Hydrothermal synthesis and structural characterization of three novel

lanthanide coordination polymers with fumarate and 1,10-phenanthroline

Liang Huang, Li-Ping Zhang*

Department of Chemistry, Anyang Teachers College, Anyang 455000, China

Received 25 December 2003; revised 7 February 2004; accepted 11 February 2004

Abstract

Three novel lanthanide complexes, [Ln2(fum)3(phen)2(H2O)2]n (Ln ¼ La, 1; Pr, 2. fum ¼ fumarate dianion; phen ¼ 1,10-phenanthroline)

and [Er2(fum)3(phen)2]n (3), were synthesized hydrothermally and characterized by X-ray crystallography. Single crystal X-ray diffraction

analysis shows that complex 1 is isostructural with 2. Ln(III) centers are nine-coordinated in 1 and 2 but eight-coordinated in 3 duo to

lanthanide contraction. The coordination modes of fumarate and phen ligands are identical in three complexes. So structures of three

complexes are very similar. In three structures, Ln(III) ions are bridged by fumarate anions in two modes, forming polymeric sheets. These

sheets are further assembled into 3D supramolecular network by different intermolecular hydrogen bonding and p–p stacking interactions

duo to the lack of coordinated water in 3. IR spectra are assigned based on the molecular structures.

q 2004 Elsevier B.V. All rights reserved.

Keywords: Lanthanide; Complex; Hydrothermal synthesis; Crystal structure; IR

1. Introduction

Research on metal-directed supramolecular compounds

has rapidly been expanding duo to their interesting

topologies and potential applications as functional materials

[1–3]. Though the use of various saturated aliphatic a,v-

dicarboxylic acid to form bridges between metal centers has

been extensively studied [4], the use of unsaturated aliphatic

a,v-dicarboxylic acid is scanty in the literature [5]. Fumaric

acid is the simplest compound of unsaturated aliphatic

diacids, and 1,10-phenanthroline (phen) is a good ligand for

lanthanide ions and can construct supramolecular structure

via C – H· · ·O hydrogen bonding and p–p stacking

interactions. Therefore, we selected the two compounds as

mixed ligands and hope to construct novel lanthanide

complexes with fascinating structures. Several structural

studies have been published on lanthanide fumarates [6].

But the lanthanide complexes containing both the ligands

of fumarate and phen have not been synthesized so far.

Herein, we report three novel lanthanide fumarate com-

plexes, [Ln2(fum)3(phen)2(H2O)2]n (Ln ¼ La, 1; Pr, 2)

and [Er2(fum)3(phen)2]n (3), which were characterized by

single crystal X-ray diffraction.

2. Experimental

2.1. Materials and apparatus

LnCl3·n H2O (Ln ¼ La and Pr, n ¼ 7; Ln ¼ Er, n ¼ 6)

were prepared by dissolving their oxides in dilute

hydrochloric acid, respectively and then dried. All other

chemicals were purchased and used as received without

further purification. C, H and N data were obtained using the

PE 2400 II CHNS/O elemental analyzer. Infrared spectra

were recorded with the Nicolet Avatar 360 FT-IR

spectrometer.

2.2. Preparation of complexes

LnCl3·nH2O (0.3 mmol; La, n ¼ 7; 0.1114 g; Pr, n ¼ 7;

0.1120 g; Er, n ¼ 6; 0.1145 g) and H2fum (0.3 mmol,

0.0348 g) were dissolved in 10 ml deionized water,

respectively, to which phen·H2O (0.3 mmol, 0.0595 g) was

added and the pH value was adjusted to about four with

NaOH aqueous solution. The mixture was placed in

0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.molstruc.2004.02.012

Journal of Molecular Structure 692 (2004) 249–253

www.elsevier.com/locate/molstruc

* Corresponding author. Tel.: þ86-30-6443-3577; fax: þ86-37-2290-

2048.

E-mail address: lpzhang@aytc.edu.cn (L.-P. Zhang).

a Teflon-lined stainless steel vessel (23 ml). The vessel was

sealed and heated at 140 8C for 3d under autogenous

pressure and then cooled to room temperature. After filtered,

the product was washed with ethanol and then dried under

ambient. Columnlike crystals of the complexes 1–3 were

collected (yields: 0.0465 g, 30.5% for 1; 0.0554 g, 36.2%

for 2; 0.0638 g, 41.0% for 3).

[La2(fum)3(phen)2(H2O)2]n 1. Found (Calcd., %): C,

42.28(42.54); H, 2.42(2.58); N, 5.53(5.51). IR(KBr pellet,

cm21): 3601(m), 3078(w), 2933(w), 1575(vs), 1366(vs),

1199(s), 1138(m), 1103(m), 1011(m), 989(m), 966(w),

850(s), 802(s), 731(s), 685(s), 658(s), 576(m), 562(m).

[Pr2(fum)3(phen)2(H2O)2]n 2. Found (Calcd., %): C,

42.01(42.37); H, 2.41(2.57); N, 5.48(5.49). IR(KBr pellet,

cm21): 3603(m), 3386(m, br), 3082(w), 2926(w), 2855(w),

1578(vs), 1397(vs), 1365(vs), 1200(s), 1140(m), 1104(m),

1009(m), 991(m), 981(w), 850(s), 802(s), 731(s), 686(s),

658(s), 577(m), 562(m).

[Er2(fum)3(phen)2]n 3. Found (Calcd., %): C,

41.46(41.69); H, 1.95(2.14); N, 5.58(5.40). IR(KBr pellet,

cm21): 3448(m, br), 3059(w), 2925(w), 2854(w), 1597(vs),

1421(vs), 1407(vs), 1340(s), 1262(m), 1196(s), 1145(m),

1106(m), 1017(m), 1000(m), 987(w), 848(s), 806(s), 730(s),

702(s), 661(s), 583(m), 421(m).

2.3. Single-crystal X-ray diffraction

Single-crystal X-ray data were collected on a Bruker

SMART 1000 CCD diffractometer equipped with graphite

monochromatized Mo Ka radiation ðl ¼ 0:71073 A).

Semiempirical absorption corrections were applied using

the SADABS program. All calculations were carried out

with use of SHELXS 97 and SHELXL 97 programs [7]. The

structures were solved by the direct methods. All structures

were refined on F2 by full-matrix least-squares methods.

The crystallographic data of the complexes are summarized

in Table 1 and the selected bond lengths in Table 2.

3. Results and discussion

3.1. Structural description of [Ln2(fum)3(phen)2(H2O)2]n

(Ln ¼ La, 1; Pr, 2) and [Er2(fum)3(phen)2]n (3)

Single-crystal X-ray diffraction studies reveal that

complexes 1 and 2 are isostructural and the complexes 1

and 3 will be described in detail. As shown in Fig. 1, there is

only one type of Ln(III) ion environment in the asymmetric

units of 1 and 3. The coordination modes of fumarate and

phen ligands are identical in both complexes. The obvious

difference between 1 and 3 is that there is a coordinated

water molecule in 1. So La(1) is nine-coordinated and

surrounded by two nitrogen atoms from a phen molecule,

six carboxylate oxygen atoms from five fumarate ligands

and one oxygen atom from coordinated water molecule.

While Er(1) is eight-coordinated and possesses an N2O6

environment by virtue of two N atoms from a phen ligand

and six oxygen from five fumarate ligands. Two types of

coordination modes of fumarate ligands exist in complex 1:

(i) bridging bidentate and monodentate [Scheme 1 (a)], the

fumarate anions are bonded in this mode to La(III) cations

along b-axis; (ii) two chelating/bridging tridentate [Scheme

1 (b)], the fumarate anions are centrosymmetric and bonded

in this mode to La(III) cations along a-axis. Thus a 2D

polymeric sheet is formed via bridging fumarate ligands

(Fig. 2). The 2D sheet is parallel to the ab plane and has

rhombus grids with a cavity of ca. 9.1 £ 10.1 A. All the

La(III) ions in a 2D sheet are not coplanar but distributed in

Table 2

Selected bond lengths (A) for complexes 1, 2 and 3

Bond lengths in 1

La(1)–O(1) 2.417(3) La(1)–O(5) 2.598(3)

La(1)–O(3A) 2.471(3) La(1)–O(7) 2.605(4)

La(1)–O(4B) 2.491(3) La(1)–N(1) 2.746(4)

La(1)–O(6C) 2.498(3) La(1)–N(2) 2.697(4)

La(1)–O(6) 2.820(3)

Bond lengths in 2

Pr(1)–O(4A) 2.380(4) Pr(1)–O(6B) 2.555(4)

Pr(1)–O(2B) 2.427(3) Pr(1)–O(7) 2.583(4)

Pr(1)–O(5) 2.450(3) Pr(1)–N(1) 2.702(4)

Pr(1)–O(1) 2.452(3) Pr(1)–N(2) 2.635(4)

Pr(1)–O(5B) 2.798(4)

Bond lengths in 3

Er(1)–O(3A) 2.170(3) Er(1)–O(5B) 2.578(3)

Er(1)–O(1) 2.279(3) Er(1)–O(6B) 2.403(3)

Er(1)–O(2B) 2.294(3) Er(1)–N(1) 2.529(4)

Er(1)–O(5) 2.311(3) Er(1)–N(2) 2.485(4)

Symmetry transformations used to generate equivalent atoms for 1: A

2x þ 1;2y þ 1;2z; B x; y 2 1; z; C 2x þ 1;2y;2z: Symmetry trans-

formations used to generate equivalent atoms for 2: A x; y 2 1; z; B 2x þ 1;

2y þ 1;2z þ 1: Symmetry transformations used to generate equivalent

atoms for 3: A 2x;2y;2z þ 1; B 2x;2y þ 1;2z þ 1:

Table 1

Crystallographic data for complexes 1–3

1 2 3

Formula LaC18H13N2O7 PrC18H13N2O7 ErC18H11N2O6

Formula weight 508.21 510.21 518.55

Crystal system Triclinic Triclinic Triclinic

Space group P�1 P�1 P�1

a (A) 9.0567(18) 9.013(3) 8.842(3)

b (A) 10.072(2) 9.999(3) 9.352(4)

c (A) 10.610(2) 10.546(3) 10.686(4)

a (deg) 72.54(3) 72.551(5) 80.278(6)

b (deg) 77.83(3) 77.538(5) 76.543(6)

g (deg) 70.02(3) 70.006(5) 73.357(5)

Z 2 2 2

V (A3) 861.4(3) 845.2(5) 818.4(5)

dcalcd (g/cm3) 1.959 2.005 2.104

Temperature (K) 291(2) 293(2) 293(2)

Fð000Þ 496 500 498

m (mm21) 2.527 2.930 5.168

R½I . 2sðIÞ�R1 0.0309 0.0297 0.0257

wR2 0.0790 0.0623 0.0580

L. Huang, L.-P. Zhang / Journal of Molecular Structure 692 (2004) 249–253250

two parallel planes. The distance between the two planes is

ca. 3.3 A. The uncoordinated carboxylate oxygen atoms,

coordinated water molecules and phen ligands are situated

at both sides of the polymeric sheet. The uncoordinated

oxygen atoms form two kinds of C–H· · ·O hydrogen bonds

with C–H of phen molecules and one kind of O–H· · ·O

hydrogen bonds with coordinated water molecules in the

crystal [Fig. 3(a)]. The relevant hydrogen bond parameters

are summarized in Table 3. In addition, weak p–p stacking

interactions exist between the phen molecules of neighbor-

ing sheets, and the average distances between two phen

planes are 3.1 and 3.3 A, respectively. Such intermolecular

hydrogen bonding and p–p stacking interactions between

sheets result in a 3D supramolecular structure [Fig. 3 (a)].

Fig. 3 (b) shows the packing of the sheets in complex 3.

Similar to 1, the Er(III) ions are bridged by fumarate ligands

in two coordination modes (Scheme 1) into a 2D polymeric

sheet which has rhombus grids with a cavity of ca.

8.8 £ 9.4 A. Due to the lack of coordinated water, in 3

exist only one kind of weak C–H· · ·O hydrogen bonds

between the uncoordinated carboxylate oxygen atom and

C–H of phen from adjacent sheet (Table 3). Phen ligands

locate at both sides of the sheets. p–p interactions exist

between phen ligands of adjacent sheets with the average

distances of 3.3 and 3.5 A, respectively. Thus a 3D

supramolecular network is formed via C–H· · ·O hydrogen

bonds and p–p interactions between the sheets (Fig. 3(b)).

3.2. IR spectra

In both spectra of complexes 1 and 2, the characteristic

bands of the carboxylate groups occur within the range

1545–1598 cm– 1 for asymmetric stretching and the range

1365–1425 cm21 for symmetric stretching. The relatively

large values of DOCOðyOCOasym 2 yOCOsymÞ calculated for 1

(209 cm21) and 2 (212 cm21) are close to the value

expected for a monodentate coordination mode of the

carboxylate moiety [8]. The IR spectrum of complex 3

shows the positions of yOCOasym band at 1597(vs) cm21 and

yOCOsym bands at 1407(vs) and 1340(s) cm21. The

symmetric stretching band at 1340 cm21 is unusual

(D ¼ 257 cm21) and maybe it is duo to the marked

Fig. 1. The coordination environments of La(III) in 1 and Er(III) in 3 showing 50% thermal ellipsoids.

Scheme 1. Coordination modes of fumarate groups in complexes 1–3.

Fig. 2. Projection down the c-axis for complex 1. All the hydrogen atoms

are omitted for clarity.

L. Huang, L.-P. Zhang / Journal of Molecular Structure 692 (2004) 249–253 251

difference of 0.084 A between the two C–O distances of the

monodentate coordinated carboxylate group implying a

partial single bond character of the C(16)–O(3) bond

(1.296 A). Comparing the spectra of three complexes, C–H

stretching vibrations appear above 3000 cm21 [9] and

characteristic C–H out-of-plane bending vibrations are seen

at about 731 and 850 cm21, indicating the presence of

phen ligands [10]. The bonds at about 991 cm21 is assigned

to C–H out-of-plane bending vibrations of anti-configur-

ation of fumarate ligands [6].

4. Supporting information available

The crystallographic data have been deposited at Cam-

bridge Crystallographic Data Centre, CCDC Nos 227337

for 1, 227338 for 2 and 227339 for 3. Copies of this

information may be obtained free of charge from the

director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK

(E-mail: deposit@ccdc.cam.ac.uk; fax: þ 44-1223-336033;

http://www.ccdc.cam.ac.uk).

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