Preparation of N , N , N ’ , N ’-tetrakis-( 2-benzimidazolyl-methyl )-1 , 2-ethanediamine and crystal assemblies of the relative complexes

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 TBIMEDA) SO4·5H2O, 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 (fivemember ring). These cores then were linked together by multi hydrogen bond interactions with sulfate ions and water molecules to construct their 3D crystal architectures.


Materials and Physical Measurements
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.

Synthesis of Ligand
Preparation of the ligand, N,N,N',N'-tetrakis-(2-benzimidazolylmethyl)-1,2-ethanediamine (TBIMEDA) was described as below [10][11][12][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 16 h.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  N 7.08 (7.12).This IR data were similar to the reported values.[10] The preparation of TBIMEDA was described as Scheme 1.

Ni(TBIMEDA)•SO 4 •5H 2 O(2)
Keeping under stirring, TBIMEDA (0.0706 g, 0.1 mmol), NiSO 4 •6H 2 O (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 NiC 34 H 42 N

Single Crystal X-Ray Diffraction Analysis
The X-ray data collections and structure determinations were performed on a Bruker SMART CCD.The data were collected using graphite-monochromatic Mo-K radiation ( = 0.71073 Å).The crystal structure was solved by direct methods and refined by full-matrix least-square calculation on F 2 with SHELX-97 program package.[14].All non-hydrogen atoms were treated anisotropically.Hydrogen atoms were placed in calculated positions.The crystallographic data for 1-3 are summarized in Tables 1 and 2.

Crystal Analyses for 1 -3
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 Figure 1.Some selected bond distances and angles are listed in Table 1, and the hydrogen bonding data are listed in Table 2. 1 adopted orthorhombic system with P2 1 2 1 2 1 space group (unit cell parameters: a = 11.2807(16) Å, b = 14.980(2)Å, c = 23.081(3)Å, β = 90.00˚,V = 3900.2(10)Å 3 , Z = 4, Dc = 1.497 mg/cm 3 ).Cadmium(II) ion in the core of complex 1 is coordinated by one neutral TBIMEDA ligand, forming five of fivemember rings (Figure 1).The octahedral coordination core around cadmium(II) ion includes six N atoms, two of them originate from the chain of ethanediamine and the others originate from the unsaturated N atoms in imidazole rings.All distances of Cd-N described above are near to or shorter than the sum of Van der Waals radii for Cd and N, and the effective chelations result in distorted octahedron around Cd(II) ions.However, the saturated N atoms in imidazoles, include N3, N5, N11 and N12, are protonated and without any coordination contribution.

Hydrogen Bond Interactions in 1
In the crystal structure of complex  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 Figure 3), and this MOF can be simplified as a topologic diagram with characters of 3 × 7 2 around Cd cores and 3 2 × 7 5 × 8 3 around sulfate cores (Figure 4).Meanwhile, if all Cd cores were ignored, the sulfate ions and water molecules will be linked together to construct a 2D chain running along the a axis (Figure 5).

Photoluminescence
Excitation under  Ex = 341 nm, ligand TBIMEDA gave a emission at  Em = 375 nm, which was contributed from its conjugated configuration with π-π * electron transition (Figure 6).After crystal assembly using the ligand with the metal ions with d 10 configuration, such as Cd(II) in 1, its crystal state also presented a strong emission peaks at  Em = 417 nm ( Ex = 339 nm).Obviously, compared with    the ligand's emission, the fluorescent peaks of 1 emerged with red shift.This photoluminescence mechanism originated from ligand-metal charge transition (LMCT) [15], and its emission peak position was decided by the coordination situation of ligand with metal ion [16].

CONCLUSION
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) SO 4 •5H 2 O(M = Cd II , Co II , Ni II ) all adopted orthorhombic crystalline with P2 1 2 1 2 1 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.

Figure 3 .
Figure 3. Crystal architecture of 1 constructed by hydrogen bonding interactions.Cd II cores and 2 4 SO  ions are linked together to form a network stretched in the ac plane.All H 2 O molecules and H atoms without hydrogen bonding contributions are omitted for clarity.

Figure 5 .
Figure 5. Simplified graph of for 1 only with water molecules and sulfate anions.