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Trans,trans,trans-[ReO2I2(PPh3)2], a rare rhenium(VI) complex — Synthesis and DFT study
Inorganic Chemistry Communications 51 (2015) 83–86
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Trans,trans,trans-[ReO2I2(PPh3)2], a rare rhenium(VI) complex — Synthesis and DFT study J. Mukiza a, T.I.A. Gerber a,⁎, E. Hosten a, A.S. Ogunlaja a, F. Taherkhani b, M. Amini c, M. Nahali d a
Department of Chemistry, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa Department of Physical Chemistry, Razi University, Kermanshah, Iran Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Iran d Department of Science, Babol Noshiravani University of Technology, Babol, Iran b c
a r t i c l e
i n f o
Article history: Received 14 August 2014 Received in revised form 12 November 2014 Accepted 15 November 2014 Available online 18 November 2014 Keywords: Rhenium(VI) Dioxo X-ray crystal structure DFT Solvent calculation Vibrational spectrum density
a b s t r a c t The heating of cis-[ReO2I(PPh3)2] at reflux in benzene in air led to the isolation of the rhenium(VI) complex [ReO2I2(PPh3)2] (1). The compound is centrosymmetric around the octahedrally coordinated rhenium center, and the Re_O bond length of 1.797(2) Å is longer than in typical trans-dioxorhenium(V) complexes. The asymmetric Re_O stretching frequency occurs at 744 cm−1. Density functional theory has been used for the calculation of the vibrational spectrum density which confirms the experimental asymmetric Re_O stretching frequency. DFT calculation within the polarizable continuum model shows that complex 1 is more stable in CH2Cl2 than in the gas phase. EPR spectroscopy confirms a single d electron in 1. The crystal structure was determined by X-ray single crystal diffraction. In addition, infra-red, redox and electronic properties are also reported. © 2014 Elsevier B.V. All rights reserved.
The versatility of the metal rhenium, a member of Group 7 on the Periodic Table, is reflected in the wide range of oxidation states (from −1 to +7) in which its coordination compounds occur [1]. Most research on this metal has focussed on the +1 and +5 oxidation states, due to the stability of the d6 and d2 electron configurations respectively [2]. The +6 oxidation state, however, is unstable due to its d1 configuration, and rhenium(VI) coordination compounds are rare. Many species in this oxidation state have been electrochemically generated [3], although the complexes trans-[ReO2(dmap)4](PF6)2 (dmap = 4-(dimethylamino) pyridine) [4] and [(HB(pyz)3)ReO(X)(OTf)] [HB(pyz)3 = hydrotris(1pyrazolyl)borate; X = Cl, Br, I; OTf = triflate, OSO2CF3] [5] have been synthesized from Re(V) starting materials. The rhenium(VI) complex trans-[ReO2I2(PPh3)2] (1) was isolated in 37% yield from the heating under reflux conditions for 24 h of cis[ReO2I(PPh3)2] only in benzene in air [6]. It was characterized by elemental analysis, infrared and electronic spectroscopy, cyclic voltammetry, X-ray diffraction and electron spin resonance spectrometry. Re(VI) complexes reported in the literature usually contain ligands which are π-donors like nitride, oxide and fluoride [7]. Complex 1 is unusual since it contains the π-acceptor PPh3 as ligand, together with the mild reducing agent iodide. In fact, no trans-dioxo-diphosphine rhenium(VI) complex has ever been reported.
⁎ Corresponding author. E-mail address: [email protected] (T.I.A. Gerber).
http://dx.doi.org/10.1016/j.inoche.2014.11.014 1387-7003/© 2014 Elsevier B.V. All rights reserved.
Complex 1 is weakly soluble in most polar solvents. A strong absorption peak in the infrared spectrum at 744 cm−1 is assigned to the asymmetric stretching band of the O_ReVI_O moiety. The UV–vis absorption spectrum in DMF exhibits absorption bands at 365 (ε 20 800 M− 1 cm− 1) and 503 nm (ε 6180). The extinction values of these bands are relatively large for typical d–d transitions [3,8], and this phenomenon has also been previously observed [9]. It was proposed that the relatively larger intensity of the absorption in the visible region is due to the proximity of charge transfer states in the coordinated ligands, termed intensity stealing [10]. This low-energy absorption probably arises from a dxy → dπ⁎ (dxz, dyz) transition [11]. The complex is electroactive in acetonitrile solution and exhibits a ReVI/ReV couple at 505 mV versus SCE. Crystals of 1 were obtained from the slow evaporation of the mother liquor of the preparative solution. The complex is centrosymmetric octahedral (Fig. 1), with identical Re\I [2.7460(2) Å], Re\P [2.5255(6) Å] and Re_O [1.797(2) Å] distances [12]. The trans angles are all equal to 180.00. The Re_O bond lengths are longer than both typical Re_O bonds in monoxo- [1.69(3) Å] and trans-dioxorhenium(V) complexes [1.76(2) Å] [13]. The I(1)\Re\P(1) angle equals 91.38(2)° [identical to Ii(1)\ Re\Pi(1)]. The O(1)\Re\P(1) and O(1)\Re\I(1) bond angles are 91.81(6)° and 89.75(6)° respectively. The bond parameters of 1 were optimized in the gas phase and in dichloromethane solution [14–16] by the DFT method with the B3LYP functional [17,18] (Table 1). The hin are close to the experimental values. The calculated deviation of the trans bond angles from linearity
84
J. Mukiza et al. / Inorganic Chemistry Communications 51 (2015) 83–86 Table 2 Natural charges of atoms bonded to Re in (a) the gas phase and (b) CH2Cl2 solvent.
Fig. 1. ORTEP drawing of [ReO2I2(PPh3)2] (1). Selected experimental bond lengths (Å): Re\O(1) = Re\O(1)i = 1.797(2), Re\P(1) = 2.5255(6); Re\I(1) = 2.7460(2); selected bond angles (°): O(1)\Re\O(1)i = I(1)\Re\I(1)i = P(1)\Re\P(1)i = 180.00, I(1)\ Re\P(1) = 91.38(2), O(1)\Re\P(1) = 91.81(6); O(1)\Re\I(1) = 89.75(6).
is higher in the solvent than in the gas phase, which in turn corresponds well to the experimental values. The largest deviation in CH2Cl2 is for the trans O\Re\O bond angle [161.4°], which is ascribed to the higher dipole moment of the solvent. The atomic charges from the Natural Population Analysis (NPA) [19] for 1 (Table 2) shows that the calculated charge on the rhenium atom is considerably lower than the formal charge of +6, which is the result of the charge donation of the oxo and iodide ligands. There are large positive charges on the phosphorus atoms, and the charges on the iodide and oxo ligands are significantly smaller than −1 and −2 respectively.
Table 1 Calculated bond lengths (Å) and bond angles (°) for 1 in the (a) gas phase and (b) CH2Cl2 solvent.
Re\I(1) Re\I(1i) Re\O(1) Re\O(1i) Re\P(1) Re\P(1i) O(1)\Re\P(1i) O(1)\Re\I(1i) O(1)\Re\O(1i) P(1)\Re\P(1i) I(1)\Re\P(1i) I(1)\Re\I(1i)
a
b
2.806(0) 2.804(7) 1.767(3) 1.767(3) 2.627(2) 2.627(8) 88.6(7) 89.8(1) 179.7(4) 179.9(4) 87.0(2) 179.9(6)
2.774 2.899 1.761 1.758 2.638 2.625 84.861 82.867 161.398 175.563 86.104 172.297
Atom
a
b
I(1) I(1i) O(1) O(1i) P(1) P(1i) Re
−0.171 −0.170 −0.648 −0.649 1.147 1.147 0.742
−0.190 −0.259 −0.650 −0.631 1.131 1.166 0.804
The bonding, anti-bonding, lone-pair wave functions and spin population orbital analysis [20] for all the ligands bonded to Re in the gas phase and in dichloromethane solvent for both the alpha and beta spin states are presented in the Supplementary material as Table 1. There is one three-centered bonding and anti-bonding orbital for both spin states of the I\P\Re bond in the gas phase. It is absent for the beta spin state, but present for the alpha state, in CH2Cl2. The Re\O bonds in the gas phase are composed of oxygen p and rhenium d orbitals. There is s orbital participation for the alpha and p orbital participation in the beta spin state in CH2Cl2. In the alpha spin state there is a lone-pair d orbital on the Re atom. For the beta spin state in the solvent there is a lone-pair on the P atoms, but not in the gas phase. The calculated bond orders (Table 3) for the Re\I and Re\P bonds are lower in CH2Cl2 than in the gas phase. A comparison of the magnitudes of the bond orders shows double bonds for Re_O, which confirms the experimental data. The vibrational spectrum for 1 was calculated in the gas phase and in CH2Cl2 solution (Fig. 2). The peak around 720 cm−1 is assigned to the asymmetric Re_O stretching frequency. The solvent does not change this frequency to any remarkable extent. The result shows that the pattern and shape of the spectrum are not influenced by the solvent, although the intensities of the vibrations are somewhat smaller than in the solvent phase. The EPR spectrum of complex 1 in chloroform is depicted in Fig. 3 [21]. Rhenium(VI) compounds (the 5d1 configuration) give rise to signals that are detectable at temperatures higher than several tens of degrees Kelvin [22,23], hence, complex 1 was dissolved in chloroform and frozen at 77 K for EPR analysis. The spectrum showed six broadened lines splitting of parallel orientation of the g-tensor resulting from magnetic interaction between the unpaired electron spin and poorly resolved lines of the perpendicular orientations of the g-tensor as expected for rhenium (I = 5/2; n = 2I + 1) [24]. The g and A values obtained from complex 1 (Table 4) falls within the values reported by Borisova et al. [23,25] and Voigt et al. [26]. The extra lines observed were probably due to the hyperfine interaction observed for coordinated halide nuclei ( 127 I, I = 5/2) with rhenium [25].
Table 3 NLMO/NPA bond orders of Re–X bonds in the (a) gas phase (b) CH2Cl2 solvent. Label
I(1) I(1i) O(1) O(1i) P(1) P(1i)
(a)
(b)
Bond order
Bond order
0.7937 0.8851 1.2524 0.9451 0.5383 0.8019
0.7263 0.6811 1.0698 1.2573 0.5141 0.4955
J. Mukiza et al. / Inorganic Chemistry Communications 51 (2015) 83–86
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105 95 85 75 65 55 45 35 3300
2800
2300
1800
1300
800
300
(a) Experimental
(b) Gas phase
(c) CH2Cl2 solvent Fig. 2. Experimental (a) and calculated vibrational spectra of complex 1 in the (b) gas phase and (c) CH2Cl2 solvent.
Acknowledgments This work was supported financially by the National Research Foundation and the Nelson Mandela Metropolitan University. Janvier Mukiza is grateful to the Rwandan Educational Board for a bursary. Appendix A. Supplementary material Supplementary data for 1 (CCDC 991829) is available f the CCDC, 12 Union Road Cambridge CB2 1EZ, UK on request. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.inoche.2014.11.014. These data include MOL file and InChiKeys of the most important compounds described in this article.
References [1] R. Alberto, Comprehensive Coordination Chemistry II, in: J.A. McCleverty, T.J. Meyer (Eds.), 5, Elsevier, Oxford, 2004, p. 127. [2] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic Chemistry, 6th ed. J. Wiley Interscience, New York, 1999. [3] A. Canlier, T. Kawasaki, S. Chowdhury, Y. Ikeda, Inorg. Chim. Acta 363 (2010) 1; H.H. Thorp, J. van Houten, H.B. Gray, Inorg. Chem. 28 (1989) 889; S. Das, Inorg. Chim. Acta 361 (2008) 2815. [4] J.C. Brewer, Ph.D. Thesis, California Institute of Technology, Pasadena, CA, 1991. [5] D.D. DuMez, J.M. Mayer, Inorg. Chem. 37 (1998) 445. [6] Method of synthesis: A suspension of cis-[ReO2I(PPh3)2] (100 mg, 112 μmol) in 20 cm3 benzene was heated under reflux for 24 h in air, during which time the colour of the solution changed from purple to green-yellow. Cooling to room temperature produced a green-yellow precipitate, which was filtered off and dried (yield = 37%). Repeating the reaction in the presence of potassium iodide (120 μmol) and reducing the reaction time to 4 h gave the same product (yield = 72%). The mother liquor was left to evaporate slowly at room temperature, and after one month light green crystals were collected by filtration. M.p. 198 °C. IR (cm−1): ν(ReO2) 744(s). UV–vis (DMF, λmax(ε, M−1 cm−1)) = 365 (20800), 503 (6180).
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J. Mukiza et al. / Inorganic Chemistry Communications 51 (2015) 83–86 Table 4 Parameters of the spin Hamiltonian for complex 1. Complex 1 g‖ g gav A‖ (cm−1) A (cm−1) Aav (cm−1)
1.941 2. 010 1.987 0.0423 0.0340 0.0368
Aav and gav are calculated from Aav = (A‖ + 2A ) / 3 and gav = (g‖ + 2g ) / 3 respectively [25].
[13]
Measured spectrum Calculated spectrum 3100
3200
3300
3400
3500
3600
Gauss (G) Fig. 3. EPR experimental and calculated spectrum of complex 1 in chloroform at 77 K.
[14] [15] [16] [17]
[18] [19] [20]
[7] A.W. Sleight, Inorg. Chem. 14 (1975) 597; G.M. Lack, J.F. Gibson, J. Mol. Struct. 46 (1978) 299; A. Voigt, U. Abram, P. Strauch, R. Kirmse, Inorg. Chim. Acta 271 (1998) 199. [8] J.C. Brewer, H.B. Gray, Inorg. Chem. 28 (1989) 3334. [9] J.C. Brewer, H.B. Gray, Preprints, Division of Petroleum Chemistry, 35American Chemical Society, Washington, DC, 1990. 187. [10] R. Winkler, H.B. Gray, Inorg. Chem. 24 (1985) 346. [11] J.C. Brewer, H.H. Thorp, K.M. Slagle, C.W. Brudvig, H.B. Gray, J. Am. Chem. Soc. 113 (1991) 3171. [12] Crystallographic data for C36H30I2O2P2Re: monoclinic; space group P21/n; a = 9. 2431(3), b = 20.2697(7), c = 9.7635(4) Å, β = 112.264(3)°; V = 1692(1) Å3;
[21] [22] [23] [24] [25] [26]
Z = 2; Dc = 1.955 g·cm−3; μ = 5.538 mm−1; data/restraints/parameters: 4230/ 0/196; S = 1.10; final R indices [I N 2σ(I)]: R1 = 0.0184, wR2 = 0.0419. W.A. Nugent, J.M. Mayer, Metal–Ligand Multiple Bonds, Wiley, New York, 1998.; T.M. Trinka, G. Parkin, Polyhedron 16 (1997) 1031. L. Onsager, J. Am. Chem. Soc. 58 (1936) 1486. C.J. Cramer, D.G. Truhlar, Chem. Rev. 99 (1999) 2161. J. Tomasi, B. Mennucci, R. Cammi, Chem. Rev. 105 (2005) 2999. E.D. Glendening, J.K. Badenhoop, A.E. Reed, J.E. Carpenter, J.A. Bohmann, C.M. Morales, F. Weinhold, NBO 5.0, Theoretical Chemistry Institute, University of Wisconsin, Madison, 2001. A.D. Becke, J. Chem. Phys. 98 (1993) 5648. A.A. Granovsky, Firefly, version 8.0.0, http://classic.chem.msu.su/gran/firefly/index. html. J.P. Perdew, Electronic Structure of Solids '91, in: P. Ziesche, H. Eschrig (Eds.), Akademie Verlag, Berlin, 1991, p. 11. EPR spectra were recorded with a Bruker ESP 300E X-band spectrometer. W. Low, Paramagnetic Resonance in Solids, New York, (1960); Inostrannaya Literatura, Moscow (1962). L.V. Borisova, A.S. Borodkov, A.A. Grechnikov, E.A. Ugolkova, V.V. Minin, Russ. J. Inorg. Chem. 58 (2013) 940. J.A. Well, J.R. Bolton, Electron Paramagnetic Resonance—Elementary Theory and Practical Application, John Wiley & Sons, Inc., Hoboken, New Jersey, 2007. L.V. Borisova, V.V. Minin, S.B. Savvin, Russ. J. Inorg. Chem. 56 (2011) 247. A. Voigt, U. Abram, R. Kirmse, Inorg. Chem. Commun. 1 (1998) 203.
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Trans,trans,trans-[ReO2I2(PPh3)2], a rare rhenium(VI) complex — Synthesis and DFT study J. Mukiza a, T.I.A. Gerber a,⁎, E. Hosten a, A.S. Ogunlaja a, F. Taherkhani b, M. Amini c, M. Nahali d a
Department of Chemistry, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa Department of Physical Chemistry, Razi University, Kermanshah, Iran Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Iran d Department of Science, Babol Noshiravani University of Technology, Babol, Iran b c
a r t i c l e
i n f o
Article history: Received 14 August 2014 Received in revised form 12 November 2014 Accepted 15 November 2014 Available online 18 November 2014 Keywords: Rhenium(VI) Dioxo X-ray crystal structure DFT Solvent calculation Vibrational spectrum density
a b s t r a c t The heating of cis-[ReO2I(PPh3)2] at reflux in benzene in air led to the isolation of the rhenium(VI) complex [ReO2I2(PPh3)2] (1). The compound is centrosymmetric around the octahedrally coordinated rhenium center, and the Re_O bond length of 1.797(2) Å is longer than in typical trans-dioxorhenium(V) complexes. The asymmetric Re_O stretching frequency occurs at 744 cm−1. Density functional theory has been used for the calculation of the vibrational spectrum density which confirms the experimental asymmetric Re_O stretching frequency. DFT calculation within the polarizable continuum model shows that complex 1 is more stable in CH2Cl2 than in the gas phase. EPR spectroscopy confirms a single d electron in 1. The crystal structure was determined by X-ray single crystal diffraction. In addition, infra-red, redox and electronic properties are also reported. © 2014 Elsevier B.V. All rights reserved.
The versatility of the metal rhenium, a member of Group 7 on the Periodic Table, is reflected in the wide range of oxidation states (from −1 to +7) in which its coordination compounds occur [1]. Most research on this metal has focussed on the +1 and +5 oxidation states, due to the stability of the d6 and d2 electron configurations respectively [2]. The +6 oxidation state, however, is unstable due to its d1 configuration, and rhenium(VI) coordination compounds are rare. Many species in this oxidation state have been electrochemically generated [3], although the complexes trans-[ReO2(dmap)4](PF6)2 (dmap = 4-(dimethylamino) pyridine) [4] and [(HB(pyz)3)ReO(X)(OTf)] [HB(pyz)3 = hydrotris(1pyrazolyl)borate; X = Cl, Br, I; OTf = triflate, OSO2CF3] [5] have been synthesized from Re(V) starting materials. The rhenium(VI) complex trans-[ReO2I2(PPh3)2] (1) was isolated in 37% yield from the heating under reflux conditions for 24 h of cis[ReO2I(PPh3)2] only in benzene in air [6]. It was characterized by elemental analysis, infrared and electronic spectroscopy, cyclic voltammetry, X-ray diffraction and electron spin resonance spectrometry. Re(VI) complexes reported in the literature usually contain ligands which are π-donors like nitride, oxide and fluoride [7]. Complex 1 is unusual since it contains the π-acceptor PPh3 as ligand, together with the mild reducing agent iodide. In fact, no trans-dioxo-diphosphine rhenium(VI) complex has ever been reported.
⁎ Corresponding author. E-mail address: [email protected] (T.I.A. Gerber).
http://dx.doi.org/10.1016/j.inoche.2014.11.014 1387-7003/© 2014 Elsevier B.V. All rights reserved.
Complex 1 is weakly soluble in most polar solvents. A strong absorption peak in the infrared spectrum at 744 cm−1 is assigned to the asymmetric stretching band of the O_ReVI_O moiety. The UV–vis absorption spectrum in DMF exhibits absorption bands at 365 (ε 20 800 M− 1 cm− 1) and 503 nm (ε 6180). The extinction values of these bands are relatively large for typical d–d transitions [3,8], and this phenomenon has also been previously observed [9]. It was proposed that the relatively larger intensity of the absorption in the visible region is due to the proximity of charge transfer states in the coordinated ligands, termed intensity stealing [10]. This low-energy absorption probably arises from a dxy → dπ⁎ (dxz, dyz) transition [11]. The complex is electroactive in acetonitrile solution and exhibits a ReVI/ReV couple at 505 mV versus SCE. Crystals of 1 were obtained from the slow evaporation of the mother liquor of the preparative solution. The complex is centrosymmetric octahedral (Fig. 1), with identical Re\I [2.7460(2) Å], Re\P [2.5255(6) Å] and Re_O [1.797(2) Å] distances [12]. The trans angles are all equal to 180.00. The Re_O bond lengths are longer than both typical Re_O bonds in monoxo- [1.69(3) Å] and trans-dioxorhenium(V) complexes [1.76(2) Å] [13]. The I(1)\Re\P(1) angle equals 91.38(2)° [identical to Ii(1)\ Re\Pi(1)]. The O(1)\Re\P(1) and O(1)\Re\I(1) bond angles are 91.81(6)° and 89.75(6)° respectively. The bond parameters of 1 were optimized in the gas phase and in dichloromethane solution [14–16] by the DFT method with the B3LYP functional [17,18] (Table 1). The hin are close to the experimental values. The calculated deviation of the trans bond angles from linearity
84
J. Mukiza et al. / Inorganic Chemistry Communications 51 (2015) 83–86 Table 2 Natural charges of atoms bonded to Re in (a) the gas phase and (b) CH2Cl2 solvent.
Fig. 1. ORTEP drawing of [ReO2I2(PPh3)2] (1). Selected experimental bond lengths (Å): Re\O(1) = Re\O(1)i = 1.797(2), Re\P(1) = 2.5255(6); Re\I(1) = 2.7460(2); selected bond angles (°): O(1)\Re\O(1)i = I(1)\Re\I(1)i = P(1)\Re\P(1)i = 180.00, I(1)\ Re\P(1) = 91.38(2), O(1)\Re\P(1) = 91.81(6); O(1)\Re\I(1) = 89.75(6).
is higher in the solvent than in the gas phase, which in turn corresponds well to the experimental values. The largest deviation in CH2Cl2 is for the trans O\Re\O bond angle [161.4°], which is ascribed to the higher dipole moment of the solvent. The atomic charges from the Natural Population Analysis (NPA) [19] for 1 (Table 2) shows that the calculated charge on the rhenium atom is considerably lower than the formal charge of +6, which is the result of the charge donation of the oxo and iodide ligands. There are large positive charges on the phosphorus atoms, and the charges on the iodide and oxo ligands are significantly smaller than −1 and −2 respectively.
Table 1 Calculated bond lengths (Å) and bond angles (°) for 1 in the (a) gas phase and (b) CH2Cl2 solvent.
Re\I(1) Re\I(1i) Re\O(1) Re\O(1i) Re\P(1) Re\P(1i) O(1)\Re\P(1i) O(1)\Re\I(1i) O(1)\Re\O(1i) P(1)\Re\P(1i) I(1)\Re\P(1i) I(1)\Re\I(1i)
a
b
2.806(0) 2.804(7) 1.767(3) 1.767(3) 2.627(2) 2.627(8) 88.6(7) 89.8(1) 179.7(4) 179.9(4) 87.0(2) 179.9(6)
2.774 2.899 1.761 1.758 2.638 2.625 84.861 82.867 161.398 175.563 86.104 172.297
Atom
a
b
I(1) I(1i) O(1) O(1i) P(1) P(1i) Re
−0.171 −0.170 −0.648 −0.649 1.147 1.147 0.742
−0.190 −0.259 −0.650 −0.631 1.131 1.166 0.804
The bonding, anti-bonding, lone-pair wave functions and spin population orbital analysis [20] for all the ligands bonded to Re in the gas phase and in dichloromethane solvent for both the alpha and beta spin states are presented in the Supplementary material as Table 1. There is one three-centered bonding and anti-bonding orbital for both spin states of the I\P\Re bond in the gas phase. It is absent for the beta spin state, but present for the alpha state, in CH2Cl2. The Re\O bonds in the gas phase are composed of oxygen p and rhenium d orbitals. There is s orbital participation for the alpha and p orbital participation in the beta spin state in CH2Cl2. In the alpha spin state there is a lone-pair d orbital on the Re atom. For the beta spin state in the solvent there is a lone-pair on the P atoms, but not in the gas phase. The calculated bond orders (Table 3) for the Re\I and Re\P bonds are lower in CH2Cl2 than in the gas phase. A comparison of the magnitudes of the bond orders shows double bonds for Re_O, which confirms the experimental data. The vibrational spectrum for 1 was calculated in the gas phase and in CH2Cl2 solution (Fig. 2). The peak around 720 cm−1 is assigned to the asymmetric Re_O stretching frequency. The solvent does not change this frequency to any remarkable extent. The result shows that the pattern and shape of the spectrum are not influenced by the solvent, although the intensities of the vibrations are somewhat smaller than in the solvent phase. The EPR spectrum of complex 1 in chloroform is depicted in Fig. 3 [21]. Rhenium(VI) compounds (the 5d1 configuration) give rise to signals that are detectable at temperatures higher than several tens of degrees Kelvin [22,23], hence, complex 1 was dissolved in chloroform and frozen at 77 K for EPR analysis. The spectrum showed six broadened lines splitting of parallel orientation of the g-tensor resulting from magnetic interaction between the unpaired electron spin and poorly resolved lines of the perpendicular orientations of the g-tensor as expected for rhenium (I = 5/2; n = 2I + 1) [24]. The g and A values obtained from complex 1 (Table 4) falls within the values reported by Borisova et al. [23,25] and Voigt et al. [26]. The extra lines observed were probably due to the hyperfine interaction observed for coordinated halide nuclei ( 127 I, I = 5/2) with rhenium [25].
Table 3 NLMO/NPA bond orders of Re–X bonds in the (a) gas phase (b) CH2Cl2 solvent. Label
I(1) I(1i) O(1) O(1i) P(1) P(1i)
(a)
(b)
Bond order
Bond order
0.7937 0.8851 1.2524 0.9451 0.5383 0.8019
0.7263 0.6811 1.0698 1.2573 0.5141 0.4955
J. Mukiza et al. / Inorganic Chemistry Communications 51 (2015) 83–86
85
105 95 85 75 65 55 45 35 3300
2800
2300
1800
1300
800
300
(a) Experimental
(b) Gas phase
(c) CH2Cl2 solvent Fig. 2. Experimental (a) and calculated vibrational spectra of complex 1 in the (b) gas phase and (c) CH2Cl2 solvent.
Acknowledgments This work was supported financially by the National Research Foundation and the Nelson Mandela Metropolitan University. Janvier Mukiza is grateful to the Rwandan Educational Board for a bursary. Appendix A. Supplementary material Supplementary data for 1 (CCDC 991829) is available f the CCDC, 12 Union Road Cambridge CB2 1EZ, UK on request. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.inoche.2014.11.014. These data include MOL file and InChiKeys of the most important compounds described in this article.
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86
J. Mukiza et al. / Inorganic Chemistry Communications 51 (2015) 83–86 Table 4 Parameters of the spin Hamiltonian for complex 1. Complex 1 g‖ g gav A‖ (cm−1) A (cm−1) Aav (cm−1)
1.941 2. 010 1.987 0.0423 0.0340 0.0368
Aav and gav are calculated from Aav = (A‖ + 2A ) / 3 and gav = (g‖ + 2g ) / 3 respectively [25].
[13]
Measured spectrum Calculated spectrum 3100
3200
3300
3400
3500
3600
Gauss (G) Fig. 3. EPR experimental and calculated spectrum of complex 1 in chloroform at 77 K.
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[21] [22] [23] [24] [25] [26]
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