Substituted pyridylmethylamide ligands and their zinc complexes

Article abstract of DOI:10.1016/j.ica.2007.05.003

Mononuclear zinc complexes of a family of pyridylmethylamide ligands abbreviated as HL, HL^Ph, HL^Me3, HL^Ph3, and MeL^SMe [HL = N-(2-pyridylmethyl)acetamide; HL^Ph = 2-phenyl-N-(2-pyridylmethyl)acetamide; HL^Me3 = 2,2-dimethyl-N-(2-pyridylmethyl)propionamide; HL^Ph3 = 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide; MeL^SMe = N-methyl-2-methylsulfanyl-N-pyridin-2-ylmethyl-acetamide] were synthesized and characterized spectroscopically and by single crystal X-ray structural analysis. The reaction of zinc(II) salts with the HL ligands yielded complexes [Zn(HL)₂(OTf)₂] (1), [Zn(HL)₂(H₂O)](ClO₄)₂ (2), [Zn(HL^Ph3)₂(H₂O)](ClO₄)₂ (3), [Zn(HL^Ph)Cl₂] (4), [Zn(HL^Me3)Cl₂] (5), and [Zn(MeL^SMe)Cl₂] (6). The complexes are either four-, five- or six-coordinate, encompassing a variety of geometries including tetrahedral, square-pyramidal, trigonal-bipyramidal, and octahedral.

Full text of DOI:10.1016/j.ica.2007.05.003

Inorganica Chimica Acta 360 (2007) 3610–3618
www.elsevier.com/locate/ica
Substituted pyridylmethylamide ligands and their zinc complexes
1
Urmila Pal Chaudhuri, Laura R. Whiteaker, Arunendu Mondal , Eric L. Klein,
*
Douglas R. Powell, Robert P. Houser
Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, Oklahoma, USA
Received 27 April 2007; accepted 2 May 2007
Available online 10 May 2007
Abstract
Mononuclear zinc complexes of a family of pyridylmethylamide ligands abbreviated as HL, HLPh, HLMe3, HLPh3, and MeLSMe
[HL = N-(2-pyridylmethyl)acetamide; HLPh = 2-phenyl-N-(2-pyridylmethyl)acetamide; HLMe3 = 2,2-dimethyl-N-(2-pyridylmethyl)pro-
pionamide; HLPh3 = 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide; MeLSMe = N-methyl-2-methylsulfanyl-N-pyridin-2-ylmethyl-acet-
amide] were synthesized and characterized spectroscopically and by single crystal X-ray structural analysis. The reaction of zinc(II)
salts with the HL ligands yielded complexes [Zn(HL)2(OTf)2] (1), [Zn(HL)2(H2O)](ClO4)2 (2), [Zn(HLPh3)2(H2O)](ClO4)2 (3),
[Zn(HLPh)Cl2] (4), [Zn(HLMe3)Cl2] (5), and [Zn(MeLSMe)Cl2] (6). The complexes are either four-, five- or six-coordinate, encompassing
a variety of geometries including tetrahedral, square-pyramidal, trigonal-bipyramidal, and octahedral.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Zinc; Amide ligands; N,O ligands; Coordination modes; Ligand effects
1. Introduction
structural and reactivity properties of synthetic analogues
with those of the active-site can provide insight into
structure/function relationships. Structural studies of zinc
complexes can also provide an avenue to explore the coor-
dinating properties of different ligand systems.
Zinc, the second most abundant transition metal and
present in over 300 enzymes [1–3], is an essential element
for normal function of most biological systems, including
eukaryotes and prokaryotes. The human body contains
about 3 g of zinc, and a zinc deficiency causes abnormali-
ties in growth, decreases the resistance of the immune sys-
tem, and increases susceptibility to disease. Zinc containing
enzymes include zinc finger proteins, nucleases, peptidases
and many more [4–11]. A majority of these enzyme sites
contain a tetrahedral zinc center coordinated by three
amino acid residues and a fourth site that is typically an
aqua or hydroxo ligand. For a better understanding of
the active-site structure and function of zinc metalloen-
zymes, small molecule model complexes have been synthe-
sized and characterized [12–23]. Comparisons of the
Zinc complexes of a common nitrogen containing
ligand, tris(2-pyridylmethyl)amine (TPA), has been widely
explored in the literature [24–26]. Zinc complexes of amide
containing ligands have been extensively investigated as
well [27–29]. Those with the 6-(pivaloylamido-2-pyridyl-
methyl)amine unit have been synthesized to serve as
models for peptidases [30–33]. Zinc complexes of polyaza-
macrocyclic ligands are also of relevance, and have received
much attention in biomimetic research [34]. In our recent
work, we synthesized a family of pyridylmethylamide
ligands that have tremendous utility in forming multinu-
clear copper complexes owing to their ability to form
mono-, di- and tetranuclear complexes with different coor-
dination modes [35–37]. Inspired by our findings on the
chemistry of copper, we chose to study the coordination
chemistry of zinc with these ligands. Herein, we report
the synthesis, characterization, and structures of the first
*
Corresponding author. Tel.: +1 405 366 8986; fax: +1 405 325 6111.
E-mail address: houser@ou.edu (R.P. Houser).
Present address: Siliguri Institute of Technology, Siliguri, Darjeeling
1
734 001, WB, India.
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.05.003

U. Pal Chaudhuri et al. / Inorganica Chimica Acta 360 (2007) 3610–3618
3611
Scheme 1. Complexes 1–6.
zinc complexes of the family of ligands depicted in Scheme
1, specifically [Zn(HL)2(OTf)2] (1), [Zn(HL)2(H2O)](ClO4)2
(2), [Zn(HLPh3)2(H2O)](ClO4)2 (3), [Zn(HLPh)Cl2] (4), [Zn-
(HLMe3)Cl2] (5), and [Zn(MeLSMe)Cl2] (6).
ligands. The synthesis of MeLSMe was accomplished by
DCC-mediated coupling of (methylthio)acetic acid with
N-methyl(2-pyridyl)methaneamine (Scheme 2). With the
exception of the tertiary amide nitrogen, this ligand is iden-
tical to HLSMe whose coordination chemistry has been
thoroughly investigated [37].
2. Results and discussion
The interesting coordination properties of the pyridyla-
mide family of ligands with copper prompted us to investi-
gate the coordination behavior with zinc. The zinc
complexes 1–6 (Scheme 1) were synthesized by straightfor-
ward methods via the reaction of zinc(II) salts with solu-
tions of the ligand. The zinc(II) salts utilized for the
synthesis were zinc(II) triflate, zinc(II) perchlorate, and
zinc(II) chloride. All the zinc complexes were fully charac-
terized including X-ray crystal structure determination.
Complexes 1–6 were characterized by elemental analy-
2.1. Synthesis and characterization
Our ligand design and synthesis originates from earlier
reports wherein we synthesized a family of pyridylamide
ligands, abbreviated HL, HLPh, HLMe3, and HLPh3 [HL =
N-(2-pyridylmethyl)acetamide; HLPh = 2-phenyl-N-(2-pyr-
idylmethyl)acetamide; HLMe3 = 2,2-dimethyl-N-(2-pyridyl-
methyl)propionamide; HLPh3 = 2,2,2-triphenyl-N-(2-pyr-
idylmethyl)acetamide], and explored their coordination
chemistry with copper [35]. In addition to these previously
reported ligands, we report the synthesis of a new ligand,
MeLSMe(N-methyl-2-methylsulfanyl-N-pyridin-2-ylmethyl-
acetamide), a new member of our family of pyridylamide
1
sis, solid state FTIR, H NMR, and mass spectrometry.
The IR spectra of 2 and 3, both of which contain aqua
ligands, have characteristic mOH stretches for the water mol-
ecule around 3400 cmÀ1. The mClO stretches for 2 and 3
À
4
Scheme 2. Synthesis of MeLSMe
.

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U. Pal Chaudhuri et al. / Inorganica Chimica Acta 360 (2007) 3610–3618
are at 1088 and 1118 cmÀ1, respectively, consistent with
their structures. Complexes 1, 2, and 3 feature amide
gesting the possibility of the formation of dinuclear species
in solution. Finally, 4–6 contain peaks at m/z = 551.1,
m/z = 485.2, and m/z = 519.0 that correspond to fragments
wherein zinc is coordinated to two ligands and a chloride
ion. These data indicate the possibility of structural rear-
rangement in solution.
carbonyl stretching bands (mCO
) between 1650 and
1667 cmÀ1. These data represent trivial shifts with respect
to the free ligand (Table 1). In contrast, 4, 5, and 6 display
t
CO bands shifted to lower frequencies relative to their free
ligand by 24, 43, and 35 cmÀ1, respectively (Table 1). These
differences between 1–3 and 4–6 are likely the result of
the shorter and stronger Zn–O bonds in 4–6 (vide infra).
2.2. X-ray crystal structures
1
The H NMR spectra of the complexes are very similar
The structure of 1, determined by X-ray diffraction
(Fig. 1), consists of zinc ions in a distorted octahedral
geometry coordinated by two HL ligands and two triflate
anions. The zinc atom, which is on a crystallographic
inversion center, is coordinated by the pyridyl nitrogens
to the free ligands, with very slight shifts indicative of coor-
dination to zinc.
The electrospray mass spectrometry (ESI-MS) of 1–6
confirm the presence of the molecular species in solution.
Compound 1 has a molecular ion peak at m/z = 663.0,
corresponding to [Zn(HL)2(OTf)2+H]+. Compounds 2
and 3 exhibit similar fragmentation patterns with peaks
at m/z = 463.0 and m/z = 920.4, corresponding to
[Zn(HL)2ClO4]+ and [Zn(HLPh3)2ClO4]+, consistent with
the loss of one perchlorate and a molecule of water. Com-
plexes 4, 5, and 6 have a common trend in their fragmenta-
tion patterns. Peaks at m/z = 325.0, m/z = 291.0, and m/
z = 309.0 in 4, 5, and 6 correspond to [Zn(HLPh)Cl]+,
[Zn(HLMe3)Cl]+, and [Zn(MeLSMe)Cl]+, that arise from
the loss of a chloride ion in each of them. Complexes 4
and 5 also have peaks at m/z = 689.0 and m/z = 621.0 sug-
˚
[Zn–N = 2.1036(8) A] and carbonyl oxygens [Zn–O =
˚
2.1243(7) A] of two HL ligands forming the equatorial
plane. The apical positions are occupied by oxygen atoms
of two triflate ions at a slightly longer distance of
˚
2.1870(10) A. The bond angles involving the equivalent
trans ligands are 180° by symmetry, and the other angles
range from 86.50(4)° to 93.50(4)°. The pyridyl rings are
almost co-planar and the Zn atom lies in the square plane
formed by atoms N1A, O1A, O1, and N1. The Zn–Npyridyl
distances are similar to those observed for complexes with
pyridyl containing ligands [24], and the Zn–Ocarbonyl dis-
tances seem to follow the trend as seen in the literature
[33]. The amide NH of one molecule forms a hydrogen
bond to the triflate oxygen of another molecule (intermo-
˚
lecular) with an N2–O3 distance of 2.8812(12) A (Fig. 1).
Table 1
The crystal structures of 2 and 3 are illustrated in Figs.
2 and 3, respectively. Bond distances and angles relevant
to the zinc coordination sphere for both compounds are
listed in Table 2. Compounds 2 and 3 are both five-coor-
dinate and structurally similar with respect to the ligand
atom donor sets. Although 2 and 3 are both coordinated
by two ligands (HL for 2 and HLPh3 for 3) and one water
molecule, there are significant geometric differences
Selected vibrational data of ligands and metal complexes
Ligand
HL
mN–H
mCO
Metal complex
mN–H
mCO
3287
1653
1
2
3
4
5
6
3300
3299
3220
3312
3302
1667
1650
1666
1617
1602
1609
HLPh3
HLPh
HLMe3
MeLSMe
3209
3277
3350
1665
1641
1645
1644
Fig. 1. Thermal ellipsoid representation of the X-ray crystal structure of [Zn(HL)2(OTf)2] (1, left). Thermal ellipsoids are drawn at the 50% level. All H
atoms except for the amide H atoms are omitted for clarity. Packing diagram of 1 (right) showing hydrogen bonding interactions.

U. Pal Chaudhuri et al. / Inorganica Chimica Acta 360 (2007) 3610–3618
3613
Fig. 2. Thermal ellipsoid representation of the X-ray crystal structure of [Zn(HL)2(H2O)](ClO4)2 (2, left). Thermal ellipsoids are drawn at the 50% level.
All H atoms except for the amide H atoms and water H atoms are omitted for clarity. Packing diagram of 2 (right) showing hydrogen bonding
interactions.
Fig. 3. Thermal ellipsoid representations of the X-ray crystal structure [Zn(HLPh3)2(H2O)](ClO4)2 (3, left). Thermal ellipsoids are drawn at the 50% level.
All H atoms except for the amide H atoms and water H atoms are omitted for clarity. Packing diagram of 3 (right) showing hydrogen bonding
interactions.
between 2 and 3. Compounds 2 and 3 are both symmetri-
cal with a twofold axis passing through the metal centers
that divides the molecules into two equal halves. In com-
plex 2, which is best described as trigonal-bipyramidal,
Zn1 is coordinated to two pyridyl nitrogens (N1 and
ideal trigonal-bipyramidal geometry has been calculated
according to the method of Addison et al. [38], indicating
a geometry closest to trigonal-bipyramidal (s5 = 0.82 for
2). The pyridyl rings of the two molecules are inclined at
an angle of 99.8(2)° to each other. The crystal structure
of 2 is held together by hydrogen bonding interactions.
The coordinated water molecule (O2) hydrogen bonds
intramolecularly to the carbonyl oxygens of the same mol-
ecule (O1 and O1B), with O2–O1/O1B distances of
˚
N1A) at 2.037(2) A and a water molecule (O2) at
˚
1.976(3) A, forming the equatorial plane. The Zn atom lies
in the trigonal plane of N1, N1A, and O2, which is nearly
planar. The carbonyl oxygens (O1 and O1B) at 2.112(2)
˚
˚
A are located axially, completing the distorted trigonal-
2.710(4) and 2.810(12) A. The amide nitrogen hydrogen
bipyramid. An estimate of the degree of distortion from
bonds intermolecularly to the water oxygen O2A and the

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Table 2
[32]. This structural feature suggests that the amide oxygen
binds somewhat more strongly to the zinc center in
zinc complexes of (6-pivaloylamido-2-pyridylmethyl)amine
compared to 2 and 3. The Zn–Npyridyl distances in 2 and 3
are comparable to those reported in the literature [24–26].
Zinc complexes 4, 5, and 6 are isostructural, with slight
variations in their bond lengths and angles. Their crystal
structures are shown in Figs. 4–6, and their bond lengths
and angles are listed in Table 3. The zinc atoms in 4, 5,
and 6 are coordinated by two chlorides, and the pyridyl
˚
Selected bond distances (A) and angles (°) for 1, 2, and 3
1
2
3
Zn1–N1
Zn1–O1
Zn1–O2
2.1042(12)
2.1243(10)
2.1870(10)
2.037(2)
2.112(2)
1.976(3)
2.0353(12)
2.0971(11)
2.0148(16)
N1–Zn1–N1A
O1–Zn1–O1A/O1B
N1–Zn1–O1A/O1B
N1–Zn1–O1
179.999(1)
180
116.33(12)
171.16(12)
89.11(9)
155.48(7)
176.42(6)
89.10(5)
90.14(5)
102.26(4)
102.26(4)
91.79(3)
91.79(3)
86.90(4)
93.10(4)
86.50(4)
93.50(4)
91.21(4)
88.79(4)
95.56(8)
N1–Zn1–O2
121.84(6)
121.84(6)
85.58(6)
N1A–Zn1–O2
O1A–Zn1–O2
O1–Zn1–O2
nitrogen and carbonyl oxygen of HLPh, HLMe3, and
MeLSMe, respectively. The Zn–N distances in 4–6 range
85.58(6)
˚
from 2.039 to 2.055 A and are quite similar to each other.
The Zn–O distances are similarly quite close, ranging from
˚
perchlorate oxygens O4 and O4A of an adjacent molecule.
1.987 to 2.013 A. The remaining coordination sites are
˚
The N2–O2A distance is 3.050(14) A and the N2–O4/O4A
occupied by two chloride anions with Zn–Cl distances
ranging from 2.2093(3) to 2.2302(4) A. The Zn–O, Zn–N,
˚
˚
distances are ꢀ3.016 A (Fig. 2).
In contrast to 2, 3 possesses a coordination geometry
closer to square-pyramidal. The basal plane of the square
pyramid is made up of two pyridyl nitrogens (N1 and
N1A) and two carbonyl oxygens (O1 and O1B) at
and Zn–Cl distances are very similar to the zinc complex
of N-(2-pyridylmethy1)urea where Zn is coordinated to
the pyridyl nitrogen, carbonyl oxygen, and the third and
fourth coordination sites are occupied by chloride ions,
forming a distorted tetrahedral structure [29]. The Zn–Cl
distances are very similar to other tetrahedral zinc com-
plexes of other pyridine based amine ligands [30], and com-
plexes of benzimidazole ligands [39].
˚
2.0353(12) and 2.0971(11) A, respectively. The fifth coordi-
nation site is occupied by a water molecule located axially
˚
˚
at 2.0148(16) A. The zinc atom lies 0.248 A out of the least
squares plane. The pyridyl rings of the two molecules are
twisted by 83.3(2)° with respect to each other. The geome-
try around Zn1 is closer to distorted square-pyramidal,
with a geometric index s5 of 0.35. Intramolecular hydrogen
bonding interactions exist between the water oxygens
and the perchlorate oxygens. The O2–O4A distance is
An estimate of the degree of distortion from idealized
tetrahedral or square planar geometry for four-coordi-
nate complexes has been calculated according to the
method of Yang and Houser [40] with s4 values 0.94,
0.93, 0.90 for complexes 4, 5, and 6, indicating geome-
tries closest to distorted tetrahedral. The N–Zn–O and
Cl–Zn–Cl angles range from 99.99(4)° to 119.27(14)°,
and distortion is most pronounced in complex 6. The
dihedral angles between the N–Zn–O and the Cl1–Zn–
Cl2 planes in 4, 5, and 6 are 86.6(2)°, 89.6(2)°, and
93.1(2)°, respectively. These values deviate only slightly
˚
2.7259(15) A (Fig. 3).
˚
The Zn1–Ocarbonyl distances of ꢀ2.11 A in 2 and 3 lie in
the same range as other five-coordinate zinc complexes of
pyridyl ligands containing amino acids like L-phenylalanine
[33]. However, these distances are longer than those
observed in five-coordinate complexes containing the
ligand unit (6-pivaloylamido-2-pyridylmethyl)amine, where
from 90° of the idealized value for
a tetrahedral
˚
the Zn–Ocarbonyl distances are in the range of 2.00–2.03 A
structure.
Fig. 4. Thermal ellipsoid representations of the X-ray crystal structures of [Zn(HLPh)Cl2] (4, left). Thermal ellipsoids are drawn at the 50% level. All H
atoms except for the amide H atoms are omitted for clarity. Packing diagram of 4 (right) showing hydrogen bonding interactions.

U. Pal Chaudhuri et al. / Inorganica Chimica Acta 360 (2007) 3610–3618
3615
Fig. 5. Thermal ellipsoid representations of the X-ray crystal structures of [Zn(HLMe3)Cl2] (5, left). Thermal ellipsoids are drawn at the 50% level. All H
atoms except for the amide H atoms are omitted for clarity. Packing diagram of 5 (right) showing hydrogen bonding interactions.
Fig. 6. Thermal ellipsoid representations of the X-ray crystal structures of [Zn(MeLSMe)Cl2] (6, left). Thermal ellipsoids are drawn at the 50% level. All H
atoms are omitted for clarity. Packing diagram of 6 (right) showing no hydrogen bonding interactions.
the fact that MeLSMe does not contain an amide hydrogen,
there are no such interactions in 6 as illustrated in Fig. 6.
Table 3
˚
Selected bond distances (A) and angles (°) for 4, 5, and 6
4
5
6
The fact that the thioether S atom in the structure of 6 does
not coordinate to zinc is noteworthy, perhaps due to steric
and/or geometric constraints. A five-coordinate structure
with a S–Cu bond would lead to unfavourable geometric
constraints, while a four-coordinate structure with a S–
Cu bond in place of the O–Cu bond would lead to the for-
mation of an eight-membered ring.
Zn1–N1
Zn1–O1
Zn1–Cl1
Zn1–Cl2
2.0403(15)
1.9881(13)
2.2227(5)
2.2184(5)
2.0550(11)
1.9931(10)
2.2302(4)
2.2151(4)
2.0393(11)
2.0138(10)
2.2122(4)
2.2092(4)
N1–Zn1–O1
O1–Zn1–Cl1
O1–Zn1–Cl2
N1–Zn1–Cl1
N1–Zn1–Cl2
Cl2–Zn1–Cl1
100.12(6)
112.01(4)
108.12(4)
108.19(5)
113.52(5)
114.06(2)
102.81(4)
106.09(3)
112.40(3)
105.56(3)
112.84(3)
116.027(17)
100.00(4)
106.37(3)
108.14(3)
114.28(3)
106.92(3)
119.271(15)
3. Conclusions
The synthesis, characterization, and structures of six
new zinc complexes of the pyridylmethylamide family of
ligands have been described. The complexes are four-,
five-, and six-coordinate, possessing distorted tetrahedral,
square-pyramidal, trigonal bipyramidal, and octahedral
geometries. The counter anion plays a significant role in
the coordination environment and geometry of each of
Intermolecular hydrogen bonding interactions exist in 4
and 5 between the amide hydrogen of one molecule and the
chloride ions of an adjacent molecule forming linear
chains. The N2–Cl distances in 4 and 5 are 3.2786(14)
˚
and 3.2040(12) A, respectively (Figs. 4 and 5). Owing to

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U. Pal Chaudhuri et al. / Inorganica Chimica Acta 360 (2007) 3610–3618
the complexes formed. When zinc triflate is used in the syn-
thesis, the six-coordinate complex 1 forms with two HL
ligands in the equatorial plane and the triflate ions occupy-
ing the axial coordination sites. With zinc perchlorate, the
complexes formed are five-coordinate with either two HL
ligands as in the case for 2, or two HLPh3 ligands, as in
the case for 3, and a water molecule occupying the fifth site,
either in the equatorial position for trigonal-bipyramidal 2,
or in the axial position for square-pyramidal 3. Finally,
when zinc chloride is used in the synthesis, complexes 4–6
with strongly coordinating chlorides were isolated. They
are four-coordinate with only one ligand, and the third
and fourth sites occupied by chloride ions. Hence the coun-
ter ion, rather than the ligand, has the greatest influence on
the coordination behavior of the zinc complexes formed
with the pyridylamide ligands. This stands in contrast to
the copper(II) complexes of these ligands, which, due to
their reduced flexibility with regard to coordination geom-
etry as a result of the d9 Jahn–Teller effect, were shown to
have structures that were more strongly influenced by the
ligands [35,36]. Furthermore, the copper(I) complexes of
these ligands, which like zinc(II) are d10, are likewise quite
different structurally, likely due predominantly to the dif-
ferences in charge [40,41].
methaneamine (0.50 g, 4.09 mmol) in THF (10 mL) was
cooled to À10 °C in an ice/salt bath. N,N-Dicyclohexylcar-
bodiimide monohydrate (DCC Æ H2O) (1.01 g, 4.91 mmol)
was dissolved in a minimal volume of THF, cooled to
À10 °C, and added in one portion to the (methylthio)acetic
acid solution. The mixture was stirred at À10 °C for 1 h
and allowed to warm to room temperature. Stirring was con-
tinued at room temperature for 30 h. The reaction mixture
was then cooled to À40 °C and the DCU suspension was fil-
tered off. The filtrate was concentrated in vacuo and dissolved
in 6 mL of chloroform. This solution was loaded onto a Red-
iSep (35 g) flash column. Impurities were eluted from the col-
umn with chloroform and the desired product was obtained
in high purity as an orange oil following subsequent elution
with methanol and removal of the solvent in vacuo. Yield:
0.86 g (95%). Anal. Calc. for C10H14N2OS Æ 0.5H2O: C,
54.77; H, 6.89; N, 12.77. Found: C, 54.66; H, 6.94; N,
1
12.76%. H NMR (CDCl3, 300 MHz): d 2.14 (s, 3H), 2.91
(s, 3H), 3.28 (s, 2H), 4.70 (s, 2H), 7.08–7.22 (m, 2H), 7.60
(m, 1H), 8.47 (m, 1H) ppm. 13C{1H} NMR: d 16.16, 35.51,
53.43, 55.93, 121.90, 122.43, 137.30, 149.28, 157.22,
169.25 ppm. FTIR (KBr): 3062, 2920, 2855, 1717, 1644
(mCO), 1590, 1571, 1476, 1435, 1397, 1300, 1257, 1151,
1099, 1049, 993, 939, 783, 753, 607 cmÀ1
.
4. Experimental
4.3. [Zn(HL)2(OTf)2] (1)
4.1. General
An acetonitrile solution of HL (0.096 g, 0.64 mmol) was
added dropwise to an acetonitrile solution of Zn(OTf)2
(0.117 g, 0.32 mmol) forming a white precipitate which
was stirred for 4 h. The precipitate was collected by filtra-
tion and dissolved in methanol. Vapor diffusion of diethyl
ether into this solution gave rise to the formation of X-ray
quality crystals of 1. Yield: 0.195 g (92%). Anal. Calc. for
C18H20F6N4O8S2Zn: C, 32.56; H, 3.04; N, 8.44. Found: C,
All reagents were purchased from commercial sources
and used without further purification. Solvents were dried
and purified under nitrogen using standard methods and
distilled immediately before use. 1H NMR spectra were
measured on a Varian 300 MHz spectrometer using solvent
as an internal standard [1H d (CHCl3) = 7.27 ppm; H d
1
(CH3OH) = 4.87 ppm; 13C d (CHCl3) = 77.23 ppm]. Ele-
mental analyses were carried out by Atlantic Microlabs
(Norcross, GA). Mass spectra were recorded on a Q-TOF
quadrupole time-of-flight mass spectrometer equipped with
a Z-spray electrospray ionization (ESI) source (Micromass,
Manchester, UK). IR spectra were recorded on a Nexus
470 FTIR spectrometer. The ligands N-(2-pyridyl-
methyl)acetamide (HL), 2-phenyl-N-(2-pyridylmethyl)
acetamide (HLPh), 2,2-dimethyl-N-(2-pyridylmethyl) pro-
pionamide (HLMe3), and 2,2,2-triphenyl-N-(2-pyridylm-
ethyl)acetamide (HLPh3) were synthesized according to
published procedures [35,36]. Caution: Perchlorate salts of
metal complexes with organic ligands are potentially explo-
sive. Although no problems were encountered in this work,
only small amounts of material should be prepared and
handled with caution.
32.68; H, 2.99; N, 8.42%. H NMR (300 MHz, CH3OH-
1
d4): d2.04 (s, 3H), 4.49 (d, 2H), 7.32–7.41 (m, 2H), 7.81–
7.84 (t, 1H), 8.47–9.49 (d, 1H) ppm. ESI-MS (CH3OH):
m/z = 663.0, [Zn(HL)2(OTf)2+H]+; 513.0, [Zn(HL)2-
(OTf)]+. FTIR (KBr): 3300 (mNH), 3053, 1667 (mCO), 1612,
1558, 1443, 1378, 1356, 1266, 1175, 1142, 1046, 1038,
776, 643, 520 cmÀ1
.
4.4. [Zn(HL)2(H2O)](ClO4)2 (2)
A methanol solution of HL (0.075 g, 0.5 mmol) was
added dropwise to a methanol solution of Zn(ClO4)2
(0.093 g, 0.25 mmol). The reaction mixture was stirred for
1 h after which the solvent was removed to give a reddish
white solid. The product was dissolved in methanol and
vapor diffusion of diethyl ether gave rise to the formation
of X-ray quality crystals of 2. Yield: 0.120 g (80%). Anal.
Calc. for C16H22Cl2N4O11Zn: C, 32.96; H, 3.77; N, 9.61.
4.2. N-Methyl-2-methylsulfanyl-N-pyridin-2-ylmethyl-
acetamide (MeLSMe
1
)
Found: C, 32.77; H, 3.82; N, 9.61%. H NMR (300 MHz,
CH3CN-d3): d2.02 (s, 3H), 2.62 (bs, 2H), 4.57 (d, 2H),
7.65 (m, 2H), 8.20 (m, 2H), 8.55 (d, 1H) ppm. ESI-MS
(CH3CN): m/z = 463.0, [Zn(HL)2ClO4]+. FTIR (KBr):
A solution of (methylthio)acetic acid (0.43 g, 4.09 mmol),
HOBt (0.75 g, 4.91 mmol), and N-methyl(2-pyridyl)-

U. Pal Chaudhuri et al. / Inorganica Chimica Acta 360 (2007) 3610–3618
3617
3400 (mOH), 3299 (mNH), 2361, 1650 (mCO), 1613, 1558, 1490,
989, 967, 898, 863, 792, 779, 703, 649, 623, 591, 542, 425,
411 cm1.
À
1444, 1421, 1373, 1355, 1312, 1145, 1088 (mClO ), 776, 636,
4
627 cmÀ1
.
4.8. [Zn(MeLSMe)Cl2] (6)
4.5. [Zn(HLPh3)2(H2O)](ClO4)2 (3)
A methanol solution of MeLSMe (0.250 g, 1.19 mmol)
was added dropwise to a methanol solution of ZnCl2
(0.162 g, 1.07 mmol). The reaction mixture was stirred for
1 h after which the solvent was removed to give a tan pow-
der. The tan powder was dissolved in chloroform and slow
evaporation of a concentrated solution of the tan powder
gave rise to the formation of X-ray quality crystals of 6.
Yield: (0.347 g, 93%). Anal. Calc. for C10H14Cl2N2OSZn:
C, 34.65; H, 4.07; N, 8.08. Found: C, 34.72; H, 4.07; N,
8.09%. 1H NMR (CH3OH-d4): d 2.14 (s, 3H), 3.14
(s, 3H), 3.44 (s, 2H ), 4.71–4.77 (m, 2H), 7.33–7.35 (m,
2H), 7.81–7.83 (t, 1H), 8.49–8.52 (m, 1H) ppm. ESI-MS
A
dichloromethane solution of HLPh3 (0.10 g,
0.13 mmol) was added dropwise to a methanol solution
of Zn(ClO4)2 (0.05 g, 0.13 mmol), resulting in a clear and
colorless solution. Slow evaporation resulted in the
formation of X-ray quality crystals of 3. Yield: 0.12 g
(86%). 1H NMR (300 MHz, CH3OH-d4): d 4.54 (d,
2H), 6.93–6.95 (m, 1H), 7.24–7.32 (m, 17H), 7.64 (t, 1H),
8.38–8.40 (d, 1H) ppm. ESI-MS (CH3OH): m/z = 920.4,
[Zn(HLPh3)2ClO4]+; 410.6, [Zn(HLPh3)2]2+. FTIR (KBr):
3415 (mOH), 3220 (mNH), 3056, 1666 (mCO), 1620, 1596,
À
1572, 1518, 1491, 1443, 1256, 1118 (mClO ), 1034, 1001,
4
765, 699, 639, 616, 516 cmÀ1
.
(CH3OH):
m/z = 519.0,
[Zn(MeLSMe)2Cl]+;
309.0,
[Zn(MeLSMe)Cl]+. FTIR (KBr): 3435, 3106, 3054, 3031,
2991, 2959, 2916, 2829, 1609 (mCO), 1587, 1486, 1459,
1442, 1406, 1352, 1323, 1280, 1225, 1150, 1123, 1095,
1059, 1029, 1001, 986, 874, 836, 797, 775, 707, 660, 652,
4.6. [Zn(HLPh)Cl2] (4)
A methanol solution of HLPh (0.1013 g, 0.45 mmol) was
added dropwise to a methanol solution of ZnCl2 (0.06 g,
0.45 mmol). Within minutes there was a formation of a
white precipitate. The solution was allowed to stir over-
night after which it was warmed and the solution was com-
pletely clear. Slow evaporation resulted in the formation of
X-ray quality crystals of 4. Yield: 0.14 g (85%). Anal.
Calc. for C14H14Cl2N2OZn: C, 46.38; H, 3.89; N, 7.73.
618, 571, 534, 480, 464, 422 cmÀ1
.
4.9. X-ray crystal structure determination
Single crystals of 1–6 were obtained by either slow evap-
oration of methanol or acetonitrile solutions of the com-
plex or by vapor diffusion of diethyl ether into solutions
of the complex. Intensity data for 1–6 were collected on a
Bruker Apex CCD area detector diffractometer with graph-
1
Found: C, 46.09; H, 3.83; N, 7.71%. H NMR (300 MHz,
CH3OH-d4): d 3.59 (d, 2H), 4.50 (d, 2H), 7.27–7.31 (m,
7H), 7.77–7.78 (m, 1H), 8.47–8.49 (d, 1H) ppm. ESI-MS
˚
ite-monochromated Mo Ka (k = 0.71073 A) radiation. Cell
parameters were determined from a non-linear least
squares fit of the data. The data were corrected for absorp-
tion by the semi-empirical method. The structures were
solved by direct methods by use of the SHELXTL program,
(CH3OH):
m/z = 689.0,
[Zn2(HLPh)2Cl3]+;
551.1,
[Zn(HLPh)2Cl]+; 325.0, [Zn(HLPh)Cl]+. FTIR (KBr): 3312
(mNH), 3083, 3033, 2931, 2361, 1617 (mCO), 1583, 1557,
1496, 1485, 1444, 1363, 1348, 1324, 1198, 1180, 1112,
1063, 1028, 1010, 919, 844, 764, 775, 732, 698, 667, 652,
616, 534, 510, 445, 416 cmÀ1
.
Table 4
Crystallographic data for 1–3
4.7. [Zn(HLMe3)Cl2] (5)
1
2
3
Formula
C
18H20F6N4-
C16H22Cl2-
N4O11Zn
582.65
120(2)
C2/c
19.724(8)
8.578(3)
15.147(5)
90
113.23(2)
90
4
2355.0(15)
1.643
1.333
C52H46Cl2-
N4O11Zn
1039.20
120(2)
P2/c
15.468(2)
8.7668(14)
18.578(2)
90
113.786(5)
90
2
2305.3(5)
1.497
0.718
A methanol solution of HLMe3 (0.100 g, 0.51 mmol) was
added dropwise to a methanol solution of ZnCl2 (0.070 g,
0.51 mmol). Within minutes there was a formation of a
white precipitate. The solution was allowed to stir over-
night after which it was warmed and the solution was com-
pletely clear. Slow evaporation resulted in the formation of
X-ray quality crystals of 5. Yield: 0.13 g (76%). Anal.
Calc. for C11H16Cl2N2OZn: C, 40.21; H, 4.91; N, 8.53.
Found: C, 40.18; H, 4.87; N, 8.54%. ESI-MS (CH3OH):
m/z = 621.0, [Zn2(HLMe3)2Cl3]+; 485.2, [Zn(HLMe3)2Cl]+;
291.0 [Zn(HLMe3)Cl]+. 1H NMR (CH3OH-d4): d 1.20–
1.22 (m, 9H), 4.53 (s, 2H), 7.36–7.39 (m, 2H), 7.87
(t, 1H), 8.52–8.54 (d, 1H) ppm. FTIR (KBr): 3302 (mNH),
3066, 2974, 2361, 1602 (tCO), 1584, 1547, 1484, 1443,
1396, 1363, 1307, 1253, 1161, 1105, 1061, 1027, 1057,
O8S2Zn
663.87
110(2)
P2(1)/n
8.6860(6)
16.8188(12)
9.0827(7)
90
103.0670(10)
90
2
1292.52(16)
1.706
1.206
M
T (K)
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
Z
3
˚
V (A )
qcalc (g cm3)
l (mmÀ1
)
R1 [I > 2r(I)]
0.0230
0.0607
1.093
0.0320
0.0912
1.004
0.0291
0.0812
1.002
wR2 [I > 2r(I)]
Goodness-of-fit on F2

3618
U. Pal Chaudhuri et al. / Inorganica Chimica Acta 360 (2007) 3610–3618
[7] L.C. Myers, M.P. Terranova, A.E. Ferentz, G. Wagner, G.L.
Table 5
Crystallographic data for 4–6
Verdine, Science 261 (1993) 1164.
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A.L. Rheingold, Inorg. Chem. 39 (2000) 4347.
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332.
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[14] E. Szajna-Fuller, G.K. Ingle, R.W. Watkins, A.M. Arif, L.M.
Berreau, Inorg. Chem. 46 (2007) 2353.
[15] E. Szajna, M.M. Makowska-Grzyska, C.C. Wasden, A.M. Arif, L.M.
Berreau, Inorg. Chem. 44 (2005) 7595.
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3239.
4
5
6
Formula
M
C14H14Cl2N2OZn C11H16Cl2N2OZn C10H14Cl2N2OSZn
362.54
120(2)
328.53
100(2)
P-1
346.56
120(2)
P2(1)/n
10.5046(5)
8.6334(4)
15.4007(8)
90
97.0570(10)
90
4
T (K)
Space group P2(1)/c
˚
a (A)
8.0075(7)
15.1720(13)
13.3883(11)
90
105.4550(10)
90
7.5486(10)
8.7671(12)
11.9684(16)
70.469(5)
86.480(5)
67.720(5)
2
688.81(16)
1.584
2.156
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
Z
4
3
˚
V (A )
1567.7(2)
1.536
1.903
1386.11(12)
1.661
2.292
qcalc (g cm3)
l (mmÀ1
)
R1 [I > 2r(I)] 0.0269
wR2 0.0714
[I > 2r(I)]
Goodness-of- 1.059
fit on F2
0.0176
0.0463
0.0178
0.0476
[18] G.K. Ingle, M.M. Makowska-Grzyska, E. Szajna-Fuller, I. Sen, J.C.
Price, A.M. Arif, L.M. Berreau, Inorg. Chem. 46 (2007) 1471.
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Carrano, L.N. Zakharov, A.L. Rheingold, Inorg. Chim. Acta 346
(2003) 227.
1.003
1.083
[20] D.K. Garner, R.A. Allred, K.J. Tubbs, A.M. Arif, L.M. Berreau,
Inorg. Chem. 41 (2002) 3533.
and refined by full-matrix least squares on F2 by use of all
reflections [42,43]. Hydrogen atom positions were initially
determined by geometry and refined by a riding model.
Non-hydrogen atoms were refined with anisotropic dis-
placement parameters. Crystal data for 1–6 are summa-
rized in Tables 4 and 5, and selected bond lengths and
angles are listed in Tables 2 and 3.
[21] L.M. Berreau, M.M. Makowska-Grzyska, A.M. Arif, Inorg. Chem.
40 (2001) 2212.
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39 (2000) 4390.
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Chem. Commun. (2000) 1423.
[24] D. Schnieders, M. Merkel, S.M. Baldeau, B. Krebs, Z. Anorg. Allg.
Chem. 630 (2004) 1210.
[25] W.Y. Yang, H. Schmider, Q.G. Wu, Y.S. Zhang, S.N. Wang, Inorg.
Chem. 39 (2000) 2397.
5. Supplementary material
[26] H. Adams, N.A. Bailey, D.E. Fenton, Q.-Y. He, J. Chem. Soc.,
Dalton Trans. (1997) 1533.
[27] A. Mohamadou, C. Gerard, J. Chem. Soc., Dalton Trans. (2001)
3320.
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1062.
[30] J.C.M. Rivas, E. Salvagni, R.T.M. de Rosales, Parsons S. Dalton
Trans. (2003) 3339.
[31] J.C.M. Rivas, R.T.M. de Rosales, Parsons S. Dalton Trans. (2003)
2156.
CCDC 625121, 625122, 625123, 625124, 625125, and
625126 contain the supplementary crystallographic data
for 1, 2, 3, 4, 5, and 6. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
[32] J.C.M. Rivas, E. Salvagni, R. Prabaharan, R.T.M. de Rosales,
Parsons S. Dalton Trans. (2004) 172.
Acknowledgements
[33] N. Niklas, O. Walter, F. Hampel, R. Alsfasser, J. Chem. Soc., Dalton
Trans. (2002) 3367.
[34] W.J. Niu, E.H. Wong, G.R. Weisman, L.N. Zakharov, C.D.
Incarvito, A.L. Rheingold, Polyhedron 23 (2004) 1019.
[35] U. Pal Chaudhuri, L.R. Whiteaker, L. Yang, R.P. Houser, Dalton
Trans. (2006) 1902.
The National Science Foundation (CHE-0094079 and
CHE-0616941) and the Herman Frasch Foundation sup-
ported this work. We also thank the NSF (CHE-
0130835) and the University of Oklahoma for the purchase
of a CCD equipped X-ray diffractometer.
[36] A. Mondal, Y. Li, M.A. Khan, J.H. Ross, R.P. Houser, Inorg. Chem.
43 (2004) 7075.
[37] E.L. Klein, M.A. Khan, R.P. Houser, Inorg. Chem. 43 (2004) 7272.
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