КООРДИНАЦИОННАЯ ХИМИЯ, 2015, том 41, № 7, с. 437-448
УДК 541.49
SYNTHESIS, CRYSTAL STRUCTURE, AND POROSITY OF 1D COORDINATION POLYMER OF NEODYMIUM(III) WITH ISONICOTINIC ACID AND DIMERIC COMPLEX
OF NEODYMIUM(III) WITH NICOTINIC ACID © 2015 S. Sharma, M. Yawer, M. Kariem, R. Singh, and H. N. Sheikh*
Post-Graduate Department of Chemistry, University of Jammu, Baba Sahib Ambedkar Road, Jammu Taw, 180006India *E-mail: hnsheikh@rediffmail.com
A 1D coordination polymer [Nd3(INA)9(H2O)6]n (I) and a dimeric complex with mononuclear asymmetric unit [Nd(NA)3(H2O)2] (II) (HINA = isonicotinic acid and HNA = nicotinic acid) were synthesized. The compounds were characterized by elemental analyses, infrared spectroscopy and single crystal X-ray diffraction studies (CIF file CCDC nos. 938976 (I) and 939 061(II). X-ray crystal structure analysis reveals that both compounds exhibit rich structural chemistry. Compounds I and II belong to the monoclinic system with space group P2j/c. Thermogravimetric analysis has been performed to investigate their thermal stability. The coordination polymer I has meso-porous structure with average diameter of pores (~4 nm) and BET surface area 13.62 m2/g.
DOI: 10.7868/S0132344X15060067
INTRODUCTION
Lanthanide coordination polymers have currently provoked considerable interest owing to their enormous variety of intriguing structural topologies as well as great potential applications in the areas of catalysis [1—3], gas storage [4], separation [5], magnetism [6, 7], and luminescence [8, 9]. Large number of lanthanide metal organic frameworks (MOFs) with various structures and interesting properties have been obtained by the self-assembly of metal ions and organic ligands [10—13]. The design and control over lanthanides based frameworks are strongly influenced by various factors such as organic ligands [14], systematic pH value [15, 16], template effect [17], and reaction temperature [18]. The synthesis and functionality of MOFs and self-assembled supramolecular coordination complexes have been recently reviewed [19, 20]. Lanthanide ions have high affinity for ligands containing oxygen or hybrid oxygen—nitrogen atoms. Lanthanide ions are known to form condensed structures due to their high coordination numbers and flexible coordination environments [21—23]. Because ofthese characteristics, lanthanides ions are best choices to develop high-dimensional MOFs through self-assembly processes. However, design and control of lanthanide based high-dimensional frameworks are more difficult in contrast to transition metal polymers [24].
Multicarboxylate ligands are usually employed in the architectures of lanthanide coordination polymers with unique structure and useful properties. The heterocyclic aromatic carboxylic acid, such as isonicotinic acid and nicotinic acid can bridge metal ions together using both N-donors from pyridine ring and
O-donors from the carboxyl group [25]. On the basis of above mentioned considerations, we selected isonicotinic acid and nicotinic acid as potential linker between lanthanides metal ions. A variety of metal organic frameworks of transition metal with isonicotinic acid and nicotinic acid have been reported [26—28], but the reports on the lanthanides MOF with such heterocyclic ligands are rare. In continuation of our work on coordination polymers with multifunctional ligands [29, 30], we report here the systematic synthesis and structures of two Nd(III) coordination frameworks by using isonicotinic acid (HINA) and nicotinic acid (HNA) as ligands under hydrothermal conditions.
EXPERIMENTAL
Materials and methods. All materials used for synthesis were of reagent grade and used without further purification. Neodymium nitrate hexahydrate was purchased from Alfa Aesar. Nicotinic acid and isonicotinic acid were purchased from Sigma Aldrich. The Fourier Transform Infrared spectra were recorded in the range 4000—400 cm-1 on PerkinElmer-Spectrum RX-IFTIR spectrophotometer with solid KBr pellets. C, H, and N microanalyses were carried out on CHNS-932 Leco elemental analyzer. Thermogravimetric analysis (TGA—DTA) was carried out on Mettler Toledo TGA/SDTA 851e in nitrogen atmosphere with a heating rate of 10°C min-1.
Synthesis of [Nd3(INA)9(H2O)6]„ (I). The 5 mL aqueous solution of Nd(NO3)3 • 6H2O (0.2199 g, 0.5 mmol) was added drop wise to 10 mL aqueous solution of
isonicotinic acid (HINA) (0.184 g, 1.5 mmol), and the pH value was adjusted to about 6.5 with NaOH. The mixture was stirred for 2 h. The resulting solution was filtered and the filtrate was allowed to stand at room temperature. After one week, purple crystals of I suitable for X-ray single crystal diffraction analysis were obtained. The yield was ~0.160 g (59%) based on Nd.
For C54H46N9O24Nd3
anal. calcd., %: C, 39.60; H, 2.83; N, 7.70. Found, %: C, 39.67; H, 2.70; N, 7.58.
IR (v, cm-1): 3300 m, br, 3087 w, 2430 m, 1956 w, br, 1628 m, 1586 s, 1539 s, 1496 w, 1405 s, 1224 s, 1060 s, 1006 s, 862 s, 769 s, 686 s, 534 m.
Synthesis of [Nd(NA)3(H2O)2] (II). The synthetic procedure used to synthesize II was same as that for I except that ligand HNA (0.184 g, 1.5 mmol) was used instead of HINA to obtain purple crystals of II. The yield was ~0.166 g (61%) based on Nd.
For C^H^N^Nd
anal. calcd., %: Found, %:
C, 39.55; C, 39.59;
H, 2.95; H, 2.80;
N, 7.69. N, 7.55.
IR (v, cm-1): 3363 w, br, 3095 w, 2427 w, 1628 s, 1598 s, 1541 s, 1477 w, 1432 w, 1402 w, 1246 w, 1196 s, 1159 s, 1093 s, 1027 s, 858 s, 769 s, 703 s, 634 s, 557 m.
X-ray structures determination. Single crystal X-ray diffraction measurements were performed on a CCD Agilent Technologies (Oxford Diffraction) SUPER NOVA diffractometer. Data were collected at 150(2) K using graphite-monochromated Mo^a radiation (X = = 0.71073 A). The strategy for data collection was evaluated by using the CrysAlisPro CCD software. The data were collected by standard 9—w scan techniques, and were scaled and reduced using CrysAlisPro RED software. Data was corrected for Lorentz, polarisation and absorption factors. The structures were solved by direct methods using SHELXS-97 [31] and refined by full matrix least-squares with SHELXL-97, refining on F2 [32]. The positions of all the atoms were obtained by direct methods. All non-H-atoms were refined anisotropically. The remaining H atoms were placed in geometrically constrained positions and refined with isotropic temperature factors, generally 1.2^eq of their parent atoms. The crystal and refinement data are summarized in Table 1. Selected bond distances and bond angles are shown in Tables 2 and 3.
Supplementary material has been deposited with the Cambridge Crystallographic Data Centre (nos. 938976 (I) and 939061(II); deposit@ ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
N2 TPD and BET surface area. The specic surface area, total pore volume and average pore diameter
were measured by N2 adsorption-desorption method using a NOVA 1200 (Quanta chrome) instrument. The bath temperature was maintained at 77 K. The sample was degassed at 423 K for 12 h before measurement. Pore size distribution and pore volume were obtained by applying the Barrett—Joyner—Halenda (BJH) analysis to the adsorption branch of the nitrogen adsorption—desorption isotherms. The specic surface area of the sample was calculated using the BET method. Micropore surface area and micropore volume were determined from t-plot analysis. All the ow rates were maintained at normal temperature and pressure.
RESULTS AND DISCUSSION
The reaction of Nd(NO3)3 • 6H2O with the requisite heterocyclic aromatic carboxylic acid in water under controlled pH resulted in formation of purple colored crystals of coordination polymer I and dinuclear complex II. Both polymer I and complex II are stable in air and have been characterized by elemental analysis, FT—IR spectroscopy, single-crystal X-ray diffraction, N2 TPD-BET surface area and TGA studies.
FT—IR spectra of I and II show indicative vibrational bands of carboxylate groups and water molecules Broad, weak spectral bands in the vicinity of 3050—3400 cm—1 and strong band at 1628 cm—1 are attributed to v(O—H) and 5(H2O) modes of coordinated water molecules, respectively. Sharp bands at 862 cm—1 for I and 858 cm—1 for II are assigned to pr(H2O) rocking mode of coordinated water whereas weak bands at 534 cm—1 for I and 557 cm—1 for II are contributed by pw(H2O) wagging modes of coordinated water molecule. Intense, slightly broadened bands due to vas(COO) and vs(COO) were observed at 1586 and 1405 cm—1 in I and 1598 and 1402 cm—1 in II. The v— vs is 181 and 196 cm—1 in I and II, respectively. Sharp and strong bands were observed at 1590 and 1432 cm—1 in II which also can be assigned to vas(COO) and vs(COO). The Av = vas — vs for this pair is 158 cm—1. The value of Av = 181 cm—1 in I indicates that carbox-ylato group of isonicotinate anion is bonded in bridging mode whereas values of Av = 196 and 158 cm—1 in II suggest that carboxylate groups are bonded in bi-dentate bridging as well as bidentate chelating mode [33, 34]. The in-plane 5(OCO) vibration modes appear as sharp bands at 686 and 703 cm—1 for I and II, respectively. Absorption band at 1496 and 1477 cm—1 are assigned to v(C=N) of pyridine ring of I and II, respectively.
The asymmetric unit of I consists of three crystal-lographically independent Nd3+ sites [Nd(1), Nd(2), Nd(3)], nine INA— fragments and six coordinated water molecules (Fig. 1a). All nine isonicotinate anions (INA—) adopt bidentate bridging bonding mode through carboxylate oxygen atoms. This is shown as
Table 1. Crystallographic data and structure refinement for complexes I and II
Parameter Value
I II
Formula weight 1637.72 546.58
Crystal system Monoclinic Monoclinic
Space group P2i/c P2i/c
a, A 11.9973(2) 9.65980(10)
b, A 19.7599(3) 12.00480(10)
c, A 26.0246(5) 17.1045(2)
P, deg 91.683(2) 93.2370(10)
V, A 6166.87(18) 1980.34(4)
Z 4 4
p., mm-1 2.575 2.673
Limiting indices hkl — 14 <
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