N, N, N′, N′-tetrakis-(2-benzimidazolylmethyl)-1, 2-ethanediamine(TBIMEDA), was prepared by reaction of ethylenediamine tetra-acetic acid disodium salt(EDTA) with 1, 2-diaminobenzene in a refluxed glycol solution, and furthermore, three allomeric complexes[(M IITBIMEDA) SO 4·5H 2O, M = Cd, Co, Ni] were selfassembled by solvothermal method based on reaction of this ligand with the relative sulfates respectively. These allomeric complexes were characterized by elemental analysis and IR spectroscopy and their crystal structures were determined by single crystal X-ray structural analysis. In the crystal architecture of these complexes, every metal(II) ion is chelated by one neutral TBIMEDA ligand to form an octahedral core with configuration of five heterocyclic rings (five- member ring). These cores then were linked to- gether by multi hydrogen bond interactions with sul- fate ions and water molecules to construct their 3D crystal architectures.
Azaheterocyclic compounds, with strong coordination ability during complex preparations and as better acceptors in hydrogen bonding formation, were more frequently selected in coordination research [1-4]. After selfassemblies, the conjugated p bonds in the heterocyclic ligands provided abounding information on electromagnetism and photoelectrochemistry, and these special complex’s aggregation was well known as functionalized material in future applications [5-9]. Meanwhile EDTA (ethylenediamine tetra-acetic acid) was regard as the most useful multidentate ligand using in analytic chemistry. In this work, based on reaction of EDTA with benzene-1,2-diamine, a multidentate ligand with four benzoimidazole groups, N,N,N’,N’-tetrakis-(2-benzim-idazolyl methyl)-1,2-ethanediamine(TBIMEDA), was prepared according to the reported method (Scheme 1) [10-13]. Furthermore, by self-assembly of TBIMEDA reacting with different sulfates, three single-nuclear complexes with same crystal configuration were constructed by sovothermal methods, and their crystal structures were well defined by X-ray analysis.
All chemicals and solvents were of analytical reagent grade and used as received. Elemental analysis was performed in a Perkin-Elmer 240 elemental analyzer. IR spectrum was obtained using a Nicolet IR200 infrared spectrometer. The fluorescence spectra were taken on an Edinburgh Instruments FLS920 fluorescence spectrumeter respecttively.
Preparation of the ligand, N,N,N’,N’-tetrakis-(2-benzimidazolylmethyl)-1,2-ethanediamine (TBIMEDA) was described as below [10-13]: A solution of EDTA (2.92 g, 0.01 mol) and 1, 2-diaminobenzene (4.32 g, 0.04 mol) in 100 mL of glycol was heated to boiling and kept in reflux for 16h. After cooling down to room temperature, the mixture was added to water (ac. 400 mL) for precipitation over night. The crude product was separated by filtration, purified by recrystallization with small volume of ethanol for three times and dried in air. A white powder product in yield of 70% was obtained with m. p. = 156˚C - 158˚C. IR data (KBr, cm−1): 3186 vs (nN-H), 2966 w, 2823 w, 1617 s, 1535 s, 1486 w(sN-H), 1454 s, 1433 vs, 1348 s, 1311 m, 1274 vs, 1245 m, 1217 w, 1094 s, 1049 m, 1021 m, 996 m, 963 w, 845 m, 747 vs, 616 w, 485 m. Calc. (found) for C34H32N10:C 72.88 (72.90), H 3.84 (3.82), N 7.08 (7.12). This IR data were similar to the reported values. [
Keeping under stirring, TBIMEDA (0.0706 g, 0.1 mmol), CoSO4·7H2O (0.0422 g, 0.15 mmol) are mixed with water (8 mL). The mixture was sealed in an autoclave and the autoclave was placed in an oven at 120˚C for 60 h. After cooling down to room temperature at rate of 5˚C/h, filtrating and washing, several large and transparent orange crystals were collected (in yield of 34%). Found (Calc.) for CoC34H42N10O9S: C, 49.44(49.45); H, 5.11(5.13); N, 16.98(16.96)%. IR data(KBr, cm−1): 3415 s, 3101 w, 3056 w, 2917 w, 2774 w, 2643 w, 1621 m, 1540 m, 1470 m, 1450 vs,1392 m, 1274 vs, 1119 vs, 1029 m, 939 m, 910 w, 910 w, 857 w, 743 vs, 620 vs, 555 w, 514 w.
Keeping under stirring, TBIMEDA (0.0706 g, 0.1 mmol), NiSO4·6H2O (0.0262 g, 0.1 mmol) were mixed with water (8 mL). The mixture was sealed in an autoclave and the autoclave was placed in an oven at 140˚C for 60 h. After cooling down to room temperature at rate of 5˚C/h, filtrating and washing, several large and transparent blue crystals were collected (in yield of 45%). Found (Calc.) for NiC34H42N10O9S:C, 46.48(46.47); H, 5.13(5.11); N, 16.97(16.99) %. IR data (KBr, cm−1): 3415 s, 3105 m, 3064 w, 2913 w, 2765 w, 2639 w, 1544 m, 1405 vs, 1392 s, 1331 vs, 1278 vs, 1221 w, 1115 vs, 1029 s, 988 w, 939 s, 906 m, 849 m, 743 vs, 616 vs, 545 w, 518 w.
Similar to the assembly of 1, when NiSO4·6H2O was replaced by CdSO4·8H2O (0.0385 g,0.05 mmol), large and transparent blue crystals were obtained in yield of 45% by the same hydrothermal method. Found(Calc.) for CdC34H42N10O9S:C, 49.44(49.45); H, 5.07(5.09); N, 15.95(15.93)%. IR data (KBr, cm−1): 3395 s, 3096 m, 2761 w, 1621 m, 1540 m, 1446 vs, 1384 s, 1335 m, 1278 s, 1094 vs, 1025 s, 755 s, 620 m.
The X-ray data collections and structure determinations were performed on a Bruker SMART CCD. The data were collected using graphite-monochromatic Mo-Ka radiation (l = 0.71073 Å). The crystal structure was solved by direct methods and refined by full-matrix least-square calculation on F2 with SHELX-97 program package. [
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Complexes 1 - 3 are alloisomers with each other, 1 is therefore selected as a typical example for discussing their crystal configurations. The view of the single core of 1 is depicted in
In the crystal structure of complex 1, the Cd(II) coordination cores are linked through intermolecular N-H···O and O-H···O hydrogen bonds with sulfate ions and water molecules (
coordination water molecules are omitted, the Cd(II) coordination cores and sulfate ions will be linked by hydrogen bonding interactions to form a metal organic framework (MOF, as describing in
Excitation under lEx = 341 nm, ligand TBIMEDA gave a emission at lEm = 375 nm, which was contributed from its conjugated configuration with π-π* electron transition (
the ligand’s emission, the fluorescent peaks of 1 emerged with red shift. This photoluminescence mechanism originated from ligand-metal charge transition (LMCT) [
Ligands of diamine with imidazole group exhibited potentially application in biodegradation. In this work, after preparation of N,N,N’,N’-tetrakis-(2-benzimidazolylmethyl)-1,2-ethanediamine(TBIMEDA), and using it as ligand reacting with different salts, three crystal architectures were self-assembled under solvothermal conditions. In crystal assembly, beside coordination between metal and ligands, the crystal architectures were also sustained by multi hydrogen bonding interactions from the complex cores with sulfate anions and water molecules. Three crystal architectures of M(TBIMEDA) SO4·5H2O(M = CdII, CoII, NiII) all adopted orthorhombic crystalline with P212121 space group. The metal center was chelated by three TBIMEDA to construct an octahedral configuration with five 5-numbered chelating rings, where the coordinating atoms were unsaturated N in imidazole ring and saturated N from ethylenediamine chain. These complexes can be used as a model to study
the effect of stereochemistry on the coordination polyhedron of M(II) ions. Although these M(II) ions were coordinated by six atoms, their coordination bonds were different in length, and therefore they may use different hybrid obits to form inner orbital or outer orbital coordination compounds. Obviously, these conclusions should be supported by magnetic determination and thermal gravimetric analysis. Further study should be intensively investigated.
This work was financially supported by the National Natural Science Foundation of China (No. 20771073); by the “211” Project of Guangdong Province (the third time): The Key and Common Technologies in Fine Chemical Engineering; and by The Key Project of Education Office from Guangdong Province, China.