Abstract
A new two-dimensional (2D) bismuth(III) coordination polymer, {[Bi(μ-C4H4O6)(NO3)(H2O)]. 4H2O}∞ (
Introduction
Coordination polymers are of great interest in coordination chemistry. Their design and synthesis can be controlled by varying the reaction materials and reaction conditions, including temperature, metal-to-ligand ratio, pH value, solvents, and counter ions [1]. Rigid di- and polycarboxylates bridging ligands such as Benzene-1,4-dicarboxylic acid, pyridine-2,3-dicarboxylic acid, pyridine-2,5-dicarboxylic acid, benzene-1,3,5-tricarboxylic acid and benzene-1,2,4,5-tetracarboxylic are used in coordination polymer synthesis to build neutral frameworks [2–6].
Tartaric acid (HOOC-CH(OH)-CH(OH)-COOH) contains two mobile protons in carboxylic groups. In strongly alkaline media, the third proton of the OH-group can also dissociate. The deprotonated carboxylate group possesses polarizable π electron and can be used as magnetic superexchange pathway between the metal ions (superexchange is used for the large distances, occupied by normally diamagnetic ions, radicals, or molecules). Tartaric acid possess two chiral centers and can be used in the preparation of chiral complexes. With six oxygen atoms as potential donors, it can act as a bridging ligand to construct 1D, 2D and 3D frameworks [7–10].
Bismuth is an interesting choice of main metal for metal–organic-based polymers because it forms complexes with high coordination numbers [11–15]. The final thermal decomposition product of such complexes is bismuth oxide. This oxide has five different polymorphs with different structures and properties, α-Bi2O3 (monoclinic), β-Bi2O3 (tetragonal), γ- Bi2O3 (BCC), δ-Bi2O3 (Cubic), ɛ-Bi2O3 (triclinic) [16–18].
Bi2O3 is a semiconductor with band gaps of 2.85 eV for the monoclinic α-Bi2O3 and 2.58 eV for the tetragonal β-Bi2O3 phases and it is used in electronic and optical applications. α-Bi2O3 is one of the stable polymorphs and it was synthesized with various methods including sol-gel method, hydrothermal synthesis, precipitation process and using nano-sized bismuth(III) supramolecular compound [19–21].
In continuation of our ongoing research of the synthesis and characterization of coordination polymers of transition metals with bridging carboxylate groups [3, 22–26], we recently selected tartaric acid as a building block for preparation of polymeric complexes, {[M2(μ-C4H4O6)2(H2O)]. 3H2O}∞ (M = Mn and Cd) and {[Cd(μ-C4H4O6)(H2O)3]·2H2O}∞ [27, 28]. These coordination polymers were found to be useful precursors for preparation of metal oxides in a form of nanoparticles [24–26]. The structures and complexation sites of the complexing agent play important roles in the formation of the nanocrystals. Carboxylic acids are good complexing agents for synthesize of metal-organic hybrids and thermal decomposition of metal-organic hybrids can be led to preparation of nanocrystalline metal oxides. In this work, tartaric acid was used as oxygen donor ligands for synthesis of a new bismuth coordination polymer, {[Bi(μ-C4H4O6)(NO3)(H2O)]. 4H2O}∞ (
Experimental
Materials and instrumentation
All chemicals were used without further purification and purchased from commercial sources. IR spectra were recorded on the Shimadzu spectrometer 470 (KBr pellets, 4000-400 cm–1). Elemental analyses were performed using the Costech ECS 4010 CHNS analyzer. X-ray powder diffraction (XRD) measurements were performed using the Bruker, Advance D8 with Cu Kα (λ= 1.5406 Å) incident radiation. The size distribution and morphology of the thermally decomposed sample was analyzed by scanning electron microscopy (SEM, Tescan Vega3SB – EasyProbe, Czech Republic) and transmission electron microscopy (TEM, Philips CM120)
X-ray crystallographic analysis
The data collection was carried out on a SuperNova diffractometer of Rigaku Oxford Diffraction, using mirror-collimated MoKα(λ= 0.71073 Å)radiation of a microfocus X-ray tube, and CCD detector Atlas S2. The data reduction and cell refinement were performed using CrysAlis PRO [29]. The structures was solved by SHELXT [30] and Superflip [31] and refined by the full-matrix least-squares methods based on F2using Jana2006 [32]. Due to the presence of the quite heavy atom Bi, refinement of anisotropic displacement parameters of light atoms was unreliable and did not improve R values. Therefore, we only refined anisotropic displacement of bismuth.
Hydrogen atoms bonded to carbon were attached geometrically. Hydrogen atoms of OH group could be found (with difficulties cause but very noisy difference Fourier maps due to heavy atom Fourier maps due to the heavy atom) in the difference Fourier map and refined using a bond length restraint 0.84Å and C-O-H angle restraint 109.47°. Determination of the lattice water hydrogen atoms was not possible.
The structure visualizations were done with ORTEP-III [31] and MERCURY (Version 3.5.1) [33]. The crystal parameters, data collection and refinement results for
Synthesis of the complex
Preparation of { 4H2O}∞ (
IR (KBr) (, cm–1): 3530-3330 (b), 1577 (s), 1453 (m), 1405 (s) 1375 (s), 1330(s), 1310 (s), 1296 (s), 1152 (m), 1119 (m), 947 (m), 674 (m), 599 (m), 492 (w).Anal. Calc. for C4H14BiNO14: C, 9.43, H, 2.75, N, 2.75%. Found: C, 9.34, H, 2.68, N, 2.70%.
Preparation of Bi2O3 Nano structure
For thermal decomposition of complex and preparation of nanostructure of Bi2O3,
Results and discussion
Crystal structure
The asymmetric unit of
There is some hydrogen bond of the O–H...O type between crystalline water molecule and complex (Fig. 5, Table 3).
IR spectra
The IR spectra of the complex show two sets of vibrations due to the water molecules and tartrate ligands. Bands at 1590–1119 cm–1 areassigned to the L-tartrate ligand while broad strong bands at the region 3500–3300 cm–1 are assigned to O–H...O hydrogen bonds between water molecules [34, 35]. The coordinated nitrate ion show strongly split bands at 1453–1405 and 1296–1152 cm–1. The magnitude of the peak splitting (157 and 253 cm–1) corresponds with the bidentate coordination mode of the nitrate ion [36, 37].
Characterization of Bi2O3 nanoparticles
The conversion of the complex to Bi2O3 is accompanied by disappearance of the IR bands characteristic for the L-tartrate ligand at 1590–1119 cm–1 and broad strong bands at the region 3500–3300 cm–1 and bands at 1453–1405 and 1296–1152 cm–1 for nitrate ion. The remaining absorption bands at 580 and 505 cm–1 can be assigned to Bi–O vibrations of Bi-O bonds in BiO6 octahedral units [38].
The PXRD profile (Fig. 6) confirms that the product of the thermal decomposition of
The morphology of the sample was examined by a scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM and TEM images of the nanosized Bi2O3 powder is shown in Figs. 7 and 8.
Conclusions
A novel 2D-Bismuth(III) coordination polymer, { 4H2O}∞ (
Footnotes
Acknowledgments
This research was supported by Science and Research Branch, Islamic Azad University.The crystallographic part was supported by the project 15-12653S of the Czech Science Foundation using instruments of the ASTRA lab established within the Operation program Prague Competitiveness – project CZ.2.16/3.1.00/24510.
