Organotin Compounds: New Chemistry and Applications

18 The Structural Chemistry of Some Organotin Oxygen-Bonded Compounds PHILIP G. HARRISON

Downloaded by CORNELL UNIV on August 19, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0157.ch018

Department of Chemistry, University of Nottingham, University Park, Nottingham, England

Crystallographic structural data for organotin compounds of composition R SnOE and R Sn(OE) (E = an organic residue) were examined. Preferred coordination numbers for these species are five and six, respectively. The stereochemistry at tin in six-coordinated dimethyltin compounds depends not only on the nature of the electronegative ligands but also on the structure of the crystal lattice. The magnitude of the tin119m Mössbauer quadrupole splitting is characteristic of the stereochemistry at tin in both tri- and diorganotin derivatives. In addition, the temperature dependence of the Mössbauer recoil free fraction of several compounds of known structure has been used to illustrate how this parameter can be used to distinguish different lattice types. 3

2

2

D

etermination of molecular and lattice structure are problems fundamental to chemists in general. Of the "direct" methods which may be used, x-ray crystallography is now at that stage where, for most materials, procurement of the single crystal is virtually the only obstacle to complete structural identification. Organotin chemists, however, now have a vast array of "indirect" physicochemical techniques, which, when used together, can provide just as potent (though only qualitative) a source of structural information. Tin 119m Môssbauer spectroscopy in particular is perhaps the most rewarding single technique available. Careful interpretation of the parameter data that it yields can furnish structural information for those materials which frustrate the crystallographer—amorphous powders which resist crystallization. The validity of any such interpretation relies on confirmation from model compounds for which both Môssbauer and x-ray structural data are available. This article describes some major aspects of the structural chemistry of d i - and triorganotin(IV) oxygen-bonded compounds and the applicability of the Môssbauer quadrupole splitting and recoil-free fraction in determining molecular and lattice structure. 258 Zuckerman; Organotin Compounds: New Chemistry and Applications Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

18.

HARRISON

Oxygen-Bonded Organotins

259

X-ray Crystallographic Results Crystallographic data for simple four-coordinated compounds of the types R S n O E and R2Sn(OE)2 are, surprisingly, lacking. To date, the structures of only two rather sophisticated examples, Et^SnOCôCUOSnEts (1) (by two-dimensional methods) and P h S n O C 5 P h [ M n ( C O ) ] (2), both containing slightly distorted tetrahedral configurations, have been determined. Tetrahedral geometries are also undoubtedly possessed by derivatives of more bulky - O E ligands, and it seems likely that the bis(triorganotin) oxides as well as Ph SnOG e P t i 3 and P h S n O S i P h 3 have angular structures similar to that of Ph PbOSiPh 3

3

4

3

3

3

3

3

(3).

A reduction in the steric bulk of R and Ε in R S n O E derivatives permits the oxygen atom to function as a bridging ligand which links adjacent planar R S n units and raises the coordination number of the tin to five. M e S n O H (4), Me SnOMe (5), and M e S n O N = C H i o (6) have structures of this type in the crystal, with the Ε groups pendant from the oxygen atoms of the parallel infinite - f Me SnO-)- chains. The resultant trigonal bipyramidal geometry of the tin in the repeating unit of M e S n O N = C 6 H i o and projections of the unit cell illus trating the infinite chain structure of the solid are shown in Figures 1 and 2 , re spectively.


3

3

3

3

3

6

3

3

Figure 1. Repeating unit of Me^nON=C H 6

l0

Zuckerman; Organotin Compounds: New Chemistry and Applications Advances in Chemistry; American Chemical Society: Washington, DC, 1976.


260

ORGANOTIN COMPOUNDS: NEW CHEMISTRY AND APPLICATIONS

plane illustrating the infinite chain structure

Figure 3. Molecular geometry in Ph^Sn(dibenzoylmethanate )




HARRISON

Figure 4.

Molecular geometry in

Ph^nONPhCO-Ph

Figure 5. Repeating unit in Me Sn0 CCF s

2

3


262

ORGANOTIN COMPOUNDS: NEW CHEMISTRY AND APPLICATIONS


The inclusion of a second potential donor site in the Ε residue allows the - O E ligand to function in three possible ways: (a) as a unidentate group, (b) as a chelating ligand, or (c) as a bridging group giving rise to chain structures similar to those of the MesSnOE (Ε = H , Me, N=C6Hio) compounds mentioned earlier. Only when the organic groups attached to tin are so bulky as to preclude chelation or bridging does coordination in a unidentate fashion persist, and the only example of this type as yet characterized is (CôHn^SnOAc (7) which has a distorted tetrahedral geometry. The second tin-oxygen bond distance, however, is only 2.95 Â, and might represent some degree of bonding interaction. Two geometries are possible when the ligand functions as a chelating group: the cis and meridional trigonal bipyramidal configurations I and II, respectively. R

c

Sn—X R

X

Sn—R R

X

Π

m

The meridional geometry has not been conclusively identified although it has been proposed for the trimethyltin derivatives of β-ketoenolates (8) and tricyclohexyltin glycylglycinate. The cis configuration, on the other hand, has been distinguished for the triphenyltin derivatives of the anions of 1,3-diphenylpro-

C(8)

C(7)

C(2)'

Figure 6. (a) Environment about tin in Me^nO^PhH 0. (b) Projection of the unit cell of Me$SnOzSPh*H 0 onto the be plane illustrating the hydro gen-bonded chain structure. Hydrogen bonds are broken lines. 2

2



18.


HARRISON

263

Figure 7. (a) Environment about tin in Me$Sn(picolinate\H 0. (b) Projection of the unit cell of the Me^Sn(picolinateyH20 onto the ac plane. Hydrogen bonds are dotted and broken lines. 2

pane-l,3-dione and N-phenyl-N-benzoylhydroxylamine (9,10). These derivatives have very similar geometries, though both are somewhat distorted from ideality (Figures 3 and 4). The trans-trigonal bipyramidal geometry, III, is exhibited by the three triorganotin carboxylates, Me SnOAc (II), Me SnC>2CCF (II), and (PhCH ) SnOAc (12), the carboxylate group bridging planar C S n moieties in each case. Figure 5 shows the repeating unit in Me Sn02CCF . Analogous chain structures have also been proposed for triorganotin arylsulfonates (13) and nitrates (14). 3

2

3

3

3

3

3

3

Trimethyltin nitrate (IS), phenylsulfonate (13), and picolinate (2-pyridylcarboxylate) (16) all form stable monohydrates. The trans trigonal bipyramidal stereochemistry is preserved in all three cases, but now a water molecule occupies the second axial coordination site (Figures 6a and 7a). The lattice structures of M e S n 0 S P h - H 0 and M e S n N 0 - H 0 are similar, and both consist of infinite chains of [ M e S n L - H 0 ] units linked together by hydrogen bonds (Figure 6b). That of Me Sn(picolinate) is more complex, with both carboxyl oxygen atoms and the pyridyl nitrogen atom taking part in hydrogen bonding with the coordinated water molecule, thus affording a more rigid lattice (Figure 7b). Even though the picolinate anion is potentially terdentate, the preferred 3

3

2

3

3

3

2

2

3


264

ORGANOTIN COMPOUNDS: NEW CHEMISTRY AND APPLICATIONS Me

X

x

X

^

Me

IV


l VI

coordination number at tin is still five, and no six-coordinated trimethyltin de rivatives have been characterized crystallographically. The introduction of a second electronegative substituent increases the ef fective nuclear charge of the tin and hence the tendency for tin to seek coordi nation numbers greater than four. Crystal data for simple diorganotin derivatives of monofunctional oxygen ligands are unavailable, and the same situation exists for diorganotin biscarboxylates. However, the structures of the dimethyltin derivatives of several other bifunctional ligands have been determined, and all contain hexacoordinated tin. Observed structures encompass nearly the whole range of CSnC valence bond angles (0) from almost ideal cis-(IV) (Θ = 90°) to the trans geometry (VI) (0 = 180°), via many intermediate cases (V) where 90° < 0 < 180°. Examples of both bridging and chelating bifunctional ligands are also known. The structure of dimethyltin bis(fluorosulfonate) (17) consists of infinite sheets in which fluorosulfonate groups bridge linear dimethyltin units although (Me2Sn)3(P0 )2-8H 0 has a similar structure in which phosphate groups bridge both linear and nonlinear (0 = 147°, 150°) dimethyltin units to give a lattice consisting of infinite ribbons. Water molecules also coordinate to the nonlinear dimethyltin species. β-Ketoenolate, N-acylhydroxylamino, nitrate, dithiocarbamate, and oxinate all function as chelating ligands towards the dimethyltin residue. Table I gives the available CSnC bond angle data for Me2Sn(chelate)2 derivatives as well as the angle subtended by the ligands at tin (the ligand "bite" angle) in each case. Table I.

18

2

4

Valence B o n d Angl.Ph 2

—

3

ax. 2 . 1 8 ( 1 ) Compound Me Sn(ONH.CO.Me) Me Sn(ONH.CO.Me) H 0 top molecule bottom molecule Me Sn(ONMe.CO. Me) Ph3SnONPh.CO.Ph

0-Sn-0(°)

2

2

2

2

2

2

(A)

2


18.

269


HARRISON

Implications of the Structural Data to Tin 119m Môssbauer Spectroscopy Môssbauer spectroscopy can give information on electronic distribution and stereochemistry about tin through isomer shift and quadrupole splitting data. The use of the technique in this respect has been amply reviewed (at least annually), and the point charge approximation has been used to assign different isomeric stereochemistries of compounds of the same coordination number (26, 27). Available structural data corroborate the predictions of such treatment for the five-coordinate R S n L and six-coordinate R S n L (L = electronegative l i gands such as Ο, N , halogen, etc.). In the former case, the point charge treatment predicts values of ca. 1.75 mm sec"" (R = Me) and ca. 1.65 m m s e c (R = Ph) for the cis geometry I but much larger values for the trans-(lll) [ca. 3.09 mm sec" (R = Me) and ca. 2.85 mm sec" (R = Ph)] and mendional-(U) [ca. 3.55 mm sec" (R = Me) and ca. 3.28 m m sec" (R = Ph)] geometries (28). Observed quadru pole splitting values for five-coordinate compounds of known structure are col lected in Table III and show that splitting values can be used to distinguish the cis from trans and meridional geometries but are equivocal for the two latter types. However, since (CôHn^SnOAc exhibits a splitting of 3.27 mm sec" caution is necessary, and severe distortion from regular tetrahedral geometry can increase the quadrupole splitting considerably. 3

2

2

4

1

-1


1

1

1

1

1

Using the point charge approximation Bancroft (29) has calculated the expected variation of the quadrupole splitting with the CSnC bond angle for d i methyltin compounds. Predicted values increase smoothly from ^ 2 mm sec" for cis-(IV) to £ 4 mm sec" for the trans-(\\). The available structural data again support the model, and observed quadrupole splittings for six-coordinate dimethyltin compounds are related in a fairly simple way to the value of the CSnC bond angle (Table I, Figure 12). The converse deduction—i.e., an estimate of the CSnC bond angle from the value of the quadrupole splitting for such species—therefore has reasonable foundation. Dimethyltin dinitrate is obviously exceptional, and the high observed quadrupole splitting for this compound is probably a result of the high electronegativity of the nitrate group. 1

1

Table III. T i n 119m Môssbauer D a t a for Five-Coordinate T r i o r g a n o t i n Derivatives of K n o w n G e o m e t r y (mm s e c ) 1

Compound Ph SnONPh.CO.Pha Ph Sn0 C HPh * Me SnOAcc Me Sn0 CCF c Me SnOHc Me SnON=C H rf 3

3

2

3

2

3

3

2

3

3

3

6

10

Isomer Shift 1.26 1.23 1.31-1.35 1.38 1.08-1.19 1.43

Quadrupole Splitting 1.94 2.25 3.43-3.68 4.22 2.71-2.95 2.96

Geometry distorted cis distorted cis trans trans trans trans

« R é f . 30. *>Ref. 28. ReL31.

Organotin Compounds: New Chemistry and Applications

Recommend Documents