Catalytic Cleavage of the Amide Bond in Urea Using a Cobalt(III) Amino-Based Complex

Article abstract of DOI:10.1002/ejic.201800975

The urease mimetic activity of Co^III amine complexes with respect to cleavage of urea was explored using SCXRD and spectroscopic techniques. The reaction of [Co^III(tren)Cl₂]Cl [tren = tris(2-aminoethyl)amine] with urea results in the formation of an isocyanato complex {[Co^III(tren)(NH₃)(NCO)]Cl₂} and ammonia, following the cleavage of the amide bond. The reaction progress and the subsequent formation of cleavage products were confirmed by SCXRD analysis of the reactants as well as the products obtained during the reaction. The reaction was found to be pH and temperature dependent, and the reaction conditions were optimized to maximize conversion. The reaction kinetics was followed spectroscopically (¹H NMR and UV/Vis), following the decrease in urea concentration or the increase in pH succeeding ammonia formation. A detailed kinetic study revealed an overall second order rate law and k_obs was found to be 3.89 × 10^–4 m^–1 s^–1.

Full text of DOI:10.1002/ejic.201800975

A Journal of
Accepted Article
Title: Catalytic cleavage of the amide bond in urea using a Co(III)
amino-based complex
Authors: Bhawna Uprety, Charmaine Arderne, and Ivan Bernal
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10.1002/ejic.201800975
European Journal of Inorganic Chemistry
FULL PAPER
Catalytic cleavage of the amide bond in urea using a Co(III)
amino-based complex
Bhawna Uprety,[a] Charmaine Arderne,* [a] and Ivan Bernal[b]
Abstract: The urease mimetic activity of Co(III) amine complexes with
respect to cleavage of urea was explored using SCXRD and
spectroscopic techniques. The reaction of [CoIII(tren)Cl2]Cl (tren =
tris(2-aminoethyl)amine) with urea results in the formation of an
isocyanato complex ([CoIII(tren)(NH3)(NCO)]Cl2) and ammonia,
following the cleavage of the amide bond. The reaction progress and
the subsequent formation of cleavage products was confirmed by
SCXRD analysis of the reactants as well as the products obtained
during the reaction. The reaction was found to be pH and temperature
dependent, and the reaction conditions were optimized to maximize
conversion. The reaction kinetics was followed spectroscopically (1H
NMR and UV-Vis), following the decrease in urea concentration or the
increase in pH succeeding ammonia formation. A detailed kinetic
study revealed an overall second order rate law and kobs was found to
be 3.89 × 10-4 M-1 s-1.
At the active site, Urease contains two nickel ions bridged by a
carbamylated lysine and a hydroxide ion[16–18]. Although, the exact
mechanism of its action is still under debate, there are two globally
accepted hypotheses. The first is: urea binds to one of the Ni
centres through its carbonyl moiety, while the hydroxide
coordinated to the second Ni then initiates a nucleophilic attack
on urea, thus beginning the hydrolysis reaction. The second is:
urea coordinates in a bidentate fashion to one of the Ni(II) centres
and an amino acid residue on the second Ni(II) centre, leaving the
hydroxide bridge intact. The hydroxide bridge then attacks the
urea carbonyl group in a nucleophilic manner, initiating the
hydrolysis[9,19–22]. Subsequently, the coordinated hydroxide ligand
is crucial to the active site of Urease. This observation might play
a pivotal role in designing synthetic Urease mimics, as was
evident in our study as well. There is sufficient evidence of several
Urease mimics based on polydentate as well as linear ligands
documented in literature. Most of them report the coordination of
urea to the metal centres via the carbonyl oxygen while
coordination via nitrogen is rather scarce[23–26]. Nevertheless, the
majority of synthetic urease mimics follow an elimination
mechanism giving iso/cyanates as the major products along with
ammonia, and therefore designing of a true Urease mimic has
been an intriguing challenge globally. However, in a few cases,
the subsequent decomposition of iso/cyanates into carbon
dioxide and ammonia under suitable reaction conditions has also
Introduction
Urease (urea amidohydrolase; E.C.3.5.1.5) is a nickel–dependent
dinuclear metallohydrolases, present in various plants and
microorganisms, that catalyses the hydrolysis of urea to ammonia
and carbon dioxide (and small amides to the corresponding
carboxylic acids)[1–4]. This enzymatic hydrolysis causes an abrupt
increase of
pH, having direct medical and agricultural
been observed[25,27–29]
.
consequences[3–6]. The enzyme plays vital roles in nitrogen
metabolism of plants and microorganisms[7,8]. Urease is an
interestingly skilled enzyme system, since its substrate urea, has
a remarkable stability with a half-life of about 3.6 years; and it
does not undergo spontaneous hydrolysis in aqueous
solutions[9,10]. Instead its aqueous decomposition follows an
elimination route, giving isocyanic acid or ammonium cyanate as
one of the reaction products irrespective of the pH of the
solution[7,11–13]. However, this non catalytic elimination proceeds
sluggishly with a rate constant ranging from 8.3 × 10–10 – 1.2 ×
Recently, there has been an emerging interest in the
catalytic activity of Cobalt (III) complexes[30–32]. The mechanistic
studies suggest catalytic activation via different kinds of
interactions with diverse organic substrates[33]. The applicability of
Co(III) amine complexes towards mediating peptide/amide bond
hydrolysis
in
carnosine
and
pyrazine–2–monoamide,
salicylaldehyde, etc. have been reported recently by some of
us[34–36]. This encouraged us to examine whether these Co(III)
amine complexes could also hydrolyse urea; and if so, could we
determine the underlying mechanistic and/or kinetic pathways.
Therefore, this study focuses on the catalytic activity of a
compound of the tris(2-aminoethyl)amine (tren) ligand complexed
to a Co(III) metal centre on urea.
10–11 s–1 at 25 oC[14,15]
.
[a]
[b]
B, Uprety; C, Arderne
Department of Chemistry
University of Johannesburg
PO Box 524, Auckland Park 2006, Johannesburg, South Africa
E-mail: carderne@uj.ac.za
Results and Discussion
I, Bernal
Molecular Sciences Institute, School of Chemistry
University of the Witwatersrand, 2050
Johannesburg, South Africa
[CoIII(tren)Cl2]Cl (1) was prepared in excellent yields following a
two–step synthetic method as reported in literature[37]. The
intermediate nitro complex, [CoIII(tren)(NO2)2]Cl[38] (1a) as well as
the final [CoIII(tren)Cl2]Cl (1) compound, were well characterized
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejic.201800975
European Journal of Inorganic Chemistry
FULL PAPER
by various spectroscopic techniques (FT–IR, NMR, UV–Vis,
HRMS) as well as by Single-crystal XRD (SCXRD) analysis. They
are both air stable solids soluble in water, and sparingly soluble
in alcohols. Compound (1) was recrystallized from both water and
concentrated HCl (32%), resulting in two different complexes,
Phenolphthalein is a good indicator of choice in this case, since it
shows a visible colour change in alkaline pH range 8.2 – 12. The
catalytic reactions were performed at pH 9  0.05 in the presence
of hydroxide ions. Interestingly, no reaction was observed in the
absence of hydroxide, whereas the reaction was too slow to be
quantified at lower pH ranges.
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3),
((1)2·(Cl)(H7O3))
and
[CoIII(tren)Cl2]Cl·H2O, (1·H2O) respectively. The first is complex
(I): Dichloro(tris-2-amino(ethylamine))cobalt(III) chloride hydrate
whose crystals were obtained from the reaction mixture mother
liquor and recrystallized from 32% HCl. The second is complex
(II): Bis-(dichloro(tris-2-amino(ethylamine))cobalt(III)dichloride)
dihydrate hydroxonium chloride whose crystals were obtained
from the reaction mixture mother liquor and recrystallized from
water. Therefore, the solvent of crystallization plays an important
role in stabilizing the resulting structure of the compound. This
was corroborated by recording the HRMS (Figures S1 and S2) of
the complex before and after crystallization. The HRMS spectrum
of the crude compound before crystallization displays an intense
peak at 275.0232 which corresponds to [CoIII(tren)Cl2] (calc.
275.0241). However, the HRMS spectrum for the complex (II)
obtained after crystallization from water, has an intense molecular
ion peak at 735.1824 which can be attributed to
([CoIII(tren)Cl2]Cl)2·(Cl)(3H2O)(Na) (calc. 735.5320) in solution. All
reactions of [CoIII(tren)Cl2]Cl (1) were carried out using complex
(II), ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3), ((1)2·(Cl)(H7O3)), as we
reasoned that since our reactions were aqueous, we should use
catalysts purified from water. The crystal structures of both
complex (1·H2O) and ((1)2·(Cl)(H7O3)) are presented and
discussed in this work for completeness.
In
a
typical
reaction,
an
aqueous
solution
of
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)), (10 mL, 4.5 × 10–
4
M) was set to pH 9  0.05 using 1 % LiOH solution, and was
then allowed to incubate at the same pH at room temperature for
about 1 hr, to stabilize the pH of the solution. Over the 1 hr of
incubation, the colour of the solution changed from purple to red
indicating the complete replacement of coordinated chlorides to
the aqua and/or hydroxide ligands. This conversion was also
monitored by UV–Visible spectroscopy following the progressive
addition
of
LiOH
solution
to
a
solution
of
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)) in water; and the
results are presented in supplementary information (Figure S3).
Next, an aqueous solution of urea (2 mL, 1 × 10–2 M) was mixed
with a pH adjusted aqueous solution of the catalyst (2 mL, 4.5 ×
10–4 M). The pH of the reaction mixture at this stage was still 9 
0.05. Phenolphthalein indicator (1 mL, 1 %) was added to this
solution and the resulting reaction mixture was incubated at 45 oC.
The reaction was then followed by monitoring the increase in
absorbance at 552 nm, due to the alkaline quinone form of
phenolphthalein which is only prevalent at basic pH, for a period
of 1 hr to obtain initial rates for the relevant kinetic calculations.
(Figure 1).
The application of Co(III) amine complexes similar to
[CoIII(tren)Cl2]Cl (1) towards hydrolysis of several bio–relevant
substrates such as phosphoesters, phosphodiesters, as well as
some dipeptides etc. are well documented in literature[34–36,39–41]
.
The present work explores the ability of [CoIII(tren)Cl2]Cl (1) to
catalyse the hydrolysis of amide bonds. For this purpose, we have
employed the simplest amide molecule – urea (Scheme 1). The
catalytic reactions were monitored by 1H NMR as well as UV–Vis
spectroscopy following the decrease in Urea concentration and
the formation of ammonia respectively.
Scheme 1. Hydrolysis of urea at pH 9  0.05 in the presence of LiOH and
catalysed by ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)) at 45 oC in water.
Figure 1. Increase in absorbance at 552 nm and the progress of reaction as
monitored by UV–Visible spectroscopy with the aid of phenolphthalein indicator.
Catalytic hydrolysis of urea: UV–Vis studies
Urease like hydrolysis of urea yields ammonia and carbamate
which decomposes to yield a second molecule of ammonia and
bicarbonate. The catalytic reaction induces an overall increase in
pH[3]; consequently, the reaction progress can be monitored
passively, with the help of a pH dependent colour indicator assay.
Similar Urease studies involving different pH dependent indicator
assays such as phenol red and phenolphthalein are well
Co(III) chlorido systems are known to undergo rapid hydrolysis in
aqueous systems, giving the corresponding [CoIII(L)(OH)(H2O)]2+
species in solution. The [CoIII(L)(OH)(H2O)]2+ species is believed
to be the dominant species at alkaline pH and is actively involved
in catalysing hydrolysis reactions[44]. This can be corroborated
with the actual Urease enzyme activity; where the carbamate
bridge between the two Ni centres is hydrolysed to a hydroxide
documented in literature[4,8,42,43]
.
We have performed our
bridge initiating the catalytic activity in Urease[16–18] Therefore,
.
reactions using phenolphthalein indicator assay to measure the
catalytic activity of ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)).
formation of the hydroxido active intermediate can be considered
crucial to catalytic activity. This can partly explain the inactivity of
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10.1002/ejic.201800975
European Journal of Inorganic Chemistry
FULL PAPER
the precursor [CoIII(tren)(NO2)2]Cl (1a) complex towards urea
hydrolysis, since the nitro groups are resistant to hydrolysis under
alkaline aqueous conditions. The formation of this active
intermediate hydroxide species in solution during our reaction,
was followed by sequential additions of an aqueous solution of
However, the reaction was also performed with larger
quantities, in an attempt to isolate any possible intermediates
and/or products. Therefore, to an aqueous solution of urea (17
mmol, 30 mL) was added 0.535
g (0.75 mmol) of
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)). The pH of the
LiOH (1
×
10–3 M) to an aqueous solution of
resulting solution was set to 9  0.05 with freshly prepared
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)), (25 mL, 4.5 × 10–
10 % LiOH solution, and the solution was stirred at 45 C for
o
4
M) at room temperature. The reaction was monitored by UV–
about 2 hr. The reaction was then allowed to cool and stand at
room temperature, for a few days, after which diffraction quality
orange rod–like crystals precipitated out. The isolated product,
has a molecule of ammonia and an isocyanato group
coordinated to the metal centre, along with the base ligand,
tris(2–aminoethyl)amine [CoIII(tren)(NH3)(NCO)]Cl2 (2). The
isocyanic acid and ammonia are proposed to be the catalytic
products of urea cleavage reactions.
Visible spectroscopy and the results are included in the SI section.
The catalytic reaction conditions were optimized to maximize
reaction conversion. For this, some reaction parameters such
as reaction pH, temperature and catalyst amount were
evaluated. As mentioned earlier, the reaction was too slow at
pH below 9 to be quantified kinetically. The reaction did not
proceed at all at acidic pH; therefore, the reaction pH was
incubated to alkaline pH using the mild base LiOH. Similar
results have been reported by some of us, in the investigation
of conglomerate crystallization, where the cleavage of amide
bonds in small peptide molecules mediated by [Co(tren)Cl2]Cl
was observed[34–36]. Therefore, a reaction pH of 9  0.05 was
concluded essential for catalytic activity.
Next, the effect of temperature on the reaction rates was
evaluated. For this, six reactions, with the conditions as
o
described above, but with temperatures between 20 – 45 C
were performed. Thus, a solution of urea (2 mL, 1 × 10–2 M)
was treated with a solution of ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3)
((1)2·(Cl)(H7O3)) (2 mL, 4.5 × 10–4 M) set at pH 9  0.05 with
o
o
o
o
o
LiOH at six temperatures, 20 C, 25 C, 30 C, 35 C, 40 C
o
and 45 C in the presence of phenolphthalein indicator (1 ml,
Next, the effect of catalyst concentration was evaluated. A set
of different reactions, with the same conditions as described
above, but with varying catalyst concentration were performed.
The reaction progress was monitored by UV–Visible
spectroscopy as described above. Three parallel reactions
1%). The reactions were monitored by UV–Visible
spectroscopy on a kinetic run mode and the initial rates were
obtained as triplicates assuming pseudo first order kinetics. As
can be seen from Figure 3, the rate of the reaction increased
with increasing temperature and thus 45 oC was chosen as the
ideal temperature for catalytic activity.
were set using 4.5 × 10–5 M, 4.5 × 10–4 M and 4.5 × 10–3
M
catalyst concentrations (~ 1:1000, 1:100, 1:10 catalyst :
substrate ratio respectively) set at pH 9  0.05 with LiOH and
1×10–2 M urea solution at 45 oC in the presence of
phenolphthalein indicator (1 ml, 1%). The resulting spectral
changes are presented in Figure 2. As can be seen from Figure
2, increasing the catalyst concentration increased the rate of
the reaction, a common observation in catalysed reactions.
However, to perform kinetic studies, and have quantifiable
results, the average ratio (~ 1:100) for catalyst and substrate
concentration was chosen for kinetic experiments.
Figure 3. Effect of temperature on the increment in absorbance at 552 nm
with time for the hydrolysis of urea (1
×
10–2 M) catalysed by
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)) (4.5 × 10–4 M) at pH 9  0.05,
in the presence of LiOH, at temperature ranging from 20 – 45 oC.
Furthermore, the initial rates obtained at different temperatures
were then fitted to the Arrhenius equation, according to
equation 1 (Figure 4). The activation energy, Ea, for the
generation of ammonia during the initial steps of urea
hydrolysis was found to be 10.2 kJ mol–1. The literature
activation energy values for the actual Urease enzyme ranges
between 18 – 30 kJ mol–1[42]. The optimised temperature and
Figure 2. Change in absorbance at 552 nm during the course of reaction,
with different catalyst to substrate ratios.
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10.1002/ejic.201800975
European Journal of Inorganic Chemistry
FULL PAPER
pH for the catalytic reaction were found to be considerably
higher than the enzymatic hydrolysis. The intermediate
isolated
during
the
catalytic
reaction,
[CoIII(tren)(NH3)(NCO)]Cl2 (2) contains isocyanato and
ammonia ligands coordinated to the metal centre, both of
which are proposed to result from an elimination mechanism
rather than hydrolytic cleavage of urea (vide infra).
k = A exp (-Ea/RT)
Equation (1)
Figure 5. 1H NMR monitoring of the hydrolysis of urea catalysed by
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)) at pH
9  0.05, in the
presence of LiOH, at 45 oC. Reaction conditions: urea (4 mmol),
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)) (0.17 mmol), pH 9  0.05,
temperature 45 oC, solvent D2O + CH3OD. (The signals for the catalyst are
not seen prominently due to low concentration as compared to the catalyst
as well as the internal standard)
As the reaction progressed, the intensity of the urea signal
decreased over time. The formation of ammonia could not be
1
ascertained from H NMR studies, since the reactions were
Figure 4. Arrhenius plot for ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3))
catalysed hydrolysis of urea at pH 9  0.05. Reaction conditions: urea (2 ml,
1 × 10–2 M), [Co(tren)Cl2]Cl (2 mL, 4.5 × 10–4 M), phenolphthalein (1 ml, 1%),
temperature ranging from 20 – 45 oC.
performed in D2O, and therefore the ammonia protons could
not be seen in the spectra. It is important to note that although
the urea amine protons also merge with the signal for D2O, the
integration with respect to the internal standard at t = 0 time
was six, allowing a possible kinetic monitoring of the reaction,
following the decrease in urea concentration. The reaction was
monitored for a period of 12 hr during which a total conversion
of 60 % was estimated. However, since the signals for
ammonia protons could not be properly identified, the exact
Catalytic hydrolysis of urea: NMR studies
1
The catalytic hydrolysis of urea was also followed by H
NMR spectroscopic reaction monitoring. The reaction progress
was analysed by following the decrease in urea concentration
over time. In a typical reaction, urea (0.240 g, 4.0 mmol) was
conversion cannot be stated unequivocally.
All kinetic calculations were performed assuming pseudo
first order kinetics, thus maintaining an ~ 25-fold excess of
substrate concentration with respect to the catalyst
concentration. All calculations were performed using initial
reaction rates. The rate of the catalytic reaction can be
obtained by considering the integrated rate law (equation 2).
The plot of log of decrease in concentration of urea with time
is shown in Figure 6. Since the concentration of the catalyst
can be assumed to be remaining almost constant during the
reaction, the reaction can be assumed to be following first
order kinetics with respect to the substrate, i.e. urea. This is
also apparent from the straight-line fit obtained in Figure 6.
Consequently, the resulting pseudo first order rate constant
was found to be 3.5 × 10–5 s–1.
added to
a
solution of ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3)
((1)2·(Cl)(H7O3)) (0.124 g, 0.17 mmol, 10 mL D2O) and
adjusted to pH 9  0.05 with LiOH. A small aliquot of the
reaction mixture (0.5 µL) was withdrawn into an NMR tube and
analysed by 1H NMR spectroscopy at 45 oC in the presence of
CH3OD as the internal reference, every 15 minutes on a 12 hr
time scale. Figure 5 presents the spectral changes during the
initial two hours.
Rate = kobs[Urea]a[Catalyst]b
Rate = k1[Urea]a
Equation (2)
(assuming pseudo first order kinetics)
where k1 = kobs[Catalyst]b
lnk1 = lnkobs + bln[Catalyst]
Equation (3)
Equation (4)
Equation (5)
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10.1002/ejic.201800975
European Journal of Inorganic Chemistry
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1
Based on all the kinetic calculations using UV–Visible and H
NMR reaction monitoring, we propose the following catalytic
mechanism (Scheme 2). The catalyst (precursor)
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)), reacts with
LiOH to give the active catalytic species, [CoIII(L)(OH)(H2O)]2+,
the formation of which is quite well documented in
literature[41,44]. This active catalytic species then hydrolyses
urea to yield ammonia and possibly isocyanic acid, which
coordinates
to
the
metal
centre
yielding
[CoIII(tren)(NH3)(NCO)]Cl2 (2), the formation of which was
confirmed by SC–XRD studies. However, the formation of
[CoIII(tren)(NH3)(NCO)]Cl2 (2) is reversible, otherwise it would
lead to catalyst poisoning rendering the catalyst inactive for the
next catalytic cycle; our reactions worked even at 1:1000
catalyst to substrate ratio, indicating the catalytic nature of the
reaction. The possibility of catalyst poisoning is also negated
by the fact that the order of the reaction with respect to the
catalyst was found to be close to unity. However, it must also
be noted that no signal due to the isocyanato carbon could be
observed in the reaction mixture even after 12 hr of reaction
time. Interestingly, most synthetic Urease models coordinate
urea via the carbonyl oxygen resulting in the formation of
cyanato complexes and the liberation of ammonia. However,
the coordination of urea to the metal centre via one of the
nitrogen atoms has also been observed in a few cases,
especially with soft metal centres. Some of these reports also
account for an increased tendency of the coordinated urea to
decompose into ammonia and carbon dioxide[14,29,45]. A similar
elimination reaction pathway is proposed to operate in our
reactions as well. The reaction is initiated by the coordination
of urea to the Co(III) centre through nitrogen which is followed
by a subsequent electrophilic attack by the coordinated
hydroxide ligand onto the carbonyl carbon of urea (Scheme 2).
This coordination of urea is substantiated by the isolation of
[CoIII(tren)(NH3)(NCO)]Cl2 (2). Thus, we can conclude that
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)) successfully
hydrolyses the amide bond in urea to give ammonia and
possibly a molecule of isocyanic acid. The liberation of
ammonia and the subsequent increase in reaction pH was
confirmed and monitored by UV–Visible spectroscopy.
However, the exact fate of isocyanic acid and/or its
decomposition into carbon dioxide could not be ascertained
unambiguously. All the determined kinetic data has been
compiled in Table 1.
Figure 6. Variation of [Urea] with time for the catalytic hydrolysis reaction of
urea catalysed by ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)) at pH 9 
0.05, in the presence of LiOH, at 45 oC. Reaction conditions: [Urea]0 = 4
mmol, [catalyst] = (0.17 mmol), solvent D2O + CH3OD.
Using equations 2 – 5, the order of the reaction with respect to
the catalyst can also be determined. Thus, the initial rates for
the hydrolysis of urea by ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3)
((1)2·(Cl)(H7O3)) at pH 9  0.05, in the presence of LiOH, at 45
oC were determined for different initial concentrations of the
catalyst (and consequently LiOH). The reactions were
performed similarly as explained above and the resulting plot
from equation 5 is shown in Figure 7. Thus, the order of the
reaction with respect to the catalyst was found to be 0.81, and
kobs for the catalytic hydrolysis of urea was found to be 3.89 ×
10–4 M–1 s–1.
Table 1. Kinetic data obtained for the catalytic hydrolysis of urea catalysed
by [Co(tren)Cl2]Cl at pH 9  0.05, in the presence of LiOH, at 45 oC.
Figure 7. Plot of ln k1 versus ln[catalyst] for the hydrolysis of urea catalysed
by ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)) at pH 9  0.05, in the
presence of LiOH, at 45 oC.
Catalyst
kobs
Ea*
TOF
h-1
(TON)
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3),
3.89 × 10–4
M–1 s–1
10.2 kJ
mol-1
1.2
The overall integrated rate law for the hydrolysis of urea in the
presence of excess alkali can be represented as:
((1)2·(Cl)(H7O3))
(14.11)
* The activation energy corresponds to only the genration of ammonia and
does not necessarily relate to the overall reaction.
Rate = kobs [Urea][catalyst] at 45 oC and pH = 9  0.05.
kobs = 3.89 × 10–4 M–1 s–1
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10.1002/ejic.201800975
European Journal of Inorganic Chemistry
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Table 2. Hydrogen-bond geometry of [CoIII(tren)Cl2]Cl)2·(Cl)(H7O3),
(1)2·(Cl)(H7O3) (Å, º)
D—H···A
D—H
H···A
D···A
D—H···A
142 (2)
144 (2)
143 (2)
165 (3)
161 (3)
146 (2)
141 (2)
155 (3)
154 (2)
176 (3)
170 (2)
165 (2)
169 (3)
N2—H2A···Cl4i
N2—H2B···Cl1ii
N3—H3A···Cl2i
N3—H3B···Cl7i
N4—H4A···Cl1ii
N4—H4B···Cl7i
N6—H6C···Cl6iii 0.90 (3)
N6—H6D···Cl5iii 0.73 (3)
N7—H7A···Cl7iv 0.88 (1)
N7—H7B···Cl5iii 0.87 (1)
0.87 (1)
0.88 (1)
0.87 (1)
0.88 (1)
0.86 (1)
0.86 (1)
2.69 (2)
2.58 (2)
2.65 (2)
2.43 (2)
2.66 (2)
2.53 (2)
2.58 (3)
2.68 (3)
2.45 (2)
2.41 (1)
2.54 (2)
2.57 (2)
2.16 (2)
3.417 (2)
3.331 (2)
3.380 (2)
3.290 (2)
3.483 (2)
3.281 (2)
3.325 (3)
3.359 (3)
3.270 (2)
3.279 (2)
3.409 (2)
3.425 (2)
2.997 (2)
Scheme 2. Proposed mechanism for the hydrolysis of urea by
[Co(tren)Cl2]Cl at pH 9  0.05, in the presence of LiOH, at 45 oC (showing
urea attack via nitrogen atom)
N8—H8A···Cl2i
N8—H8B···Cl7iv 0.88 (1)
0.88 (1)
Structural characterization
O1S—
H1SA···Cl5v
0.85 (1)
0.86 (1)
0.86 (1)
0.85 (1)
0.85 (1)
0.83 (1)
0.84 (1)
Bis-(dichloro(tris-2-amino(ethylamine))cobalt(III) chloride)
O1S—
1.62 (2)
1.61 (2)
2.26 (2)
2.16 (2)
2.20 (2)
2.35 (2)
2.472 (3)
2.460 (3)
3.098 (2)
2.991 (2)
3.021 (2)
3.134 (2)
177 (3)
173 (3)
173 (3)
166 (3)
170 (3)
155 (3)
hydroxonium
chloride,
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3),
H1SB···O2Svi
O1S—
H1SC···O3Si
((1)2·(Cl)(H7O3))
Complex II, [2(C6H18Cl2CoN4Cl2)∙2H2O H3O+ Cl−], is a dimeric
neutral Co(III) complex bearing two tris(2-aminoethyl)amine
(tren) ligands coordinated to two Co(III) cations. Charge
balance on the Co(III) occurs via four coordinated and two free
Cl− anions; one hydroxonium (H3O+) cation is found to be
present in the structure and this cation is charge balanced with
one chloride anion. There are also two water molecules
present, both of which are adjacent to the H3O+, yielding a
O2S—
H2SA···Cl5iv
O2S—
H2SB···Cl6i
O3S—
H3SA···Cl6i
O3S—
+
combined hydroxonium ionic aggregate of the form H7O3 ,
H3SB···Cl7
which stabilizes the entire structure. The complex crystallizes
in the centrosymmetric space group, P21/n (see Figure 8). As
mentioned above, this complex is an example of a molecular
ionic aggregate as described by Bernal and Watkins[47] in the
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+3/2, y+1/2, −z+3/2; (iii) x,
y−1, z; (iv) −x+1/2, y−1/2, −z+1/2; (v) −x+1/2, y−1/2, −z+3/2; (vi) −x+1, −y,
−z+1.
+
form H7O3 . This is derived from the fact that the hydroxonium
The classification of this structure as a molecular ionic
aggregate comes from the analysis of the hydrogen-bonding
pattern that arises from a chain of hydrogen bonding evident
between a centralized hydroxonium cation and two adjacent
water molecules (see Figure 8). This structure fits in perfectly
ion hydrogen bonds to the two water molecules resulting in
three oxygen atoms and seven hydrogen atoms in the
aggregate. As previously mentioned, the hydroxonium cation
is charged balanced by a corresponding chloride anion. In
each of the cations, there are four N atoms of the tren ligand
that bind to one each of the Co(III) atoms in a quadridentate
mode, resulting in a tripodal-type conformation with Co−N
bond distances ranging from 1.935(2) – 1.966(2) Å. The
coordination environment of the both of the Co(III) atoms is
observed to have distorted octahedral geometry where the
bond angles range from 86.28(9) – 95.17(7) . (Refer to the
Supplementary Information for detailed geometrical
parameters). These distances and angles are similar to related
complexes that have been published previously where a full
geometry check carried out with the Mogul Geometry Check
tool[46], within the CSD suite of programs, showed no unusual
geometrical parameters.
+
with the previous analysis[47] carried out, especially for H7O3
cases. The O∙∙∙O distance between O1S and O2S = 2.472(3)
Å and between O1S and O3S = 2.460(3) Å, which fits their
description and analysis of these complexes and thus adds to
their work on these aggregates.
There is evidence of hydrogen bonding present in this structure
(see Figure 8 – indicated by the dashed lines). Details of the
hydrogen bonding geometry appears in Table 2 below:
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10.1002/ejic.201800975
European Journal of Inorganic Chemistry
FULL PAPER
Table 3. Hydrogen-bond geometry of [CoIII(tren)(NCO)(NH3)]Cl2 (2) (Å, º)
D—H···A
D—H
H···A
D···A
D—H···A
146 (3)
N3—H3A···Cl1ii 0.88 (1)
N3—H3B···Cl1i 0.88 (1)
N6—H6A···Cl1ii 0.88 (2)
2.47 (2)
2.40 (2)
2.50 (5)
2.46 (4)
3.243 (3)
3.232 (3)
3.326 (2)
3.326 (2)
160 (3)
157 (10)
168 (14)
N6—
0.88 (2)
H6B···Cl1iii
N6—H6C···O1iv 0.87 (2)
N4—H4A···Cl1 0.88 (2)
N4—H4B···Cl1i 0.88 (2)
2.10 (2)
2.34 (2)
2.58 (4)
2.952 (5)
167 (4)
177 (6)
131 (5)
3.2222 (16)
3.2222 (16)
Symmetry codes: (i) x, −y+1/2, z; (ii) −x+1/2, y−1/2, z+1/2; (iii) −x+1/2,
−y+1, z+1/2; (iv) x, y, z−1.
The yield of this material was extremely low with only a few
single crystals obtained and therefore this complex was only
characterized by Single-crystal X-ray Diffraction. There was
insufficient material for analyses by FTIR, NMR and UV-VIS.
Figure 8. Molecular structure of ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3),
((1)2·(Cl)(H7O3)) with displacement ellipsoids drawn at 50% probability,
showing the atomic numbering scheme where the heteroatoms have been
labelled only for clarity. Dashed red and green lines indicate hydrogen
bonds.
Ammonio(tris-2-amino(ethylamine))isocyanatocobalt(III)
dichloride [CoIII(tren)(NCO)(NH3)]Cl2 (2)
Complex III, [C7H21CoN6O∙2(Cl)], is a neutral Co(III) complex
bearing one tris(2-aminoethyl)amine (tren) ligand coordinated
to the Co(III) cation. Charge balance on the Co(III) occurs via
one coordinated isocyanato group (NCO−) and two free Cl−
anions. The complex crystallizes in the centrosymmetric space
group, Pnma (see Figure 9). A portion of this crystal structure
exhibits disorder – atoms N4, C4 and C5 (together with their
bonded H-atoms) are disordered over a mirror plane and the
occupancies for these atoms have been refined to 0.5. For the
cation, there are five N atoms of the tren ligand that bind to the
Co(III) atom in a quadridentate mode, resulting in a tripodal-
type conformation with Co−N bond distances ranging from
1.920(3) – 1.960(2) Å. There is a sixth N atom coordinated to
the Co(III) atom in the form of an ammonio-group (NH3). We
postulate that the ammonio-coordination results from the fact
that NH3 is generated from the cleavage of the amide bond of
urea and because Co has a high nitrogen affinity, coordination
results from the free NH3 generated. The coordination
environment of the Co(III) atom is observed to have distorted
octahedral geometry where the bond angles range from
86.54(8) – 93.49(8) . (Refer to the Supplementary Information
for detailed geometrical parameters). These distances and
angles unfortunately could not be compared to other related
structures in the CSD as this complex is the first Co(III)
isocyanato compound reported of its kind. A full geometry
analysis was performed with the Mogul Geometry Check
tool[46], within the CSD suite of programs. This analysis yielded,
in many instances, no comparable hits while unusual
geometrical parameters were highlighted simply because the
database had nothing to actually compare the geometry with.
There is evidence of hydrogen bonding present in this structure
(see Figure 9 – indicated by the dashed lines). Details of the
hydrogen bonding geometry appears in Table 3 below:
Figure 9. Molecular structure of [CoIII(tren)(NCO)(NH3)]Cl2 (2) with
displacement ellipsoids drawn at 50% probability, showing the atomic
numbering scheme where the heteroatoms have been labelled only for
clarity, and showing the atoms that are disordered across the mirror plane.
Dashed green lines indicate hydrogen bonds.
Conclusions
[CoIII(tren)Cl2)]Cl can be prepared in excellent yields following a
two step synthetic protocol using CoCl2.6H2O and tris(2-
aminoethyl)amine (tren) under ambient conditions. The solvent
used for crystallization plays a crucial role in stabilizing the
resulting compound by involvement in intermolecular H bonding.
The complex isolated by crystallizing in water, displays a rare
hydroxonium (H7O3)+ molecular ion aggregate mediated by
extensive hydrogen bonding, which stabilizes the dimeric
asymmetric unit by intermolecular H bonds.
The said compound successfully cleaves urea, following a
dissociation mechanism forming isocyanic acid and ammonia.
The isocyanic acid then coordinated to the metal centre and was
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10.1002/ejic.201800975
European Journal of Inorganic Chemistry
FULL PAPER
[CoIII(tren)(NH3)(NCO)]Cl2 (2): Urea (1.0020 g, 17 mmol) was dissolved in
30 mL deionised H2O and then [Co(tren)Cl2]Cl (0.535 g, 0.75 mmol) was
added to the stirring solution. The pH of the solution was adjusted to 9.0
with freshly prepared 10% LiOH and then stirred at 40 ºC for 2 hours. The
reaction was allowed to cool to room temperature and then left to stand
and evaporate at room temperature for a couple of days after which orange
rod–like crystals suitable for SC–XRD precipitated out. The concentrations
of LiOH used for pH regulations were adjusted according to the
concentration of the catalyst used for analysis to obtain a pH range of 9 –
9.2.
isolated as an isocyanato complex (2). The products are
eventually released, generating the catalytic species available for
the next catalytic cycle. Although, the results are similar to some
of the reported Urease mimics in literature, to the best of our
knowledge, the cobalt-isocyanato complex (2) is the first of its kind
to be reported in literature. The reaction mechanism does not fit
well into the Michaelis-Menten enzyme kinetics equation.
Nevertheless, the reaction follows a first order kinetics with
respect to both urea as well as the catalyst.
Catalytic hydrolysis of Urea as monitored by 1H NMR
Experimental Section
A solution of ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3), ((1)2·(Cl)(H7O3)) (0.124 g, 0.17
mmol) in 10 mL D2O was incubated at pH 9  0.05 for 2 h in the presence
of LiOH. Urea (0.240 g, 4.0 mmol) was added to this solution, and 0.5 mL
of the solution was sealed in an NMR tube and the solution was maintained
at 45 °C for about 12 h. The progress of reaction was monitored by
recording 1H NMR spectra of the reaction mixture every 15 minutes.
Materials and instrumentation
All chemicals were used as received without further purification and were
of the analytical grade. CoCl2.6H2O(Sigma Aldrich), tris(2–
aminoethyl)amine (Sigma Aldrich), Urea (Saarchem) were used as
obtained. FT-IR spectra were recorded in Attenuated total reflection mode
on a Spectrum BX, Perkin Elmer FT–IR spectrometer. Electronic spectra
of complexes were recorded in water on a Shimadzu 1800 UV–Vis
spectrophotometer. 1H NMR and 13C NMR spectra were recorded in
D2O/CH3OD on a Bruker Ultrashield 400 Nuclear Magnetic Resonance
Spectrometer. NMR kinetics were performed on a Bruker Ascend 500
Nuclear Magnetic Resonance Spectrometer. High resolution mass spectra
(HRMS) in positive ion electrospray ionization mass spectrometry mode
were obtained on a Waters Synapt G2 mass spectrometer in CH3CN.
SCXRD data were obtained on a Bruker Apex – II Duo CCD diffractometer.
Catalytic hydrolysis of Urea as monitored by UV–Vis
The Ureases activity of ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3) ((1)2·(Cl)(H7O3)) was
also analysed by monitoring the release of NH3 by use of suitable dye
indicators
– phenolphthalein. Therefore, the reaction was followed
employing UV–Visible spectroscopy by monitoring the absorbance
increment at 552 nm due the alkaline quinone form of phenolphthalein.
The reaction was initiated by adding an aqueous solution of Urea (2 mL, 1
× 10–2 M) to an aqueous solution of ((1)2·(Cl)(H7O3)) (2 mL, 4.5 × 10–3 M)
pH incubated at 9  0.05 with 1 % LiOH solution in water. Phenolphthalein
(1 mL, 1%) was added to this reaction mixture, and it was incubated at
45 °C. The UV–Visible spectrum of the resulting reaction mixture was then
recorded every 2 minutes as a function of time in repeat scan mode for 2
h. Steady state kinetics was performed similarly over a period of 3 minutes
at different temperatures ranging from 20 °C to 50 °C, and the initial rates
were calculated from the slope of absorbance vs time plots. The initial
rates were then fitted to Arrhenius plot to calculate activation energy Ea for
the reaction from nonlinear curve fit using Origin 8.0 software. The stability
of the indicator, phenolphthalein at the reaction pH was monitored by
UV/Vis spectroscopy (see Figure S 11).
Syntheses
[Co(tren)(NO2)2]Cl (1a): NaNO2 (7.2664 g, 0.105 mol) was added to a
solution of CoCl2·6H2O (11.9819 g, 0.05 mol) in 10 mL deionised H2O in a
100 mL side–arm flask. To this solution, a solution of HCl (4.4 mL, 32%)
and 7.5 mL tris(2–aminoethyl)amine (tren) in 10 mL deionised H2O was
added and placed in an ice bath. Air oxidation was done for 2 hours and
then a yellow–brown product was obtained and collected by suction
filtration. The product was recrystallized in a minimum amount of warm
water and recovered by suction filtration and dried. Yield: 9.7931 g, 67.3%.
Selected IR bands (Figure S4) (ѵmax, cm–1): ѵ(N–H): 3281, 3156, 3091;
ѵ(N–O) 1589; ѵ(CH2) 1474; ѵ(NO2) 1339, 1304; ѵ(C–N) 1146; ѵ(NH) 827;
ѵ(CH2) 745. UV-Vis (Figure S10) (H2O): 438 nm (ε, 46.33 M-1 cm-1), 322
nm (ε, 788 M-1 cm-1). 1H NMR (Figure S5) (D2O, 400MHz): δ (ppm) 3.48 –
3.24 (m, 8H, –N–CH2–CH2–N–), 3.08 – 3.01 (m, 4H, –N–CH2–CH2–NH2).
13C NMR (Figure S6) (D2O + CH3OD, 400 MHz): δ (ppm) 62.46, 60.22,
44.43.
Single Crystal Data - Experimental
Dichloro(tris-2-amino(ethylamine))cobalt(III)
[CoIII(tren)Cl2]Cl·H2O, (1·H2O)
chloride
hydrate,
Single purple block-shaped crystals of Complex I were obtained by
recrystallisation from concentrated hydrochloric acid (32% solution). A
suitable crystal (0.27×0.18×0.13) mm3 was selected and mounted on the
tip of a MiTeGen MicroMount© and then placed on a Bruker APEX-II CCD
diffractometer. The crystal was kept at T = 100(2) K during data collection.
Using Olex2[48], the structure was solved with the ShelXT 2014/5[49,50]
structure solution program, using the Intrinsic Phasing solution method.
The model was refined with ShelXL-2017/1[49,50] using Least Squares
minimisation.
([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3)
((1)2·(Cl)(H7O3)):
[Co(tren)(NO2)2]Cl
(7.0008 g, 0.021 mol) was added into a 100 mL beaker and then 32% HCl
(50 mL) was added to it. The solvent was then evaporated on a hot water
bath to dryness and then the precipitate was dissolved in a minimum
amount of warm deionised H2O. The precipitate was isolated by vacuum
filtration and washed with cold deionised H2O and MeOH. Yield: 5.9011 g,
90%. Selected IR bands (Figure S7) (ѵmax, cm–1): ѵ(N–H): 3234, 3135,
3081; ѵ(CH2) 1591, 1480; ѵ(C–N) 1160, 1032; ѵ(NH) 896; ѵ(CH2) 743.
UV-Vis (Figure S10) (H2O): 533 nm (ε, 561 M-1 cm-1), 370 nm (ε, 385 M-1
cm-1). 1H NMR (Figure S8) (D2O, 400MHz): δ (ppm). 3.60 – 3.56 (m, 2H, –
N–CH2–CH2–N–), 3.39 – 3.32 (m, 4H, –N–CH2–CH2–N–), 3.25 – 3.22 (t,
2H, –N–CH2–CH2–N–), 2.86 – 2.82 (m, 2H, –N–CH2–CH2–N–), 2.74 – 2.70
(t, 2H, –N–CH2–CH2–N–). 13C NMR (Figure S9) (D2O + CH3OD, 400 MHz):
δ (ppm) 61.04, 60.00, 44.63, 43.47.
A detailed structural description is included in the SI.
Bis-(dichloro(tris-2-amino(ethylamine))cobalt(III)
chloride
hydroxonium chloride, ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3), ((1)2·(Cl)(H7O3))
Single clear dark violet plank-shaped crystals of Complex II were obtained
by recrystallisation from water. A suitable crystal (0.39×0.29×0.20) mm3
was selected and mounted on the tip of a MiTeGen MicroMount©.and then
placed on a Bruker APEX-II CCD diffractometer. The crystal was kept at T
= 100.1 K during data collection. Using Olex2[48] the structure was solved
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10.1002/ejic.201800975
European Journal of Inorganic Chemistry
FULL PAPER
with the ShelXS−97[49,50] structure solution program, using the Direct
methods solution method. The model was refined with ShelXL-2017/1[49,50]
using Least Squares minimisation.
which corrects for Lorentz polarisation. The final completeness is 100.00 %
out to 28.391° in . A multi-scan absorption correction was performed
using SADABS-2012/1[54] was used for absorption correction. wR2(int) was
0.0695 before and 0.0645 after correction. The ratio of minimum to
maximum transmission is 0.8852. The /2 correction factor is 0.0015. The
absorption coefficient  of this material is 1.677 mm-1 at this wavelength
( = 0.71073Å) and the minimum and maximum transmissions are 0.6602
and 0.7458. Structure refinement was carried out such that all non-
hydrogen atoms were refined anisotropically Most hydrogen atom
positions were calculated geometrically and refined using the riding model,
but some hydrogen atoms were refined freely. The value of Z' is 0.5. This
means that only half of the formula unit is present in the asymmetric unit,
with the other half consisting of symmetry equivalent atoms.
Ammonio(tris-2-amino(ethylamine))isocyanatocobalt(II)
[CoIII(tren)(NCO)(NH3)]Cl2 (2)
chloride
Single clear dark brown block-shaped crystals of Complex III were
obtained by recrystallisation from the mother liquor of the catalytic reaction
mixture. A suitable crystal (0.15×0.14×0.14) mm3 was selected and
mounted on the tip of a MiTeGen MicroMount©.and then placed on a
Bruker APEX-II CCD diffractometer. The crystal was kept at T = 100(2) K
during data collection. Using Olex2[48], the structure was solved with the
ShelXS−97[49,50] structure solution program, using the Direct methods
solution method. The model was refined with ShelXL-2017/1[49,50] using
Least Squares minimisation.
Some details of the crystal structure determination are also given in Table
5. CCDC 1848991 ([CoIII(tren)Cl2]Cl·H2O, (1·H2O)), 1848992
(([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3)
((1)2·(Cl)(H7O3)))
and
1848993
Single Crystal Data and Structure Quality Indicators
([CoIII(tren)(NH3)(NCO)]Cl2 (2)) contain the supplementary crystallographic
data for the structures reported in this paper. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.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. Supplementary data associated with this article
can be found, in the online version, at doi: $$$$$.
Bis-(dichloro(tris-2-amino(ethylamine))cobalt(III)
chloride)
hydroxonium chloride, ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3), ((1)2·(Cl)(H7O3))
C12H43Cl7Co2N8O3, Mr = 713.55, monoclinic, P21/n (No. 14), a =
19.732(3) Å, b = 8.0255(12) Å, c = 20.161(3) Å,  = 118.466(3)°,  =  =
90°, V = 2806.7(7) Å3, T = 100.1 K, Z = 4, Z' = 1, (MoKa) = 1.879, 39625
reflections measured, 7021 unique (Rint = 0.0830) which were used in all
calculations. The final wR2 was 0.0770 (all data) and R1 was 0.0356 (I >
2(I)). Data were measured using  and  scans of 0.50 ° per frame for 10
s using MoK radiation (graphite monochromated, 50 kV, 30 mA). The
total number of runs and images was based on the strategy calculation
from the program APEX2[51]. The maximum resolution achieved was  =
28.387°. Cell parameters were retrieved using SAINT[52] software and
refined using SAINT[52] on 3885 reflections, 10 % of the observed
reflections. Data reduction was performed using the SAINT[52] software
which corrects for Lorentz polarisation. The final completeness is 100.00 %
out to 28.387° in . A multi-scan absorption correction was performed
using SADABS-2012/1[54] was used for absorption correction. wR2(int) was
0.0728 before and 0.0648 after correction. The ratio of minimum to
maximum transmission is 0.8776. The /2 correction factor is 0.0015. The
absorption coefficient  of this material is 1.879 mm-1 at this wavelength
( = 0.71073Å) and the minimum and maximum transmissions are 0.6544
and 0.7457. Structure refinement was carried out such that all non-
hydrogen atoms were refined anisotropically Most hydrogen atom
positions were calculated geometrically and refined using the riding model,
but some hydrogen atoms were refined freely. The H atoms that were
allowed to refine freely were, in most cases, restrained by DFIX
parameters as their refinement had a slight tendency to become unstable,
resulting in unequal N−H bond lengths.
Table 5. Crystal data and structure refinement for ([CoIII(tren)Cl2]Cl)2·(Cl)(H7O3)
((1)2·(Cl)(H7O3)), [CoIII(tren)(NH3)(NCO)]Cl2 (2)
(1)2·(Cl)(H7O3)
(2)
Formula
T
2(C6H18Cl2CoN4)·3(Cl)·H3O·2(H2O)
C7H21CoN6O·2(Cl)
100 K
100 K
Wavelength,
Å
0.71073 Å
0.71073 Å
Formula
weight
713.55
335.13
Crystal
System
Monoclinic
P21/n
Orthorhombic,
Pnma
Space
Group
a
19.732 (3) Å
8.0255 (12) Å
20.161 (3) Å
118.466 (3)°
2806.7 (7) Å3
4
16.162 (3) Å
11.562 (2) Å
7.1615 (12) Å
Ammonio(tris-2-amino(ethylamine))isocyanatocobalt(III) dichloride
[CoIII(tren)(NCO)(NH3)]Cl2 (2)
b
C7H21Cl2CoN6O, Mr = 335.13, orthorhombic, Pnma (No. 62), a =
16.162(3) Å, b = 11.562(2) Å, c = 7.1615(12) Å,  =  =  = 90°, V =
1338.2(4) Å3, T = 100(2) K, Z = 4, Z' = 0.5, (MoKa) = 1.677, 12702
reflections measured, 1763 unique (Rint = 0.0810) which were used in all
calculations. The final wR2 was 0.1053 (all data) and R1 was 0.0414 (I >
2(I)). Data were measured using  and  scans of 0.50 ° per frame for 10
s using MoK radiation (graphite monochromated, 50 kV, 30 mA). The
total number of runs and images was based on the strategy calculation
from the program APEX2[51]. The maximum resolution achieved was  =
28.391. Cell parameters were retrieved using SAINT[52] software and
refined using SAINT[52] on 1483 reflections, 12 % of the observed
reflections. Data reduction was performed using the SAINT[52] software
c

V
1338.2 (4) Å3
Z
4
F(000)
1472
696
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10.1002/ejic.201800975
European Journal of Inorganic Chemistry
FULL PAPER
1.689 Mg m-3
1.663 Mg m-3
1.68 mm-1
2.5–26.5°
0.081
[17]
[18]
I. S. Park, R. P. Hausinger, Biochemistry 1996, 35, 5345–5352.
F. Musiani, E. Arnofi, R. Casadio, S. Ciurli, J. Biol. Inorg. Chem.
2001, 6, 300–314.
B. P. Roberts, B. R. Miller, A. E. Roitberg, K. M. Merz, J. Am. Chem.
Soc. 2012, 134, 9934–9937.
D. Volkmer, B. Hommerich, K. Griesar, W. Haase, B. Krebs, P.
Chemie, T. H. Darmstadt, D.- Darmstadt, R. V December, H. O. C.
H. O. Et, 1996, 1669, 3792–3803.
A. Balasubramanian, K. Ponnuraj, J. Mol. Biol. 2010, 400, 274–283.
B. Zambelli, F. Musiani, S. Benini, S. Ciurli, Acc. Chem. Res. 2011,
44, 520–530.
Dx

1.88 mm-1
[19]
[20]

2.3–28.3°
[21]
[22]
Rint
0.083
[23]
[24]
[25]
[26]
[27]
F. Meyer, E. Kaifer, P. Kircher, K. Heinze, H. Pritzkow, Chem. - A
Eur. J. 1999, 5, 1617–1630.
W.-Z. Lee, H.-S. Tseng, M.-Y. Ku, T.-S. Kuo, Dalt. Trans. 2008, 2,
2538–2541.
A. M. Barrios, S. J. Lippard, J. Am. Chem. Soc. 2000, 122, 9172–
9177.
T. Koga, H. Furutachi, T. Nakamura, N. Fukita, M. Ohba, K.
Takahashi, H. Ōkawa, Inorg. Chem. 1998, 37, 989–996.
Z. Khan, M. Z. A. Rafiquee, Kabir-ud-din, M. Arif Niaz, A. Aziz Khan,
Indian J. Chem. - Sect. A Inorganic, Phys. Theor. Anal. Chem.
1996, 35, 1116–1119.
Crystal Size
0.39 × 0.30 × 0.20 mm
0.15 × 0.14 × 0.14
mm
Goodness–
of–fit on F2
1.01
1.01
R[F2
>
0.036
0.041
2(F2)]
[28]
[29]
A. M. Barrios, S. J. Lippard, Inorg. Chem. 2001, 40, 1250–1255.
L. Roecker, J. Akande, L. N. Elam, I. Gauga, B. W. Helton, M. C.
Prewitt, A. M. Sargeson, J. H. Swango, A. C. Willis, T. Xin, J. Xu,
Inorg. Chem. 1999, 38, 1269–1275.
wR2
data) b
(all
0.077
0.105
[30]
[31]
[32]
[33]
C. te Grotenhuis, N. van den Heuvel, J. I. van der Vlugt, B. de Bruin,
Angew. Chemie - Int. Ed. 2018, 57, 140–145.
C. F. Harris, C. S. Kuehner, J. Bacsa, J. D. Soper, Angew. Chemie -
Int. Ed. 2018, 57, 1311–1315.
K. Kawai, Y. Bunno, T. Yoshino, S. Matsunaga, Chem. - A Eur. J.
2018, 24, 10231 – 10237.
S. K. Ghosh, A. Ehnbom, K. G. Lewis, J. A. Gladysz, Coord. Chem.
Rev. 2017, 350, 30–48.
M. K. Saha, I. Bernal, Chem. Commun. 2003, 612–613.
M. K. Saha, U. Mukhopadhyay, I. Bernal, Dalt. Trans. 2004, 1466–
1473.
U. Mukhopadhyay, R. Galian, I. Bernal, Inorganica Chim. Acta 2009,
362, 4237–4240.
D. A. Buckingham, P. J. Cresswell, A. M. Sargeson, Inorg. Chem.
1975, 14, 1485–1490.
I. A. Guzei, C. Arderne, Acta Crystallogr. Sect. C Struct. Chem.
2015, 71, 695–700.
D. A. Buckingham, J. P. Collman, D. A. R. Happer, L. G. Marzilli, J.
Am. Chem. Soc. 1967, 89, 1082–1087.
D. A. Buckingham, J. P. Collman, Inorg. Chem. 1967, 6, 1803–
1807.
A. A. Phulambrikar, C. Chatterjee, Order A J. Theory Ordered Sets
Its Appl. 2002, 1519, 1515–1519.
B. Krajewska, R. Van Eldik, M. Brindell, J. Biol. Inorg. Chem. 2012,
17, 1123–1134.
C.-F. Wang, Z.-J. Chen, K.-D. Zhao, X.-F. Chen, C.-Y. Zhang, G.-H.
Sheng, H.-L. Zhu, J. Coord. Chem. 2016, 69, 2656–2665.
R. W. Hay, N. Govan, Transit. Met. Chem. 1998, 725, 721–725.
N. V. Kaminskaia, N. M. Kostic, Inorg. Chem. 1997, 36, 5917–5926.
I. J. Bruno, J. C. Cole, M. Kessler, J. Luo, W. D. S. Momerwell, L. H.
Purkis, B. R. Smith, R. Taylor, R. I. Cooper, S. E. Harris, A. G.
Orpen, J. Chem. Inf. Comput. Sci. 2004, 44, 2133–2144.
I. Bernal, S. F. Watkins, Acta Crystallogr. Sect. C Struct. Chem.
2014, 70, 566–574.
O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H.
Puschmann, J. Appl. Crystallogr. 2009, 42, 339–341.
G. M. Sheldrick, Acta Crystallogr. Sect. C Struct. Chem. 2015, 71,
3–8.
Largest
0.59 and –0.57
2.74 and –0.53
differences
peak
hole (eÅ–3
and
)
Acknowledgements
[34]
[35]
The authors acknowledge the University of Johannesburg and the
NRF Thuthuka Programme (Grant no: 99164) for funding for this
study. Mr. D. Harris and Dr R. Meyer from Shimadzu South Africa
are also gratefully acknowledged for the equipment (UV-Visible
spectrometer) we used to conduct this project.
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
Keywords: cobalt complexes • kinetics • stucture elucidation •
urea • urease activity
References
[1]
[2]
L. S. B. Upadhyay, Indian J. Biotechnol. 2012, 11, 381–388.
W. Z. Lee, H. S. Tseng, T. L. Wang, H. L. Tsai, T. S. Kuo,
Organometallics 2010, 29, 2874–2881.
E. L. Carter, N. Flugga, J. L. Boer, S. B. Mulrooney, R. P.
Hausinger, Metallomics 2009, 1, 207–221.
H. L. Mobley, M. D. Island, R. P. Hausinger, Microbiol. Rev. 1995,
59, 451–480.
Z.-L. You, L.-L. Ni, D.-H. Shi, S. Bai, Eur. J. Med. Chem. 2010, 45,
3196–3199.
H. Deng, G. Hong, F. Lin, A. Liu, X. Xia, W. Chen, Anal. Chim. Acta
2016, 915, 74–80.
G. Estiu, K. M. Merz, J. Am. Chem. Soc. 2004, 126, 11832–11842.
Y. Cui, X. Dong, Y. Li, Z. Li, W. Chen, Eur. J. Med. Chem. 2012, 58,
323–331.
P. A. Karplus, M. A. Pearson, R. P. Hausinger, Acc. Chem. Res.
1997, 30, 330–337.
M. N. Belzile, A. A. Neverov, R. S. Brown, Inorg. Chem. 2014, 53,
7916–7925.
D. A. Daramola, D. Singh, G. G. Botte, J. Phys. Chem. A 2010, 114,
11513–11521.
[44]
[45]
[46]
[3]
[4]
[5]
[6]
[47]
[48]
[49]
[50]
[51]
[52]
[53]
[54]
[7]
[8]
G. M. Sheldrick, Acta Crystallogr. Sect. A Found. Crystallogr. 2015,
71, 3–8.
Bruker, 2014., APEX2, SAINT, SADABS, Bruker AXS, Inc.,
Madison, Wisconsin, USA
Bruker, 2013., APEX2, SAINT, SADABS, Bruker AXS, Inc.,
Madison, Wisconsin, USA
Bruker, 2016., APEX2, SAINT, SADABS, Bruker AXS, Inc.,
Madison, Wisconsin, USA
[9]
[10]
[11]
Bruker, 2012., APEX2, SAINT, SADABS, Bruker AXS, Inc.,
Madison, Wisconsin, USA
[12]
[13]
[14]
G. Estiu, K. M. Merz, J. Phys. Chem. B 2007, 111, 10263–10274.
B. Krajewska, J. Mol. Catal. B Enzym. 2009, 59, 9–21.
M. Belzile, A. A. Neverov, R. S. Brown, Inorg. Chem. 2014, 53,
7916−7925.
[15]
[16]
B. P. Callahan, Y. Yuan, R. Wolfenden, J. Am. Chem. Soc. 2005,
127, 10828–10829.
J. F. Marlier, L. I. Robins, K. A. Tucker, J. Rawlings, M. A.
Anderson, W. W. Cleland, Biochemistry 2010, 49, 8213–8219.
This article is protected by copyright. All rights reserved.

10.1002/ejic.201800975
European Journal of Inorganic Chemistry
FULL PAPER
Entry for the Table of Contents
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FULL PAPER
We have explored the catalytic activity
of [CoIII(tren)Cl2]Cl towards the
cleavage of he amide bond in urea,
with respect to Urease mimetic activity.
The reaction kinetics were followed
spectroscopically; and the formation of
products was confirmed by SC XRD
technique.
Enzyme Mimetics
Bhawna Uprety, Charmaine Arderne*,
Ivan Bernal, Charmaine Arderne*
Page No. – Page No.
Catalytic cleavage of the amide bond
in urea using a Co(III) amino-based
complex
This article is protected by copyright. All rights reserved.