Carbonate and Semicarbazide Tin(IV) Derivatives of Aminoguanidine Bicarbonate

Carbonate and Semicarbazide Tin(IV) Derivatives of Aminoguanidine Bicarbonate

Flaviana T. Vieira1 , Jose Roberto da S. Maia1*, Jose D. Ardisson 2 and Geraldo M. de Lima3

1 Departamento de Quimica, CCET/ UFV, Αν. P. H. Rolfs s/n, Vigosa - MG., 36570-000, Brasil. 2 Laboratörio de Fisica Aplicada, CDTN/CNEN, Belo Horizonte - MG., 31270-901, Brasil.

3 Departamento de Quimica, IC Ex / UFMG, Belo Horizonte - MG., 31270-901, Brasil.

A B S T R A C T

Equimolar reac t ions be tween o rgano t in ( IV) precursors of SnCl x R 4 . x (R = Bu, Ph, χ = 1, 4) and

aminoguan id ine b i ca rbona t e in methanol has a f fo rded 2:1 and 1:1 ( M : L ) ca rbona t e c o m p l e x e s as well as 1:2

semicarbaz ide der iva t ive . T h e p roduc t s were charac ter i sed by spec t roscop ic m e t h o d s such as mul t inuclear

N M R ( ' Η , i 3 C and l l 9 S n ) , Müssbaue r and infrared spec t roscopy as well as mic roana lys i s and mel t ing point.

T h e butyl and phenyl der iva t ives have a 4- and 5 -coord ina ted metal cent re respec t ive ly with br idging-

bidentate and br idg ing- t r iden ta te ca rbona te . For the te t rahal ide metal p recursor , a 6 -coord ina ted t in(IV)

der ivat ive has been ach ieved with a b identa te semica rbaz ide t owards the metal centre .

I N T R O D U C T I O N

Aminoguan id ine has been k n o w n for more than one hundred years and it was first p repared in 1892 f rom

a reduct ion react ion o f n i t roguanid ine . Recent d i scover ies conce rn ing pha rmaco log ica l proper t ies of

aminoguan id ine / I / have been at t ract ing the interest of b iochemis t s . T h i s c o m p o u n d has a l ready been

acknowledged as potent ia l med ic ine for lung hyper tens ion t rea tment as well as in d iabet ic pat ients /2, 3/.

Within the b iomedica l f ield, howeve r , the current interest is concen t ra ted upon research onorganot in

c o m p o u n d s and their appl ica t ions , par t icular ly against ca rc inogen ic tumours . In genera l , t r iorganot in

c o m p o u n d s d isp lay a h igher b iological act ivi ty than their di- and m o n o - ana logues . For instance, t r iphenylt in

der ivat ives are h ighly act ive , showing very low ID5Ü va lues against M C F - 7 and W i D r type cel ls /4, 5/. On the

other hand, the coord ina t ion chemis t ry involving aminoguan id ine b ica rbona te has not been invest igated so

far. A m i n o g u a n i d i n i u m ( + ) s eems to be unl ikely to bind meta ls as the l i terature p rov ides with the first

example of a h y d r o b r o m i d e c o p p e r ( I I ) der ivat ive of aminoguan id ine hydroch lor ide . Th i s c o m p o u n d was

prepared in the p resence of an excess of hydrobromic acid 161. In such condi t ions , the aminoguan id in ium(+)

* Cor re spond ing au thor : irsmaiara,u1v.hr .(J. R. D. S. Maia )

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Vol. 31, Nos. 1-2, 2008 Carbonate and Semicarbazide Tin(IV)Derivatives ofAminoguanidine Bicarbonate

is converted into aminoguanidinium(2+) by proton abstraction from the solution. The pronounced positive

charge density over this cation excludes itself as an electron-donor molecule. This is evident by structural

molecular determination, where the aminoguanidinium(2+) is acting as counter ion within the lattice 161. In

this context, aminoguanidinium(+) can in principle achieve a metal-ligand bond formation. The coordination

site can be envisaged through the NH2 moiety, which does not participate effectively on the charge

dereal izat ion as shown in Scheme 1.

N H - , MH-

Hj-N, ^ N H , Λ

NN,

Η,Ν, 'ΝΗΛ Ν Ης.

unmio£uanidinium(+)

η·λΝ.

ΝΗ3 ΝΗΙ

Λ ' Ν Η,

Ν Η-, Η;. Ν.

ΝΗ.

miiiiiojiiiumdiiiiuui(2+)

υ

. Α Ο ^ ΟΗ

υ

. . Λ Ο ΟΗ

bicarbonate

Scheme 1

Canonical configurations of aminoguanidinium and bicarbonate ions

Bicarbonate is also a potential ligand, as palladium(II) 111 and tungsten(O) /8/ derivatives have been

prepared under a C 0 2 atmosphere by the use of a pressurized vessel. Other researchers have isolated stable

monodentate bicarbonate derivatives of nickel(II) 191 and copper(II) /10/ by pH control of the reaction

medium. Transition metal carbonate complexes have also been prepared from sodium bicarbonate / l l /

among other carbonate salts /11-16/. The versatile coordination property of bicarbonate and carbonate

through mono-, bi- and tridentate modes contrasts to the aminoguanidinium(+). The latter might only act as a

monodentate ligand as shown in Scheme 2.

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Vieria et al. Main Group Metal Chemistry

Bicarbonate conirfination modes

Μ

Ο

O ^ O H

monudo i lu l c

Μ Ο

Ύ OH

iTiiljjmg bidciilalc

Μ. I Ο

OH

hidcni

CurbonaU· UM.miination mtuk'S

. Μ

Y 0

0° Ή ί

Μ — Ο \

\

O . .0

/ Y \ M — 0 Μ

h idjiiilj; hi- ; i iul liiikiii;ik· minies

\»lll>Op.Nill)ufll)ltlllt( ι CrWt'tlMllOII H.VXÄ·

Μ-η N H ? Hj J

• \ A Ν NH?

niontKicnliilc

Scheme 2

Coordinat ion modes of bicarbonate, carbonate and aminoguanid in ium(+)

Bridging bi- and tr identate mode of metal carbonate derivatives are also known. Those coordinat ion

modes have been revealed by structural molecular determination in cobal t ( l l l ) /12, 13/, copper(I I ) /14/ and

zinc(II) /15/ compounds . In this context, the variety of coordination possibili t ies and competi t ion for a metal

centre between bicarbonate , carbonate and aminoguanidinium(+) species has led us to investigate the

coordination chemistry of aminoguanidine bicarbonate towards strong Lewis acids. In the present work, we

report the resulting data regarding the derivative products of reactions involving t r iorganot in(IV) and SnCl4

precursors. The spectroscopic characterisation was performed by the use of techniques such as mult inuclear

N M R ( 'Η , 13C and " 9 S n N M R ) , infrared and Mxssbauer spectroscopy.



Vol. 31, Νos. 1-2, 2008 Carbonate and Semicarbazide Tin(IV)Derivatives ofAminoguanidine Bicarbonate

MATERIALS AND METHODS

'H and l3C NMR spectra were recorded using a Varian Mercury 300 MHz spectrometer with

tetramethylsilane (SiMe4) as internal standard (δ = 0). The ' l9Sn NMR was recorded using a Bruker DPX-400

spectrometer equipped with an 89 mm wide-bore magnet. "9Sn NMR shifts are reported relative to SnMe4as

internal standard. "9Sn Mössbauer spectroscopy data were collected at 30 Κ in constant acceleration

equipment moving a CaSn03 source at room temperature. All spectra were computer-fitted assuming

Lorentzian single lines. Infrared spectra were recorded on a Perkin Elmer Spectrum 1000 grating

spectrometer, using Csl pellets, scanning from 4000 to 200 cm"'. Microanalysis data were collected by means

of a Perkin Elmer 2400 CHN analyzer. Vacuum techniques, nitrogen atmosphere, and Schlenk glassware

were used throughout the experimental work.

1. Purification of the aminoguanidine bicarbonate

Aminoguanidine bicarbonate (10 g) was added to 120 ml of distilled water and heated for approximately 0

2 Vi hrs at 60 C. The suspended white solid was filtered off under reduced pressure in air to remove an

orange-coloured impurity. Then it was washed with diethyl ether, affording 9.5 g of yield.

2. Preparation of organotin(IV) derivatives of aminoguanidine bicarbonate

The tin(IV) derivatives were prepared according to the procedure described below involving the metal

precursors SnClBu3(l) SnClPh3(2, 3), and SnCl4(4).

2.1. [(SnBu3)2(CO,)J (1):

An equimolar reaction between SnClBu3 and aminoguanidine bicarbonate was carried out in methanol at

room temperature under stirring for 4 h. An insoluble white solid was removed by filtration. From the filtrate,

after evaporating the solvent to dryness, the colourless oil separated together with a colourless solid. Diethyl

ether (20 ml) was then added into the mixture, dissolving the oil and leaving behind an insoluble crystalline

material. By evaporating the diethyl ether, the oil has separated affording 4.70 g (50%) of yield. Required for

C25H5403Sn2: C, 46.91; H, 8.49; Found: C, 46.51; H, 8.77; 'H NMR: (CDC13, 300 MHz): δ 0.91-1.60 (t, m, t,

Bu); l3C NMR (CDC13, 75.4 MHz): δ 28.3, 27.3, 18.1, 14.1 (Bu); IR (Csl): 2296, 2294, 2876, 2854 (CH3and

CH2), 1521, 1375 (C03), 1463, 1415 (C=C), 831, 750 (C03 out-of-plane), 524 (Sn-C), 392 (Sn-O); "9Sn

NMR (CH3OH, 149.2 MHz): δ 39.2 (broad). The white solid materials have been identified by elemental

analysis as aminoguanidine bicarbonate, {required for C2H8N403: C, 17.65; H, 5.91; N, 41.16, Found: C,

17.83; H, 5.84, N, 41.90} and aminoguanidine hydrochloride {required for CH7N4C1: C, 10.87; H, 6.38; N,

50.68, Found: C, 10.68; H, 6,39, N, 50.72}.

2.2. [SnPh3(C03)]n (2):

The procedure was analogous to that described in section 2.1 except that no oil has been isolated in this




case. The main product, a white solid, was separated by filtration in air after evaporating the solvent 2/3 in 0

volume. From the filtrate a colourless crystalline solid was separated. Yield: 1.53 g (81%). Mp 89-91 C.

Required for C l 9 H l 5 0 3 S n : C, 55.66; H, 3.69; Found: C, 54.75; H, 3.80; 'H N M R (CDC13, 300 MHz): δ 7.26-

7.67 (m, Ph); 13C N M R (CDClj , 75.4 MHz): δ 136.5, 130.2, 129.5; 1R (Csl): 3063 (CH, Ar), 1651 (C0 3 ) ,

1478, 1429 (C=C), 728, 695 (Ph), 537 (Sn-O), 278 (Sn-C); " 9 S n N M R (CH 3 OH, 149.2 MHz): δ -178.9;

Mössbauer: δ = 1.27(5) mm/s, Δ = 2.69(5) mm/s, Γ = 1.00(5) mm/s; SnClPh3 : δ = 1.33(1) mm/s, Δ = 2.54(1)

mm/s /17/.

2.3. [(SnPh3)2(C03)].H20 (3):

The procedure was similar to that outlined in section 2.1 with the exception of being carried out at 60°C.

The main product was removed by filtration as a white solid after allowing it to evaporate 2/3 in solvent

volume at room temperature. Excess of aminoguanidine bicarbonate as well as aminoguanidine 0

hydrochloride have also been isolated as by-products herein. Yield: 1.28 g (68%) of product. Mp 90-92 C.

Required for C 3 7 H 3 2 0 4 Sn 2 : C, 57.12; H, 4.15; Found: C, 57.86; H, 4.11; 'H N M R (CDCI3 , 300 MHz): δ 7.26-

7.46 (m, Ph, 30H); l 3C N M R (CDC13, 75.4 MHz): δ 136.5, 130.2, 129.5, 128.6; IR (Csl): 3406 (H 2 0) , 3064

(CH, Ar), 1660, ( C 0 3 ) , 1480, 1428 (C=C), 722, 694 (Ph), 732 ( C 0 3 , out-of-plane) 455, 373, 307 (Sn-O), 272

(Sn-C); " 9 S n N M R (CH 3 OH, 149.2 MHz): δ -164.3; Mössbauer: δ = 1.18(5) mm/s, Δ = 2.86(5) mm/s, Γ =

0.95(5) mm/s.

2.4. [SnCl2(NH2NHC0NH2)2ia2.H20 (4):

The procedure was carried out as described in section 2.1. A yellowish material was separated affording

1.97 g (73%) of product. Evolution of gas has been observed after adding the metal precursor into the 0

methanol solution, containing already the aminoguanidine bicarbonate at room temperature. Mp 127d ( C).

Required for C 2 H, 2 N 6 0 3 Cl 4 Sn: C, 5.60; H, 2.82; N, 19.61; Found: C, 5.05; H, 2.51; N, 19.54. I 3C NMR:

(D 2 0 , 75.4 MHz): δ 158.2 ( C = 0 ) ; 1R: (Csl): 3445, 3336 (lattice H 2 0 ) , 3290, 3256, 3166 (N-H), 1666 (C=0) ,

450, 418 (Sn-N), 516 (Sn-O), 304 (Sn-Cl); " 9 S n (CH 3 OH, 149.2 MHz; R m t %): δ -657.3 (100), δ -623.2 (63),

δ -602.3 (60, broad); Mössbauer: δ = 0.30(5) mm/s, Δ = 0.19(5) mm/s, Γ = 1.00(5) mm/s; δ = 0.28(5) mm/s,

Δ = 0.82(5) mm/s, Γ = 1.20(5) mm/s; SnCl4: δ = 0.82 mm/s, Δ = 0.00 mm/s /18-20/.

RESULTS AND DISCUSSION

The aminoguanidine bicarbonate is an insoluble material in methanol and water, in contrast to the

aminoguanidine hydrochloride. The latter, a colourless material, was isolated and characterized by elemental

analysis and infrared spectroscopy as by-product in 1 , 2 , and 3, but not in 4. The elemental analysis of those

compounds supports a 2:1, 1:1 as well as a 1:2 metal-ligand molar ratio reaction. An equimolar reaction has

occurred only in 2. Excess of aminoguanidine bicarbonate was also isolated in the preparation of 1 and 3. All

compounds are soluble or slightly soluble in usual organic solvents.



Vol. 31, Νos. 1-2, 2008 Carbonate and Semicarbazide Tin(IV)Derivatives of Aminoguanidine Bicarbonate

Infrared spectroscopy

The infrared spectrum of aminoguanidine bicarbonate exhibited two strong bands at 1609 and 1353 cm"1

corresponding to the asymmetr ic and symmetric vibrational modes of bicarbonate. Those bands were

assigned by comparison to the spectrum Of ammonium bicarbonate. In the latter, the vibrational bands

associated to the bicarbonate group occur at 1601 and 1278 cm'1 , due to a weaker cation-anion interaction in

comparison to the aminoguanidine bicarbonate. The butyl derivative (1) exhibited strong infrared absorptions

in the range of 1300 to 1550 cm'1 , and the phenyl ones (2 and 3) strong to medium vibrational bands

in the range of 1600 to 1670 cm"1 upon coordinat ion. These higher f requencies can be correlated to bidentate,

bridging-bidentate or bridging-tridentate coordinat ion modes. The latter have been characterized by infrared

and X-ray crystal lography in copper(II ) -carbonate complexes /13, 14/. These vibrational band frequencies

are also in agreement with those correlated to bridging cobalt(III) and nickel(II)-carbonate complexes

/12, 16/.

At the low frequency, a vibrational band in the region of 740 cm"1 corroborates the coordination of

carbonate moiety in 1 and 3. In 2 this band could not be assigned due to over lapping in that region. This

infrared band has been regarded as the out-of-plane bending m o d e of carbonate in a

(diphosphine)plat inum(II) derivat ive /21 /. The out-of-plane bending mode of carbonate was not revealed

within the infrared spectrum of complex 4. For the latter, just one absorption at 1666 cm"1 has been displayed.

This band is most likely a vibrational stretching f rom coordinated semicarbazide through carbonyl moiety as

in lanthanide-semicarbazone derivat ives 1221. In addition, a non-coordinated semicarbazide-carbonyl moiety

has been reported for several f irst-row transition metal derivatives at 1687 cm'1 /23/. Vibrational bands in the

region of 3100 to 3350 cm"1 in 4 were assigned to coordinate as well as to non-coordinated amine fragment.

This is consistent with the infrared of semicarbazide derivatives 1211. The released gas in the preparation of 4

is possibly a mixture of carbon dioxide and ammonia. This is reasonable since no amoniguanidinium

hydrochloride has been isolated as by-product in that reaction. Nucleophil ic attack on coordinated ligands has

been observed before in plat inum(II) and palladium(II)-N-sulphinylarylamine complexes /24/. Nevertheless,

the mechanism of semicarbazide formation is still questionable. At the low f requency region, new vibrational

bands in the range of 300 to 550 cm"1 have been assigned to the v(Sn-O) stretching mode in those compounds

/25-28/. T w o bands at 307 and 373 cm"' in 3 are suggestive of coordinating water 1211. Infrared bands at 418

and 450 cm'1 , associated to v(Sn-N), have been revealed within the spectrum of 4, which are in agreement

with the literature /23, 28/. A sharp intense band at 304 cm"1, due to the v(Sn-CI) stretching in the latter,

reinforces either all four chloride ions or only two in trans position to the metal. In this context, several

structural arrangements can be envisaged, with the semicarbazide acting in several coordination modes

through nitrogen and oxygen atoms. Account ing for the fact that the stretching associated to the carbonyl

moiety in 4 is within the range of coordinated carbonyl species of Ni(II) /29/, all arrangements containing a

bidentate semicarbazide through the amine fragment have been disregarded. Proposed structural

arrangements for the t in(IV) derivatives are shown in Figure 1.




R Κ Ο \

. . κ u \» \

UK - Liu

it" ο " S

«· SI, ο Ν . nii—R·

k' \

,A 2. R" = ΙΊι

\H

4« 4b 4c

Fig. 1: Possible structural patterns of the tin(IV) derivatives of aminoguanidine bicarbonate in solid state

(3a in solution)

NMR spectroscopy

In solution, the 'H and l3C NMR of all phenyl and butyl derivatives have shown the expected chemical

shift associated to those moieties. Coordination of bicarbonate has been disregarded in 1, 2 and 3, accounting

for the fact that no signal in the region of δ 11.9 has been revealed within the 'H NMR III. The signal

associated to coordinated carbonate is expected within the range of 166.9 to 169.4 /21/. In this context no

signal related to carbonate moiety has been distinguished by l3C NMR technique in 1, 2, and 3. This is most

likely due to the relaxation time of the carbon atom towards its fundamental state. The spectrum of 4 has

exhibited a l3C NMR singlet at δ 158.2. This may suggest the presence of coordinated bicarbonate, since a

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Vol. 31, Νos. 1-2, 2008 Carbonate and Semicarbazide Tin(IV)Derivatives of Aminoguanidine Bicarbonate

doublet at δ 159.0 ( J C . H = 15 Hz) has been assigned to the bicarbonate moiety in [ E t 4 N ] [ W ( C 0 ) 5 ( C 0 2 0 H ) ]

/8/. However, the singlet in 4 is most likely related to the resonance signal f rom coordinated semicarbazide-

carbonyl moiety. A similar assignment has been reported at δ 157.5 for a zinc(II) derivative of N - ( l -

morpholinobenzyl) semicarbazide /28/.

The " 9 S n N M R of complex 1 has revealed a resonance peak, which is in the typical range of four-fold

coordination organotin species /30, 31/. The broad signal of 1 is most likely due to a subtle magnetic

variation at the metal centre account ing for the variety of stereochemical ar rangements along the C-C bond of

the butyl groups. In 2 and 3 a singlet was exhibited in the range of chemical shift of f ive-fold coordination

species /30, 32/. The former has exhibited a signal at δ -178.9 and the latter at δ -164.3 in methanol. The

difference of 14.6 in chemical shift between those peaks reinforces dissimilar magnet ic environments for the

metal centre in those compounds . The signal of 2 is very close to that of the starting material, suggesting

dissociation in solution. However , this has been disregarded, accounting for the fact that the " 9 S n N M R

signal of SnClPh 3 in the same solvent occurs at δ -176.0. Although both compounds have the SnCIPhj as a

common reactant, d i f ferent products have been achieved as corroborated by " 9 S n N M R spectroscopy. The

only di f ference between them is related to the temperature employed in the experimental procedure. The

molecular formula of both complexes is supported by the elemental analysis. Hence, temperature has affected

the reaction pathway for those complexes . In this context the di f ference in chemical shift between them is

most likely a result of carbonate coordinat ion mode towards the metal centre. The upfield resonance peak of

2 could be due to bidentate or bridging-bidentate mode of carbonate and the downfie ld signal of 3 to

bridging-tridentate one (see Figure 1, 3a). In the case of 4, several peaks have been displayed, all consistent

to six-fold coordinat ion /32, 33/. The number of signals revealed in the spectrum of 4 is presumably a result

of magnetic variation on the Sn(IV) nucleus in consequence of spatial conformat ions of the coordinated

semicarbazide or solvent coordinat ion. Proposed structural patterns are shown in Figure 1.

Mössbauer spectroscopy

Mössbauer spect roscopy is an important tool for structural elucidation in organotin chemistry. Two

Mössbauer parameters are crucial in this technique, the isomer shift (δ) and the quadrupole splitting (Δ). Both

give evidence concerning the s tereochemistry surrounding the metal centre and the coordination number,

respectively. The decreasing in isomer shift is related to the s-character reduction on the hybrid orbital at the

metal centre. The coordinat ion number increases as the hybrid metal s-character decreases, for instance, f rom

tetrahedral (25%, sp3) to octahedral arrangement (17%, cfsp3). The electronegativi ty of the ligands, however,

does influence the values of those parameters. Substantial quadrupole splitting is distinguished only in

compounds in which the l igands differ appreciably in electronegativity. It arises f rom the interaction of the

tin atom with an electric field gradient (EFG) , provided by the quadrupole moment of the excited state of a

Sn(IV) nucleus. The EFG depends on the dif ferences in electron densit ies within the various bonds of a

Sn(IV) compound, ref lect ing the dissimilarities in electronegativity among the ligands. The Mössljauer

parameters can be s trongly perturbed by the stereochemistry of organotin compounds . For instance, in a

tetrahedral or an octahedral arrangement , the quadrupole splitting only appears in mixed-l igand systems. For




those geometrical patterns, the EFG reflects the differences in electronegativity among the ligands only when

they are not identical. The quadrupole splitting therefore is an important parameter in structural

determination. In addition, distortions from the regular geometrical pattern can give values outside of the

typical range for those parameters.

The isomer shifts of 2 and 3 are consistent with five- and six-fold coordination respectively in solid state

/17/. In the case of the latter the isomer shift put forward a bridging water molecule coordinated to the metal

centre, as shown in Figure 1. The isomer shift of the former corroborates to the " 9 Sn NMR datum reinforcing

five-fold coordination in solution as in solid state. A polymeric or an oligomeric material is likely in 2 due to

the lack of counter ion correlated to the formula given by elemental analysis. The possible candidate for a

counter ion assuming the formation of a monomeric material would be the aminoguanidinium(+). However,

the latter has been separated as by-product of aminoguanidine hydrochloride. The quadrupole splitting of 2

and 3 indicates the phenyl groups in axial position as shown in Figure 1. Values of Δ for triorganotin

derivatives with a planar SnR3 are typically found in the range 3.0 to 4.1 mm s"1 /34/. The Mössbauer

spectroscopy has revealed a distinct geometrical pattern of 3 in solid state (see Figure 1, 3b). The unusual

value of isomer shift found in this compound is comparable to those in 6-coordinated derivatives of SnCl2Ph2

mi. Complex 4 has revealed an isomer shift and quadrupole splitting consistent to six-fold coordination as

for SnCl4 derivatives /18, 35, 36/. The Lorentzian single-line adjustment reinforces two different metal

centres in solid state, corroborating the signals revealed by the " 9 S n NMR. The Msssbauer spectra of

complex 2, 3 and 4 are shown in Figure 2.

Τ i 1 ' Γ

W C a>

• M

<u S:

j ?

« CY.

-2 0 2

V e l o c i t y ( m m / s )

Fig. 2 Mössbauer spectra of complexes: a) [SnPh3(C03)]„ (2), b) [(SnPh3)2(C03)] .H20 (3) and c)

[SnCl 2 (NH 2NHC0NH 2 ) 2 ]Cl 2 .H 20 (4)



Vol. 31, Νos. 1-2, 2008 Carbonate and Semicarbazide Tin(lV)Derivatives of Aminoguanidine Bicarbonate

CONCLUSION

A competition between aminoguanidinium(+) and bicarbonate for the metal centre has taken place

leading to carbonate and semicarbazide derivatives. The aminoguanidinium(+) moiety has the tendency to

bind the most acid precursor, with the opposite direction for the bicarbonate ([SnClBu3] ξ [SnCIPh3] <

SnCl4)]. Although the reaction-mechanism involving those compounds is still questionable, the temperature

seems to be crucial concerning the preparation of the triphenylorganotin(IV) derivatives.

ACKNOWLEDGEMENTS

The authors would like to thank the Brazilian Agency CNPq for granting a Scholarship to Flaviana T.

Vieira as well as FAPEMIG for financial support.

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