New coordination modes of substituted benzohydroxamic acid with dialkyltin(IV): Structural diversity through ligand isomerization

Article abstract of DOI:10.1002/ejic.200600546

When R₂SnCl₂ (R = Me, nBu) reacted with substituted benzohydroxamic acid (substituent = 4-F; 2,4-Cl₂; 2,5-F₂) and potassium hydroxide in aqueous methanol solution, two types of condensation products could be obtained, depending on the molar ratio R₂SnCl ₂/RCONHOH/KOH. When a 1:1:2 molar ratio was used, 1:1 alkyltin hydroxamates {(n-C₄H₉)₂Sn[4-FC ₆H₄C(O)NO]}_n (1) and {(CH₃) ₂Sn[2,5-F₂C₆H₃C(O)NO]}_n (2) were formed. When a 1:2:2 ratio was used, another two unexpected 2:3 alkyltin hydroxamates, {(CH₃)₄Sn₂[(2,4-Cl ₂C₆H₃C(O)NHO)₂][2,4-Cl ₂C₆H₃C(O)NO]}_n (3) and {(n-C ₄H₉)₄Sn₂[(4-FC₆H ₄C(O)NHO)₂][4-FC₆H₄C(O)NO]} _n (4), were obtained. All these complexes were characterized by elemental analysis, IR, ¹H, ¹³C, ¹¹⁹Sn NMR spectra and X-ray diffraction analysis. The results indicated overall (Z)-iminol coordination mode in the hydroximic tautomeric form for 1 and 2, and keto-iminol mixed-coordination mode including both in (Z)-hydroxamic and -hydroximic tautomeric forms for 3 and 4. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200600546

FULL PAPER
DOI: 10.1002/ejic.200600546
New Coordination Modes of Substituted Benzohydroxamic Acid with
Dialkyltin(IV): Structural Diversity through Ligand Isomerization
Xian-mei Shang,[a,b] Ji-zhou Wu,*[b] and Qing-shan Li*[a,b]
Keywords: Coordination modes / Organotin / Hydroxamic / Hydroximic / Isomerization
When R2SnCl2 (R = Me, nBu) reacted with substituted benzo- C4H9)4Sn2[(4-FC6H4C(O)NHO)2][4-FC6H4C(O)NO]}n
(4),
hydroxamic acid (substituent = 4-F; 2,4-Cl2; 2,5-F2) and po-
tassium hydroxide in aqueous methanol solution, two types
of condensation products could be obtained, depending on
the molar ratio R2SnCl2/RCONHOH/KOH. When a 1:1:2 mo-
lar ratio was used, 1:1 alkyltin hydroxamates {(n-C4H9)2Sn[4-
FC6H4C(O)NO]}n (1) and {(CH3)2Sn[2,5-F2C6H3C(O)NO]}n
(2) were formed. When a 1:2:2 ratio was used, another two
unexpected 2:3 alkyltin hydroxamates, {(CH3)4Sn2[(2,4-
Cl2C6H3C(O)NHO)2][2,4-Cl2C6H3C(O)NO]}n (3) and {(n-
were obtained. All these complexes were characterized by
elemental analysis, IR, 1H, 13C, 119Sn NMR spectra and X-ray
diffraction analysis. The results indicated overall (Z)-iminol
coordination mode in the hydroximic tautomeric form for 1
and 2, and keto-iminol mixed-coordination mode including
both in (Z)-hydroxamic and -hydroximic tautomeric forms for
3 and 4.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Introduction
Hydroxamic acids (HAs) have attracted considerable at-
tention recently as supporting ligands in organometallic
chemistry and biology because of their tautomerization,[1]
and potential as therapeutics agents.[2] The biological im-
portance and different conformation of HAs may make
their organometallic derivatives exert a subtle influence on
their medicinal applications. In principle, each of the two
oxygen atoms of the hydroxamato ligand is capable of act-
ing as a coordination site, and the bonding modes are flexi-
ble. Moreover, tautomers of HAs assume different confor-
mations or configurations, as indicated in Scheme 1. The
HAs preferentially adopt the (Z) configurations when bind-
ing with metal ions to form a complex, either through the
hydroxamic acid form or the hydroximic acid form. In ad-
dition, it is well documented by both theoretical[3] and ex-
perimental studies that the hydroxamic form is the domi-
nant one in free acids[4] or metal hydroxamates.[5]
Despite these attractive features, studies on the coordina-
tion modes of the complexes possessing hydroxamic ligands
are still relatively scarce. According to the literature,[6] the
complexes of hydroxamic derivatives with metal formed
O,O five-membered chelate rings in most cases, and the li-
gands were usually in the hydroxamic form rather than hy-
droximic form. To the best of our knowledge, the complexes
in which ligands are only in the hydroximic form are rarely
observed, and indeed, a case with the ligands coordinated
Scheme 1. Isomers of hydroxamic acids.
to the metal center both in the hydroxamic and hydroximic
forms in the same complex has not yet been reported.
On the other hand, in contrast to the extensive chemistry
of transition-metal hydroxamato complexes,[7,8] little is
known about the hydroxamato organotin(IV) complexes,[9]
especially their coordination modes. The synthesis and
structure of 1:2 diorganotin(IV)/hydroxamato complexes
have been previously reported by our group,[10,11] which
provides a novel coordination mode for hydroxamato dior-
ganotin(IV) complexes. To obtain a deeper insight into the
influence of the ligand and to further explore structural di-
versity, in this work, an extension of the work on the 1:2
diorganotin(IV)/hydroxamato complexes was carried out,
and four unusual complexes containing the (Z) isomer hy-
droximic ligand were obtained, presenting novel 1:1 and 2:3
organotin(IV)/hydroxamato complexes with hydroximic li-
gands. Furthermore, the reaction of substituted benzohy-
droxamic acid with dialkyltin(IV) compounds, leading to
[a] School of Pharmaceutical Science, Shanxi Medical University,
Taiyuan 030001, P. R. China
[b] School of Pharmaceutical Science, Tongji Medical College,
Huazhong University of Science and Technology,
13 Hangkong Road, Wuhan 430030, P. R. China
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X.-M. Shang, J.-Z. Wu, Q.-S. Li
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the formation of these special organotin(IV) complexes firms that these ligands are coordinated to the tin atoms
with hydroximato ligands, is also discussed.
through the hydroximic form. The characteristic absorp-
tions at both 1661–1610 cm–1 in the spectra of 1 and 2 indi-
cate the presence of a C=N group.[12–15] For 1, the Bu–Sn–
Bu angle of 129° calculated from the equation of Holecˇek
and Lycˇka[16] is very close to the value of 130.1(4)° found
by X-ray analysis (Table 1). The Me–Sn–Me angle for 2 in
solution calculated from the equation of Lockhart and
Manders[17] is 128°, also close to the 131.45(19)° observed
in the solid state (Table 2). The 119Sn NMR spectroscopic
data show only one signal at δ Ϸ –124.8 ppm for 1 and
δ Ϸ –129.9 ppm for 2, indicating a typical five-coordinate
species,[16] which was further confirmed by single-crystal X-
ray analysis.
Results and Discussion
Reaction of Dialkyltin Dichloride with Substituted
Benzohydroxamic Acid
To obtain a deeper insight into the coordination of hy-
droxamic acid to the tin center, the reaction of dialkyltin
dichloride with substituted benzohydroxamic acid was
studied. It was found that the reaction of dialkyltin dichlo-
ride (Bu2SnCl2 and Me2SnCl2) with substituted benzohy-
droxamic acid and potassium hydroxide at a 1:1:2 ratio in
methanol/water gave 1:1 dialkyltin hydroxamates {(n-
C4H9)2Sn[4-FC6H4(O)C=NO]}n (1) and {(CH3)2Sn[2,5-2F-
C6H3C(O)NO]}n (2). When a 1:2:2 ratio was used, another
two unexpected 2:3 alkyltin hydroxamates, {(CH3)4Sn2[(2,4-
Cl2C6H3C(O)NHO)2][2,4-Cl2C6H3C(O)NO]}n (3) and {(n-
C4H9)4Sn2[(4-FC6H4C(O)NHO)2][4-FC6H4C(O)NO]}n (4),
were obtained. All of these complexes contain chelating hy-
droximic acid ligands [(Z) isomer], which is obviously dif-
ferent from well-known dialkyltin hydroxamates. Although
the reactions of metal ions with hydroxamic acid have been
studied extensively, most of them form 1:2 complexes con-
taining hydroxamic acid ligands [(Z) conformer], and very
little is reported on complexes containing hydroximic acid
ligands [(Z) isomer]. Presumably, complexes 1, 2, 3, and 4
could result from the tautomerism of the hydroxamic acid
ligand, as shown in Scheme 1. The present observation
might be attributed to three favorable factors: (1) the alka-
line reaction conditions might make the equilibrium (as
shown in Scheme 1) move from hydroxamic acid [(Z) con-
former] toward hydroximic acid [(Z) isomer] easily, and
thus, the hydrogen atom linked to the nitrogen atom could
migrate to the oxygen atom of the carbonyl group; then
the ratio of hydroximic acid in the keto-iminol tautomerism
equilibrium would be raised in this way, resulting in these
complexes with new coordinated modes; (2) the strong elec-
tron-withdrawing nature of F or Cl may enhance the 1,3-
migratory aptitude of the hydrogen atom in the hydroxamic
acid ligands; (3) it is also conceivable that a hydroxamic
acid in the (E) conformation could also give the observed
products, as any energy requirement for isomerism to the
(Z) form would be compensated for by the favorable ener-
getics associated with the formation of a stable five-mem-
bered chelate ring (i.e. chelate effect).
Scheme 2.
Reaction of dialkyltin dichloride (Me2SnCl2; Bu2SnCl2)
with substituted benzohydroxamic acid (substituent = 2,4-
Cl2; 4-F) in 1:2 stoichiometry yields 2:3 condensation prod-
ucts 3 and 4 (Scheme 3). In their free ligands, a strong band
near 3207 cm–1 is observed, assigned to be the ν(NH) ab-
sorption, which is shifted to higher frequency (near
3290 cm–1) in the two complexes. This shows that the NH
1
group is retained in the two complexes. In the H NMR
spectra of complex 3, two single resonances for the proton
in the –NH–O– group are observed at δ = 9.21 and
10.56 ppm, indicating that the proton of the –NH–O–
group exists in complex 3, and confirming the ligand coor-
dinates to the tin atom in the keto (hydroxamato) form.
Syntheses and Characterizations of 1 and 2
Scheme 3.
When dialkyltin dichloride (Bu2SnCl2; Me2SnCl2) reacts
with substituted benzohydroxamic acid (substituent = 4-F;
The 119Sn NMR spectroscopic data show two signals at
2,5-F2) and potassium hydroxide, 1:1 condensation prod- δ Ϸ –222.6 and –221.0 ppm for 3 (δ Ϸ –217.4, –216.6 ppm
ucts 1 and 2 can be obtained (Scheme 2). In the IR spectra for 4), indicating the presence of two different tin sites in
for the two complexes, a remarkable difference is the com- solution, which has been confirmed in the solid state for 3
plete disappearance of the stretching vibration bands of N– and 4. The δ(119Sn) values of compounds 3 and 4 belong in
H in contrast to their free ligands. This unambiguously con- the range of six-coordinate compounds.[16,18] In complexes
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New Coordination Modes of Substituted Benzohydroxamic Acid with Dialkyltin(IV)
FULL PAPER
3 and 4, the ligands are also coordinated to the tin atom in
the iminol (hydroximato) form, which was verified by X-ray
crystal diffraction technique and is discussed below.
Crystal Structures of Complexes 1 and 2
Selected bond lengths and angles of complexes 1 and 2
are listed in Tables 1 and 2, respectively. The molecular
structures of the two complexes are shown in Figures 1 and
2 for a single chain based on the one-dimensional oxygen-
bridged dialkyltin(IV) complex. The substituted benzohy-
droximic ligands are found to be chelated to the Sn atom
through the carbonyl O atom and the hydroxy O atom, and
Sn–O bond lengths are 2.065(6) and 2.191(5) Å for 1, and
2.064(2) and 2.155(2) Å for 2. The SnIV atoms are bonded
to two alkyl groups, and the C(8)–Sn1–C(12) linkage for 1
[C(8)–Sn1–C(9) for 2] is not linear, having an angle of
130.1(4)° for 1 [131.45(19)° for 2]. All these Sn–C and Sn–
O bond lengths and also all bond angles around the Sn
center are typical values compared with other diorgano-
tin(IV) complexes.[19,20]
However, the endocyclic C–N and C–O bond lengths are Figure 1. Diagram of a section of polymeric 1. Hydrogen atoms
are omitted for clarity.
special in contrast with those of well-known 1:2 diorganotin
hydroxamates. The bond length C(7)–N(1) in complex 1 is
1.237(9) Å, and is significantly shorter than the values in be concluded that the ligand is coordinated to the tin(IV)
the known 1:2 complexes [the average C–N distance of atom in the hydroximic acid form, and complex 1 is a hy-
1.32 Å is comparable to the corresponding distance in dior- droximate rather than a hydroxamate.
ganotin(IV) hydroxamates]. Moreover, no hydrogen atom is
For complex 2, the overall structure (Figure 2, Table 2)
at the N1 position, suggesting that the C–N bond in com- is similar to that of complex 1. The Sn4+ ion is bonded
plex 1 is a typical double bond.[21] Meanwhile, the bond with two CH3 groups and one substituted benzohydroximic
length C(7)–O(1) in complex 1 is 1.378(9) Å, and is signifi- ligand. The coordination number of the Sn atom is 5. The
cantly longer than the typical value of C=O [the average complex has no unusual distances or angles in the Me2Sn
C=O distance of 1.25 Å is comparable to the corresponding unit.
distance in diorganotin(IV) hydroxamates],[22] which shows
Like complex 1, the bond length C(7)–N(1) in complex
the C–O bond in the complex should be a typical single 2 is 1.286(5) Å, and is significantly shorter than those val-
bond. The bonding mode is in good agreement with hy- ues in the known 1:2 complexes.[11] Consistently, the average
droximic acid [(Z) isomer]. From the above analysis it could C(7)–O(2) distance [1.318(4) Å] of complex 2 is significantly
Table 1. Selected bond lengths [Å] and angles [°] for 1. Symmetry operators: #1: –x + 2, y + 1/2, –z + 1/2; #2: –x + 2, y – 1/2, –z + 1/2.
O(1)–Sn(1)
O(2)–Sn(1)
O(2)–Sn(1)#1
Sn(1)–O(2)#2
C(8)–Sn(1)–C(12)
O(1)–Sn(1)–C(8)
C(8)–Sn(1)–O(2)#2
O(1)–Sn(1)–O(2)
C(12)–Sn(1)–O(2)
2.065(6)
2.191(5)
2.134(4)
1.512(14)
130.1(4)
115.7(3)
96.3(3)
C(7)–N(1)
C(7)–O(1)
N(1)–O(2)
C(8)–Sn(1)
O(1)–Sn(1)–C(12)
O(1)–Sn(1)–O(2)#2
C(12)–Sn(1)–O(2)#2
C(8)–Sn(1)–O(2)
O(2)#2–Sn(1)–O(2)
1.237(9)
1.378(9)
1.428(8)
2.085(10)
114.2(4)
76.4(2)
95.3(3)
96.0(3)
151.45(9)
75.0(2)
96.3(3)
Table 2. Selected bond lengths [Å] and angles [°] for 2. Symmetry operators: #1: –x + 1, y – 1/2, z + 1/2; #2: –x + 1, y + 1/2, –z + 1/2.
Sn(1)–O(1)
Sn(1)–O(2)
Sn(1)–O(1)#1
O(1)–Sn(1)#2
C(8)–Sn(1)–C(9)
O(2)–Sn(1)–C(8)
O(2)–Sn(1)–C(9)
O(2)–Sn(1)–O(1)#1
C(8)–Sn(1)–O(1)#1
2.155(2)
2.064(2)
2.151(2)
C(7)–N(1)
C(7)–O(2)
N(1)–O(1)
Sn(1)–C(8)
C(9)–Sn(1)–O(1)#1
O(2)–Sn(1)–O(1)
C(8)–Sn(1)–O(1)
C(9)–Sn(1)–O(1)
O(1)#1–Sn(1)–O(1)
1.286(5)
1.318(4)
1.430(4)
2.097(4)
95.40(15)
74.03(9)
98.71(14)
94.63(15)
150.78(5)
2.151(2)
131.45(19)
111.39(16)
117.15(15)
76.97(9)
95.00(13)
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X.-M. Shang, J.-Z. Wu, Q.-S. Li
FULL PAPER
Figure 2. ORTEP drawing of a section of polymeric 2 with atomic numbering scheme.
longer than the corresponding distance of C=O, indicating Crystal Structures of Complexes 3 and 4
the C–O bond in complex 2 should be a typical single bond.
These data show that the ligand is coordinated to the
The molecular structures of 3 and 4 are shown in Fig-
tin(IV) atom in the hydroximic acid form and the coordina- ures 3 and 4, respectively. Selected bond lengths and angles
tion mode of complex 2 is similar to that of complex 1.
for complexes 3 and 4 are listed in Tables 3 and 4, respec-
Figure 3. Diagram of the dimeric repeating units in polymeric 3. Hydrogen atoms are omitted for clarity.
4146 Eur. J. Inorg. Chem. 2006, 4143–4150
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New Coordination Modes of Substituted Benzohydroxamic Acid with Dialkyltin(IV)
FULL PAPER
tively. The crystal structure of the two compounds consists
In complex 3, the bond lengths N(2)–C(10) and N(3)–
of one-dimensional linear chains in which Me4Sn2[(2,4- C(19) are 1.314(6) and 1.314(5) Å respectively. The dis-
Cl2C6H3C(O)NHO)2][2,4-Cl2C6H3C(O)NO] or (n-C4H9)4- tances are in the range of a typical single bond, and nearly
Sn2{[4-FC6H4C(O)NHO]2}[4-FC6H4C(O)NO] units are se- equivalent N(2)–C(10) and N(3)–C(19) bond lengths sug-
quentially bridged by the oxygen atom of the N–O bond in gest two similar hydroxamate ligands attached to the same
the ligands and contain a central planar Sn2O2 four-mem- Sn2 atom. Bond lengths C(10)–O(4) and C(19)–O(6) are
bered ring. The ligands in the two complexes have been 1.247(6) and 1.255(5) Å, respectively, which are in the ex-
combined with dialkyltin(IV), forming many five-mem- pected range for C=O bond interaction with obvious
bered heterometallacycles. However, the number and con- double and donor-bond character. The bonding mode of
figuration of the ligand bonded to a different Sn atom are the ligand is well in agreement with the (Z) conformer of
obviously not consistent with each other. Only one ligand hydroxamic acid, indicating that ligands are coordinated to
is coordinated to Sn1 through the hydroximic form, while Sn2 through the hydroxamic ligand [(Z) conformer] form.
the other two ligands are coordinated to Sn2 through the
hydroxamic form. In contrast to the behavior observed for
the 1:2 or 1:1 diorganotin hydroxamate complexes, both 3
and 4 are 2:3 condensation products with an unusual coor-
dinating mode.
Complex 4 is similar to complex 3 in molecular structure.
The bond lengths N(1)–C(7) and N(3)–C(31) are 1.323(5)
and 1.311(5) Å, respectively, indicating the distances are in
the range of a typical single bond in diorganotin(IV) hydro-
xamates. The slight difference in the bond lengths N(1)–
C(7) and N(3)–C(31) may be a result of the existence of
solvent molecules (benzene). Bond lengths C(7)–O(1) and
C(31)–O(6) are 1.241(5) and 1.255(5) Å, respectively, which
are in the expected range for the C=O bond. The bonding
mode of the ligand is in good agreement with the (Z) con-
former of hydroxamic acid, indicating that the ligands are
coordinated to Sn1 through the hydroxamic ligand [(Z)
conformer] form.
Characteristically, the distance between the central car-
bon atom and the coordinated oxygen atom, C(1)–O(2), is
1.305(5) Å in complex
3 {the C(16)–O(4) distance
[1.307(4) Å] in complex 4}, significantly longer than that of
the expected C=O double bond in typical diorganotin(IV)
hydroxamates, indicating a typical single bond. Concur-
rently, the relatively short N(1)–C(1) [1.280(5) Å] bond in
complex 3 and N(2)–C(16) [1.302(5) Å] bond in complex 4
exist in the same ligand and no hydrogen atom is at the
nitrogen atom, indicating a C=N double bond. The ligand-
bonding mode is consistent with hydroximic acid [(Z) iso-
mer], indicating the ligand is coordinated to Sn1 in complex
3 (Sn2 in complex 4) in the hydroximic ligand [(Z) isomer]
form.
Figure 4. Diagram of the dimeric repeating units in polymeric 4.
Hydrogen atoms are omitted for clarity.
Table 3. Selected bond lengths [Å] and angles [°] for 3. Symmetry operator: #1: –x, y, –z + 1/2.
Sn(1)–C(9)
Sn(1)–C(8)
Sn(1)–O(1)
Sn(1)–O(2)
Sn(1)–O(1)#1
Sn(1)–O(3)
Sn(2)–C(18)
Sn(2)–C(17)
Sn(2)–O(3)
C(9)–Sn(1)–C(8)
C(9)–Sn(1)–O(1)
C(8)–Sn(1)–O(1)
C(9)–Sn(1)–O(2)
O(1)–Sn(1)–O(2)
C(9)–Sn(1)–O(1)#1
C(8)–Sn(1)–O(1)#1
O(2)–Sn(1)–O(1)#1
C(8)–Sn(1)–O(3)
O(2)–Sn(1)–O(3)
2.097(5)
2.100(5)
2.167(3)
2.190(3)
2.274(3)
2.450(3)
2.095(5)
2.105(5)
2.109(3)
163.48(19)
95.54(16)
99.78(15)
98.94(17)
71.72(11)
88.95(17)
90.24(16)
142.31(11)
88.23(16)
75.54(11)
N(1)–C(1)
N(1)–O(1)
N(2)–C(10)
N(2)–O(3)
N(3)–C(19)
N(3)–O(5)
O(2)–C(1)
O(4)–C(10)
1.280(5)
1.422(4)
1.314(6)
1.381(5)
1.314(5)
1.381(4)
1.305(5)
1.247(6)
1.255(5)
108.87(18)
101.7(2)
101.99(17)
110.8(2)
89.25(17)
82.62(19)
139.41(11)
85.51(17)
68.37(12)
151.28(11)
O(6)–C(19)
C(18)–Sn(2)–O(3)
C(17)–Sn(2)–O(3)
C(18)–Sn(2)–O(5)
C(17)–Sn(2)–O(5)
C(18)–Sn(2)–O(6)
C(17)–Sn(2)–O(6)
O(3)–Sn(2)–O(6)
C(18)–Sn(2)–O(4)
O(3)–Sn(2)–O(4)
O(6)–Sn(2)–O(4)
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X.-M. Shang, J.-Z. Wu, Q.-S. Li
FULL PAPER
Table 4. Selected bond lengths [Å] and angles [°] for 4. Symmetry operator: #1: –x + 1, –y + 2, –z + 1.
Sn(1)–C(12)
Sn(1)–C(8)
Sn(1)–O(1)
Sn(1)–O(2)
Sn(1)–O(3)
Sn(1)–O(6)
Sn(2)–C(27)
Sn(2)–C(23)
2.109(5)
2.111(5)
2.492(3)
2.130(3)
2.137(3)
2.353(3)
2.110(4)
2.112(5)
2.167(3)
N(1)–C(7)
N(1)–O(2)
N(2)–C(16)
N(2)–O(5)
N(3)–C(31)
N(3)–O(3)
O(1)–C(7)
O(4)–C(16)
1.323(5)
1.379(4)
1.302(5)
1.434(4)
1.311(5)
1.363(4)
1.241(5)
1.307(4)
1.255(5)
161.25(18)
97.45(14)
98.38(15)
72.66(9)
141.74(9)
85.07(14)
86.91(15)
147.69(9)
Sn(2)–O(4)
C(31)–O(6)
C(12)–Sn(1)–C(8)
C(12)–Sn(1)–O(2)
C(8)–Sn(1)–O(2)
C(12)–Sn(1)–O(3)
O(2)–Sn(1)–O(3)
C(12)–Sn(1)–O(6)
C(8)–Sn(1)–O(6)
O(2)–Sn(1)–O(6)
138.4(2)
C(27)–Sn(2)–C(23)
C(27)–Sn(2)–O(5)
C(23)–Sn(2)–O(5)
O(5)–Sn(2)–O(4)
O(4)–Sn(2)–O(5)#1
C(27)–Sn(2)–O(2)
C(23)–Sn(2)–O(2)
O(5)–Sn(2)–O(2)
103.17(16)
107.81(17)
112.64(17)
68.75(10)
84.36(15)
90.49(17)
138.10(10)
NMR spectra were recorded with a Varian INOVA 600 spectrome-
Based on the above studies, it could be concluded that a
keto-iminol mixed-coordination mode including both hy-
droxamic and hydroximic tautomeric forms existed for
complexes 3 and 4.
1
ter (600.0 MHz for H, 150.8 MHz for 13C, 223.6 MHz for 119Sn)
at ambient temperature [δ values in ppm relative to Me4Si (1H, 13C)
or Me4Sn (119Sn)].
Synthesis of {(n-C4H9)2Sn[4-FC6H4(O)C=NO]}n (1): Dibutyltin di-
chloride (0.304 g, 1.0 mmol) in methanol (10 mL) was added drop-
wise to an aqueous methanol solution (water/methanol, 1:3, v/v,
30 mL) of 4-fluorobenzohydroxamic acid (0.150 g, 1.0 mmol) and
KOH (0.112 g, 2.0 mmol). The solution was stirred under N2 at
room temperature overnight. Water (30 mL) was added to form a
white precipitate, which was separated by filtration. The white solid
was then recrystallized from methanol/water. Colorless sheet-
shaped crystals of 1 were slowly formed at room temperature.
Yield: 0.12 g, 32%. M.p. 176–178 °C. C15H22FNO2Sn (385.69):
calcd. C 46.67, H 5.74, N 3.63; found C 46.48, H 5.85, N 3.56. IR
Conclusion
Under alkaline condition, dialkyltin dichloride
(Bu2SnCl2; Me2SnCl2) and substituted benzohydroxamic
acid (substituent = 4-F; 2,4-Cl2; 2,5-F2) in aqueous meth-
anol solution form two types of condensation products: 1:1
dialkyltin hydroxamate complexes (1 and 2) and unexpected
2:3 alkyltin hydroxamate complexes (3 and 4). All of them
have been verified by spectral methods and X-ray single-
crystal diffraction analysis. The present results demonstrate
that all of these alkyltin hydroxamates contain hydroximic
ligands [(Z) isomer], presenting two kinds of new coordina-
tion modes. Concurrently, dialkyltin hydroxamate com-
plexes exhibit structural diversity through the isomerism of
hydroxamic ligand, which develops the coordination chem-
istry of diorganotin hydroxamic complexes. So far, the re-
sult proves that diorganotin complexes containing substi-
tuted hydroxamate ligands could take on three different co-
ordination modes. Namely, ligands of the diorganotin com-
plexes are only in hydroxamic form [(Z) conformer], or only
in hydroximate form [(Z) isomer] or in both hydroxamate
form and hydroximate form [(Z) conformer and (Z) iso-
mer], forming diversiform hydroxamate complexes.
(KBr): ν = 1661 s, 1601 s (CO/NC), 913 s (N–O), 587 w (Sn–C),
˜
531 s (Sn–O) cm–1. 1H NMR (CDCl3): δ = 7.12–7.70 (m, 4 H,
2
C6H4), 1.64 [m, J(Sn,H) = 76 Hz, 4 H, 2 CH1 ], 1.52 (m, 4 H, 2
2
CH2 ), 1.37 (m, 4 H, 2 C3H2), 0.79 (t, J = 7.2 Hz, 6 H, 2 C4H3)
2
ppm. 13C NMR (CDCl3): δ = 164.2 (CO), 161.4, 131.4, 127.6, 115.4
and 114.9 (Carom), 27.3 [1J(119Sn,13C) = 537 Hz, CH2–Sn], 23.7
[2J(119Sn,13C) = 40 Hz, CH2CH2Sn], 26.1 [3J(119Sn,13C) = 138 Hz,
CH2CH2CH2Sn], 14.0 (R–Sn) ppm. 119Sn NMR (CDCl3): δ =
–124.8 ppm.
Synthesis of {(CH3)2Sn[2,5-F2C6H3(O)C=NO]}n (2): Dimethyltin
dichloride (0.220 g, 1.0 mmol) in methanol (10 mL) was added
dropwise to an aqueous methanol solution (water/methanol, 1:3,
v/v, 30 mL) of 2,5-difluorobenzohydroxamic acid (0.173 g, 1.0 mmol)
and KOH (0.112 g, 2.0 mmol). The solution was stirred under N2
at room temperature overnight. Water (30 mL) was added to form
a white precipitate, which was separated by filtration. The white
solid was then recrystallized from methanol/water. Colorless sheet-
shaped crystals of 2 were slowly formed at room temperature.
Yield: 0.10 g, 28.2%. M.p. 262 °C dec. C9H9F2NO2Sn (319.86):
calcd. C 33.79, H 2.84, N 4.38; found C 33.52, H 2.96, N 4.29. IR
Experimental Section
Materials and Methods: Dibutyltin(IV) dichloride, ethyl 4-fluoro-
benzoate, ethyl 2,5-difluorobenzoate, and 2,4-dichlorobenzoic acid
were purchased from Aldrich and used as received. The other rea-
gents were of analytical grade. 4-Fluorobenzohydroxamic acid, 2,5-
difluorobenzohydroxamic acid, and 2,4-dichlorobenzohydroxamic
acid were prepared according to reported methods.[23] Elemental
analyses were performed with a PE-2400-II elemental analyzer. IR
spectra in the range 4000–400 cm–1 were recorded with a Perkin–
(KBr): ν = 1665 s, 1616 s (CO/NC), 926 s (N–O), 586 w (Sn–C),
˜
528 s (Sn–O) cm–1. 1H NMR (CDCl3): δ = 7.70–7.16 (m, 3 H,
C6H3), 0.89 [s, 2J(Sn,H) = 79 Hz, 6 H, 2 CH3, R–Sn] ppm. 13C
NMR (CDCl3): δ = 165.0 (CO), 163.4, 162.6, 132.3, 127.4 and
115.7 (Carom), 6.6 [1J(119Sn,13C) = 584 Hz, CH3, R–Sn] ppm. 119Sn
NMR (CDCl3): δ = –129.9 ppm.
Synthesis of {(CH3)4Sn2[(2,4-Cl2C6H3C(O)NHO)2][2,4-Cl2C6H3-
(O)C=NO]}n (3): Dimethyltin dichloride (0.220 g, 1.0 mmol) was
Elmer FTIR spectrophotometer as KBr discs. H, 13C, and 119Sn
1
4148
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 4143–4150

New Coordination Modes of Substituted Benzohydroxamic Acid with Dialkyltin(IV)
FULL PAPER
Table 5. Crystal and data collection parameters of complexes 1–4.
1
2
3
4
Empirical formula
Formula mass
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C15H22FNO2Sn
385.69
monoclinic
P2(1)/c
10.3740(17)
7.8608(13)
22.078(4)
90
102.119(3)
90
1760.3(5)
4
1.457
1.462
776
C9H9F2NO2Sn
319.86
C50H54Cl12N6O12Sn4 C86H112F6N6O12Sn4
1829.83
monoclinic
C2/c
2010.58
triclinic
P1
orthorhombic
P2(1)2(1)2(1)
6.7490(8)
7.7636(9)
20.754(2)
90
90
90
1079.0(2)
4
1.969
¯
22.5882(18)
19.8408(16)
16.2922(13)
90
115.1810(10)
90
13.6579(12)
14.1315(13)
14.3894(13)
110.0320(10)
94.206(2)
114.0800(10)
2307.5(4)
1
β [°]
γ [°]
Volume [Å3]
6607.8(9)
4
Z
Dcalcd. [Mg/m3]
Absorption coefficient [mm–1]
F(000)
1.833
2.039
1.447
1.140
2.375
616
3552
1020
Crystal size [mm]
Total no. of reflections measured 16283
0.20×0.10×0.06
0.12×0.06×0.01
12746
0.20×0.20×0.20
34228
0.20×0.10×0.10
26012
No. of unique reflections
R(int)
Max./min. transmission
3113
0.1624
0.9174/0.7587
2580
0.0755
0.9766/0.7637
2580/0/138
1.029
6506
0.0832
0.6859/0.6859
6506/0/383
0.956
9990
0.0853
0.8945/0.8040
9990/2/518
0.945
No. of data/restraints/parameters 3113/2/184
Goodness-of-fit on F2
0.953
Final R indices [I Ͼ 2σ(I)]
R1 = 0.0664
wR2 = 0.1248
R1 = 0.1196
wR2 = 0.1390
0.860/–0.686
R1 = 0.0295
wR2 = 0.0557
R1 = 0.0313
wR2 = 0.0561
0.637/–0.670
R1 = 0.0436
wR2 = 0.0985
R1 = 0.0572
wR2 = 0.1023
0.942/–0.582
R1 = 0.0461
wR2 = 0.0976
R1 = 0.0737
wR2 = 0.1133
1.599/–0.606
R indices (all data)
Largest diff. peak/hole [e/Å3]
added dropwise to an aqueous methanol solution (water/methanol,
1:4, v/v, 30 mL) of 2,4-dichlorobenzohydroxamic acid (0.412 g,
2.0 mmol) and KOH (0.112 g, 2.0 mmol). The solution was stirred
under N2 at room temperature overnight. Water (30 mL) was added
to form a white precipitate, which was separated by filtration. The
white solid was then recrystallized from methanol/benzene. Color-
less block-shaped crystals of 3 were slowly formed at room tem-
7.2 Hz, 12 H, 4 C4H3) ppm. 13C NMR (CDCl3): δ = 165.5, 164.1
(CO), 163.9, 161.9, 133.9, 130.7, 128.8, 126.1, 120.4, 115.7 and
114.9 (Carom), 28.5 [1J(119Sn,13C) = 701 Hz, CH1 , R–Sn] and 27.4
2
[1J(119Sn,13C) = 830 Hz, CH1 , R–Sn], 26.6, 23.2, 13.9–13.7 (R–Sn)
2
ppm. 119Sn NMR (CDCl3): δ = –217.4, –216.6 ppm.
X-ray Data Collection, Structure Determination, and Refinement:
Suitable single crystals of the four complexes were mounted in glass
capillaries for X-ray structural analysis. Diffraction data were col-
lected with a Bruker SMART CCD diffractometer with Mo-Kα (λ
= 0.71073 Å) radiation at room temperature. During the intensity
data collection, no significant decay was observed. The intensities
were collected for Lorentz-polarization effects and empirical ab-
sorption with the SADABS program. The structures were solved by
direct methods using the SHELXL-97 program. All non-hydrogen
atoms were found from difference Fourier syntheses. The H atoms
were included in calculated positions with isotropic thermal param-
eters related to those of the supporting carbon atoms but were not
included in the refinement. All calculations were performed using
the Bruker Smart program.[24] A summary of the crystallographic
data and selected experimental information are given in Table 5.
CCDC-610570, -610571, -610572, and -610573 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
perature.
Yield:
0.12 g,
26.3%.
M.p.
188 °C
(dec).
C50H54Cl12N6O12Sn4 (1829.83): calcd. C 32.79, H 2.97, N 4.59;
found C 32.62, H 3.01, N 4.55. IR (KBr): ν = 3290 s (N–H), 1591
˜
s, 1569 s (CO/NC), 918 s (N–O), 575 s, 477 m (Sn–C), 541 s (Sn–
O) cm–1. 1H NMR (CDCl3): δ = 10.56 (s, H, N–H), 9.21 (s, H, N–
H), 7.81–7.27 (m, 6 H, 2 C6H3), 1.25 [s, 2J(Sn,1H) = 91 Hz, 2 CH3,
2
R–Sn], 0.94 [d, J(Sn,H) = 77 Hz, 4 CH3, R–Sn] ppm. 13C NMR
(CDCl3): δ = 164.2, 162.7 (CO), 158.4, 157.2, 131.1, 113.3, 111.1
and 103.3 (Carom), 5.3 [1J(119Sn,13C) = 717 Hz, CH3, R–Sn] and 6.9
[1J(119Sn,13C) = 845 Hz, CH3, R–Sn] ppm. 119Sn NMR (CDCl3): δ
= –222.6, –221.0 ppm.
Synthesis of {(C4H9)4Sn2[(4-FC6H4C(O)NHO)2][4-FC6H4(O)-
C=NO]}n (4): Dibutyltin dichloride (0.304 g, 1.0 mmol) in meth-
anol (10 mL) was added dropwise to an aqueous methanol solution
(30 mL) of 4-fluorobenzohydroxamic acid (0.310 g, 2.0 mmol) and
KOH (0.112 g, 2.0 mmol). The solution was stirred under N2 at
room temperature overnight. Water (30 mL) was added to form a
white precipitate, which was separated by filtration. The white solid
was then recrystallized from methanol/benzene. Colorless block-
shaped crystals of 4 were slowly formed at room temperature.
Yield: 0.26 g, 56%. M.p. 160–161 °C. C86H112F6N6O12Sn4
(2010.58): calcd. C 51.33, H 5.57, N 4.18; found C 51.20, H 5.71,
Acknowledgments
Financial support from the Program for New Century Excellent
Talents at the University of China (No. NCET-04-0258), from the
Science and Technology Commission of Shanxi Province of China
N 4.03. IR (KBr): ν = 3287 s (N–H), 2956 (Bu), 1617 s, 1559 s
˜
(CO/NC), 904 s (N–O), 579 s, 471 m (Sn–C), 579 s (Sn–O) cm–1.
1H NMR (CDCl3): δ = 7.68–6.94 (m, 16 H, 4 C6H4), 1.67–1.62 (m, (No. 051105-2), and from the Education Commission of Shanxi
8 H, 4 CH2 CH1 ), 1.35–1.34 (m, 8 H, 4 C3H2), 0.92–0.84 (t, J =
Province of China (No. 200413) is gratefully acknowledged.
2
2
Eur. J. Inorg. Chem. 2006, 4143–4150
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4149

X.-M. Shang, J.-Z. Wu, Q.-S. Li
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