Reaction of 2-pyridylmethylthiourea derivatives with [(en) 2Co(OSO2CF3)2]+ induces hypodentate coordination of an ethylenediamine ligand

Article abstract of DOI:10.1071/CH14029

Pyridylmethylthiourea derivatives coordinate with [(en)2Co(OSO ₂CF₃)₂]+ in a tridentate manner resulting in the formation of a hypodentate ethylenediamine ligand. Four ligands were studied: N-(R)phenyl-N′-2-pyridylmethylthiourea (R≤H (1a), CH ₃ (1b), OCH₃ (1c)) and N-benzyl-N′-2- pyridylmethylthiourea (2). These bind through the sulfur, a deprotonated exo nitrogen, and the pyridyl nitrogen atoms forming four and five-membered rings, respectively. The ligand also coordinates in a bidentate manner through the sulfur and deprotonated endo or exo nitrogen atoms, forming two additional coordination isomers. The solid state structure (X-ray) of one of the bidentate isomers of Co-1b2+ (endo isomer) shows that the coordinated thiourea sulfur induces a structural trans effect of 0.035A on the trans Co-N bond while that of the tridentate isomer of Co-1a3+ confirms the coordination mode of the ligand and the presence of a protonated hypodentate ethylenediamine ligand as suggested by 1H and 13C NMR spectroscopy. CSIRO 2014.

Full text of DOI:10.1071/CH14029

CSIRO PUBLISHING
Aust. J. Chem. 2014, 67, 933–943
Full Paper
http://dx.doi.org/10.1071/CH14029
Reaction of 2-Pyridylmethylthiourea Derivatives
with [(en)2Co(OSO2CF3)2]1 Induces Hypodentate
Coordination of an Ethylenediamine Ligand
A B C F
, , ,
A
A
Lee Roecker,
Alison Anderson, Aladdin Al-Haddad,
A
A
A
A
Cawas Engineer, Joan Fetty, Charles Kiaza, Nicholas Noinaj,
D
D
E F
,
Nathan L. Coker, Jeanette Krause, and Sean Parkin
A
Department of Chemistry, Berea College, Berea, KY 40404, USA.
Department of Chemistry, Bates College, Lewiston, ME 04240, USA.
B
C
Department of Chemistry, Northern Michigan University, Marquette, MI 49855, USA.
D
Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221, USA.
E
Department of Chemistry, University of Kentucky, Lexington, KY 40506, USA.
F
Corresponding authors. Email: lroecker@nmu.edu; s.parkin@uky.edu (crystallographic work)
Pyridylmethylthiourea derivatives coordinate with [(en)2Co(OSO2CF3)2]þ in a tridentate manner resulting in the
formation of a hypodentate ethylenediamine ligand. Four ligands were studied: N-(R)phenyl-N0-2-pyridylmethylthiourea
(R ¼ H (1a), CH3 (1b), OCH3 (1c)) and N-benzyl-N0-2-pyridylmethylthiourea (2). These bind through the sulfur, a
deprotonated exo nitrogen, and the pyridyl nitrogen atoms forming four and five-membered rings, respectively. The ligand
also coordinates in a bidentate manner through the sulfur and deprotonated endo or exo nitrogen atoms, forming two
additional coordination isomers. The solid state structure (X-ray) of one of the bidentate isomers of Co-1b21 (endo isomer)
˚
shows that the coordinated thiourea sulfur induces a structural trans effect of 0.035 A on the trans Co–N bond while that of
the tridentate isomer of Co-1a31 confirms the coordination mode of the ligand and the presence of a protonated
hypodentate ethylenediamine ligand as suggested by 1H and 13C NMR spectroscopy.
Manuscript received: 21 January 2014.
Manuscript accepted: 12 February 2014.
Published online: 26 March 2014.
Introduction
in a bidentate manner through the pyridyl nitrogen and depro-
tonated exo urea nitrogen atom (Fig. 3).[2] Our original intent in
pursuing this work was to prepare the thiourea analogues of the
complex illustrated in Fig. 3 to complement our previous study
on the acid hydrolysis of the urea analogues.[2] While each of the
previously studied ligands afforded relatively simple chemistry
when reacted with the cobalt precursor—forming predomi-
nately two structural isomers upon reaction with non-pyridyl-
containing thiourea ligands or the desired urea complex upon
reaction with pyridyl urea ligands—reaction with pyridyl-
containing thiourea ligands was complicated by the unexpected
cleavage of a single Co–N(en) bond in the usually robust
[(en)2Co]3þ fragment, which facilitated tridentate coordination
of the hybrid ligand (Fig. 4d) in up to 55 % yield. The reaction of
[(en)2Co(OSO2CF3)2]þ with the pyridylthiourea ligands was
also complicated by formation of a black precipitate that
accounts for 10–15 % of the starting materials. Smaller amounts
of other side products are formed by bidentate chelation through
the thiourea moiety. This paper describes the isolation and
characterisation of the reaction products (Fig. 4a, b, d) by NMR
spectroscopy. Single-crystal X-ray diffraction on two reaction
products confirms the bidentate chelation though the thiourea
This study examines the products formed from the reaction of
four 2-pyridylmethylthiourea derivatives (Fig. 1) with [(en)2Co
(OSO2CF3)2]þ in tetramethylene sulfone. Substituted thiourea
ligands that do not contain a pyridyl group coordinate to the
[(en)2Co]3þ subunit in a bidentate manner through the thiourea
sulfur atom and a deprotonated nitrogen atom (Fig. 2),[1] while
the urea analogues of the ligands illustrated in Fig. 1 coordinate
R
S
N
H
N
H
N
1
S
N
H
N
H
N
2
Fig. 1. Structures of the ligands in this study. The substituents, R, in 1 are
as follows: H (1a), CH3 (1b), and OCH3 (1c).
moiety (endo coordination) of ligand 1b in Co 1b21 (Fig. 5) and
]
Journal compilation Ó CSIRO 2014
www.publish.csiro.au/journals/ajc

934
L. Roecker et al.
2ϩ
such as thiosemicarbazones[3] and the ability of the thiourea
moiety to form four-membered rings,[1] but rupture of the
Co–N(en) bond, which allowed it to do so, was unexpected.
Hypodentate coordination[4] of ethylenediamine has been
documented previously in CoIII complexes of [(en)2(Cl)CoN-
CH3
HN
S
H2
N
H2CH2CH2NH3]3þ [5,6]
,
[(NH3)5CoNH2CH2CH2NH3]4þ [7]
but they are prepared by a
,
and
N
[(en)2Co(NH2CH2CH2NH3)2]5þ [8]
,
Co
NH2
different synthetic route. [(NH3)5CoNH2CH2CH2NH3]4þ, for
example, is prepared in 40 % yield from the reaction of ethyle-
nediamine with excess [(NH3)5CoOSMe2]3þ while [(en)2Co
(NH2CH2CH2NH3)2]5þ is formed in 19 % yield from the reac-
tion of cis-[(en)2CoCl2]þ in neat ethylenediamine.[5,8] The
complexes coordinated by a tridentate thiourea ligand along
with a hypodentate ethylenediamine ligand (Fig. 4d) are formed
in 40–55 % yield with the bidentate thiourea isomers (Fig. 4a, b)
each accounting for ,5–10 % of the overall yield. All reactions
are accompanied by the rapid formation of a black precipitate
upon mixing the ligand with [(en)2Co(OSO2CF3)2]þ—this
product accounts for 10–15 % of the total starting materials and
remains unidentified. Small amounts of the carbonato complex,
[(en)2CoO2CO]þ, are also formed.
N
H2
H2N
2a
endo isomer
2ϩ
HN
S
H2
N
N
H3C
Co
N
The reaction products (after filtration to remove the black
product) are easily separated by column chromatography
(Sephadex SPC-25) using a gradient of increasing NaClO4
concentrations. The singly and doubly charged complexes elute
as expected with 0.1 and 0.2 M NaClO4, respectively, while the
tripositive hypodentate complex requires 0.4 M NaClO4, higher
than expected. This confused initial interpretation of the results
as our experience has found that tripositive cations usually elute
with 0.3 M salt solutions from Sephadex SPC-25. Elemental
analysis and X-ray crystallography, however, confirm the
3þ charge. Dilution and subsequent re-elution of each fraction
with 0.5 M Ba(ClO4)2 affords concentrated solutions from
which pure products precipitate after cooling and/or evapora-
tion. These complexes were characterised by a variety of NMR
experiments in addition to X-ray crystallography of two
complexes.
H2N
H2
NH2
2b
exo isomer
Fig. 2. Substituted thiourea ligands without a pyridyl group form two
coordination isomers with [(en)2Co]3þ
.
2ϩ
NH2
H2N
H2N
N
Co
R
N
NH2
N
H
O
Crystallographic Investigations
Single-crystal X-ray diffraction analysis of the perchlorate salt
of the endo isomer of Co-1b21 confirms one possible hypo-
dentate binding mode for pyridyl-substituted thiourea ligands in
which the potentially tridentate ligand is coordinated in a
bidentate manner through the thiourea sulfur and a deprotonated
thiourea nitrogen atom, forming a four-membered ring (Fig. 5).
Selected bond lengths and angles are given in Table 1. Details of
how coordination though the thiourea moiety affects bond
lengths and angles within the ligand has been recently des-
cribed and the results obtained here are consistent with those
observations.[1] The four-membered ring has a bite angle of
72.04 (7)8 with the CoIII centre with the remaining angles of the
ring being 76.9(1)8, 109.3(2)8, and 101.6(2)8 for the Co–S–C,
N–C–S, and Co–N–C angles, respectively. This arrangement is
facilitated by deformation of the trigonal planar environment
about the thiourea carbon atom with bond angles of 109.3(2)8,
125.7(3)8, and 124.9(2)8 along with lengthening of the C–S bond
Fig. 3. Known structure of the urea analogues of the thiourea ligands
coordinated to the [(en)2Co]3þ fragment.
the tridentate binding mode of ligand 1a in Co-1a31 (Fig. 6).
The X-ray studies suggest that structural trans effects contribute
to the formation of the hypodentately coordinated ethylenedia-
mine ligand.
Results and Discussion
Synthesis
The reaction of [(en)2Co(OSO2CF3)2](CF3SO3) in tetra-
methylenesulfone with thiourea ligands containing a pendant
pyridyl moiety was expected to lead to the formation of
three structural isomers (Fig. 4a–c) in which the added ligand
coordinates in a bidentate manner consistent with the estab-
lished reactivity of related ligands.[1,2] The target complex
(Fig. 4c), however, was not isolated because the pyridylthiourea
ligand bonded in a tridentate manner (Fig. 4d) through the open
coordination site arising from cleavage of a Co–N(en) bond.
That the ligand is capable of bonding in a tridentate manner is
not unexpected as evidenced by coordination of similar ligands
˚
˚
to 1.741(3) A from the 1.68(1) A found in non-coordinated
thiourea ligands.[9–12] The Co–S distance is 2.2946(8) A, similar
˚
in length to that observed in CoIII complexes bonded to neutral
thioether sulfur atoms where Co–S(thioether) bond lengths
range from 2.217 to 2.301 A.[13] That the bond in the coordinated
˚
thiourea complexes studied here is not shorter (expected
because of charge delocalisation in the deprotonated ligand

Hypodentate Coordination of Ethylenediamine
935
N
2ϩ
2ϩ
X
HN
N
HN
S
S
H2
N
H2
N
N
X
Co
Co
N
H2
N
H2
N
H2N
H2N
NH2
NH2
4a
4b
endo isomer
exo isomer
X
3ϩ
2ϩ
X
S
NH
NH
N
N
N
H2
N
S
N
Co
Co
NH2
H2N
N
H2
H2N
NH2
NH2
NH3
4c
4d
Fig. 4. Four possible coordination isomers of 2-pyridylmethylthiourea ligands with ethylenediamine complexes
of CoIII
.
C16
C13
C12
C11
C14
C15
C7
C10
N9
C6
C24
N8
N25
C23
C17
N5
N18
C20
C22
Co1
C21
C19
N4
S1
N1
C3
Fig. 5. Ellipsoid plot of one of the cations of Co-1b21 (endo isomer). Hydrogen atoms have been omitted for clarity.
C2

936
L. Roecker et al.
compared with a neutral thioether ligand) could be a conse-
quence of distortions arising from coordination of the four-
membered ring.
The Co–N(en) bond distance trans to the thiourea sulfur,
˚
1.992(3) A, is longer than those of the Co–N(en) bonds which
coordinated by atoms possessing a full negative formal charge
as in thiolato complexes of CoIII.[15,16] The Co–N(en) bond
distance trans to the deprotonated thiourea nitrogen also shows a
˚
small, but not unexpected, STE of 0.015(3) A relative to the
˚
trans Co–N(en) bonds. STEs as large as 0.03 A have been
˚
are trans to each other, 1.957(4) A. The structural trans
˚
effect (STE) of 0.035(5) A induced by the partially negatively
observed in structures containing deprotonated urea
ligands.[2,17] While the STEs observed here are larger than those
observed in our previous report,[1] they are more consistent with
data that we have collected on related structures (J. Krause and
L. Roecker, unpubl. data). Thus, it appears that the coordinated
thiourea ligand induces lengthening, and presumably weaken-
ing, of select Co–N(en) bonds that may help to explain forma-
tion of the hypodentate ethylendiamine ligand.
charged thiourea sulfur atom is larger than that observed when
neutrally charged sulfur atoms coordinate. Thioether ligands
coordinated to CoIII and S-bonded thiourea ligands coordi-
[13,14]
nated to RuIII both induce a STE of 0.02 A.
˚
A larger
STE of 0.044(2) A has been found in complexes that are
˚
Single-crystal X-ray diffraction analysis of the perchlorate
salt of Co-1a31 confirms the tridentate binding of the pyridyl-
substituted thiourea ligand and the monodentate binding of an
ethylenediamine ligand to CoIII (Fig. 6). Selected bond lengths
and angles are given in Table 2. The ligand binds in a meri-
dional fashion through the pyridyl nitrogen, the deprotonated
exo thiourea nitrogen, and the thiourea sulfur atoms forming five
and four-membered rings, respectively. The coordinated triden-
tate ligand is planar, with the root mean square deviation from
the plane, defined by all ligand atoms except C12–C17, being
C9B
C8B
N4B
N3B
C1B
N1B
C2B
Co1B
S1B
C3B
C5B
C13B
C14B
˚
C7B
C4B
N5B
0.086 and 0.015 A for the A and B cations, respectively. Co1A
˚
and N4A both lie above the plane at 0.032(3) and 0.126(8) A;
˚
Co1B is above the plane by 0.017(3) A and N4B below the
˚
plane by 0.01(1) A. The N(py)–Co–S angle observed here is
N2B
C12B
C6B
C10B
N7B
C15B
only 153.88(4), much smaller than that observed in tridentate
ligands that form two five-membered rings to CoIII. In mer-[Co
(dien)2]3þ, for example, the trans N–Co–N bond angles of
the tridentate ligands are 171.78 and 170.78.[18] The N(en) atom
in the plane of the tridentate ligand (N4) splits the diff-
erence between the N(py) and S with the N(py)–Co–N(en)
and S–Co–N(en) angles being 1028 and 1048, respectively.
C11B
C17B
C16B
N6B
Fig. 6. Ellipsoid plot of one of the cations of Co-1a31 (hypdodentate).
Hydrogen atoms have been omitted for clarity.
˚
Table 1. Selected bond lengths (A) and angles (deg.) for the monomeric cations of
[Co-1b]21 (endo isomer)
Standard deviations are in parentheses. The unit cell contained two cations unrelated by sym-
metry. Refer to Fig. 5 for the numbering scheme
˚
Bond length (A)
˚
Bond length (A)
Cation 1
Cation 2
Co(1)–S(1)
Co(1)–N(9)
Co(1)–N(4)
Co(1)–N(8)
Co(1)–N(1)
Co(1)–N(5)
S(1)–C(17)
N(9)–C(17)
N(9)–C(10)
C(17)–N(18)
2.2895(6)
1.9431(16)
1.9545(18)
1.9558(19)
1.9732(18)
1.9916(18)
1.7394(19)
1.315(2)
Co(2)–S(2)
2.2996(6)
1.9261(17)
1.963(2)
Co(2)–N(34)
Co(2)–N(29)
Co(2)–N(30)
Co(2)–N(26)
Co(2)–N(33)
S(2)–C(42)
1.950(2)
1.9704(19)
1.9922(19)
1.743(2)
N(34)–C(42)
N(34)–C(35)
C(42)–N(43)
1.312(3)
1.423(2)
1.425(3)
1.336(3)
1.335(3)
Bond angle (deg.)
Bond angle (deg.)
N(9)–Co(1)–S(1)
N(8)–Co(1)–N(5)
N(4)–Co(1)–N(1)
C(17)–S(1)–Co(1)
C(17)–N(9)–C(10)
C(17)–N(9)–Co(1)
C(10)–N(9)–Co(1)
N(9)–C(17)–N(18)
N(9)–C(17)–S(1)
N(18)–C(17)–S(1)
72.11(5)
85.39(8)
N(34)–Co(2)–N(30)
N(30)–Co(2)–N(33)
N(29)–Co(2)–N(26)
C(42)–S(2)–Co(2)
C(42)–N(34)–C(35)
C(42)–N(34)–Co(2)
C(35)–N(34)–Co(2)
N(34)–C(42)–N(43)
N(34)–C(42)–S(2)
N(43)–C(42)–S(2)
91.73(8)
85.34(9)
85.21(8)
85.23(9)
77.14(7)
76.75(7)
123.16(16)
101.18(12)
135.38(13)
126.03(18)
109.55(14)
124.41(15)
122.06(17)
102.07(13)
135.67(14)
125.43(19)
109.10(15)
125.46(16)

Hypodentate Coordination of Ethylenediamine
937
The coordinated atoms perpendicular to the tridentate ligand
(atoms N2–N3–N4–N5) are planar with a root mean square
˚
deviation of 0.018 A. Bond lengths and angles within the two
subunits of the tridentate ligand are similar to those of bidentate
complexes of related ligands.
The structure contains a protonated hypodentate ethylene-
diamine ligand—all three hydrogen atoms attached to the
terminal nitrogen atom were located in the difference map.
Protonation is also indicated by the presence of three perchlorate
anions for each cation. The average Co–N5 bond length is 1.957
(OSO2CF3)2]þ in tetramethylene sulfone. The upper spectrum
is that of the uncoordinated ligand—important signals to note
are the singlet attributable to –NH(phenyl) at 9.80 ppm and the
triplet attributable to –NHCH2(py) at 8.13 ppm. The following
two spectra are those of the maroon endo isomer (Fig. 4a) and of
the orange exo isomer (Fig. 4b). The most obvious way to
distinguish between the endo and the exo coordination mode is
the presence or absence of the signal attributable to the appro-
priate –NH. The absence of the signal at 9.80 ppm in the second
spectrum suggests coordination as the endo isomer while the
absence of the signal at 8.13 ppm in the one that follows suggests
coordination as the exo isomer. Consistent with our previous
observations, in the endo coordination mode, signals attribut-
able to the ethylenediamine hydrogen atoms are spread over the
range of 3 to 6 ppm while in the exo isomer they are bunched
more tightly together from 4 to 5.2 ppm. In addition, the endo
mode is characterised by a single –CH2NH2 signal being shifted
upfield to 1.6 ppm.[1]
The lower spectrum in Fig. 7 is that of the tripositive complex
containing the hypodentate, protonated ethylenediamine ligand
and the pyridyl thiourea ligand coordinated in a tridentate
manner. Coordination of the pyridyl group is indicated by the
downfield shifts of the doublet at 8.5 and triplet at 7.4 to 8.8 and
8.1 ppm, respectively. The –NHCH2(py) signal at 8.14 ppm
disappears, while that attributable to –NH(phenyl) shifts from
9.8 to 10.7 ppm. Signals in the region from 2 to 3 ppm are
attributable to –CH2NH2 and –CH3 and integrate as eleven
protons. The region from 3.7 to 5.7 ppm integrates as eight
˚
˚
(7) A, similar to the average of 1.963(6) A found in four other
CoIII structures.[6–8] The coordinating atom of the hypodentate
ligand is trans to a N(en), 175.3(4)8. The hypodentate ligand on
cation A adopts a gauche conformation when viewed down the
C–C bond while that on cation B adopts an anti arrangement,
presumably because of different hydrogen bonding environ-
ments. In cation B, the dangling hypodentate ligand is well
ordered and involved in hydrogen bonding with the water
solvate while in cation A the ligand is disordered over two
distinct conformations. These two disordered conformations are
correlated with the disordered perchlorate anions. Both gauche
and anti conformations have been observed previously.[6–8]
Spectroscopic Analysis
NMR Spectroscopy
Fig. 7 illustrates the 1H NMR spectra for the ligand 1b and
the three complexes it forms upon reaction with [(en)2Co
Table 2. Selected bond lengths (A) and angles (deg.) for the monomeric cations of Co-1a31 (hypodentate)
˚
Standard deviations are in parentheses. The unit cell contained two cations unrelated by symmetry. Refer to Fig. 6
for the numbering scheme
˚
Bond length (A)
˚
Bond length (A)
Cation A
Cation B
Co(1A)–N(2A)
Co(1A)–N(3A)
1.850(5)
1.952(5)
Co(1B)–N(2B)
Co(1B)–N(3B)
Co(1B)–N(3D)
Co(1B)–N(5B)
Co(1B)–N(4B)
Co(1B)–N(4D)
Co(1B)–N(1B)
Co(1B)–S(1B)
S(1B)–C(7B)
N(1B)–C(5B)
C(5B)–C(6B)
C(6B)–N(2B)
N(2B)–C(7B)
C(7B)–N(7B)
N(7B)–C(12B)
1.865(5)
1.959(18)
1.91(6)
Co(1A)–N(5A)
Co(1A)–N(4A)
1.976(5)
1.983(5)
1.974(5)
2.003(16)
1.96(5)
Co(1A)–N(1A)
Co(1A)–S(1A)
S(1A)–C(7A)
N(1A)–C(5A)
C(5A)–C(6A)
C(6A)–N(2A)
N(2A)–C(7A)
C(7A)–N(7A)
N(7A)–C(12A)
1.982(5)
2.3224(19)
1.737(7)
1.359(8)
1.509(9)
1.448(8)
1.291(8)
1.369(8)
1.417(8)
1.958(5)
2.3002(17)
1.758(6)
1.344(7)
1.517(8)
1.446(7)
1.292(7)
1.346(7)
1.411(7)
Bond angle (deg.)
Bond angle (deg.)
N(3A)–Co(1A)–N(5A)
N(2A)–Co(1A)–N(4A)
175.3(3)
174.5(2)
N(3B)–Co(1B)–N(5B)
N(2B)–Co(1B)–N(4B)
N(2B)–Co(1B)–N(4D)
N(1B)–Co(1B)–S(1B)
N(2B)–Co(1B)–S(1B)
N(2B)–Co(1B)–N(1B)
N(2B)–C(7B)–S(1B)
N(1B)–Co(1B)–N(4B)
N(1B)–Co(1B)–N(4D)
N(4B)–Co(1B)–S(1B)
N(4D)–Co(1B)–S(1B)
175.5(3)
172.7(5)
174(2)
N(1A)–Co(1A)–S(1A)
N(2A)–Co(1A)–S(1A)
N(2A)–Co(1A)–N(1A)
N(2A)–C(7A)–S(1A)
N(4A)–Co(1A)–N(1A)
152.77(18)
71.17(17)
81.6(2)
154.89(15)
71.54(15)
83.3(2)
107.6(5)
102.4(2)
106.5(4)
101.7(7)
102(2)
N(4A)–Co(1A)–S(1A)
104.85(16)
103.3(7)
103(2)

938
L. Roecker et al.
11
10
9
8
δ [ppm]
Fig. 8. 1H NMR spectra from 7.0 to 11.5 ppm of the hypodentate
complexes Co 1a31 (lower) followed by Co-1b31 and Co-231 in d6-
]
DMSO. The upper spectrum is that of Co-231 in d6-DMSO after three drops
of D2O have been added.
10
9
8
7
6
5
4
3
2
and must be a result of additional delocalisation throughout the
tridentate ligand. An expanded version (0 to 11 ppm) of Fig. 8 is
available (see Fig. S1 in the Supplementary Material).
δ [ppm]
Fig. 7. 1H NMR spectra of the ligand 1b (upper) followed by its bidentate
complexes endo Co-1b21, exo Co-1b21, and its tridentate complex Co-1b31
(lower) in d6-DMSO.
Fig. 9 illustrates the 13C-APT NMR spectra for the same
complexes used to generate Fig. 7. Most of the signals of the
thiourea ligand shift only slightly upon coordination, but two
shift by 10 ppm. The –CH2py resonance at 48.9 ppm of the non-
coordinated ligand shifts upfield to 45.8 upon endo coordina-
tion, slightly downfield to 50.4 upon exo coordination, and even
more downfield to 59.4 ppm in the tridentate complex. The
–C¼S resonance at 180.8 ppm shifts upfield to 175.0, 172.9, and
170.0 ppm in endo Co-1b21, exo Co-1b21, and tridentate
Co-1b31, respectively.
protons — two are accounted for by the AB quartet attributable
to –CH2py centred at 5.3 ppm with the remaining six attributable
to –CH2NH2. Between the doublets at 7.4 and 7.3 ppm attribut-
able to the para-substituted amine and the four signals arising
from the pyridyl hydrogen atoms from 8.8 to 7.7 ppm is a broad
singlet at 7.6 ppm that integrates as three hydrogen atoms
attributed to the protonated hypodentate ethylenediamine,
–CH2NHþ3 . Isolation of the protonated complex from aqueous
solution is not unexpected given the pKa values of related
Fig. 9 also illustrates that in the absence of hypodentate
coordination of an ethylenediamine ligand—when the pyridyl
thiourea ligand is bonded in a bidentate manner—that the
signals attributable to –CH2NH2 appear as four distinct peaks
around 45 ppm, always downfield of the solvent peak
(d6-DMSO) centred at 39.5 ppm. Upon Co–N(en) bond cleav-
age, these signals spread out over a larger range down to 38 ppm.
This is shown more clearly (Fig. 10) for the phenyl, 4-methoxy,
and benzyl complexes (bottom to top) where each has signals at
41.1 and 38.6 ppm attributable to the hypodentate ethylene-
diamine ligand. In [(en)2Co(NH2CH2CH2NH3)2]5þ the carbon
atoms of the bidentate ethylenediamines appear at 45.2 and
44.0 ppm while those of the hypodentate ethylenediamines
appear at 40.6 and 38.9 ppm in D2O.[8] Location of these peaks
in the complexes studied here shift only slightly in D2O
compared with d6-DMSO. These shifted 13C signals are a clear
indication of the hypodentate coordination mode of ethylene-
diamine. HMQC NMR experiments (Figs S2–S3 in the
complexes (7.36 and 7.96 for [(en)2Co(NH2CH2CH2NH3)2]5þ
for example)[8] and the higher charged, protonated complex
apparently precipitates first.
,
Fig. 8 illustrates the 1H NMR region from 7 to 11 ppm for the
phenyl, 4-methyl, and benzyl tridentate complexes (bottom to
top). Each has a broad singlet at 7.6 ppm, which integrates as
three hydrogens. When a drop of D2O is added the resonances
attributed to –NH and –CH2NHþ3 quickly disappear (upper
spectrum). The spectra also illustrate the consistency of the
pyridyl portion of the 1H NMR spectrum and how the location of
the –NH(phenyl) or –NH(benzyl) peak shifts depending on the
substituent. The large shifts in the location of these resonances
compared with the uncoordinated ligand is not observed in the
exo isomers of complexes that coordinate in a bidentate manner

Hypodentate Coordination of Ethylenediamine
939
[(en)2CoO2CO]þ
[(en)2CoO2CO]þ was formed during all preparations.
Despite being a relatively minor product, it warranted charac-
terisation as the amount produced appeared to correlate with the
amount of black product formed. The combination of 1H and 13
C
NMR spectra of this pink product confirms the presence of the
ethylenediamine and carbonato ligands; the absence of any
aromatic residues rules out coordination by the thiourea
ligand. Electrospray mass spectrometry shows the presence of
[(en)2CoO2CO]þ with a peak at 238. Stirring a sample of
[(en)2Co(OSO2CF3)2](CF3SO3) in tetramethylene sulfone for
three days without the addition of thiourea ligand produces only
[(en)2Co(H2O)2]3þ after work-up. Thus, it does not appear that
[(en)2CoO2CO]þ is a contaminant in the starting material. It is
unclear whether the carbonate originates from ligand oxidation
products or from CO2 that is converted into carbonate under the
basic conditions induced by the ligand.
Conclusion
While not our original intent, this work suggests an alternate
strategy to the synthesis of hypodentate amine complexes—a
potentially useful tool since the dangling amines can be modi-
fied or bound to other metals. While previous strategies have
relied on the addition of an excess of the potentially hypodentate
ligand to reactive or labile starting materials, the method
described here generates the hypodentate ligand by cleavage of
an existing metal–ligand bond. The structural evidence suggests
that introducing a multidentate ligand that contains a function-
ality capable of inducing a significant STE onto CoIII will
enhance the hypodentate coordination of multidentate ligands.
We are currently exploring this idea by studying the reaction of
various tridentate and tetradentate ligands with [(en)2Co
(OSO2CF3)2]þ and [(dien)Co(OSO2CF3)3], respectively.
180
160
140
120
60
40
20
δ [ppm]
Experimental
Fig. 9. 13C NMR (APT) spectra of the ligand 1b (upper) and its bidentate
complexes endo Co-1b21, exo Co-1b21, and its tridentate complex Co-1b31
(lower) in d6-DMSO.
General Data
All chemicals were of reagent grade and used as received
with the exception of tetramethylene sulfone, which was
vacuum-distilled before use. H and 13C NMR spectra were
recorded with a JOEL JNM-FX-200 (Berea College) or a Bruker
400 (Bates College) NMR spectrometer in DMSO-2H6 with
TMS as an internal reference. Mass spectra were recorded on
a Thermo Finnigan LQC Deca Max (Berea College). Elemental
analyses were performed by Galbraith Laboratories, Inc.,
Knoxville, TN, USA.
1
Supplementary Material) confirm that all signals in the 1H NMR
spectrum attributed to –CH arise from hydrogen atoms that are
connected to carbon atoms and that all signals attributed to –NH
arise from hydrogen atoms that are not connected to
carbon atoms.
Comments on Other Reaction Products
Black Product
Preparation of Ligands
Copious amounts of a black product rapidly form dur-
ing the reaction of pyridyl thiourea ligands with [(en)2Co
(OSO2CF3)2]þ and need to be removed before purification of
the other complexes by chromatography. IR and elemental
analysis (the latter of which indicates about three sulfur atoms
per cobalt) suggest that some form of the ligand is present, but
1H NMR spectra in d6-acetone show no signals suggesting the
black product contains CoII. It is tempting to suggest that a redox
reaction occurs between the ligand and [(en)2Co(OSO2CF3)2]þ
after initial binding through the pyridine since no black product
is formed during the reaction with non-pyridyl containing
ligands, but the issue remains unresolved. We have been unable
to propose a structure for the black material that is consistent
with the experimental observations.
A typical preparation is described here for the preparation of 1b.
p-Tolyisothiocyanate (5.0 g, 33.6 mmol) was slowly added to a
stirred solution of 2-aminomethylpyridine (4.4 g 40.6 mmole)
that had been dissolved in 100 mL absolute ethanol. A white
precipitate formed quickly. After stirring for 20 min, the solu-
tion was filtered and the solid recrystallised from hot ethanol
(7.9 g, 92 % yield).
Compound 1a: dH (400 MHz, d6-DMSO) 4.80 (d, J 4.8, 2H),
7.13 (d, J 7.7, 1H), 7.28 (t, J 6.4, 1H), 7.35 (m, 3H), 7.50 (d, J 7.9,
2H), 7.78 (t, J 7.5, 1H), 8.30 (s, 1H), 8.53 (d, J 4.6, 1H), 9.90
(s, 1H). dC (400 MHz, d6-DMSO) (CH, CH3) 121.4, 122.17,
123.18, 124.29, 128.65, 136.69, 148.71; (C, CH2) 48.88, 139.16,
157.53, 180.69.

940
L. Roecker et al.
60
58
56
54
52
50
48
46
44
42
40
38
δ [ppm]
Fig. 10. 13C NMR (APT) spectra of the hypodentate complexes with the ligand 1a (lower), 1c (middle), and 2 (upper) in
d6-DMSO.
Compound 1b: dH (400 MHz, d6-DMSO) 2.28 (s, 3H), 4.83
An orange band closely followed that was easily removed with
0.3 M NaClO4. Continued elution with 0.4 M NaClO4 results in
the resolution of the remaining brown/maroon band into two
components with the most rapidly moving band being by far
the most abundant. The minor upper band was physically
removed by decanting the top portion of the column after which
the remaining band was removed with 0.5 M Ba(ClO4)2. Refrig-
eration of the solution results in the deposition of the product as a
brown/maroon powder (0.50 g, 43 % yield). All complexes were
characterised by 1H NMR and 13C NMR (APT) spectroscopy as
well as by the 2D-NMR experiment HMQC (Figs S2 and S3 in
the Supplementary Material).
(d, J 4.5, 2H), 7.15 (d, J 8.5, 2H), 7.27 (t, J 6.1, 1H), 7.35 (d, 3H),
7.77 (t, J 7.6, 1H), 8.14 (s, 1H), 8.52 (d, J 4.8, 1H), 9.80 (s, 1H).
dC (400 MHz, d6-DMSO) (CH, CH3) 20.49, 121.34, 122.12,
122.60, 129.16, 136.65, 148.69; (C, CH2) 48.92, 133.67, 136.42,
157.65, 180.75.
Compound 1c: dH (400 MHz, d6-DMSO) 3.74 (s, 3H), 4.83
(d, J 5.0, 2H), 6.94 (d, J 8.7, 2H), 7.26 (d, J 6.4, 1H), 7.34
(m, 3H), 7.77 (t, J 7.5, 1H), 8.09 (s, 1H), 8.51 (d, J 5.3, 1H), 9.70
(s, 1H). dC (400 MHz, d6-DMSO) (CH, CH3) 55.22, 113.98,
121.25, 122.08, 125.94, 136.63, 148.68; (C, CH2) 48.97, 131.61,
156.62, 157.80, 181.09. Mp 183—1868C.
Compound 2: dH (200 MHz, d6-DMSO) 4.76 (s, 2H), 4.84
(s, 2H), 7.34 (m, 7H), 7.76 (t, J 4.9, 1H), 8.12 (t, J 3.1, 1H), 8.27
(br s, 1H), 8.53 (d, J 4.9, 1H). dC (200 MHz, d6-DMSO) (CH)
121.9, 122.8, 127.5, 127.9, 128.8, 137.2, 149.3; (C, CH2) 47.8,
49.5, 139.8, 158.6, C¼S not observed. Mp 156–1618C.
The following changes were made for the isolation of the
product obtained from the reaction of 2. After the reaction, the
supernatant was loaded as a broad purple band. Elution was
begun with 200 mL of 0.2 M NaClO4 and quickly ramped up to
0.4 M NaClO4 until only a broad purple band remained on the
column. The bands eluted during this time were not charac-
terised. Continued elution with 0.4 M NaClO4 results in
the resolution of the purple band into three components with
the most rapidly moving band being by far the most abundant.
The minor upper two bands were physically removed by
decanting the top portion of the column, after which the
remaining purple band was removed with 0.5 M Ba(ClO4)2.
Refrigeration of the purple solution results in the deposition of
an iridescent purple solid (0.65 g, 55 % yield).
Complex Co-1a31 (hypodentate): dH (400 MHz, d6-DMSO)
2.08 (s, 1H), 2.35 (br s, 3H), 2.85 (s, 4 H), 3.40 (s, 2H {water}),
3.85 (t, J, 11.5, 1H), 4.05 (t, J 11.5, 1H), 4.39 (s, 1H), 4.50
(s, 1H), 5.26 (q, J 10.3, 20.0, 2H) 5.44 (s, 1H), 5.61 (s, 1H), 7.22
(t, J 7.6, 1H), 7.48 (m, 4H), 7.58 (br s, 3H), 7.70 (t, J 7.5, 1H),
7.84 (d, J 7.5, 1H), 8.11 (t, J 7.5, 1H) 8.79 (d, J 5.6, 1H) 10.76
(s, 1H). dC (400 MHz, d6-DMSO) (CH, CH3) 121.48, 122.14,
Reaction of Ligands with [(en)2Co(OSO2CF3)2](CF3SO3)
Isolation of Tridentate Complexes (Fig. 4d)
Compound 1b (0.49 g, 1.91 mmol) was dissolved in 10 g of
tetramethylene sulfone and [(en)2Co(OSO2CF3)2](CF3SO3)
(1.00 g, 1.60 mmol) was added; the reaction mixture was sealed
and stirred. The solution quickly darkened and a black precipi-
tate formed. After 3 days the reaction solution was diluted with
300 mL of water and stirred for 20 min before filtering to remove
the black precipitate and unreacted ligand (0.22 g total). The
supernatant was sorbed onto Sephadex SPC-25 (3 cm internal
diameter ꢀ 20 cm) and loaded as a broad brown/maroon band.
After washing with water, elution with 200 mL of 0.2 M NaClO4
quickly removed a pink band and separated a maroon band that
was then removed with an additional 300 mL of 0.2 M NaClO4.

Hypodentate Coordination of Ethylenediamine
941
Table 3. Crystal data and structure refinement for the perchlorate salts of the cations Co 1b21 (endo isomer)
]
and Co 1a31 (hypodentate)
]
Parameters
Co 1b21 (endo isomer)
Co 1a31 (hypodentate)
]
]
Empirical formula
Formula weight
T [K]
[C18H31CoN7S](ClO4)2 ꢁ H2O
[C17H30CoN7S](ClO4)3 ꢁ 0.5H2O
653.40
729.82
150(2)
90.0(2)
´
˚
Wavelength [A]
0.71073
Triclinic, P-1
1.54178
Crystal system, space group
Unit cell dimensions:
Monoclinic, P21/c
´
˚
a [A]
12.8586(4)
16.3321(17)
´
˚
b [A]
13.9798(5)
9.2677(8)
´
˚
c [A]
15.8054(5)
37.298(3)
a [deg.]
b [deg.]
g [deg.]
84.507(1)
90
76.564(1)
97.291(6)
79.001(1)
90
´
3
˚
V [A ]
2708.73(15)
5599.9(9)
Z
4
4
Dcalc [g cmꢂ3
]
1.602
1.731
Absorption coefficient [mmꢂ1
]
0.968
8.807
F(000)
1356
3000
Crystal size [mm]
0.42 ꢀ 0.26 ꢀ 0.12
1.33 to 32.22
ꢂ19 , h , 19
ꢂ20 , k , 20
ꢂ23 , l , 23
49 467/19 118 (Rint 0.0311)
99.9 % to y 32.228
Multi-scan
0.20 ꢀ 0.10 ꢀ 0.02
2.388 to 67.991
ꢂ19 # h # 19
ꢂ4 # k # 10
ꢂ44 # l # 44
57 821/9614 (Rint 0.0487)
94.5 % to y 67.6798
Semi-empirical from equivalents
0.8643 and 0.4714
Full-matrix least-squares on F2
9614/284/810
1.117
y range for data collection [deg.]
Limiting indices
Reflections collected/unique
Completeness
Absorption correction
Max. and min. transmission
Refinement method
0.8927 and 0.6866
Full-matrix least-squares on F2
19 118/0/761
1.083
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I . 2s(I)]
R indices (all data)
R1 0.0562, wR2 0.1282
R1 0.0713, wR2 0.1346
0.941 and ꢂ1.064
R1 0.0664, wR2 0.1722
R1 0.0916, wR2 0.1931
0.615 and ꢂ0.371
´
ꢂ3
˚
Largest diff. peak and hole [e A
]
125.10, 129.02, 139.73, 152.78; (C, CH2) 38.67, 41.23, 44.58,
46.03, 59.47, 136.65, 162.54, 169.92.
4.20 (s, 1H), 4.48 (s, 3H), 5.14 (q, J 2.5, 19.9, 2H), 5.48 (s, 1H),
5.61 (s, 1H), 7.34 (t, J 6.9, 1H), 7.43 (m, 4H), 7.56 (br s, 3H),
7.67 (t, J 6.3, 1H), 7.80 (d, J 8.5, 1H), 8.09 (t, J 8.2, 1H), 8.79 (d,
J 5.6, 1H), 9.36 (t, J 5.6, 1H). dC (400 MHz, d6-DMSO) (CH,
CH3) 122.09, 124.96, 127.48, 127.70, 128.50, 139.66, 152.89;
(C, CH2) 38.60, 41.05, 44.47, 44.53, 45.96, 58.98, 137.81,
163.25. Anal Calc. for CoSC18H31N7Cl3O12 ꢁ 2H2O: S 4.16,
Co 7.64, Cl 13.76. Found: S 4.21, Co 7.69, Cl 13.42 %.
Complex Co-1b31 (hypodenate): dH (400 MHz, d6-DMSO)
2.06 (s, 1H), 2.34 (s, 3H), 2.40 (s, 2H), 2.60 (s, 1H), 2.86 (s, 4H),
3.38 (s, 2H {water}), 3.86 (t, J 10.7, 1H), 4.05 (t, J 10.5, 1H), 4.37
(s, 1H), 4.51 (s, 1H), 5.22 (q, J 7.7, 19.1, 2H), 5.45 (s, 1H), 5.61
(s, 1H), 7.25 (d, J 7.5, 2H), 7.36 (d, J 7.5, 2H), 7.56 (br s, 3H), 7.69
(t, J 6.4, 1H), 7.84 (d, J 7.8, 1H), 8.11 (t, J 7.2, 1H), 8.78 (d, J 5.6,
1H), 10.69 (s, 1H). dC (400 MHz, d6-DMSO) (CH, CH3) 20.47,
121.82, 122.14, 125.10, 129.43, 139.71, 152.80; (C, CH2) 38.64,
41.21, 44.57, 46.01, 59.42, 133.96, 134.47, 162.63, 170.03. Anal
Calc. for CoSC18H31N7Cl3O12 ꢁ H2O: S 4.26, C 28.72, H 4.42,
N 13.02. Found: S 4.39, C 28.66, H 4.39, N 13.02 %.
Isolation of Bidentate Products (Fig. 4a, b)
The maroon and orange bands collected from the column
(see above) for the reaction of ligand 1b were diluted 10-fold
with water and resorbed onto SPC-25, washed with water, and
then removed with 0.5 M Ba(ClO4)2. Dark maroon crystals were
formed from the maroon band (endo isomer) and an orange
powder was formed from the orange band (exo isomer) upon
refrigeration at 48C.
Complex Co-1c31 (hypodentate): dH (400 MHz, d6-DMSO)
2.06 (s, 1H), 2.27 (s, 1H), 2.37 (s, 1H), 2.50 (s, 1H), 2.85 (s, 4H),
3.40 (s, 6H {water}), 3.75 (s, 3H), 3.80 (t, J 10.7, 1H), 3.99 (t, J
10.5, 1H), 4.29 (s, 1H), 4.43 (s, 1H), 5.19 (q, J 7.7, 19.1, 2H),
5.38 (s, 1H), 5.56 (s, 1H), 7.00 (d, J 8.2, 2H), 7.36 (d, J 8.2, 2H),
7.56 (br s, 2H), 7.66 (t, J 6.2, 1H), 7.79 (d, J 8.2, 1H), 8.08 (t, J
7.6, 1H), 8.77 (d, J 5.1, 1H), 10.59 (s, 1H). dC (400 MHz, d6-
DMSO) (CH, CH3) 55.27, 114.13, 122.10, 124.26, 125.07,
139.67, 152.98; (C, CH2) 38.66, 41.13, 44.53, 45.97, 59.26,
128.98, 156.98, 162.68, 170.33.
Co-1b21 (endo) maroon: dH (400 MHz, d6-DMSO) 1.61 (s,
1H), 2.28 (s, 3H), 2.50 (m, 7H), 3.33 (s, 1H), 3.40 (s, 2H
{water}), 3.91 (s, 1H), 4.42 (q, J 45.4, 16.5, 2H), 4.48 (s,
1H),4.64 (s, 1H), 4.74 (s, 1H), 4.84 (s, 1H), 5.16 (s, 1H), 5.38
(s, 1H), 7.21 (m, 5H), 7.31 (t, J 6.6, 1H), 7.48 (d, J 8.1, 1H), 7.82
(t, J 8.1, 1H), 8.13 (t, J 6.6, 1H), 8.50 (d, J 4.0, 1H). dC (400 MHz,
d6-DMSO) (CH, CH3) 20.68, 121.04, 121.30, 126.05, 130.57,
136.82, 148.67; (C, CH2) 43.47, 44.68, 44.78, 44.99, 45.82,
135.45, 137.90, 157.75, 175.00.
Complex Co-231 (hypodentate): dH (400 MHz, d6-DMSO)
2.03 (br s, 1H), 2.25 (br s, 1H), 2.37 (br s, 2H), 2.84 (br s, 4H),
3.40 (s, 4H {water}), 3.78 (t, J 11.8, 1H), 3.99 (t, J 11.8, 1H),

942
L. Roecker et al.
Co-1b21 (exo) orange: dH (400 MHz, d6-DMSO) 2.20
bond lengths (Tables S1 and S3) and angles (Tables S2 and S4)
are provided as Supplementary Material. Crystallographic
information files have been deposited with the Cambridge
Crystallographic Data Centre and assigned the deposition codes
178348 and 981038. These can be obtained free of charge via
http://www.ccdc.cam.ac.uk/data_request/cif.
(s, 1H), 2.29 (s, 3H), 2.5 (m, 7 H), 3.40 (s, 8H {water}), 3.98
(s, 1H), 4.37 (q, 4H), 4.66 (s, 1H), 4.78 (s, 2H), 4.95 (s, 1H), 5.16
(s, 1H), 7.19 (m, 5H), 7.37 (t, J 6.6, 1H), 7.52 (d, J 8.1, 1H), 7.86
(t, J 8.1, 1H), 8.63 (d, J 3.8, 1H), 9.74 (s, 1H). dC (400 MHz,
d6-DMSO) (CH, CH3) 20.46, 122.57, 122.99, 123.56, 137.46,
148.96; (C, CH2) 43.75, 44.47, 44.96, 45.50, 50.39, 133.97,
134.37, 156.85, 172.92.
Supplementary Material
Tables of all bond lengths and angles for the two structures
(Tables S1–S4), an expanded version of Fig. 8 (Fig. S1), along
with HMQC NMRs of Co-1b31 and Co-231 (Figs S3 and S4)
are available on the Journal’s website.
Isolation of Side Products
[(en)2Co(CO3)]ClO4. The pink band that eluted first
was allowed to evaporate until dark pink crystals formed.
dH (200 MHz, D2O) 2.92 (br m); (200 MHz, d6-DMSO) 2.5
(br, 8H), 3.88 (s, 2H), 4.40 (s, 2H), 4.52 (s, 2H), 4.98 (s, 2H).
dC (200 MHz, d6-DMSO) 43.76, 44.20, 164.71. m/z 239 ([Mþ]) .
Calc. molecular weight 338.6.
Acknowledgements
Funding for the Thermo Finnigan LCQ Deca Max was through NSF Grant
0421581 to Matthew Saderholm at Berea College. The authors thank Emily
Fletcher and Say Lee Teh for obtaining the mass spectrometry data. Initial
funding for this work was provided by the Appalachian College Association,
Berea, KY. JK thanks Dr Alan Pinkerton (Department of Chemistry,
University of Toledo, Toledo, OH 43606 USA) for the use of the SMART
6000 diffractometer.
Black Product. The black product accounts for 10–15 % of
the total mass of the reactants in all preparations and can be
brought to constant mass after two washings in refluxing
ethanol—the following results are for the product obtained
from the reaction of 1b. Found: Co 6.44, S 11.89, C 40.09, H
3.23, N 13.88 %. nmax (KBr)/cmꢂ1 3269, 3189, 1900, 1621,
1515, 1288 1166, 1032. m/z: [z ¼ ?] 633.
References
Caution: Although we have not experienced explosions,
perchlorate salts are potentially explosive and should be handled
only on very small quantities.
[1] L. Roecker, M. Aiyegbo, A. Al-Haddad, E. Fletcher, R. Kc, J. Hurst,
T. Lane, R. Larsen, N. Noinaj, S. L. Teh, S. K. Wade, S. Parkin, Aust.
J. Chem. 2013, 66, 944. doi:10.1071/CH13150
[2] L. Roecker, J. Akande, L. N. Elam, I. Gagua, B. W. Helton,
M. C. Prewitt, A. M. Sargeson, J. H. Swango, A. C. Willis, T. Xin,
J. Xu, Inorg. Chem. 1999, 38, 1269. doi:10.1021/IC980287P
[3] D. R. Richardson, D. S. Kalinowski, V. Richardson, P. C. Sharpe,
D. B. Lovejoy, M. Islam, P. V. Bernhardt, J. Med. Chem. 2009, 52,
1459. doi:10.1021/JM801585U
X-Ray Crystallography
[C18H31CoN7S](ClO4)2 ꢁ H2O {Co-1b21 (endo)}
and [C17H30CoN7S](ClO4)3 ꢁ 0.5H2O {Co-1a31
(hypodentate)}
X-Ray diffraction data were collected at either 150(2) K on a
standard Siemens SMART 6000 CCD diffractometer using
MoKa radiation (endo isomer) or at 90 K on a Bruker-Nonius
X8 Proteum diffractometer using CuKa radiation (hypodentate).
Crystalsofthe endoisomer wereobtained as darkpink-redplates,
while those of the hypodentate compound were thin red flakes. In
each case, crystals were mounted in polyisobutene oil and
mounted directly into a cold-stream of N2 gas. Data frames were
integrated using either SAINT or SAINT-Plus.[19] The data were
corrected for decay, Lorentz and polarisation effects. Absorption
and beam irregularities were corrected by the multi-scan tech-
nique in SADABS[20] and by XABS2[21] (hypodentate). Both
structures were solved using direct methods in SHELXS,[22] and
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Both the endo isomer and the hypodentate compound were
perchlorate salts, and each crystallised as hydrates with two
independent molecules in the asymmetric unit. In addition, both
compounds exhibited disorder, as is common with ethylenedia-
mine ligands.[23,24] Hydrogen atoms were found in difference
maps and refined using a combination of riding models and free
refinement with isotropic displacement parameters derived from
their carrier atoms. Water hydrogen atoms in the endo isomer
structure were fixed, while those in the hypodentate structure
were refined with restraints. Non-hydrogen atoms were refined
with anisotropic displacement parameters. Atomic scattering
factors were taken from the International Tables for Crystallo-
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the hypodentate compound by an R-tensor.[27]
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[8] D. B. Cordes, R. T. Tarak, S. M. McDonald, S. A. Cameron,
C. R. Clark, A. G. Blackman, Polyhedron 2013, 52, 1227. doi:10.1016/
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1451 and references therein. doi:10.1021/IC00332A038
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U. Bierbach, Inorg. Chem. 2002, 41, 7159. doi:10.1021/IC025744N
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1973, 12, 2690. doi:10.1021/IC50129A038
[16] M. H. Dickman, R. J. Doedens, E. Deutsch, Inorg. Chem. 1980, 19,
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[17] D. P. Fairlie, W. G. Jackson, G. M. McLaughlin, Inorg. Chem. 1989,
28, 1983. doi:10.1021/IC00309A043
Crystal data and relevant details of the structure determina-
tion are summarised in Table 3 and selected geometrical para-
meters are given in Tables 1 (endo) and 2 (hypodentate). All
[18] F. D. Sancilio, L. F. Druding, D. M. Lukaszewski, Inorg. Chem. 1976,
15, 1626. doi:10.1021/IC50161A031
[19] Bruker-AXS, SAINT/SAINT-Plus 2008 (Bruker-AXS: Madison, WI).

Hypodentate Coordination of Ethylenediamine
943
[20] G. M. Sheldrick, SADABS 1996 (University of Goettingen:
Goettingen).
[25] International Tables for Crystallography, Vol. C: Mathematical,
Physical and Chemical Tables (Ed. A. J. C. Wilson) 1992
(Kluwer Academic Publishers: Dordrecht).
[21] S. Parkin, B. Moezzi, H. Hope, J. Appl. Crystallogr. 1995, 28, 53.
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[22] G. M. Sheldrick, Acta Crystallogr. 2008, 64, 112. doi:10.1107/
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[23] L. Pu, T. Hasegawa, S. Parkin, H. Taube, J. Am. Chem. Soc. 1992, 114,
7609. doi:10.1021/JA00045A070
[26] A. L. Spek, J. Appl. Cryst. 2003, 36, 7. doi:10.1107/
S0021889802022112
[27] S. Parkin, Acta Crystallogr. 2000, 56, 157. doi:10.1107/
S010876739901497X
[24] T. Hasegawa, A. Li, S. Parkin, H. Hope, R. K. McMullan,
T. F. Koetzle, H. Taube, J. Am. Chem. Soc. 1994, 116, 4352.
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