Self-assembly of diorganotin(IV) moieties and 2-pyrazinecarboxylic acid: Syntheses, characterizations and crystal structures of monomeric, polymeric or trinuclear macrocyclic compounds

Article abstract of DOI:10.1039/b404477k

A series of diorganotin(IV) compounds of the type [R ₂Sn(pca)Cl]₃ (R = CH₃ 1;ⁿBu 2; C₆H₅ 3; C₆H₅CH₂ 4; Hpca = 2-pyrazinecaiboxylic acid), R₂Sn(pca)₂(mH ₂O)nH₂O (m = 1: R = CH₃, n = 2 5, R = ⁿⁿBu 7, C₆H₅ 8, C₆H ₅CH₂ 9) and (Et₃NH)⁺[R ₂Sn(pca)₂Cl]-mH₂O (m = 0: R = CH₃ 10, ⁿBu 11, C₆H₅CH₂ 13; m = 1: R = C₆H₅ 12) have been obtained by reactions of 2-pyrazinecarboxylic acid with diorganotin(IV) dichloride in the presence of sodium ethoxide or triethylamine. All compounds were characterized by elemental, IR and NMR spectra analyses. Except for compounds 3, 4, 7, 11 and 13, the others were also characterized by X-ray crystallography diffraction analyses, which revealed that compounds 1 and 2 were trinuclear macrocyclic structures with six-coordinate tin(IV) atoms, compounds 5 and 6 were monomeric structures with seven-coordinate tin(IV) atoms, compounds 8 and 9 were polymeric chain structures with seven-coordinate tin(IV) atoms and compounds 10 and 12 were stannate with seven-coordinate tin(IV) atoms. The Royal Society of Chemistry 2004.

Full text of DOI:10.1039/b404477k

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F U L L P A P E R
Self-assembly of diorganotin(IV) moieties and
2-pyrazinecarboxylic acid: syntheses, characterizations and
crystal structures of monomeric, polymeric or trinuclear
macrocyclic compounds
Chunlin Ma,*ab Yinfeng Han,a Rufen Zhanga and Daqi Wanga
a
Department of Chemistry, Liaocheng University, Liaocheng 252059, People’s Republic of China
Taishan University, Taian 271021, People’s Republic of China. E-mail: macl@lctu.edu.cn;
b
Fax: +86-538-6715521; Tel: +86-635-8238121
Received 24th March 2004, Accepted 30th April 2004
First published as an Advance Article on the web 13th May 2004
A series of diorganotin(IV) compounds of the type [R2Sn(pca)Cl]3 (R = CH3 1; nBu 2; C6H5 3; C6H5CH2 4; Hpca =
2-pyrazinecarboxylic acid), R2Sn(pca)2(mH2O)·nH2O (m = 1: R = CH3, n = 2 5, R = nBu, n = 0 6; m = 0, n = 0: R = nBu 7,
C6H5 8, C6H5CH2 9) and (Et3NH)+[R2Sn(pca)2Cl]−·mH2O (m = 0: R = CH3 10, nBu 11, C6H5CH2 13; m = 1: R = C6H5 12)
have been obtained by reactions of 2-pyrazinecarboxylic acid with diorganotin(IV) dichloride in the presence of sodium
ethoxide or triethylamine. All compounds were characterized by elemental, IR and NMR spectra analyses. Except for
compounds 3, 4, 7, 11 and 13, the others were also characterized by X-ray crystallography diffraction analyses, which
revealed that compounds 1 and 2 were trinuclear macrocyclic structures with six-coordinate tin(IV) atoms, compounds 5
and 6 were monomeric structures with seven-coordinate tin(IV) atoms, compounds 8 and 9 were polymeric chain structures
with seven-coordinate tin(IV) atoms and compounds 10 and 12 were stannate with seven-coordinate tin(IV) atoms.
via the heterocycles (mode B, C, E and F) rather than chelation is
Introduction
possible.9a,9c
Metal-directed self-assembly of organic ligands and metal ions or
The above considerations stirred our interest in some detailed
organometallic substances with various intriguing topologies have
syntheses, and structure patterns for diorganotin derivatives of the
been extensively studied.1,2 The increasing interest in this field is
ligand. To our surprise, we obtained a series of diorganotin(IV)
due to the potential relevance of such compounds in catalysis.3
compounds by reaction of diorganotin(IV) dichloride with 2-pyr-
An important objective is also the synthesis of new higher soluble
azinecarboxylic acid in the presence of sodium ethoxide or triethyl-
metal complexes useful for testing the distinctive reactivity patterns
amine. When using a 1:1:1 molar ratio of R2SnCl2 :Hpca:EtONa,
of the multimetallic systems. In recent years organotin(IV) deriva-
we obtained four trinuclear macrocyclic compounds 1, 2, 3 and 4
tives have received much attention, both in academic and applied
n
of the type [R2Sn(pca)Cl]3 (R = CH3 1; Bu 2; C6H5 3; C6H5CH2
research, because of the ability of the tin to afford stable bonds with
4). With a 1:2:2 ratio, another five monomeric or polymeric com-
carbons as well as with heteroatoms: a wide range of compounds
pounds 5–9 compounds are obtained and the general formula is
found in organic synthesis and catalysis (synthesis of polyesters,
R2Sn(pca)2(mH2O)·nH2O (m = 1: R = CH3, n = 2 5, nBu, n = 0 6; m =
polyurethanes, cross-linking of silicons, esterification, transesteri-
0, n = 0: R = nBu 7, C6H5 8, C6H5CH2 9). When using a 1:2:2 molar
fication, polymerization, etc.) have been reported.4 Especially,
ratio of R2SnCl2 :Hpca:Et3N, we obtained four stannate compounds
organotin compounds react with the ligands with nitrogen atoms,
10–13 of the type (Et3NH)+[R2Sn(pca)2Cl]−·mH2O (m = 0: R = CH3
yielding products characterized by Sn–N bonds.5 This fact has led
10, nBu 11, C6H5CH2 13; m = 1: R = C6H5 12). Determinations by
to considerable effort being devoted to characterizing model com-
elemental, IR and NMR spectra analyses of all the compounds are
pounds obtained from the ligands which have other donor atoms
given and except for compounds 3, 4, 7, 11 and 13, the others are
or groups. A biologically interesting donor is the carboxyl group,
also characterized by X-ray crystallography diffraction analyses.
which coexists with the nitrogen atom in several relevant species,
such as pyridine-2,6-dicarboxylic acid and pyridinecarboxylic acid.
Experimental
In our previous work, we have reported on the chemical, structural,
spectroscopic properties of a series of similar organotin(IV) com-
pounds, characterized by different coordinating properties.6,7 As an
extension of this research program and in connection with our cur-
rent interest in the coordination chemistry of organotin compounds
with heterocyclic ligands, we choose another fascinating ligand:
2-pyrazinecarboxylic acid (Hpca).
This ligand is interesting because of its potential multiple bi-
dentate coordinate possibilities. As exhibited in Scheme 1, at least
six bonding modes between this ligand and tin are conceivable al-
though nobody has investigated its actual coordination mode until
now. However, its analogical ligands, such as pyridinecarboxylic
acid and pyridinedicarboxylic acid systems which commonly
possess a coordination atom and additional donor atom, have pre-
viously been extensively studied.8–10 For example, organotin com-
plexes with chelation by both N and O atoms (mode A, B and C)
have been reported, the ligand is pyridinecarboxylic acid.10 The O,
O chelations (mode D and E) are commonly observed in organotin
carboxylates.11 In addition, bridging between different molecules
Materials and methods
Dimethyltin dichloride, di-n-butyltin dichloride, diphenyltin dichlo-
ride and 2-pyrazinecarboxylic acid are commercially available, and
they are used without further purification. Dibenzyltin dichlorides
were prepared by a standard method reported in the literature.12
The melting points were obtained with Kofler micro-melting point
apparatus and were uncorrected. Infrared-spectra were recorded
on a Nicolet-460 spectrophotometer using KBr discs and sodium
1
chloride optics. H, 13C and 119Sn NMR spectra were recorded on
a Varian Mercury Plus 400 spectrometer operating at 400, 100.6
and 149.2 MHz, respectively. The spectra were acquired at room
temperature (298 K) unless otherwise specified; 13C spectra are
broadband proton decoupled. The chemical shifts were reported
in ppm with respect to the references and were stated relative to
external tetramethylsilane (TMS) for 1H and 13C NMR, and to neat
tetramethyltin for 119Sn NMR. Elemental analyses (C, H, N) were
performed with a PE-2400II apparatus.
1 8 3 2
D a l t o n T r a n s . , 2 0 0 4 , 1 8 3 2 – 1 8 4 0
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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Scheme 1
Syntheses
2 mmol) and sodium ethoxide (0.136 g, 2 mmol). The solid is
then recrystallized from 95% ethanol and the white crystal com-
pound 5 is formed. Yield: 81%. Mp 156–158 °C. Anal. Found:
C, 30.76; H, 4.30; N, 11.92. Calc. for C12H20N4O8Sn: C, 30.86;
H, 4.32; N, 11.99%. IR (KBr, cm−1): (O–H), 3346; as(COO),
1635; s(COO), 1326; (CN), 1597; (Sn–C), 543; (Sn–O),
[(CH3)2Sn(pca)Cl]3 1. The reaction is carried out under a nitro-
gen atmosphere. The 2-pyrazinecarboxylic acid (0.248 g, 2 mmol)
and sodium ethoxide (0.136 g, 2 mmol) was added to the solution
of dry benzene (20 ml) in a Schlenk flask and stirred for 0.5 h.
After the dimethyltin dichloride (0.438 g, 2 mmol) was added to
the reactor, the reaction mixture was stirred for 12 h at 40 °C and
then filtered. The solvent is gradually removed by evaporation
under vacuum until a solid product is obtained. The solid is then
recrystallized from ethanol and the white crystal compound 1 is
formed. Yield: 78%. Mp 106–108 °C. Anal. Found: C, 27.27; H,
2.89; N, 9.10. Calc. for C21H27Cl3N6O6Sn3: C, 27.36; H, 2.95; N,
9.12%. IR (KBr, cm−1): as(COO), 1627; s(COO), 1451; (CN),
1591; (Sn–C), 583; (Sn–O), 476; (Sn–N), 457; (Sn–Cl), 270.
1H NMR (CDCl3, ppm):  0.84 (t, 18H, 2JSnH = 94.6 Hz), 8.46 (dd,
3H), 8.90 (d, 3H), 9.42 (d, 3H). 13C NMR (CDCl3, ppm):  10.2
(1J(119Sn–13C), 893 Hz), 143.6, 145.4, 147.1, 147.5, 173.5. 119Sn
NMR (CDCl3, ppm): −223.1.
1
480; (Sn–N), 444. H NMR (CDCl3–D2O, ppm):  0.82 (s, 6H),
3.01 (s, 2H), 8.56 (dd, 2H), 8.90 (d, 2H), 9.36 (d, 2H). 13C NMR
(CDCl3. ppm):  11.1, 143.2, 145.1, 146.9, 147.5, 170.1. 119Sn NMR
(CDCl3, ppm): −226.7.
(nBu)2Sn(pca)2(H2O) 6. Compound 6 is prepared in the same
way as that of compound 1, by adding di-n-butyltin dichloride
(0.303 g, 1 mmol) to 2-pyrazinecarboxylic acid (0.248 g, 2 mmol)
and sodium ethoxide (0.136 g, 2 mmol). The solid is then recrys-
tallized from 95% ethanol and the white crystal compound 6 is
formed. Yield: 80%. Mp 186–188 °C. Anal. Found: C, 43.32;
H, 5.11; N, 11.33. Calc. for C18H26N4O5Sn: C, 43.49; H, 5.27; N,
11.27%. IR (KBr, cm−1): (O–H), 3357; as(COO), 1640; s(COO),
1333; (CN), 1603; (Sn–C), 536; (Sn–O), 475, (Sn–N), 461.
1H NMR (CDCl3–D2O, ppm):  0.82 (t, 6H), 1.27–1.71 (m, 12H),
3.23 (s, 2H), 8.42 (dd, 2H), 8.97 (d, 2H), 9.31 (d, 2H). 13C NMR
(CDCl3. ppm):  13.4, 25.8, 26.5, 27.0, 143.3, 145.4, 147.8, 148.0,
173.7. 119Sn NMR (CDCl3, ppm): −201.5.
[(nBu)2Sn(pca)Cl]3 2. Compound 2 is prepared in the same
way as that of compound 1, by adding di-n-butyltin dichloride
(0.606 g, 2 mmol) to 2-pyrazinecarboxylic acid (0.248 g, 2 mmol)
and sodium ethoxide (0.136 g, 2 mmol). The solid is then recrystal-
lized from ethanol and the white crystal compound 2 is formed.
Yield: 85%. Mp 52–54 °C. Anal. Found: C, 39.81; H, 5.41; N,
7.08. Calc. for C39H63Cl3N6O6Sn3: C, 39.89; H, 5.41; N, 7.16%.
IR (KBr, cm−1): as(COO), 1621; s(COO), 1447; (CN), 1595;
(Sn–C), 558; (Sn–O), 475; (Sn–N), 458; (Sn–Cl), 263. 1H NMR
(CDCl3, ppm):  0.91(t, 18H), 1.28–1.70 (m, 36H), 8.61 (dd, 3H),
8.87 (d, 3H), 9.28 (d, 3H). 13C NMR (CDCl3, ppm):  13.4, 25.8,
26.5, 27.0, 143.1, 144.8, 147.0, 147.6,173.0. 119Sn NMR (CDCl3,
ppm): −341.5.
(nBu)2Sn(pca)2 7. Compound 7 is prepared in the same way as
that of compound 1, by adding di-n-butyltin dichloride (0.303 g,
1 mmol) to 2-pyrazinecarboxylic acid (0.248 g, 2 mmol) and so-
dium ethoxide (0.136 g, 2 mmol). The solid is then recrystallized
from ethanol and the white crystal compound 7 is formed. Yield:
87%. Mp 112–114 °C. Anal. Found: C, 45.08; H, 5.01; N, 11.59.
Calc. for C18H24N4O4Sn: C, 45.13; H, 5.05; N, 11.69%. IR (KBr,
cm−1): as(COO), 1651; s(COO), 1439; (CN), 1598; (Sn–C),
549; (Sn–O), 482; (Sn–N), 455. 1H NMR (CDCl3, ppm):  0.85
(t, 6H), 1.30–1.77 (m, 12H), 8.58 (dd, 2H), 8.92 (d, 2H), 9.41 (d,
2H). 13C NMR (CDCl3, ppm):  13.6, 26.3, 26.5, 27.1, 143.5, 145.2,
147.6, 147.9, 172.1. 119Sn NMR (CDCl3, ppm): −221.3.
[(Ph)2Sn(pca)Cl]3 3. Compound 3 is prepared in the same way
as that of compound 1, by adding diphenyltin dichloride (0.686 g,
2 mmol) to 2-pyrazinecarboxylic acid (0.248 g, 2 mmol) and so-
dium ethoxide (0.136 g, 2 mmol). The solid is then obtained from
ethanol. Yield: 84%. Mp 78–80 °C. Anal. Found: C, 47.23; H,
3.14; N, 6.49. Calc. for C51H39Cl3N6O6Sn3: C, 47.33; H, 3.04; N,
6.49%. IR (KBr, cm−1): as(COO), 1633; s(COO), 1444; (CN),
1597; (Sn–C), 558; (Sn–O), 481; (Sn–N), 457; (Sn–Cl), 267.
1H NMR (CDCl3, ppm):  7.35–7.78 (m, 30H), 8.58 (dd, 3H),
8.81 (d, 3H), 9.35 (d, 3H). 13C NMR (CDCl3, ppm):  129.3,
130.0, 136.9, 148.0, 143.0, 144.5, 147.2, 147.6, 172.5. 119Sn NMR
(CDCl3, ppm): −371.4.
(Ph)2Sn(pca)2 8. Compound 8 is prepared in the same way as
that of compound 1, by adding diphenyltin dichloride (0.343 g, 1
mmol) to 2-pyrazinecarboxylic acid (0.248 g, 2 mmol) and sodium
ethoxide (0.136 g, 2 mmol). The solid is then recrystallized from
ethanol and the white crystal compound 8 is formed. Yield: 84%.
Mp > 200 °C (dec.). Anal. Found: C, 50.81; H, 3.10; N, 10.72. Calc.
for C22H16N4O4Sn: C, 50.91; H, 3.11; N, 10.79%. IR (KBr, cm−1):
as(COO), 1649; s(COO), 1448; (CN), 1607; (Sn–C), 550;
(Sn–O), 471; (Sn–N), 451. 1H NMR (CDCl3, ppm):  7.34–7.68
(m, 10H), 8.68 (dd, 2H), 8.92 (d, 2H), 9.47 (d, 2H). 13C NMR
(CDCl3. ppm):  129.2, 130.3, 136.6, 148.1, 143.2, 144.6, 147.2,
147.5, 172.7. 119Sn NMR (CDCl3, ppm): −386.6.
[(PhCH2)2Sn(pca)Cl]3 4. Compound 4 is prepared in the same
way as that of compound 1, by adding dibenzyltin dichloride
(0.742 g, 2 mmol) to 2-pyrazinecarboxylic acid (0.248 g, 2 mmol)
and sodium ethoxide (0.136 g, 2 mmol). The solid is then obtained
from ethanol. Yield: 86%. Mp 112–116 °C. Anal. Found: C, 49.56;
H, 3.71; N, 6.01. Calc. for C57H51Cl3N6O6Sn3: C, 49.66; H, 3.73; N,
6.10%. IR (KBr, cm−1): as(COO), 1624; s(COO), 1453; (CN),
1601; (Sn–C), 528; (Sn–O), 478; (Sn–N), 463; (Sn–Cl), 265.
1H NMR (CDCl3, ppm):  3.16 (s, 12H), 7.31–7.58 (m, 30H), 8.64
(dd, 3H), 8.61 (d, 3H), 9.37 (d, 3H). 13C NMR (CDCl3. ppm):  38.2,
127.1, 129.3, 141.0, 143.3, 144.1, 146.9, 147.4, 172.5. 119Sn NMR
(CDCl3, ppm): −305.2.
(PhCH2)2Sn(pca)2 9. Compound 9 is prepared in the same way
as that of compound 1, by adding dibenzyltin dichloride (0.371 g,
1 mmol) to 2-pyrazinecarboxylic acid (0.248 g, 2 mmol) and so-
dium ethoxide (0.136 g, 2 mmol). The solid is then recrystallized
from ethanol and the white crystal compound 9 is formed. Yield:
80%. Mp 100–102 °C. Anal. Found: C, 52.62; H, 3.58; N, 10.21.
Calc. for C24H20N4O4Sn: C, 52.69; H, 3.68; N, 10.24%. IR (KBr,
cm−1): as(COO), 1647; s(COO), 1434; (CN), 1596; (Sn–C),
540; (Sn–O), 472; (Sn–N), 454. 1H NMR (CDCl3, ppm):  3.26 (s,
4H), 7.34–7.68 (m, 10H), 8.65 (dd, 2H), 8.76 (d, 2H), 9.37 (d, 2H).
13C NMR (CDCl3. ppm):  38.0, 127.4, 129.7, 141.3, 143.7, 144.1,
147.2, 147.6, 172.8. 119Sn NMR (CDCl3, ppm): −334.9.
(CH3)2Sn(pca)2(H2O)·2H2O 5. The compound 5 is prepared in
the same way as that of compound 1, by adding dimethyltin di-
chloride (0.219 g, 1 mmol) to 2-pyrazinecarboxylic acid (0.248 g,
D a l t o n T r a n s . , 2 0 0 4 , 1 8 3 2 – 1 8 4 0
1 8 3 3

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(Et3NH)+[(CH3)2Sn(pca)2Cl]− 10. Compound 10 is prepared in
the same way as that of compound 1, by adding dimethyltin di-
chloride (0.219 g, 1 mmol) to 2-pyrazinecarboxylic acid (0.248 g,
2 mmol) and triethylamine (0.202 g, 2 mmol). The solid is then
recrystallized from ethanol and the white crystal compound 10 is
formed. Yield: 76%. Mp 122–124 °C. Anal. Found: C, 40.48; H,
5.32; N, 13.11. Calc. for C18H28ClN5O4Sn: C, 40.59; H, 5.30; N,
13.15%. IR (KBr, cm−1): (N–H), 3430; as(COO), 1647; s(COO),
1331; (CN), 1602; (Sn–C), 576; (Sn–O), 474; (Sn–N), 458;
(Sn–Cl), 270. 1H NMR (CDCl3, ppm):  0.78 (s, 6H), 1.10 (t, 9H),
2.84 (m, 6H), 8.37 (dd, 2H), 8.80 (d, 2H), 9.41(d, 2H), 11.21(s,
1H). 13C NMR (CDCl3. ppm):  7.8, 52.2, 10.9 (1J(119Sn–13C),
920 Hz), 143.1, 145.3, 147.5, 148.0, 171.6. 119Sn NMR (CDCl3,
ppm): −359.1.
(Et3NH)+[(nBu)2Sn(pca)2Cl]− 11. Compound 11 is prepared in
the same way as that of compound 1, by adding di-n-butyltin di-
chloride (0.303 g, 1 mmol) to 2-pyrazinecarboxylic acid (0.248 g,
2 mmol) and triethylamine (0.202 g, 2 mmol). The solid is then
obtained from ethanol. Yield: 80%. Mp 131–133 °C. Anal. Found:
C, 46.69; H, 6.51; N, 11.27. Calc. for C24H40ClN5O4Sn: C, 46.74;
H, 6.54; N, 11.36%. IR (KBr, cm−1): (N–H), 3412; as(COO),
1652; s(COO), 1326; (CN), 1600; (Sn–C), 537; (Sn–O), 481;
1
(Sn–N), 460; (Sn–Cl), 272. H NMR (CDCl3, ppm):  0.83 (t,
6H), 1.28–1.81 (m, 12H), 1.08 (t, 9H), 2.76 (m, 6H), 8.52 (dd, 2H),
8.90 (d, 2H), 9.37 (d, 2H), 11.32 (s, 1H). 13C NMR (CDCl3. ppm): 
7.5, 53.1, 13.6, 26.2, 26.6, 27.9, 142.9, 145.4, 147.6, 148.1, 172.0.
119Sn NMR (CDCl3, ppm): −374.8.
(Et3NH)+[(Ph)2Sn(pca)2Cl]−·H2O 12. Compound 12 is prepared
in the same way as that of compound 1, by adding diphenyltin di-
chloride (0.343 g, 1 mmol) to 2-pyrazinecarboxylic acid (0.248 g,
2 mmol) and triethylamine (0.202 g, 2 mmol). The solid is then
recrystallized from 95% ethanol and the white compound 12 is
formed. Yield: 82%. Mp 146–148 °C. Anal. Found: C, 49.75; H,
5.05; N, 10.29. Calc. for C28H34ClN5O5Sn: C, 49.84; H, 5.08; N,
10.38%. IR (KBr, cm−1): (N–H), 3423; (O–H), 3351; as(COO),
1642 and 1621; s(COO), 1432 and 1432; (CN), 1597; (Sn–C),
536; (Sn–O), 479; (Sn–N), 451; (Sn–Cl), 273. 1H NMR
(CDCl3–D2O, ppm):  1.15 (t, 9H), 2.81 (m, 6H), 7.26–7.67 (m,
10H), 8.57 (dd, 2H), 8.84 (d, 2H), 9.29 (d, 2H), 11.25 (s, 1H). 13
C
NMR (CDCl3. ppm):  7.7, 52.9, 128.9, 130.2, 136.7, 148.1, 143.2,
144.1, 147.2, 147.9, 172.6. 119Sn NMR (CDCl3, ppm): −421.0.
(Et3NH)+[(PhCH2)2Sn(pca)2Cl]− 13. Compound 13 is prepared
in the same way as that of compound 1, by adding dibenzyltin di-
chloride (0.371 g, 1 mmol) to 2-pyrazinecarboxylic acid (0.248 g,
2 mmol) and triethylamine (0.202 g, 2 mmol). The solid is then
obtained from ethanol. Yield: 79%. Mp 166–168 °C. Anal. Found:
C, 52.49; H, 5.25; N, 10.11. Calc. for C30H36ClN5O5Sn: C, 52.62;
H, 5.30; N, 10.23%. IR (KBr, cm−1): (N–H), 3425; as(COO),
1646; s(COO), 1331; (CN), 1601; (Sn–C), 534; (Sn–O), 469;
1
(Sn–N), 450; (Sn–Cl), 268. H NMR (CDCl3, ppm):  1.09 (t,
9H), 2.82 (m, 6H), 3.21 (s, 4H), 7.36–7.71 (m, 10H), 8.52 (dd, 2H),
8.74 (d, 2H), 9.40 (d, 2H), 11.28 (s, 1H). 13C NMR (CDCl3. ppm):
 7.2, 52.6, 38.1, 127.5, 129.4, 141.5, 143.6, 144.6, 146.9, 147.7,
172.3. 119Sn NMR (CDCl3, ppm): −401.7.
X-ray crystallography
Crystals were mounted in Lindemann capillaries under nitrogen.
Diffraction data were collected on a Smart CCD area-detector
with graphite monochromated Mo-K radiation ( = 0.71073 Å).
A semiempirical absorption correction was applied to the data. The
structure was solved by direct methods using SHELXS-97 and
refined against F2 by full matrix least-squares using SHELXL-97.
Hydrogen atoms were placed in calculated positions. Crystal data
and experimental details of the structure determinations are listed
in Table 1.
CCDC reference numbers 220183 1, 222014 2, 220176 5, 220168
6, 220184 8, 220171 9, 209701 10 and 220165 12.
1 8 3 4
D a l t o n T r a n s . , 2 0 0 4 , 1 8 3 2 – 1 8 4 0

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Scheme 2
See http://www.rsc.org/suppdata/dt/b4/b404477k/ for crystal-
lographic data in CIF or other electronic format.
of about 180 cm−1 for compounds 1–4 is comparable to those for
the corresponding sodium salts, which indicates the presence of
bidentate carboxyl groups.16 Moreover, the magnitude of  occur-
ing at about 315 cm−1 for compounds 5, 6, 10, 11 and 13 indicates
that the carboxylate ligand functions as monodentate ligand under
the conditions employed,17,18 which was also confirmed by X-ray
structure analyses.
Results and discussion
Syntheses
Reactions of diorganotin(IV) dichloride with 2-pyrazinecarboxylic
acid in 1:1 or 1:2 stoichiometry depending on the nature of the
starting acceptor and reaction condition affords air-stable com-
pounds. The syntheses procedures are shown in Scheme 2.
NMR. In 1H NMR spectra of the free ligand, single resonances
are observed at 7.46 ppm, which are absent in the spectra of the com-
pounds, indicating the replacement of the carboxylic acid proton by
a diorganotin moiety. The spectra shows that the chemical shifts
of the methyl groups, 0.78–0.82 ppm, 0.82–1.81 ppm for the butyl
group, 7.26–7.78 ppm for the phenyl group and the benzyl group in
3.17–3.26 and 7.32–7.86 ppm. All upfield shifts as compared with
those of their corresponding precursors. The 2JSnH of dimethyltin de-
rivative 1 has a value of 95.6 Hz, comparable with those previously
reported for six-coordinated octahedral tin(IV) adducts.19
The 13C NMR spectra of all compounds show a significant down-
field shift of all carbon resonance, compared with the free ligand.
The shift is a consequence of an electron density transfer from the
ligand to the acceptor. Although at least two different types of car-
boxyl groups are present, only single resonances are observed for
the COO group in the 13C spectra. The possible reason is that either
accidental magnetic equivalence of the carbonyl carbon atoms or
the separations between the two sets of resonance are small to be
resolved. Complementary information is given by the values of the
coupling constant. The 1JSnC value for 1 is 893 Hz, similar to that of
the hexa-coordinate compound, and the calculated (C–Sn–C) by
the Holeček and Lyčka equation20 are 163.9°, which are close to the
angles observed in the solid state for compound 1.
Spectroscopic studies
IR. The stretching frequencies of interest are those associated
with the acid COO, Sn–C, Sn–O and Sn–N groups. The spectra
of all the compounds show some common characters. The explicit
feature in the infrared spectra of all compounds, strong absorption
appearing at about 477 cm−1 in the respective spectra of the com-
pounds, which is absent in the free ligand, is assigned to the Sn–O
stretching mode of vibration. The (CN) band, occurring at about
1598 cm−1, is considerably shifted towards lower frequencies with
respect to that of the free ligand, confirming the coordination of
the heterocyclic N to the tin. The stretching frequency is lowered
owing to the displacement of electron density from N to Sn atom,
thus resulting in the weakening of the CN bond as reported in the
literature.13 The weak- or medium-intensity band in the region 444–
463 cm−1 can be assigned to Sn–N stretching vibrations. All these
values are consistent with that detected in a number of organotin(IV)
derivatives.14,15
Some obvious differences among the spectra of the compounds
are also observed. A strong band at about 268 cm−1 for 1–4 and
10–13 are assigned to (Sn–Cl) stretching mode of vibration.
Besides, in organotin carboxylate complexes, the IR spectra can
provide useful information concerning the coordinate formation
of the carboxyl. The magnitude of  ( = as(COO) − s(COO))
The 119Sn NMR data show only one signal for compounds 1–4,
typical of a six-coordinate species, and has been found in accor-
dance with the solid state structure.21 However, The chemical shift
for compound 8 shows −386.6 ppm.Although (119Sn) is influenced
D a l t o n T r a n s . , 2 0 0 4 , 1 8 3 2 – 1 8 4 0
1 8 3 5

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Table 2 Selected bond lengths (Å) and bond angles (°) for compounds 1
and 2
is partly because of the bonding variance and they occupy cis posi-
tions in the range of 67.22(19)–119.51(14)°. The Sn–N bond lengths
are 2.479(6) Å [Sn(1)–N(5)], 2.477(6) Å [Sn(2)–N(1)], 2.507(6) Å
[Sn(3)–N(3)] for 1 and 2.442(5) [Sn(1)–N(1)] Å for 2. All these
values lie in the range recorded in the Cambridge Crystallographic
Database from 2.27 to 2.58 Å,22 slightly greater than the sum of the
covalent radii of tin and nitrogen atoms (2.15 Å) but are consider-
ably less than the van der Waal’s radii of the two atoms (3.74 Å).23
The carboxylate ligand chelates two Sn atoms with asymmetric
Sn–O bond distances and this asymmetry is reflected in the associa-
tion with the shorter Sn–O bonds. The degree of asymmetry in the
Sn–O bond distances is not equal, with the difference between Sn–O
bond distance for the three carboxylate ligands being 0.202, 0.122,
0.257 Å for 1 and 0.132 Å for 2, respectively. Although the Sn–O
ranges from 2.239(5) to 2.527(5) Å which is longer than the sum of
the covalent radii of the tin and oxygen 2.13 Å,24 both of which are
similar to those reported in the literature.25 The Sn–Cl bond length
[Sn(1)–Cl(1) 2.439(2) Å, Sn(2)–Cl(2) 2.447(2) Å] and 2.427(2) Å
for 1 and 2.412(2) Å for 2 lies in the range of the normal covalent
radii (2.37–2.60 Å).22 The Sn–C distances fall in a narrow range
from 2.076(8) to 2.119(8) Å, typical of organotin derivatives.
[(CH3)2Sn(pca)Cl]3 1
Sn(1)–C(21)
Sn(1)–C(20)
Sn(1)–O(1)
Sn(1)–Cl(1)
Sn(1)–O(6)
Sn(1)–N(5)
Sn(2)–C(17)
Sn(2)–C(16)
Sn(2)–O(3)
Sn(2)–Cl(2)
Sn(2)–O(2)
Sn(2)–N(1)
2.109(8)
2.119(8)
2.239(5)
2.439(2)
2.440(5)
2.479(6)
2.076(8)
2.111(8)
2.331(5)
2.447(2)
2.453(5)
2.477(6)
Sn(3)–C(18)
Sn(3)–C(19)
Sn(3)–O(5)
Sn(3)–Cl(3)
Sn(3)–O(4)
Sn(3)–N(3)
O(1)–C(1)
O(2)–C(1)
O(3)–C(6)
O(4)–C(6)
O(5)–C(11)
O(6)–C(11)
2.095(7)
2.105(9)
2.270(5)
2.427(2)
2.527(5)
2.507(6)
1.265(8)
1.241(8)
1.247(9)
1.250(9)
1.245(9)
1.257(9)
C(21)–Sn(1)–C(20)
C(21)–Sn(1)–O(1)
C(20)–Sn(1)–O(1)
C(21)–Sn(1)–Cl(1)
C(20)–Sn(1)–Cl(1)
O(1)–Sn(1)–Cl(1)
C(21)–Sn(1)–O(6)
C(20)–Sn(1)–O(6)
O(1)–Sn(1)–O(6)
Cl(1)–Sn(1)–O(6)
C(21)–Sn(1)–N(5)
C(20)–Sn(1)–N(5)
O(1)–Sn(1)–N(5)
Cl(1)–Sn(1)–N(5)
O(6)–Sn(1)–N(5)
C(18)–Sn(3)–C(19)
C(18)–Sn(3)–O(5)
C(19)–Sn(3)–O(5)
C(18)–Sn(3)–Cl(3)
C(19)–Sn(3)–Cl(3)
O(5)–Sn(3)–Cl(3)
C(18)–Sn(3)–N(3)
C(19)–Sn(3)–N(3)
[(nBu)2Sn(pca)Cl]3 2
Sn(1)–C(6)#1
159.7(4)
90.4(3)
88.6(3)
C(17)–Sn(2)–C(16)
C(17)–Sn(2)–O(3)
C(16)–Sn(2)–O(3)
C(17)–Sn(2)–Cl(2)
C(16)–Sn(2)–Cl(2)
O(3)–Sn(2)–Cl(2)
C(17)–Sn(2)–O(2)
C(16)–Sn(2)–O(2)
O(3)–Sn(2)–O(2)
Cl(2)–Sn(2)–O(2)
C(17)–Sn(2)–N(1)
C(16)–Sn(2)–N(1)
O(3)–Sn(2)–N(1)
Cl(2)–Sn(2)–N(1)
O(2)–Sn(2)–N(1)
O(5)–Sn(3)–N(3)
Cl(3)–Sn(3)–N(3)
C(18)–Sn(3)–O(4)
C(19)–Sn(3)–O(4)
O(5)–Sn(3)–O(4)
Cl(3)–Sn(3)–O(4)
O(4)–Sn(3)–N(3)
161.9(3)
92.8(3)
87.1(3)
99.4(2)
97.9(3)
100.8(3)
87.94(15)
79.9(3)
100.0(2)
81.50(14)
82.3(3)
83.0(3)
83.7(3)
119.51(18)
152.48(14)
90.3(3)
128.86(18)
149.64(14)
93.0(3)
93.0(3)
91.9(3)
173.2(2)
85.31(16)
67.22(19)
152.7(4)
93.5(3)
164.0(2)
82.97(16)
66.74(19)
166.2(2)
83.86(16)
77.7(3)
87.6(3)
101.9(3)
105.3(3)
82.85(15)
93.0(3)
80.3(3)
128.57(19)
148.56(13)
64.87(19)
92.3(3)
2.090(8)
2.090(8)
2.292(4)
1.253(8)
157.2(4)
86.29(17)
Sn(1)–Cl(1)
Sn(1)–O(1)
Sn(1)–N(1)
O(2)–C(1)
O(2)#2–Sn(1)–O(1) 124.71(14)
Cl(1)–Sn(1)–O(1)
2.412(2)
2.424(4)
2.442(5)
1.250(7)
Sn(1)–C(6)
Sn(1)–O(2)#2
O(1)–C(1)
C(6)#1–Sn(1)–C(6)
C(6)#1–Sn(1)–
O(2)#2
150.98(11)
C(6)–Sn(1)–O(2)#2
C(6)#1–Sn(1)–Cl(1) 100.3(2)
86.29(17)
C(6)#1–Sn(1)–N(1)
C(6)–Sn(1)–N(1)
95.77(17)
95.77(17)
Fig. 1
C(6)–Sn(1)–Cl(1)
O(2)#2–Sn(1)–O(1)
C(6)#1–Sn(1)–O(1)
C(6)–Sn(1)–O(1)
100.3(2)
84.31(11)
83.3(2)
O(2)#2–Sn(1)–N(1) 168.51(16)
Cl(1)–Sn(1)–N(1)
O(1)–Sn(1)–N(1)
84.20(13)
66.78(15)
83.3(2)
by several factors, including the aromatic or aliphatic of the R group
bound to the tin atom (and possibly the type of donor atoms of the
ligand), it may be used with a cation to infer the coordination num-
ber of the tin atom.21b In the case of diphenyltin(IV) compounds,
different coordination numbers are clearly associated with differ-
ent ranges of (119Sn) values, and the chemical shift of compound
8 is well within the range corresponding to coordination number
6, −360 to −540 ppm.21b Therefore it can reasonably be assumed
that the structure in solution of compound 8 is likely different from
that observed in the solid state.
Crystal structures
Crystal structure of [(CH3)2Sn(pca)Cl]3 1 and [(nBu)2Sn(p
ca)Cl]3 2. The molecular structures are illustrated in Fig. 1 and
Fig. 2, respectively. Selected bond lengths (Å) and angles (°) are
listed in Table 2. The compounds prove to be trinuclear macrocyclic
compounds with 2-pyrazinecarboxylic acid bridging the adjacent
tin atoms with a fifteen-member Sn3O6N3C3 ring. The units are
[(CH3)2Sn(pca)Cl] and [(nBu)2Sn(pca)Cl], in which the primary
bonds of the ligand to tin occur through its nitrogen atom and two
oxygen atoms of the carboxyl (mode C). The compounds exist in
distorted octahedron geometry about all three tin atoms with six-co-
ordinate tin(IV) atom. Distortion from strict octahedral coordination
Fig. 2
Furthermore, we investigated the distance between the three
endocyclic oxygen atoms and found the separations in compound
1 are 3.358, 3.644 and 3.345 Å for O(2)O(4), O(4)O(6) and
O(6)O(2), respectively. The corresponding values in compound 2
are 3.470 Å. It does not mean some significant interactions between
1 8 3 6
D a l t o n T r a n s . , 2 0 0 4 , 1 8 3 2 – 1 8 4 0

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Table 3 Selected bond lengths (Å) and bond angles (°) for compound 5
(CH3)2Sn(pca)2(OH2)·2H2O 5
these atoms, however, what attracts us is the center cavity formed
in these macrocyclic and the potential function of the endocyclic
oxygen atoms similar to crown ethers.26 Out of consideration for
molecular design, the compounds may be regarded as a potential
ligand for the recognition of special molecules.
Sn(1)–C(6)
Sn(1)–C(6)#1
2.09(11)
Sn(1)–O(3)
Sn(1)–N(1)#1
Sn(1)–N(1)
2.33(10)
2.55(9)
2.55(9)
2.09(10)
2.22(8)
2.22(8)
172(6)
94(4)
Sn(1)–O(1)#1
Sn(1)–O(1)
C(6)–Sn(1)–C(6)#1
C(6)#1–Sn(1)–O(1)
C(6)–Sn(1)–O(1)
Crystal structure of (CH3)2Sn(pca)2(H2O)·2H2O 5. The mo-
lecular structures are illustrated in Fig. 3 and Fig. 4, selected bond
lengths (Å) and angles (°) are listed in Table 3. The molecule pos-
sesses a monomeric structure, but this structure differs from those of
Me2Sn(2-Pic)2 and Et2Sn(O2CC4H3S)2.27,28 The compound contains
a seven-coordinated tin atom and has a pentagonal bipyramidal
environment with C(6) and C(6)#1 atoms occupying the axial
sites and the axial–Sn–axial, C(6)–Sn–C(6)#1 [ −x + 4/3, −x + y +
2/3, −z + 7/6] is 172(6)°. The tin atom lies on a crystallographic 2-
fold structure, Sn(1), O(1), O(1)#1, O(3), N(1) and N(1)#1 [ −x +
4/3, −x + y + 2/3, −z + 7/6] are completely coplanar with the tin
atom existing in the plane. The sum of angles between the tin atom
and the equatorial atoms is 360°, consistent with the ideal value of
360°. In the structure, two carbon atoms and two nitrogen atoms of
2-pyrazinecarboxylic acid and the oxygen atom of water are cova-
lently linked to the tin. The Sn–O bond lengths (2.22(8) Å) are lon-
ger than those in {[nBu2Sn(2-pic)]2O}2 (2.0544 and 2.110 Å), near
to the sum of the covalent radii of Sn and O (2.13 Å).24 The Sn–N
bond lengths [Sn(1)–N (1) and Sn(1)–N(1)#1, 2.55 (9) Å] are longer
C(6)–Sn(1)–N(1)
O(1)–Sn(1)–N(1)
O(1)#1–Sn(1)–N(1)
O(3)–Sn(1)–N(1)
90(3)
68(3)
142(3)
75(2)
92(3)
C(6)#1–Sn(1)–O(1)#1 92(3)
C(6)–Sn(1)–O(1)#1
O(1)#1–Sn(1)–O(1)
C(6)#1–Sn(1)–O(3)
C(6)–Sn(1)–O(3)
94(4)
74(4)
86(3)
86(3)
C(6)#1–Sn(1)–N(1)#1 90(3)
C(6)–Sn(1)–N(1)#1
O(1)–Sn(1)–N(1)#1
88(3)
142(3)
O(1)#1–Sn(1)–N(1)#1 68(3)
O(1)–Sn(1)–O(3)
O(1)#1–Sn(1)–O(3)
C(6)#1–Sn(1)–N(1)
142.9(19) O(3)–Sn(1)–N(1)#1
142.9(19) N(1)#1–Sn(1)–N(1)
88(3)
75(2)
150(4)
n
than those in Bu2Sn(pca)2(H2O) [2.2522(6) Å],29 similar to those
in Me2Sn(2-Pic)2 (2.507 and 2.477 Å),27 but much shorter than the
sum of the van der Waal’s radii of Sn and N, 3.74 Å,23 and Sn–O(3)
2.33(10) Å is also below the sum of the van der Waal’s radii of these
atoms, 3.68 Å.24 The intermolecular interactions exist between the
coordinate water and two adjacent molecules and result in hydrogen
bonds O(3)–HO(2)(2.674 Å). Through these, a two-dimensional
hydrogen bonded network is formed. Besides, co-crystallization is
found in the crystals and the co-crystallized solvent is water with the
molar ratio (CH3)2Sn(pca)2(H2O):H2O of 1:2. It is worthwhile to
note that the co-crystallized waters do not participate in the interac-
tion with the units, but six neighboring co-crystallized waters form
a six-member ring through the hydrogen bonds O–HO.
Fig. 3
sum of the covalent radii of tin and oxygen, 2.13 Å,24 create a con-
tinuous polymeric chain.
For compounds 8 and 9, both ligands chelate to one tin, bonding
through one carboxyl oxygen and the nitrogen atom; an additional
intermolecular Sn(1)O(2)#1 [x + 1/2, y, −z + 3/2] interaction be-
tween each tin and the carboxylic oxygen of a neighboring molecule
gives rise to the polymeric structure (mode C). Therefore, there are
two distinct coordinate ligands in the compounds, one is bidentate
and the other is tridentate. The overall configuration at tin is best
described as pentagonal bipyramidal: tin and the bonded oxygen
and nitrogen atoms are nearly coplanar and deviate only slightly
from regular pentagonal geometry, mean deviation from plane is
0.0783 Å for 8 and 0.0344 Å for 9. The alkyl groups occupy the
apical position, the axial–Sn–axial, C(17)–Sn–C(11) is 171.2(2)°
for 8 and C(18)–Sn–C(11) is 174.0(3)° for 9. The Sn–N distances
2.393(5) and 2.638(4) Å for 8, 2.422(6) and 2.632(5) Å for 9, are in
keeping with those reported in Sn–N compounds Me2SnCl(2-Pic),31
Me2Sn(2-Pic)227 and {[nBu2Sn(2-Pic)]2O}2.32
The structure of compound 6 is similar to compound 5. Although
we obtained compound 6 by a different method, its structure has
been reported in our previous work.30
Crystal structure of (Ph)2Sn(pca)2 8 and (PhCH2)2Sn(pca)2 9.
The R2Sn(pca)2 units are connected in polymeric structures as
shown in Fig. 5–8, respectively, selected bond lengths (Å) and
angles (°) are listed in Table 4. Intermolecular tin–oxygen bonds
[2.319(4) for 8 and 2.312(4) Å for 9] that are comparable in strength
to the intramolecular tin–oxygen bonds and close in length to the
Fig. 4
D a l t o n T r a n s . , 2 0 0 4 , 1 8 3 2 – 1 8 4 0
1 8 3 7

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Table 4 Selected bond lengths (Å) and bond angles (°) for compounds 8
and 9
(Ph)2Sn(pca)2 8
Sn(1)–C(17)
Sn(1)–C(11)
Sn(1)–O(3)
Sn(1)–O(1)
2.106(6)
2.116(7)
2.180(4)
2.260(4)
171.2(2)
91.41(19)
93.4(2)
89.54(19)
90.9(2)
143.51(14)
91.22(19)
82.3(2)
80.76(14)
135.69(13)
95.4(2)
Sn(1)–O(2)#1
Sn(1)–N(3)
Sn(1)–N(1)
Sn(1)#2–O(2)
C(11)–Sn(1)–N(3)
O(3)–Sn(1)–N(3)
O(1)–Sn(1)–N(3)
2.319(4)
2.396(5)
2.638(4)
2.319(4)
93.2(2)
C(17)–Sn(1)–C(11)
C(17)–Sn(1)–O(3)
C(11)–Sn(1)–O(3)
C(17)–Sn(1)–O(1)
C(11)–Sn(1)–O(1)
O(3)–Sn(1)–O(1)
C(17)–Sn(1)–O(2)#1
C(11)–Sn(1)–O(2)#1
O(3)–Sn(1)–O(2)#1
O(1)–Sn(1)–O(2)#1
C(17)–Sn(1)–N(3)
(PhCH2)2Sn(pca)2 9
Sn(1)–C(18)
70.85(16)
72.75(15)
O(2)#1–Sn(1)–N(3) 150.96(15)
C(17)–Sn(1)–N(1)
C(11)–Sn(1)–N(1)
O(3)–Sn(1)–N(1)
O(1)–Sn(1)–N(1)
O(2)#1–Sn(1)–N(1)
N(1)–Sn(1)–N(3)
82.13(18)
90.1(2)
150.67(14)
65.38(13)
70.68(13)
138.05(15)
2.129(7)
2.138(7)
2.191(5)
2.312(4)
174.0(3)
93.4(2)
92.2(2)
93.3(2)
85.7(2)
79.01(17)
89.1(2)
Sn(1)–O(1)
Sn(1)–N(3)
Sn(1)–N(1)
Sn(1)#2–O(2)
C(11)–Sn(1)–N(3)
O(3)–Sn(1)–N(3)
2.327(5)
2.422(6)
2.632(5)
2.312(4)
94.8(2)
Sn(1)–C(11)
Sn(1)–O(3)
Sn(1)–O(2)#1
Fig. 5
C(18)–Sn(1)–C(11)
C(18)–Sn(1)–O(3)
C(11)–Sn(1)–O(3)
C(18)–Sn(1)–O(2)#1
C(11)–Sn(1)–O(2)#1
O(3)–Sn(1)–O(2)#1
C(18)–Sn(1)–O(1)
C(11)–Sn(1)–O(1)
O(3)–Sn(1)–O(1)
O(2)#1–Sn(1)–O(1)
C(18)–Sn(1)–N(3)
70.04(18)
O(2)#1–Sn(1)–N(3) 149.02(18)
O(1)–Sn(1)–N(3)
C(18)–Sn(1)–N(1)
C(11)–Sn(1)–N(1)
O(3)–Sn(1)–N(1)
O(2)#1–Sn(1)–N(1)
O(1)–Sn(1)–N(1)
N(1)–Sn(1)–N(3)
74.69(17)
88.1(2)
86.0(2)
149.99(17)
70.98(15)
65.34(15)
139.96(18)
87.6(2)
144.58(16)
136.15(15)
89.1(2)
Fig. 6
the axial sites and the C(11)–Sn–C (12) is 174.6(3)°. Two oxygen
atoms, two nitrogen atoms and one chlorine atom occupy the equa-
torial plane. The sum of the angles subtended at the tin atom in the
pentagonal plane is 360.04°, so the atoms Sn(1), N(1), O(1), N(3),
O(3) and Cl(1) are almost in the same plane where the Sn atom is
only 0.0086 Å away from the equatorial plane. The Sn–Cl bond
length is longer than those in C5H4C(SiMe2)2NSnCl (2.440 Å),33
but much shorter than the sum of the van der Waal’s radii of Sn and
Cl(3.85 Å).24 The Sn–N bond lengths (2.552(4) and 2.577(5) Å)
are appreciably greater than those for the pentagonal bipyramidal
neutral compounds [(CH3)2Sn(C3H2N2Me2)2] (Sn–N 2.378 Å)34 and
[(CH3)2SnS2(C3H3N2Me)2] (Sn–N 2.351 Å),35 but much shorter than
the sum of the van der Waal’s radii of Sn and N, 3.74 Å,23 indicating
the coordination at these sites.
Compound 12 is similar to compound 10, but there are some
differences between the two compounds. The biggest difference
exists in the coordinate formation of the ligand. In compound
Fig. 7
Fig. 8
Crystal structure of (Et3NH)+[(CH3)2Sn(pca)2Cl]− 10 and
(Et3NH)+[(Ph)2Sn(pca)2Cl]−·H2O 12. The molecular structures are
illustrated in Fig. 9 and Fig. 10, selected bond lengths (Å) and angles
(°) are listed in Table 5. X-ray crystal structure analysis reveals that
compound 10 is a stannate and contains a seven-coordinate tin atom.
The geometry of the tin atom of the anion [(CH3)2Sn(pca)2Cl]− is
distorted pentagonal bipyramidal with C(11) and C(12) occupying
Fig. 9
1 8 3 8
D a l t o n T r a n s . , 2 0 0 4 , 1 8 3 2 – 1 8 4 0

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Table 5 Selected bond lengths (Å) and bond angles (°) for compounds
10 and 12
Conclusion
The 2-pyrazinecarboxylic acid has been shown to be able to form
monomeric, stannate, polymeric and trinuclear macrocyclic com-
pounds. The nuclearity and stiochiometry were found to depend
on the nature of the starting acceptor and reaction conditions. The
ligand chelates to one tin, bonding through the oxygen of carboxyl
and the nitrogen atoms. In the monomeric and stannate compounds,
the ligand is bidentate and the coordinate number of the tin atom
is seven. The trinuclear macrocyclic compounds possess six-co-
ordinate tin atoms and the ligand is tridentate. In the polymeric
compounds, the seventh coordinate atoms are not held in the co-
ordination sphere of tin as part of a bi- or tridentate ligand system.
Preliminary studies show that 2-pyrazinecarboxylic acid has poten-
tial for the design of heteromulti-metallic systems containing both
transition and post-transition metals.
[Et3H]+[(CH3)2Sn(pca)2Cl]− 10
Sn(1)–C(12)
Sn(1)–C(11)
Sn(1)–O(1)
Sn(1)–O(3)
2.092(6)
2.104(6)
2.256(4)
2.204(3)
Sn(1)–N(3)
Sn(1)–N(1)
Sn(1)–Cl(1)
2.552(4)
2.577(5)
2.687(3)
C(12)–Sn(1)–C(11)
C(12)–Sn(1)–O(3)
C(11)–Sn(1)–O(3)
C(12)–Sn(1)–O(1)
C(11)–Sn(1)–O(1)
O(3)–Sn(1)–O(1)
C(12)–Sn(1)–N(3)
C(11)–Sn(1)–N(3)
O(3)–Sn(1)–N(3)
O(1)–Sn(1)–N(3)
C(12)–Sn(1)–N(1)
174.6(3)
92.3(2)
93.2(2)
91.0(2)
90.8(2)
71.90(14)
92.5(2)
89.5(2)
C(11)–Sn(1)–N(1)
O(3)–Sn(1)–N(1)
O(1)–Sn(1)–N(1)
N(3)–Sn(1)–N(1)
C(12)–Sn(1)–Cl(1)
C(11)–Sn(1)–Cl(1)
O(3)–Sn(1)–Cl(1)
O(1)–Sn(1)–Cl(1)
N(3)–Sn(1)–Cl(1)
N(1)–Sn(1)–Cl(1)
87.8(2)
138.34(13)
66.44(14)
154.11(14)
87.4(2)
88.1(2)
144.17(10)
143.92(10)
76.71(10)
77.48(11)
67.51(13)
139.36(12)
88.2(2)
We thank the National Nature Science Foundation of China
(20271025) and the National Nature Science Foundation of Shan-
dong Province for financial support.
[Et3H]+[(Ph)2Sn(pca)2Cl]−·H2O 12
Sn(1)–C(11)
Sn(1)–C(17)
Sn(1)–O(3)
Sn(1)–N(3)
2.128(6)
2.131(6)
2.281(4)
2.566(5)
Sn(1)–O(1)
Sn(1)–O(2)
Sn(1)–Cl(1)
2.323(4)
2.465(4)
2.4793(19)
References
C(11)–Sn(1)–C(17)
C(11)–Sn(1)–O(3)
C(17)–Sn(1)–O(3)
C(11)–Sn(1)–O(1)
C(17)–Sn(1)–O(1)
O(3)–Sn(1)–O(1)
C(11)–Sn(1)–O(2)
C(17)–Sn(1)–O(2)
O(3)–Sn(1)–O(2)
O(1)–Sn(1)–O(2)
C(11)–Sn(1)–Cl(1)
169.6(2)
C(17)–Sn(1)–Cl(1)
O(3)–Sn(1)–Cl(1)
O(1)–Sn(1)–Cl(1)
O(2)–Sn(1)–Cl(1)
C(11)–Sn(1)–N(3)
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O(3)–Sn(1)–N(3)
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94.43(17)
82.50(10)
83.70(12)
137.92(12)
85.23(19)
84.69(18)
67.23(15)
126.56(16)
72.36(16)
149.71(13)
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