The isotropic constant (a) and the dipolar tensor (B) have
been calculated for the radical H2NO bonded to HF. The semiempirical
SCF (INDO) method has been used to describe the electronic
configuration of the complex radical H2NO ... HF. It is
suggested that a and B of the proton from HF are amenable to
experimental verification

A. Ažman

E. Zakrajšek

J. Koller

M. Žaucer

English

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CR 0 AT IC A CHEMIC A ACT A 44 (1972) 289 CCA-705 538:541.57:109.71 i I Note A Calculation of the ESR Parameters of the Hydrogen Bonded Complex Radical (H2NO ... HF) M. Zaucer, E; Zakrajsek, J. Koller, and A. A.zman Chemical Institute »Boris Kidric« and Department of Chemistry, University of Ljubljana, 61000 Ljubljana, Slovenia, Yugoslavia Received September 18, 1971 The isotropic constant (a) and the dipolar tensor (B) have been calculated for the radical H2NO bonded to HF. The semi-empirical SCF (INDO) method has been used to describe the ele-ctronic configuration of the complex radical H2NO ... HF. It is suggested that a and B of the proton from HF are amenable to experimental verification. INTRODUCTION The study reported in this paper attempts to predict the values of some parameters that could be observed in ESR. It is well known that solvents have a pronounced effect on the g-factor and a of radicals1• This study describes the calculation of B and a for the H2NO radical hydrogen-bonded with HF. The primary aim is to calculate a and B for HF in the complex H2NO ... HF and to show that these quantities could be experimentally observed. CALCULATION AND DISCUSSION The geometry of the H 2NO radical was taken from ref. 2 and the complex radical H 2NO ... HF was supposed to be linear (Fig. 1). The wave functions that have been used were obtained by the all-valence electrons SCF method H""' . N--o--- - H(sJ- - F Hi"..- .· Fig. 1. The geometry of the H2NO .. . HF . . in the INDO approximationa with the parametrization from ref. 4. The values of the isotropic contact constant (a) and dipolar tensor (B) have been evaluated for atoms H (2), N, H (5) and F at various distances R. i) Calculation · of Dipolar Tensor B Dipcilar tensor B has the following form: 3x2 - r 2 3yx 3zx r2 r2 r2 I cp.) ' J 3y2 -x2 3yz rz r2 3yz 3z2 -r2 r2 r2 where qii, (jlj are atomic orbitals. 290 M. ZAUCER ET AL. For the atoms N and F only the one-center local terms were retained: B = y y h.2 ( - 1-)t l: c D r3 p µ ~' 2 2 2 5 \2 cµx ~ Cµy - c µz ) 6 5 Cµy CµX 6 5 cµx cµz 6 5 c~,x c~,Y unuaired MO's 6 S cµy cµz 2 2 2 2 5 -<2 cµz- cµx- cµy) The inclusion of the non-local terms changes the values only slightly5 (about 0.2) and the approximation is thus justified. The expeCtation values ( ~) for N and F were calculated using Slater 2p orbitals. r 3 2p The calculation of B for atom H, e.g. H (5), is more complicated. The local term is zero and we calculated the contribution of non-local terms with the center of the operator B being on atom H and the wave functions <p; and <Jli on atoms 0 (cp; = <Jli), N (<pi = <Jli), F (<ri = <Jli) and on N (<p;) and 0 (<pi) . The integrals were calculated using Slater orbitals with the method from ref. 5. ii) Calculation of the Isotropic Contact Constants (a) H 2NO and the complex radical H 2NO ... HF have a half-occupied n: molecular orbital and thus the restricted SCF method predicts zero spin density (s orbitals) on all atoms. Finite values can be obtained with e. g. the unrestricted SCF method. The difference between Hartree-Fock operators for electrons with spin a and spin ~ is small and it is allowed to use the per-turbation theory6 in connection with the restricted SCF. The spin densities were calculated from: 1 !.>· · = - - l: l: Jt. ·kl ~ ~ P 0 (kt/ul) where Jtijkl = 2 l: w unpaired vacant MO's lJ 2 k 1 JJ t µ tµ • l: [(cvi CWi + Cwi c,,) Cwk cvl /(Ev - Ew )] v occupied MO's p?µ is the bond order and (kt/µl) is the exchange integral. The exchange integrals only between atomic orbitals centered on the one center were included. [<p28 (0)]2 for N and F and [<p18(0)] 2 for H were taken from ref. 7. Calculated values of B and a at various distances R are in Tables I, II, III and IV. The calculated values for the H 2NO radical are in good agreement with experiment. Experimentally8 a (N) and a (H) have both values 11.9. Recently the united molecule approach of the hydrogen bond complex based on the molecular orbital approach proved to . be useful in describing its stability and its con-figuration. The same approach with only one Slater determinant does not ESR PARA.METERS 291 TABLE I Dipolar Tensor B (Gauss) for N and F B~ B~x = 00 -10.0893 20.1786 1.82 - 10.0599 20.1198 0 0 1.62 -10.2404 20.4808 0 0 1.42 -10.2201 20.4402 0 0 1.32 -10.2162 20.4324 -26 . 57. 10-4 53 . 11 . 10- 4 TABLE II Dipolar Tensor B (Gauss) for H(2) R (A) B xx B xy 00 - 4.939 10.412 -5.547 -15.72 1.82 - 4.912 10.378 -5.541 -15.69 1.62 -5.083 10.584 -5.577 -15.90 1.42 -5.064 10.565 -5.574 -15.87 1.32 -5.062 10.565 -5.574 -15.87 TABLE III Di polar Tensor B (Gauss) for H(S) R (A) B xx B yy B zz 1.82 3.692 -1.968 -1.724 1.62 4.654 -2.526 -2.128 1.42 6.182 -3.454 -2.729 1.32 7.176 -4.093 -3.088 TABLE IV Isotropic Constant a (Gauss) R(A) a (N) I a [H (2)] I a [H (5)] a (F) 00 12.71 I -10.84 1.82 12.93 -10.97 -0.0623 0 1.62 12.92 I -10.90 -0.1201 1.42 12.91 -10.81 -0.2199 1.32 12.89 -10.76 -0.2912 292 M. 2AUCER ET AL. necessarily describe various spectroscopically observable properties. However, recent results obtained with the molecular orbital approach suggest that the approach using one determinant is adequate for the calculation of ESR para-meters9. This point and the good agreement between the calculated a and B for the H 2NO radical are the bases for the following conclusion: it would be possible not only to observe experimentally changes of a and B of the radical but also a and B of the hydrogen donor. The calculated a and B increase with the strenght of the complex resulting in quite large values if a strong hydrogen bond is formed.-REFERENCES 1. T. Kawamura, S. Ma tsunami, T. Yonezawa, and K. Fukui, Bun. Chem. Soc. Japan, 38 (1965) 1935. 2. 0. Kikuchi, Bun. Chem. Soc. Japan, 42 (1969) 47. 3. J. A. Pop 1 e, D. L. Beveridge, and P. A. Dobosh, J. Chem. Phys. 47 (1967) 2026. 4. J. M. S i ch e 1 and M. A. W hi t eh e a d, Theoret. Chim. Acta (Berlin) 11 (1968) 220. 5. E. Zakrajsek, M. Z au c er, and A. A z man, Z. Naturforsch. 26a (1971) 326. 6. T. Y o n e z aw a, T. Kaw a mu r a, and H. Kato, J. Chem. Phys. 50 (1969) 3482. 7. J. R. Morton, J. R. Rowlands, and D. H. Whiff en, National Physical Laboratory Report BPR 13 (1963). 8. J. Q. A d ams, S. K. Ni c ks i c, and J. R. Tho m a s, J. Chem. Phys. 45 (1966) 654; J. W. Gut ch and W. A. Waters, Proc. Chem. Soc. (London) (1964) 330. 9. J. Ko 11 er and A. A z man, Croat. Chem. Acta 42 (1970) 583. IZVLECEK Racun ESR parametrov kompleksa H 2NO-HF M. Zaucer, E. Zakrajsek, J. Koller in A. A.zman Izracunana sta izotropna konstanta in dipolarni tenzor kompleksa H2NO radikala vezanega na HF. Racun potrjuje domnevo da je mozno meriti obe kolicini protona donorja. KEMICNI INSTITUT »BORISA KIDRICA« IN ODDELEK ZA KEMIJO UNIVERZA V LJUBLJ ANI 61000 LJUBLJANA Primljeno 18. rujna 1971. 

A Calculation of the ESR Parameters of the Hydrogen Bonded Complex Radical (H2NO ... HF)

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