Synthesis, crystal structure and spectral properties of diammonium dihydrogen N-(methylene-2-pyridine)-N,N,-di-(methylenephosphonate)

Article abstract of DOI:10.1016/j.molstruc.2012.09.051

In this paper synthesis, crystal structure and spectral properties of a new, N-(methylene-2-pyridine)-N,N,-di-(methylenephosphonic) acid (hereinafter IV) are reported. The X-ray structure analysis revealed that in crystal of the ammonium dihydrogen N-(methylene-2-pyridine)-N,N-di(methylenephosphonate) (hereinafter V) two of the six oxygen atoms from phosphonic groups are protonated and form strong hydrogen bonds, moreover the N(pyridine) and N(amino) atoms are deprotonated. The acid-base properties of studied compound in aqueous solution indicated that the dissociation constants pK_1dis 0.70 ± 0.03 and pK_2dis 0.98 ± 0.05 are very similar to that determined for nitrilotri(methylphosphonic) acid.

Full text of DOI:10.1016/j.molstruc.2012.09.051

Journal of Molecular Structure 1036 (2013) 35–41
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, crystal structure and spectral properties of diammonium dihydrogen
N-(methylene-2-pyridine)-N,N,-di-(methylenephosphonate)
⇑
Rafał Janicki
Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
h i g h l i g h t s
"
"
Synthesis, X-ray structural and spectroscopic characterization of N-(methylene-2-pyridine)-N,N,-di(methylenephosphonic) acid are presented.
Lowest dissociation constants (unavailable with other methods) were determined.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 March 2012
Received in revised form 3 September 2012
Accepted 19 September 2012
Available online 2 October 2012
In this paper synthesis, crystal structure and spectral properties of a new, N-(methylene-2-pyridine)-
N,N,-di-(methylenephosphonic) acid (hereinafter IV) are reported. The X-ray structure analysis revealed
that in crystal of the ammonium dihydrogen N-(methylene-2-pyridine)-N,N-di(methylenephosphonate)
(hereinafter V) two of the six oxygen atoms from phosphonic groups are protonated and form strong
hydrogen bonds, moreover the N(pyridine) and N(amino) atoms are deprotonated. The acid–base prop-
erties of studied compound in aqueous solution indicated that the dissociation constants pK1dis
Keywords:
0.70 ± 0.03 and pK2dis 0.98 ± 0.05 are very similar to that determined for nitrilotri(methylphosphonic)
Aminophosphonic acid
Heterocyclic compound
X-ray crystal structure
NMR spectroscopy
Acid-base equilibria
acid.
Ó 2012 Elsevier B.V. All rights reserved.
1
. Introduction
Since the polyaminophosphonic acids were synthesized for the
The basic research of these compounds includes multi-faceted as-
pects, e.g. X-ray [5,7] and NMR [6,8] structural characterization,
photophysical properties (UV–Vis–NIR–IR) [5,7], thermodynamic
studies [2,4], theoretical calculations [3,9] as well as more
specialized investigations such as analysis of experimental electron
density distribution [3,9].
first time [1], interest in these compounds has continually been
growing [2]. Due to high basicity of the phosphonic oxygen atoms
[
3], phosphonic ligands interact with metal cations more strongly
than their carboxylic analogs, hence the stability constants of
metal phosphonates are often several orders greater than those
of carboxylates [4]. For this reason aminophosphonates are a
promising group of chelate ligands for d- and f-elements [5]. Such
compounds have been investigated for their biological activity
Several methods of synthesis of aminophosphonic acids are
known, but most of them are based on Mannich type reaction
(Scheme 1) [10].
The synthesis of these compounds is relatively difficult because
obtaining of the pure substance and then good quality single
crystals is not straightforword; it is often connected with high
solubility of their salts in aqueous solution.
Another important problem concerns the acid–base properties
of aminophosphonic acids in strong acidic solutions. As it was
shown previously the determination of the first dissociation
constants encounters some difficulties because of strong acidity
of the phosphonic groups [2,11]. On the other hand, such thermo-
dynamic parameters are important for quantitative understanding
of complexation equilibria of metal ions by these kind of ligands
and, furthermore, such studies may be very useful for determining
pH of the solution in which the ligand molecule starts to bind to
the metal ion. This is key information determining selection of an
[
2c,2l,5b], potential applications as MRI contrast agents [6] as well
as their photophysical properties [7]. However tailoring of the
compound with desired properties require addition of specifically
customized functional groups; for example substitution of one of
the phosphonic group by an aromatic substituent predispose such
a ligand to investigate its photoluminescence properties. Therefore
the polyaminophosphonic acids with specific chemical activity as
well as outstanding physical properties have been extensively sought.
⇑
Tel.: +48 71 375 7234; fax: +48 71 328 2348.
E-mail address: rafal.janicki@chem.uni.wroc.pl
0
022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.09.051

3
6
R. Janicki / Journal of Molecular Structure 1036 (2013) 35–41
Scheme 1. Aminoalkylphosphonic acids synthesis – Mannich–type reaction.
appropriate coordination model for studies of stability constants.
3
1
By using the P NMR spectroscopy some authors managed to
determine the lowest dissociation constants of the nitrilotri
(
methylphosphonic) acid (H
affinity toward transition metal cations and has been widely used
as scale inhibitors in industry [12]. The estimated values of pK1dis
.5 ± 0.2 and pK2dis = 1.0 ± 0.1 for H NTP confirm high acidity of
6
NTP) [11], which demonstrates high
=
0
6
aminophosphonates. It seems to be important to find out, whether
and to what extent the substitution of methylphosphonic group by
a group of another kind may affect the dissociation constants
values of polyphosphonic acid?
Therefore in this work the synthesis as well as structural and
6
spectroscopic studies of the new derivative of the H NTP acid, in
which one of the phosphonic groups was replaced by the
methylene-2-pyridine arm, are presented.
2 2
Fig. 1. Molecular structure of [H NP
py]2 anion together with atom labels.
ꢁ
2
. Results and discussion
Table 1
4 2 2 2
Selected bond lengths (Å) and angles (°) in (NH ) H NP py salt.
The synthesis of the aminophosphonic acid (IV) (Scheme 2) was
started from the reaction of 2-pyridinecarboxaldehyde (I) with
hydroxylamine hydrochloride. Next the prepared oxime was con-
verted into 2-(aminomethyl)pyridine (III) by the reduction with
hydrogen in statu nascendi in acetic acid (80%). Treatment of (III)
Bond
Distance (Å)
Angle (°)
P1–O1
P1–O2
P1–O3
P2–O4
P2–O5
P2–O6
P1–C1
P2–C2
N1–C1
N1–C2
N1–C3
N2–C8
N2–C4
C4–C9
C6–C7
C6–C9
C7–C8
C3–C4
1.5050(11)
1.4958(11)
1.5774(12)
1.4988(11)
1.5740(11)
1.5085(11)
1.8053(15)
1.8088(15)
1.4764(19)
1.4758(18)
1.4589(19)
1.342(2)
1.3383(19)
1.386(2)
1.380(2)
1.382(2)
1.380(2)
O2–P1–O1
O2–P1–O3
O1–P1–O3
O2–P1–C1
O1–P1–C1
O3–P1–C1
O4–P2–O6
O4–P2–O5
O6–P2–O5
O4–P2–C2
O6–P2–C2
O5–P2–C2
116.49(7)
107.99(7)
109.25(7)
109.09(7)
106.55(6)
107.09(7)
115.52(7)
107.49(6)
109.60(6)
111.43(7)
109.95(7)
101.93(6)
with formaldehyde and phosphonic acid (H
of hydrochloric acid gave N-(methylene-2-pyridine)-N,N-di
methylenephosphonic) acid (IV). Next to a metanolic solution of
3 3
PO ) in solution
(
N-(methylene-2-pyridine)-N,N-di(methylenephosphonic) acid aque-
ous solution of NH3(aq) was added and crystals of the ammonium
salt (V) were obtained.
2.1. Crystal structure
The compound with the formula (NH
4
)
2
pyCH
2
N(CH
2
PO
3
2
H )
2
(V)
crystallizes in the monoclinic P2
salt consist of ammonium cations and doubly protonated
phosphonic anions H L (Fig. 1). The selected bond lengths and
1
/c space group. The crystals of the
1.501(2)
2
angles are compared in the Table 1.
The elongation of P1–O3 and P2–O5 bonds (ꢀ0.07 Å) in compar-
rings interleaved with ones formed by phosphonic groups as well
as NH4 cations. The layers are parallel to the (010) plane (Fig. 2).
The crystal packing is determined mainly by the hydrogen
bonds O–Hꢂ ꢂ ꢂO and N–Hꢂ ꢂ ꢂO (Table 2). The strongest D–Hꢂ ꢂ ꢂA
interaction is observed between phosphonic oxygen atoms O5
and O1 from a neighboring molecule (2.580(2) Å).
þ
ison with the remaining P–O bonds indicates that the respective
ꢁ
oxygen atoms are protonated. The charges of both –CPO
2
(OH)
are compensated by two ammonium cations. The valence angles
2
3
ꢁ
of ꢁCPO groups change between 101.93(6)° and 116.49(7)°. In
the studied crystal one may distinguish layers composed of pyridyl
Scheme 2. Synthesis of 2-pyridinealdoxime – (II), 2-(aminomethyl)-pyridine – (III), N-(methylene-2-pyridine)-N,N,-di-(methylenephosphonate) acid – (IV), diammonium
dihydrogen N-(methylene-2-pyridine)-N,N,-di-(methylenephosphonate) – (V).

R. Janicki / Journal of Molecular Structure 1036 (2013) 35–41
37
py]2 anion along the ac diagonal [101] direction.
ꢁ
Fig. 2. The arrangement of the [H
2
NP
2
Table 2
Geometry of hydrogen bonds D–Hꢂ ꢂ ꢂA in (NH
these reasons the neighboring pyridine planes are inclined 30.8°
4 2 2 2
) H NP py.
(
see Figs. 2 and 3).
D–Hꢂ ꢂ ꢂA
O5–H5ꢂ ꢂ ꢂO1
O3–H3ꢂ ꢂ ꢂN2
D–H (Å)
Hꢂ ꢂ ꢂA (Å)
D ꢂ ꢂ ꢂ A (Å)
D–Hꢂ ꢂ ꢂA (°)
The hydrogen bonds together with rather weak
(distance between the centers of the rings about 4.09 Å) give rise
to a bonded network observed in the crystal structure of V.
p p stacking
ꢂ ꢂ ꢂ
(
i)
0.82(2)
0.72(3)
0.94(2)
0.89(2)
0.91(2)
0.87(2)
0.89(2)
0.88(2)
0.92(2)
0.85(2)
1.79(2)
1.98(3)
1.79(2)
1.88(2)
2.03(2)
2.11(2)
1.95(2)
2.20(2)
1.84(2)
2.01(2)
2.580(2)
2.699(2)
2.713(2)
2.768(2)
2.842(2)
2.953(2)
2.796(2)
3.022(2)
2.748(2)
2.850(2)
162
177
166
176
149
164
158
154
171
169
(
ii)
(
(
(
(
(
(
(
(
iii)
N3–H32ꢂ ꢂ ꢂO2
N4–H44ꢂ ꢂ ꢂO2
N3–H31ꢂ ꢂ ꢂO4
N3–H34ꢂ ꢂ ꢂO4
N4–H41ꢂ ꢂ ꢂO1
N4–H42ꢂ ꢂ ꢂO4
N4–H43ꢂ ꢂ ꢂO6
N3–H33ꢂ ꢂ ꢂO6
iv)
v)
vi)
iii)
iv)
vii)
iv)
2.2. NMR spectroscopy (studies in solution)
The proton spectra consist of six groups of signals with intensity
ratio 1:1:1:1:2:4. The signals at 8.51, 7.92, 7.55, 7.44, 4.57 and
3
.15 ppm, at pH = 6.25, correspond to positions of 6, 4, 3, 5,
and b, respectively, as it was shown in Fig. 4.
The determined coupling constants of hydrogen pyridine group
a
Symmetry operations: (i) x, 3/2 ꢁ y, 1/2 + z; (ii) ꢁx, 1 ꢁ y, ꢁz; (iii) x, y, z; (iv) x, 1/
2
ꢁ y, ꢁ1/2 + z; (v) 1 ꢁ x, 1/2 + y, 1/2 + z; (vi) x, 1 + y, z; (vii) 1 ꢁ x, 1 ꢁ y, ꢁz.
3
4
5
are as follows:
J
H6–H5 = 5.4 Hz
J
H6–H4 = 1.6 Hz,
J
H6–H3 ꢀ 1.5 Hz,
3
4
H5–H3 = 2.2 Hz and 3JH4–H3 = 6.4 Hz. Their values
J
H5–H4 = 7.7 Hz, J
The analysis of the nitrogen N1 – neighbor atom distances and
are rather typical for pyridine derivatives [15].
the overall network of the hydrogen bonds may suggest that N1
atom is deprotonated, as otherwise expected from the crystal elec-
troneutrality condition. Interestingly in spite of that the basicity
N–amino atoms are usually higher that N–pyridyl and O–phosphonic
atoms [13] in studied crystals both phosphonic groups are
protonated and the N2(pyridyl) atom forms hydrogen bond with
an oxygen atom while the N1(amino) atom is deprotonated. If
the N1(amino) atom was protonated the distance between H9
and hipotetical H(amino) would be too small (about 2 Å).
The resonance of methylene protons H splits into a doublet by
b
2
4
coupling with phosphorus
JHb–P = 11.2 Hz
JHa–P < 1 Hz at
pH = 6.25. Generally the chemical shift of Hi=3,4,5,6 pyridyl protons
undergoes a upfield transition (Fig. 5).
Among the observed pyridyl protone signals the H and H are
4
5
especially sensitive to pH variation hence may corresponds to
deprotonation of pyridyl nitrogen atom which occur at about
pH ꢀ 5–6. This result is consistent with potentiometric and spec-
troscopic data obtained for 6-phosphonopyridine-2-carboxylic
acid and -3-carboxylic acid and (pyridyl-2-ylmethyl)-phosphonic
acid for which deprotonation of the pyridyl ring nitrogen occurs
2 6
Neutronographic structure of K H EDTMP salt (where EDTMP –
ethylenediaminotetra(methylenephosphonate) anion) indicates
that similarly deprotonated N(amino) atoms exist in K
crystal [14].
Because of the rotation freedom of the pyridyl group around the
single C3–C4 bond the N2 atom may form the hydrogen bond with
O3 from the phosphonic group belonging to an adjacent anion. For
2
H
6
EDTMP
between pH 3 and 6 [16].
Also the coupling constants J
of solution as it was shown in Fig. 6. The largest J
observed between pH 3–6 and 10.5–14, what may be connected
with deprotonation of O(PO ) and N(amino) atoms, respectively.
2
Hb–P
is sensitive to changes of pH
2
Hb–P
changes are
2
3
ꢁ

3
8
R. Janicki / Journal of Molecular Structure 1036 (2013) 35–41
4 2 2 2
Fig. 3. The selected hydrogen bonds in (NH ) H NP py crystal.
Fig. 4. 1H NMR spectra of (NH
) H NP py salt in D O at pH 6.25.
4 2 2 2 2
6
Fig. 6. pH dependence of coupling constants of methylene protons H signal.
(3
coupling with two equivalent phosphorus ( J
Cb–Pb a
J = 4.9 Hz). The C resonance splits into a triplet (1:2:1) by
0
3
C
a
–P = 4.36 Hz). Both
JC–P are similar with these observed in
1
3
values of
J
C–P and
1
ethylenediaminotetra(methylephosphonic) acid (EDTMP) ( JC–P
=
3
1
30.9 Hz and JC–P = 4.4 Hz) [17].
3
1
In the P NMR spectra the resonance line splits into a triplet
peak with the intensity 1:2:1 by coupling with two protons H of
b
the adjacent methylene groups. The phosphorus resonance line be-
comes a singlet peak by complete decoupling with the protons and
indicates that both phosphonic groups are equivalent.
The observed spectral pattern of studied compound (six reso-
1
31
nances in H NMR spectra, one signal in P NMR and seven in
1
3
C NMR) indicates that the symmetry of studied molecule is C
S
.
The chemical shift of phosphorus signal varies with the pH
following an approximately parabolic pattern, due to acid–base
equilibria in the aqueous solution (Fig. 8).
The chemical shift of 31P undergoes upfield transition from
3 4 5 6
Fig. 5. The chemical shifts of pyridyl protons H , H , H , and H as a function of pH.
1
7.98 ppm at pH 1.3–6.77 ppm at pH = 8.18 and next a downfield
transition at higher pH values of solution. It is caused by the depro-
tonation of phosphonic groups in the pH range 0–8 and then by
probable binding of counteraction(s) such as Na , K at higher pH
(P8). On the other hand the influence of deprotonation of N(amino)
atoms cannot be excluded due to strong intramolecular hydrogen
In the spectra of 13C NMR 7 resonances is observed (Fig. 7). The
methylene C resonance splits into a doublet (1:1) by coupling
with adjacent P
doublet by three-bond coupling with the neighboring P
+
+
b
1
b
nucleus ( JCb–Pb = 133.5 Hz) and splits into a
atom
0
b

R. Janicki / Journal of Molecular Structure 1036 (2013) 35–41
39
Fig. 7. 13C NMR spectra in D
O at pH 6.25.
2
Fig. 8. pH dependence of 31P chemical shift.
Fig. 9. 31P NMR titration curve of NP py.
2
2
ꢁ
of HClO
c < 2.5 M pK
strength I = 2.5 M by the addition of appropriate amounts of
NaClO
In this pH range the dissociation of two protons from
phosphonic group(s) should be expected. The shape of the titration
curve strongly suggests that both dissociation constants are very
similar.
4
is valid at concentration used in these experiments
bonding formation between N(amino) and O(PO3 ) atoms. This
behavior is rather typical for aminophosphonates with N–C–P skel-
eton [18].
(
a
ꢃ ꢁ10) [19]. All solutions were prepared with ionic
4
.
The analysis of the experimental and theoretical electron den-
sity distribution studies in aminomethylphosphonates [3] and
methylphosphonates [9b] indicates that covalent P–O bonds are
highly polarized, moreover the protonation of oxygen atom gives
rise to increased polarization of the P–O bond (50% for P–O(depro-
tonated) and 60% for P–O(H)). Obviously, the protonation of
oxygen atom usually causes the elongation of P–O bond (ꢀ5% in
studied compounds), as it was shown above. The variation of elec-
tron density distribution near the P–O bonds results in the change
of the phosphorus atom shielding, and consequently changes of P
resonance chemical shift. Hence at higher pH of solution the P res-
½HLꢄ
H þ L $ HL b1 ¼
¼ K
1
ð1Þ
ð2Þ
½Hꢄ ꢂ ½Lꢄ
½H Lꢄ
2
2
H þ L $ H
2
L
b2 ¼
¼ K
1
ꢂ K
2
2
½
Hꢄ ꢂ ½Lꢄ
2
The next third dissociation constant for analogous phosphonic
onance line shifts to lower fields and the coupling constants JHb–P
compounds is at least one or two orders larger, therefore when cal-
culating the first two dissociation constants the higher ones may
increase.
For estimation of the two first dissociation constants the 31P
NMR the titration of V between pH ꢁ0.5 and 1.5 were carried
out (Fig. 9).
The total concentration of the salt was 0.011 M. The hydrogen
ion concentration was varied by addition of appropriate amount
of perchloric acid. It is worth to note that complete dissociation
P
2
be neglected. The minimization the sum of ðdexp ꢁ dcalc
Þ
using
the following Eq. (3) leads to determination of the b
1
and b
2
values.
2
d
L
þ ½Hꢄ ꢂ b ꢂ dHL þ ½Hꢄ ꢂ b ꢂ dH2
L
1
2
d
calc
¼
ð3Þ
2
1
þ ½Hꢄ ꢂ b þ ½Hꢄ ꢂ b
1
2

4
0
R. Janicki / Journal of Molecular Structure 1036 (2013) 35–41
the solvent was evaporated under the reduced pressure. 1H NMR
CDCl , 300 MHz) d (ppm): 8.6 (6), 8.34 ( ), 7.82 (3), 7.71 (4),
.27 (5), C NMR (CDCl , 300 MHz) d (ppm): 152.0 (2), 149.9 (6),
149.3 ( ), 137.7 (4), 124.4 (5), 121.5 (3).
Table 3
Protonation and dissociation constants of NP
phonic) acid).
2
py and NTP (nitrilotri(methylphos-
(
7
3
a
13
3
NP
2
py
NTP [11b]
a
b
b
1
2
9.62 ± 0.013
48.2 ± 0.012
0.70 ± 0.03
0.98 ± 0.05
4.2. Synthesis of 2-(aminomethyl)-pyridine(III)
pK1dis
pK2dis
0.5 ± 0.2–1.1 ± 0.2
1.0 ± 0.1–1.2 ± 0.2
The crude 2-pyridinealdoxime (II) was dissolved in 30 ml of 80%
acetic acid, next 6 g of metallic Zn was added and the whole was
stirred at ꢀ40 °C for 48 h under reflux. Next the insoluble residue
was filtered away and the solution was alkalized to pH ꢀ14 using
The best fit of the data set were obtained for the following
chemical shifts of L, HL and species: = 15.25 ppm,
HL = 16.3 ppm and dH2 = 19.8. The determined values of b and
are compared in the Table 3. The obtained values of pKdys are
H
2
L
d
L
3
NaOH, then the amine was extracted using CHCl (POCH). Next the
d
b
L
1
amine was extracted using the concentrated hydrochloric acid
36%, POCH). The solution was evaporated under the reduced pres-
2
(
close to that for nitrilotris(methylenephosphonic) acid (NTP) re-
ported by Grossmann et al. [11b].
sure and the solid residue (crude 2-(aminomethyl)-pyridine
hydrochloride) was recrystalised four times from hot ethanol.
The changes of chemical shift of 31P resonance above pH 1.5
The yellow white 2-(aminomethyl)-pyridine hydrochloride
1
(Fig. 8) indicate that the next steps of IV acid deprotonation occur
powder was obtained with the yield 2.99 g, 73%. H NMR (D
2
O,
between pH 2–3 and 4–7. Above the pH > 8.2 deprotonation of the
phosphonic groups is complete.
3
C
00 MHz) d (ppm): 8.65 (6), 8.15 (
a), 7.71 (3), 7.66 (4), 4.42 (5).
6 12 2
H N
calc.: C 39.78, H 5.52, N 15.47; found: C 39.1, H 5.2, N 15.7.
4
.3. Synthesis of N-(methylene-2-pyridine)-N,N-
3
. Conclusions
di(methylenephosphonic) acid (IV)
The structural (X-ray) and spectroscopic (NMR) properties of V
0
.5 g (4.8 mmol) of 2-(aminomethyl)pyridine (AMpy) were
were investigated. The reported crystal structure results indicate
that the studied compound is in the form of diprotonic H L acid.
mixed together with appropriate amounts of H PO (Aldrich)
3
3
2
and HCl solution (cHCl ꢀ 6 M) and heated under the reflux. Next,
small portion of paraformaldehyde (Sigma Aldrich) was added.
The temperature of reaction was 120–125 °C. The resulting
aminomethylphosphonic acid was isolated by standard procedures
described in literature [10]. The P NMR were used to monitor
quantitatively the course of the reaction.
Both phosphonic groups are monoprotonated as manifested by
elongation of P–OH bond lengths of about 0.07 Å, in comparison
with the remaining P–O bonds. The analysis of the nitrogen
(
N1(amino)) – neighbor atom distances and the network of the
3
1
hydrogen bonds suggests that the N1(amino) atom is
L]2ꢁ anion is compensated by
2
deprotonated. The charge of [H
two ammonium cations.
III
H
2
CO
H
3
PO
3
Time
(h)
Yield
(%)
Temp.
(°C)
The NMR studies of aqueous solution of V indicate that both
phosphonic groups are equivalent and the spectral pattern sug-
gests that the symmetry of the molecule of IV is C . The studied
s
(
mmol) (mmol)
(mmol)
4.8
4.8
4.8
4.8
9.6
9.6
9.6
3
24
3
45
50
52
57
120–
1
25
acid potentially possesses 6 protonation sites (four at oxygen
atoms from phosphonic groups and two at nitrogen atoms). Below
9.6
14.4
14.4
120–
125
120–
3
1
the pH = ꢁ0.5 the H
6
L acid is completely protonated. The P NMR
14.4
14.4
titration between pH ꢁ0.5 and 1.5 indicate that the first two disso-
ciation constants are pK1dis = 0.70 ± 0.03 and pK2dis = 0.98 ± 0.05.
These results may suggest that the coordination of synthesised li-
1
25
24
120–
125
3
+
gand to Ln cations may begin around pH 0.5–2.
The next steps of dissociation occur between pH 2–3 and 4–7.
Above the pH > 8.2 deprotonation of the phosphonic groups is
complete. The observed changes of chemical shifts of pyridyl pro-
tons suggest that the deprotonation of pyridyl nitrogen atoms oc-
4.4. Preparation of crystals (V)
cur between pH 5 and 6.
2
A solution of IV was alkalized with NH3(aq) solution to pH
around 11. Next the mother solution was evaporated and concen-
trated to about one-fifth of the staring volume and the hot CH OH
was added until the resulting precipitate stopped to redissolve. The
colorless triangular prisms of (NH (pyCH )N(CH PO were
formed during slow evaporation of the solution after 2 months.
calc.: H 6.1, N 17.0, found: H 6.0, N 16.9.
The increase of the
JHb–P coupling constants together with pH
31
as well as the observed changes of P NMR chemical shifts above
pH ꢀ8 possibly arise from deprotonation of N(amino) atoms. In
spite of that in crystal of V the N(amino) atoms are deprotonated
in aqueous solution in broad pH range (ꢁ0.5 to 10) the N(amino)
atoms are protonated; the difference is probably brought about
by different conformations of the compound in solution and in
the crystalline state.
3
4
)
2
2
2
3 2 2
H )
8 20 4 6 2
C H N O P
4.5. Single-crystal X-ray diffraction analysis
4
. Experimental section
The appropriate crystal was cut from a larger one and mounted
on a Kuma KM4 diffractometer equipped with a CCD counter. The
collected data were corrected for polarization, Lorentz, and absorp-
tion, the last of which was calculated from the crystal habit
that was captured from the photo scans. The structure was
solved routinely with direct methods. The positions of the
C(methylene)-bonded hydrogen atoms were calculated geometri-
cally, the C-(pyridine), O- and N-bonded H atoms were found from
4
.1. Synthesis of 2-pyridinealdoxime (II)
Pyridinecarboxaldehyde (I) 2.2 g (0.021 mol) was dissolved in
4
1
2 3
5 ml of H O/CH OH 1:2 solution. Next potassium carbonate
.59 g (0.011 mol) and hydroxylamine hydrochloride 1.45 g
(
0.021 mol) was added. The mixture was refluxed for 24 h, then

R. Janicki / Journal of Molecular Structure 1036 (2013) 35–41
(f) A. Clearfield, Curry. Opin. Solid St. Mat Sci. 6 (2002) 495–506;
41
a difference Fourier map and were refined freely. The refinement
(
(
(
g) A. Mondry, R. Janicki, Dalton Trans. (2006) 4702–4710;
h) A. Clearfield, J. Alloys Compd. 418 (2006) 128–138;
was full-matrix with all of the non-H atoms anisotropic. All of
the computations were performed with the SHELXS97 and SHEL-
XL97 programs [20]. The molecular graphics were prepared with
XP program [21].
i) E.D. Naydenova, P.T. Todorov, K.D. Troev, Amino Acids 38 (2010) 23–30;
(j) J.W. Walton, L. Di Bari, D. Parker, G. Pescitelli, H. Puschmann, D.S. Yufit,
Chem. Comm. 45 (2011) 12289–12291;
(
l) J. Gal e˛ zowska, E. Gumienna-Kontecka, Coord. Chem. Rev. 256 (2012) 105–
24.
[3] R. Janicki, P. Starynowicz, Acta Cyst. B66 (2010) 559–567.
4] (a) T. Kiss, J. Balla, G. Nagy, H. Kozłowski, J. Kowalik, Inorg. Chim. Acta 1 (1987)
5–30;
b) T. Kiss, E. Farkas, H. Kozłowski, Inorg. Chim. Acta 155 (1989) 281–287;
(c) T. Kiss, I. Lázár, P. Kaflarski, Metal-Based Drugs 1 (1994) 247–264.
1
4.6. Summary of crystallographic data
[
2
(
C H
8 20
N
4
O
P
6 2
1
, monoclinic, space group P2 /c, a = 14.3830(14),
b = 8.0306(7), c = 13.2769(15) Å, b = 109.802(12)°, Z = 4,
d
calc
=
=
rI):
ꢁ3
[5] (a) A.D. Sherry, J. Ren, J. Huskens, E. Brücher, E. Tóth, C.F.C.G. Geraldes, M.M.C.A.
Castro, W.P. Cacheris, Inorg. Chem. 35 (1996) 4604–4612;
1
0
R
.520 gꢂcm , 10183 reflections collected, 3475 unique (Rint
.0261), data/parameters: 3475/237, final indices (I_2
= 0.0310, wR = 0.0776, final R indices (all data): R = 0.0427,
R
(
b) T. Kiss, I. Lazar, in: P.V. Kukhar, H.R. Hudson (Eds.), Aminophosphonic and
Aminophosphinic Acids: Chemistry and Biological Activity, Wiley, New York,
000, p. 285;
(c) J. Gał e˛ zowska, R. Janicki, A. Mondry, R. Burgada, T. Bailly, M. Lecouvey, H.
Kozłowski, Dalton Trans. (2006) 4384–4394.
2
1
1
2
2
wR = 0.0803, goodness of fit: 1.030, highest and deepest residual
ꢁ3
ꢁ3
electron density: 0.45e Å , ꢁ0.29e Å
.
CCDC – 864221 these data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
[6] A.L. Tiwari, H. Ojha, A. Kaul, A. Dutta, P. Srivastava, G. Shukla, R. Srivastava, A.K.
Mishra, Chem. Biol. Drug Des. 74 (2009) 87–91.
[
7] (a) J.-G. Mao, Coord. Chem. Rev. 251 (2007) 1493–1520;
(
(
b) R. Janicki, A. Mondry, Polyhedron 27 (2008) 1942–1946;
c) J. Gał e˛ zowska, R. Janicki, H. Kozlowski, A. Mondry, P. Młynarz, L. Szyrwiel,
4
.7. NMR measurements
Eur. J. Inorg. Chem. (2010) 1696–1702.
[
[
8] K.M. Bła z_ ewska, T. Gajda, Tetrah. Assym. 20 (2009) 1337–1361.
9] (a) H. Krawczyk, Ł. Albrecht, J. Wojciechowski, W.M. Wolf, Tetrahedron 64
2 2 2
The spectra of the H NP py (c = 5.7 mM I = 0.1 M KCl) in D O at
(
2008) 5051–5054;
different pH values were recorded on a Bruker AMX 300, Bruker
Avance 500 MHz and Bruker Avance III 600 MHz at 298 K. 5%
(b) A. Mermer, P. Starynowicz, Acta Cryst. Sec. B B67 (2011) 399–408.
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11] (a) K. Popov, E. Niskanen, H. Rönkkömäki, L.H.J. Lajunen, New J. Chem. 23
[
[
3 4 2
H PO (POCH) and dioxan in D O (Aldrich) solutions were used
(
1999) 1209–1213;
31
13
as an external standards in P NMR and C NMR measurements,
respectively. The pH of solutions was adjusted by addition of HCl
(b) G. Grossmann, K.A. Burkov, G. Hägele, L.A. Myund, S. Hermes, C. Verwey,
S.M. Arat-ool, Inorg. Chim. Acta 357 (2004) 797–808.
[
12] (a) K. Sawada, M. Kuribayashi, T. Suzuki, H. Miyamoto, J. Sol. Chem. 20 (1991)
´
(
Swierk) or NaOH (POCh). For NMR titrations under conditions of
constant volume (2.00 ml) and ionic strength (I = 2.5 M, NaClO
the series of 27 aqueous solutions of IV (0.011 M) contained ꢅ M
HClO and 0.1 ml D O were prepared.
, (2.5 ꢁ x) M NaClO
829–839;
4
)
(b) A. Cabeza, X. Ouyang, C.V.K. Sharma, M.A.G. Aranda, S. Bruque, A. Clearfield,
Inorg. Chem. 41 (2002) 2002–2325;
(
c) M. Siek, D. Kołody n´ ska, Z. Hubicki, Ind. Eng. Chem. Res. 49 (2010) 4700–
4
4
2
4709.
[
13] G. Kortum, W. Vogel, K. Andrussow in Dissociation Constants of Organic Acids
in Aqueous Solution Butterworth, London, 1961, pp. 474–492.
14] R. Janicki, P. Starynowicz, in preparation.
15] E. Pretsch, T. Clerc, J, Seibl, W. Simon in Tabellen zur Strukturaufklärung
organischer Verbindungen mit spectroscopischen Methoden, Springer, New
York, 1976, pp. H115.
16] B. Boduszek, M. Dyba, M. Je z_ owska-Bojczuk, T. Kiss, H. Kozłowski, J. Chem. Soc.
Dalton Trans. (1997) 973–976.
17] K. Sawada, T. Miyagawa, T. Sakaguchi, K. Doi, J. Chem. Soc. Dalton (1993)
Acknowledgement
This work was supported by MNiSW 2273/M/WCH/12.
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