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Synthesis, spectroscopic characterization, X-ray structure and DFT calculations of novel mononuclear Re(V) complex with imidazole-derived ligand
Inorganic Chemistry Communications 14 (2011) 1358–1361
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Inorganic Chemistry Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i n o c h e
Synthesis, spectroscopic characterization, X-ray structure and DFT calculations of novel mononuclear Re(V) complex with imidazole-derived ligand B. Machura a,⁎, M. Wolff a, J. Palion a, R. Kruszynski b a b
Department of Crystallography, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland Department of X-ray Crystallography and Crystal Chemistry, Institute of General and Ecological Chemistry, Lodz University of Technology,116 Żeromski St., 90-924 Łódź, Poland
a r t i c l e
i n f o
Article history: Received 17 March 2011 Accepted 20 May 2011 Available online 27 May 2011 Keywords: Oxorhenium(V) complexes 2-Hydroxymethylbenzimidazole X-ray structure UV-Vis spectrum DFT and TDDFT calculations
a b s t r a c t The paper presents a combined experimental and computational study of the mononuclear oxorhenium(V) complex [ReOBr(hmbzim)(PPh3)2]Br·MeCN·H2O. The compound has been studied by IR, UV-Vis spectroscopy and X-ray crystallography. The electronic structure of [ReOBr(hmbzim)(PPh3)2] + has been calculated with the density functional theory (DFT) method, and the electronic spectrum of the complex was investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ. © 2011 Elsevier B.V. All rights reserved.
The coordination chemistry of rhenium is a field of current growing interest from various viewpoints. The attention of scientists concentrates on synthetic aspects, structural, physicochemical properties and reactivity, as well as on topics with an applied character such as the development of radiotherapeutic cancer agents, nitrogen fixation and catalysis [1]. The favorable nuclear properties of 186Re (1.07 MeV βemitter, t1/2 = 90 h) and 188Re (2.12 MeV β-emitter, t1/2 = 17 h) nuclides make the rhenium compounds with radioactive isotopes useful for applications in radioimmunotheraphy [2,3]. The diazenido and dinitrogen rhenium complexes are important in view of their significance in the field of nitrogen fixation [4–6], whereas the Re≡ O moiety is a potentially excellent oxygen atom transfer reagent [7–12]. Transfer reactions promoted by enzymatic oxo sites based on iron, molybdenum, and tungsten are important in the chemistry of life. Rhenium is not a biometal, but as an element in the periodic group next to that of molybdenum and tungsten, transfer reactions involving Re ≡ O are of value as potential models [7–12]. In this context, the design, synthesis and reactivity of novel rhenium complexes have become the aim of several laboratories, including ours. The [ReOX3(PPh3)2] (X = Cl or Br) complexes have proven to be useful precursor in the synthesis of Re(V) oxocompounds [1]. In this report we focus on the examination of the reaction of [ReOBr3(PPh3)2] towards 2-hydroxymethylbenzimidazole (Hhmbzim; Scheme 1) in acetonitrile. Imidazole and its derivatives are an important class of heterocycle with N-donor atoms, which can be excellent organic ligands to generate ⁎ Corresponding author. E-mail addresses: [email protected] (B. Machura), [email protected] (R. Kruszynski). 1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2011.05.020
various complexes upon ligation. The imidazole ring possesses two adjacent nucleophilic sites and its steric and electronic properties can be modified by the substituents of the heterocyclic ring. As a monodentate ligand it coordinates to the metal ion via the pyridine-type nitrogen. The other pyrrole-type nitrogen (N–H) is usually involved in hydrogen bond formation with available hydrogen acceptor and/or hydrogen donor sites. In many cases these hydrogen bonds dictate interesting molecular packing and arrangements in the solid state. On the other hand, the imidazolate anion can function as a bridge ligand through both nitrogens affording polynuclear complexes of intriguing structural diversities, properties and reactivities, not found for mononuclear complexes [13,14]. The complex [ReOBr(hmbzim)(PPh3)2]Br·MeCN·H2O, being a product of the reaction of [ReOBr3(PPh3)2] with 2-hydroxymethylbenzimidazole [15], has been studied by IR, UV-Vis spectroscopy and X-ray crystallography. A strong intensity ν(Re ≡ O) stretching band of [ReOBr(hmbzim) (PPh3)2]Br appears at 959 cm −1. Characteristic bands corresponding to the ν(CN), ν(C = C) modes of the hmbzim − ligand appear in the range 1620–1570 cm − 1. The bands at ~ 3050 cm − 1 confirm the presence of an N–H group in the coordinated hmbzim − ligand of the examined complexes [16,17]. The complex [ReOBr(hmbzim)(PPh3)2]Br.MeCN.H2O crystallizes in P-1 space group [18]. The asymmetric unit consists of the cation [ReOBr (hmbzim)(PPh3)2] +, bromide ion and molecules of acetonitrile and water. The two complex cations, two water molecules and two anion are assembled via N–H(pyrrole)•••O(water) and O–H(water)•••Br- hydrogen bonds to the supramolecular dimeric complex (Fig. 1). [19]. These supramolecular units are interlinked by C–H•••Br [19] short contacts (which can be classified as weak hydrogen bonds) and thus they are
B. Machura et al. / Inorganic Chemistry Communications 14 (2011) 1358–1361
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N OH N H Scheme 1. Structure of Hhmbzim ligand.
expanded to the ribbon extending along crystallographic [100] axis. Additionally, in the structure, C–H•••O and C–H•••Br intramolecular hydrogen bonds exist [19] and they provide additional stabilization the complex cation. The molecular structure and selected bond distances and angles of the complex are presented in Fig. 2. The pseudooctahedral environment of Re center in [ReOBr(hmbzim)(PPh 3)2] + shows clear distortions induced by narrow bite angle of the chelating ligand and presence of multiple bonding oxo ligand. The oxo ligand, bromide ion and hmbzim − ligand hold the equatorial positions, and the oxygen atom of hmbzim − lies is trans related to the terminal oxo ion. The axial positions of the distorted octahedron are occupied by triphenylphosphine molecules. The cis-location of PPh3 molecules in relation to the linear O ≡ Re–O unit in [ReOBr(hmbzim)(PPh3)2] + is governed by electronic influence of the multiply bonded ligand, which forces the metal nonbonding d electrons to lie in the plane perpendicular to the M–O bond axis. The Re–N, Re–O and Re–P bond lengths in [ReOBr(hmbzim) (PPh3)2] + agree well with the comparable values found in the related compounds [20]. The Re–Ot (Ot = terminal oxygen) bond length falls in the range 1.639–1.76 Å, typical of mononuclear complexes of rhenium(V) having [ReO] 3+ core, and indicates the presence of a triple bond Re ≡ O [21]. The interatomic distance between the rhenium atom and the oxygen atom of hmbzim − ligand is somewhat shorter than an ideal single Re–O bond length (ca. 2.04 Å) [22], indicating small delocalization in the O ≡ Re–O moiety. The geometry of the cation [ReOBr(hmbzim)(PPh3)2] + was optimized in a singlet state by the DFT method with the B3LYP
Fig. 1. The supramolecular dimeric complex formed via N–H(pyrrole)•••O(water) and O–H(water)•••Br- hydrogen bonds.
Fig. 2. Molecular structure of [ReOBr(hmbzim)(PPh3)2]Br.MeCN.H2O.Selected bond lengths [Å]: Re(1)–O(1) 1.693(2); Re(1)–O(2) 11.922(2); Re(1)–N(1) 2.143(2); Re(1)–Br(1) 2.4952(3); Re(1)–P(1) 2.5149(7); Re(1)–P(2) 2.5171(7).Bond angles [°]: O(1)-Re(1)-O(2) 164.95(9); O(1)-Re(1)-N(1) 90.40(10); O(2)-Re(1)-N(1) 74.60(9); O(1)-Re(1)-Br(1) 102.76(7); O(2)-Re(1)-Br(1) 92.23(6); N(1)-Re(1)-Br(1) 166.82(7); O(1)-Re(1)-P(1) 93.45(7); O(2)-Re(1)-P(1) 88.19(6); N(1)-Re(1)-P(1) 91.16(7); Br(1)-Re(1)-P(1) 88.75 (2); O(1)-Re(1)-P(2) 92.48(7); O(2)-Re(1)-P(2) 86.22(6); N(1)-Re(1)-P(2) 89.32(7); Br (1)-Re(1)-P(2) 89.427(19); P(1)-Re(1)-P(2) 174.05(3).
functional of GAUSSIAN-03 [23]. The calculations were performed using ECP basis set LANL2DZ [24] with an additional d and f function with the exponent α = 0.3811 and α = 2.033 [25] for rhenium and the standard 6-31G basis set for other atoms. For bromide, oxygen and nitrogen, diffuse and polarization functions were added. The absence of imaginary frequency in the calculated vibrational frequencies of [ReOBr(hmbzim)(PPh3)2] + ensures that the optimized geometry corresponds to true energy minimum. The predicted bond lengths and angles are in reasonable agreement with the values based upon the X-ray crystal structure data [26]. The B3LYP method in combination with the LANL2DZ basis gives a very good estimation of Re–Ooxo bond length (with deviation equal to −0.008 Å). The Re–N and Re–Ohmbzim distances are also sufficiently reproduced with deviations of + 0.035 and 0.051 Å, respectively. For Re–Br and Re–P bond lengths the errors are larger (from 0.048 to 0.078 Å), but similar overestimation has been observed previously [27]. It may come from the basis sets which are approximated to a certain extent or may indicate the influence of the crystal packing on the values of the experimental bond lengths. The theoretical calculations do not consider the effects of chemical environment. The complex [ReOBr(hmbzim)(PPh3)2]+ is a closed-shell structure. Its partial molecular orbital diagram with several HOMO and LUMO contours is presented in Fig. 3. The highest occupied MO is of rhenium dxy type with an antibonding contribution from pπ bromide and hmbzim− orbitals. The LUMO and LUMO+1 are predominately localized on the rhenium atom (dxz and dyz orbitals) with some contribution of pπ oxygen orbitals. They can be ascribed as π-antibonding rhenium–oxygen molecular orbitals. The LUMO+2 is of rhenium dx2-y2 character, and dz2 rhenium orbital contributes mainly to the LUMO+8. The value of the energy separation between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) equals to 3.18 eV.
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B. Machura et al. / Inorganic Chemistry Communications 14 (2011) 1358–1361
-1.00
L+6 L+5 π*(PPh3) L+4 L+3 π*(PPh3), π*(hmbizm)
π*(PPh3) π*(PPh3)
L+2
dx2-y2, π*(PPh3)
L+1
dxz, π(O), π(Ohmbzim)
-2.00
-3.00
LUMO
dyz, π(O), π(Ohmbzim)
HOMO
dxy, π(Br), π(hmbzim)
-4.00
-5.00
-6.00
-7.00
H-1
π(Br), n(P), π(PPh3), π(Ohmbzim)
H-2 H-3 H-4
π(hmbzim), π(PPh3) π(hmbzim), π(PPh3), π(Br) π(PPh3)
Fig. 3. The energy (eV), character and some contours of the highest occupied and lowest unoccupied molecular orbitals of [ReOBr(hmbzim)(PPh3)2]+. Positive values of the orbital contour are represented in blue (0.04 au) and negative values in yellow (−0.04au).
3.00
2.00
Absorbance
The nature of the rhenium–terminal oxygen (Ot) interaction in [ReOBr (hmbzim)(PPh3)2]+ has been studied by NBO analysis [28]. In the cation [ReOBr(hmbzim)(PPh3)2]+, three Re–Ot natural bond orbitals were detected. The s and p oxygen orbitals and s and d rhenium orbitals take part in the σRe–Ot bond formation, whereas the πRe–Ot bond orbitals result from overlapping of the empty dxy and dyz rhenium orbitals with the occupied px and pz orbitals of the terminal oxygen ligands. Both σ and π Re–O bonds are clearly polarized towards the oxygen end. The experimental [29] and calculated electronic spectra of [ReOBr (hmbzim)(PPh3)2]Br are compared in Fig. 4. The solvent effect was simulated using the polarizable continuum model with the integral equation formalism (IEF-PCM) [30]. Each calculated transition is represented by a Gaussian function 2 y = ce − bx with the height (c) equal to the oscillator strength and b equal to 0.04 nm − 2. The longest wavelength experimental bands at 784.4 and 604.7 nm originate in the HOMO→LUMO and HOMO→LUMO+1 transitions, respectively. As can be seen from Fig. 3, the LUMO and LUMO+1 orbitals are mainly formed from rhenium d atomic orbital, and the HOMO orbital is delocalized among rhenium ion, bromide and hmbzim − ligands. Accordingly, the transitions assigned to the longest wavelength experimental bands can be seen as mixed bromide/hmbzim→Re (ligand-metal charge transfer; LMCT) and d → d (ligand field; LF) transitions.
1.00
0.00 400.00
800.00
[nm] Fig. 4. The experimental (black) and calculated (red) electronic absorption spectra of [ReOBr(hmbzim)(PPh3)2]Br.λmax [nm] (ε; [dm3·mol-1 ·cm−1]): 784.4 (60), 604.7 (100), 370.5 (7360), 273.3 (145165) and 202.1 (505870).
B. Machura et al. / Inorganic Chemistry Communications 14 (2011) 1358–1361
The transitions leading to the experimental band at 370.5 nm can be assigned to ligand-metal charge transfer transitions occurring from the bromide, hmbzim − and PPh3 ligands to the d rhenium orbitals. The experimental absorption band at 273.5 nm is mainly attributed to ligand-ligand charge transfer transitions calculated for [ReO (hmbzim)(PPh3)2] +. However, some contribution of the ligand-metal charge transfer from the bromide, triphenylphosphine and hmbzim− orbitals to the d rhenium orbitals in these bands is also confirmed by the calculations. The absorption band at 202.1 nm results mainly from ligandligand charge transfer and interligand (IL) transitions. In summary, a novel mononuclear rhenium(V) complex incorporating imidazole-derived ligand was structurally and spectroscopically characterized. DFT and TDDFT calculations applied to [ReO(hmbzim) (PPh3)2] + resulted in appropriate prediction of the UV-Vis spectra and enabled a detailed assignment of the electronic transitions to the experimental absorptions. BD
Occupancy
Composition of NBO
BD*
Occupancy
Re–Ot
1.95 1.99
Re–Ot
1.98
0.879 (sp0.33d3.36)Re − 0.477 (sp1.14)O 0.817 (d)Re − 0.577 (p)O 0.836 (d)Re − 0.549 (p)O
0.19
Re–Ot
0.477 (sp0.33d3.36)Re + 0.879 (sp1.14)O 0.577 (d)Re + 0.817 (p)O 0.549 (d)Re + 0.836 (p)O
[16] [17] [18]
[19]
0.20 0.26
BD denotes 2-center bond; * denotes antibond NBO. Acknowledgements
[20] [21] [22] [23]
The GAUSSIAN-03 calculations were carried out in the Wrocław Centre for Networking and Supercomputing, WCSS, Wrocław, Poland, http://www.wcss.wroc.pl, under calculational Grant No. 18. Appendix A. Supplementary data Supplementary data for C46H42Br2N3O3P2Re are available from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK on request, quoting the deposition number CCDC 817456. Supplementary data to this article can be found online at doi:10.1016/j.inoche.2011.05.020.
[24] [25] [26]
References [1] U. Abram, in: J.A. McCleverty, T.J. Meyer (Eds.), 2nd ed, Comprehensive Coordination Chemistry, vol. 5, Elsevier, 2003, pp. 271–402, chapter 5.3. [2] J.R. Dilworth, S.J. Parrott, Chem. Soc. Rev. 27 (1998) 43. [3] P. Blower, Dalton Trans. (2006) 1705. [4] R.L. Richards, Coord. Chem. Rev. 154 (1996) 83. [5] M.D. Fryzuk, S.A. Johnson, Coord. Chem. Rev. 200–202 (2000) 379. [6] A.J.L. Pombeiro, M.F.C. Guedes da Silva, R.A. Michelin, Coord. Chem. Rev. 218 (2001) 43. [7] S. Das, I. Chakraborty, A. Chakravorty, Polyhedron 22 (2003) 901. [8] I. Chakraborty, S. Bhattacharyya, S. Banerjee, B.K. Dirghang, A. Chakravorty, J. Chem. Soc., Dalton Trans (1999) 3747. [9] S. Bhattacharyya, I. Chakraborty, B.K. Dirghangi, A. Chakravorty, Chem. Commun. (2000) 1813. [10] S. Sengupta, J. Gangopadhyay, A. Chakravorty, Dalton Trans. (2003) 4635. [11] S. Bhattacharyya, I. Chakraborty, B.K. Dirghangi, A. Chakravorty, Inorg. Chem. 40 (2001) 286. [12] J. Gangopadhyay, S. Sengupta, S. Bhattacharyya, I. Chakraborty, A. Chakravorty, Inorg. Chem. 41 (2002) 2616. [13] M. Tadokoro, K. Nakasuji, Coord. Chem. Rev 198 (2000) 205. [14] Y. Sunatsuki, Y. Motoda, N. Matsumoto, Coord. Chem. Rev. 226 (2002) 199. [15] [ReOBr3(PPh3)2] (0.50g, 0.52mmol) was added to 2-hydroxymethylbenzimidazole (0.08g, 0.54mmol) in acetonitrile (60 ml) and the reaction mixture was refluxed for
[27] [28]
1361
4h. The resulting solution was allowed to cool to room temperature and reduced in volume to ~10 ml. A green crystalline precipitate of [ReOBr(hmbzim)(PPh3)2]Br. MeCN.H2O was filtered off and dried in the air. Yield 75%. X-ray quality crystals were obtained by recrystallization from acetonitrile. Calc. for C46H42Br2N3O3P2Re: C, 50.56; H, 3.87; N, 3.85%. Found: C, 50.73; H, 3.91; N, 3.79%. IR spectrum was recorded on a Nicolet Magna 560 spectrophotometer in the spectral range 4000-400cm− 1 with the samples in the form of KBr pellets. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 4th. Ed. Wiley-Interscience, New York, 1986. The X-ray intensity data were collected on a KM-4-CCD automatic diffractometer equipped with CCD detector and graphite monochromated MoKα radiation (λ = 0.71073Å) at room temperature. Lorentz, polarization and absorption correction [STOE & Cie (1999). X-RED. Version 1.18. STOE & Cie GmbH, Darmstadt, Germany] were applied. The structure was solved by the Patterson method and subsequently completed by the difference Fourier recycling. All the non-hydrogen atoms were refined anisotropically using full-matrix, least-squares technique. The hydrogen atoms were treated as „riding” on their parent carbon atoms and assigned isotropic temperature factors equal 1.2 times the value of equivalent temperature factor of the parent atom. SHELXS97 and SHELXL97 [G.M. Sheldrick Acta Cryst. A64 (2008) 112] programs were used for all the calculations. Crystallographic data for C46H42Br2N3O3P2Re: triclinic; space group P-1; a = 11.3587(4), b = 12.5482(4), c = 15.3751(4)Å, α = 100.088(2), β = 94.349 (2), γ = 90.339(3)º; V = 2150.93(12)Å3; Z = 2; Dc = 1.687Mg/m3; μ = 4.801mm1 ; data/restraints/parameters: 7604 / 0 / 515; S = 1.006; Final R indices [I N 2σ(I)] R1 = 0.0206, wR2 = 0.0531; R indices (all data) R1 = 0.0270, wR = 0.0541. Hydrogen bond parameters; hydrogen bond donor (D), hydrogen bond acceptor A, D—H distance [Å], H•••A distance [Å], D•••A distance [Å], D—H•••A angle [°]: N (2), O(99), 0.86, 2.22, 2.937(5), 140.2; O(99), Br(99), 0.79, 2.49, 3.265(5), 169.3; O (99), Br(99)#(1: -x, 1-y, 1-z), 0.91, 2.51, 3.415(4), 177.0; C(6), O(2), 0.93, 2.33, 3.151(4), 147.6; C(12), Br(1), 0.93, 2.83, 3.682(4), 152.3; C(20), O(2), 0.93, 2.34, 3.137(4), 143.7; C(36), Br(1), 0.93, 2.85, 3.703(3), 153.0; C(41), Br(1)#(−1 + x, y, z), 0.93, 2.90, 3.630(5), 136.6. F.H. Allen, Acta Crystallogr. B58 (2002) 380. J.M. Mayer, Inorg. Chem. 27 (1988) 3899. S.R. Flechter, A.C. Skapski, J. Chem. Soc, Dalton Trans, 1972 1073. Gaussian 03, Revision D.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, and J. A. Pople, Gaussian, Inc., Wallingford CT, 2004. P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299. K. Eichkorn, F. Weigend, O. Treutler, R. Ahlrichs, Theor. Chem. Acc. 97 (1997) 119. Calculated bond lengths [Å]: Selected bond lengths [Å]: Re(1)–O(1) 1.685; Re(1)–O (2) 1.973; Re(1)–N(1) 2.178; Re(1)–Br(1) 2.543; Re(1)–P(1) 2.589; Re(1)–P(2) 2.595. Calculated Bond angles [°]: O(1)-Re(1)-O(2) 163.48; O(1)-Re(1)-N(1) 89.56; O(2)-Re(1)-N(1) 73.93; O(1)-Re(1)-Br(1) 103.83; O(2)-Re(1)-Br(1) 92.68; N(1)-Re (1)-Br(1) 166.60; O(1)-Re(1)-P(1) 93.60; O(2)-Re(1)-P(1) 87.50; N(1)-Re(1)-P(1) 91.04; Br(1)-Re(1)-P(1) 88.51; O(1)-Re(1)-P(2) 92.50; O(2)-Re(1)-P(2) 86.92; N (1)-Re(1)-P(2) 89.97; Br(1)-Re(1)-P(2) 89.10; P(1)-Re(1)-P(2) 173.83. J.S. Gancheff, P.A. Denis, F.E. Hahn, J. Mol. Struct. (Theochem) 941 (2010) 1. Natural bond orbital (NBO) calculations were performed with the NBO code [35] included in Gaussian03 (NBO Version 3.1, E. D. Glendening, A. E. Reed, J. E. Carpenter, and F. Weinhold).
BD
Occupancy
Composition of NBO
Re–Ot
1.95
Re–Ot
1.99
Re–Ot
1.98
0.477 0.879 0.577 0.817 0.549 0.836
(sp0.33d3.36)Re + (sp1.14)O (d)Re + (p)O (d)Re + (p)O
BD* 0.879 0.477 0.817 0.577 0.836 0.549
Occupancy (sp0.33d3.36)Re (sp1.14)O (d)Re (p)O (d)Re (p)O
0.19 0.20 0.26
BD denotes 2-center bond, * - denotes antibond NBO. [29] Electronic spectra were measured on a spectrophotometer Lab Alliance UV-VIS/8500 in the range 1000-200nm in methanol solution. [30] M.E. Casida, Recent Developments and Applications in Modern Density Functional Theory, in: J.M. Seminario (Ed.), Theoretical and Computational Chemistry, Vol. 4, Elsevier, Amsterdam, 1996.
Contents lists available at ScienceDirect
Inorganic Chemistry Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i n o c h e
Synthesis, spectroscopic characterization, X-ray structure and DFT calculations of novel mononuclear Re(V) complex with imidazole-derived ligand B. Machura a,⁎, M. Wolff a, J. Palion a, R. Kruszynski b a b
Department of Crystallography, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland Department of X-ray Crystallography and Crystal Chemistry, Institute of General and Ecological Chemistry, Lodz University of Technology,116 Żeromski St., 90-924 Łódź, Poland
a r t i c l e
i n f o
Article history: Received 17 March 2011 Accepted 20 May 2011 Available online 27 May 2011 Keywords: Oxorhenium(V) complexes 2-Hydroxymethylbenzimidazole X-ray structure UV-Vis spectrum DFT and TDDFT calculations
a b s t r a c t The paper presents a combined experimental and computational study of the mononuclear oxorhenium(V) complex [ReOBr(hmbzim)(PPh3)2]Br·MeCN·H2O. The compound has been studied by IR, UV-Vis spectroscopy and X-ray crystallography. The electronic structure of [ReOBr(hmbzim)(PPh3)2] + has been calculated with the density functional theory (DFT) method, and the electronic spectrum of the complex was investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ. © 2011 Elsevier B.V. All rights reserved.
The coordination chemistry of rhenium is a field of current growing interest from various viewpoints. The attention of scientists concentrates on synthetic aspects, structural, physicochemical properties and reactivity, as well as on topics with an applied character such as the development of radiotherapeutic cancer agents, nitrogen fixation and catalysis [1]. The favorable nuclear properties of 186Re (1.07 MeV βemitter, t1/2 = 90 h) and 188Re (2.12 MeV β-emitter, t1/2 = 17 h) nuclides make the rhenium compounds with radioactive isotopes useful for applications in radioimmunotheraphy [2,3]. The diazenido and dinitrogen rhenium complexes are important in view of their significance in the field of nitrogen fixation [4–6], whereas the Re≡ O moiety is a potentially excellent oxygen atom transfer reagent [7–12]. Transfer reactions promoted by enzymatic oxo sites based on iron, molybdenum, and tungsten are important in the chemistry of life. Rhenium is not a biometal, but as an element in the periodic group next to that of molybdenum and tungsten, transfer reactions involving Re ≡ O are of value as potential models [7–12]. In this context, the design, synthesis and reactivity of novel rhenium complexes have become the aim of several laboratories, including ours. The [ReOX3(PPh3)2] (X = Cl or Br) complexes have proven to be useful precursor in the synthesis of Re(V) oxocompounds [1]. In this report we focus on the examination of the reaction of [ReOBr3(PPh3)2] towards 2-hydroxymethylbenzimidazole (Hhmbzim; Scheme 1) in acetonitrile. Imidazole and its derivatives are an important class of heterocycle with N-donor atoms, which can be excellent organic ligands to generate ⁎ Corresponding author. E-mail addresses: [email protected] (B. Machura), [email protected] (R. Kruszynski). 1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2011.05.020
various complexes upon ligation. The imidazole ring possesses two adjacent nucleophilic sites and its steric and electronic properties can be modified by the substituents of the heterocyclic ring. As a monodentate ligand it coordinates to the metal ion via the pyridine-type nitrogen. The other pyrrole-type nitrogen (N–H) is usually involved in hydrogen bond formation with available hydrogen acceptor and/or hydrogen donor sites. In many cases these hydrogen bonds dictate interesting molecular packing and arrangements in the solid state. On the other hand, the imidazolate anion can function as a bridge ligand through both nitrogens affording polynuclear complexes of intriguing structural diversities, properties and reactivities, not found for mononuclear complexes [13,14]. The complex [ReOBr(hmbzim)(PPh3)2]Br·MeCN·H2O, being a product of the reaction of [ReOBr3(PPh3)2] with 2-hydroxymethylbenzimidazole [15], has been studied by IR, UV-Vis spectroscopy and X-ray crystallography. A strong intensity ν(Re ≡ O) stretching band of [ReOBr(hmbzim) (PPh3)2]Br appears at 959 cm −1. Characteristic bands corresponding to the ν(CN), ν(C = C) modes of the hmbzim − ligand appear in the range 1620–1570 cm − 1. The bands at ~ 3050 cm − 1 confirm the presence of an N–H group in the coordinated hmbzim − ligand of the examined complexes [16,17]. The complex [ReOBr(hmbzim)(PPh3)2]Br.MeCN.H2O crystallizes in P-1 space group [18]. The asymmetric unit consists of the cation [ReOBr (hmbzim)(PPh3)2] +, bromide ion and molecules of acetonitrile and water. The two complex cations, two water molecules and two anion are assembled via N–H(pyrrole)•••O(water) and O–H(water)•••Br- hydrogen bonds to the supramolecular dimeric complex (Fig. 1). [19]. These supramolecular units are interlinked by C–H•••Br [19] short contacts (which can be classified as weak hydrogen bonds) and thus they are
B. Machura et al. / Inorganic Chemistry Communications 14 (2011) 1358–1361
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N OH N H Scheme 1. Structure of Hhmbzim ligand.
expanded to the ribbon extending along crystallographic [100] axis. Additionally, in the structure, C–H•••O and C–H•••Br intramolecular hydrogen bonds exist [19] and they provide additional stabilization the complex cation. The molecular structure and selected bond distances and angles of the complex are presented in Fig. 2. The pseudooctahedral environment of Re center in [ReOBr(hmbzim)(PPh 3)2] + shows clear distortions induced by narrow bite angle of the chelating ligand and presence of multiple bonding oxo ligand. The oxo ligand, bromide ion and hmbzim − ligand hold the equatorial positions, and the oxygen atom of hmbzim − lies is trans related to the terminal oxo ion. The axial positions of the distorted octahedron are occupied by triphenylphosphine molecules. The cis-location of PPh3 molecules in relation to the linear O ≡ Re–O unit in [ReOBr(hmbzim)(PPh3)2] + is governed by electronic influence of the multiply bonded ligand, which forces the metal nonbonding d electrons to lie in the plane perpendicular to the M–O bond axis. The Re–N, Re–O and Re–P bond lengths in [ReOBr(hmbzim) (PPh3)2] + agree well with the comparable values found in the related compounds [20]. The Re–Ot (Ot = terminal oxygen) bond length falls in the range 1.639–1.76 Å, typical of mononuclear complexes of rhenium(V) having [ReO] 3+ core, and indicates the presence of a triple bond Re ≡ O [21]. The interatomic distance between the rhenium atom and the oxygen atom of hmbzim − ligand is somewhat shorter than an ideal single Re–O bond length (ca. 2.04 Å) [22], indicating small delocalization in the O ≡ Re–O moiety. The geometry of the cation [ReOBr(hmbzim)(PPh3)2] + was optimized in a singlet state by the DFT method with the B3LYP
Fig. 1. The supramolecular dimeric complex formed via N–H(pyrrole)•••O(water) and O–H(water)•••Br- hydrogen bonds.
Fig. 2. Molecular structure of [ReOBr(hmbzim)(PPh3)2]Br.MeCN.H2O.Selected bond lengths [Å]: Re(1)–O(1) 1.693(2); Re(1)–O(2) 11.922(2); Re(1)–N(1) 2.143(2); Re(1)–Br(1) 2.4952(3); Re(1)–P(1) 2.5149(7); Re(1)–P(2) 2.5171(7).Bond angles [°]: O(1)-Re(1)-O(2) 164.95(9); O(1)-Re(1)-N(1) 90.40(10); O(2)-Re(1)-N(1) 74.60(9); O(1)-Re(1)-Br(1) 102.76(7); O(2)-Re(1)-Br(1) 92.23(6); N(1)-Re(1)-Br(1) 166.82(7); O(1)-Re(1)-P(1) 93.45(7); O(2)-Re(1)-P(1) 88.19(6); N(1)-Re(1)-P(1) 91.16(7); Br(1)-Re(1)-P(1) 88.75 (2); O(1)-Re(1)-P(2) 92.48(7); O(2)-Re(1)-P(2) 86.22(6); N(1)-Re(1)-P(2) 89.32(7); Br (1)-Re(1)-P(2) 89.427(19); P(1)-Re(1)-P(2) 174.05(3).
functional of GAUSSIAN-03 [23]. The calculations were performed using ECP basis set LANL2DZ [24] with an additional d and f function with the exponent α = 0.3811 and α = 2.033 [25] for rhenium and the standard 6-31G basis set for other atoms. For bromide, oxygen and nitrogen, diffuse and polarization functions were added. The absence of imaginary frequency in the calculated vibrational frequencies of [ReOBr(hmbzim)(PPh3)2] + ensures that the optimized geometry corresponds to true energy minimum. The predicted bond lengths and angles are in reasonable agreement with the values based upon the X-ray crystal structure data [26]. The B3LYP method in combination with the LANL2DZ basis gives a very good estimation of Re–Ooxo bond length (with deviation equal to −0.008 Å). The Re–N and Re–Ohmbzim distances are also sufficiently reproduced with deviations of + 0.035 and 0.051 Å, respectively. For Re–Br and Re–P bond lengths the errors are larger (from 0.048 to 0.078 Å), but similar overestimation has been observed previously [27]. It may come from the basis sets which are approximated to a certain extent or may indicate the influence of the crystal packing on the values of the experimental bond lengths. The theoretical calculations do not consider the effects of chemical environment. The complex [ReOBr(hmbzim)(PPh3)2]+ is a closed-shell structure. Its partial molecular orbital diagram with several HOMO and LUMO contours is presented in Fig. 3. The highest occupied MO is of rhenium dxy type with an antibonding contribution from pπ bromide and hmbzim− orbitals. The LUMO and LUMO+1 are predominately localized on the rhenium atom (dxz and dyz orbitals) with some contribution of pπ oxygen orbitals. They can be ascribed as π-antibonding rhenium–oxygen molecular orbitals. The LUMO+2 is of rhenium dx2-y2 character, and dz2 rhenium orbital contributes mainly to the LUMO+8. The value of the energy separation between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) equals to 3.18 eV.
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B. Machura et al. / Inorganic Chemistry Communications 14 (2011) 1358–1361
-1.00
L+6 L+5 π*(PPh3) L+4 L+3 π*(PPh3), π*(hmbizm)
π*(PPh3) π*(PPh3)
L+2
dx2-y2, π*(PPh3)
L+1
dxz, π(O), π(Ohmbzim)
-2.00
-3.00
LUMO
dyz, π(O), π(Ohmbzim)
HOMO
dxy, π(Br), π(hmbzim)
-4.00
-5.00
-6.00
-7.00
H-1
π(Br), n(P), π(PPh3), π(Ohmbzim)
H-2 H-3 H-4
π(hmbzim), π(PPh3) π(hmbzim), π(PPh3), π(Br) π(PPh3)
Fig. 3. The energy (eV), character and some contours of the highest occupied and lowest unoccupied molecular orbitals of [ReOBr(hmbzim)(PPh3)2]+. Positive values of the orbital contour are represented in blue (0.04 au) and negative values in yellow (−0.04au).
3.00
2.00
Absorbance
The nature of the rhenium–terminal oxygen (Ot) interaction in [ReOBr (hmbzim)(PPh3)2]+ has been studied by NBO analysis [28]. In the cation [ReOBr(hmbzim)(PPh3)2]+, three Re–Ot natural bond orbitals were detected. The s and p oxygen orbitals and s and d rhenium orbitals take part in the σRe–Ot bond formation, whereas the πRe–Ot bond orbitals result from overlapping of the empty dxy and dyz rhenium orbitals with the occupied px and pz orbitals of the terminal oxygen ligands. Both σ and π Re–O bonds are clearly polarized towards the oxygen end. The experimental [29] and calculated electronic spectra of [ReOBr (hmbzim)(PPh3)2]Br are compared in Fig. 4. The solvent effect was simulated using the polarizable continuum model with the integral equation formalism (IEF-PCM) [30]. Each calculated transition is represented by a Gaussian function 2 y = ce − bx with the height (c) equal to the oscillator strength and b equal to 0.04 nm − 2. The longest wavelength experimental bands at 784.4 and 604.7 nm originate in the HOMO→LUMO and HOMO→LUMO+1 transitions, respectively. As can be seen from Fig. 3, the LUMO and LUMO+1 orbitals are mainly formed from rhenium d atomic orbital, and the HOMO orbital is delocalized among rhenium ion, bromide and hmbzim − ligands. Accordingly, the transitions assigned to the longest wavelength experimental bands can be seen as mixed bromide/hmbzim→Re (ligand-metal charge transfer; LMCT) and d → d (ligand field; LF) transitions.
1.00
0.00 400.00
800.00
[nm] Fig. 4. The experimental (black) and calculated (red) electronic absorption spectra of [ReOBr(hmbzim)(PPh3)2]Br.λmax [nm] (ε; [dm3·mol-1 ·cm−1]): 784.4 (60), 604.7 (100), 370.5 (7360), 273.3 (145165) and 202.1 (505870).
B. Machura et al. / Inorganic Chemistry Communications 14 (2011) 1358–1361
The transitions leading to the experimental band at 370.5 nm can be assigned to ligand-metal charge transfer transitions occurring from the bromide, hmbzim − and PPh3 ligands to the d rhenium orbitals. The experimental absorption band at 273.5 nm is mainly attributed to ligand-ligand charge transfer transitions calculated for [ReO (hmbzim)(PPh3)2] +. However, some contribution of the ligand-metal charge transfer from the bromide, triphenylphosphine and hmbzim− orbitals to the d rhenium orbitals in these bands is also confirmed by the calculations. The absorption band at 202.1 nm results mainly from ligandligand charge transfer and interligand (IL) transitions. In summary, a novel mononuclear rhenium(V) complex incorporating imidazole-derived ligand was structurally and spectroscopically characterized. DFT and TDDFT calculations applied to [ReO(hmbzim) (PPh3)2] + resulted in appropriate prediction of the UV-Vis spectra and enabled a detailed assignment of the electronic transitions to the experimental absorptions. BD
Occupancy
Composition of NBO
BD*
Occupancy
Re–Ot
1.95 1.99
Re–Ot
1.98
0.879 (sp0.33d3.36)Re − 0.477 (sp1.14)O 0.817 (d)Re − 0.577 (p)O 0.836 (d)Re − 0.549 (p)O
0.19
Re–Ot
0.477 (sp0.33d3.36)Re + 0.879 (sp1.14)O 0.577 (d)Re + 0.817 (p)O 0.549 (d)Re + 0.836 (p)O
[16] [17] [18]
[19]
0.20 0.26
BD denotes 2-center bond; * denotes antibond NBO. Acknowledgements
[20] [21] [22] [23]
The GAUSSIAN-03 calculations were carried out in the Wrocław Centre for Networking and Supercomputing, WCSS, Wrocław, Poland, http://www.wcss.wroc.pl, under calculational Grant No. 18. Appendix A. Supplementary data Supplementary data for C46H42Br2N3O3P2Re are available from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK on request, quoting the deposition number CCDC 817456. Supplementary data to this article can be found online at doi:10.1016/j.inoche.2011.05.020.
[24] [25] [26]
References [1] U. Abram, in: J.A. McCleverty, T.J. Meyer (Eds.), 2nd ed, Comprehensive Coordination Chemistry, vol. 5, Elsevier, 2003, pp. 271–402, chapter 5.3. [2] J.R. Dilworth, S.J. Parrott, Chem. Soc. Rev. 27 (1998) 43. [3] P. Blower, Dalton Trans. (2006) 1705. [4] R.L. Richards, Coord. Chem. Rev. 154 (1996) 83. [5] M.D. Fryzuk, S.A. Johnson, Coord. Chem. Rev. 200–202 (2000) 379. [6] A.J.L. Pombeiro, M.F.C. Guedes da Silva, R.A. Michelin, Coord. Chem. Rev. 218 (2001) 43. [7] S. Das, I. Chakraborty, A. Chakravorty, Polyhedron 22 (2003) 901. [8] I. Chakraborty, S. Bhattacharyya, S. Banerjee, B.K. Dirghang, A. Chakravorty, J. Chem. Soc., Dalton Trans (1999) 3747. [9] S. Bhattacharyya, I. Chakraborty, B.K. Dirghangi, A. Chakravorty, Chem. Commun. (2000) 1813. [10] S. Sengupta, J. Gangopadhyay, A. Chakravorty, Dalton Trans. (2003) 4635. [11] S. Bhattacharyya, I. Chakraborty, B.K. Dirghangi, A. Chakravorty, Inorg. Chem. 40 (2001) 286. [12] J. Gangopadhyay, S. Sengupta, S. Bhattacharyya, I. Chakraborty, A. Chakravorty, Inorg. Chem. 41 (2002) 2616. [13] M. Tadokoro, K. Nakasuji, Coord. Chem. Rev 198 (2000) 205. [14] Y. Sunatsuki, Y. Motoda, N. Matsumoto, Coord. Chem. Rev. 226 (2002) 199. [15] [ReOBr3(PPh3)2] (0.50g, 0.52mmol) was added to 2-hydroxymethylbenzimidazole (0.08g, 0.54mmol) in acetonitrile (60 ml) and the reaction mixture was refluxed for
[27] [28]
1361
4h. The resulting solution was allowed to cool to room temperature and reduced in volume to ~10 ml. A green crystalline precipitate of [ReOBr(hmbzim)(PPh3)2]Br. MeCN.H2O was filtered off and dried in the air. Yield 75%. X-ray quality crystals were obtained by recrystallization from acetonitrile. Calc. for C46H42Br2N3O3P2Re: C, 50.56; H, 3.87; N, 3.85%. Found: C, 50.73; H, 3.91; N, 3.79%. IR spectrum was recorded on a Nicolet Magna 560 spectrophotometer in the spectral range 4000-400cm− 1 with the samples in the form of KBr pellets. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 4th. Ed. Wiley-Interscience, New York, 1986. The X-ray intensity data were collected on a KM-4-CCD automatic diffractometer equipped with CCD detector and graphite monochromated MoKα radiation (λ = 0.71073Å) at room temperature. Lorentz, polarization and absorption correction [STOE & Cie (1999). X-RED. Version 1.18. STOE & Cie GmbH, Darmstadt, Germany] were applied. The structure was solved by the Patterson method and subsequently completed by the difference Fourier recycling. All the non-hydrogen atoms were refined anisotropically using full-matrix, least-squares technique. The hydrogen atoms were treated as „riding” on their parent carbon atoms and assigned isotropic temperature factors equal 1.2 times the value of equivalent temperature factor of the parent atom. SHELXS97 and SHELXL97 [G.M. Sheldrick Acta Cryst. A64 (2008) 112] programs were used for all the calculations. Crystallographic data for C46H42Br2N3O3P2Re: triclinic; space group P-1; a = 11.3587(4), b = 12.5482(4), c = 15.3751(4)Å, α = 100.088(2), β = 94.349 (2), γ = 90.339(3)º; V = 2150.93(12)Å3; Z = 2; Dc = 1.687Mg/m3; μ = 4.801mm1 ; data/restraints/parameters: 7604 / 0 / 515; S = 1.006; Final R indices [I N 2σ(I)] R1 = 0.0206, wR2 = 0.0531; R indices (all data) R1 = 0.0270, wR = 0.0541. Hydrogen bond parameters; hydrogen bond donor (D), hydrogen bond acceptor A, D—H distance [Å], H•••A distance [Å], D•••A distance [Å], D—H•••A angle [°]: N (2), O(99), 0.86, 2.22, 2.937(5), 140.2; O(99), Br(99), 0.79, 2.49, 3.265(5), 169.3; O (99), Br(99)#(1: -x, 1-y, 1-z), 0.91, 2.51, 3.415(4), 177.0; C(6), O(2), 0.93, 2.33, 3.151(4), 147.6; C(12), Br(1), 0.93, 2.83, 3.682(4), 152.3; C(20), O(2), 0.93, 2.34, 3.137(4), 143.7; C(36), Br(1), 0.93, 2.85, 3.703(3), 153.0; C(41), Br(1)#(−1 + x, y, z), 0.93, 2.90, 3.630(5), 136.6. F.H. Allen, Acta Crystallogr. B58 (2002) 380. J.M. Mayer, Inorg. Chem. 27 (1988) 3899. S.R. Flechter, A.C. Skapski, J. Chem. Soc, Dalton Trans, 1972 1073. Gaussian 03, Revision D.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, and J. A. Pople, Gaussian, Inc., Wallingford CT, 2004. P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299. K. Eichkorn, F. Weigend, O. Treutler, R. Ahlrichs, Theor. Chem. Acc. 97 (1997) 119. Calculated bond lengths [Å]: Selected bond lengths [Å]: Re(1)–O(1) 1.685; Re(1)–O (2) 1.973; Re(1)–N(1) 2.178; Re(1)–Br(1) 2.543; Re(1)–P(1) 2.589; Re(1)–P(2) 2.595. Calculated Bond angles [°]: O(1)-Re(1)-O(2) 163.48; O(1)-Re(1)-N(1) 89.56; O(2)-Re(1)-N(1) 73.93; O(1)-Re(1)-Br(1) 103.83; O(2)-Re(1)-Br(1) 92.68; N(1)-Re (1)-Br(1) 166.60; O(1)-Re(1)-P(1) 93.60; O(2)-Re(1)-P(1) 87.50; N(1)-Re(1)-P(1) 91.04; Br(1)-Re(1)-P(1) 88.51; O(1)-Re(1)-P(2) 92.50; O(2)-Re(1)-P(2) 86.92; N (1)-Re(1)-P(2) 89.97; Br(1)-Re(1)-P(2) 89.10; P(1)-Re(1)-P(2) 173.83. J.S. Gancheff, P.A. Denis, F.E. Hahn, J. Mol. Struct. (Theochem) 941 (2010) 1. Natural bond orbital (NBO) calculations were performed with the NBO code [35] included in Gaussian03 (NBO Version 3.1, E. D. Glendening, A. E. Reed, J. E. Carpenter, and F. Weinhold).
BD
Occupancy
Composition of NBO
Re–Ot
1.95
Re–Ot
1.99
Re–Ot
1.98
0.477 0.879 0.577 0.817 0.549 0.836
(sp0.33d3.36)Re + (sp1.14)O (d)Re + (p)O (d)Re + (p)O
BD* 0.879 0.477 0.817 0.577 0.836 0.549
Occupancy (sp0.33d3.36)Re (sp1.14)O (d)Re (p)O (d)Re (p)O
0.19 0.20 0.26
BD denotes 2-center bond, * - denotes antibond NBO. [29] Electronic spectra were measured on a spectrophotometer Lab Alliance UV-VIS/8500 in the range 1000-200nm in methanol solution. [30] M.E. Casida, Recent Developments and Applications in Modern Density Functional Theory, in: J.M. Seminario (Ed.), Theoretical and Computational Chemistry, Vol. 4, Elsevier, Amsterdam, 1996.