New Cu(II) and Zn(II) complexes of benzolamide with diethylenetriamine: Synthesis, spectroscopy and X-ray structures

Article abstract of DOI:10.1016/S0277-5387(00)00319-3

New benzolamide (H₂bz, 5-phenylsulfonamide-1,3,4-thiadiazole-2-sulfonamide) zinc(II) and copper(II) complexes with diethylenetriamine were synthesized and characterized. The crystal structures of the [M(Hbz)₂(dien)] (M = Cu(II), Zn(II); dien = diethylenetriamine) complexes were determined. The metal centre adopts a near regular square pyramidal geometry. The benzolamidate anion acts as a monodentate ligand through the thiadiazole N atom contiguous to the deprotonated sulfonamido group. Spectroscopic properties are in good agreement with the crystal structures. The EPR and electronic spectroscopic studies showed that the copper(II) species doped into the zinc(II) complex adopts a near square planar geometry. The energy and composition of the SOMO of [Cu(Hbz)₂(dien)] and of copper substituted [Zn(Hbz)₂(dien)] were studied. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(00)00319-3

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 725–730
New Cu(II) and Zn(II) complexes of benzolamide with
diethylenetriamine: synthesis, spectroscopy and X-ray structures
a
a
a,
b
´
´
´
´
´
*
Gloria Alzuet , Sacramento Ferrer-Llusar , Joaquın Borras , Ramon Martınez-Manez
a
´
´
´
Departamento de Quımica Inorganica, Facultad de Farmacia, Universidad de Valencia, Avda. Vicent Andres Estelles s/n, 46100 Burjassot, Spain
b
´
´
Departamento de Quımica, Universidad Politecnica de Valencia, Camino de Vera s/n, 46071 Valencia, Spain
Received 24 November 1999; accepted 28 January 2000
Abstract
New benzolamide (H2bz, 5-phenylsulfonamide-1,3,4-thiadiazole-2-sulfonamide) zinc(II) and copper(II) complexes with diethylenetri-
amine were synthesized and characterized. The crystal structures of the [M(Hbz)2(dien)] (MsCu(II), Zn(II); diensdiethylenetriamine)
complexes were determined. The metal centre adopts a near regular square pyramidal geometry. The benzolamidateanionactsasamonodentate
ligand through the thiadiazole N atom contiguous to the deprotonated sulfonamido group. Spectroscopic properties are in good agreement
with the crystal structures. The EPR and electronic spectroscopic studies showed that the copper(II) species doped into the zinc(II) complex
adopts a near square planar geometry. The energy and composition of the SOMO of [Cu(Hbz)2(dien)] and of copper substituted
[Zn(Hbz)2(dien)] were studied.
q2000 Elsevier Science Ltd All rights reserved.
Keywords: Divalent metals; Zinc; Copper; Benzolamide; Diethylenetriamine; Ternary complexes
1. Introduction
electron-withdrawing effect increases its acidity and in the
deprotonated form sulfonamide anions are effective sigma-
donor ligands. Our previous studies on the interaction of
sulfonamides with metal ions (Zn(II), Co(II), Ni(II) and
Cu(II)) have shown that these can bind in several ways and
not only as unidentate anionsthroughthe sulfonamideNatom
[6–11]. Recently, as a continuation of our investigation, we
initiated the study ofthe coordinationbehaviourofbenzolam-
ide (H2bz, 5-phenylsulfonamide-1,3,4-thiadiazole-2-sulfon-
amide). Benzolamide (Fig. 1) contains two dissociable
protons and affords potentially chelating thiadiazole and sul-
fonamide N donor binding sites, hence different coordination
possibilities can be expected.
We have reported ternary zinc and copper benzolamide
complexes with amines (ammomia, diethylenetriamine
(dien), dipropylenetriamine (dpt) and tris(2-benzimidazo-
lyl-methylamine) (L)) [12,13]. In these complexes the
coordination behaviour of the benzolamide was different.
Thus, in Cu(bz)(NH3)4, Cu(bz)(dien)PH2O and Cu(bz)-
(dpt)PH2O the dideprotonated sulfonamide coordinates
the metal ion through the N atom of the free sulfonamido
There are many areas of considerable potential interest for
sulfonamide coordination chemistry. Metal complexes of 2-
sulfanilamidopyrimidine (sulfadiazine) have been used to
prevent bacterial infections of burns, and many of these com-
plexes have been structurally characterized [1,2]. A tungsten
complex of the bis-sulfonamide of 2,6-bis(aminomethyl)-
pyridine catalyses cleavage of N–N bonds and is therefore of
interest as a model for fixation ofnitrogen [3]. Morerecently,
a chiral zinc-sulfonamide complex has been demonstrated to
be a relevant catalyst in enantioselective cyclopropanations
[4]. Moreover, aromatic and heteroaromatic sulfonamides
are well known as inhibitors of carbonic anhydrase (CA)
and they have been extremely useful in the study of molecular
properties and of the catalytic mechanismsofzinc-containing
carbonic anhydrases [5].
A part of our investigation is focused on the study of these
heteroaromatic sulfonamides as ligands. Neutral sulfona-
mides are expected to be poor ligands because of the with-
drawal of the electron density from the nitrogen atom onto
the electronegative oxygen atoms. However, if the sulfon-
amide N atom bears a dissociable hydrogen atom, this same
* Corresponding author. Tel.: q34-6-3864530; fax: q34-6-3864960;
e-mail: Joaquin.Borras@uv.es
Fig. 1. Benzolamide.
0277-5387/00/$ - see front matter q2000 Elsevier Science Ltd All rights reserved.
PII S0277-5387(00)00319-3
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G. Alzuet et al. / Polyhedron 19 (2000) 725–730
group, whereas in the polymer {[Zn2(bz)2(NH3)4]P
2H2O}` the dinegative benzolamide anion acts as a bridge,
linking two metal centres through the N atom of the free
sulfonamido group and the thiadiazole N closest to the sub-
stituted sulfonamido moiety. In the [Zn(Hbz)L]ClO4PH2O
compound the monodeprotonated benzolamide interacts via
thiadiazole N contiguous to the substituted sulfonamido moi-
ety [13]. In this paper, as a part of our continuing interest in
the coordination behaviour of benzolamide, we report the
synthesis, structure and spectroscopic properties of the new
benzolamide M(Hbz)2(dien) (MsCu(II) and Zn(II))
complexes in which the sulfonamide in itsmonodeprotonated
form interacts through one of the thiadiazole N atoms.
matic colourless crystals were obtained from the resulting
solution at room temperature. Yield 30%. Anal. Found: C,
29.57; H, 3.31; N, 19.32. Calc. for C20H27ZnN11O8S6: C,
29.76; H, 3.34; N, 19.10%.
2.3.3. Doped Zn,Cu(Hbz)(dien)
0.25 mmol of dien was added to 40 ml of an ethanolic
solution containing 0.225 mmol of Zn(ClO4)2P6H2O and
0.025 of Cu(ClO4)2P6H2O under stirring. The solution
turned dark blue and then 0.5 mmol of benzolamide was
added. It was stirred for about half an hour and then was left
to stand at room temperature. Slow evaporation of the solvent
gives a violet precipitate. Yield 65%.
2.4. Crystal data and structure refinement
2. Experimental
A
well-shaped blue crystal of [Cu(Hbz)2(dien)]
2.1. Materials
(0.22=0.25=0.27 mm) and a colourless crystal of
[Zn(Hbz)2(dien)] (0.17=0.18=0.18 mm) were mounted
on a Siemens P4 four circle diffractometer coupled to Mo Ka
radiation. The unit cell dimensions were determined from the
angular settings of 25 reflections with 1.88-u-22.58 for the
Cu(II) compound and 1.87-u-22.58 for the Zn(II) com-
plex. A total of 4376 and 4415 reflections were measured for
[Cu(Hbz)2(dien)] and [Zn(Hbz)2(dien)], respectively,of
which 4130 (Rints0.0248) and 4161 (Rints0.0452) were
unique (0FhF12, y12FkF11, y14FlF14). Semi-
empirical absorption corrections from c scans were applied
for [Zn(Hbz)2(dien)] and no absorption corrections were
applied for [Cu(Hbz)2(dien)]. Each structure was solved
by direct methods [14] and refined by full-matrix least-
squared analysis on F2. Largest peak and hole in the final
Benzolamide (H2bz, 5-phenylsulfonamide-1,3,4-thiadi-
azole-2-sulfonamide) was provided by Professor C.T.
Supuran (University of Florence, Italy). All reagents were
of the highest grade commercially available and usedwithout
further purification.
2.2. Methods
IR spectra were recorded on a Perkin-Elmer 843 instru-
ment. Samples were prepared using the KBr technique. Elec-
tronic spectra were registered on a Shimadzu UV 2101PC
spectrophotometer. EPR spectra were carried out with a Bru-
ker ER 200 D spectrometer. Magnetic susceptibility meas-
urements at room temperature were taken with a fully
automated AZTEC DSM8 pendulum-type susceptometer.
Mercury tetrakis(thiocyanato)cobaltate(II) was used as a
susceptibility standard. Corrections for diamagnetism were
estimated from Pascal’s constants.
y3
˚
difference map were q0.767 and y0.664 e A (Cu(II)
compound) and 0.415 and y0.563 e Ay3 (Zn(II)complex).
˚
Other relevant parameters of crystal structure determination
are collected in Table 1.
2.5. EHMO calculations
2.3. Synthesis
All calculations were performed using the Package of Pro-
grams for Molecular Orbital Analysis by Mealli and Proser-
pio [15] based on CDNT (atom Cartesian coordinate
2.3.1. Cu(Hbz)2(dien)
0.25 mmol of diethylenetriamine was added with contin-
uous stirring to 40 ml of an ethanolic solution containing0.25
mmol of Cu(NO3)2P3H2O and 0.5 mmol of benzolamide.
Immediately, a little amount of a blue solid was formed. It
was separated by filtration and the filtrate was left to stand at
48C. After a few days prismatic blue crystals suitable for X-
ray measurements were obtained. The crystals were filtered,
washed with cooled ethanol and dried under vacuum. Yield
40%. Anal. Found: C, 29.45; H, 3.28; N, 19.23. Calc. for
C20H27CuN11O8S6: C, 29.83; H, 3.35; N, 19.14%.
¨
calculations), ICON (extended Huckel method with the
weighted Hij formula) and FMO (fragment molecular
orbital), including the drawing program CACAO (computer
aided composition of atomic orbitals).
¨
The extended Huckel parameters are as follows. Hij: Cu
4s, y11.40 eV; Cu 4p, y6.06 eV; Cu 3d, y14.00 eV; Zn
4s, y12.41 eV; Zn 4p, y6.53 eV; N 2s, y26.00 eV; N 2p,
y13.40 eV; S 3s, y20.00 eV; S 3p, y13.30 eV; O 2s,
y32.30 eV; O 2p, y14.80 eV; C 2s, y21.40 eV; C 2p,
y11.40 eV; H 1s, y13.60 eV. Orbital exponents (contrac-
tion coefficients in double-j expansion giveninparentheses):
Cu 4s, 4p, 2.200; Cu 3d, 5.950 (0.5933), 2.300 (0.5744);
Zn 4s, 2.010; Zn 4p, 1.700; N 2s, 2p, 1.950; S 3s, 3p, 1.817;
O 2s, 2p, 2.275; C 2s, 2p, 1.625; H 1s, 1.300.
2.3.2. Zn(Hbz)2(dien)
The synthesis procedure is similar to that described above
but Zn(ClO4)2P6H2O was used and no solid was obtained
after the addition of diethylenetriamine. After 3–4 days pris-
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G. Alzuet et al. / Polyhedron 19 (2000) 725–730
727
Table 1
pyramidal but with significant differences in the local molec-
ular stereochemistry. In particular, in the Zn complex the
Crystal data and structure refinement
˚
Zn–N(6) (2.202(7) A) is the longest bond distance while
[Cu(Hbz)2(dien)]
[Zn(Hbz)2(dien)]
˚
in the Cu compound the Cu–N(6) (2.035(5) A) distance is
one of the shorter distances. Moreover, the equatorial Cu–
N(thiadiazole) (Cu–N(3), 2.070(5) A) is markedly shorter
Formula
Formula weight
C20H27CuN11O8S6
805.43
C20H27ZnN11O8S6
806.25
˚
Symmetry, space group
triclinic, P1
11.284(2)
11.790(2)
13.359(2)
103.582(10)
100.939(13)
105.225(13)
1606.0(4)
2
triclinic, P1
11.256(5)
11.827(5)
13.405(2)
102.82(3)
101.58(4)
105.41(3)
1612.2(12)
2
than the axial Cu–N(thiadiazole) distance (Cu–N(9),
˚
a (A)
˚
2.233(5) A) but the equatorial Zn–N(thiadiazole) (Zn–
˚
b (A)
˚
N(3), 2.188(7) A) is longer than the axial Zn–N-
˚
c (A)
˚
a (8)
b (8)
g (8)
(thiadiazole) distance (Zn–N(9), 2.042(7) A). The
equatorial Cu–N(thiadiazole) is found to be comparable to
the corresponding bond in Cu(II) complexes with related
sulfonamides [7,9] and the equatorial Zn–N(thiadiazole) is
comparable to the same distance in the [Zn(Hbz)L]ClO4P
H2O compound (Lstris(2-benzimidazolyl-methylamine))
3
˚
U (A )
Z
Dc (g cmy3
)
1.666
826, 11.33
415
1.663
828, 12.13
416
F(000), m (cmy1
)
Refined parameters
GOF
˚
[13]. The axial Cu–N(thiadiazole) length is ca. 0.23 A
1.077
0.973
shorter than that of the Cu(Hacm)2(en)2 complex
(H2acmsacetazolamide, ensethylenediamine) [8]. The
R (I)2s(I)) a
R1s0.0489,
wR2s0.1310
R1s0.0748,
wR2s0.1531
R1s0.0600,
wR2s0.1401
R1s0.1137,
wR2s0.17524
R (all data)
2
4
1/2
a Rs8(NFoNyNFcN)/8NFoN, Rws[8w(Fc )/8wFo
]
.
3. Results and discussion
3.1. Synthesis of the complexes
The ternary complexes [M(Hbz)2(dien)] were obtained
by reaction of the metal salt, the triamine and benzolamide
in a molar ratio 1:1:2. The ratio of reagents is important to
obtain the compounds described here since the addition of an
equimolecular amount of triamine and benzolamide leads
to the formation of the previously reported [M(bz)-
(dien)]PH2O compounds in which the benzolamide is pres-
ent in its dideprotonated form [12].
3.2. Description of the crystal structures
Fig. 2. Drawing of the [Cu(Hbz)2(dien)] complex.
Table 2
A drawing of [Cu(Hbz)2(dien)] including the atomic
numbering scheme is shown in Fig. 2. Interatomic distances
and angles relevant to the coordination sphere for the
[Cu(Hbz)2(dien)] and [Zn(Hbz)2(dien)] complexes are
given in Table 2.
˚
Selected bond lengths (A) and angles (8) with e.s.d.s in parentheses
[Cu(Hbz)2(dien)]
[Zn(Hbz)2(dien)]
Cu(1)–N(5)
Cu(1)–N(6)
Cu(1)–N(9)
Cu(1)–N(7)
Cu(1)–N(3)
2.014(5)
2.035(5)
2.233(5)
2.017(5)
2.070(5)
Zn(1)–N(5)
Zn(1)–N(6)
Zn(1)–N(9)
Zn(1)–N(7)
Zn(1)–N(3)
2.093(7)
2.202(7)
2.045(7)
2.082(8)
2.188(7)
The metal ion is pentacoordinated by five N atoms, the
structure being best described as a regular square pyramid.
The three N atoms (N(5), N(6) and N(7)) of thedienligand
occupy equatorialpositions. TheremainingtwoM(II)square
pyramidal coordination sites are occupied by two benzolam-
idate anions that interact through the thiadiazole N atom con-
tiguous to the deprotonated sulfonamido group (N(3),
N(9)). The Cu–N(dien) bond distances are in the narrow
N(5)–Cu(1)–N(7)
N(5)–Cu(1)–N(6)
N(7)–Cu(1)–N(6)
N(5)–Cu(1)–N(3)
N(5)–Cu(1)–N(9)
N(6)–Cu(1)–N(9)
N(6)–Cu(1)–N(3)
N(7)–Cu(1)–N(3)
N(7)–Cu(1)–N(9)
N(3)–Cu(1)–N(9)
163.4(2)
82.8(2)
83.8(2)
90.8(2)
100.8(2)
94.6(2)
162.3(2)
99.2(2)
90.8(2)
102.8(2)
N(7)–Zn(1)–N(5)
N(5)–Zn(1)–N(6)
N(7)–Zn(1)–N(6)
N(5)–Zn(1)–N(3)
N(9)–Zn(1)–N(5)
N(9)–Zn(1)–N(6)
N(3)–Zn(1)–N(6)
N(7)–Zn(1)–N(3)
N(9)–Zn(1)–N(7)
N(3)–Zn(1)–N(9)
149.8(3)
80.1(3)
80.2(3)
88.7(3)
109.2(3)
99.5(3)
153.4(3)
98.9(3)
96.5(3)
107.0(3)
˚
range from 2.014(5) to 2.035(5) A and the Zn–N(dien)
˚
lengths range from 2.082(7) to 2.202(7) A. As expected
from the ionic radii of the divalent metal ions, the average of
these Zn–N bond distances is considerably longer than those
involving Cu. Both MN5 chromophores are essentiallysquare
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G. Alzuet et al. / Polyhedron 19 (2000) 725–730
Cu–N(dien) bond distances are similar to those in other
Cu(II) complexes with dien [16–19].
atom. However, it differs from that found in [Cu(bz)-
(NH3)4] [12] where the dideprotonated benzolamide acting
as monodentate ligand binds the metal ion through the free
sulfonamide N atom. Although it is difficult to rationalize the
coordination behaviour of benzolamide, our investigation of
its coordination properties has demonstrated that in the mon-
odeprotonated form it behaves as a monodentate ligand coor-
dinating the metal through the thiadiazole N atom closest to
the substituted sulfonamido group. When dideprotonated it
shows a more variable coordination behaviour, acting as a
bridge through the thiadiazole and free sulfonamido N atoms
[13] or as monodentate via free sulfonamido N atom [12].
It is interesting to compare the coordination behaviour
of benzolamide and the structurally related acetazolamide
(H2acm, 5-acetamido-1,3,4-thiadiazole-2-sulfonamide) when
both are monodeprotonated. Although both sulfonamides
offer the same donor sites, a N thiadiazole atom and a N
sulfonamido, the coordination behaviour of acetazolamide in
the previously reported [Cu(Hacm)(dien)]PH2O and
[Cu(Hacm)(dpt)]PH2O compounds [26] contrasts with
that of benzolamide. Acetazolamide in these complexes acts
as a monodentate ligand through the N sulfonamido atom.
The in-plane angular distortions described by the ratio t
represent a percentage trigonal distortion of a square pyram-
idal geometry (1 for perfect trigonal bipyramidal, 0 for per-
fect square pyramidal). The calculated t value from bond
angles of 0.02 for the Cu(II) compound and of 0.06 for the
Zn(II) complex clearly indicates a quasi regular pyramidal
geometry [20]. For the two structures the major changes in
the angles subtended at the metal centre are found in N(5)–
M–N(7) and N(6)–M–N(3) which expand from 149.8(3)
and 153.4(3)8 [Zn(Hbz)2(dien)] to 163.4(2) and
162.3(2)8 [Cu(Hbz)2(dien)]. The cis equatorial N–M–N
bond angles differ from 908 owing to the presence of a chelate
ring that produces rhombic in-plane effects [21].
In the copper compound the atoms that constitute the equa-
˚
torial plane deviate 0.050 A from planarity and those of the
˚
zinc complex deviate 0.006 A. The copper atom is displaced
˚
0.2543 A from the equatorial plane towards the apical posi-
˚
tion and the zinc ion is situated at 0.4876 A from this plane.
It is also interesting to note that the copper compound
presents a square pyramidal geometry since of the dien com-
plexes structurally characterized, very few contain dien and
a monodentate ligand [17] and these adopt six-coordinate
tetragonally elongated octahedral geometries, with both
ligands located equatorially and anions weakly bound axially
[17]. Square pyramidal geometries are found only in copper
dien complexes with bidentate ligands [22]. This geometry
is also exhibited by Cu(II) compounds with pentamethyldi-
ethylenetriamine and a monodentate ligand, but in thesecases
a third ligand (either solvent or anion) binds in the axial
position [23–25].
The uninegative benzolamidate anions behave as mono-
dentate ligand through the thiadiazole N atom (N(3), N(9))
contiguous to the deprotonated sulfonamido group. This
coordination behaviour is also exhibited by the monodepro-
tonated benzolamide in the [Zn(Hbz)L]ClO4PH2O com-
pound (Lstris(2-benzimidazolyl-methylamine)) [13]. In
these complexes the coordination mode of the benzolamide
is determined by the fact that the deprotonation takes place
on the substituted sulfonamido moiety. This makes the thia-
diazole N closest to this sulfonamido group the best donor
3.3. IR spectra
In Table 3 are collected the most significant IR data for the
complexes reported here. For comparison the IR data for
related compounds are also included.
The modifications of the characteristic bands of the ben-
zolamide ligand give some informationabout itscoordination
and/or its deprotonation. It is found that the changes in the
asymmetricandsymmetricstretchingmodesoftheSO2 group
afford some evidence of the deprotonated nature of the ben-
zolamide. When monodeprotonated, two bands are associ-
ated with each vibration, whereas when dideprotonated, one
band for each vibration is observed. These bands show some
splitting in the [Zn(Hbz)2(dien)] complex that probably
arises from hydrogen bonding or crystal packing effects.
Moreover, it is noteworthy that in all the complexes, the
n(C_N) vibration is strongly modified. Since the changes
occur in the complexes where the benzolamide is monode-
protonated and in the complexes where the benzolamide is
Table 3
a
IR selected bands (cmy1
)
Compound
n(C_N)ring
n(SO2)asym
n(SO2)sym
n(S–N)
Benzolamide(H2bz)
[Cu(Hbz)2(dien)]
[Zn(Hbz)2(dien)]
Cu(bz)(deta)(H2O) b
Cu(bz)(dpt)(H2O) b
1580–1570d, 1500
1460
1480–1465d
1430
1430
1475
1360, 1320
1360,1270
1360–1350d, 1280–1260d
1275
1300–1280d
1356,1275
1180, 1140
1180, 1150
1170, 1140
1140
1140–1130d
1160, 110
940, 910
940, 920
930, 915
970, 950
950–940d
920
[Zn(Hbz)L]ClO4PH2O c
a d doublet.
b From Ref. [12].
c From Ref. [13].
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G. Alzuet et al. / Polyhedron 19 (2000) 725–730
729
˚
dideprotonated, this fact could be attributed to the modifica-
tions that take place on the thiadiazole p-system upon depro-
tonation of the substituted sulfonamido group.
(Zn)), in the M–N(6) (2.035(5) (Cu) and 2.202(7) A
(Zn)) bond lengths and in the trans angles N(5)–M–N(7)
and N(6)–M–N(3), which expand from 149.8(3) and
153.4(3)8 [Zn(Hbz)2(dien)] to 163.4(2) and 162.3(2)8
[Cu(Hbz)2(dien)]. Moreover, the [Cu(Hbz)2(dien)]
complex presents electronic properties (see Section 3.4) dif-
ferent to those of the copper doped compound that suggests
that when the Cu(II) substitutestheZn(II)iondoesnotadopt
the geometry observed in the pure copper compound. In order
to understand how these structural differences can affect the
energy and composition of the relevant molecular orbitals of
3.4. Magnetic susceptibility, electronic and EPR spectra
The [Cu(Hbz)2(dien)] compound exhibits a normal
value of magnetic moment for an orbitally non-degenerate
ground state, 1.76 BM.
The solid electronic spectrum of [Cu(Hbz)2(dien)] is in
agreement with the crystallographic data. It presents a single
broad ligand field absorption with a maximum at 630 nm as
expected for copper(II) complexes having a square pyrami-
dal geometry [27].
¨
the complexes we have undertaken extended Huckel molec-
ular orbital (EHMO) calculations by means of the CACAO
program [15]. These calculations have been performedusing
the crystallographic coordinates derived from the crystal
structures of the [Cu(Hbz)2(dien)] compound and
[Zn(Hbz)2(dien)] in which the Zn(II) has been replaced
by Cu(II) as a ‘model’ of the copper doped compound.
The SOMO of the [Cu(Hbz)2(dien)] presents an energy
of y11.049 eV (Fig. 3). The contribution of metal d orbitals
(28%), dxz (8%), dxy (2%) and
(1%)). The atomic orbitals of the ligands that participate
in SOMO formation are the three N atoms of the dien (N(5),
px 12%, py 2%; N(6), py 18%; N(7), px 10%, pz 3%) and
one N thiadiazole atom (N(3), py 9%) from one of the
benzolamidate ligands.
At room temperature the solid-state EPR spectrum of
[Cu(Hbz)2(dien)] is axial with the parallel component
poorly resolved. The calculated EPR parametersareg≤f2.30
and gHs2.13. The EPR of the copper doped into its zinc
counterpart is also axial in nature. The low-field regionshows
the quartet hyperfinestructurefromCu(Is3/2). Theground
state parameters extracted from the experimental spectrum
by simulation [28] are g≤s2.21, gHs2.05 and A≤s
191=10y4 cmy1. This A≤ value of the complex diluted in
the isomorphous zinc lattice is larger than the valuesexpected
for a five-coordinated geometry. It is well known that Cu(II)
square planar and octahedral complexes with tetragonalelon-
gation lead to a large parallel Cu hyperfine coupling. Further,
the quotient g≤/A≤ lies in the range 105–135 cm, supporting
a square planar geometry [29]. So, it seems that the Cu(II)
assumes a stereochemistry much more close to that ofaplanar
CuN4 chromophore [30]. This change in the geometry is
supported by the mull spectrum of the copper(II) complex
doped in the corresponding zinc complex that exhibits a shift
from 630 nm in the pure copper to 575 nm.
2
2
to the SOMO is 39% (
dx yy
2
dz
When these calculations are performed on the ‘model’
copper doped compound, a SOMO with an energy of
y11.649 eV is obtained (Fig. 4). The overall contribution
2
2
of the copper d atomic orbitals to this MO is 34% (dx yy
(25%), dxz (7%) dxy (1%) and dyz (1%)), although the
ligand orbitals involved are the same as in Cu(Hbz)2(dien)
their contribution is slightly different (N(5), px 12%; N(6),
py 21%; N(7), px 7%, pz 5%; N(3), py 9%).
The electronic and EPR spectra of the [Cu(Hbz)2(dien)]
and ofthe copperdopedcompoundsuggestachangeofgeom-
etry for the Cu(II) ion when it replaces the Zn(II) ion in the
[Zn(Hbz)2(dien)] complex. The EHMO calculations have
In acetonitrilethe EPR spectrumofthe[Cu(Hbz)2(dien)]
displayed axial anisotropy with some rhombic perturbation.
The EPR features obtained from simulation are g≤f2.29,
gHs2.13 and A≤s185=10y4 cmy1. They are indicative of
a square planar based structure. The UV–Vis spectrumshows
a d–d band atca. 600 nm(´s130moly1 cmy1)whichagrees
well with a square planar arrangement around the copper ion.
Apart from the d–d transition, the spectrum displays an
intense absorption at 300 nm (´s29120 moly1 cmy1) and
a less intense absorption at 245 nm (´s16990 moly1 cmy1
)
associated with ligand p–p* transitions. Both EPR and elec-
tronic spectra indicate that the geometry of the copper ion in
solution is, like in the doped compound, nearer to square
planar with weak apical interactions.
¨
3.5. Extended Huckel molecular orbitals calculations
The crystal structures of the isomorphous [Cu(Hbz)2-
(dien)] and [Zn(Hbz)2(dien)] complexes have shown that
both compounds present some differences in their local
molecular stereochemistry. The most significant differences
˚
are found in the M–N(9) (2.233(5) (Cu) and 2.045(7) A
Fig. 3. SOMO of the [Cu(Hbz)2(dien)] complex.
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730
G. Alzuet et al. / Polyhedron 19 (2000) 725–730
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´
´
[12] G. Alzuet, J. Casanova, J. Borras, S. Garcıa Granda, A. Gutierrez-
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´
Rodrıguez, C.T. Supuran, Inorg. Chim. Acta 273 (1998) 334.
´
´
´
[13] G. Alzuet, S. Ferrer-Llusar, J. Borras, J. Server-Carrio, R. Martınez-
´
shown that the energy difference between the SOMOsofboth
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Supplementary data
Supplementary crystallographicdata areavailablefromthe
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: q44-1223-336033; e-mail:
deposit@ccdc.cam.ac.uk) on request, deposition numbers
CCDC 132907/CCDC 132908.
¨
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Acknowledgements
The authors acknowledge financial support from the Span-
ish CICYT (PM97-0105-C02-01). We thank Professor C.T.
Supuran for providing us the benzolamide.
´
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