Synthesis and Spectral Properties of Dinuclear Bis (Acetylacetonato) Nickel(II) Aqua Complex.

 

Md. Kudrat-E-Zahan1* and Hiroshi Sakiyama2

1Department of Chemistry, Faculty of Science, Rajshahi University, Bangladesh.

2Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, Japan

*Corresponding Author E-mail:

 

 

ABSTRACT:

Dinuclear Bis(acetylacetonato)nickel(II) aqua complex was synthesized and electronic spectra were studied in noncoordinating solvent. Elemental analyses data, IR spectra and electronic spectral components showed that the complex retain dinuclear structure in solid and solution.

 

KEYWORDS: Bis(acetylacetonato)nickel(II) complex, Electronic spectra, Angular overlap model (AOM).

 

 

1. INTRODUCTION:

Synthesizing new kinds of metal complexes and the complete understanding of their geometric and electronic structures is an all important goal in coordination chemistry. It is only through the development of innovative synthetic tools, as well as the structural understanding of metal complexes, that a rational basis for their application in various fields of chemistry can be achieved [1].

 

Bis(acetylacetonato)nickel(II) complex has been extensively studied. Single-crystal X-ray study revealed its trinuclear structure [2], which is stable in non-donor solvents [3]. The trinuclear complex converted into mononuclear and dinuclear complexes in coordinating solvents, such as water, pyridine, and alcohols [4-6]. Several dimeric derivatives of bis(acetylacetonato)nickel(II) with pyridine, piperidine and isopropanol were reported[7-9]. The complex is also well known for its catalytic properties [10].

 

Earlier, we studied the electronic spectra of nickel(II) complexes and a relationship was found between spectral pattern and the cis/trans isomers [11].We also determined the equilibrium ratio between the cis and the trans isomers using electronic spectra [12]. In present study, we focused on the spectra of dinuclear [Ni2(acac)4(H2O)2] complex in noncoordinating solvent for the purpose of comparing structure in solution and in solid state.

 

2. EXPERIMENTAL:

2.1. Measurements and computations:

Elemental analyses (C and H) were performed at the Elemental Analysis Service Center of Kyushu University. IR spectra were recorded on a Hitachi 270-50 spectrometer. Electronic spectra were measured at room temperature on Jasco v-560 (200-800 nm) and Hitachi 330 (800-1600 nm) spectrophotometers. From the observed spectroscopic data, spectral components were obtained by Gaussian curve analyses. The obtained components were simulated usingD2 symmetry based on the angular overlap model (AOM) calculation using AOMX program developed by Adamsky.

2.2. Materials

 

[Ni(acac)2(H2O)2] was prepared according to the literature method [13]. [Ni2(acac)4(H2O)2] was obtained by the removal of water from [Ni(acac)2(H2O)2] by azeotropic method in toluene. Anal. Found: C, 43.36; H, 5.97; Ni, 21.52%. Calcd for C10H16NiO5: C, 43.69; H, 5.86; Ni, 21.36%. Selected IR data [ν/cm-1] on KBr: 3344, 1590, 1512, 1392. All other chemicals were commercial products and were used as supplied.

 

3. RESULTS AND DISCUSSION:

Electronic spectra of Ni(acac)2 in dichloromethane is shown in Fig. 1. Two major band maxima observed in the spectra at around 8500 and 15600 cm-1. These two were associated with the spin-allowed transitions from the ground 3A2 state to the excited triplets 3T2(3F) and 3T1(3F) in O symmetry. An small shoulder band was observed at 13100 cm-1, which was assigned as 3A2 → 1E.The shape of the first band was not symmetrical, and it inclined slightly toward the lower energy. Therefore, this band could not be reproduced by only one Gaussian component, and it was analyzed using three equivalent components. In the first band, the lower two components are close in energy, but the other one is separated from them. The whole band is well described by the axial symmetry, and the doublet is lower than the singlet. The second band was also analyzed using three equivalent components. It was also well described by the axial symmetry, but, in contrast with the first band, the singlet was lower than the doublet. Therefore, the spectrum is typical for the trans pattern with two weak donor atoms [11]. The characteristic appearance of the spectra is that the first band is inclined toward lower energy and the second allowed band, toward the higher energy. It is noteworthy that, although these inclinations are subtle to the eye, they are clearly evident in a Gaussian curve analysis.

 

Fig. 1.Observed electronic spectra (–) and spectral components     (---) analyses for [Ni(acac)2(H2O)]2 in  dichloromethane. The concentration of Ni(acac)2 was 2×10-2moldm-3. The number “2” indicates that two components are superimposed at almost the same position.

 

The spectra was analyzed by Gaussian curve fitting based on the D2 symmetry up to 2000 cm-1 because of the superposition of the charge transfer bands above this. The observed spectral components together with their assignments are shown in Table 1.The obtained spectra and spectral splitting patterns of the Gaussian components indicated the presence of trans-octahedral Ni(II) complex with weak donors in axial positions. The structure was predicted as trans-[Ni2(acac)4(H2O)2], in which two water molecules were bound at axial positions of two adjacent nickel center.The observed data were well simulated by the AOM calculation with the parameters eσ.A= 2600 cm-1, eσ,B= 3400 cm-1, eσ,C= 3600 cm-1, B = 1020 cm-1 and C = 2900 cm-1. The simulated energy values for the transitions with the optimized parameters and the Racah parameters B, C are summarized in Table 1. In this case assuming rotation group D2, eσ,A value corresponds to the average of the two donor oxygen atoms from acetone ligand on axial positions. eσ,B and eσ,C values to the average of the two oxygen donor atoms of acetylacetonato ligands on equatorial positions. The complex remain as adimer containing coordinated aqua ligands with bridging and non-bridging acetylacetonato groups. The optimized parameters showed that the coordination of the water oxygen to the metal center was much weaker than the acetylacetonateoxygen. Obtained B value was ~98% of the B value for free nickel(II) ion (1042 cm-1) [14]. The geometrical structure around for Ni(acac)2 in dichloromethane was predicted  as trans-[Ni2(acac)4(H2O)2] as shown in Fig. 2.

 

Table 1. Assignments of spectra of Ni(acac)2 in dichloromethane (cm-1).

Exptl.  ∆E

Spectral Components

Transition

D2 symmetry

Transition (O)

Observed

Calculated(D2) a

8400 (6.3)

3A2→ 3T2(3F)

8068(2.8)

  8302

3B1 → 3B3 (1)

8343(2.8)

  8588

3B1 → 3A2 (1)

 

10298(2.8)

10521

3B1 → 3B2 (1)

11000 (2.5)

3A2→ 1E(1D)

12843(0.8)

12716

3B1 → 1A (1)

13183(0.8)

13312

3B1 → 1A (2)

15600 (5.8)

3A2→3T1(3F)

14909(2)

14674

3B1 → 3A2 (2)

15878(2)

15705

3B1 → 3B2 (2)

15964(2)

15828

3B1 → 3B3 (2)

aParameters: eσ.A = 2600 cm-1,  eσ.B = 3400 cm-1, eσ.C = 3600 cm-1, B = 1020 cm-1, and C = 2900 cm-1.

 

Fig. 2. Proposed structure for [Ni(acac)2(H2O)]2

 

4. CONCLUSION:

In this study, analyzing the electronic spectra of newly synthesized [Ni2(acac)4(H2O)2], spectral components and AOM parameters were described. An interpretation of electronic spectral properties may led to rules which can be used by experimentalists to improve the performance of their compound.

 

5. ACKNOWLEDGEMENTS:

We thank Drs. Thomas Schönherr and Heribert Adamsky at Heinrich-Heine-Universität Düsseldorf for providing a copy of the AOMX program.

 

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Received on 04.08.2013          Modified on 08.09.2013

Accepted on 27.09.2013         © AJRC All right reserved

Asian J. Research Chem. 6(11): November 2013; Page 1072-1074