These structural investigations by the dipole moment m ethod follow earlier
reported papers. On the basis of the influence of bond length, valence
angles and electronegativity differences on the dipole moment, we expected to get some structural informations on these compounds

M. Kesler

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CCA-341 CR 0 AT IC A CHEMIC A ACT A 36 (1964) 165 539.19 :547 .254.9 :546.221 Note Structural Investigations of Alkyl Mercury Sulphide, Alkyl Mercury Oxide and Alkyl Mercury Selenide by Dipole Moment Method M. Kesler Laboratory of General and Inorganic Chemistry, Faculty of Science, University of Zagreb, Zagreb, Croatia, Yugoslavia Received February 22, 1964 These structural investigations by the dipole moment method follow ear-lier reported papers.1•2 On the basis of the influence of bond length, valence angles and electronegativity differences on the dipole moment, we expected to get some structural informations on these compounds. Dipole moment values wtth some experimental data are given in Table I. TABLE I Compound Dipole I x2 . 103 moment n I X2. 103 I v (CHaHg)20 3.34 D 0.00 2.2725 0.00 1.49756 0.00 1.1469 0.44 2.2741 0.35 1.49766 0.35 1.1457 0.50 2.2743 0.65 1.49774 0.50 1.1454 0.67 2.2749 0.80 1.49778 0.80 1.1446 0.97 2.2759 1.05 1.49779 L05 1.1438 (CHaHg)2S 1.78 D 0.00 2.2725 0.00 1.49725 0.00 1.1463 0.41 2.2729 0.43 1.49730 0.26 1.1461 0.52 2.2731 0.82 1.49735 0.41 1.1460 0.70 2.2733 1.04 1.49738 0.83 1.1457 0.83 2.2734 1.22 1.49740 1.04 1..1454 (CH3Hg)2Se 2.21 D 0.00 2.2725 0.00 1.49750 0.00 1.1459 0.30 2.2730 0.30 1.49757 0.26 1.1456 0.32 2.2731 0.43 1.49759 0.38 1.1455 I 0.46 2..2733 0.68 1.49764 0.08 1.1451 0.71 2.2737 0.86 1.49769 0.95 1.1447 x2 = molar concentration, £ = dielectriic constant, v = specific volume, n = refractive index. It has been observed that the dipole moment value in methyl mercury derivatives invest~gated ·shows an interest1ng change on substituting oxygen with ,sulphur and selenium. The oxygen derivative has the highest value of the dtpole moment, as eX!pected from the oxygen atom electronegativity. Likewise, M. KESLER the dipole moment value .of sulphur and selenium deriivatives should decrease. However, a d1stinct minimum for sulphur derivative has been found. This lower value may be attr1buted fo the following three tendencies: 1) decrease of the electronegat1vity from oxygen to sulphur, 2) increase of the bond length with respect to selenium, 3) change of :the valence angle. If ·it is supposed that electronegativi:ty has not decreased much from sulphur to selenium, with the increase of the bond lenigth at the same time, than the Jncrease of the dipole moment from ·sulphur to selenium can be understood. According to the Pauling electronegativiity scale:i for oxygen, sulphur, selenium and mercury, and taking into account the 'iinterntomic distances from oxiide4, su1phide4 and selenide4 (calculated from :the unit cell dimensions) the f,igures collected in the Table II. are obtained. TABLE II Electronegativity difference Bond length (A.) Hg-0 1.6 2.03 Hg-S 0.6 2.53 Hg-Se 0.5 2.62 Precise calculations of the dipole moment in these molecules could be performed only if the exact values for bond length and bond angles were availaible. It fa n ot justified to use simply the distances obrtained from mercuric OXiide, sulphide anid selenide. However, on the basis of •the ex.JDerimental values of the dipole moments it is possiJble to discuss the bond lffillgth Hg- X (X = = 0 , S, Se), the bond angles Hg - X - Hg and the effective differences of electronegativity in these compounds. It has been shown previou1sly that the bond angle Hg - S - Hg in methyl mercury sulphide amounts to cp = 105~. The possible bond angle change in .oxide and selen1de may explain the change of the dipole moment. We can ,su~pose that the folloWiing factors are of influence in these consi-derations: bond mome.IlJt CH3 - Hg, the bond moment Hg - X and the bond angle Hg - X - Hg. Assuming that the bond moment Hg - X is proportional to the bond length (r) and electronegativity difference (e), µ(Hg_ Xl = k · r · e, it follows y = k · r · e + y 0 , where y = bond moment CH3- Hg-X Yo = bond moment CH3Hg k = constant The bond moment CH3-Hg-X (y) depends on the total dipole moment and valence arrugle Hg-X-Hg. Assuming that the valence angles are the same for all the compounds (cp = 105°) and using r and e from Table II, we abtain three points in the diagram representing y = f (e, r) STRUCTURAL INVESTIGATIONS BY DIPOLE MOMENT METHOD 167 We cam. then fit the most probaible straight line D, shown in FJg. 1. The deviations frcim this line and the calculated values are relatively large. Bond J Moment CH,-Hg-X 3.0 2.5 2D 1.5 D c B 0.5 A '""----+----I---~1-------1--0.5 1.0 1.5 2.0 (er) 4 4' 4 .. 8. 8: 8 .. i.:l2 .. 6. 6'.6" • 2.5 •4oL •4fe· -/Jol 4ol .5· ( o!.•110.) t..x. •. 5• < .c..too•J tJfe·rJ• Q05(r+eJ tJ(erJ•-Q05(r+eJ . . 1 o!.•105• and e-r from Table I · 3.0 3.5 'fhe bond angle difference between oxide and selenide causes the change in the CH3-Hg-X bond. If the effective angle in the oxide and ,selenide molecule is .smaller or larger than 105° by cp = + 5°, the bond moment values are :modifoed and this can be followed in the diagram. Paints 4' and 4" are obtained with the bond moment values for the valence angle cp = 110°, and. points 8' and 8" for the valence angle cp = 100°. A .similar discussion is possible for the change of the product fl. (e · r) = ~ e · r + Ii r · e If, for example, the effective difference for electronegativity and interatomic distances deviate for 0.05 from the values given :in Table I. :points 2, 2' and 2" for 'Positive and 6, 6' and 6" f.or negative devia.tions of (e. r) aire obtained. It has been already mein.tioned that the standard deviations from D are relatively large. Much smaller deviations from the most probable straight lime D could be obtained by drawing this line between :points 6, 1' and 5" (lime A). In this case it is necessary to assume that the valence angle Hg-Se-Hg is smaller than 105°, being aipprox;imately 100°. A larger value for r Hg-Se and a smaller one for Hg-S than found in mercury selenide and sulphide is also ex;pected. An increase, or a decrease .of the effective dVforence of the electr()-negativirty may perhaps be ex;pected too. Based . on the ·line A for oxygen, a bond angle change from 105° to 110° is to be expected. 16_§_ M. KESLER Satisfactory results may be obtained taking .into account points 4" a.nd 3" (lines B and C) and therefore a detailed discussion of Hg-0 bond change cannot be performed. From the diagram it is obvious .that only points 6 and 1' give small deviations from the most probable line D. All the other combina-tions of po1nts for sulphide and selenide .give larger .deviations. In th:is whole discussion a bond angle Hg-S-Hg amounting to q; = 105° was considered. From the lines A, B and C the bond moment values CH3-Hg {y0 ) between 0.5 and 0.7 D were obtained. We get the largest deviation from the line by taking into account points 2, 5' and 1" (line E) with the correStPOil1d-ing bond moment value 1,05. The bond moment value for CR,-Hg is between 0.5 and 0.7 D, which is in agreement with our earlier investigatioos.2 The above discussion shows that the dipole moment values allow ·some ccms1derations of ·the structural characteristics of the compounds examined. Fol1owing the argument according to which the calculated points must show the least possible deviation from the line A, the conclusion is plausiible that the bond angle .in .selenide and ox.ide amounts to about 100° and 110°, respectively. For Hg-S and Hg-Se a bond length of about 2.47 A and 2.67 A, respectively, is also to be expected. EXPERIMENTAL The methyl mercury oxide and sulphide were prepared as described before.• The selenide was not known before and was prepared by introducing hydrogen seleni.de into an alcoholic solution of methyl mercury bromide.8 It is a light sensitive white substance, m. p. 1230 C. The d.ip0'le moments were determined ,by a method described by Halver -stadt and Kumler.5 The instrument used for the dielectric constant measure-ments has tbeen described earlier.6 All the experiments have been carried out at 25° C, in .benzene solutions, follow.ing the technique already given. 1•2 REFERENCES 1. M. Ke s 1 er, Croat. Chem. Acta 34 (1962) 123. 2. idem. ibidum., 35 (1963) 101. 3. L. Pa u 1 in g, Nature of the Chemical Bond, Cornell University Press, N. Y., 1961. 4. A. F. We 11 s, Structural Inorganic Chemistry, Oxford University Press, 1961. 5. I. F. Ha 1 v erst a d t and W. D. Kum 1 er, J. Am. Chem. Soc. 64 (1942) 2988. 6. M. Ke s 1 er and A. Pre g er n i k, Arhiv Kem. 27 (1955) 37. 7. D. Gr den i c i F. Z ado, Croat. Chem. Acta 29 (1957) 425. 8. M. Ke s 1 er, Thesis, Faculty of Science, University of Zagreb, 1958. IZVOD Strukturna istrazivanja alkilmerkuri sulfida, alkilmerkuri oksida alkilmerkuri selenida metodom dipolnoga momenta M. K esler Odredeni su dipolni momenti alkilmerkuri oksida, sulfida i selenida i njihove vrijednosti diskutirane na bazi duljine veze, va,lentnog kuta . i razlike elektronega-tivnosti izmedu zive i kisika, sumpora, te selena. Diskusijom je prikazano kako se vrijednosti dipoln.ih momenata ovih molekula mogu dovesti u vezu s veliCinom kuta i duljinom veze Hg - 0 , Hg - S i Hg - Se, odnosno kako se iz dipolnih momenata mogu izvesti strukturni parametri ispitivanih molekula. ZA VOD ZA OPCU I ANORGANSKU KEMIJU PRIRODOSLOVNO-MATEMATICKI FAKULTET ZAGREB Primljeno 22. veljace 1964. 

Structural Investigations of Alkyl Mercury Sulphide, Alkyl Mercury Oxide and Alkyl Mercury Selenide by Dipole Moment Method

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