Synthesis, structure and magnetic properties of [Cu4(Hmbpp)2(H2NC(O)NH2)2 (H2O)8]·4H2O

Article abstract of DOI:10.1039/b309475h

[Cu₄(Hmbpp)₂(H₂NC(O) NH₂)₂(H₂O)₈]·4H₂O 1, the first example of a discrete polynuclear copper phosphonate complex isolated from aqueous media was synthesised by the add

Full text of DOI:10.1039/b309475h

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis, structure and magnetic properties of
[
Cu (Hmbpp) (H NC(O)NH ) (H O) ]ؒ4H O
4
2
2
2 2
2
8
2
a
a
a
a
a
Andrew Harrison, David K. Henderson,* Paul A. Lovatt, Andrew Parkin, Peter A. Tasker*
b
and Richard E. P. Winpenny
School of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh,
a
UK EH9 3JJ
b
Department of Chemistry, The University of Manchester, Oxford Road, Manchester,
UK M13 9PL
Received 7th August 2003, Accepted 10th September 2003
First published as an Advance Article on the web 22nd September 2003
[
Cu (Hmbpp) (H NC(O)NH ) (H O) ]ؒ4H O 1, the first example of a discrete polynuclear copper phosphonate
4 2 2 2 2 2 8 2
complex isolated from aqueous media was synthesised by the addition of urea to a solution of a copper() salt and
the bisphosphonic acid ligand 4-methyl-2,6-bis(phosphonomethyl)phenol (H mbpp). 1 contains four distorted square
5
pyramidal copper atoms and the Cu units are linked by a complicated hydrogen bonded network involving
4
co-crystallised water molecules.
Introduction
Earlier work
Experimental
1–3
on the design of ligating groups to attach
Preparation of compounds
organic actives to metal oxide surfaces, and thus control prop-
erties such as corrosion inhibition or the adhesion of polymers
and dyes has shown that molecules containing several donor
atoms which can address an array of surface metals via ‘multi-
site attachment’, form very stable complexes. A systematic
approach to improving the efficacy of such ligands requires an
understanding of their modes of binding. We have shown that
the preparation and structure-determination of polynuclear
cage compounds can assist in this process by providing inform-
ation on the donor atom dispositions which can then be related
to the requirements to address arrays of metal ions in oxide
All reagents, metal salts and ligands were used as obtained from
Acros or Aldrich. Analytical data were obtained on a Perkin-
Elmer 2400 Elemental Analyser by the University of Edinburgh
Microanalytical Service. Infrared spectra were obtained as
potassium bromide discs using a Perkin-Elmer Paragon 1000
FT-IR spectrometer. EPR spectra were recorded on a Bruker
ESP300E spectrometer Q-band (ca. 34 GHz) between 115 K
and 300 K. Variable temperature magnetic measurements in the
region 1.8–350 K were made using a SQUID magnetometer
(
Quantum Design) with samples sealed in gelatin capsules.
1,2
surfaces. In this context, ligands containing several phos-
phonic acid groups are of great interest because they form very
4
-Methyl-2,6-bis(phosphonomethyl)phenol (H mbpp). 2,6-Bis-
5
4
(
hydroxymethyl)-p-cresol (8.4 g, 50 mmol) and trimethyl
stable/insoluble metal complexes which have received a great
phosphite (13.0 g, 105 mmol) were heated under reflux for four
hours. The solution was cooled to room temperature and the
excess trimethyl phosphite removed on a rotary evaporator to
give a colourless oil. Diethyl ether was added to the flask and
the solution placed in the fridge overnight. The white precipi-
tate that formed was filtered off and dried under vacuum to give
deal of attention in recent years due to the diverse range of
potential applications for such materials. These include cation
5
6
7
8
exchange, catalysis/catalyst supports, sorption, sensors, non-
9
10
linear optics and magnetic materials.
Discrete cage complexes featuring phosphonate ligands are
rare due to their propensity to form insoluble polymeric
species. The few that have been structurally characterised
[3-(dimethoxy-phosphorylmethyl)-2-hydroxy-5-methyl-benzyl]-
1
1
12
13
phosphonic acid dimethyl ester as a white crystalline solid. This
was dissolved in water (100 ml) and methanol (100 ml) and the
solution heated under reflux overnight. The solution was
cooled to room temperature and the solvent removed on a
rotary evaporator to give a white solid which was recrystallised
from methanol/ethyl acetate, washed with ethyl acetate then
diethyl ether and dried under vacuum to give 4-methyl-2,6-bis-
include several vanadium, zinc and aluminium complexes,
10
1
4
a dodecanuclear copper cluster, a tridecanuclear cobalt cage,
10
15
and manganese and iron cages where carboxylate triangles
are linked through phosphonates. The aluminium, zinc and
copper complexes were synthesised under rigorously anhydrous
conditions to avoid hydrolysis and polymerization. Once
formed the aluminium cages are stable to hydrolysis in air due
to the protection afforded by the lipophilic sheath of organic
ligands encapsulating the metal core.
(
≈
phosphonomethyl)phenol as a white solid (9.1 g, 61%); mp
250 ЊC (Found: C, 36.7; H, 4.6%; C H O P requires C, 36.5;
9
14
7
2
1
H, 4.7%); H NMR (D O, 200 MHz) δ 6.88–6.85 (m, 2H), 3.07
Metal surfaces of commercial interest are usually coated by a
thin oxide/hydroxide layer. Consequently, if we are to under-
stand the ligand design features required for strong binding,
model structures should ideally contain similar oxo or
hydroxo bridged components. Two- and three-dimensional
materials of this type are generally synthesised by hydrothermal
methods. 16An alternative method used by Zhang and
Clearfield exploits the hydrolysis of urea which slowly
2
13
(
d, 4H, 2 × CH ), 2.10 (d, 3H, CH ); C NMR (D O, 63 MHz)
2
3
2
δ 149.45 (1C), 131.24 (1C), 130.54 (2C), 121.64 (2C), 29.36
3
1
(
d, 2C, 2 × CH ), 19.41 (1C, CH ); P NMR (D O, 101 MHz)
2
3
2
Ϫ1
δ 26.92 (2P); FABMS m/z 297 (LH); IR (cm , KBr disc)
ν 2926m (CH), 1636w, 1485s, 1398w, 1377w, 1310m, 1264m
(
P᎐O), 1229s, 1159s, 1116s, 1013s, 952s, 927s, 868w, 845w,
᎐
7
31m, 688w, 606w, 541w, 510m, 464w.
generates NH , raising the pH of an aqueous solution con-
3
taining a metal salt and the phosphonic acid. A variation
on this method was used to produce [Cu (Hmbpp) (H NC-
[Cu (Hmbpp) (H NC(O)NH ) (H O) ]ؒ4H O 1. Copper per-
chlorate hexahydrate (1.0 g, 2.7 mmol) and 4-methyl-2,6-
4
2
2
2
2
2
8
2
4
2
2
(
O)NH ) (H O) ]ؒ4H O 1.
bis(phosphonomethyl)phenol (H mbpp) (0.40 g, mmol) were
2
2
2
8
2
5
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 4 2 7 1 – 4 2 7 4
4271

View Article Online
dissolved in distilled water (40 ml) and sodium hydroxide
2.75 ml of a 1 M solution) was added dropwise. The solution
(
colour changed from blue through yellow to brown. The
solution was filtered into a 100 ml thick walled test tube, urea
(
0.40 g) was added and the tube was sealed and heated (65 ЊC)
overnight. A small quantity of brown precipitate was removed,
more urea (0.40 g) was added and the sealed tube left to stand
at room temperature. Brown crystals of 1 were collected after
four days, yield 0.23 g, 29% (Found: C, 20.5; H, 4.4; N, 4.8%;
Ϫ1
C H Cu N O P requires C, 20.4; H, 4.4; N, 4.8%); IR (cm
,
20
52
4
4
28
4
KBr disc) ν 3456s (OH), 3325s (NH), 3246s, 2922m (CH), 1657s
(
C᎐O), 1578m, 1503w, 1460m, 1409w, 1310w, 1240m (P᎐O),
᎐ ᎐
1
8
218w, 1207w, 1141s, 1110s, 1083s, 1026s, 984s, 941m, 866w,
60w, 782w, 751m, 627w, 581m, 557m, 502m. Crystals of 1
suitable for X-ray analysis were grown from a similar reaction
substituting copper sulfate pentahydrate in place of copper
perchlorate hexahydrate.
Fig. 1 Structure of 1 in the crystal.
Crystallography
Cu(2)–O(2) 2.3685(17) Å. The angles between the axial oxygen
and the equatorial oxygens range from 89.61(6) to 101.62(6)Њ.
The distance between the central copper atoms is 3.0886(8) Å
while that between Cu(1) and the outer copper, Cu(2), is
5.2289(9) Å. The central core of the complex can be described
Data collection and processing. Data for 1 were collected at
50(2) K on a Bruker SMART APEX CCD diffractometer
1
equipped with an Oxford Cryosystems low-temperature device
using graphite monochromated Mo-K radiation (λ = 0.71073
α
Å). Formula C H Cu N O P , M 1174.70, monoclinic, space
as a Cu O dimer, in which the two Cu(1) centres are bridged
2 2
20
52
4
4
28
4
group P21/c, a = 7.9478(18), b = 14.715(3), c = 17.977(4) Å,
β = 99.129(4)Њ, V = 2075.9(8) Å , Z = 2, µ = 2.275 mm , 4219
unique data, R1 = 0.0227, wR2 = 0.0665.
[Cu(1)–O(11)–Cu(1) 103.79(6)Њ] by the phenolate oxygens of
two Hmbpp ligands. Two phosphonate oxygens, one from
each Hmbpp ligand and a water molecule in the axial position
complete the coordination of the Cu(1) sites, which are crystal-
lographically identical.
3
Ϫ1
Structure analysis and refinement. The structure was solved
The outer copper atom, Cu(2), is coordinated to one phos-
phonate oxygen, three water molecules, one of which is in the
axial coordination site, and the oxygen atom of a urea molecule.
The presence of a urea ligand was unexpected as this has
not been reported in other polynuclear complexes which have
been prepared using urea as a base. Coordinated urea is not
1
7
2
by direct methods (SHELXTL ) and refined against F using a
17
full matrix least squares procedure (SHELXTL ). An absorp-
tion correction was applied using the multi-scan method of
18
19
Blessing (SADABS ).
All hydrogen atoms bound to oxygen atoms were located
on the difference map and refined with distance restraints of
21
uncommon in copper complexes, particularly in copper
0
.85 Å. All twelve of these hydrogen atoms refined to distances
22
carboxylate dimers where it occupies the terminal sites. The
between 0.789(16) and 0.877(17) Å. All other hydrogen
atoms were placed at calculated positions and refined as riding
groups or rotating groups. All non-H atoms were included with
anisotropic displacement parameters.
CCDC reference number 217024.
See http://www.rsc.org/suppdata/dt/b3/b309475h/ for crystal-
lographic data in CIF or other electronic format.
involvement of the urea in both intra- and inter-molecular
hydrogen bonding within complex 1 may explain its presence in
this case.
The Hmbpp ligands have not been fully deprotonated in 1
and as a result are unsymmetrical with one phosphonate group
doubly deprotonated and the second only singly deprotonated.
The phenolic oxygen is also deprotonated. As might be
expected it is the doubly deprotonated phosphonate which
performs the bridging function between Cu(1) and Cu(2). The
phenyl rings of the Hmbpp ligands are twisted out of the plane
formed by the Cu O core by an angle of 62.8Њ. Interestingly the
Results and discussion
2
2
Synthesis and structure of [Cu (Hmbpp) (H NC(O)NH ) -
4
2
2
2 2
ligands adopt the same trans conformation of the methylene
(
H O) ]ؒ4H O 1
2 8 2
23
phosphonic acid arms as seen in the structure of the free
The ligand 4-methyl-2,6-bis(phosphonomethyl)phenol (H -
mbpp) was synthesised in two steps via a modified literature
method. Slowly raising the pH of an aqueous solution of
ligand.
5
2
0
The tetranuclear complex contains six strong inter-ligand
hydrogen bonds. The central [Cu (Hmbpp) (H O) ] unit in
4Ϫ
2 2 2 2
copper perchlorate hexahydrate, H mbpp and sodium
1 is enclosed by hydrogen bonding between the terminal
phosphonate oxygens O(63)–H ؒ ؒ ؒ O(23) 2.4941(19) Å. A
5
hydroxide using urea, on standing gave brown crystals that were
identified by a combination of X-ray and elemental analysis as
the tetranuclear copper complex [Cu (Hmbpp) (H NC(O)-
24,25
similar effect is believed to impart stability
to the bis-sali-
cylaldoximatocopper() complexes formed in the commercial
solvent extraction of copper, where a ring structure is generated
by inter-ligand hydrogen bonding between the oxime protons
and phenolate oxygen atoms. The two outer coppers are co-
ordinated to the cage via a single bond to a phosphonate
oxygen but are further stabilised by two additional hydrogen
bonds, the first between an equatorial water molecule co-
ordinated to Cu(2) and a phosphonate oxygen coordinated to
Cu(1), O(3)–H ؒ ؒ ؒ O(21) 2.6160(19) Å, and the second between
a nitrogen donor from the coordinated urea and a phosphonate
oxygen coordinated to Cu(1), N(1U)–H ؒ ؒ ؒ O(22) 2.797(2) Å.
The crystal structure determination also reveals a very com-
plicated intermolecular hydrogen bond network involving
4
2
2
NH ) (H O) ]ؒ4H O 1 (Fig. 1). Initially, due to the poor quality
2
2
2
8
2
of the crystals, identification of the terminal ligands as urea
groups was made on the basis of elemental analysis data.
Changing the copper salt to copper sulfate resulted in higher
quality crystals, but lower yield (15%), enabling the structure to
be definitively assigned (R-factor 0.0227). Elemental analysis
for both products was identical.
Complex 1 contains four, distorted square pyramidal copper
atoms with all oxygen donor sets. The equatorial Cu–O bond
lengths range from 1.9371(13) to 1.9931(15) Å (see Table 1) and
the axial bonds to the oxygen donors of water, which are longer
due to Jahn–Teller distortion, are Cu(1)–O(1) 2.2060(15) Å and
4
272
D a l t o n T r a n s . , 2 0 0 3 , 4 2 7 1 – 4 2 7 4

View Article Online
Table 1 Selected bond lengths (Å) and angles (Њ) for 1
Cu(1)–O(21)
Cu(1)–O(11)#1
Cu(1)–O(11)
Cu(1)–O(61)#1
Cu(1)–O(1)
1.9371(13)
1.9426(13)
1.9825(12)
1.9819(13)
2.2060(15)
Cu(2)–O(22)
Cu(2)–O(2U)
Cu(2)–O(3)
Cu(2)–O(4)
Cu(2)–O(2)
1.9637(13)
1.9420(13)
1.9635(15)
1.9931(15)
2.3685(17)
O(21)–Cu(1)–O(11)#1
O(21)–Cu(1)–O(11)
O(11)#1–Cu(1)–O(11)
O(21)–Cu(1)–O(61)#1
O(11)#1–Cu(1)–O(61)#1
O(11)–Cu(1)–O(61)#1
O(21)–Cu(1)–O(1)
O(11)#1–Cu(1)–O(1)
O(11)–Cu(1)–O(1)
O(61)#1–Cu(1)–O(1)
Cu(1)#1–O(11)–Cu(1)
165.56(5)
94.45(5)
76.21(6)
91.22(5)
95.29(5)
164.81(5)
90.53(6)
101.62(6)
98.43(6)
95.60(5)
103.79(6)
O(2U)–Cu(2)–O(3)
O(2U)–Cu(2)–O(22)
O(3)–Cu(2)–O(22)
O(2U)–Cu(2)–O(4)
O(3)–Cu(2)–O(4)
O(22)–Cu(2)–O(4)
O(2U)–Cu(2)–O(2)
O(3)–Cu(2)–O(2)
O(22)–Cu(2)–O(2)
O(4)–Cu(2)–O(2)
169.16(6)
97.19(6)
89.72(6)
88.83(6)
83.85(6)
173.14(6)
89.61(6)
98.36(6)
93.25(5)
90.06(6)
Symmetry transformations used to generate equivalent atoms: #1 Ϫx,Ϫy, Ϫz.
hydrogen bond acceptors/donors in the complex and the four
water molecules within the unit cell. The packing of the com-
Table 2 Hydrogen bond contacts within 1
Bond type
Donor atom
Acceptor atom
Bond length/Å
plex in the crystal is shown (Fig. 2). Within the crystal the
molecules of [Cu (Hmbpp) (H NC(O)NH ) (H O) ] are linked
4
2
2
2
2
2
8
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
N–H ؒ ؒ ؒ O
N–H ؒ ؒ ؒ O
N–H ؒ ؒ ؒ O
N–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O–H ؒ ؒ ؒ O
O(63)
O(3)
N(1U)
N(1U)
N(3U)
N(3U)
O(1)
O(1)
O(2)
O(2)
O(3)
O(4)
O(4)
O(1W)
O(1W)
O(2W)
O(2W)
O(23)
O(21)
O(22)
O(3)
2.4941(19)
2.6160(19)
2.797(2)
3.042(2)
3.334(2)
2.909(2)
2.722(2)
2.805(2)
3.091(2)
3.017(2)
2.558(2)
2.781(2)
2.678(2)
2.838(2)
2.849(2)
2.697(2)
2.781(2)
both via direct hydrogen bonds and through the water mole-
cules within the crystal lattice. Each water molecule is situated
at the hub of four hydrogen bonds, one of which is to the other
water and the remaining three to oxygens or nitrogens on the
complex. A full list of all intra- and inter-molecular hydrogen
bonds in 1 is given (Table 2).
O(4)
O(1W)
O(23)
O(2W)
O(61)
O(63)
O(62)
O(61)
O(2W)
O(2)
O(22)
O(62)
O(1W)
Fig. 2 Packing of 1 in the crystal.
Fig. 3 EPR spectrum of 1 at 115 K.
EPR Studies
to have a simple Curie–Weiss form (Fig. 4), but when the effec-
tive moment is calculated from these data as a function of
temperature, the value at relatively high temperatures is found
to be significantly lower than would be expected for para-
The EPR spectrum (Fig. 3) of a solid sample of 1 at room
temperature is broad and typical of a spectrum due to an S = ½
spin state. At 115 K the powder spectrum is much sharper, with
three g-values resolved at g = 2.335, 2.020 and 2.009. This is
therefore typical for a Cu() centre with an unpaired electron in
2ϩ
magnetic Cu with g ≈ 2.0 (Fig. 4). One interpretation of these
data is that the central copper ions, Cu(1), bound through
bridging phenolic oxygen atoms, O(11), have strong anti-
ferromagnetic coupling such that by 350 K they effectively form
the dx
2
2
orbital. No copper hyperfine structure is resolved.
Ϫ y
The EPR behaviour suggests that there is very strong anti-
ferromagnetic exchange within the central Cu O ring of the
complex, causing this part of the compound to be EPR silent.
The two external Cu() centres are non-interacting, and the
EPR signal is presumably due to these copper sites.
2
2
2ϩ
a singlet pair, and the Cu ions Cu(1) and Cu(2) bonded
through a phosphonate linkage O(21)–P(2)–O(22) are more
weakly coupled. The data were least-squares fitted to an expres-
sion for the susceptibility of a linear tetrameric cluster of
2ϩ
Cu ions in which the exchange interaction between the central
Magnetic behaviour
pair of ions is J , and between these ions and the nearest-
2
26,27
The magnetic behaviour of 1 was studied in the range 1.8 to
neighbour terminal ions is J1;
the expression also included a
2ϩ
3
50 K. The susceptibility per mole of Cu appears at first sight
TIP term, and the possibility of paramagnetic impurities, for
D a l t o n T r a n s . , 2 0 0 3 , 4 2 7 1 – 4 2 7 4
4273

View Article Online
2
3
M. Frey, S. G. Harris, J. M. Holmes, D. A. Nation, S. Parsons,
P. A. Tasker and R. E. P. Winpenny, Chem. Eur. J., 2000, 6,
1
407.
S. S. De Silva, P. A. Camp, D. K. Henderson, D. C. R. Henry,
H. McNab, P. A. Tasker and P. Wight, Chem. Commun., 2003,
1
702.
4
5
A. Clearfield, Prog. Inorg. Chem., 1998, 47, 371.
(a) A. Clearfield, Inorganic Ion Exchange Materials, CRC Press,
Boca Raton, FL, 1982; (b) G. Alberti, Acc. Chem. Res., 1978, 11,
1
63; (c) J. D. Wang, A. Clearfield and G.-Z. Peng, Mater. Chem.
Phys., 1993, 35, 208.
6
7
(a) B.-Z. Wan, R. G. Anthony, G.-Z. Peng and A. Clearfield,
J. Catal., 1994, 19, 101; (b) D. Deniaud, B. Schollorn, D. Mansuy,
J. Rouxel, P. Battion and B. Bujoli, Chem. Mater., 1995, 7, 995.
(a) F. Fredoueil, D. Massiot, P. Janvier, F. Gingle, M. Bujoli-Doeuff,
M. Evain, A. Clearfield and B. Bujoli, Inorg. Chem., 1999, 38,
1831; (b) G. Cao, V. M. Lynch and L. N. Yacullo, Chem. Mater.,
½
Fig. 4 Magnetic susceptibility, χ (᭺) and (8χT) (᭹) of 1; the solid
1
993, 5, 583.
8 (a) G. Alberti and R. Polombari, Solid State Ionics, 1989, 35, 153;
b) G. Alberti, M. Casciola and R. Polombari, Solid State Ionics,
line represents a least-squares fit of the copper tetramer expression to
½
values of (8χT) , as discussed in the text.
(
2
ϩ
2ϩ
1992, 52, 291.
instance arising from monomeric Cu species. All Cu ions
were assumed to have the same value of g = 2.12, chosen to be
consistent with the EPR data. The result of this procedure is
displayed in Fig. 4 for |J | = 17.3 (0.4) K, J = Ϫ432 (12) K,
9
S. B. Ungashe, W. L. Wilson, H. E. Katz, G. R. Scheller and
T. M. Putvinsky, J. Am. Chem. Soc., 1992, 114, 8717.
10 E. K. Brechin, R. A. Coxall, A. Parkin, S. Parsons, P. A. Tasker and
R. E. P. Winpenny, Angew. Chem., Int. Ed., 2001, 40, 2700.
1
Ϫ1
2
1
1 I. Khan and J. Zubieta, Prog. Inorg. Chem., 1995, 43, 1–149 and
χTIP = 60 (20) emu mol and 3 mol% paramagnetic (S = ½)
impurity. We have chosen to represent the optimised form
of the expression in Fig. 4 as the variation of (8χT) (which
is approximately the magnetisation of each copper ion) with
temperature because it is more sensitive to the optimised
parameters.
references therein.
½
12 (a) V. Chandrasekhar, S. Kingsley, B. Hatigan, M. K. Lam and
A. L. Rheingold, Inorg. Chem., 2002, 41, 1030; (b) Y. Yang, J. Pinkas,
M. Nolyemeyer, H.-G. Schmidt and H. W. Roesky, Angew. Chem.,
Int. Ed., 1999, 38, 664.
13 M. G. Walawalker, H. W. Roesky and R. Murgugavel, Acc. Chem.
Res., 1999, 32, 117 and references therein.
4 V. Chandrasekhar and S. Kingsley, Angew. Chem., Int. Ed., 2000,
39, 2320.
5 E. I. Tolis, M. Helliwell, S. Langley, J. Raftery and R. E. P.
Winpenny, Angew. Chem., Int. Ed., 2003, 42, 2556.
1
Conclusions
1
In the context of our original intention to develop H mbpp as a
5
surface modifying ligand, we have shown that it can function in
a trinucleating mode, with the possibility of further complex
stabilisation through hydrogen bonding of the protonated
phosphonate arm to surface oxides. Further deprotonation
would allow the coordination of additional surface metal ions.
The central phenolic oxygen can address metal oxide surfaces
with an M ؒ ؒ ؒ M separation of ca 3.1 Å which compares with
16 J. Zhang and A. Clearfield, Inorg. Chem., 1992, 31, 2821.
17 G. M. Sheldrick, SHELXTL Programs for Crystal Structure
Analysis (Release 97-2), Göttingen University, Germany, 1998.
1
1
8 R. H. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33.
9 SADABS: Area-Detector Absorption Correction, Siemens
Industrial Automation, Inc., Madison, WI, 1996.
2
0 V. Bohmer and W. Vogt, Helv. Chim. Acta, 1993, 76, 139.
21 For examples see: (a) K. K. Palkina, N. E. Kuz’mina and
V. T. Orlova, Zh. Neorg. Khim., 1994, 39, 1133; (b) R. Cuesta, J. Ruiz,
J. M. Moreno and E. Colacio, Inorg. Chim. Acta, 1994, 227, 43;
28
the Cu ؒ ؒ ؒ Cu distances found in the CuO mineral tenorite of
.9005(3), 3.0830(4) and 3.1734(4) Å.
2
(
c) M. Koman, E. Jona and D. Nagy, Z. Kristallogr., 1995, 210, 873.
2
2 For examples see: H. Uekusa, S. Ohba, Y. Saito, M. Kato, T. Tokii
and Y. Muto, Acta Crystallogr., Sect. C, 1989, 45, 377.
3 G. Ferguson and J. F. Gallagher, Acta Crystallogr., Sect. C, 1993, 49,
1024.
Acknowledgements
2
The authors would like to thank the national EPR service in
Manchester for the Q-band EPR spectrum of 1 and the EPSRC
24 A. Jarski and E. C. Lingafelter, Acta Crystallogr., 1964, 17,
1
109.
(
UK) for support (D. K. H. and P. A. L.).
2
2
5 K. Burger and I. Egyed, J. Inorg. Nucl. Chem., 1965, 27, 2361.
6 G. V. Rubenacker, J. E. Drumheller, K. Emerson and R. D. Willett,
J. Magn. Magn. Mater., 1986, 54–57, 1483.
7 A. Ayllon, I. C. Santos, R. T. Henriques, M. Almeida, L. Alcacer
and M. T. Duarte, Inorg. Chem., 1996, 35, 168.
References
2
1
M. Frey, S. G. Harris, J. M. Holmes, D. A. Nation, S. Parsons,
P. A. Tasker, S. J. Teat and R. E. P. Winpenny, Angew. Chem., Int.
Ed., 1998, 37, 3246.
28 S. Asbrink and L.-J. Norrby, Acta Crystallogr., Sect. B, 1970,
26, 8.
4
274
D a l t o n T r a n s . , 2 0 0 3 , 4 2 7 1 – 4 2 7 4