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The electron relaxation and UP spectra of metal coordination compounds
ELSPEC 3515
Journal of Electron Spectroscopy and Related Phenomena 96 (1998) 141–148
The electron relaxation and UP spectra of metal coordination compounds V.I. Vovna*, I.B. Lvov, Y.V. Ivanov, S.N. Slabzhennikov, A.I. Streltsov, A.Yu. Ustinov Physical and Technical Research Institute, Far-Eastern State University, 25, Uborevitcha Str., 690600 Vladivostok, Russia Received 5 December 1997; accepted 14 January 1998
Abstract The electronic structure of 3d-metals bis and tris-b-diketonates was studied by methods of UP spectroscopy and quantum chemistry in ab initio, Xa-DV and INDO approximations. According to PE data, the covalent interaction metal-legand is realized, on the whole, by n-electrons, and IE 1 in all compounds caused by d-electrons. The Xa-DV calculations give a good agreement with experimental picture of interaction of metal AOs and ligand orbitals. Ab initio calculations showed the main role of high j-orbitals in covalent interaction. All quantum chemical methods overstate multiplet splitting of ligand levels caused by overestimation of a delocalization factor of d-electrons. 䉷 1998 Elsevier Science B.V. All rights reserved. Keywords: Electron relaxation; Electronic structure; Photoelectron spectra
1. Introduction The method of gas phase photoelectron spectroscopy of valent electrons takes a leading place among experimental methods of studies of electronic structure and the nature of chemical bonds of molecules and complexes. The electron ionization energies (IE) of canonical multi-centered molecular orbitals (MO) with other spectral information (vibration structure, the splitting of electronic states, bands intensities) allow establishing the character of high occupied MOs, the orbital nature of chemical bonds, including the coordination bonds, the electronic effects of substitution etc. [1–3]. But the correlation of orbital IE with energies of canonical MO in Koopmans approximation is restricted, firstly, by the violation of one-electronic photionization picture, * Corresponding author. Tel: +7-4232-25-77-19; Fax: +7-423225-77-19; E-mail: [email protected]
secondly, by the electron relaxation (E rel) in final states, which depends on types of ionized orbital. For the row of high occupied MOs (IE i ⬍ 15 eV), as a rule, the ionization can be considered as oneelectronic. This allows correlating the PE bands with defined MOs. For compounds of non-transition elements the electron relaxation can change the IE sequence for closed by energy MOs, but PE data is usually in good agreement with quantum chemical calculations for ground state. Another situation is possible for molecules and complexes of transition metals, which contain localized d-electrons on one atom. The great difference in E rel for delocalized and localized electrons can change the IE i sequence in comparison with e i so that the scheme of interactions of metal and ligand levels built on the base of the experiment can contradict with MO structure in a neutral state. In order to investigate the influence of electron relaxation to PE spectra of metal complexes of different groups of periodic
0368-2048/98/$ - see front matter 䉷 1998 Elsevier Science B.V. All rights reserved. PII: S 03 68 - 20 4 8( 9 8) 0 02 3 0- 8
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table we studied the electronic structure of metal tris and bis-b-diketonates by methods of UPS and quantum chemistry. In this paper we present the results for the row of M(acac) 3 (M = Al, Sc, Ti, V, Cr, Mn, Fe, Co) and M(acac) 2 (M = Ni, Cu).
2. Methods of experiment and calculations HeI PE spectra were obtained on electron spectrometer EC-3201 that was modernized for the best spectra reproduction of hard-volatile metal complexes. The method of obtaining was described by us earlier [4,5]. Theoretical calculations of ground states were fulfilled in the approximations: Xa-DV, ab initio (HONDO, GAUSSIAN-92, GOMESS), INDO, CNDO (restricted and unrestricted variants of HF SCF). IE values were calculated in transition state approximation by Xa-DV methods and as the full energy differences of ions and starting complexes. For a reduction of calculation time in ab initio and Xa-DV approximations for ML 3 the Ch 3-groups in bpositions were substituted to H-atoms. As it was shown in an example of Cr(acac) 3 nd Cr(mal) 3 [6], such substitution leads to destabilization of four pairs of high MOs without significant changes of their nature. The IE values in approximation of a transition state were calculated for M(mal) 2 (M = Ni, Cu) and M(mal) 3 (M = Al, Sc, Ti, V). During the correlation of calculation data of a Xa-DV method we used the values of one-electronic energy, which were different from theoretical IE by (2.5 ⫾ 0.5) eV. As showed the calculations for four tris-malonates, the shift of levels in half-electron approximation for p and n-levels of ligands does not depend on a contribution of metal dAO. For half-occupied d-levels of Ti and V complexes the shifts are insignificantly higher: 2.23 eV for da 1 (Ti) and 2.59 eV for de (V). The geometry for metalocycles was taken from [7,8] for ML 3 and from [9] for ML 2.
of complexes of the third group, Al and Sc, correlate with orbitals p 3 (a 2 + e), n − (a 2 + e), n + (a 1 + e) and p 2 (a 1 + e). The value of a–e splitting depends on efficiency of interligand interaction and interaction of ligand levels with metal AOs. In Al(acac) 3 spectra the wide Frank–Condon band outlines do not allow to detect a–e splitting for four high MO pairs, which with a high limit can be estimated at 0.2 eV. In spectra of Ga(acac) 3 and In(acac) 3 a higher degree of covalent bonds of metals leads to splitting of bands of n − and n +− levels. Based on PE data, the sequence of IE of high levels is: a2 p3 ⬍ ep3 ⬍ en − ⬍ a2 n − ⬍ en + ⬍ a1 n + :
3. Metals tris-b-diketonates The PE spectra of M(acac) 3 with other b-diketonate complexes were considered by us in the survey [10]. One can interpret low-energy regions of spectra: from IE 1 to ⬇ 12 eV (Fig. 1). The first four bands in spectra
Fig. 1. The PE spectra of M(acac) 3:M = Al(1), Sc(2), Ti(3), V(4), Cr(5), Mn(6), Fe(7), Co(8)
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The covalent of an M-L bond caused by, on the whole, levels a 2n −, en + and a 1n +. Bands contrasting in Sc(acac) 3 spectra allowed to detect the splitting for three high MO pairs, the IE sequence is different from that presented previously only by inversion of a 2n − and en −-levels caused by binding characters of Sc 3d-orbitals in degenerated MO. The calculation results of ground states in M(mal) 3 complexes by Xa-DV method are presented in Fig. 2 with the contributions of metal d-orbitals (%). Calculation results for the first two complexes are in good agreement with the experiment, but half-occupied a 1d-orbital of Ti(mal) 3, according to calculation data for ground and ionized states, is significantly nearer to a 2p 3 than in PE spectra (1.0 eV and 2.4 eV, correspondingly). The similar energies understating of half-occupied
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oribitals of d-type Xa-DV methods showed for other d-element complexes too. The correlation of energies of b-spin orbitals (Fig. 2) showed the significant increasing of contribution of 3-d and 4s-orbitals of metal into ligand MO ep 3, en −, a 1n +. This regularity is in agreement with increasing a a–e splitting value for n −-electrons from 0.35 eV (Sc) to 0.55 eV (Co). The splitting of orbital energies and calculated IE (transition state) for a and b-spin-orbitals of ligand levels in complexes V, Cr, Mn and Fe are in direct dependence from d-AO contribution (Fig. 2a). Predicted by Xa-DV methods the spin splitting of ligand levels for V and Cr complexes did not confirm by PES methods. The coinciding in the limits of experimental error of width of halfheight of ligand MOs bands for complexes d 0, d 1, d 2 and d 3 indicates a significant value of multiplet splitting ( ⬍ 0.1 eV) caused by interaction of non-coupled
Fig. 2. The correlation of energies of spin-orbitals of a (a) and b (b) electrons (Xa-DV method).
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d-electrons and non-coupled ligand electron in an ionized state. Therefore, for final states the Xa-DV method, firstly, overestimates the IE values of d-electrons, secondly, significantly overestimates the contributions of d-electrons into ligand levels. In Cr(acac) 3 spectra the first weak band (7.5 eV) correlates with two edelectrons, but among degenerated a-spin-orbitals of the Xa-DV method it’s absent e-orbital with predominated localization of metal. For d 4 (Mn) and d 5 (Fe) complexes the Xa-DV method showed similar full mixing of a-spin-orbitals of ed-electrons with ligand levels. For d 6-complex of Co(mal) 3 with occupied orbitals two orbitals close for energy to n −-orbitals, whereas according to PE data, they lie higher. The correlation of experimental ionization energies for M(acac) 3 row, obtained by us from the analysis of regularities in PE spectra for different d-metal tris-bdiketonates, is presented in Fig. 3. The differences of diagrams on Figs 2 and 3 are most essential for Cr, Mn and Fe complexes. Ab initio calculation results for complexes of transition metals are significantly different from the results of Xa-DV calculations. The correlation of one-electronic energy for a and b-spin orbitals is presented on Fig. 4. In the row of 3d-metal complexes the results for V(mal) 3 and Mn(mal) 3 are absent. For V complex the iteration procedure was failed and the
Fig. 3. The correlation diagram of vertical IE for M(acac) 3.
results for Mn complex, by our opinion, are incorrect because the fourth non-coupled d-electron occupies anti-binding p 4-orbital. For Sc complex it’s necessary to point out two significant differences of electronic structure from XaDV calculation. First, four n-orbitals have close energies, whereas energy intervals between p 2 and p 3levels achieves 5.9 eV (3.2 eV in Xa-DV and 3.5 eV in PES). Secondly, Sc 3d orbitals give maximal contributions not in n-orbitals, but in high orbitals. In the row of complexes M(mal) 3 (M = Ti, Cr, Fe) the contribution of 3d-AO into both b-spin-orbitals of n +-type insignificantly increases and leads to their stabilization. Similar regularity can be seen for two high j-orbitals [numbers 52 (a 1) and 53, 54 (e), high occupied — 66 (a 2)] which contain maximal contributions of 3d-AO (5–7%). In low-spin complexes Co(mal) 3 these MOs rise up because b-spin-orbitals da 1 and de are occupied and lie lower than p 1-MO [numbers 49 (a 1) and 47, 48 (e)]. The ab initio method showed less significant delocalization of both orbitals of d-type in comparison with the Xa-DV method (metal contribution is 96% and 90% against 76 and 63%). In Fig. 4 a-spin-orbitals, presented d-orbitals have maximal contributions of metal. For Ti(mal) 3 da 1level (69% 3d) is lying between p 3 and n −-MOs. For Cr(mal) 3 two d-type levels de e and da 1 with localization on metal (50–60%) are close by energy to p 1-MO. For high-spin Fe complexes the electronic configuration for five non-coupled electrons is: da11 de2t de2e : On Fig. 4 d-orbitals can be correlated with the group of close levels in the energy region of 18–19 eV (MO numbers 40–44). Two high MOs, lying in this region, contain significant Fe 3d contributions (74% and 58% correspondingly). These orbitals are de e and da 1. The de t orbital, according to calculations, is strongly delocalized and metal contributions into MOs 40 and 41 does not exceed 1/3. As one can see from presented contributions of metal dAO, Fe de t-orbital is shared between three neighboring e-MOs. According to semi-empirical calculations, d-electrons on a-spin-orbitals of M(mal) 3 row (M = Ti, Cr, Fe, Co) lie in the energy region of g-MO. In comparison with Xa-DV calculations the MO numbers are lower by 12 (Cr), 15 (Fe) and 17 (Co) (Figs 3, and 5).
V.I. Vovna et al. / Journal of Electron Spectroscopy and Related Phenomena 96 (1998) 141–148
Fig. 4. The correlation of energies of spin-orbitals of a (a) and b (b) electrons (ab initio method).
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Fig. 4. Continued
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V.I. Vovna et al. / Journal of Electron Spectroscopy and Related Phenomena 96 (1998) 141–148 Table 1 The IE values of MO complexes MO
p3− ,b 2 g p3+ ,b 1 u d,a g d,a g d,b 3g d,b 2g n −,b 2u n +,b 3u n −,b 1g n +,a g p2− ,a u p2+ ,b 3 g
Ni(ac ac) 2 Ni(Mal ) 2, Ni(Mal) 2, Ni(Mal) 2 , Cu(mal) 2 exp. Xa-DV INDO/2 ab initio (a), exp. 7.50 8.80 7.95 8.15 8.45 8.45 9.30 10.15 10.30 11.00 11.60 11.60
−9.19 −9.79 −9.74 −10.08 −10.22 −10.74 −10.15 −11.27 −11.28 −12.29 −12.76 −13.09
−11.50 −12.87 −7.53 −9.52 −7.70 −8.25 −13.26 −14.19 −13.62 −15.26 −16.86 −18.12
−9.07 −9.21 −16.37 −19.79 −17.27 −17.38 −11.56 −12.84 −11.61 −12.97 −14.79 −14.82
8.09 8.51 10.22 10.22 10.22 10.22 9.07 9.77
4. Nickel and cooper bis-b-diketonates The IE values for high occupied MOs of Ni(mal) 2 and Cu(mal) 2 are shown in Table 1. The experimental data on MO energies are presented for correspondent acetylacetonate complexes. As we can see from Table 1, the most real picture gives the calculations in Xa-DV approximation. On
Cu(Mal) 2 Cu(Mal) 2 Cu(Mal) 2 Cu(Mal) 2 CU(Mal 2 Cu(Mal) 2 (a), Xa- (a), INDO/ (a), ab (b), Xa- (b), INDO/ (b), ab DV 2 initio DV 2 initio −9.35 −9.61 −12.84 −13.85 −13.81 −12.98 −10.50 −11.27 −9.19 −11.14 −12.69 −12.36
−11.77 −12.91 −9.88 −10.91 −10.35 −9.93 −12.85 −14.84 −14.18 −14.99 −17.31 −17.49
−8.13 −8.52 −14.84 −15.67 −16.70 −18.92 −10.99 −12.35 −9.48 −12.26 −13.68 −13.40
−9.18 −9.46 −12.57 −13.57 −13.56 −12.82 −9.94 −10.73 −8.44 −10.67 −12.54 −12.18
MO
Ni(Mal) 2
Cu(mal) 2 a
Cu(mal) 2 b
p3− ,b 2 g
0.53 0.06 0.39 0.87 0.54 0.94 0.97 0.51 0.95 0.83 0.58 0.91 0.94 0.58 0.93 0.41 0.07 0.24 0.49 0.10 0.23
0.17 0.06 0.57 0.92 0.62 0.96 0.90 0.53 0.95 0.71 0.58 0.87 0.83 0.54 0.98 0.56 0.28 0.46 0.43 0.20 0.32
0.18 0.06 0.41 0.91 0.56 0.97 0.92 0.53 0.96 0.76 0.45 0.91 0.80 0.56 0.98 0.59 0.07 0.16 0.43 0.12 0.25
d,a g
d,b 2g
d,b 3g
n −,b 1g n +,a g
−8.21 −8.45 −13.82 −16.54 −15.72 −10.99 −12.35 −9.48 −12.26 −13.68 −13.40
the whole, the sequence of n and p-orbitals is similar for all methods. As for metal d-orbitals, the ab initio and INDO methods give quite different orbital sequences in comparison with the experiment. Specifically, INDO-calculations strongly understate IE of d-orbitals (in Koopmans theorem approach), that caused by deficiency of method parameterization for calculations of metal complex compounds. As in
Table 2 The contributions of d-AOs into molecular orbitals (Xa/ab initio/INDO), a.u.
d,a g
−11.53 −12.89 −8.88 −10.39 −9.41 −9.22 −12.76 −14.79 −12.89 −14.86 −17.28 −17.45
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tris-chelate complexes, ab initio methods shows that d-AO are lower than all n and p-orbitals. The contributions of metal d-AOs into ligand and dorbitals of complexes are significantly different according to calculation results in different methods (Table 2). INDO methods show a high degree of individuality of d-orbitals in complexes, but ab initio results show the significant degree of mixing of ligand and d-orbitals.
5. Conclusions The interpretation of PE spectra of metal acetylacetonates based on the regularities in spectra of presented and kindred compounds and based on theoretical modelling, showed that oxygen n-orbitals give the general contribution in metal-ligand covalent interaction. The Xa-DV method overestimates IE values in the transition state method and for ground state shows the interaction scheme of metal and ligand levels which is close to experimental. Ab initio calculations of tris and bis-malonates of delements showed qualitative differences from experimental data and Xa-DV methods both in levels sequence and in the nature of metal-ligand covalent interactions. Both calculation methods together with semiempirical INDO methods overstate delocalization of the metal d-orbital. It can be confirmed by
insignificant values of multiplet splitting of ligand n and p-levels in spectra of Ti, V, Cr and Cu complexes. Based on ab initio calculation results, the value of electron relaxation for complexes of the second half of the transition period can be estimated in 8–9 eV. Acknowledgements This work was financially supported by the Russian Fund of Fundamental Research (Grant no. 96-0334214a). References [1] V.I. Nefedov, V.I. Vovna, Electronic Structure of Chemical Compounds, Nauka Moscow, 1987, pp. 347. [2] V.I. Nefedov, V.I. Vovna, Electronic Structure of Organic and Elementoorganic Compounds, Nauka, Moscow, 1989, pp. 199. [3] V.I. Vovna, Electronic Structure of Organic Compounds, Nauka Moscow, 1991, pp. 247. [4] A.Yu. Ustinov, J. Phys. Chem. 69 (1995) 1268. in Russian. [5] V.I. Vovna, I.B. Lvov, S.N. Slabzhennikov, A.Yu. Ustinov, J. Electon Spectrosc. 88–91 (1998) 103. [6] A.Yu. Ustinov, V.I. Vovna, J. Phys. Chem. 67 (1993) 1929. in Russian. [7] E.C. Zingafelter, Coordination Chem. Rev. 1 (1966) 151. [8] D. Kipert, Inorganic Stereochemistry, Mir Moscow, 1985, p. 117. [9] N.I. Giritceva, N.V. Belova, G.V. Giritcev, J. Struct. Chem. 33 (1992) 63. in Russian. [10] V.I. Vovna, Coordination Chem. 21 (1995) 435. in Russian.
Journal of Electron Spectroscopy and Related Phenomena 96 (1998) 141–148
The electron relaxation and UP spectra of metal coordination compounds V.I. Vovna*, I.B. Lvov, Y.V. Ivanov, S.N. Slabzhennikov, A.I. Streltsov, A.Yu. Ustinov Physical and Technical Research Institute, Far-Eastern State University, 25, Uborevitcha Str., 690600 Vladivostok, Russia Received 5 December 1997; accepted 14 January 1998
Abstract The electronic structure of 3d-metals bis and tris-b-diketonates was studied by methods of UP spectroscopy and quantum chemistry in ab initio, Xa-DV and INDO approximations. According to PE data, the covalent interaction metal-legand is realized, on the whole, by n-electrons, and IE 1 in all compounds caused by d-electrons. The Xa-DV calculations give a good agreement with experimental picture of interaction of metal AOs and ligand orbitals. Ab initio calculations showed the main role of high j-orbitals in covalent interaction. All quantum chemical methods overstate multiplet splitting of ligand levels caused by overestimation of a delocalization factor of d-electrons. 䉷 1998 Elsevier Science B.V. All rights reserved. Keywords: Electron relaxation; Electronic structure; Photoelectron spectra
1. Introduction The method of gas phase photoelectron spectroscopy of valent electrons takes a leading place among experimental methods of studies of electronic structure and the nature of chemical bonds of molecules and complexes. The electron ionization energies (IE) of canonical multi-centered molecular orbitals (MO) with other spectral information (vibration structure, the splitting of electronic states, bands intensities) allow establishing the character of high occupied MOs, the orbital nature of chemical bonds, including the coordination bonds, the electronic effects of substitution etc. [1–3]. But the correlation of orbital IE with energies of canonical MO in Koopmans approximation is restricted, firstly, by the violation of one-electronic photionization picture, * Corresponding author. Tel: +7-4232-25-77-19; Fax: +7-423225-77-19; E-mail: [email protected]
secondly, by the electron relaxation (E rel) in final states, which depends on types of ionized orbital. For the row of high occupied MOs (IE i ⬍ 15 eV), as a rule, the ionization can be considered as oneelectronic. This allows correlating the PE bands with defined MOs. For compounds of non-transition elements the electron relaxation can change the IE sequence for closed by energy MOs, but PE data is usually in good agreement with quantum chemical calculations for ground state. Another situation is possible for molecules and complexes of transition metals, which contain localized d-electrons on one atom. The great difference in E rel for delocalized and localized electrons can change the IE i sequence in comparison with e i so that the scheme of interactions of metal and ligand levels built on the base of the experiment can contradict with MO structure in a neutral state. In order to investigate the influence of electron relaxation to PE spectra of metal complexes of different groups of periodic
0368-2048/98/$ - see front matter 䉷 1998 Elsevier Science B.V. All rights reserved. PII: S 03 68 - 20 4 8( 9 8) 0 02 3 0- 8
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table we studied the electronic structure of metal tris and bis-b-diketonates by methods of UPS and quantum chemistry. In this paper we present the results for the row of M(acac) 3 (M = Al, Sc, Ti, V, Cr, Mn, Fe, Co) and M(acac) 2 (M = Ni, Cu).
2. Methods of experiment and calculations HeI PE spectra were obtained on electron spectrometer EC-3201 that was modernized for the best spectra reproduction of hard-volatile metal complexes. The method of obtaining was described by us earlier [4,5]. Theoretical calculations of ground states were fulfilled in the approximations: Xa-DV, ab initio (HONDO, GAUSSIAN-92, GOMESS), INDO, CNDO (restricted and unrestricted variants of HF SCF). IE values were calculated in transition state approximation by Xa-DV methods and as the full energy differences of ions and starting complexes. For a reduction of calculation time in ab initio and Xa-DV approximations for ML 3 the Ch 3-groups in bpositions were substituted to H-atoms. As it was shown in an example of Cr(acac) 3 nd Cr(mal) 3 [6], such substitution leads to destabilization of four pairs of high MOs without significant changes of their nature. The IE values in approximation of a transition state were calculated for M(mal) 2 (M = Ni, Cu) and M(mal) 3 (M = Al, Sc, Ti, V). During the correlation of calculation data of a Xa-DV method we used the values of one-electronic energy, which were different from theoretical IE by (2.5 ⫾ 0.5) eV. As showed the calculations for four tris-malonates, the shift of levels in half-electron approximation for p and n-levels of ligands does not depend on a contribution of metal dAO. For half-occupied d-levels of Ti and V complexes the shifts are insignificantly higher: 2.23 eV for da 1 (Ti) and 2.59 eV for de (V). The geometry for metalocycles was taken from [7,8] for ML 3 and from [9] for ML 2.
of complexes of the third group, Al and Sc, correlate with orbitals p 3 (a 2 + e), n − (a 2 + e), n + (a 1 + e) and p 2 (a 1 + e). The value of a–e splitting depends on efficiency of interligand interaction and interaction of ligand levels with metal AOs. In Al(acac) 3 spectra the wide Frank–Condon band outlines do not allow to detect a–e splitting for four high MO pairs, which with a high limit can be estimated at 0.2 eV. In spectra of Ga(acac) 3 and In(acac) 3 a higher degree of covalent bonds of metals leads to splitting of bands of n − and n +− levels. Based on PE data, the sequence of IE of high levels is: a2 p3 ⬍ ep3 ⬍ en − ⬍ a2 n − ⬍ en + ⬍ a1 n + :
3. Metals tris-b-diketonates The PE spectra of M(acac) 3 with other b-diketonate complexes were considered by us in the survey [10]. One can interpret low-energy regions of spectra: from IE 1 to ⬇ 12 eV (Fig. 1). The first four bands in spectra
Fig. 1. The PE spectra of M(acac) 3:M = Al(1), Sc(2), Ti(3), V(4), Cr(5), Mn(6), Fe(7), Co(8)
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The covalent of an M-L bond caused by, on the whole, levels a 2n −, en + and a 1n +. Bands contrasting in Sc(acac) 3 spectra allowed to detect the splitting for three high MO pairs, the IE sequence is different from that presented previously only by inversion of a 2n − and en −-levels caused by binding characters of Sc 3d-orbitals in degenerated MO. The calculation results of ground states in M(mal) 3 complexes by Xa-DV method are presented in Fig. 2 with the contributions of metal d-orbitals (%). Calculation results for the first two complexes are in good agreement with the experiment, but half-occupied a 1d-orbital of Ti(mal) 3, according to calculation data for ground and ionized states, is significantly nearer to a 2p 3 than in PE spectra (1.0 eV and 2.4 eV, correspondingly). The similar energies understating of half-occupied
143
oribitals of d-type Xa-DV methods showed for other d-element complexes too. The correlation of energies of b-spin orbitals (Fig. 2) showed the significant increasing of contribution of 3-d and 4s-orbitals of metal into ligand MO ep 3, en −, a 1n +. This regularity is in agreement with increasing a a–e splitting value for n −-electrons from 0.35 eV (Sc) to 0.55 eV (Co). The splitting of orbital energies and calculated IE (transition state) for a and b-spin-orbitals of ligand levels in complexes V, Cr, Mn and Fe are in direct dependence from d-AO contribution (Fig. 2a). Predicted by Xa-DV methods the spin splitting of ligand levels for V and Cr complexes did not confirm by PES methods. The coinciding in the limits of experimental error of width of halfheight of ligand MOs bands for complexes d 0, d 1, d 2 and d 3 indicates a significant value of multiplet splitting ( ⬍ 0.1 eV) caused by interaction of non-coupled
Fig. 2. The correlation of energies of spin-orbitals of a (a) and b (b) electrons (Xa-DV method).
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d-electrons and non-coupled ligand electron in an ionized state. Therefore, for final states the Xa-DV method, firstly, overestimates the IE values of d-electrons, secondly, significantly overestimates the contributions of d-electrons into ligand levels. In Cr(acac) 3 spectra the first weak band (7.5 eV) correlates with two edelectrons, but among degenerated a-spin-orbitals of the Xa-DV method it’s absent e-orbital with predominated localization of metal. For d 4 (Mn) and d 5 (Fe) complexes the Xa-DV method showed similar full mixing of a-spin-orbitals of ed-electrons with ligand levels. For d 6-complex of Co(mal) 3 with occupied orbitals two orbitals close for energy to n −-orbitals, whereas according to PE data, they lie higher. The correlation of experimental ionization energies for M(acac) 3 row, obtained by us from the analysis of regularities in PE spectra for different d-metal tris-bdiketonates, is presented in Fig. 3. The differences of diagrams on Figs 2 and 3 are most essential for Cr, Mn and Fe complexes. Ab initio calculation results for complexes of transition metals are significantly different from the results of Xa-DV calculations. The correlation of one-electronic energy for a and b-spin orbitals is presented on Fig. 4. In the row of 3d-metal complexes the results for V(mal) 3 and Mn(mal) 3 are absent. For V complex the iteration procedure was failed and the
Fig. 3. The correlation diagram of vertical IE for M(acac) 3.
results for Mn complex, by our opinion, are incorrect because the fourth non-coupled d-electron occupies anti-binding p 4-orbital. For Sc complex it’s necessary to point out two significant differences of electronic structure from XaDV calculation. First, four n-orbitals have close energies, whereas energy intervals between p 2 and p 3levels achieves 5.9 eV (3.2 eV in Xa-DV and 3.5 eV in PES). Secondly, Sc 3d orbitals give maximal contributions not in n-orbitals, but in high orbitals. In the row of complexes M(mal) 3 (M = Ti, Cr, Fe) the contribution of 3d-AO into both b-spin-orbitals of n +-type insignificantly increases and leads to their stabilization. Similar regularity can be seen for two high j-orbitals [numbers 52 (a 1) and 53, 54 (e), high occupied — 66 (a 2)] which contain maximal contributions of 3d-AO (5–7%). In low-spin complexes Co(mal) 3 these MOs rise up because b-spin-orbitals da 1 and de are occupied and lie lower than p 1-MO [numbers 49 (a 1) and 47, 48 (e)]. The ab initio method showed less significant delocalization of both orbitals of d-type in comparison with the Xa-DV method (metal contribution is 96% and 90% against 76 and 63%). In Fig. 4 a-spin-orbitals, presented d-orbitals have maximal contributions of metal. For Ti(mal) 3 da 1level (69% 3d) is lying between p 3 and n −-MOs. For Cr(mal) 3 two d-type levels de e and da 1 with localization on metal (50–60%) are close by energy to p 1-MO. For high-spin Fe complexes the electronic configuration for five non-coupled electrons is: da11 de2t de2e : On Fig. 4 d-orbitals can be correlated with the group of close levels in the energy region of 18–19 eV (MO numbers 40–44). Two high MOs, lying in this region, contain significant Fe 3d contributions (74% and 58% correspondingly). These orbitals are de e and da 1. The de t orbital, according to calculations, is strongly delocalized and metal contributions into MOs 40 and 41 does not exceed 1/3. As one can see from presented contributions of metal dAO, Fe de t-orbital is shared between three neighboring e-MOs. According to semi-empirical calculations, d-electrons on a-spin-orbitals of M(mal) 3 row (M = Ti, Cr, Fe, Co) lie in the energy region of g-MO. In comparison with Xa-DV calculations the MO numbers are lower by 12 (Cr), 15 (Fe) and 17 (Co) (Figs 3, and 5).
V.I. Vovna et al. / Journal of Electron Spectroscopy and Related Phenomena 96 (1998) 141–148
Fig. 4. The correlation of energies of spin-orbitals of a (a) and b (b) electrons (ab initio method).
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Fig. 4. Continued
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V.I. Vovna et al. / Journal of Electron Spectroscopy and Related Phenomena 96 (1998) 141–148 Table 1 The IE values of MO complexes MO
p3− ,b 2 g p3+ ,b 1 u d,a g d,a g d,b 3g d,b 2g n −,b 2u n +,b 3u n −,b 1g n +,a g p2− ,a u p2+ ,b 3 g
Ni(ac ac) 2 Ni(Mal ) 2, Ni(Mal) 2, Ni(Mal) 2 , Cu(mal) 2 exp. Xa-DV INDO/2 ab initio (a), exp. 7.50 8.80 7.95 8.15 8.45 8.45 9.30 10.15 10.30 11.00 11.60 11.60
−9.19 −9.79 −9.74 −10.08 −10.22 −10.74 −10.15 −11.27 −11.28 −12.29 −12.76 −13.09
−11.50 −12.87 −7.53 −9.52 −7.70 −8.25 −13.26 −14.19 −13.62 −15.26 −16.86 −18.12
−9.07 −9.21 −16.37 −19.79 −17.27 −17.38 −11.56 −12.84 −11.61 −12.97 −14.79 −14.82
8.09 8.51 10.22 10.22 10.22 10.22 9.07 9.77
4. Nickel and cooper bis-b-diketonates The IE values for high occupied MOs of Ni(mal) 2 and Cu(mal) 2 are shown in Table 1. The experimental data on MO energies are presented for correspondent acetylacetonate complexes. As we can see from Table 1, the most real picture gives the calculations in Xa-DV approximation. On
Cu(Mal) 2 Cu(Mal) 2 Cu(Mal) 2 Cu(Mal) 2 CU(Mal 2 Cu(Mal) 2 (a), Xa- (a), INDO/ (a), ab (b), Xa- (b), INDO/ (b), ab DV 2 initio DV 2 initio −9.35 −9.61 −12.84 −13.85 −13.81 −12.98 −10.50 −11.27 −9.19 −11.14 −12.69 −12.36
−11.77 −12.91 −9.88 −10.91 −10.35 −9.93 −12.85 −14.84 −14.18 −14.99 −17.31 −17.49
−8.13 −8.52 −14.84 −15.67 −16.70 −18.92 −10.99 −12.35 −9.48 −12.26 −13.68 −13.40
−9.18 −9.46 −12.57 −13.57 −13.56 −12.82 −9.94 −10.73 −8.44 −10.67 −12.54 −12.18
MO
Ni(Mal) 2
Cu(mal) 2 a
Cu(mal) 2 b
p3− ,b 2 g
0.53 0.06 0.39 0.87 0.54 0.94 0.97 0.51 0.95 0.83 0.58 0.91 0.94 0.58 0.93 0.41 0.07 0.24 0.49 0.10 0.23
0.17 0.06 0.57 0.92 0.62 0.96 0.90 0.53 0.95 0.71 0.58 0.87 0.83 0.54 0.98 0.56 0.28 0.46 0.43 0.20 0.32
0.18 0.06 0.41 0.91 0.56 0.97 0.92 0.53 0.96 0.76 0.45 0.91 0.80 0.56 0.98 0.59 0.07 0.16 0.43 0.12 0.25
d,a g
d,b 2g
d,b 3g
n −,b 1g n +,a g
−8.21 −8.45 −13.82 −16.54 −15.72 −10.99 −12.35 −9.48 −12.26 −13.68 −13.40
the whole, the sequence of n and p-orbitals is similar for all methods. As for metal d-orbitals, the ab initio and INDO methods give quite different orbital sequences in comparison with the experiment. Specifically, INDO-calculations strongly understate IE of d-orbitals (in Koopmans theorem approach), that caused by deficiency of method parameterization for calculations of metal complex compounds. As in
Table 2 The contributions of d-AOs into molecular orbitals (Xa/ab initio/INDO), a.u.
d,a g
−11.53 −12.89 −8.88 −10.39 −9.41 −9.22 −12.76 −14.79 −12.89 −14.86 −17.28 −17.45
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tris-chelate complexes, ab initio methods shows that d-AO are lower than all n and p-orbitals. The contributions of metal d-AOs into ligand and dorbitals of complexes are significantly different according to calculation results in different methods (Table 2). INDO methods show a high degree of individuality of d-orbitals in complexes, but ab initio results show the significant degree of mixing of ligand and d-orbitals.
5. Conclusions The interpretation of PE spectra of metal acetylacetonates based on the regularities in spectra of presented and kindred compounds and based on theoretical modelling, showed that oxygen n-orbitals give the general contribution in metal-ligand covalent interaction. The Xa-DV method overestimates IE values in the transition state method and for ground state shows the interaction scheme of metal and ligand levels which is close to experimental. Ab initio calculations of tris and bis-malonates of delements showed qualitative differences from experimental data and Xa-DV methods both in levels sequence and in the nature of metal-ligand covalent interactions. Both calculation methods together with semiempirical INDO methods overstate delocalization of the metal d-orbital. It can be confirmed by
insignificant values of multiplet splitting of ligand n and p-levels in spectra of Ti, V, Cr and Cu complexes. Based on ab initio calculation results, the value of electron relaxation for complexes of the second half of the transition period can be estimated in 8–9 eV. Acknowledgements This work was financially supported by the Russian Fund of Fundamental Research (Grant no. 96-0334214a). References [1] V.I. Nefedov, V.I. Vovna, Electronic Structure of Chemical Compounds, Nauka Moscow, 1987, pp. 347. [2] V.I. Nefedov, V.I. Vovna, Electronic Structure of Organic and Elementoorganic Compounds, Nauka, Moscow, 1989, pp. 199. [3] V.I. Vovna, Electronic Structure of Organic Compounds, Nauka Moscow, 1991, pp. 247. [4] A.Yu. Ustinov, J. Phys. Chem. 69 (1995) 1268. in Russian. [5] V.I. Vovna, I.B. Lvov, S.N. Slabzhennikov, A.Yu. Ustinov, J. Electon Spectrosc. 88–91 (1998) 103. [6] A.Yu. Ustinov, V.I. Vovna, J. Phys. Chem. 67 (1993) 1929. in Russian. [7] E.C. Zingafelter, Coordination Chem. Rev. 1 (1966) 151. [8] D. Kipert, Inorganic Stereochemistry, Mir Moscow, 1985, p. 117. [9] N.I. Giritceva, N.V. Belova, G.V. Giritcev, J. Struct. Chem. 33 (1992) 63. in Russian. [10] V.I. Vovna, Coordination Chem. 21 (1995) 435. in Russian.