Control of copper(II) coordination geometry via supramolecular assembly of ligands in the solid state

Article abstract of DOI:10.1039/a902196e

The high density and strength of intermolecular hydrogen bonding between amine and sulfonamide units in the complex [Cu(Tstn)₂] [TstnH = N-(3-aminopropyl)-4-methylbenzenesulfonamide] give rise to energetically unfavourable coordination geometries at the copper centres in the solid state, in a manner analogous to the entatic state forced on metal active sites in metalloenzymes through secondary and tertiary protein structures.

Full text of DOI:10.1039/a902196e

Control of copper(ii) coordination geometry via supramolecular assembly of
ligands in the solid state
David J. White,*a Leroy Cronin,a Simon Parsons,a Neil Robertson,a Peter A. Tasker*a and Adrian P. Bissonb
a Department of Chemistry, The University of Edinburgh, Joseph Black Building, Kings Buildings, West Mains Rd.,
Edinburgh, UK EH9 3JJ. E-mail: P.A.Tasker@ed.ac.uk
b Zeneca Specialties plc, PO Box 42, Hexagon House, Blackley, Manchester, UK M9 8ZS
Received (in Cambridge, UK) 19th March 1999, Accepted 6th May 1999
The high density and strength of intermolecular hydrogen
bonding between amine and sulfonamide units in the
complex [Cu(Tstn)2] [TstnH = N-(3-aminopropyl)-4-me-
thylbenzenesulfonamide] give rise to energetically unfavour-
able coordination geometries at the copper centres in the
solid state, in a manner analogous to the entatic state forced
on metal active sites in metalloenzymes through secondary
and tertiary protein structures.
chelate planes 36.4 and 34.5° in the two independent mole-
cules). All the amine protons form intermolecular hydrogen
bonds (Table 2) to sulfonamide oxygens resulting in zigzag
The blue copper sites, present in several protein environments,
exhibit a number of characteristics, derived from unusual
electronic structures, that distinguish them from small mole-
cule, copper(ii) complexes.1,2 These characteristics arise from
distorted coordination geometries at the metal centre. The
mismatch between the coordination environment supplied by
the protein (determined by its amino acid sequence and
hydrogen bonded structure), and that preferred by the metal
centre (determined by electronic and steric effects) leads to this
metastable ‘entatic’ or ‘rack’ state.3,4 Entatic states have been
modelled in small molecules by using rigid, predisposed5 or
sterically hindered ligands.6 Although hydrogen bonded sys-
tems have been widely studied due to their potential to control
solid state geometries7 their application in imposing ‘entatic
states’ in simple metal complexes has not been described
previously.
In the system presented here we have used an unhindered
ligand to engineer a high density of hydrogen bond donors and
acceptors into a copper(ii) complex, which lead to a large
number of intermolecular interactions in the solid state. The
copper(ii) complex [Cu(Tstn)2] exists in two crystalline forms
which differ only in the disposition of intermolecular hydrogen
bonds, but which have distorted copper coordination geometries
that differ markedly from each other and from that seen in
solution.
Fig. 1 Molecular structure of 2. Only amine hydrogens are shown. Selected
bond distances and angles for 2 are given in Table 1.
Table 1 Selected bond distances (Å) and angles (°) in 2 and 3
2
3
2
3
Cu1–N1A 2.023(7) 2.001(5) N1A–Cu1–N1B 91.8(2) 95.01(16)
Cu1–N1B 2.013(7) 2.009(5) N1A–Cu1–N5A 91.2(3) 93.3(2)
Cu1–N5A 1.970(8) 1.946(6) N1A–Cu1–N5B 154.5(4) 138.3(2)
Cu1–N5B 1.954(8) 1.959(6) N1B–Cu1–N5A 153.7(4) 137.1(2)
S6A-O61A 1.448(7) 1.445(4) N1B-Cu1-N5B 90.5(3) 93.7(2)
S6A-O62A 1.449(7) 1.463(5) N5A-Cu1-N5B 97.9(2) 107.33(18)
Reaction of TstnH, 1, with copper acetate in boiling methanol
gives a deep blue solution which, on evaporation at ambient
temperature, deposits a dark blue crystalline compound, 2,
identified as [Cu(Tstn)2].† If evaporation is prevented and the
solution is instead left to stand at ambient temperature in a
sealed vessel, it deposits a bright green crystalline compound, 3,
with the same molecular formula, [Cu(Tstn)2]. In solution
(DMF) the electronic and electrospray mass spectra of 2 and 3
are identical, suggesting that a single species is present. The
compounds can be interconverted by dissolution in hot
methanol; evaporation produces 2, whilst crystallization on
cooling and standing produces 3, regardless of the starting
complex. The marked difference in colour and in the measured
solid state visible spectra, in the FTIR spectra and in the melting
behaviour of the two solids led us to determine X-ray crystal
structures for both to define the origin of these differences.‡
The asymmetric unit of the blue compound, 2, contains two
almost isostructural but independent [Cu(Tstn)2] molecules
(weighted rms deviation 1.062 Å) in which the ligands chelate
the metal through deprotonated sulfonamide and amine ni-
trogens (Fig. 1). The coordination geometry (Table 1) at copper
is highly distorted square planar (dihedral angles between the
Table 2 Hydrogen bonded distances (Å) and angles (°) in 2 and 3
H···O
N–H···O
N···O
2
N1A–H1A1···O61D
N1A–H1A2···O62B
N1B–H1B1···O61B
N1B–H1B2···O62D
N1C–H1C1···O62C
N1C–H1C2···O62A
N1D–H1D1···O61A
N1D–H1D2···O61C
2.170
2.068
2.181
2.072
2.178
2.052
2.139
1.996
172.6(9)
170.5(9)
172.9(9)
173.1(8)
168.3(9)
163.2(9)
172.7(9)
170.4(9)
3.075(12)
2.969(12)
3.086(11)
2.977(11)
3.075(11)
2.934(12)
3.044(12)
2.898(12)
3
N1A–H1A1···O62A
N1A–H1A2···O62B
N1B–H1B1···O62B
N1B–H1B2···O62A
2.086
2.344
2.058
2.405
153.1(6)
141.2(5)
151.9(5)
140.4(5)
2.927(6)
3.106(6)
2.893(6)
3.160(6)
Note: the N-H distances were fixed at 0.91 Å. H-bonds were assigned using
the Platon program13 to interactions of the oxygen and nitrogen atoms that
were < 3.12 Å.
Chem. Commun., 1999, 1107–1108
1107

consequence of the system seeking the lowest free energy in the
solid state via formation of very stable hydrogen bonding
networks favoured by the ligands. This offers the intriguing
possibility of controlling the electronic and magnetic properties
of metal centres in the solid state using simple ligands designed
to provide a matrix with unusual coordination sites for metals.
Whilst such an approach is analogous to the entatic state3
binding sites in proteins, unlike these, the unusual geometries
are unlikely to be preserved in solution.
We thank Mr J. Millar and Mr. W. Kerr for obtaining NMR
spectra, Mr A. Taylor and Mr H. MacKenzie for mass spectra,
Ms. L Eades for elemental analyses and Dr R. O. Gould and Mr.
S. G. Harris for help in collecting X-ray data. Thanks to the
Royal Society of Edinburgh (N. R.), the Leverhume Trust
(L. C.) and Zeneca Specialties plc for funding.
Fig. 2 Hydrogen bonded interactions in the solid state structure of 2 and a
schematic representation of these interactions. Selected distances are given
in Table 1.
chains of the complex extending through the structure (Fig.
2).
Notes and references
The asymmetric unit of the green compound, 3, contains a
single [Cu(Tstn)2] molecule (Fig 3). The copper centre has a
more nearly tetrahedral geometry; the dihedral angle between
the two chelate planes is 58.4° and the N1–Cu–N5 chelate
angles are larger, 93.3(2) and 93.7(3)°, than in 2 (average
90.9°). One of the oxygen atoms on each sulfonamide group
forms two hydrogen bonds to amine protons. All of the amine
protons are therefore involved in hydrogen bonds and each
complex has eight SNO···H–N interactions, four as the donor
and four as the acceptor. This results in the formation of a linear
one dimensional hydrogen bonded polymer of [Cu(Tstn)2]
molecules (Fig. 4). Both 2 and 3 are very insoluble materials,
dissolving only very slowly in polar solvents, reflecting the
large number of intermolecular interactions. The number of
hydrogen bonds that each molecule is involved in is the same in
each structure. However, the mean of the O···N distances is
shorter in 2 and the mean of the O···H–N angles is closer to
180°, suggesting that the hydrogen-bonded interactions are
stronger than those in 3. A survey of the CSD8 reveals that the
majority of copper(ii) N4 complexes with 1,3-diaminopropane
based ligands are square planar9 and deviation from this
geometry is only observed with very bulky ligands.6 The
significant distortion toward the energetically unfavourable
tetrahedral geometry observed in 2 and 3 appears to be a
† Experimental procedures: 1: this was prepared by a modification of the
method described by Kirsanov and Kirsanova.10
2: A solution of 1 (0.228 g, 1 mmol) in boiling methanol (10 mL) was
added to a solution of copper acetate hydrate (0.1 g, 0.5 mmol) also in
methanol (10 mL). Immediately a dark, ink blue solution was obtained. The
solution was filtered hot then allowed to cool to room temperature.
Evaporation of solvent at ambient temperature over 24 h gave dark blue
crystals. These were collected by filtration, washed with methanol (3 3 5
mL), then diethyl ether (2 3 5 mL) and dried in vacuo (22 mg, 20% yield).
Crystals suitable for X-ray diffraction were obtained by evaporation of a
saturated methanol solution of the complex; mp 170 °C, decomp. 200 °C
(Found: C, 46.39; H, 5.60; N, 10.60. Calc. for C20H30N4CuO4S2: C, 46.36;
H, 5.84; N, 10.81%); UV–VIS [lmax/nm (e dm3 mol21 cm21)]: dmf, 620
(135); reflectance, 495; MS (FAB, nba) m/z [Cu(Tstn)2]+ 518.
3: This complex was prepared in an identical manner to 2. However,
instead of evaporating the dark blue solution it was left to stand in a sealed
vessel at ambient temperature for 48 h giving bright green crystals. These
were collected by filtration, washed with methanol (3 3 5 mL), then diethyl
ether (2 3 5 mL) and dried in vacuo (24 mg, 22% yield). Crystals suitable
for X-ray diffraction could be obtained using this method; mp (18 °C
decomp.) 200 °C (Found: C, 46.36; H, 5.91; N, 10.79. Calc. for
C20H30N4CuO4S2: C, 46.36; H, 5.84; N, 10.81%). UV–VIS [lmax/nm
(e dm3 mol21 cm21)]: dmf, 620 (135); reflectance, 510. MS (FAB, nba)
m/z [Cu(Tstn)2]+ 518.
‡ Crystal data: both structures were solved by Patterson methods
(DIRDIF)11 and refined against F2 (SHEXL-97).12 2: C20H30N4CuO4S2, M
= 518.14, monoclinic, space group P21/c, a = 15.019(6), b = 24.783(10),
c = 12.873(8) Å, b = 101.43(4)°, U = 4696(4), Z = 8, Dc = 1.466 g cm23
,
T = 220(2) K, m (Cu-Ka) = 3.26 mm21, wR2 = 0.1923 (8543 independent
reflections), R = 0.0612 [F > 4s(F)].
3: C20H30N4CuO4S2, M = 518.14, monoclinic, space group C2/c, a =
32.427(7)), b = 6.1076(15), c = 23.254(5) ≈ , b = 96.30(3)°, U =
4577.6(19), Z = 8, Dc = 1.504 gcm23, T = 220(2) K, m (Mo-Ka) = 1.171
mm21, wR2
= 0.1157 (4050 independent reflections), R = 0.0524
[F > 4s(F)]. CCDC 182/1246. See http://www.rsc.org/suppdata/cc/
1999/1107/ for crystallographic files in .cif format.
1 H. B. Gray and E. I. Solomon, in Copper Proteins, ed. T. G. Spiro,
Wiley, New York, 1981, pp 1–39.
2 E. I. Solomon, in Copper Coordination Chemistry, ed. K. Karlin and J.
Zubieta, Adenin Press, New York, 1982, pp 1–22.
3 R. J. P. Williams, Eur. J. Biochem., 1995, 234, 363.
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and C. D. Garner, Chem. Eur. J., 1996, 2, 685.
Fig. 3 Molecular structure of 3. Only amine hydrogens are shown. Selected
bond distances and angles are given in Table 1.
7 D. Braga and F. Grepioni, J. Chem. Soc., Dalton Trans., 1999, 1.
8 D. A. Fletcher, R. F. McMeeking and D. J. Parkin, J. Chem. Inf. Comput.
Sci., 1996, 36, 746.
9 See, for example B. Morosin and J. Howatson, Acta Crystallogr., Sect.
B, 1970, 26, 2062.
10 A. V. Kirsanov and N. A. Kirsanova, J. Gen. Chem. USSR, 1962, 32,
877.
11 P. T. Beurskens, G. Beurskens, W. P. Bosman, R. d. Gelder, S. Garc`ıa-
Granda, R. O. Gould, R. Israe¨l and J. M. M. Smits, DIRDIF-96,
University of Nijmegen, The Netherlands, 1996.
12 G. M. Sheldrick, SHELXL-97, University of Go¨ttingen, Germany,
1997.
Fig. 4 Hydrogen bonded interactions in the solid state structure of 2 and a
schematic representation of these interactions. Selected distances are given
in Table 1.
13 A. L. Spek. Acta Crystallogr., Sect. A, 1990, 46, C34.
Communication 9/02196E
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Chem. Commun., 1999, 1107–1108