Mononuclear and dinuclear model hydrolases of nickel and cobalt

Article abstract of DOI:10.1016/j.ica.2005.01.029

Reaction between the dinuclear model hydrolases [M₂(μ-OAc) ₂(OAc)₂(μ-H₂O)(tmen)₂]; M = Ni (1); M = Co (2) and trimethylsilyltrifluoromethanesulphonate (TMS-OTf) under identical reaction conditions gives the mononuclear complex [Ni(OAc)(H ₂O)₂(tmen)][OTf] ? H₂O (3) in the case of nickel and the dinuclear complex [Co₂(μ-OAc)₂(μ- H₂O)₂(tmen)₂][OTf]₂ (4) in the case of cobalt. Reaction of (3) with urea gives the previously reported [Ni(OAc)(urea)₂(tmen)][OTf] (5), whereas (4) gives [Co ₂(OAc)₃(urea)(tmen)₂][OTf] (6) previously obtained by direct reaction of (2) with urea. Both (3) and (4) react with monohydroxamic acids (RHA) to give the dihydroxamate bridged dinuclear complexes [M₂(μ-OAc)(μ-RA)₂(tmen)₂][OTf]; M = Ni (7); M = Co (8) previously obtained by the reaction of (1) and (2) with RHA, illustrating the greater ability of hydroxamic acids to stabilize dinuclear complexes over that of urea by means of their bridging mode, and offering a possible explanation for the inhibiting effect of hydroxamic acids by means of their displacing bridging urea in a possible intermediate invoked in the action of urease.

Full text of DOI:10.1016/j.ica.2005.01.029

Inorganica Chimica Acta 358 (2005) 2755–2762
www.elsevier.com/locate/ica
Mononuclear and dinuclear model hydrolases of nickel and cobalt
a,
a
a
b
b
D.A. Brown *, W.K. Glass , N.J. Fitzpatrick , T.J. Kemp , W. Errington ,
a
H. Muller-Bunz , A.J. Hussein , H. Nimir
a
c
¨
a
Department of Chemistry, Centre for Synthesis and Chemical Biology (CSCB), Conway Institute of Biomolecular and
Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
b
Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
c
Department of Chemistry, University of Khartoum, Sudan
Received 5 January 2005; accepted 28 January 2005
Available online 14 April 2005
Abstract
Reaction between the dinuclear model hydrolases [M2(l-OAc)2(OAc)2(l-H2O)(tmen)2]; M = Ni (1); M = Co (2) and trim-
ethylsilyltrifluoromethanesulphonate (TMS-OTf) under identical reaction conditions gives the mononuclear complex [Ni(OAc)
(H2O)2(tmen)][OTf]ÆH2O (3) in the case of nickel and the dinuclear complex [Co2(l-OAc)2(l-H2O)2(tmen)2][OTf]2 (4) in the case
of cobalt.
Reaction of (3) with urea gives the previously reported [Ni(OAc)(urea)2(tmen)][OTf] (5), whereas (4) gives [Co2(OAc)3(urea)
(tmen)2][OTf] (6) previously obtained by direct reaction of (2) with urea. Both (3) and (4) react with monohydroxamic acids
(RHA) to give the dihydroxamate bridged dinuclear complexes [M2(l-OAc)(l-RA)2(tmen)2][OTf]; M = Ni (7); M = Co (8) previ-
ously obtained by the reaction of (1) and (2) with RHA, illustrating the greater ability of hydroxamic acids to stabilize dinuclear
complexes over that of urea by means of their bridging mode, and offering a possible explanation for the inhibiting effect of hydroxa-
mic acids by means of their displacing bridging urea in a possible intermediate invoked in the action of urease.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Cobalt; Nickel hydroxamates; Model hydrolases; Crystal structures
1. Introduction
ing Zn(II), Ni(II), Co(II) and Mn(II) and carboxylate
bridges which occur, respectively, in leucine aminopepti-
dase (LAP) [2], urease [3], methionine aminopeptidase
(MAP) [4] and arginase [5].
Dinuclear metallohydrolases are an important group
of metalloenzymes, which catalyse the hydrolysis of a
range of peptide and phosphate ester bonds and include
the amidohydrolases, amidinohydrolases and peptide
hydrolases [1]. A common structural feature of these
metallohydrolases is a dinuclear metal active site featur-
The inhibition of metalloenzymes by hydroxamic
acids is important because of therapeutic applications.
Generally, the inhibition involves chelation of a mono-
nuclear zinc centre by the hydroxamate function
(RCONR0OH) [6] but in the case of urease the structure
of the acetohydroxamate-inhibited Cys319Ala variant of
KAU shows the deprotonated hydroxyl oxygen of the
hydroxamic acid bridging the two nickel centres with
the carbonyl oxygen bridging one nickel centre only
[7]. This unusual mode of bonding by a hydroxamate
bridging two metal centres was modelled first in the
Abbreviations: OAc, CH3COOꢀ; tmen, N,N,N0,N0-tetramethyle-
thylenediamine; OTf (triflate), CF3SO3ꢀ; AHA, acetohydroxamic acid;
AA, acetohydroxamate anion; BHA, benzohydroxamic acid; BA, be-
nzohydroxamate anion; NPhAHA, N-phenylacetohydroxamic acid;
NPhAA, N-phenylacetohydroxamate anion.
*
Corresponding author. Tel.: +353 1 707 2495; fax: +353 1 706 2127.
E-mail address: noel.fitzpatrick@ucd.ie (D.A. Brown).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.01.029

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D.A. Brown et al. / Inorganica Chimica Acta 358 (2005) 2755–2762
complex [Ni2(H2shi)(Hshi)(pyr)4(OAc)], where Hshi is
deprotonated salicylhydroxamic acid, prepared by self-
assembly [8]. Subsequently, it was shown that the struc-
tural model hydrolases [M2(l-OAc)2(OAc)2(H2O)
(tmen)2] (M = Mn, Co, Ni) react rapidly with a range
of hydroxamic acids (e.g., AHA) to give hydroxamate-
bridged dinuclear complexes such as [M2(l-OAc)
(l-AA)2(tmen)2] [OTf] [9], in which the hydroxamate
hydroxyl is deprotonated and the oxygen then bridges
the two metal centres whilst the carbonyl oxygen bonds
to one metal centre only, thereby modelling the structure
observed in the acetohydroxamate-inhibited Cys319Ala
variant of KAU [7].
In this paper, we report the synthesis and structural
characterization of two new hydrolase model complexes:
[Ni(OAc)(H2O)2(tmen)][OTf]ÆH2O (3) and [Co2(l-
OAc)2(l-H2O)2(tmen)2][OTf]2 (4) and their reactions
with urea and selected monohydroxamic acids (RHA:
R = Me and Ph).
further characterized by microanalysis, infrared and
UV/vis spectra (Supplementary Material I).
2.2. Crystal structure of [Ni(OAc)(H2O)2(tmen)][OTf]Æ
H2O (3)
Crystals suitable for X-ray analysis were obtained di-
rectly from the above preparative methods. Data were
collected using a Siemens SMART CCD area-detector
diffractometer. A full hemisphere of reciprocal space
was scanned by a combination of three sets of exposures;
each set has a different / angle for the crystal and each
exposure of 10 s covered 0.3ꢁ in x. The crystal to detec-
tor distance was 5.01 cm. Crystal decay was monitored
by repeating the initial frames at the end of the data col-
lection and analysing the duplicate reflection; a multi-
scan absorption correction was applied using SADABS
[10]. The structures were solved by direct methods using
SHELXTL-PC [11] and refined by full-matrix least-squares
on F2 for all data using SHELXTL 97. The water protons
were located in the difference fourier map and their posi-
tional parameters were allowed to refine freely. Their
isotropic temperature factors were fixed at 150% of the
equivalent temperature factor of the oxygen atom to
which they are attached. All other hydrogens were
added at calculated positions and refined using a riding
model [12]. The temperature factors were fixed at 120%
(150% for methyl hydrogens) of the equivalent tempera-
ture factor of the atom to which the hydrogen is at-
tached. Anisotropic temperature factors were used for
all non-H atoms.
2. Results and discussion
2.1. Nickel complexes
The mononuclear nickel complex (3) is formed on
treatment of the dinuclear complex [Ni2(l-OAc)2
(OAc)2(H2O)(tmen)2] (1) with trimethylsilyltrifluorome-
thanesulphonate (TMS-OTf) in dichloromethane when
a rapid change in colour from green to yellow–green oc-
curs (Scheme 1).
Extraction in acetonitrile and diffusion of diethyle-
ther gave crystals suitable for X-ray crystallography
The structure of (3) shown in Fig. 1 confirms that (3)
is a mononuclear nickel (II) complex in which the nickel
(II) atom is surrounded by an N2O4 core consisting of
one chelating acetate, two cis water ligands and one
tmen ligand. Crystallographic data and selected bond
lengths and angles are given in Table 1 and Fig. 1,
respectively. Lattice water is hydrogen bonded as shown
also in Fig. 1.
OTf.H2O
O
OH2
H
O
N
O
O
O
N
triflate
O
N
N
Ni
Ni
Ni
H
N
O
O
O
N
O
O
OH2
2.3. Spectroscopic studies of [Ni(OAc)(H2O)2(tmen)]
[OTf]ÆH2O (3)
(1)
(3)
R`
O
R
triflate
2.3.1. UV/visible spectrum
C
N
R`
urea
O
R
OH
The electronic spectrum of (3), measured in metha-
nol, is typical of a distorted octahedral environment
about a Ni(II) centre with three bands at (1079, 653,
391) nm being assigned to the three spin-allowed transi-
C
N
OH
R`
NH2
N
H2N
O
OTf
R
OTf
N
N
3
3
3
3
3
O
O
N
N
tions A2g(F) ! T2g(F), A2g(F) ! T1g(F), A2g(F) !
O
O
3T2g(P) for an octahedral d8 ion.
Ni
R`
Ni
N
Ni
O
O
O
O
N
O
N
2.3.2. Infrared spectra
R
(5)
(7a)
NH2
H2N
The infrared spectrum of (3) in KBr, dichlorometh-
ane and methanol showed a peak in the region
1540–1553 cmꢀ1 indicating partial dissociation of the
bidentate acetate.
`
R = Me or Ph; R = H or Ph
Scheme 1.

D.A. Brown et al. / Inorganica Chimica Acta 358 (2005) 2755–2762
2757
2.4. Reactions of (3) with urea and monohydroxamic
acids
2.4.1. Urea reactions
Complex (3) reacts readily with urea in methanol
followed by removal of solvent and recrystallization
from acetone to give [Ni(OAc)(urea)2(tmen)][OTf] (5)
(Scheme 1) previously reported by the direct reaction
of the dinuclear (1) with urea in addition to the dinu-
clear [Ni2(l-OAc)3(urea)(tmen)2][OTf], [13]. Satisfactory
microanalysis was obtained for (5).
2.5. Reactions of (3) with monohydroxamic acids
Treatment of complex (3) with acetohydroxamic acid,
AHA, in methanol at room temperature gave rapid for-
mation of the dihydroxamate bridged dinuclear complex
[Ni2(l-OAc)(l-AA)2(tmen)2][OTf] (7a) (Scheme 1) pre-
viously obtained by direct reaction of the dinuclear
model hydrolase [Ni2(l-OAc)2(OAc)2(H2O)(tmen)2] (1)
with AHA [9]. Similar products, [Ni2(l-OAc)(l-BA)2
(tmen)2][OTf] (7b) and [Ni2(l-OAc)(l-NPhA)2(tmen)2]
[OTf] (7c) were obtained by analogous reactions of com-
plex (3) with benzohydroxamic acid (BHA) and N-phen-
ylacetohydroxamic acid (NPhAHA). In all cases,
satisfactory microanalysis was obtained for (7a)–(7c)
Fig. 1. The molecular structure of [Ni(OAc)(H2O)2(tmen)][OTf]ÆH2O
(3). Selected bond lengths (A) and angles (ꢁ): Ni–O3, 2.063(3); Ni1–N1,
2.099(4); Ni1–O1, 2.120(3); Ni–O4, 2.079; Ni1–O2, 2.116(3); Ni1–N2,
2.128(4); O3–Ni1–O4, 89.54(14); O4–Ni1–N1, 90.95(16); O4–Ni1–N2,
175.97(15); O4–Ni1–O2, 90.77(15); O4–Ni1–O1, 86.48(14); N1–Ni1–
N2, 85.34(16); O3–Ni1–N2, 89.38(15); O3–Ni1–N1, 97.78(15); O2–
Ni1–O1, 61.66(13).
˚
Table 1
Crystal data and structure refinement for (3) and (4)
(3)
(4)
Empirical formula
C9H25F3N2O8SNi
437.08
C18H42N4O12F6S2Co2
802.54
Formula weight
Crystal system
Space group
triclinic
ꢀ
monoclinic
C2/m (#12)
19.388(2)
8.9782(10)
10.0216(11)
90
P1 ð#2Þ
˚
a (A)
9.2378(5)
10.5436(9)
10.6841(9)
84.622(3)
64.631(3)
88.780(4)
935.93(12)
180(2)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
102.123(2)
90
3)
˚
V (A
1705.6(3)
293(2)
T (K)
Z
2
1.551
2
1.563
qcalc (Mg/m3)
Crystal size (mm3)
0.26 · 0.12 · 0.10
1.213
0.95 · 0.40 · 0.15
1.184
l (mmꢀ1
hkl ranges
)
ꢀ8,11; ꢀ12,10; ꢀ12,12
4909
ꢀ25,25; ꢀ11,11; ꢀ12,13
7265
Reflections collected
Independent reflections
Max. and min. transmission
R(F)[I > 2r(I)] (%)
3395 [Rint = 0.0291]
0.8883 and 0.7434
6.18
2115 [Rint = 0.0231]
0.8424 and 0.3993
4.71
Rw(F2) (all data) (%)
Goodness-of-fit on F2
Largest peak and hole (e/A )
17.4
1.066
13.27
1.053
3
˚
1.423 and ꢀ0.784
0.861 and ꢀ0.385
3.130(3)
˚
M–M distance (A)
[Ni(OAc)(H2O)2(tmen)][OTf]ÆH2O (3); [Co2(l-OAc)2(l-H2O)2(tmen)2][OTf]2 (4).

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D.A. Brown et al. / Inorganica Chimica Acta 358 (2005) 2755–2762
and infrared and UV/vis spectra were in good agreement
with previously reported data [9] (Supplementary Mate-
rial II).
The structure of the dicobalt model hydrolase (4) is
shown in Fig. 2 together with selected bond lengths
and angles confirming formation of a dinuclear cobalt
complex with two bridging water molecules, two bridg-
ing acetates and two tmen capping ligands. Crystallo-
graphic data are given in Table 1. Comparison of the
structures of the two dinuclear cobalt complexes (2)
and (4) reveals that there is hydrogen bonding of the
bridging water molecules with the monodentate carbox-
ylate free oxygens in (2) and with an oxygen of the coun-
ter ion triflate in (4).
2.6. Cobalt complexes
In contrast to the isolation and characterization of
the mononuclear nickel complex, [Ni(OAc)(H2O)2
(tmen)][OTf]ÆH2O (3) formed by the reaction of the
dinuclear nickel complex [Ni2(l-OAc)2(OAc)2(H2O)
(tmen)2] (1) with TMS-OTf, reaction of the analogous
cobalt complex [Co2(l-OAc)2(OAc)2(H2O)(tmen)2] (2)
with TMS-OTf in methanol gave pink crystals of the
dinuclear, diaqua bridged cobalt (II) complex, [Co2-
(l-OAc)2(l-H2O)2(tmen)2][OTf]2 (4) (Scheme 2).
Removal of solvent, extraction with acetonitrile and dif-
fusion of diethylether gave crystals suitable for X-ray
crystallography. Crystal data were collected using a Bru-
ker SMART APEX CCD area detector diffractometer.
A full sphere of the reciprocal space was scanned by
/–x scans. Semi-empirical absorption correction based
on redundant reflections was performed by the program
SADABS [10]. The structure was solved by direct methods
using SHELXS-97 [14] and refined by full-matrix least-
squares on F2 for all data using SHELXTL-97 [12]. Disor-
dered hydrogens were added at calculated positions and
refined using a riding model. Their isotropic tempera-
ture factors were fixed to 1.2 (1.5 for methyl hydrogens)
times the equivalent isotropic displacement parameters
of the carbon atom the H-atom is attached to. The water
proton was located in the difference fourier map and al-
lowed to refine freely with an isotropic temperature fac-
tor. Anisotropic temperature factors were used for all
non-hydrogen atoms. Satisfactory microanalysis was
also obtained.
The respective H-bond distances are O(9)ꢁ ꢁ ꢁO (free)
˚
˚
of 2.557(4) A in (2) and O(1)ꢁ ꢁ ꢁO(OTf) of 2.711(3) A
in (4).
˚
The Co–Co distance in (4) 3.130(3) A compared
˚
with 3.597(1) A in (2) is presumably due to the pres-
ence of an extra bridging water molecule in the former
complex.
2.7. Spectroscopic studies of [Co2(l-OAc)2(l-H2O)2
(tmen)2][OTf]2 (4)
2.7.1. UV/visible spectrum
The electronic spectrum of (4) in methanol is typical
of a distorted octahedral Co(II) complex and very close
to that of complex (2) with two broad bands at 519 and
1095 nm assigned to the spin-allowed transitions (Sup-
plementary Material III).
2.7.2. Infrared spectrum
The infrared spectrum of [Co2(l-OAc)2(l-H2O)2(t-
men)2][OTf]2 (4) in KBr showed a different pattern to
that of (2) in the carboxylate region. Thus (4) and (2)
showed carboxylate vibrations of m(CO) at 1578 and
1630 cmꢀ1 assigned to bidentate bridging acetates and
the carboxylate stretching vibration of acetate in (4) is
lower than that in (2) because of the presence of the sec-
ond aqua bridge and absence of the monodentate ace-
tate in (4) (Supplementary Material III).
O
[OTf]2
H
O
H
H
O
O
H
O
O
N
O
O
N
N
N
N
N
N
Depending upon the particular carboxylate ligand
and metal ion in these dinuclear complexes, two broad
bands, often accompanied by a shoulder, are observed
in the region 2000–2400 cmꢀ1 assigned to the bridging
water. This enormous lowering compared to free water
is ascribed to very strong hydrogen-bond formation
with the monodentate coordinating carboxylato group.
Thus, the complexes (2) and (4) show weak broad
peaks at (2024–2088), (2), in the presence of monoden-
triflate
Co
Co
Co
Co
O
H
O
O
N
O
H
O
O
O
(4)
(2)
R`
O
R
R`
O
urea
triflate
C
N
C
N
OH
R
OH
NH2
R
tate acetates and weak sharp peaks (1998–2070) cmꢀ1
,
H2N
H
N
OTf
C
O
OTf
O
O
(4), in the absence of monodentate acetates, assigned
to the bridging water. These two water peaks are
diagnostic in assigning (2) and (4) as dinuclear
complexes.
In methanol (4) gives a single carboxylate peak at
1563 cmꢀ1 assigned to the monodentate acetate group
indicating dissociation of the dinuclear system.
N
O
N
N
O
N
N
O
O
Co
Co
O
Co
Co
N
N
O
O
N
H
O
O
N
O
(6)
(8a)
R
R = Me or Ph
Scheme 2.

D.A. Brown et al. / Inorganica Chimica Acta 358 (2005) 2755–2762
2759
O4
F1
S
F2
O5
C6
O4
F1
C2A
C2A
C1A
N
C1A
C4
O1
N
C3A
C3A
Co
O2
C5
O3
C3B
O3
O2
C3B
N
N
C2B
C1B
C2B
C1B
˚
Fig. 2. The molecular structure of [Co2(l-OAc)2(l-H2O)2(tmen)2][OTf]2 (4). Selected bond lengths (A) and angles (ꢁ): Co–Co#2, 3.130(3); Co–O(3),
1.995(2); Co–O(2), 2.018(2); Co–N, 2.167(2); Co–N#1, 2.167(2); Co–O(1)#2, 2.281(19); Co–O(1), 2.281(19); O(1)–Co#2, 2.281(19); Co#2– O(1)–Co,
86.63(9); O(3)–Co–O(2), 154.16(10); O(3)–Co–N, 99.74(8); O(2)–Co–N, 99.42(8); N–Co–N#1, 83.77(13); O(3)–Co–O(1), 81.04(5); O(2)–Co–O(1),
81.31(5); N–Co–O(1), 91.43(8).
2.7.3. Reaction of (4) with urea
bridged dinuclear complex [Co2(l-OAc)(l-AA)2(tmen)2]
[OTf] (8a) (Scheme 2) previously obtained upon treat-
ment of the dinuclear model hydrolase [Co2(l-OA-
c)2(OAc)2(H2O)(tmen)2] (2) with AHA [15]. A similar
product [Co2(l-OAc)(l-BA)2(tmen)2][OTf] (8b) was ob-
tained by analogous reaction of complex 4 with BHA. In
all cases satisfactory microanalyses were obtained for
complexes (8a) and (8b).
Reaction of (4) with urea in methanol occurred rap-
idly with formation of [Co2(l-OAc)3(urea)(tmen)2][OTf]
(6) (Scheme 2). Removal of the solvent, extraction with
acetone and vapour diffusion gave pink crystals of (6)
suitable for X-ray crystallography. The structure there-
by obtained was identical with that obtained previously
as were microanalysis, IR and UV/vis spectra (Supple-
mentary Material III). The product obtained from (4)
is thus identical with that reported previously by the
reaction of the dinuclear monobridged aqua complex
(2) with urea [15].
Infrared and UV/vis spectra were in good agreement
with previously reported data [15] (Supplementary
Material IV).
2.8. Reactions of (4) with monohydroxamic acids
3. Conclusions
Treatment of (4) with AHA in methanol at room
temperature gave rapid formation of the dihydroxamate
The dinuclear model hydrolases, [M2(l-OAc)2(OAc)2
(H2O)(tmen)2], M = Co (2); Ni (1) react under identical

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D.A. Brown et al. / Inorganica Chimica Acta 358 (2005) 2755–2762
conditions with TMS triflate to give in one case the
mononuclear nickel diaqua complex [Ni(OAc)(H2O)2
(tmen)][OTf]ÆH2O (3) and in contrast in the second case
the dinuclear diaqua complex [Co2(l-OAc)2(l-H2O)2
(tmen)2][OTf]2 (4).
Complex [Ni2(OAc)4(H2O)(tmen)2] (1) (1.818 g,
3.0 mmol) was reacted with 3 mmol of TMS-OTf
(0.54 ml) in 15 ml of dichloromethane and stirred for
1 h. Removal of solvent gave an oil which was dissolved
in acetonitrile. Vapour diffusion of diethylether into the
solution resulted in a bluish/green crystals of [Ni(OA-
c)(H2O)2(tmen)][OTf]ÆH2O (3). Yield: 0.49 g (37%).
Anal. Calc. for C9H25F3N2O8SNi: C, 24.73; H, 5.76;
N, 6.40. Found: C, 24.80; H, 5.71; N, 6.28%. FT-IR data
(KBr, cmꢀ1) major peak 1540.
Complex (3) reacts with urea to retain its mononu-
clear structure and forms [Ni(OAc)(urea)2(tmen)][OTf]
(5) whereas with monohydroxamic acids (e.g., AHA) it
forms the dihydroxamate bridged dinuclear [Ni2
(l-OAc)(l-AA)2(tmen)2][OTf], previously prepared by
direct reaction of AHA and (1) [9], illustrating the great-
er ability of hydroxamic acids to stabilize dinuclear com-
plexes over that of urea by means of their bridging
bonding mode which leads to a possible explanation
for the inhibiting effect of hydroxamic acids by means
of displacing a bridging urea molecule in a possible
intermediate invoked in the action of urease [16].
However, the dinuclear cobalt complex [Co2(l-OAc)2
(l-H2O)2(tmen)2][OTf]2 (4) reacts with both urea and
hydroxamic acids to form [Co2(l-OAc)3(urea)(tmen)2]
[OTf] (6) and [Co2(l-OAc)(l-AA)2(tmen)2][OTf] (8a),
respectively, both previously prepared by direct reaction
of (2) with urea and hydroxamic acid [15].
4.4. Preparation of [Ni(OAc)(urea)2(tmen)][OTf] (5)
The reaction was carried out under oxygen-free dry
nitrogen.
0.437 g (1 mmol) of [Ni(OAc)(H2O)2(tmen)][OTf]Æ
H2O (3) was reacted with 0.376 g (1.5 mmol) of urea in
10 ml dried methanol. Filtration and removal of solvent
gave a solid residue. Crystallization from acetone gave
(5).
Anal. Calc. for C11H27F3N6O7SNi: C, 26.3; H, 5.45;
N, 16.80. Found: C, 26.5; H, 5.55; N, 16.90%. FT-IR
data (KBr, cmꢀ1) major peaks 1548, 1675.
Tables of electronic and infrared spectra are available
in the Supplementary Material.
5. Preparation of hydroxamate dinuclear tmen complexes
from the mononuclear [Ni(OAc)(H2O)2(tmen)][OTf]Æ
H2O (3)
4. Experimental
4.1. Materials
5.1. Preparation of the dibridged acetohydroxamate
dinickel complex [Ni2(OAc)(AA)2(tmen)2][OTf] (7a)
Reagent and solvents were used as obtained from
commercial sources, without further purification unless
otherwise stated. Methanol, dichloromethane and dieth-
ylether were dried by standard procedures. Nickel (II)
acetate tetrahydrate (98%) and urea (99.5%),
N,N,N0,N0-tetramethylethylenediamine (98%), TMS-
OTf (99%) and hydroxylamine hydrochloride (99%) were
purchased from Aldrich Chemical Co. Ltd., London.
Under nitrogen, 0.136 g (0.311 mmol) of compound
[Ni(OAc)(H2O)2(tmen)][OTf]ÆH2O (3) was dissolved in
3 ml of dry methanol. A solution of acetohydroxamic
acid 0.023 g (0.311 mmol) in 2 ml of dried methanol
was added and the mixture stirred for 30 min. After fil-
tering, solvent was removed under vacuum to give an
oil, which was dissolved in acetonitrile. Vapour diffusion
of diethylether into the solution gave bluish/green crys-
tals of (7a). Yield: 0.123 g (54.6%). Anal. Calc. for
C19H43F3N6O9SNi2: C, 31.52; H, 6.26; N, 11.61. Found:
4.2. Instrumentation
Elemental analyses were performed by the Micro
Analytical Laboratory, Chemical Services Unit, Univer-
sity College Dublin. Infrared spectra were recorded in
the solid state 1–2% KBr (potassium bromide) discs
and solution in a calcium fluoride cell, path length
0.1 mm using a Perkin–Elmer FT-IR Paragon 1000
Spectrometer. UV/vis spectra were recorded on ATI
Unicam UV/visible Spectrometer.
C, 31.14; H, 6.09; N, 11.31%. FT-IR data (KBr, cmꢀ1
major peaks 1632, 1596.
)
5.2. Preparation of the dibridged benzohydroxamate
dinickel complex [Ni2(OAc)(BA)2(tmen)2][OTf]ÆH2O
(7b)
Under nitrogen, 0.874 g (2 mmol) of compound [Ni
(OAc)(H2O)2(tmen)][OTf]ÆH2O (3) was dissolved in
15 ml of methanol. A solution of BHA 0.274 g
(2 mmol) in 5 ml of methanol was added and the mix-
ture stirred for 30 min. After filtering, solvent was re-
moved under vacuum to give an oil, which was
4.3. Preparation of [Ni(OAc)(H2O)2(tmen)][OTf]Æ
H2O (3)
The reaction was carried out under oxygen-free dry
nitrogen.

D.A. Brown et al. / Inorganica Chimica Acta 358 (2005) 2755–2762
2761
dissolved in acetonitrile. Vapour diffusion of diethyle-
ther into the solution gave bluish/green crystals of
(7b). Yield: 0.862 g (50.8%). Anal. Calc. for C29H49-
F3N6O10SNi2: C, 41.07; H, 5.82; N, 9.91. Found: C,
6. Preparation of hydroxamate dinuclear tmen complexes
from [Co2(OAc)2(H2O)2(tmen)2][OTf]2 (4)
6.1. Preparation of the dibridged acetohydroxamate
dicobalt complex [Co2(OAc)(AA)2(tmen)2][OTf]
(8a)
41.19; H, 5.56; N, 9.80%. FT-IR data (KBr, cmꢀ1
major peaks 1623, 1583.
)
5.3. Preparation of the dibridged N-phenylacetohydroxa-
mate dinickel complex [Ni2(OAc)(NPhAA)2(tmen)2]
[OTf]Æ2H2O (7c)
Under nitrogen, 0.241 g (0.3 mmol) of compound
[Co2(OAc)2(H2O)2(tmen)2][OTf]2 (4) was dissolved in
6 ml of methanol. A solution of acetohydroxamic acid
0.045 g (0.6 mmol) in 4 ml of methanol was added and
the mixture stirred for 1 h. After filtering, solvent was
removed under vacuum to give an oil, which was dis-
solved in acetonitrile. Vapour diffusion of diethylether
into the solution gave pink crystals of (8a). Yield:
0.091 g (43%). Anal. Calc. for C19H43F3N6O9SCo2:
C, 30.73; H, 6.38; N, 11.31. Found: C, 31.02; H,
5.81; N, 10.89%. FT-IR data (KBr, cmꢀ1) major
peaks 1632, 1590.
Under nitrogen, 0.437 g (1 mmol) of compound
[Ni(OAc)(H2O)2(tmen)][OTf]ÆH2O (3) was dissolved in
5 ml of methanol. A solution of N-phenylacetohydroxa-
mic acid 0.151 g (1 mmol) in 5 ml of methanol was
added and the mixture stirred for 30 min. After filtering,
solvent was removed under vacuum to give an oil, which
was dissolved in acetonitrile. Vapour diffusion of dieth-
ylether into the solution gave bluish/green crystals of
(7c). Yield: 0.463 g (41.5%). Anal. Calc. for C31H55-
F3N6O11SNi2: C, 41.64; H, 5.97; N, 9.40. Found: C,
41.88; H, 6.10; N, 9.44%. FT-IR data (KBr, cmꢀ1) ma-
jor peaks 1608, 1596.
6.2. Preparation of the dibridged benzohydroxamate
dicobalt complex [Co2(OAc)(BA)2(tmen)2][OTf]Æ
4H2O (8b)
5.4. Preparation of [Co2(OAc)2(H2O)2(tmen)2][OTf]2
(4)
Under nitrogen, 0.351 g (0.437 mmol) of compound
[Co2(OAc)2(H2O)2(tmen)2][OTf]2 (4) was dissolved in
10 ml of methanol. A solution of BHA 0.120 g
(875 mmol) in 5 ml of methanol was added and the
mixture stirred for 1 h. After filtering, solvent was re-
moved under vacuum to give an oil, which was dis-
The reaction was carried out under oxygen-free dry
nitrogen.
Complex [Co2(OAc)4(H2O)(tmen)2] (2) (3.02 g,
5.0 mmol) was reacted with 5 mmol of TMS-OTf
(0.9 ml) in 20 ml of dichloromethane and stirred for
1 h. Removal of solvent gave an oil which was dissolved
in acetonitrile. Vapour diffusion of diethylether into the
solution resulted in pink crystals of [Co2(OAc)2
(H2O)2(tmen)2][OTf]2 (4). Yield 1.9 g (47%). Anal. Calc.
for C18H42F6N4O12S2Co2: C, 26.94; H, 5.28; N, 6.98.
Found: C, 27.21; H, 5.29; N, 6.91%. FT-IR data (KBr,
cmꢀ1) major peaks 1578, 1998–2070.
solved
in
acetonitrile.
Vapour
diffusion
of
diethylether into the solution gave a pink solid of
(8b). Yield: 0.181 g (46%). Anal. Calc. for C29H55-
F3N6O13SCo2: C, 38.59; H, 6.14; N, 9.31. Found: C,
38.82; H, 5.29; N, 8.75%. FT-IR data (KBr, cmꢀ1
major peaks 1614, 1581.
)
Acknowledgement
5.5. Preparation of [Co2(OAc)3(urea)(tmen)2][OTf]
(6)
We thank the EU COST D21 programme, Project
D21/0001/00 and Dublin City Council for support.
[Co2(OAc)2(H2O)2(tmen)2][OTf]2
(4)
2.314 g
(2.22 mmol) was reacted with urea 0.199 g (3.33 mmol)
in 10 ml dried methanol under nitrogen in 1:1.5 molar
ratio. Removal of solvent gave a pink oil which upon
extraction using n-pentane resulted in a pink powder
which was dissolved in acetone. Vapour diffusion of
petroleum spirit into the solution resulted in pink crys-
tals of [Co2(OAc)3(urea)(tmen)2][OTf] (6). Yield: 1.83 g
(30%). Anal. Calc. for C20H45F3N6O10SCo2: C, 32.62;
H, 6.16; N, 11.42. Found: C, 32.34; H, 6.06; N,
11.16%. FT-IR data (KBr, cmꢀ1) major peaks 1617,
1561, 1669.
Appendix A. Supplementary data
Crystallographic data for (3) and (4) have been
deposited with the Cambridge Crystallographic Data
Centre (12 Union Road, Cambridge CB2 1EZ, e-mail:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk)
as Supplementary Material, CCDC number 260975 for
(3) and 260976 for (4). Supplementary data associated
with this article can be found, in the online version, at
doi:10.1016/j.ica.2005.01.029.

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D.A. Brown et al. / Inorganica Chimica Acta 358 (2005) 2755–2762
[10] G.M. Sheldrick, SADABS, Emprirical Absorption Corrections
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