Geometric Factors in the Structural and Thermodynamic Properties of Copper(II)
Complexes with Tripodal Tetraamines
Andreas M. Dittler-Klingemann and Chris Orvig*
Department of Chemistry, University of British Columbia, 2036 Main Mall,
Vancouver, British Columbia, Canada V6T 1Z1
F. Ekkehardt Hahn*
Institut fu ¨r Anorganische und Analytische Chemie, Freie Universita ¨t Berlin,
Fabeckstrasse 34-36, 14195 Berlin, Germany
Florian Thaler, Colin D. Hubbard, Rudi van Eldik, and Siegfried Schindler
Institut fu ¨r Anorganische Chemie, Universita ¨t Erlangen-Nu ¨rnberg,
Egerlandstrasse 1, 91058 Erlangen, Germany
Istva ´ n Fa ´ bia ´ n
Department of Inorganic and Analytical Chemistry, Lajos Kossuth University,
4010 Debrecen 10, Hungary
ReceiVed May 22, 1996
X
The tripodal tetramine ligands N(CH
2
CH
2
CH
2
NH
2
)
3
(trpn) and N[(CH
2
CH
2
CH
2
NH
2
)
2
(CH
2
CH
2
NH
2
)] (332) react
with Cu(NO
3
)
2
‚3H
2
O in water to give light blue copper(II) complexes. These were characterized by X-ray
crystallography to be the square-pyramidal binuclear Cu(II) species [Cu(trpn)(NO
3
)]
2
(NO
3
)
2
and [Cu(332)(NO
3
)]
2
-
(NO
3
)
2
‚2H
2
O. Selected crystallographic details are as follows, respectively: formula C
18
H
48
Cu
2
N
12
O
12
,C
16
H
48
-
Cu
2
N
12
O
14
; M ) 751.74, 759.72 Da; both triclinic; both P1 h; a ) 8.4346(8), 8.446(4) Å; b ) 9.0785(9), 8.744(3)
Å; c ) 11.9310(12), 12.007(3) Å; R) 94.50(1), 102.68(2)°; ) 103.56(1), 94.79(3)°; γ ) 117.42(1), 117.69-
(4)°; V ) 769.7(5), 748.2(13) Å
3
; both Z ) 1; R ) 4.16, 4.00; R
w
) 11.34, 6.74 for 2887 (I g 2σ(I)), 2457 (F
o
2
g 3σ(F
o
2
)) structure factors and 199, 209 refined parameters. The binuclear complex dications exhibit a square-
pyramidal coordination geometry around the copper atoms. Three amine functions (one tertiary and two primary)
are coordinated to one copper atom and the remaining primary amine arm bridges to the second copper center.
Potentiometric and visible spectrophotometric studies show that a protonated square-pyramidal [Cu(HL)(H
2
O)
2
]
3+
cation (L ) trpn, 332, 322 (322 ) N[(CH
2
CH
2
CH
2
NH
2
)(CH
2
CH
2
NH
2
)
2
])) predominates in the intermediate pH
region, in contrast to the established trigonal-bipyramidal structure of the tren (tren ) tris(2-aminoethyl)amine))
complex of Cu(II). Each [Cu(HL)(H
2
O)
2
]
3+
has one protonated uncoordinated ligand arm which explains the
formation of the binuclear species at neutral pH.
Introduction
Extensive and elegant studies of different aspects of copper-
(II) and copper(I) chemistry have shown that this transition metal
possesses a wide repertoire of coordination geometries and
properties.
1
Investigations are stimulated, in part, by widespread
interest in the bioinorganic chemistry of copper because of the
presence of the metal in many metalloproteins and metallo-
enzymes.
1
Copper(II) aqua ions have a distorted (Jahn-Teller) octa-
hedral structure of coordinated water, which has the consequence
of conferring extreme lability of water exchange, a fact which
thwarted the efforts at a detailed kinetic characterization until
recently.
2,3
In turn, hexaaquacopper(II) reacts to form com-
plexes with extreme rapidity. Upon coordination of the ligand
tren [tren ) tris(2-aminoethyl)amine] the geometry at the copper
center is changed to trigonal-bipyramidal from octahedral. From
a combination of temperature-jump relaxation kinetics measure-
ments and NMR spectroscopy measurements of water exchange
at ambient and elevated pressures, it has been concluded
4
that
ligand substitution occurs by an I
a
mechanism, whereas an I
d
mechanism is operative for octahedral copper aqua complexes.
These findings have encouraged us to determine which factors
influence the geometry and reactivity of copper complexes with
tripodal tetraamine ligands. To address this problem, we have
studied the coordination chemistry of copper(II) with the
symmetric and unsymmetric tripodal N
4
ligands (Figure 1) and
X
Abstract published in AdVance ACS Abstracts, December 1, 1996.
(1) For example: (a) Zubieta, J.; Karlin, K. D. Copper Coordination
Chemistry: Biochemical and Inorganic PerspectiVes; Adenine Press:
New York, 1983. (b) Wei, N.; Murthy, N. N.; Karlin, K. D. Inorg.
Chem. 1994, 33, 6093. (c) Knowles, P. F.; Brown, R. D., III; Koenig,
S. H.; Wang, S.; Scott, R. A.; McGuirl, M. A.; Brown, D. H.; Dooley,
D. M. Inorg. Chem. 1995, 34, 3895. (d) Karlin, K. D.; Tyeklar, Z.
Bioinorganic Chemistry of Copper; Chapman and Hall: New York,
1993.
(2) Swift, T. J.; Connick, R. E. J. Chem. Phys. 1962, 37, 307.
(3) Powell, D. H.; Furrer, P.; Pittet, P.-A.; Merbach, A. E. J. Phys. Chem.
1995, 99, 16622.
(4) Powell, D. H.; Merbach, A. E.; Fabian, I.; Schindler, S.; van Eldik,
R. Inorg.Chem. 1994, 33, 4468.
7798 Inorg. Chem. 1996, 35, 7798-7803
S0020-1669(96)00585-X CCC: $12.00 © 1996 American Chemical Society