Synthesis and structural diversity of rare earth anthranilate complexes

Article abstract of DOI:10.1016/j.poly.2005.07.005

Four structural classes have been established for rare earth anthranilates, which have been prepared from the lanthanoid chloride or triflate and anthranilic acid (anthH) followed by pH adjustment to 4. [La(anth) ₃]_n is a polymeric complex with nine coordinate lanthanum and bridging tridentate (O,O,O′) anthranilate ligands, whereas [Nd(anth)₃(H₂O)₃]·3H₂O is monomeric with nine coordinate neodymium and solely chelating (O,O) anthranilate groups. Both chelating (O,O) and bridging bidentate (O,O′) ligands are observed in dimeric [Er₂(anth)₆(H₂O) ₄]·2H₂O, in which erbium is eight coordinate and the water ligands are in a trans arrangement. A polymer is observed for [Yb(anth)₃(H₂O)]_n with solely bridging bidentate (O,O′) ligands and seven coordination for ytterbium. The NH ₂ groups of the anthranilate ligands are not coordinated to the metal but is unusually involved in hydrogen-bond networks with water molecules for Ln = Er, Yb.

Full text of DOI:10.1016/j.poly.2005.07.005

Polyhedron 25 (2006) 379–386
www.elsevier.com/locate/poly
Synthesis and structural diversity of rare earth anthranilate complexes
a,c
Glen B. Deacon *, Maria Forsyth b,c, Peter C. Junk
a,c,
,
a,c
Stuart G. Leary a,c, Graeme J. Moxey
a
School of Chemistry, Box 23, Monash University, Clayton, Vic. 3800, Australia
b
School of Physics and Materials Engineering, Monash University, Clayton, Vic. 3800, Australia
ARC Special Research Centre for Green Chemistry, Monash University, Clayton, Vic. 3800, Australia
c
Received 3 May 2005; accepted 6 July 2005
Available online 15 August 2005
Dedicated to Professor Malcolm Chisholm F.R.S. on the occasion of his 60th birthday.
Abstract
Four structural classes have been established for rare earth anthranilates, which have been prepared from the lanthanoid chloride
or triflate and anthranilic acid (anthH) followed by pH adjustment to 4. [La(anth)3]n is a polymeric complex with nine coordinate
lanthanum and bridging tridentate (O,O,O0) anthranilate ligands, whereas [Nd(anth)3(H2O)3] Æ 3H2O is monomeric with nine coor-
dinate neodymium and solely chelating (O,O) anthranilate groups. Both chelating (O,O) and bridging bidentate (O,O0) ligands are
observed in dimeric [Er2(anth)6(H2O)4] Æ 2H2O, in which erbium is eight coordinate and the water ligands are in a trans arrangement.
A polymer is observed for [Yb(anth)3(H2O)]n with solely bridging bidentate (O,O0) ligands and seven coordination for ytterbium.
The NH2 groups of the anthranilate ligands are not coordinated to the metal but is unusually involved in hydrogen-bond networks
with water molecules for Ln = Er, Yb.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Rare earths; Anthranilates; X-ray crystal structures; Amino acids
1. Introduction
Structural proposals have been made for rare earth
anthranilates Ln(anth)3 Æ nH2O (n = 0, Ln = La, Ce,
Pr, Nd, Sm; n = 2, Ln = Y, Tb–Lu; and n = 1, Ln = Eu,
Gd) on the basis of analytical, IR, and X-ray powder
data [13,14]. It was suggested that the lighter rare earth
anthranilates form two isostructural groups, (i) La–Sm,
and (ii) Y, Eu, Gd [13]. A subsequent study found
Tb–Lu to be isostructural [14]. IR data suggested coor-
dination of both carboxylate and amino groups.
The insoluble nature of lanthanoid anthranilates
makes growing crystals suitable for X-ray diffraction dif-
ficult. However because of our interest in lanthanoid
anthranilates as possible ‘‘green’’ corrosion inhibitors
[15], we have undertaken a study of the structures of rep-
resentative lanthanoid anthranilates to assist in under-
standing the structural basis of corrosion inhibitors.
Although there have been widespread studies of com-
plexes of rare earth ions with amino acids [1], there are
only two structurally characterised complexes with
anthranilate ions (anth) (Fig. 1), viz. [Y(anth)3(H2O)]n
[2] and [Eu2(anth)6(bpy)2] (bpy = 2,20-bipyridine) [3].
This contrasts the extensive structural chemistry of
anthranilate ions with alkali metals [4,5], alkaline earth
metals [6,7], and transition metals [8–12].
*
Corresponding author. Tel.: +61 3 9905 4568/4570; fax: +61 3 9905
4597.
E-mail addresses: glen.deacon@sci.monash.edu.au (G.B. Deacon),
peter.junk@sci.monash.edu.au (P.C. Junk).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.07.005

380
G.B. Deacon et al. / Polyhedron 25 (2006) 379–386
Yield: 0.21 g (45%). Anal. Calc. for C21H18N3O6La:
C, 46.09; H, 3.32; N, 7.68; La, 25.38. Found: C, 46.23;
H, 3.40; N, 7.83; La, 25.40%. Infrared (cmꢀ1): 3467 m,
3421 m, 3356 m, 3324 m, 1615 s, 1574 m, 1505 s, 1456
s, 1385 s, 1338 m, 1309 m, 1258 m, 1156 m, 1133 m,
1027 w, 978 w, 946 w, 875 m, 853 w, 811 m, 753 m,
707 m, 669 m.
H
N
H
C
O
O
Fig. 1. A line drawing of the anthranilate anion.
2.2.2. [Nd(anth)3(H2O)3] Æ 3H2O (2)
The compound was synthesised using the above pro-
cedure except that NdCl3 (4.0 mL, 3.3 mmol) and
anthranilic acid (0.21 g, 1.5 mmol) were used.
2. Experimental
2.1. Materials and instrumentation
Yield: 0.12 g (36%). Anal. Calc. for C21H30N3O12Nd:
C, 38.18; H, 4.58; N, 6.36; Nd, 21.83. Found: C, 38.17;
H, 4.43; N, 6.16; Nd, 22.65%. Infrared (cmꢀ1): 3593 m,
3431 s, 1656 m, 1614 s, 1574 m, 1506 s, 1446 m, 1398 s,
1331 m, 1308 m, 1256 m, 1158 m, 1128 w, 1030 w, 981 w,
959 w, 875 m, 821 m, 770 s, 707 m, 672 m.
Lanthanoid oxides (Nd2O3 and Yb2O3) were obtained
from Honeywell. Er2O3 was supplied by Aldrich. Lantha-
noid chlorides (other than LaCl3) were prepared by
dissolving lanthanoid oxides in hydrochloric acid.
Er(OTf)3 was prepared by dissolving Er2O3 in trifluorom-
ethanesulfonic acid (HOTf). The resulting solutions were
diluted, and the concentrations of the prepared solutions
were accurately determined by complexometric titration
with standardised 0.01 M Na2H2–EDTA. LaCl3 Æ 7H2O
was obtained from Chempur. Reagent grade anthranilic
acid was obtained from Merck, and used without further
purification. All other starting materials were used as re-
ceived. Microanalyses were performed in duplicate by the
Campbell Microanalytical Laboratory of the University
of Otago, Dunedin, New Zealand. Rare earth analyses
were carried out by digesting accurately weighed samples
in concentrated nitric and sulphuric acid and boiling the
solutions to dryness. The resulting residues were diluted
with water, and aliquots were buffered with hexamethy-
lenetetramine and titrated against standardised 0.01 M
Na2H2–EDTA with Xylenol Orange as the indicator.
Infrared spectra were recorded as Nujol mulls sand-
wiched between NaCl plates using a Perkin Elmer 1600
2.2.3. [Er2(anth)6(H2O)4] Æ 2H2O (3)
The compound was synthesised using the above pro-
cedure except that Er(OTf)3 (4.0 mL, 3.5 mmol) and
anthranilic acid (0.21 g, 1.5 mmol) were used. Single
crystals of 3 were separated by hand picking. The bulk
product analysed as [Er2(anth)6(H2O)4] Æ HO3SCF3 Æ
2H2O, (3 Æ HO3SCF3).
Yield: 0.18 g. Anal. Calc. for C43H49F3N6O21SEr2
(3 Æ HO3SCF3): C, 36.64; H, 3.50; N, 5.96; Er, 23.73.
Found: C, 36.23; H, 3.54; N, 5.25; Er, 24.30%. Infrared
(cmꢀ1): 3627 m, 3478 s, 3361 m, 3343 s, 3312 m, 1614 m,
1574 m, 1538 m, 1514 m, 1506 m, 1485 s, 1421 s, 1340 m,
1302 m, 1262 m, 1260 m, 1159 m, 1156 m, 1032 m, 960
w, 879 m, 820 m, 770 m, 750 m, 704 m, 673 m, 641 m.
19F NMR (d6-acetone) d = ꢀ37.66 ppm.
2.2.4. [Yb(anth)3(H2O)]n (4)
The compound was synthesised using the above pro-
cedure except that YbCl3 (9.5 mL, 7.6 mmol) and
anthranilic acid (0.52 g, 3.8 mmol) were used. Single
crystals of 4 were separated but the bulk crystalline
product analysed as 4 Æ 2H2O after prolonged desicca-
tion at room temperature.
Yield: 0.22 g. Anal. Calc. for C21H24N3O9Yb
(4 Æ 2H2O): C, 39.69; H, 3.81; N, 6.61; Yb, 27.23. Found:
C, 39.91; H, 4.10; N, 6.49; Yb, 27.26%. Infrared (cmꢀ1):
3479 m, 3394 m, 3343 m, 3278 m, 3178 m, 1682 m, 1613
m, 1572 m, 1542 m, 1521 m, 1506 m, 1483 m, 1416 s,
1339 w, 1303 m, 1272 w, 1260 m, 1155 m, 1024 w, 880
m, 820 w, 767 w, 750 m, 704 w, 674 w. TGA: % mass loss
50–200 ꢁC: 8.2%. Calculated mass loss of three H2O
molecules: 8.5%.
FTIR instrument in the range 4000–500 cmꢀ1 19F
.
NMR spectra were recorded on a Bruker DPX 300 spec-
trometer, using CFCl3 in d6-acetone as an external refer-
ence. Thermogravimetric analysis (TGA) was performed
using a Perkin Elmer Pyris 1 instrument at a heating rate
of 10 ꢁC minꢀ1, using a platinum sample pan.
2.2. Synthesis
2.2.1. [La(anth)3]n (1)
Anthranilic acid (0.35 g, 2.6 mmol) was dissolved in
2 mL of MeOH, and the solution added to a stirred aque-
ous solution of LaCl3 (5.0 mL, 5.0 mmol) heated to
70 ꢁC. The pH of the reaction mixture was raised by the
dropwise addition of 0.5 M NaOH. At a pH of approxi-
mately 4, a faint permanent precipitate formed. The reac-
tion mixture was then cooled, and the precipitate filtered
off. Crystals appeared following the slow evaporation of
the reaction mixture at room temperature.
2.3. X-ray crystallography
Intensity data for complexes 1–4 were collected using
an Enraf–Nonius KAPPA CCD at 123 ꢁK with Mo Ka

G.B. Deacon et al. / Polyhedron 25 (2006) 379–386
381
˚
radiation (k = 0.7170 A). Suitable crystals were im-
mersed in viscous hydrocarbon oil, mounted on a glass
fibre which was mounted on the diffractometer. Using
psi and omega scans Nt (total) reflections were mea-
sured, which were reduced to No unique reflections, with
Fo > 2r(Fo) being considered observed. Data were cor-
rected for absorption with a SORTAV multi-scan
absorption correction [16]. The structures were solved
using direct methods, and observed reflections were used
in least squares refinement on F2, with anisotropic ther-
mal parameters refined for non-hydrogen atoms. Aro-
matic hydrogen atoms were constrained in calculated
positions and refined with a riding model. All other
hydrogen atoms were found directly from the difference
Fourier map and refined isotropically. Structure solu-
tions and refinements were performed using the pro-
grams SHELXS-97 [17] and SHELXL-97 [18] through the
graphical interface X-Seed [19]. Crystal data and struc-
tural refinement data for complexes 1–4 are given in
Table 1. Selected bond lengths for complexes 1–4 are
listed in Table 2, and hydrogen bond lengths and angles
for complexes 2–4 are given in Table 3.
Bond angles and other crystallographic data (exclud-
ing structure factors) for the structures reported in this
paper have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary Publication
No. CCDC-270607 for compound 1, CCDC-270608
for compound 2, CCDC-270609 for compound 3 and
CCDC-270610 for compound 4. Copies of the data
can be obtained free of charge on application to the
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: (+44) 1223 336 033; deposit@ccdc.cam.ac.uk).
3. Results and discussion
3.1. Synthesis of the complexes
Lanthanoid carboxylate complexes are typically syn-
thesised by adding the carboxylate salt to a solution of
the lanthanoid salt. An alternative procedure is to add
the carboxylic acid to precipitated lanthanoid hydrox-
ides, a method utilised by Brzyska and Rzaczynska
[13,14] during their study of lanthanoid anthranilates.
The insolubility of lanthanoid anthranilates limits the
usefulness of these two methods to grow crystals suit-
able for single crystal X-ray analysis. The use of a diffu-
sion apparatus yielded crystals of the complex
[Y(anth)3(H2O)]n [2]. We have found that the use of a
simpler method can yield suitable crystals. The addition
of anthranilic acid to lanthanoid chloride solutions fol-
lowed by the addition of NaOH dropwise to the reaction
mixture to form the Na anthranilate salt led to the iso-
lation of La, Nd, Er and Yb anthranilates after slow
evaporation of the reaction mixture (pH ca. 4) at room
temperature. This approach has been previously em-
ployed using higher pH conditions in the synthesis of
lanthanoid hydroxo clusters [20].
Both the La and Nd anthranilates crystallise as large
(diameter greater than 2 mm) single crystals, and the mi-
cro and metal analysis results of the La and Nd anthran-
ilates confirm the stoichiometry obtained from the X-ray
crystallography results. The Er and Yb anthranilates
crystallise as clusters of thin needles, the clusters par-
tially decomposing into watery solution as they are bro-
ken apart with a needle. Consequently, suitable crystals
Table 1
Crystallographic and data collection parameters for complexes 1–4
Complex
1
2
3
4
Formula
C
42H36La2N6O12
C21H30N3NdO12
660.72
dark brown block
0.30 · 0.25 · 0.20
hexagonal
C21H24ErN3O9
629.69
light brown needle
0.25 · 0.25 · 0.20
orthorhombic
Pbca
C21H20N3O7Yb
599.44
light brown needle
0.20 · 0.10 · 0.10
monoclinic
Formula weight
Colour, habit
Crystal size (mm)
Crystal system
Space group
1094.59
brown block
0.20 · 0.20 · 0.10
monoclinic
P21/c
R3c
C2/c
Unit cell dimensions
˚
a (A)
24.760(5)
7.4954(15)
24.485(5)
90
119.29(3)
90
3963.1(14)
4
1.835
18.566(3)
18.566(3)
12.282(3)
90
90
120
3666.4(10)
6
1.795
1998
8.4910(17)
19.645(4)
28.129(6)
90
90
90
4692.0(16)
8
1.783
2488
31.234(6)
9.0441(18)
15.596(3)
90
108.44(3)
90
4179.2(14)
8
1.905
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
Dcalc (g/cm3)
F(000)
2160
2344
Measured reflections
25192
9027
0.0272
1.084
0.0264
0.0582
12462
1871
0.0502
1.064
0.0195
0.0428
43956
4612
0.0804
1.006
0.0378
0.0929
30452
4094
0.0544
1.065
0.0247
0.0577
Independent reflections
R(int)
Goodness-of-fit on F2
R
Rw

382
G.B. Deacon et al. / Polyhedron 25 (2006) 379–386
Table 2
Table 3
˚
˚
Selected bond lengths (A) for complexes 1–4
Hydrogen bond lengths (A) and bond angles (ꢁ) for complexes 2–4
Complex 1
D–Hꢁ ꢁ ꢁA
Complex 2
d(D–H)
d(Hꢁ ꢁ ꢁA) d(Dꢁ ꢁ ꢁA) \(DHA)
La(1)–O(1)
La(1)–O(1)#1
La(1)–O(2)
La(1)–O(3)
La(1)–O(3)#2
La(1)–O(4)
La(1)–O(5)
La(1)–O(5)#1
La(1)–O(6)
La(2)–O(7)
La(2)–O(7)#3
La(2)–O(8)
La(2)–O(9)
La(2)–O(9)#3
La(2)–O(10)
La(2)–O(11)
La(2)–O(11)#4
La(2)–O(12)
2.635(2)
2.473(2)
2.567(2)
2.634(2)
2.507(2)
2.530(2)
2.636(2)
2.475(2)
2.548(2)
2.634(2)
2.473(2)
2.566(2)
2.683(2)
2.475(2)
2.543(2)
2.655(2)
2.487(2)
2.524(2)
O(3)–H(3A)ꢁ ꢁ ꢁO(2)#3 0.971(19) 1.796(19) 2.765(3)
176(4)
177(3)
O(3)–H(3B)ꢁ ꢁ ꢁO(4)#1 0.955(18) 1.840(19) 2.794(3)
Complex 3
O(7)–H(7A)ꢁ ꢁ ꢁO(9)#3 0.99(2)
O(7)–H(7B)ꢁ ꢁ ꢁN(1)#3 0.99(2)
O(8)–H(8B)ꢁ ꢁ ꢁO(1)#2 0.98(2)
1.67(3)
1.89(3)
2.01(6)
1.76(2)
2.644(6)
2.864(6)
2.825(6)
2.748(6)
166(8)
166(6)
138(6)
171(6)
O(9)–H(9A)ꢁ ꢁ ꢁO(3)
Complex 4
0.99(2)
O(1)–H(4A)ꢁ ꢁ ꢁN(3)#3 0.79(5)
2.07(5)
2.01(5)
2.845(5)
2.845(5)
171(5)
170(4)
O(1)–H(4B)ꢁ ꢁ ꢁN(1)#4 0.85(5)
Symmetry transformations used to generate equivalent atoms for:
Complex (2): #1 ꢀx + y, ꢀx + 1, z; #3 x, x ꢀ y + 1, z + 1/2.
Complex (3): #2 ꢀx + 2, ꢀy, ꢀz + 1; #3 x ꢀ 1/2,ꢀy + 1/2, ꢀz + 1.
Complex (4): #3 ꢀx + 3/2, ꢀy + 3/2, ꢀz + 1; #4 x, ꢀy + 2, z + 1/2.
Complex 2
Nd(1)–O(1)
Nd(1)–O(2)
Nd(1)–O(3)
the samples were dried in a desiccator to constant weight
and they remained at constant weight for 2 days after re-
moval from the desiccator. No disordered water was evi-
dent in the crystal structure but it is possible that highly
disordered waters could be present in holes in the lattice.
The issue of hydration in lanthanoid anthranilates is
also observed in comparing the anhydrous Nd(anth)3
composition proposed by Brzyska and Rzaczynska [13]
from a synthesis in water with the composition of 2,
which contains six water molecules. Possibly small dif-
ferences in reaction conditions and drying techniques
have a major effect on hydration and structure.
2.464(2)
2.549(2)
2.492(2)
Complex 3
Er(1)–O(1)
Er(1)–O(2)
Er(1)–O(3)
Er(1)–O(4)
Er(1)–O(5)
Er(1)–O(6)#1
Er(1)–O(7)
Er(1)–O(8)
2.397(4)
2.400(4)
2.369(4)
2.356(4)
2.272(4)
2.241(4)
2.354(4)
2.360(4)
Complex 4
Yb(1)–O(1)
Yb(1)–O(2)
Yb(1)–O(3)#1
Yb(1)–O(4)
Yb(1)–O(5)#1
Yb(1)–O(6)#1
Yb(1)–O(7)
2.285(3)
2.276(2)
2.317(3)
2.301(3)
2.274(2)
2.199(3)
2.213(3)
An even more marked difference between single crys-
tal structure and bulk composition is observed with 3,
where the bulk composition corresponds more closely
to 3 Æ HO3SCF3, and the 19F NMR spectrum shows
clear evidence of a CF3 resonance, somewhat paramag-
netically shifted (by Er3+) from the free acid value
(d = ꢀ77.9 ppm). Plausibly, isolation at pH 4 leads to
protonation of one amino group of 3 giving 3H+(OTfꢀ).
Symmetry transformations used to generate equivalent atoms for:
Complex (1): #1 ꢀx, y + 1/2, ꢀz + 1/2; #2 ꢀx, yꢀ1/2, ꢀz + 1/2; #3
ꢀx + 1, y ꢀ 1/2, ꢀz + 1/2; #4 ꢀx + 1, y + 1/2, ꢀz + 1/2.
Complex (3): #1 ꢀx + 1, ꢀy, ꢀz + 1.
3.2. Crystal structure descriptions
Complex (4): #1 ꢀx + 3/2, y + 1/2, ꢀz + 1/2.
Complexes 1–3 represent new structural classes of
lanthanoid anthranilates, while complex 4 is isostruc-
tural with the previously reported Y anthranilate [2].
In all four structures, the anthranilate ligand is bound
to the lanthanoid solely through the carboxylate group,
in contrast to carboxylate and NH2 coordination found
in transition metal anthranilates and proposed for rare
earth anthranilates [13,14]. Although the amino group
is not bound to the lanthanoid cation, the amino group
participates in hydrogen bonding in complexes 3 and 4,
stabilising the crystal structures. The results of this study
demonstrate that lanthanoid anthranilates exhibit a
range of structural classes, even more diverse than the
closely related lanthanoid p-aminobenzoates [21].
of Er and Yb anthranilates for X-ray analysis were
handpicked from the bulk product. The unit cells of sev-
eral crystals obtained from the Yb anthranilate reaction
mixture were in agreement with that of the crystal of the
solved structure. The discrepancy between the X-ray
determined composition and the observed micro and
metal analysis values is likely to be due to the presence
of additional water molecules trapped within the clusters
of crystals. Microanalyses of bulk products from two
preparations and a metal analysis were all consistent
with [Yb(anth)3(H2O)] Æ 2H2O, i.e., 4 Æ 2H2O, as was
the TGA weight loss over 60–200 ꢁC. Prior to analysis,

G.B. Deacon et al. / Polyhedron 25 (2006) 379–386
383
Complex 1 crystallises as an anhydrous species in the
monoclinic space group P21/c. Selected bond lengths are
given in Table 2. The structure consists of two crystallo-
graphically distinct polymer chains. The bonding in the
two chains is almost identical with only negligible differ-
ences in bond lengths (Table 2). Only bridging tridentate
(O,O,O0) ligands are present. The asymmetric unit con-
sists of two independent La mononuclear units, each
bound to three anthranilate ligands. Each polymer
strand (Fig. 2) is built up from the monomeric units
by links to two adjacent La cations, through bridging
tridentate anthranilate ligands. Overall, each lanthanum
is surrounded by six bridging tridentate ligands, three of
which chelate (O,O) to a given lanthanum, and three are
unidentate (O). Consequently, each La ion displays a
coordination number of nine. In chain 1 the average
most closely resembles a doubled trigonal prism [22].
The Nd–O (carboxylate) distances are markedly differ-
˚
˚
ent, being 2.464 (2) A (Nd–O(1)) and 2.549 (2) A
(Nd–O(2)), indicating asymmetric chelation of the
anthranilate ligands. The carboxylate angles (O(1)–
C(1)–O(2)) are 119.1 (3)ꢁ. The angle between the Nd
cation and centroids generated between the carboxylate
oxygens of the anthranilate ligands is 99.36ꢁ, indicating
that the anthranilate ligands adopt a cisoid geometry
around the Nd cation. The Nd–O (water) distances
˚
are 2.492 (2) A, comparable with the Nd–O carboxylate
distances. The angle between the O atoms of coordi-
nated water molecules and the Nd is 74.25 (10)ꢁ, indi-
cating the coordinated water molecules are also
arranged in a cisoid geometry. Three water molecules
(two are symmetry generated) reside in the lattice and
hydrogen bonding links coordinated water and lattice
water molecules. Hydrogen bonding also occurs be-
tween the coordinated water and the carboxylate oxy-
gen of the anthranilate ligand. Hydrogen bond lengths
and angles are given in Table 3. Surprisingly, the struc-
ture is isostructural with the closely related lanthanoid
m-aminobenzoate hydrate structures, despite the differ-
ent positions of the NH2 substituent. Lanthanoid com-
plexes of m-aminobenzoates have been shown to be
isostructural from La to Lu including Y [24], unlike
the anthranilates.
Complex 3 crystallises in the orthorhombic space
group Pbca and is a dimer. Selected bond lengths are
listed in Table 2. In addition to two bound water mole-
cules, each Er cation is encircled by four anthranilate li-
gands which exhibit two different binding modes
(Fig. 4). Two chelating anthranilate ligands and two
bridging bidentate anthranilate ligands give an overall
˚
La(1)–O (carboxylate) bond distance is 2.556 A, and
˚
the distances between adjacent La ions is 3.901 A. In
chain 2, the average La(2)–O carboxylate distance is
˚
˚
2.560 A and the distance between adjacent La ions is
3.893 A. The coordination environment around La(1)
is best described as a doubled trigonal prism [22], while
for La(2) the coordination environment most closely
resembles a capped cube [22]. The presence of two inde-
pendent polymer chains with the same composition but
slightly different structures in the same crystal is uncom-
mon, but it has been previously reported in a praseo-
dymium b-alanine complex [23].
Complex 2 crystallises in the hexagonal space group
R3c and is monomeric. Selected bond lengths are listed
in Table 2. As displayed in Fig. 3, the Nd cation is sur-
rounded by three chelating anthranilate ligands, and
three water O atoms giving a coordination number of
nine. The coordination environment around the Nd
Fig. 2. An ORTEP representation of one of the unique polymer strands of 1, displaying the bridging tridentate anthranilate ligands present in
polymer strands. The second polymer strand is very similar to the pictured polymer strand. Hydrogen atoms have been omitted for clarity (ellipsoids
at 50% probability). Inset – stylised diagram showing the ligand connectivity in both polymer strands (aromatic groups omitted for clarity).

384
G.B. Deacon et al. / Polyhedron 25 (2006) 379–386
Fig. 3. An ORTEP representation of 2, exhibiting the chelating anthranilate ligands. Lattice water molecules and hydrogen atoms on anthranilate
ligands have been omitted for clarity (ellipsoids at 50% probability). Inset – stylised diagram displaying the ligand connectivity (aromatic groups
omitted for clarity).
Fig. 4. An ORTEP representation of 3, displaying the dimeric structure. Lattice water molecules and hydrogen atoms on anthranilate ligands have
been omitted for clarity (ellipsoids at 50% probability). Inset – stylised diagram showing the ligand connectivity (aromatic groups omitted for clarity).
˚
coordination number of eight for each Er cation. The
coordination geometry around each Er centre most clo-
sely resembles a square antiprism [22]. The average car-
boxylate bite angle for the chelating anthranilate ligands
is 118.95ꢁ, while for the bridging anthranilate ligands it
is 122.82ꢁ. The chelating anthranilate ligands adopt a
cisoid geometry around the Er cation, while the coordi-
nated water molecules are arranged in a transoid geom-
etry. The average Er–O distance for chelating
nilate ligands is 2.257 A. The average Er–O (water) dis-
˚
tance is 2.357 A. Two water molecules reside in the
lattice. Hydrogen bonding links the lattice water mole-
cule to the carboxylate group of the anthranilate ligand.
The coordinated water molecules also participate in
hydrogen bonding, and are linked to lattice water
molecules and additionally to the amino groups of
anthranilate ligands bound to neighbouring Er cations,
therefore generating a polymeric supramolecular struc-
ture. Hydrogen bond lengths and angles are given in
˚
anthranilate ligands is 2.381 A, and for bridging anthra-

G.B. Deacon et al. / Polyhedron 25 (2006) 379–386
385
Fig. 5. An ORTEP representation of 4, illustrating the bridging bidentate anthranilate ligands present in the polymeric structure. Hydrogen atoms
on anthranilate ligands have been omitted for clarity (ellipsoids at 50% probability). Inset – stylised diagram displaying the ligand connectivity
(aromatic groups omitted for clarity).
˚
Table 3. The structure of complex 3 is similar to that of
the related Er salicylate [25].
(water) distance (2.301 A) and the Yꢁ ꢁ ꢁY distance
˚
(4.742 A), are comparable with analogous values for
Complex 4 crystallises in the monoclinic space group
C2/c. Selected bond lengths are listed in Table 2. The
polymeric structure consists of Yb cations linked by
six bridging bidentate anthranilate ligands, resulting in
the formation of linear polymer chains (Fig. 5). In addi-
tion to one O atom from each of six anthranilate li-
gands, each Yb cation is also bound to one water
molecule giving a coordination number of seven. The
coordination environment around the Yb cation is best
described as a pentagonal bipyramid [22]. The average
complex 4 allowing for ionic radius differences.
Selected rare earth anthranilate complexes have been
tested as potential ‘‘green’’ corrosion inhibitors. The re-
sults of these tests indicate that rare earth anthranilates
do act as corrosion inhibitors; however they are less
effective inhibitors than the closely related rare earth sal-
icylates [15].
4. Conclusions
˚
Yb–O carboxylate distance is 2.263 A, while the Yb–O
˚
(water) distance corresponds closely (2.285 A). The
By employing an alternative synthetic route we have
synthesised and crystallised a range of lanthanoid
anthranilates, and probed the solid state structures using
X-ray crystallography. The results reveal a diverse range
of structural classes exhibited by lanthanoid anthrani-
lates. In all cases, the amino group of the anthranilate
ligand is not coordinated to the lanthanoid cation. The
carboxylate groups of the anthranilate ligand exhibited
three different binding modes, chelating, bridging biden-
tate and bridging tridentate. The variations in structural
˚
Ybꢁ ꢁ ꢁYb distance is 4.714 A. Hydrogen bonding links
the coordinated water molecule to the amino groups
of two anthranilate ligands in an adjacent polymer
chain. Hydrogen bond lengths and angles are given in
Table 3. The complex is isostructural with the reported
Y anthranilate [2]. Significant differences in the C–O dis-
tances of the carboxylate groups were reported for the Y
anthranilate, but in the Yb anthranilate structure the
C–O carboxylate distances are comparable. The Y–O

386
G.B. Deacon et al. / Polyhedron 25 (2006) 379–386
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325.
class can be related to the lanthanoid contraction, with a
decline from nine coordination (La) to seven (Yb).
However other factors such as slight variations in reac-
tion conditions including pH may influence the struc-
tural class isolated. Further investigation is required to
unravel completely the origin of the structural diversity.
[12] M. Hernandez-Molina, P.A. Lorenzo-Luis, P. Gili, C. Ruiz-Perez,
Cryst. Growth Des. 3 (2003) 273.
Acknowledgements
[13] W. Brzyska, Z. Rzaczynska, Pol. J. Chem. 60 (1986) 27.
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A. Phanasgoankar, Corrosion 58 (2002) 953.
We are grateful to the ARC Centre for Green
Chemistry for support, and to Monash University for
a Monash Graduate Scholarship awarded to S.G.L.
We also acknowledge Honeywell Specialty Chemicals,
Seelze GmbH for a gift of rare earth oxides.
[16] R.H. Blessing, Acta Cryst. A 51 (1995) 33.
[17] G.M. Sheldrick, SHELXS-97 Program for Crystal Structure Solu-
tion, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
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ment, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
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