ORIGINAL PAPER

Hydrothermal Synthesis, Crystal Structure and Propertiesof Two Organic Amine Templated Lanthanide Sulfates

Jie Fu • Lei Zheng • Yan Yuan • You Song •

Yan Xu

Received: 4 November 2010 / Accepted: 29 June 2011 / Published online: 15 July 2011

� Springer Science+Business Media, LLC 2011

Abstract Two new lanthanide sulfates [C6H14N2]2[Ln2

(SO4)4(H2O)4][SO4]�6H2O (Ln = Pr 1, Nd 2) have been

hydrothermally synthesized and structurally characterized

by single-crystal X-ray diffraction, IR and TGA. Single

crystal X-ray diffraction illuminates that both 1 and 2

crystallize in orthorhombic crystal system, space group

Pbna with cell dimensions: a = 10.1362(13) A,

b = 13.4782(17) A, c = 25.565(3) A, V = 3492.6(8) A3,

Z = 4 for 1; a = 10.1243(12) A, b = 13.4438(16) A,

c = 25.550(3) A, V = 3477.6(7) A3, Z = 4 for 2. Structure

analysis indicates that both 1 and 2 are layered structures

and the sulfate ions as well as the organic templates reside

among the layers. Magnetic property of compound 1 was

investigated further.

Keywords Hydrothermal synthesis � Lanthanide

sulfates � Crystal structures � Magnetic property

Introduction

Great efforts have been made to synthesize non alumino-

silicate solid state materials due to their diverse structural

flexibility and superior catalysis, ion exchange and magnetic

properties [1–3]. Recently, one of the important advances in

the solid state chemistry has been the study of open-frame-

work architectures containing organic amine templated

sulfates [4–10]. Compared with other transition metals, rare-

earth elements’ ability to adopt a large range of coordination

numbers allows them to obtain new topologies, basing on the

variation of the polyhedra [11–23]. One of the strategies

used in the synthesis of solid state materials is to employ a

special organic amine as the structure-directing agent (SDA)

under hydrothermal (solvothermal) conditions. Successful

examples with organic amine templated lanthanide sulfates

materials have been reported. In the previous literatures,

there are a lot of 2D layered lanthanide sulfates have been

reported. For examples, [C2N2H10][La2(H2O)4(SO4)4]

�2H2O is the first example of organic templates 2D layered

lanthanum sulfate constructed by the fusion of 4-membered

ring ladders [22]; [Ln2(SO4)4(H2O)4][C6N2H14]2[C2N2H8]

[SO4][H2O]3 (Ln = La, Pr or Nd) is a layered structure

wherein the SO4 tetrahedra and the LnO9 polyhedra join

together to form (4, 4) net sheets, with two different amines

as well as the sulfate ions residing in the interlamellar space

[13]; [C2N2H10]1.5[Nd(SO4)3(H2O)]�2H2O is the first neo-

dymium sulfate exhibits of a novel two-dimensional zigzag

layer structure with 8-membered rings window [23] and

La2(H2O)2(C2H10N2)3(SO4)6�4H2O is built from inorganic

anionic sheets of lanthanum sulfates between which are

located the ethylenediammonium cations and water mole-

cules [10]. In this work, we used a new method to synthesize

two new 2-D layered lanthanide sulfates of [C6H14N2]2

[Ln2(SO4)4(H2O)4][SO4]�6H2O (Ln = Pr 1, Nd 2) in

Electronic supplementary material The online version of thisarticle (doi:10.1007/s10870-011-0166-8) contains supplementarymaterial, which is available to authorized users.

J. Fu � L. Zheng � Y. Yuan � Y. Xu (&)

State Key Laboratory of Materials-Oriented Chemical

Engineering, College of Chemistry and Chemical Engineering,

Nanjing University of Technology, Nanjing 210009,

People’s Republic of China

e-mail: yanxu@njut.edu.cn

Y. Song

State Key Laboratory of Coordination Chemistry,

Coordination Chemistry Institute, Nanjing University,

Nanjing 210093, People’s Republic of China

123

J Chem Crystallogr (2011) 41:1737–1741

DOI 10.1007/s10870-011-0166-8

hydrothermal by using 1,4-diazabicyclo[2.2.2]octane

(DABCO) as template. Although the inorganic framework is

similar with the reported literature, the guest molecules are

different. In the synthesis of 1 and 2, we used isonicotinic

acid and water as solvent to prevent the decomposed of

DABCO.

Experimental

General Remarks

Compounds 1 and 2 were prepared under hydrothermal

conditions. All chemicals purchased were of reagent grade

and used without further purification. The crystalline

product was characterized by thermogravimetric analysis,

single crystal XRD and IR spectrum. The element analyses

for C, H, and N analyses were performed on a Perkin-

Elmer 2400 elemental analyzer. IR spectra were recorded

on a Nicolet Impact 410 FTIR spectrometer using KBr

pellets. Thermogravimetric analyses were carried out in N2

atmosphere on a Diamond thermogravimetric analyzer

from 50 to 1,000 �C at a heating rate of 10 �C min-1.

X-ray Crystallographic Study

The single crystals of the 1 and 2 were affixed onto a thin

glass fiber by epoxy glue in air for data collection. And the

diffraction data were collected on a Bruker Apex 2 CCD

with Mo Ka radiation (k = 0.71073 A) at 296 K using

x - 2h scan method. An empirical absorption correction

was applied. All the non-hydrogen atoms were refined

anisotropically, while the hydrogen atoms of organic

molecule were refined in calculated positions, assigned

isotropic thermal parameters, and allowed to ride on their

parent atoms. All calculations were performed using the

SHELX97 program package [24]. Further details of the

X-ray structural analyses for compound 1 are given in

Table 1 and the selected bond lengths and angles are listed

in Table 2. CCDC 788161 and 788162.

Synthesis of Compounds 1 and 2

All the two compounds were prepared by a hydrothermal

method from a mixture of Ln2O3 (99.9%), HNO3

(65–68%), H2SO4 (95–98%) and DABCO (99.0%). In a

typical synthesis of 1, a solution was prepared by dis-

solving 0.0842 g Pr2O3 into 10.0 mL diluted nitric acid

(0.1596 g HNO3/10.0 mL H2O) under constant stirring for

an hour. Then 0.1205 g isonicotinic acid and 0.2233 g

DABCO was added into the solution under constant stirring

for 30 min. At last 0.2045 g H2SO4 was dropped into the

solution under stirring for 30 min, the final pH was 2.5.

The resulting mixture was transferred into a 25 mL Teflon-

lined stainless-steel autoclave and heated at 433 K for

3 days. The autoclave was slowly cooled to the room

temperature, and the product was washed with water and

dried in air for 1 day to give the green tabular crystals

(yield 30%, with respect to Pr). Elemental analyses for 1,

Anal. Calcd. (%): C, 12.30; H, 4.10; N, 4.78. Found: C,

12.44; H, 4.18; N, 4.54. IR (KBr pellet, cm-1): 3417 (m),

3191 (s), 1653 (m), 1635 (m), 1472 (m), 1095 (s), 604 (m).

The violet tabular crystals of 2 were prepared in the

same way as 1 by using Nd2O3 (0.0914 g) instead of Pr2O3.

The final yield was 46% (with respect to Nd). Elemental

analyses for 2, Anal. Calcd. (%): C, 12.25; H, 4.10; N,

4.76. Found: C, 12.06; H, 4.15; N, 4.68. IR (KBr pellet,

cm-1): 3417 (m), 3176 (s), 1653 (m), 1635 (m), 1473 (m),

1097 (s), 603 (m). The IR spectra of compounds 1 and 2

show the characteristic bands for DABCO in the region

1,400–1,600 cm-1. The strong bands around 1,097 cm-1

Table 1 Crystal data and structure refinement for 1

Compounds 1

Empirical formula C12H48N4O30Pr2S5

Formula weight 1170.66

Temperature 296(2) K

Wavelength 0.71073 A

Crystal system Orthorhombic

Space group Pbna

Unit cell dimensions a = 10.1362(13) A

b = 13.4782(17) A

c = 25.565(3) A

a = b = c = 90.00�Volume 3492.6(8) A3

Z 4

Calculated density 2.226 mg/m3

Absorption coefficient 3.170 mm-1

F(000) 2344

Crystal size 0.17 9 0.16 9 0.10 mm

h range for data collection 1.59–25.50�Limiting indices -12 B h B 12

16 B k B 14

Reflections collected unique 20470/3254 [Rint = 0.0376]

Absorption correction Semi-empirical from

equivalents

Refinement method Full-matrix least-squares on

F2

Data restraints parameters 3254/6/250

Goodness-of-fit on F2 1.322

Final R indices [I [ 2r(I)]R indices

(all data)

R1 = 0.0489,

wR2 = 0.1467

R1 = 0.0524,

wR2 = 0.1562

Largest diff. peak and hole 2.121 and -0.845 e A-3

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can be attributed to the sulfate ion. Absorption at 603 cm-1

is due to Ln–O vibration. A band around 3,417 cm-1 can

be attributed to the presence of water and hydrogen bands.

Results and Discussion

Structural Description

Compounds 1 and 2 are isostructural and crystallize in

orthorhombic space group Pbna, and structures of both

compounds are similar to the reported layered lanthanide

sulfates. Take 1 as an example, the asymmetric unit of 1

contains 27 non-hydrogen atoms and of which 13 belong to

the inorganic layers, 8 to two organic moieties, 3 to the

interstitial sulfate ion with a � occupied S and two crystal-

lized water molecules, as shown in Fig. 1. In the layer of 1, Pr

is nine-coordinated by seven O atoms from four sulfates and

two O atoms from coordination water, forming a distorted

tricapped trigonal-prismatic geometry. The bond distances of

Pr–O vary from 2.464(4) to 2.604(4) A, whereas the angles of

O–Pr–O are between 54.09(12) and 156.15(14)�, which are in

accordance to other reported Pr compounds [13]. There are

two crystallographic independent S atoms: S(1) makes four

S–O–Pr linkages and links two adjacent Pr atoms through four

l2-O atoms (Pr–O–S bridges) to generate a zigzag [Ln–O–S–O]n

chain (Fig. 2a); S(2) makes three S–O–Pr linkages and

connects adjacent zigzag [Ln–O–S–O]n chains by using a

8-membered ring (Fig. 2b) to form an inorganic zigzag layer

of 1 along [0 0 1] plan as shown in Fig. 3. The inorganic

layer can be viewed as being built up of eight-membered

rings [–Pr–S(1)–Pr–S(2)–Pr–S(1)–Pr–S(2)–] forming of

four PrO9 polyhedra and four SO4 tetrahedra linked through

vertices, zigzag [Ln–O–S–O]n chains. All the S atoms are

tetrahedrally coordinated by four O atoms with the S–O

distances 1.449(8) to 1.498(6) A, which is similar to the

reported lanthanide sulfates [9, 11–13]. The layers are held

together by the N–H���O, C–H���O and O–H���O hydrogen

bonding assembly by diprotonated DABCO cations, water

molecules and free sulfate moieties, which of them are

located in the interlamellar space. The lanthanide sulfate

structure possesses a large number of hydrogen bond

Table 2 Selected bond lengths (A) and angles (�) for 1

Pr(1)–O(2W) 2.464(4) O(5)–Pr(1)–O(2) 75.66(13)

Pr(1)–O(1W) 2.470(4) O(5)–Pr(1)–O(4) 116.03(13)

Pr(1)–O(5) 2.538(4) O(2)–Pr(1)–O(4) 54.88(13)

Pr(1)–O(2) 2.543(4) O(5)–Pr(1)–O(8) 55.09(13)

Pr(1)–O(4) 2.551(4) O(2)–Pr(1)–O(8) 70.70(13)

Pr(1)–O(8) 2.557(4) O(4)–Pr(1)–O(8) 123.81(12)

S(1)–O(6) 1.470(4) O(6)–S(1)–O(8) 112.1(2)

S(1)–O(8) 1.491(4) O(5)–S(1)–O(8) 105.0(2)

S(2)–O(1) 1.466(4) O(1)–S(2)–O(2) 111.7(2)

S(2)–O(4) 1.483(4) O(2)–S(2)–O(4) 104.8(2)

S(3)–O(9) 1.449(8) O(9)–S(3)–O(10) 107.7(4)

S(3)–O(10) 1.498(6) C(2)–C(1)–N(1) 107.7(5)

C(1)–C(2) 1.501(9) N(2)–C(2)–C(1) 108.5(5)

C(1)–N(1) 1.521(9) N(1)–C(3)–C(4) 108.0(5)

C(2)–N(2) 1.496(8) N(2)–C(4)–C(3) 108.3(5)

C(3)–N(1) 1.484(8) N(1)–C(5)–C(6) 107.4(5)

C(3)–C(4) 1.512(9) N(2)–C(6)–C(5) 108.0(5)

C(4)–N(2) 1.504(8) C(3)–N(1)–C(5) 110.9(5)

C(5)–N(1) 1.487(9) C(5)–N(1)–C(1) 109.0(5)

C(5)–C(6) 1.533(10) C(6)–N(2)–C(2) 109.3(5)

C(6)–N(2) 1.495(9) C(6)–N(2)–C(4) 109.4(5)

O(2W)–Pr(1)–O(1W) 75.20(16)

Fig. 1 Molecular structure of the [C6H14N2]2[Pr2(SO4)4(H2O)4]

[SO4]�6H2O 1

Fig. 2 The SBUs of 1: zigzag Pr–O–S chain (a) and 8-membered

ring (b)

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interactions involving the hydrogen atoms attached to the

protonated organic amine and free water molecule with

framework oxygen atoms (Fig. 4).

It is interesting to compare the structure of 1 with that of

b-(NH4)La(SO4)2 [25], (N2H5)Nd(H2O)(SO4)2 [26], and [Ln2

(SO4)4(H2O)4][C6H14N2]2[SO4][C2H8N2][H2O]3 (Ln = La,

Pr or Nd) [13]. In all these compounds, the interlamellar space

depends on the size and orientation of the guest species and

the distance increasing from 4.50 A for ammonium ion to 7.88

A for hydrazinium ion and 12.8–13.4 A for diprotonated

DABCO ion. According to the reported [Ln2(SO4)4(H2O)4]

[C6H14N2]2[SO4][C2H8N2][H2O]3 [13] the diprotonated

DABCO decomposed into ethylene and ethylenediamine,

whereas the same thing didn’t happen during the synthesis of

1. It is may be attributed to the mixed solvent of isonicotinic

acid and water.

The TGA curves of 1 and 2 given in Fig. 5 show distinct

mass losses. The total weight loss of 1 is 66.9%, which is in

agreement with the calculated value (68.5%). The weight

loss of 8.6% in the range of 40–150 �C corresponds to the

removal of three free water (the calculated value is 9.2%),

while the weight loss of 25.3% in the range of 150–480 �C

can be attributed to the loss of two coordination water and

DABCO molecules (the calculated value is 24.9%). The

last loss of 32.7% in the range of 480–980 �C can be

attributed to the loss of SO3 (the calculated value is

34.1%). The final product is Pr2O3. The weight loss of 2 is

similar to 1 and the final product is Nd2O3.

The magnetic susceptibility of compound 1 was measured

in the temperature ranging from 2 to 300 K and under 100 Oe

field. The vM value (Fig. 6) increases from 0.01

03 cm3 mol-1 at 300 K to a maximum of 0.0877 cm3 mol-1

at about 2 K. The vMT value of compound 1 is equal to

3.09 cm3 mol-1 K at room temperature, which is smaller

than the calculated value (3.20 cm3 mol-1 K) of one

uncoupled S = 1 spins of Pr(III) atoms. As the temperature

decreases, the value of vMT decreases continuously and

Fig. 3 The structure of inorganic layer in 1 along [0 0 1] plane

Fig. 4 Water, organic amine cations and sulfates are involved

hydrogen bonding interactions with inorganic layers. Yellow dottedlines represent the hydrogen bond interactions

Fig. 5 TG curves of 1 and 2

1740 J Chem Crystallogr (2011) 41:1737–1741

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reaches 0.175 cm3 mol-1 K at 2 K, resulting from the

occurrence of intermolecular antiferromagnetic interaction

among neighbor Pr(III) ions. The 1/vM versus T plot for 1

could fit with Curie–Weiss equation from 90 to 300 K, giving

C = 3.557 cm3 mol-1 K and h = -44.4 K. The negative

Weiss constant indicates the existence of antiferromagnetic

interaction among the nearest magnetic centers.

Conclusions

In summary, we have successfully synthesized two lan-

thanide sulfates under hydrothermal conditions. Structure

analysis indicates that the inorganic frameworks of 1 and 2

are layered structure, while the free sulfate ions and the

organic template are resided among the layers. The for-

mation both compounds 1 and 2 indicates that the mixture

of isonicotinic acid and water as solvent plays an important

role to prevent the decomposed of DABCO during the

synthesis.

Acknowledgments We thank the National Natural Science Foundation

of China (20971068) for financial support.

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Fig. 6 The plots of vMT and 1/vM (inset) versus T for 1

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