/7.3
(PꢀOR): 7.35m (C6H5), 4.77/7.6
(PꢀOR): 7.49m (C6H5), 4.85m
7.05m (C6H4), 2.20 (CH3)
−15.8d/18.4
−22.2t,
2f
7.01m (C6H4), 2.20 (CH3)
−15.8d/16.0
12.2/10.3
1g a (P(OR)2): 1.20/7.1(CH3), 4.01/7.1, 7.2
(OCH2)
2g b (P(OR)2): 1.35m (CH3), 4.06/7.2, 7.6
12.2/9.7
26.7/10.3
26.7/9.7
(OCH2)
1g a (PꢀOR): 1.09/7.1 (CH3), 3.70/7.0, 7.1
(OCH2)
2g b (PꢀOR): 1.35m (CH3), 3.87/7.2, 7.2
(OCH2)
3. Conclusions
a PꢀCH2ꢀP: 2.09t/20.1.
b PꢀCH2ꢀP: 2.34t/19.6.
In the purely inorganic zinc oligophosphates the zinc
ion is almost exclusively in a octahedral ZnO6 environ-
ment [11–16]. It seems unlikely to us that this is also
the case in all complexes described here. Our assump-
tion is based on the fact that almost always less than six
terminal PꢀO functions are available per zinc ion. Fur-
thermore we have crystallized a series of zinc complexes
bearing tridentate nitrogen donors and organodiphos-
phates as ligands, which contain five-coordinate or
tetrahedral zinc [24]. We therefore propose that the
species described here contain four- or five-coordinate
zinc and that the principal coordination pattern is that
of a chelating OꢁPꢀOꢀPꢁO attachment.
Table 2
IR data (in KBr, 6˜ in cm−1
)
No.
PꢁO
PO2
PꢀOꢀP
1a
2a
1b
2b
1c
2c
1d
2d
1e
2e
1f
1270
1216
12498
1230
1239
1258
1136
1128
1133
1129
1259
1233
1168
1146
1140
1148
1141
1137
1141
1140
963
927
936
968
974
967
968
1291
1259
1273
1260
Applied to the polymeric complexes 2a, b, and c this
means that one such chelating pattern per diphosphate
ligand as well as per zinc ion is possible and that the
two remaining PꢀO functions are used to bind to
neighbouring zinc ions thereby establishing the poly-
1151
1165
2f
1g
2g
1237
1213

534
A. Mu¨ller-Hartmann, H. Vahrenkamp / Inorganica Chimica Acta 300–302 (2000) 531–536
meric network. Additional ZnꢀO bonds are possible if
some of the PꢀO functions are used to bridge two zinc
ions. Likewise in the triphosphate derivative 2f two
chelating patterns are provided by each triphosphate
anion which may be used for the same or for two
different zinc ions, the remaining PꢀO functions being
available for linking up the polymeric network again.
Complexes 2d, e, and g which are likely to be molec-
ular allow a much simpler formulation which is given
below. Taking the monoanionic diphosphates as only
bidentate ligands we get tetrahedral coordination in
monomolecular species. Including the remaining termi-
nal PꢀO function as a donor would produce five or
six-coordinate zinc, most likely in the form of dinuclear
complexes. Again it must be said that we have proved
the bidentate coordination of the diphosphates for
LZn(diphosphate) complexes where L is a tridentate
nitrogen donor [24]. The bonding alternatives for 2d, e,
and g can be realized strain-free and correspond to
molecular entities with a predominantly organic exte-
rior, in accord with the observed solubility of the
complexes and their susceptibility to mass spectro-
metry.
1a: 877 mg (4.61 mmol) of p-tolyl-OꢀPO(OH)2 were
dissolved in a nitrogen atmosphere in 6 ml of anhy-
drous acetonitrile and 2 ml of pyridine. 1.800 g (4.61
mmol) of triethylammonium-N-butylcarbamoyl-O-p-
tolyl-phosphate were added and the mixture stirred at
40°C for 20 h. Then a solution of 391 mg (9.22 mmol)
of LiCl in 1.4 ml of water was added with stirring. The
precipitate which resulted after a few minutes was
filtered off and washed several times with small por-
tions of warm 1:1 acetone/ethanol and once with cold
acetonitrile. After drying in vacuo 1.07 g (52%) of
1a·pyridine remained which melts above 300°C. Anal.
Calc. for C14H14Li2O7P2·C5H5N (370.1+79.1): C,
50.80; H, 4.26; N, 3.12. Found: C, 49.83; H, 4.12; N,
3.10%.
1b: Like 1a from 2.41 g (10.45 mmol) p-t-butyl-
phenyl-OꢀPO(OH)2 and 4.50 g (10.45 mmol) of triethyl-
ammonium-N-butylcarbamoyl-O-p-t-butylphenyl-phos-
phate in 7 ml of anhydrous acetonitrile and 5.5 ml of
pyridine. Addition of 886 mg (20.90 mmol) of LiCl and
workup yielded 3.45 g (70%) of 1b which according to
NMR contained less than one equivalent of pyridine
per formula unit. In order to free the product from
pyridine 205 mg of it were dissolved in 100 ml of
boiling ethanol. The solution was reduced to 30 ml in a
rotary evaporator when 1b began to precipitate. Cool-
ing to −24°C, filtration and drying in vacuo left 39 mg
(19%) of analytically pure 1b·H2O, melting above
300°C. Anal. Calc. for C20H26Li2O7P2·H2O (454.3+
18.0): C, 50.87; H, 5.98. Found: C, 49.22; H, 5.67%.
1f: A suspension of 1.13 g (5.92 mmol) of p-tolyl-O-
PO(OH)2 in 20 ml of toluene was cooled to 0°C and
treated dropwise with stirring with 0.60 g (0.82 ml, 5.92
mmol) of triethylamine and 0.91 g (0.54 ml, 5.92 mmol)
of POCl3. After stirring for 1 day at r.t. another 0.60 g
(0.82 ml, 5.92 mmol) of triethylamine were added and
the mixture stirred for another 12 h. After filtration and
washing of the precipitate with toluene the filtrates were
hydrolyzed by stirring with 0.71 g (17.7 mmol) NaOH
in a few millilitres of water. After decanting the solu-
tion the remaining precipitate was dissolved in 10 ml of
boiling water. Layering with 40 ml of methanol pro-
duced 0.12 g of a precipitate which according to 31P
NMR contained four different phosphate derivatives.
The filtrate was concentrated in vacuo to 10 ml yielding
a second fraction (204 mg) of colourless crystals, con-
sisting mainly of Na2 (1a). Further concentration to 5
ml and layering with 20 ml of methanol resulting in the
precipitation of 1f. Recrystallization from 6 ml of water
and 42 ml of methanol yielded 0.56 g (36%) of 1f·H2O
which melts above 300°C. Anal. Calc. for
C14H14O10P3Na3·H2O (504.2+18.0): C, 32.20; H, 3.09.
Found: C, 32.50; H, 2.69%.
The present investigation has shown that binary zinc
complexes of organic oligophosphates can be obtained.
However, even the diorganodiphosphates which bear
only two negative charges are still too ‘inorganic’ to
allow the formation of simple (i.e. soluble or molecular)
compounds. In order to obtain complexes which are
better suited for NMR spectroscopy or crystallization
the organic content of the phosphates has to be in-
creased or the available coordination sites at the zinc
ions have to be decreased. We have been successful
with the latter approach, and subsequent papers in this
series will report on molecular (ligand)zinc(pyro-
phosphate) complexes.
4. Experimental
The general experimental methods and measuring
techniques were as in Ref. [25]. The precursors p-tolyl-
OꢀPO(OH)2
[28,29],
[26,27],
p-t-butylphenylꢀOꢀPO(OH)2
triethylammonium-(N-n-butylcarbamoyl)-
OPO2OR (R=p-tolyl, p-t-butylphenyl) [19] as well as
the known organo-oligophosphates 1c [18], 1d [18], 1e
[18] and 1g [20] were prepared according to the pub-
lished procedure.
2a: A suspension of 100 mg (0.22 mmol) of 1a·py in
90 ml of boiling ethanol was treated with stirring with

A. Mu¨ller-Hartmann, H. Vahrenkamp / Inorganica Chimica Acta 300–302 (2000) 531–536
535
a solution of 83 mg (0.22 mmol) of Zn(ClO4)2·6H2O
in 10 ml of boiling ethanol. After cooling to r.t. and
filtration the filtrate was slowly concentrated to about
one third in vacuo. The precipitate of 2a was filtered
off, washed with ethanol and recrystallized from 50
ml of hot ethanol, yielding 40 mg (42%) of 2a, m.p.
270°C (dec.). Anal. Calc. for C14H14O7P2Zn (421.6):
C, 39.89; H, 3.35; Zn 15.51. Found: C, 39.25; H,
3.88; Zn, 14.95%.
was added dropwise. After addition of 1 ml of hex-
ane the precipitate (mainly NaClO4) was filtered off.
The filtrate was evaporated to dryness and the residue
washed with a small amount of hexane, leaving be-
hind 29 mg (74%) of 2g, m.p. 45.50°C, which is
highly hygroscopic and was not analytically pure.
Anal. Calc. for C14H34O12P4Zn (583.7): C, 28.81; H,
5.87; Zn, 11.20. Found: C, 26.55; H, 4.95; Zn,
10.66%. ESI-MS: m/z=583.
2b: Like 2a from 88 mg (0.19 mmol) of 1b·H2O in
50 ml of boiling methanol and 70 mg (0.19 mmol) of
Zn(ClO4)2·6H2O in 10 ml of boiling methanol.
Workup and recrystallization from 30 ml of hot
methanol yielded 37 mg (39%) of 2b, m.p. 280°C
(dec.). Anal. Calc. for C20H26O7P2Zn (505.8): C,
47.50; H, 5.18; Zn, 12.93. Found: C, 46.63; H, 5.11;
Zn, 12.72%.
2c: Like 2a from 100 mg (0.25 mmol) of 1c in 50
ml of boiling methanol and 92 mg (0.25 mmol) of
Zn(ClO4)2·6H2O in 10 ml of boiling methanol. After
heating for 15 min and cooling to r.t. the resulting
precipitate was filtered off and washed with cold
methanol and a few millilitres of hot water. Drying in
vacuo yielded 60 mg (54%) of 2c·H2O, m.p. 178°C.
Anal. Calc. for C14H14O7P2Zn·H2O (421.6+18.0): C,
38.25; H, 3.67; Zn, 14.87. Found: C, 37.54; H, 3.57;
Zn, 14.94%.
Acknowledgements
This work was supported by the Deutsche
Forschungsgemeinschaft and the Fonds der Chemi-
schen Industrie. We thank Dr W. Deck, Dr J. Wo¨rth,
M. Tesmer and M. Gelinsky for the various spectra
and P. Klose for assistance in the lab.
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2d: A solution of 75 mg (0.16 mmol) of 1d in 30
ml of boiling ethanol was treated with a solution of
30 mg (0.08 mmol) of Zn(ClO4)2·6H2O in 30 ml of
ethanol. Upon cooling to r.t. the product precipitated
which was filtered off, washed several times with
ethanol and dried in vacuo, yielding 30 mg (39%) of
2d, m.p. 134°C. Anal. Calc. for C42H42O14P4Zn
(960.1): C, 52.54; H, 4.41; Zn, 6.81. Found: C, 52.18;
H, 4.41; Zn, 6.57%.
2e: Like 2d from 114 mg (0.16 mmol) 1e and 30
mg (0.08 mmol) of Zn(ClO4)2·6H2O. Yield 64 mg
(55%) of 2e, m.p. 140°C. Anal. Calc. for C42H36-
Br6O14P4Zn (1433.5): C, 35.19; H, 2.53; Zn, 4.56.
Found: C, 35.17; H, 2.52; Zn, 4.13%; FAB-MS (p-
nitrobenzylalcohol): m/z=1433.
2f: A solution of 100 mg (0.20 mmol) of 1f in 8 ml
of water was treated dropwise with stirring with a
solution of 111 mg (0.30 mmol) of Zn(ClO4)2·6H2O in
2 ml of water. Slow diffusion of acetone into this
solution produced a precipitate which was filtered off,
washed several times with small amounts of methanol
and dried in vacuo, yielding 60 mg (57%) of 2f,
which decomposes without melting above 225°C. Anal
Calc. for C28H28O20P6Zn3 (1066.5): C, 31.53; H, 2.65;
Zn, 18.39. Found: C, 31.40; H, 2.67; Zn, 18.03%.
2g: 38 mg (0.13 mmol) of carefully dried 1g were
dissolved in 1 ml of anhydrous methanol in a nitro-
gen atmosphere. A solution of 36 mg (0.067 mmol) of
Zn(ClO4)2·6H2O in 1.5 ml of anhydrous methanol
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