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Quantum chemical calculations and X-ray crystallographic studies of cis-dioxomolybdenum(VI) Schiff base complex
*Corresponding author at: Chemistry Department, Shahid Bahonar University of Kerman, Kerman 76169, Iran. Tel./fax: +98 341 3222033 i_shoaie@yahoo.com (Iran Sheikhshoaie)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer-review under responsibility of King Saud University.
Available online 25 October 2010
Abstract
Treatment of the Schiff base 2-((E)-(2-hydroxy propylimino)methyl)phenol with MoO2(acac)2 in dry methanol gave the mononuclear complex (methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI), which was characterized by X-ray crystal analysis, and it has monoclinic space group p21/c, and a = 10.330(17) Å, b = 9.397(15) Å, c = 13.695(2) Å, V = 1252.1(3) Å3, and Z = 4. B3LYP theoretical method with DZP basis sets calculations nicely reproduces the X-ray experimental geometry, molecular orbital levels and the other structural properties for this complex.
Keywords
Quantum chemistry
B3LYP/DZP
X-ray
cis-Dioxomolybdenum(VI)
Schiff base
1 Introduction
Schiff base ligands are one of the oldest classes of ligands in the coordination chemistry, have been used extensively to complex transition metals (Goodwin and Bailar, 1961; Fenton, 2002; Piguet et al., 1997; Abu-Ragabah et al., 1992). The molybdenum Schiff base complexes have a good role in many catalytic reactions, and catalytic oxidation reactions are as an important area for many research groups during the past years. A large number of important chemical reactions are catalyzed by molybdenum(VI) compounds. The selective oxidation of organic sulfides to sulfoxides or sulfones has been thoroughly investigated for many years. Dioxomolybdenum(VI) compounds are commonly encountered in enzyme and metal surface models, oxidation catalysis and oxygen transfer reactions (Rajan and Chakravorty, 1981; Abu-Omar et al., 2005; Topich, 1981). Molybdenum complexes containing oxotransferases and hydroxylases belong to the class of molybdoenzymes with mono nuclear active sites (Eierhoss et al., 2008; Hille, 1996, 2002). Also molybdenum-oxo complexes have been studied in oxygen atom transfer processes, for instance the oxo transferase enzymes like nitrate reductase in which the active sites consist of a cis molybdenum dioxo moiety (Arzoumanian et al., 1995, 1997). Molybdenum(VI) dioxo-complexes have been extremely thoroughly investigated and there are many literature reports of their syntheses and reactivity, particularly in terms of oxo-transfer reactions (Holm, 1990; Spence, 1983).
In our previous works we reported a novel tridentate Schiff base dioxomolybdenum(VI) complex (Sheikhshoaie et al., 2009). In this work we will report the structural properties of methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex by DFT calculations. All calculations were performed by using ADF (te Velde et al., 2001; Guerra et al., 1998; ADF 2009.01) program package with B3LYP/DZP (Becke, 1993, 1988; Lee et al., 1988) basis sets. In this study we will report some comparisons to X-ray data and theoretical calculations data for the more stable geometry of this molybdenum(VI) complex. The stereo view or the stereoscopic ORTEP plot (Johnson, 1965) of the unit cell of this compound with atomic numbering of its structure is shown in Fig. 1.![Stereoscopic ORTEP20 plot of methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex showing the atomic numbering scheme.](/content/184/2013/6/4/img/10.1016_j.arabjc.2010.10.019-fig1.png)
Stereoscopic ORTEP20 plot of methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex showing the atomic numbering scheme.
Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 688077. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223336033; e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk). Supplementary data associated with this article can be found in the online version.
2 Computational details
All final calculations, whose results are reported here, were performed using the ADF program (te Velde et al., 2001) by means of density functional theory (DFT). The hybrid B3LYP density functional was applied in all calculations and DZP basis sets were employed in this study (Becke, 1993, 1988; Lee et al., 1988). Fig. 2 shows the optimized structure of methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex. Selected experimental and calculated structural parameters for are shown in Table 1.![Theoretically predicted geometry for methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex by using B3LYP/DZP method.](/content/184/2013/6/4/img/10.1016_j.arabjc.2010.10.019-fig2.png)
Theoretically predicted geometry for methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex by using B3LYP/DZP method.
Empirical formula
E50(HOMO)a (eV)
E51(LUMO)b (eV)
μc (D)
(ΔE)d (eV)
Volume (Å3)
C11–H15–Mo–N–O5
−6.798
−2.641
0.058
4.157
1252.1
Table 2 shows some selected important bond lengths and bond angles, and Fig. 3 shows the calculated UV spectrum for the optimized structure of methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex by using ADF 2009.01 and B3LYP/DZP method.
X-ray data for complex
Theoretical (B3LYP/DZP)a data for complex
Mo–O(1)
1.960
2.05
Mo–O(2)
1.952
2.00
Mo–O(3)
1.709
1.75
Mo–O(4)
1.703
1.75
Mo–O(1S)
2.355
2.52
Mo–N(1)
2.274
2.40
O(4)–Mo–O(3)
107.05
106.3
O(4)–Mo–O(2)
98.01
99.3
O(3)–Mo–O(2)
97.34
99.3
O(4)–Mo–O(1)
97.80
99.9
O(3)–Mo–O(1)
101.00
101.2
O(2)–Mo–O(1)
151.04
144.8
N(1)–Mo–O(4)
93.07
83.2
N(1)–Mo–O(3)
159.38
162.9
N(1)–Mo–O(2)
74.90
78.0
N(1)–Mo–O(1)
80.17
89.9
O(4)–Mo–O(1S)
168.84
170.5
O(3)–Mo–O(1S)
84.09
83.2
O(2)–Mo–O(1S)
79.45
77.6
O(1)–Mo–O(1S)
80.35
78.7
N(1)–Mo–O(1S)
75.77
79.9
![UV spectra calculated diagram for methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex by using B3LYP/DZP method. ∗Main transitions (1) 50 → 51, (2) 50 → 52, (3) 50 → 54, (4) 47 → 51, (5) 49 → 51.](/content/184/2013/6/4/img/10.1016_j.arabjc.2010.10.019-fig3.png)
UV spectra calculated diagram for methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex by using B3LYP/DZP method. ∗Main transitions (1) 50 → 51, (2) 50 → 52, (3) 50 → 54, (4) 47 → 51, (5) 49 → 51.
Table 3 shows all important singlet–singlet (S–S) theoretical calculated transitions of this complex.
Number of transition
E (eV)
Oscillator strength (a.u.)
Major MO → MO transitions
% Transitions
1
3.4173
0.19726E−01
50a → 51a
90
50a → 52a
3
48a → 51a
2
50a → 54a
1
2
3.6958
0.13784E−01
50a → 52a
55
50a → 53a
29
48a → 51a
3
49a → 51a
3
3
3.7903
0.38126E−02
48a → 51a
42
48a → 52a
15
50a → 53a
14
49a → 51a
10
4
3.8796
0.22098E−01
50a → 53a
53
50a → 52a
32
48a → 51a
7
48a → 52a
3
5
3.9862
0.18155E−01
50a → 54a
85
48a → 51a
1
50a → 52a
1
49a → 51a
0.4
6
4.2003
0.18006E−02
48a → 53a
41
48a → 52a
23
49a → 53a
12
47a → 51a
1
7
4.2382
0.11059E−01
47a → 51a
33
49a → 51a
22
48a → 53a
19
48a → 51a
6
8
4.4058
0.39926E−02
46a → 51a
62
48a → 49a
7
45a → 51a
6
48a → 51a
6
9
4.4992
0.30160E−02
45a → 51a
65
45a → 52a
14
48a → 54a
2
46a → 52a
2
10
4.5513
0.38832E−01
49a → 51a
34
47a → 51a
22
46a → 51a
8
49a → 52a
8
The contribution of atomic orbital in some of the molecular orbital shows in Table 4, and some of the frontier molecular-orbital diagrams are shown in Fig. 4 (for methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex).
Orbital
E (eV)
%Mo
%O
%N
%C
48
−7.902
–
41.67(py) + 25.64(pz)
1.92(pz)
1.11(pz)
49
−7.668
–
2.06(px) + 11.46(py) + 4.06(pz)
1.95(py) + 7.5(pz)
18.61(py) + 39.88(pz)
50(HOMO)
−6.798
–
2.24(px) + 6.52(py) + 13.04(pz)
1.71(py) + 3.24(pz)
18.6(py) + 43.41(pz)
51(LUMO)
−2.641
30.52(dxz)
17.05(px)
2.22(py) + 8.46(pz)
8.73(py) + 22.22(pz)
52
−2.351
10.52(dxy) + 26.31(dxz)
13(px) + 1.62(py) + 1.76(pz)
2.05(py) + 5.90(pz)
6.49(py) + 20.15(pz)
53
−2.132
50.45(dxy) + 4.2(dxz) + 2.33(dx2–y2)
29.42(px)
1.25(pz)
1.51(pz)
![Calculated (B3LYP/DZP) frontier molecular-orbital diagram for methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex illustrating the HOMO−2, HOMO−1, HOMO, LUMO, LUMO+1, LUMO+2.](/content/184/2013/6/4/img/10.1016_j.arabjc.2010.10.019-fig4.png)
Calculated (B3LYP/DZP) frontier molecular-orbital diagram for methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex illustrating the HOMO−2, HOMO−1, HOMO, LUMO, LUMO+1, LUMO+2.
Fig. 5 shows a part of calculated molecular-orbital diagram of methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex by using B3LYP/DZP method.![The calculated MO diagram for methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex by using B3LYP/DZP method.](/content/184/2013/6/4/img/10.1016_j.arabjc.2010.10.019-fig5.png)
The calculated MO diagram for methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI) complex by using B3LYP/DZP method.
3 Results and discussion
The geometry of this molybdenum complex optimized in the gas phase using tools from the density functional theory calculations. The agreement between theoretical and experimental data is for this metal complex as can be seen in Table 2. The most relevant differences are observed when the O2–Mo–O1, N1–Mo–O4, N1–Mo–O3 and N1–Mo–O1 bond angles are compared. The ideal gas phase values are O4–Mo–O3 (106.3), O4–Mo–O2 (99.3), O3–Mo–O2 (99.3), O4–Mo–O1 (99.9) and O3–Mo–O1 (101.2), respectively, whereas the experimental ones are 107, 98, 97, 97.8 and 101, respectively. These facts suggest that this molybdenum complex becomes stabilized in the solid state. The electronic excitation energies and oscillator strengths f calculated by B3LYP/DZP method for this complex are summarized in Table 3. The longest wavelength transition is belonging to HOMO–LUMO with n → π* character[the percentage composition of the lowest unoccupied and highest occupied molecular orbital levels for this compound are: For HOMO level, %Mo = 0, %O = 2.24(px) + 6.52(py) + 13.04(pz), %N = 1.71(py) + 3.24(pz) and %C = 18.6(py) + 43.41(pz). For LUMO level, %Mo = 30.52(dxz), %O = 17.05(px), %N = 2.22(py) + 8.46(pz) and %C = 8.73(py) + 22.22(pz)].
Fig. 5 shows the molecular-orbital diagram is in agreement with the calculated electronic spectra.
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