Mononuclear lanthanide complexes with tetradentate bis(phosphorylamino)- substituted 1,8-naphthyridine ligand: Synthesis and structural studies

Article abstract of DOI:10.1016/j.ica.2011.12.010

The complexes of 2,7-bis(diphenylphosphorylamino)-1,8-naphthyridine (L) with lanthanide nitrates Ln(NO₃)₃ (Ln = Nd, Lu) were investigated to elucidate the coordination ability of a novel type of potentially tetradentate ligands - bis

Full text of DOI:10.1016/j.ica.2011.12.010

Inorganica Chimica Acta 384 (2012) 266–274
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Mononuclear lanthanide complexes with tetradentate
bis(phosphorylamino)-substituted 1,8-naphthyridine ligand:
Synthesis and structural studies
a
a
b
Anna G. Matveeva a, , Tat’yana V. Baulina , Zoya A. Starikova , Mikhail S. Grigor’ev ,
⇑
Zinaida S. Klemenkova a, Sergey V. Matveev a, Larissa A. Leites a, Rinat R. Aysin a, Eduard E. Nifant’ev a
a Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul. Vavilova 28, Moscow 119991, Russian Federation
b Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskii prospekt 31, Corp. 4, Moscow 119991, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 August 2011
Received in revised form 28 November 2011
Accepted 8 December 2011
Available online 16 December 2011
The complexes of 2,7-bis(diphenylphosphorylamino)-1,8-naphthyridine (L) with lanthanide nitrates
Ln(NO3)3 (Ln = Nd, Lu) were investigated to elucidate the coordination ability of a novel type of poten-
tially tetradentate ligands – bis(phosphorylamino) substituted naphthyridines. Mononuclear complexes
of 1:1 and 1:2 composition, namely, [Nd(L)(NO3)3] (1a), [Nd(L)(NO3)3]ꢀH2O (1b), [Lu(L)(NO3)2(H2O)](NO3)
(2), [Nd(L)2(NO3)2(H2O)](NO3) (3), [Lu(L)2(NO3)(H2O)](NO3)2ꢀ0.75CH3CNꢀH2O (4a) and [Lu(L)2(NO3)
(H2O)](NO3)2 (4b) were synthesized and studied by IR, Raman, and 31P NMR spectroscopy in solid state
and in solution. Structures of the complexes 1b and 4a were determined by X-ray diffraction. According
to X-ray crystallography, vibrational spectroscopy and C, H, N, P elemental analysis data in solid 1:1 com-
plexes one neutral molecule of L serves most likely as O,O,N,N-tetradentate ligand while in the 1:2
complexes only one ligand molecule coordinates in the same O,O,N,N-tetradentate fashion, and the sec-
ond one serves as O-monodentate one. In solution the coordination mode of the ligand is preserved in all
complexes.
Keywords:
Bis(phosphorylamino)-1,8-naphthyridine
O,O,N,N-ligand
Lanthanide(III) complexes
X-ray crystallography
Vibrational spectroscopy
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
context, systems that form complexes with the f-block elements
are of special interest [7].
Derivatives of aromatic N-heterocycles attract attention of
researchers in different fields of contemporary chemistry, medi-
cine, and material science owing to their capability to bind and
strongly retain metal ions, including rare earth. The design of
ligand systems comprising N-heterocycle with additional donor
groups offers new prospects for the efficient and selective extrac-
tion of trivalent lanthanides and actinides [1], and promotes the
development of novel organolanthanide electroluminiphores [2],
and lanthanide complexes for biomedical [3] and analytical appli-
cations [4].
The derivatives of 1,8-naphthyridine with coordination-active
groups (phosphino, phosphoryl, carbonyl, or nitrogen-containing
donors) at 2- or 2,7-positions of naphthyridine ring are intensely
studied as chelating agents [5]. The ligand cavity of such polyden-
tate compounds provides a possibility to form mono-, bi-, and
poly-nuclear complexes depending on the nature of metal and
donor groups as well as the length and nature of linkers between
these donor centers and the naphthyridine moiety [6]. In this
In the course of our investigation of lanthanide(III) complexa-
tion by some naphthyridine-based ligands [8–10], the molecule
of 2,7-bis(diphenylphosphorylamino)-1,8-naphthyridine (L) attracted
our attention because its architecture (a flexible framework)
allows various possibilities of coordination to cations. Although
this ligand was synthesized previously [11], but its coordination
properties were not studied yet.
Here in, we report certain properties of ligand L, namely, its
capacity to self-association by hydrogen bonding and coordination
behavior toward lanthanide cations. Lanthanides were chosen for
several reasons: in particular, in order to study fundamental
features of 4f-elements complex formation, and to determine the
coordination mode of the studied ligand. Moreover, many lantha-
nide complexes show a number of interesting and useful proper-
ties that allow one to use them as catalysts, molecular sensors,
electroluminescent devices, and NMR shift reagents [7]. The refer-
ence metals used were neodymium and lutetium located in the
middle and at the end of lanthanide series. Furthermore, neodym-
ium is often used as a typical cation in studies of lanthanides, while
lutetium cation is not paramagnetic, that makes it possible to use
NMR spectroscopy for studying its compounds.
⇑
Corresponding author. Tel.: +7 499 135 93 66; fax: +7 499 135 50 85.
E-mail address: phoc@ineos.ac.ru (A.G. Matveeva).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.12.010

A.G. Matveeva et al. / Inorganica Chimica Acta 384 (2012) 266–274
267
The mixture was concentrated in vacuo (ꢁ5 Torr) down to ꢁ3 mL.
The precipitate formed was filtered off, washed with diethyl ether,
and dried in vacuo (1 Torr) at 120 °C, and then dissolved in
acetonitrile. White microcrystalline powder was obtained by slow
isothermal evaporation, collected by filtration, and dried in vacuo
at ambient temperature to give 0.0657 g (70%) of [Lu(L)(NO3)2-
H2O](NO3) (2). Decomposition temperature >202 °C. Anal. Calc.
for C32H28LuN7O12P2: C, 40.91; H, 3.00; N, 10.44; P, 6.59. Found:
C, 41.18; H, 2.92; N, 10.29; P, 6.60%.
2. Experimental
2.1. Materials
Salts Nd(NO3)3ꢀ6H2O (Fisher Scientific Company), and
Lu(NO3)3ꢀxH2O (Aldrich) were used without further purification.
The water content (x = 3) in commercial lutetium nitrate was
determined experimentally. The solvents were purified and dried
using standard techniques [12]. Deuterated solvents (CD3CN,
CDCl3, (CD3)2SO) manufactured by the Prikladnaya Khimiya FGUP
Russian Research Center, St. Petersburg, were used as received.
Solutions for spectral studies (c = 0.02 or 0.01 M) were prepared
by volumetric/gravimetric method.
2.2.4. [Nd(L)2(NO3)2(H2O)](NO3) (3)
To a stirred solution of L (0.0448 g, 0.08 mmol) in chloroform
(4 mL), a solution of Nd(NO3)3ꢀ6H2O (0.0175 g, 0.04 mmol) in ace-
tonitrile (1 mL) was added dropwise at room temperature. The
mixture was concentrated in vacuo (ꢁ5 Torr) down to ꢁ3 mL. The
precipitate formed was filtered off, washed with diethyl ether,
and dried in vacuo (1 Torr) at 120 °C, and then dissolved in aceto-
nitrile. White microcrystalline powder was obtained by slow iso-
thermal evaporated, collected by filtration, and dried in vacuo
(1 Torr) at 120 °C to give 0.0469 g (80%) of [Nd(L)2(NO3)2(H2O)]
(NO3) (3). Decomposition temperature >240 °C. Anal. Calc. for
2.2. Preparations
2.2.1. 2,7-Bis(diphenylphosphorylamino)-1,8-naphthyridine (L)
The ligand L was obtained by the reaction of 2,7-diam-
inonaphthyridine with diphenylchlorophosphinate in the presence
of triethylamine in boiling chloroform as described previously [11].
As distinct from the previously published data [11], we detected
only decomposition temperature rather than melting temperature
(with decomposition) of the reaction product. Our 31P NMR spec-
trum (CDCl3 solution) and signal assignment in 1H NMR spectrum
(CDCl3 solution) differed slightly from the data of [11], although
there is no doubt about the structure of the obtained compound.
Yield: 70%, decomposition temperature >320 °C (from ethanol-
hexane) [lit. m.p. (with decomp.) 321–323 °C (from ethanol)
C64H54N11NdO14P4: C, 52.32; H, 3.70; N, 10.49; P, 8.43. Found: C,
51.85; H, 3.53; N, 10.30; P, 8.20%.
2.2.5. [Lu(L)2(NO3)(H2O)](NO3)2ꢀ0.75CH3CNꢀH2O (4a) and
[Lu(L)2(NO3)(H2O)](NO3)2 (4b)
To a stirred solution of L (0.0448 g, 0.08 mmol) in chloroform
(4 mL), a solution of Lu(NO3)3ꢀ3H2O (0.0175 g, 0.04 mmol) in aceto-
nitrile (1 mL) was added dropwise at room temperature. The mix-
ture was concentrated in vacuo (ꢁ5 Torr) down to ꢁ3 mL. The
precipitate formed was filtered off, washed with diethyl ether,
and dried in vacuo (1 Torr) at 120 °C, and then dissolved in aceto-
nitrile. Colorless crystals of 4a, including transparent ones suitable
for X-ray diffraction studies, were obtained by slow isothermal
evaporation at room temperature. Yield: 0.0434 g, 70%. Anal. Calc.
for C65.50H58.25LuN11.75O15P4: C, 50.79; H, 3.79; N, 10.63; P, 8.00.
Found: C, 51.01; H, 3.63; N, 10.58; P, 8.16%.
A drying of the crystals of 4a (0.0200 g, 0.0129 mmol) in vacuo
(1 Torr) at 120 °C led to a white microcrystalline powder 4b, which
composition according to the elemental analysis data correspond
to the formula [Lu(L)2(NO3)(H2O)](NO3)2. Yield: 0.0193, 92%.
Decomposition temperature >231 °C. Anal. Calc. for C64H54Lu-
N11O14P4: C, 51.24; H, 3.63; N, 10.27; P, 8.26. Found: C, 51.38; H,
3.41; N, 10.28; P, 8.28%. The vibrational spectra of 4b in the region
of ligand and nitrato groups vibrations were identical to those of
4a, with the exception of the IR bands and the Raman lines of out-
er-sphere solvent molecules (acetonitrile and water).
[11]]. 1H NMR (CDCl3, 0.02 M, d/ppm, J/Hz): 6.97 (d, br, 2H, 4,5-
4
Hnapy
(t, 4H, p-HPh
,
3JH,H = 8.5); 7.41 (td, 8H, m-HPh
,
3JH,H = 7.3, JH,H = 3.2); 7.48
,
3JH,H = 6.8); 7.55 (d, br, 2H, 3,6-Hnapy
,
3JH,H = 8.8);
3
7.87 (dd, 8H, o-HPh
,
3JH,P = 12.5, JH,H = 7.1). 1H NMR (DMSO-d6,
0.02 M, d/ppm, J/Hz): 7.06 (d, br, 2H, 4,5-Hnapy
7.66 (m, 12H, m-HPh, p-HPh); 7.73–7.87 (m, 8H, o-HPh); 7.94 (d,
,
3JH,H = 7.3); 7.38–
br, 2H, 3,6-Hnapy,
3JH,H = 8.5); 9.35 (d, br, 1H, NHP(O), JH,H = 7.6).
3
31P NMR (CDCl3, 0.02 M, d/ppm, W1=2/ppm): 20.6 (s, br, 1.2). 31P
NMR (DMSO-d6, 0.02 M, d/ppm, W1=2/ppm): 17.3 (s, br, 0.2).
The substance is practically insoluble in nitromethane, acetoni-
trile and sparingly soluble in chloroform, alcohol, and DMSO.
2.2.2. [Nd(L)(NO3)3] (1a) and [Nd(L)(NO3)3]ꢀH2O (1b)
A solution of Nd(NO3)3ꢀ6H2O (0.0438 g, 0.1 mmol) in acetoni-
trile (2 mL) was added dropwise to a stirred solution of ligand L
(0.0560 g, 0.1 mmol) in chloroform (5 mL) at room temperature.
The mixture was concentrated in vacuo (ꢁ5 Torr) down to volume
of ꢁ4 mL. The precipitate formed was filtered off, washed with
diethyl ether, and dried in vacuo (1 Torr) at 120 °C, and then dis-
solved in acetonitrile. Resulting whity-pink microcrystalline pow-
der was collected by filtration and dried (120 °C) in vacuo
(ꢁ1 Torr) to give 0.0790 g (89%) of [Nd(L)(NO3)3] (1a). Decomposi-
tion temperature >210 °C. Anal. Calc. for C32H26N7NdO11P2: C,
43.15; H, 2.94; N, 11.01; P, 6.95. Found: C, 43.35; H, 2.99; N,
11.21; P, 7.00%. The complex 1a was characterized by vibrational
spectra, which were identical to those of 1b except for the IR bands
of water solvent molecules.
2.3. X-ray crystallography
Single-crystal X-ray diffraction experiments were carried out
with a Bruker KAPPA APEX II CCD (1b) and a Bruker APEX II CCD
(4a) diffractometers with monochromated Mo K
a radiation at
295 and 100 K, respectively. Reflection intensities were integrated
using SAINT software [13]. The structure of complex 1b was solved
and refined with a twinned crystal. The contribution of the second
domain (BASF parameter) was 0.421. Absorption correction for 1b
was made using TWINABS program [14]. Absorption correction for 4a
was made using semi-empirical method SADABS [13].
The structures were solved by direct method and refined by
full-matrix least-squares against F2 in anisotropic (for non-hydro-
gen atoms) approximation [13]. Hydrogen atoms H(Ow) in 1b
and disordered MeCN molecules in 4a were not located, however,
these H atoms were included in molecular formula and moiety for-
mula. Hydrogen atoms H(N) (in 1b and 4a) and H(Ow) (in 4a) were
located from difference Fourier maps and refined in isotropic
Light lilac monocrystals of 1b suitable for X-ray diffraction stud-
ies were obtained by ultra slow diffusion of diethyl ether into a
nitromethane solution of 1a. Yield: 0.0395 g, 50%. Anal. Calc. for
C32H28N7NdO12P2: C, 42.29; H, 3.11; N, 10.79; P, 6.82. Found: C,
42.35; H, 3.00; N, 10.90; P, 6.90%.
2.2.3. [Lu(L)(NO3)H2O](NO3) (2)
A solution of Lu(NO3)3ꢀ3H2O (0.0415 g, 0.1 mmol) in acetonitrile
(1.5 mL) was slowly added dropwise to a stirred solution of L
(0.0560 g, 0.1 mmol) in chloroform (4 mL) at room temperature.

268
A.G. Matveeva et al. / Inorganica Chimica Acta 384 (2012) 266–274
Table 1
Crystal data and structural refinement details for [Nd(L)(NO3)3]ꢀH2O (1b) and [Lu(L)2(NO3)(H2O)](NO3)2ꢀ0.75CH3CNꢀH2O (4a).
1b
4a
Empirical formula
Mr
T (K)
C
32H28N7NdO12P2
C65.50H58.25LuN11.75O15P4
1548.84
100(2)
908.79
293(2)
Scan mode
Crystal system
Color of crystals
Habit of crystals
Space group
a (Å)
u
- and
x
-scan
x-scan
triclinic
colorless
plate
Pbar1
17.5397(17)
monoclinic
lilac
prism (fragment)
P21/n
11.0208(5)
b (Å)
21.9413(9)
20.9060(19)
c (Å)
16.1977(7)
21.676(2)
a
(ꢀ)
90.00
67.432(2)
b (ꢀ)
97.215(2)
81.825(2)
c
(ꢀ)
90.00
3885.8(3)
4
1.553
1.486
65.780(2)
6692.4(11)
2
1.537
1.646
V (Å3)
Z
qc (gcmꢂ3
l
)
(mmꢂ1
)
Crystal size (mm)
F(000)
0.24 ꢃ 0.18 ꢃ 0.14
0.35 ꢃ 0.25 ꢃ 0.15
1820
3138
2hmax (ꢀ)
60.00
50.00
hkl range
ꢂ15 < h < 15, ꢂ30 < k < 30, ꢂ22 < l < 22
ꢂ20 < h < 20, ꢂ24 < k < 24, ꢂ25 < l < 25
Date/restraints/parameters
Independent reflections (Rint
Completeness
25118/0/488
25118 (0.0591)
0.988
23502/14/1727
23502 (0.1153)
0.997
)
Reflections collected
97801
57747
Independent reflections [I > 2
r(I)]
14362
0.890
12201
1.017
Goodness of fit on F2
R1, wR2 [I > 2
r
(I)]
0.0472, 0.0990
0.1002, 0.1118
1.39, ꢂ0.67
0.0537, 0.0884
0.1071, 0.1368
2.539, ꢂ1.758
R1, wR2 (all data)
Largest diff. peak/hole (eÅꢂ3
)
approximation with constrained NH and HO distances. The H(C)
atoms in 1b and 4a were placed in geometrically calculated posi-
tions and refined in isotropic approximation in riding model with
the Uiso(H) parameters equal to n Ueq(Ci), where U(Ci) are respec-
tively the equivalent thermal parameters of the atoms to which
corresponding H atoms are bonded, n = 1.2 for CH and CH2 groups,
n = 1.5 for CH3 groups.
Crystal data and structure refinement parameters are listed in
Table 1. CCDC 833989 (1b), and 833962 (4a) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif.
Elemental analyses were made in the Laboratory of Microanal-
ysis, Nesmeyanov Institute of Organoelement Compounds, Russian
Academy of Sciences.
3. Results and discussion
3.1. 2,7-Bis(diphenylphosphorylamino)-1,8-naphthyridine (L)
The molecule of the ligand L (Scheme 1) contains four donor
atoms that can participate in complex formation: two phosphoryl
oxygens and two nitrogen atoms of naphthyridine ring.
At the same time, the presence of two NH groups along with
two phosphoryl groups and two nitrogen atoms of naphthyridine
ring makes this molecule favorable for hydrogen bondings. As
shown in [15–17], the phosphoryl- and carbonyl-containing naph-
thyridines to the studied ligand L are associated via hydrogen
bonds both in the solid state and in solutions, thus, similar hydro-
gen bonds can be expected for L. In fact, the N–H. . .O@P bonding is
evidenced by the broadened signals in 1H and 31P NMR spectra (see
Section 2), low-frequency shifts in the IR spectra, poor solubility of
2.4. Measurements
1H and 31P{1H} NMR spectra were recorded on a Bruker Avance
TM-400 spectrometer operating at 400.13 and 161.98 MHz, respec-
tively, using the residual signals of the protons of deuterated sol-
vents as an internal reference (1H) and 85% H3PO4 as an external
standard (31P). We failed to detect the signals of neodymium com-
plexes 1a and 3 in 31P {1H} NMR spectra on account of considerable
signal broadening probably owing to paramagnetic properties of
the cation.
L
in aprotic polar solvents, and its high decomposition
temperature.
IR spectra in the region 400–3700 cmꢂ1 were recorded using a
Nicolet Magna IR-750 FTIR spectrometer. The samples were KBr
pellets, mulls in Nujol and hexachlorobutadiene as well as
0.01 M solutions (CHCl3, CDCl3, CD3CN and CH3CN) in NaCl and
CaF2 cuvettes.
The IR spectrum of the solid ligand L shows a m(P@O) band at
1171 cmꢂ1 and a
m
(NH) band at 3136 cm–1, these values being
shifted compared to those of the free groups [18]. In the spectrum
of 0.01 M solution of L in CDCl3, the bands of P@O and N–H vibra-
tions appear at higher frequencies at 1210 and 3380 cmꢂ1
,
Raman spectra of the solid samples were obtained in the region
200–3700 cm–1 using a Jobin–Yvon LabRAM 300 last-generation
laser Raman spectrometer equipped with a microscope and a
cooled CCD detector. Excitation was accomplished at 632.8 nm
with a He-Ne laser with 10 mW output power.
The identity of crystalline samples used for X-ray investigation
and for recording vibrational spectra was checked with a Bruker
Apex 2 diffractometer.
O
P
O
P
Ph
Ph
Ph
Ph
N
H
N
N
N
H
Scheme 1. Ligand L.

A.G. Matveeva et al. / Inorganica Chimica Acta 384 (2012) 266–274
269
respectively, while the bands of the naphthyridine moiety remain
almost unchanged (Table 2). It should be noted that an akin com-
pound containing Ph2P(O)NH fragment, namely, Ph2P(O)NH[–
C@CMeNMeNPhC(O)–], according to X-ray diffraction in solid
state exists as dimers united by NH. . .O@C bonds, and its IR spec-
trum shows the
When the compound is dissolved,
3370 cmꢂ1, the frequency of P@O group remains constant [19].
m
(P@O) band of the free P@O group at 1210 cmꢂ1
(NH) changes from 3150 to
.
m
Thus, it is evident that the molecules of L in the solid state are
associated via intermolecular N–H. . .O@P hydrogen bonds while
both N-atoms of naphthyridine moiety remain intact.
The goal of present work is to study the coordination proper-
ties of a new ligand L toward lanthanide cations, to determine
the composition of the resulting complexes as well as their struc-
tures in the solid state and in solutions.
The reaction of L with lanthanide nitrates Ln(NO3)3 (Ln = Nd,
Lu) at metal/ligand molar ratios of 1:1 and 1:2 leads to the forma-
tion of complexes 1a–4b isolated as solids. They were studied by
the IR, Raman, and 31P NMR spectroscopy. The structures of the
complexes 1b and 4a were also elucidated by X-ray diffraction.
The parameters of vibrational spectra for the complexes 1b–4a
in comparison with the data for the free ligand L are given in
Table 2.
3.2. Complexes of 1:1 composition
Complexes Ln(L)(NO3)3ꢀnH2O (Ln = Nd, Lu, n = 0, 1) are readily
formed at the reactant ratio of 1:1. A crystalline complex 1b with
composition Nd(L)(NO3)3ꢀH2O was isolated on crystallization of
the complex [Nd(L)(NO3)3] (1a) from nitromethane, the structure
of 1b was established by X-ray diffraction. The crystal structure of
1b contains separate neutral complexes [Nd(L)(NO3)3] and sol-
vate water molecules (Fig. 1).
Ligand molecule is coordinated to central neodymium cation
in O,O,N,N-tetradentate fashion, and three nitrate ions are coordi-
nated in a chelated fashion. The coordination number of neodym-
ium cation is 10: eight oxygen atoms and two nitrogen atoms. If
each nitrato group is considered to occupy one coordination posi-
tion, then the coordination polyhedron of neodymium atom can
be described to a first approximation as a distorted pentagonal
bipyramid, whose equatorial plane is formed by two oxygen
atoms O(1), O(2) and two nitrogen atoms N(2), N(3) of ligand
molecule as well as the midpoint O6(7) between the coordinated
oxygen atoms of nitrate group O(6)ꢀ ꢀ ꢀO(7) (Fig. 2). Maximal devi-
ation of equatorial atoms of the coordination polyhedron from
their least-squares plane is 0.45 Å for O(1), average deviation is
0.33 Å. Two other nitrato groups occupy apical positions.
Solvate water molecule in the structure of 1b forms a hydro-
gen bond with one of the NH groups of the coordinated ligand
molecule (Fig. 1). Hydrogen bond parameters are as follows:
r(Nꢀ ꢀ ꢀO) = 2.888(3) Å, r(Hꢀ ꢀ ꢀO) = 2.06 Å, angle (N–H...O) = 162.5°.
Several bond distances for 1b are presented in Table 3. Geometri-
cal parameters of the ligand molecule are typical for this class of
compounds [8,15,20,21].
The IR spectrum of complex 1b (Table 2) does not show any
band in the region typical for free P@O group (ꢁ1210 cmꢂ1).
The single band corresponding to the P@O bond stretching is ob-
served at 1162 cmꢂ1, which evidences the equivalence of both
coordinated P@O groups in this complex. The IR band at
ꢁ1540 cmꢂ1 corresponding to vibrations of non-coordinated
naphthyridine ring is absent, while the higher frequency region
to where the band of the coordinated naphthyridine moiety
should be shifted [8,9,22] is obscured by the intense absorption
of other groups of the ligand. The bands of the NO3 groups appear
at 1480 and 1320 cmꢂ1, that corresponds to their bidentate coor-
dination [23]. Absorption of the solvate water molecule appears

270
A.G. Matveeva et al. / Inorganica Chimica Acta 384 (2012) 266–274
Fig. 1. Structure of the neutral complex 1b. The thermal ellipsoids are given at 30% probability level.
HN
P
N
N
O
NH
P
Ph
Ph
Ph
Ph
O
O
n
Ln
Ln
H
O
O
H
m
N
O
Scheme 2. Complexes 1a,b (Ln = Nd, n = 3, m = 0), and complex cation 2 (Ln = Lu,
n = 2, m = 1).
spectrum of the complex 1b are recorded at 1400 and 810 cmꢂ1
,
being shifted to the high-frequency region by 23–25 cmꢂ1, which
is typical for the coordination of both nitrogen atoms to lanthanide
cation [8,9].
In the IR spectrum of the acetonitrile solution of 1b the bands of
the P@O and nitrate groups are virtually unchanged, the free naph-
thyridine bands are absent. This data allows to conclude that the
neutral complex [Nd(O,O,N,N-L)(O,O-NO3)3] retains its structure
in solution (Scheme 2).
Fig. 2. Visualization of the distorted pentagonal bipyramidal environment around
NdIII in 1b. One nitrate group N(6)O(6)O(7)O(8) is presented as one point O6(7)
(midpoint between the coordinated oxygen atoms of nitrate group O(6). . .O(7)).
The main difference between the IR spectra of solid lutetium
complex 2 and neodymium complex 1b is the presence in the for-
mer one of a band of free nitrate ion at 1345 cmꢂ1 and a band of
metal-coordinated water at 3200 cmꢂ1 [23]. According to these
data, compound 2 has most likely a structure of cationic complex
[Lu(O,O,N,N-L)(O,O-NO3)2(H2O)](NO3), in which the ligand shows
maximal tetradentate coordination, and the inner coordination
sphere includes also two chelate nitrate ions and one water mole-
cule (Scheme 2). The coordination number of lutetium in the com-
plex cation is equal to nine.
In the IR spectrum of the acetonitrile solution of 2, the bands of
the P@O groups and those related to coordinated and free nitrate
groups are virtually unchanged, and there is no vibrational band
of the free naphthyridine moiety. In the 31P {1H} NMR spectrum
of 2 a broadened signal of coordinated1 phosphoryl groups is
Table 3
Selected bond lengths (Å) for the structure 1b.
Bond
(Å)
Nd1–O1
Nd1–O2
Nd1–N2
Nd1–N3
Nd1–O3(NO3)
Nd1–O4(NO3)
Nd1–O6(NO3)
Nd1–O7(NO3)
Nd1–O9(NO3)
Nd1–O10(NO3)
P1–O1
2.426(2)
2.388(2)
2.646(2)
2.658(2)
2.566(2)
2.583(2)
2.559(2)
2.587(2)
2.554(2)
2.658(2)
1.494(2)
1.491(2)
P2–O2
1
Unfortunately, the ligand L is virtually insoluble in acetonitrile. However, by
analogy with the related compounds one can expect that in this solvent the signal of L
in 31P {1H} NMR spectrum should be in the range 17–20 ppm. Upon coordination with
Lu(NO3)3, the signal of phosphoryl-containing ligands is usually shifted downfield by
ꢁ10–12 ppm [24,25]. For example, the 31P {1H} NMR spectrum of complex 4a (see
below) shows the signal of the free P@O group at 17.4 ppm (W1=2 ¼ 0:3 ppm), while
the signal of the coordinated one is detected at 31 ppm (W1=2 ¼ 2:3 ppm).
in the range of
overlaps that of the free
m
(OH) vibrations at 3500–3400 cmꢂ1. This region
m(NH) bands. We managed to detect this
band at 3402 cmꢂ1 only in the IR spectrum of anhydrous complex
1a after careful removal of solvate water. The lines of coordination-
sensitive vibrations of naphthyridine moiety in the Raman

A.G. Matveeva et al. / Inorganica Chimica Acta 384 (2012) 266–274
271
Fig. 3. Complex cations A (left) and B (right) in the structure of compound 4a. The thermal ellipsoids are given at 50% probability level. Phenyl rings are represented as one
atom (Ph), the hydrogen atoms of the naphthyridine fragments are omitted for clarity.
Table 4
Selected bond lengths (Å) for the structure 4a.
Bond
Cation A (Ln = Lu1)
Cation B (Ln = Lu2)
Ln–O1/O10
2.212(5)
2.266(5)
2.201(4)
2.464(6)
2.485(6)
2.216(5)
2.403(5)
2.383(5)
1.508(5)
1.482(5)
1.490(5)
1.479(5)
2.202(6)
2.252(5)
2.196(4)
2.496(6)
2.441(6)
2.232(5)
2.425(5)
2.371(5)
1.516(6)
1.490(5)
1.482(5)
1.491(5)
Ln–O2/O20
Ln–O3/O30
Ln–N2/N20
Ln–N3/N30
Ln–O1W/O2W
Ln–O5/O50(NO3)
Ln–O6/O60(NO3)
P1/P10–O1/O10
P2/P20–O2/O20
P3/P30–O3/O30
P4/P40–O4/O40
#
#
HN
N
N
NH
Ph
Ph
Ph
Ph
P
P
O
O
O
O
Ln
Ln
#
NH
P
H
Fig. 4. Comparison of the two independent cations A (Lu1) b B (Lu2) present in the
structure of compound 4a, demonstrating the difference in the turns of aromatic
fragments. Hydrogen atoms are omitted for clarity.
*
Ph Ph
O
O
H
*
N
*
N
O
n
N
*
Thus, at the ratio M:L = 1:1, the reaction of the ligand with
lanthanide nitrates leads to the formation of mononuclear com-
plexes where the ligand exhibits maximal O,O,N,N-tetradentate
coordination. The number of nitrate groups and water molecules
coordinated by lanthanide cation varies when passing from
neodymium to lutetium, the latter is known to have smaller coor-
dination sphere (see Scheme 2).
*
O
#
P
NH
Ph Ph
Scheme 3. Complex cations present in the structures of 3 (Ln = Nd, n = 2) and 4a,b
(Ln = Lu, n = 1). The sign ⁄ designates atoms participating in the formation of
intramolecular hydrogen bonds, the sign # designates atoms participating in the
formation of intermolecular hydrogen bonds.
3.3. Complexes of 1:2 composition
detected at 30 ppm (W1=2 ¼ 2 ppm). In accordance with these data,
we can suppose the presence of an equilibrium between the complex
The reaction of ligand L with lanthanide nitrates at 1:2 ratio
leads to complexes 3, 4a,b that have Ln(L)2(NO3)3ꢀnSolv
cation [Lu(O,O,N,N-L)(O,O-NO3)2]+ and free ion NO3 in solution.
ꢂ

272
A.G. Matveeva et al. / Inorganica Chimica Acta 384 (2012) 266–274
Fig. 5. Drawings of complex cations A (left) and B (right) demonstrating the H-bonds in the structure 4a. Phenyl rings are represented as one atom (Ph), the hydrogen atoms
of naphthyridine fragments are omitted for clarity.
composition, where Solv is a solvent molecule (water, acetonitrile)
and Ln = Nd, Lu. The structure of lutetium complex 4a with compo-
sition Lu(L)2(NO3)3ꢀ0.75CH3CNꢀ2H2O was established by X-ray
diffraction.
matic fragments of the ligand (Fig. 4) and different number of in-
tra- and intermolecular hydrogen bonds that stabilize the
corresponding conformation (see Fig. 5).
In cation A, one of the hydrogen atoms of the coordinated water
molecule forms a bifurcated hydrogen bond with both nitrogen
atoms of the naphthyridine fragment of the monocoordinated li-
gand molecule. This is in contrast with the cation B (Fig. 5) where
a ‘‘normal’’ H-bond is formed with only one of the naphthyridine
nitrogen atoms: O2W–H2W2ꢀ ꢀ ꢀN60. Moreover, the structure of
the cation A comprises four intermolecular H-bonds between the
NH groups and the oxygen atoms of NO3– counterions and the sol-
vate water molecules, while the structure of the cation B contains
only three such H-bonds, one NH group remaining free. The X-ray
parameters of the hydrogen bonds are shown in Table 5.
The crystal of 4a contains two crystallographically independent
complex cations [Lu(L)2(NO3)H2O]2+ (designated further as A and
B) that differ insignificantly in their structure (Fig. 3), as well as
–
NO3 anions and solvate molecules of water and acetonitrile. The
main bond distances are given in Table 4.
Both complex cations contain two coordinated ligand mole-
cules, one molecule has O,O,N,N-tetradentate coordination to lute-
tium, while another molecule shows monodentate coordination via
oxygen atom of one of the P@O groups. The coordination polyhe-
dron is supplemented by oxygen atoms of a water molecule and
those of
a
nitrate group coordinated in
a
bidentate mode:
To a first approximation, the coordination polyhedron of lute-
tium in both complex cations of structure 4a can be represented
as a distorted pentagonal bipyramid. The equatorial plane of the
bipyramid is formed by five atoms N(2),N(3),O(1),O(2),O(3) that
are coplanar ( 0.2 Å). Two nitrogen atoms N(2), N(3) and two oxy-
gen atoms O(1), O(2) are provided by one ligand molecule, and one
{LuO6N2}. The coordination number of lutetium in both complex
cations equals to eight (see Fig. 3 and Scheme 3). The lengths of
coordination bonds in complexes A and B are close to each other
(Table 4), the main difference consists in the orientation of the aro-
Table 5
Hydrogen bonds for structure 4a [Å and °].
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
<(DHA)
O1W–H1W1...O4#1
O1W–H2W1...N6#1
O1W–H2W1...N7#1
N1–H1N...O3W#1
N4–H4N...O11S#2
N5–H5N...O9S#1
0.85
0.85
0.85
0.90
0.90
0.90
0.90
0.85
0.85
0.90
0.90
0.90
0.85
0.85
0.85
0.85
0.85
1.85
2.11
2.36
1.90
1.90
2.03
2.30
1.90
2.09
1.88
2.05
2.22
2.22
2.18
1.96
2.24
2.24
2.650(8)
2.944(8)
2.982(8)
2.793(9)
2.76(1)
2.84(1)
2.950(9)
2.707(8)
2.906(9)
2.779(9)
2.84(1)
2.94(1)
2.97(1)
2.76(1)
2.77(1)
2.93(1)
3.09(1)
156
168
130
170
160
149
128
159
162
173
146
136
147
124
157
137
179
N8–H8N...O6S#3
O2W–H1W2...O40#1
O2W–H2W2...N60#1
N40–H40N...O3S#4
N50–H50N...O9S#5
N80–H80N...O6S#6
O3W–H2W3...O4S#3
O3W–H1W3...O100#1
O4W–H1W4...O110#1
O4W–H1W4...O11S#1
O4W–H2W4...O50#2
Symmetry transformations used to generate equivalent atoms:
#1 x, y, z; #2 ꢂx + 1, ꢂy + 1, ꢂz + 1; #3 ꢂx + 2, ꢂy + 1, ꢂz + 1.
#4 ꢂx, ꢂy + 2, ꢂz; #5 ꢂx + 1, ꢂy + 2, ꢂz + 1; #6 x ꢂ 1, y + 1, z ꢂ 1.
Fig. 6. Visualization of the distorted pentagonal bipyramidic environment around
LuIII in the structure of 4a (for complex cations A).

A.G. Matveeva et al. / Inorganica Chimica Acta 384 (2012) 266–274
273
oxygen atom (O3) belongs to another ligand molecule. One water
molecule and one bidentate NO3 group occupy the apical positions
(Fig. 6).
Bond distances and valence angles of the ligand molecules in
structures 4a and 1b are typical for this class of compounds [26].
For instance, the lengths of the P@O bonds in 1b,4a (1.491(2)–
1.516(6) Å) are in a good agreement with those for such bonds
(1.51–1.53 Å) in lanthanide complexes of phosphoryl containing
1,8-naphthyridine [8] and in the related non-coordinated
(H2O)](NO3) where one ligand molecule is tetradentate, while an-
other one is coordinated only via one phosphoryl group. The inner
coordination sphere of the cation also involves one water molecule
and two chelate NO3 groups (Scheme 3). Coordination number of
neodymium in complex 3 is ten.
According to the data of the IR spectra (Table 2), the structure of
complex 3 in solution is mainly retained (the positions of the bands
of P@O groups, naphthyridine fragment, and nitrate groups are un-
changed). However, the intensity ratio of coordinated and free ni-
trate groups slightly differs, this fact allows one to suppose that in
solution cations with two and one nitrate groups, namely,
[Nd(O,O,N,N-L)(O-L)(O,O-NO3)2H2O]+ and [Nd(O,O,N,N-L)(O-L)(O,O-
compounds
2-[2-(diphenylphosphoryl)-2-methylprophyl]-1,8-
naphthyridine (1.495(2) [20]) and 2-[(diethoxyphospho-
ryl)amino)]-5,7-dimethyl-1,8-naphthyridine (1.474(1), 1.466(1) Å
[15]).
–
NO3)H2O]2+, may be in equilibrium with the free NO3 ions.
The IR spectrum of the crystalline complex 4a (Table 2) exhibits
two m
(P@O) bands at 1160 and 1190 cmꢂ1. The former corresponds
4. Conclusions
to metal-coordinated P@O groups while the latter to an H-bonded
P@O group. The region of 1600–1570 cmꢂ1, where the band of
coordinated naphthyridine system should appear, is obscured by
the intense absorption of other groups of the ligand, while the
vibrations of intact naphthyridine ring appear as a low-intensity
band at 1539 cmꢂ1. The strong broad IR bands of bidentate NO3
groups of 4a are detected at 1500 and 1309 cmꢂ1, while a strong
narrow band at 1346 cmꢂ1 corresponds to vibrations of free
(non-coordinated) nitrate ions. In the region of 3200–3400 cmꢂ1
an overlap is observed of the bands corresponding to metal-coordi-
nated and solvate water (ꢁ3200 and ꢁ3400 cmꢂ1) and bound and
free NH groups (ꢁ3150 and 3400 cmꢂ1).
Coordination properties of a new tetradentate ligand 2,7-
bis(diphenylphosphorylamino)-1,8-naphthyridine (L) toward lan-
thanide(III) were studied. The novel complexes [Nd(L)(NO3)3]
(1a), [Nd(L)(NO3)3]ꢀH2O (1b), [Lu(L)(NO3)2(H2O)](NO3) (2), [Nd(L)2
(NO3)2(H2O)](NO3) (3), and [Lu(L)2(NO3)(H2O)](NO3)2ꢀ0.75CH3
CNꢀH2O (4a), [Lu(L)2(NO3)(H2O)](NO3)2 (4b) were synthesized
and characterized by IR, Raman, and 31P NMR spectroscopy. Struc-
tures of the complexes 1b and 4a were determined by X-ray
diffraction.
The agreement among X-ray crystallography, vibrational and
NMR spectroscopy results as well as elemental analysis data allows
the assignment of the structures of all investigated complexes both
in solid state and in solutions.
According to the data of elemental analysis, the complex 4b
contains no solvate water and acetonitrile. In the IR spectrum of
4b the absorption of the only free NH group (one of eight) is too
weak to be observed. The band of metal-coordinated water is pres-
The coordination mode of ligand depends on a particular com-
plex composition: it exhibits O,O,N,N-fashion in 1:1 complexes
and (O,O,N,N + O)-fashion in 1:2 complexes. In solutions, the coor-
dination mode of the ligand is preserved in all the complexes
studied.
ent at 3200 cmꢂ1
.
The Raman spectrum of complex 4a shows lines at 1407 and
813 cmꢂ1 corresponding to vibrations of bidentate-coordinated
naphthyridine fragment, while the lines at 1381 and 794 cmꢂ1 cor-
respond to the vibrations of the naphthyridine moiety which is not
involved in coordination, but forms intramolecular H-bond with
the hydrogen atoms of an inner-sphere water molecule. Vibration
frequencies of non-coordinated naphthyridine moiety in complex
4a are slightly higher than those for the solid free ligand (Table
2). In general, the vibrational spectra agree well with the X-ray dif-
fraction data, although the both IR and Raman spectra of a crystal-
line sample of 4a did not reveal the bands of solvate acetonitrile
molecule.
Intramolecular H-bonds were found to play a significant role in
formation and stabilization of the bisligand complexes.
Acknowledgments
This work was supported by the Russian Foundation for Basic
Research(Grant No 09-03-00603a) and the Basic Research Program
of the Presidium of the Russian Academy of Science (Program P-7).
Appendix A. Supplementary material
In the IR spectrum of a solution of complex 4a, the positions of
the analytical bands are virtually unchanged (Table 2). The 31P {1H}
NMR spectrum of the same solution shows two broadened signals
at 31 ppm (W1=2 ¼ 2:3 ppm) and 17.4 ppm (W1=2 ¼ 0:3 ppm) with
the ratio of integral intensities of 3:1, respectively. According to
these data, one can suppose that the structure of complex cations
[Lu(O,O,N,N-L)(O-L)(O,O-NO3)(H2O)]2+ in acetonitrile is retained,
and the solution contains an equilibrium mixture of the complex
CCDC 833989 and 833962 contains the supplementary crystal-
lographic data for 1b and 4a, respectively. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2011.12.010.
–
cations and free NO3 ions. The intensities of the bands of coordi-
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