An experimental and theoretical (DFT) investigation of the coordination mode of 2,4-dithiouracil (2,4-dtucH2) in copper(I) complexes with 1,2-bis(diphenylphosphanyl)benzene (dppbz): The crystal structures of [Cuμ-Br(dppbz)]2 and [CuBr(dppbz)(2,4-dtucH2)]

Article abstract of DOI:10.1002/ejic.200500726

Novel copper(I) mixed-ligand complexes containing 1,2- bis(diphenylphosphanyl)benzene (dppbz) and 2,4-dithiouracil (2,4-dtucH ₂) ligands have been synthesised by addition of the thione ligand to the dinuclear [Cu(μ-X)(dppbz)]₂ intermediate in acetonitrile/methanol or acetone solution. The molecular structures of both the precursor [Cu(μ-Br)(dppbz)]₂ and the [CuBr(dppbz)(2,4-dtucH ₂)] complexes were established by single-crystal X-ray diffraction. Interestingly, the structure of the thione-free dimer involves two diphosphanechelated Cu^I centres bridged by two bromide ligands, thus forming a non-planar Cu₂Br₂ core. The structure of [CuBr(dppbz)(2,4-dtucH₂)] corresponds to a four-coordinate CuI centre in a tetrahedral coordination environment with the heterocyclic dithione ligand being coordinated to the metal centre in a unidentate fashion through its exocyclic sulfur donor atom. The structural, bonding and electronic properties of the model complexes [Cu(μ-X)(dppbz)]₂ and [CuX(dppbz)(2,4- dtucH₂)] (X = Cl, Br, or I) are adequately described by DFT/B3LYP computational techniques. All model dinuclear [Cu(μ-X)(dppbz)]₂ complexes exhibit π-type MOs delocalised over the entire four-membered Cu(μ-X)₂Cu ring, thereby accounting for the near equivalency of the Cu-X bonds. Moreover, the [Cu(μ-X)(dppbz)]₂ dimers possess a σ-type MO corresponding to weak Cu...Cu bonding interactions, which further stabilize the Cu(μ-X)₂Cu ring. According to our calculations, the interaction energies of the 2,4-dtucH₂ ligand with the Cu^I centre are predicted to be about 13-16 kcalmol^-1. The coordination of the 2,4-dtucH₂ ligand is further stabilized by an X...H-N hydrogen bond that is perpendicular to the plane of the dppbz ligand. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200500726

FULL PAPER
DOI: 10.1002/ejic.200500726
An Experimental and Theoretical (DFT) Investigation of the Coordination
Mode of 2,4-Dithiouracil (2,4-dtucH2) in Copper( ) Complexes with
I
1,2-Bis(diphenylphosphanyl)benzene (dppbz): The Crystal Structures of [Cu(μ-
Br)(dppbz)]2 and [CuBr(dppbz)(2,4-dtucH2)]
Paraskevas Aslanidis,*[a] Philip J. Cox,[b] Andreas Kaltzoglou,[a] and Athanasios C. Tsipis*[c]
Keywords: Copper / Density functional calculations / Phosphane ligands / S ligands
Novel copper(
I) mixed-ligand complexes containing 1,2-
ties of the model complexes [Cu(μ-X)(dppbz)]2 and
bis(diphenylphosphanyl)benzene (dppbz) and 2,4-dithioura- [CuX(dppbz)(2,4-dtucH2)] (X = Cl, Br, or I) are adequately
cil (2,4-dtucH2) ligands have been synthesised by addition of
the thione ligand to the dinuclear [Cu(μ-X)(dppbz)]2 interme-
diate in acetonitrile/methanol or acetone solution. The mo-
lecular structures of both the precursor [Cu(μ-Br)(dppbz)]2
and the [CuBr(dppbz)(2,4-dtucH2)] complexes were estab-
lished by single-crystal X-ray diffraction. Interestingly, the
structure of the thione-free dimer involves two diphosphane-
chelated CuI centres bridged by two bromide ligands, thus
described by DFT/B3LYP computational techniques. All
model dinuclear [Cu(μ-X)(dppbz)]2 complexes exhibit π-type
MOs delocalised over the entire four-membered Cu(μ-X)2Cu
ring, thereby accounting for the near equivalency of the Cu–
X bonds. Moreover, the [Cu(μ-X)(dppbz)]2 dimers possess a
σ-type MO corresponding to weak Cu···Cu bonding interac-
tions, which further stabilize the Cu(μ-X)2Cu ring. According
to our calculations, the interaction energies of the 2,4-dtucH2
ligand with the CuI centre are predicted to be about 13–
16 kcalmol–1. The coordination of the 2,4-dtucH2 ligand is
further stabilized by an X···H–N hydrogen bond that is per-
pendicular to the plane of the dppbz ligand.
forming
a non-planar Cu2Br2 core. The structure of
[CuBr(dppbz)(2,4-dtucH2)] corresponds to a four-coordinate
CuI centre in a tetrahedral coordination environment with
the heterocyclic dithione ligand being coordinated to the me-
tal centre in a unidentate fashion through its exocyclic sulfur
donor atom. The structural, bonding and electronic proper-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
of these compounds.[3] In this context, some examples of
three-coordinate CuI complexes, where the steric require-
ments of the phosphane ligands exert an influence on the
coordination number, have also been reported.[4] Moreover,
a number of halo- or thione-S-bridged dinuclear mixed-li-
gand complexes have been synthesised and structurally well
characterised.[3,5] In contrast to the monodentate triaryl-
phosphanes, didentate P-donor ligands, especially the oligo-
methylene-backboned symmetric diphosphanes formulated
as Ph2P(CH2)nPPh2 (n = 1, 2 or 4), favour the formation of
dinuclear complexes.[6] On the other hand, the rigid cis-1,2-
bis(diphenylphosphanyl)ethane (cis-dppen) and 1,3-bis(di-
phenylphosphanyl)propane (dppp) have been found to che-
late at a single metal centre, yielding mononuclear pseudo-
tetrahedral CuI species.[7] Another didentate P-donor ligand
capable of forming chelate five-membered symmetric rings
is the sterically demanding 1,2-bis(diphenylphosphanyl)-
benzene, hereafter abbreviated as dppbz. Although dppbz
has already been used extensively as a chelating ligand for
many metal centres,[8] no structurally characterised CuI or
AgI derivatives of this rigid diphosphane, as far as we know,
are currently known.
Introduction
The coordination chemistry of heterocyclic thiones has
grown enormously in the recent past, mainly because of
their relevance to biological systems.[1,2] The salient feature
of these heterocyclic thioamides is their ability to bind to a
metal centre in a variety of coordination modes. Along
these lines a wealth of complexes exhibiting variable nu-
clearities and often unusual geometries have been synthe-
sised and studied so far.[1–7] A large number of mixed-li-
gand complexes of the univalent coinage metals, particu-
larly those of CuI, incorporating tertiary arylphosphanes
as a second, bulky soft donor ligand have been thoroughly
investigated in an attempt to understand the factors that
may affect the stoichiometric and geometrical preferences
[a] Aristotle University of Thessaloniki, Faculty of Chemistry, In-
organic Chemistry Laboratory,
P. O. Box 135, 54124, Thessaloniki, Greece
E-mail: aslanidi@chem.auth.gr
[b] School of Pharmacy, The Robert Gordon University,
Schoolhill, Aberdeen AB10 1FR, Scotland
E-mail: p.j.cox@rgu.ac.uk
[c] Section of Inorganic and Analytical Chemistry, Department of
Chemistry, University of Ioannina,
Among the heterocyclic thiones, the coordination prop-
erties of the thio derivatives of uracil, such as 2-thiouracil
45110 Ioannina, Greece
E-mail: attsipis@cc.uoi.gr
334
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 334–344

Copper(i) Complexes of 2,4-Dithiouracil (2,4-dtucH2)
FULL PAPER
(2-tucH2), 4-thiouracil (4-tucH2) and 2,4-dithiouracil (2,4- obtained following a reverse synthetic procedure, i.e., by
dtucH2) are of particular interest as these ligands have sig- adding a twofold excess of the 2,4-dtucH2 ligand to a CuI
nificant biological interest.[9] Very recently, the gas-phase solution, followed by addition of dppbz. The orange-red
reactivity of uracil, 2-tucH2, 4-tucH2, and 2,4-dtucH2 precipitate formed before adding dppbz probably corre-
towards Cu+ and Cu2+ cations has been thoroughly investi- sponds to the polymeric species [CuI(2,4-dtucH2)]x (6),
gated using electronic structure calculation methods.[10] In which depolymerises upon addition of dppbz to give 5 as an
this work we report on the synthesis, characterisation and orange solid. The analogous polymeric species [CuBr(2,4-
electronic structure calculations of new copper(i) coordina- dtucH2)]x (7) was also isolated as an orange-red powder
tion compounds bearing dppbz and/or 2,4-dtucH2 as li- following the same synthetic procedure. To investigate the
gands. In effect, what we want to address here is the coordi- ability of 2,4-dtucH2 for further coordination to CuX
nation bonding mode of the versatile 2,4-dtucH2 ligand through both exocyclic thione-S donor atoms, a series of
(Scheme 1), which has two exocyclic sulfur donor atoms of reactions using variable stoichiometries and reaction condi-
different basicity that are capable of coordinating to CuI tions were carried out, but in all cases CuI complexes in-
metal centres.
volving 2,4-dtucH2 coordination in the mono-hapto or μ2-
coordination mode via the S donor atom at the 4-position
were isolated.
All new complexes are diamagnetic, air-stable, microcrys-
talline solids that are moderately soluble in acetonitrile and
only marginally soluble in chloroform and acetone. Their
solutions in acetone and chloroform are non-conducting.
The stoichiometry and structure of the complexes were
confirmed by elemental analysis and spectroscopic
measurements. Moreover, the molecular structures of
[CuBr(dppbz)(dtucH2)] (2) and [CuBr(dppbz)]2 (3) were de-
termined by X-ray crystallographic analyses.
Scheme 1. Resonance structures of 2,4-dtucH2.
Spectroscopy
The electronic absorption spectra of the new compounds
in chloroform solution at room temperature show an in-
tense, broad band with maxima in the region of 243–
255 nm, which can be attributed, with reference to the ab-
sorption bands of the uncoordinated dppbz, to intraligand
π*ǟπ transitions on the phenyl groups of the phosphane
ligand. Moreover, the spectra of compounds 1, 2 and 5–7
display an additional broad band in the region of 285–
310 nm, where the free thiones normally absorb. This band
experiences a small red-shift as a consequence of the coor-
dination to CuI and may be ascribed to a thione-originating
intraligand transition. The IR spectra of compounds 1–3, 6
and 7, recorded in the range 4000–250 cm–1, all show the
expected strong phosphane bands, which remain practically
unshifted upon coordination. Moreover, the spectra of
compounds 1, 2 and 4–7 contain all of the bands required
by the presence of the heterocyclic thione ligand, with shifts
due to coordination indicative of an exclusive S-coordina-
tion mode.
Results and Discussion
Synthesis
The new compounds were prepared following a synthetic
pathway that has already produced a number of mixed-li-
gand copper(i) halide complexes. Thus, 1 mmol of CuCl or
CuBr was first treated with an equimolar quantity of dppbz
to yield an intermediate adduct formulated as
[CuX(dppbz)] (X = Cl, Br). This intermediate was then al-
lowed to react with one equivalent of 2,4-dtucH2 in re-
fluxing dry acetonitrile for 2 h to afford the corresponding
pure mixed-ligand complexes [CuX(dppbz)(2,4-dtucH2)] (X
= Cl: 1; Br: 2) in good yields. During the reaction of 2,4-
dtucH2 with CuBr, a small quantity of greenish yellow crys-
tals was separated at the initial stages of the evaporation of
the diluted acetonitrile mother liquid; their analytical and
spectroscopic data were identical to those of the
[CuBr(dppbz)] intermediate. In this way we were able to
characterise the intermediate by X-ray crystallography as
the thione-free dimer [CuBr(dppbz)]2 (3). It should be
noted that 3 is inert in the reactions with a number of het-
erocyclic thiones [e.g. 5-methyl-1,3,4-thiadiazole-2-thione
(mtdztH) or 4-methyl-5-trifluoromethyl-4H-1,2,4-triazol-
ine-3(2H)-thione (mftztH)]. Treatment of CuI with equi-
X-ray Structural Investigations
The X-ray crystal structures of [CuBr(dppbz)(dtucH2)]
molar quantities of dppbz readily yielded the intermediate (2) and [Cu(μ-Br)(dppbz)]2 (3) corroborate the spectro-
1:1 adduct [CuI(dppbz)]x (4) as a white microcrystalline so- scopic results discussed above. Selected bond distances and
lid, which, however could not be converted into the corre- angles of complexes 2 and 3 are listed in Tables 1 and 2,
sponding [CuI(dppbz)(2,4-dtucH2)] (5). Compound 5 was respectively.
Eur. J. Inorg. Chem. 2006, 334–344
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335

P. Aslanidis, P. J. Cox, A. Kaltzoglou, A. C. Tsipis
FULL PAPER
Table 1. Selected bond lengths [Å] and angles [°] for 2.
The tetrahedral environment of the copper atom formed
by the two P atoms of the chelating dppbz unit, one Br and
one of the two exocyclic S donor atoms of the dithione
ligand is considerably distorted, with the largest deviation
from the ideal geometry being reflected by the P(1)–Cu(1)–
P(2) and P(1)–Cu(1)–Br(1) angles of 86.61(2)° and
122.05(19)°, respectively, which are markedly different from
the ideal tetrahedral value of 109.4°.
As expected, the carbon atoms of the phenylene back-
bone and the two adjacent phosphorus atoms are coplanar
and the CuPCCP five-membered ring adopts an envelope
conformation with the metal atom out of the plane contain-
ing the four diphos ligand donor atoms by 1.034(1) Å. The
two phenyl rings on each phosphorus atom are nearly per-
pendicular to each other. However, the C(17)–C(22) and
C(29)–C(34) phenyl rings have their planes in an almost
parallel arrangement, with a π-stacking interaction of
3.827(1) Å between them. Likewise, the inclination of the
pyrimidine ring to the C(11)–C(16) phenyl ring results in a
π-stacking interaction of 4.116(1) Å. The two Cu–P dis-
tances [2.2393(6) and 2.2953(6) Å] are significantly dif-
ferent, but are within the limits of the range expected for
tetrahedrally coordinated CuI.
Cu(1)–Br(1)
Cu(1)–P(1)
Cu(1)–P(2)
Cu(1)–S(1)
2.4366(3)
2.2953(6)
2.2393(6)
2.2921(6)
1.679(2)
S(2)–C(2)
P(1)–C(5)
P(2)–C(6)
C(5)–C(6)
1.650(2)
1.838(2)
1.833(2)
1.408(3)
S(1)–C(1)
P(1)–Cu(1)–P(2)
P(1)–Cu(1)–S(1)
P(2)–Cu(1)–S(1)
P(1)–Cu(1)–Br(1)
P(2)–Cu(1)–Br(1)
S(1)–Cu(1)–Br(1)
Hydrogen bonds
N(1)–H(1)
86.73(2)
C(1)–S(1)–Cu(1) 105.24(7)
C(5)–P(1)–Cu(1) 99.68(7)
C(6)–P(2)–Cu(1) 101.34(7)
P(1)–C(5)–C(6)
P(2)–C(6)–C(5)
108.37(2)
120.10(2)
115.586(18)
118.836(18)
106.015(18)
117.21(16)
118.10(16)
0.8800
2.5100
0.8800
2.4300
Br(1)···N(1)
Br(1)···H(1)–N(1) 152°
Br(1)···N(2)
Br(1)···H(2)–N(2) 146°
3.3175(16)
NH(1)···Br(1)
N(2)–H(2)
NH(2)···Br(1)
3.1994(19)
Table 2. Selected bond lengths [Å] and angles [°] for 3.
Cu(1)–Br(1)
Cu(2)–Br(1)
Cu(2)–Br(2)
Cu(1)–Br(2)
Cu(1)–Cu(2)
2.4556(6)
2.4958(6)
2.4279(6)
2.5317(6)
2.8410(6)
Cu(1)–P(1)
Cu(1)–P(2)
Cu(2)–P(3)
Cu(2)–P(4)
2.2586(10)
2.2549(11)
2.2600(11)
2.2546(11)
Cu(1)–Br(1)–Cu(2) 70.022(17)
Cu(2)–Br(2)–Cu(1) 69.859(17)
P(4)–Cu(2)–Br(2)
P(3)–Cu(2)–Br(1)
P(3)–Cu(2)–Br(2)
P(4)–Cu(2)–Br(1)
118.14(3)
108.96(3)
121.41 (4)
110.55(3)
The coordinated 2,4-dithiouracil ligand, which adopts its
most stable dithione tautomeric form (a, Scheme 1) is coor-
P(1)–Cu(1)–P(2)
P(2)–Cu(1)–Br(1)
P(1)–Cu(1)–Br(1)
P(2)–Cu(1)–Br(2)
P(1)–Cu(1)–Br(2)
Br(1)–Cu(1)–Br(2)
P(4)–Cu(2)–P(3)
90.50(4)
120.66(3)
121.08(3)
107.09(3)
109.88(3)
106.417(19)
87.86(4)
Br(2)–Cu(2)–Br(1) 108.425(19) dinated to the CuI metal centre in a monodentate coordina-
C(13)–P(1)–Cu(1) 102.10(12)
tion mode through the S atom in the 4-position. Consider-
C(14)–P(2)–Cu (1) 102.04(12)
ing that the corresponding carbon–sulfur bond of the unco-
C(43)–P(3)–Cu(2) 100.75(13)
ordinated 2,4-dtucH2 has been found to be significantly
C(44)–P(4)–Cu(2) 101.48(13)
longer than that in the 2-position [1.684(6) vs.
1.645(6) Å],[11] the favourable coordination of that specific
Compound 2 crystallises in the monoclinic space group sulfur atom can be interpreted as the inevitable conse-
P21/c with four formula units in the unit cell. Figure 1 de- quence of its strong polarisation towards the amidic
picts a perspective of the molecule showing the atom-label- [–HN+=C(S–)–] configuration (b). However, coordination
ling scheme.
to CuI does not affect these two bond lengths significantly.
Figure 1. Structure of complex 2 together with the atom-labelling scheme (50% probability ellipsoids with hydrogen atoms omitted for
clarity).
336
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Copper(i) Complexes of 2,4-Dithiouracil (2,4-dtucH2)
FULL PAPER
Figure 2. Structure of complex 3 together with the atom-labelling scheme (50% probability ellipsoids with hydrogen atoms omitted for
clarity).
Likewise, the structural parameters within the heterocyclic units (Table 2) are clearly different, with the larger intrali-
backbone remain practically unaffected upon coordination. gand P–Cu–P angle belonging to the more distorted
Light-green single crystals of 3 were grown from the ace- C2P2Cu ring. The four individual Cu–P bonds lie in the
tonitrile/methanol mother liquid of 2 during the earlier narrow range of 2.2546(11)–2.2600(11) Å and match those
stages of the slow evaporation. Complex 3 crystallises in the observed in [Cu(dppet)2]PF6,[12] as well as in other cop-
monoclinic space group P21 with two formula units in the per(i)–diphosphane complexes having a tetrahedral coordi-
unit cell. The structure of 3, together with the atom-label- nation environment.[6,7] Moreover, there are four clearly dif-
ling scheme, is shown in Figure 2.
ferent Cu–Br bond lengths within the Cu2Br2 backbone, ly-
The crystal structure features a dinuclear unit in which ing in the range 2.4279(6)–2.5316(6) Å.
the two copper(i) centres are joined by two bromine bridges
to form a four-membered Cu2Br2 core with a Cu···Cu sepa-
ration distance of 2.8410(6) Å, which is suggestive of a
weak metal–metal interaction, as further substantiated by
the electronic structure calculations (vide infra). The
strongly distorted tetrahedral coordination around each
copper(i) central atom is completed by the two P donor
atoms of the chelating dppbz unit.
The most salient, and quite unexpected, feature of the
structure is the remarkable non-planarity within the Cu2Br2
central core. Unlike in other bromide-bridged dinuclear
complexes that exhibit a strictly planar Cu2Br2 core, such as
[Cu(μ2-Br)(tmtp)(tzdtH)]2 (tmtp = tri-m-tolylphosphane),[5]
the two main planes in 3 through Br(1), Cu(1), Br(2) and
Br(1), Cu(2), Br(2) form a dihedral angle of 150.10(2)°, with
Br(2) being displaced from the mean plane defined by
Cu(1), Br(1) and Cu(2) by 0.7201(8) Å. The same uncom-
mon non-planarity adopted by the Cu2I2 moiety previously
observed in [Cu(μ2-I)(dppet)]2 [dppet = cis-1,2-bis(diphen-
ylphosphanyl)ethane] is noteworthy.[7b]
Computational Studies Using DFT
In an attempt to understand some marked structural fea-
tures of the complexes under investigation, we performed
electronic structure calculations based on density functional
theory for compounds 2 and 3, as well as for some related
model species. To obtain a computationally convenient size
for the compounds, we used models resulting from substitu-
tion of the phenyl groups of the diphosphane ligands by H
atoms. The use of such models does not alter the descrip-
tion of the “core” region of the compounds and is ulti-
mately the most efficient and productive route to modelling
the electronic structure and related properties of relatively
big-sized copper(i) complexes. In particular, we sought an
explanation for the exclusive coordination of 2,4-dithioura-
cil through the thione-S atom at C(4) and explored the ori-
gin of the unexpected bend of the Cu2Br2 central core in
compound 3.
Equilibrium Geometries, Electronic Structure and Bonding
Mechanism in the Series of Model Mononuclear Complexes
[CuX(dpbz)] [X = Cl, Br, or I; dpbz = 1,2-bis(diphos-
phanyl)benzene]
Each of the two CuPCCP five-membered chelate rings
adopts the envelope conformation with the metal atoms out
of the plane containing the four diphos ligand donor atoms
by 0.665(3) and –0.951(2) Å for Cu(1) and Cu(2), respec-
Selected structural and electronic properties of the mo-
tively. Consequently, the bite angles of the two diphosphane nonuclear complexes [CuX(dpbz)] (X = Cl, M1; Br, M2; I,
Eur. J. Inorg. Chem. 2006, 334–344
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337

P. Aslanidis, P. J. Cox, A. Kaltzoglou, A. C. Tsipis
FULL PAPER
M3) computed at the B3LYP/DGDZVP level of theory are halide ligand does not affect the natural electron configura-
given in Table 3.
tion of the central CuI atom significantly. Interestingly, the
All [CuX(dpbz)] species are three-coordinate CuI com- computed bond overlap populations (bop) of the Cu–Br,
plexes that adopt a trigonal planar structure with the cen- Cu–Cl and Cu–I bonds are of almost equal size.
tral copper(i) atom and the three donor atoms lying in a
It can be seen that the Cu–X bond is a composite bond
plane. As is to be expected, the Cu–X bond lengths increase that acquires a partial double-bond character involving
upon going from the chloro to bromo to iodo derivative, both σ and π components. The HOMO corresponds to a
which is compatible with the computed ν(Cu–X) stretching π*-antibonding Cu–X interaction that is strongly polarized
vibrational frequencies at 354, 260 and 235 cm–1, respec- towards the halide ligand X. Below the HOMO there is a
tively. However, no other significant structural differences set of σ- (HOMO–2) and π-bonding MOs (HOMO–3 and
could be observed for the [CuX(dpbz)] (X = Cl, Br or I) HOMO–6) that correspond to Cu–X interactions as well as
complexes. Based on the HOMO–LUMO energy gap − the describing the σ and π dative bonding of the halide ligands.
hardness values (η) are shown in Table 3 − one would ex- Finally, the LUMO is delocalised over the benzene ring of
pect the tendency for dimerisation to follow the order M3 the diphosphane ligand.
Ͼ M2 Ͼ M1.
Equilibrium Geometries, Electronic Structure and Bonding
Mechanism of the Dinuclear Compounds [Cu(μ-X)-
(dpbz)]2 (X = Cl, Br or I)
The most relevant molecular orbitals of the mononuclear
complexes [CuX(dpbz)] related to the bonding mechanism
are depicted schematically in Scheme 2. According to the
natural bond orbital (NBO) population analysis, the CuI
Selected structural parameters and electronic properties
centre acquires a positive natural atomic charge of about of the dinuclear compounds [Cu(μ-Cl)(dpbz)]2 (M4), [Cu(μ-
0.61–0.7 |e|. Moreover, the natural electron configuration Br)(dpbz)]2 (M5) and [Cu(μ-I)(dpbz)]2 (M6) computed at
(nec) indicates that the electron density is mainly transferred the B3LYP/DGDZVP level of theory are compiled in
to the 4s orbital of the copper(i) atom. The nature of the Table 4.
Table 3. Selected structural parameters and electronic properties of the mononuclear complexes [CuX(dpbz)] (X = Br or Cl) computed
at the B3LYP/DGDZVP level.
Property
[CuCl(dpbz)] (M1)
[CuBr(dpbz)] (M2)
[CuI(dpbz)] (M3)
Re(Cu–X) [Å]
Re(Cu–P1) [Å]
θe(P–Cu–X) [°]
θe(P–Cu–P) [°]
μe [D]
2.175
2.314
135.9
88.6
11.09
1.78
0.70
2.307
2.316
135.8
88.6
11.34
1.70
0.67
2.500
2.317
135.8
88.6
11.75
1.59
0.61
η [eV][a]
[b]
qCu
qX
qP
–0.78
0.23
–0.75
0.23
–0.70
0.23
bop(Cu–X)[c]
bop(Cu–P)
nec(Cu)[d]
nec(X)
nec(P)
0.25
0.21
0.26
0.21
0.28
0.21
4s0.413d9.84
3s1.963p5.80
3s1.453p3.24
4s0.433d9.86
4s1.964p5.78
3s1.453p3.24
4s0.463d9.87
5s1.955p5.74
3s1.453p3.24
[a] Hardness η = (εLUMO – εHOMO)/2. [b] Natural charges. [c] Mulliken bond-overlap population. [d] Natural electron configuration.
Scheme 2. The most relevant molecular orbitals of the mononuclear complex [CuBr(dpbz)] (isodensity contours of 0.03 a.u.). The relevant
MOs for [CuCl(dpbz)] and [CuI(dpbz)] are analogous.
338
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Copper(i) Complexes of 2,4-Dithiouracil (2,4-dtucH2)
FULL PAPER
Table 4. Selected structural parameters and electronic properties of the dinuclear model compounds [Cu(μ-X)(dpbz)]2 (X = Cl, Br or I)
computed at the B3LYP/DGDZVP level.
Property
[Cu(μ-Cl)(dpbz)]2 (M4)
[Cu(μ-Br)(dpbz)]2 (M5)
[Cu(μ-I)(dpbz)]2 (M6)
Re(Cu–X) [Å]
Re(Cu–P1) [Å]
Re(Cu···Cu) [Å]
θe(P–Cu–X) [°]
θe(P–Cu–P) [°]
θe(Cu–X–Cu) [°]
θe(X–Cu–X) [°]
μe [D]
2.402
2.316
2.972
116.2
89.1
76.4
103.6
0.00
2.525
2.327
2.948
114.7
88.8
71.5
108.5
0.00
2.720
2.335
2.887
112.4
88.5
64.1
115.9
0.00
η [eV][a]
2.02
0.75
2.00
0.70
2.40
0.62
[b]
qCu
qX
qP
–0.78
0.24
0.13
–0.75
0.24
0.15
–0.67
0.24
0.16
bop(Cu–X)[c]
bop(Cu–P)
nec(Cu)[d]
nec(X)
nec(P)
0.12
0.13
0.12
4s0.343d9.86
3s1.953p5.82
3s1.463p3.22
4s0.393d9.87
4s1.954p5.78
3s1.463p3.22
4s0.423d9.90
5s1.945p5.72
3s1.463p3.22
[a] Hardness η = (εLUMO – εHOMO)/2. [b] Natural charges. [c] Mulliken bond-overlap population. [d] Natural electron configuration.
As is to be expected, the dicopper(i) compounds adopt a a series of [CuXL]2 (X = Cl, Br or I) complexes decreases
“diamond like” structure of C2h symmetry with the plane upon increasing the size of the bridging halide ligand. The
of the Cu(μ-X)2Cu “rhombus” bisecting the P–Cu–P bond X–Cu–X bond angle in M6 was found to be more obtuse
angles and being perpendicular to the plane of the diphos- relative to that found for M5 or M4, while the opposite
phane ligands. The four equivalent Cu–X bonds defining holds true for the Cu–X–Cu bond angle (Table 4).
the Cu(μ-X)2Cu “rhombus” are elongated by about 0.2 Å
The computed νsym(X–Cu–X) stretching vibrational fre-
compared to the corresponding Cu–X bonds of the mono- quencies at 140, 110 and 87 cm–1 for the chloro, bromo and
mers. The calculated structural parameters are in line with iodo derivatives, respectively, are compatible with the elon-
those of the “real” complex 3 derived from the X-ray struc- gated Cu–X bonds in the dimers. The same also holds true
tural analysis. However, the non-planarity of the Cu2Br2 for the computed νsym(Cu–X–Cu) stretching vibrational fre-
central core of complex 3 is not observed for the Cu2X2 quencies at 202, 172 and 160 cm–1 for M4, M5 and M6,
core in the optimised structures of the model compounds respectively.
M4, M5, and M6, thus indicating that steric and/or crystal-
All [Cu(μ-X)(dpbz)]2 (X = Cl, Br, or I) molecules are
packing effects in the solid state should be responsible for predicted to be thermodynamically more stable than the
the Cu2Br2 folding across the Br···Br line and the non- corresponding monomers; the calculated heat of reaction
equivalent coordination spheres around the two CuI metal ΔRH for the dimerisation process was found to be 25–
centres.
26 kcalmol–1 at the B3LYP/DGDZVP level of theory. In
To verify this hypothesis, the rigid and relaxed PES of addition, both M4 and M5 exhibit almost equal HOMO–
the “real” complex 3 and the model compound M5 were LUMO energy gaps as well as hardness values, indicating
calculated at the B3LYP/DGDZVP level of theory. It was comparable stability. On the other hand, M6 exhibits the
found that the bending of the Cu2Br2 core in the “real” highest HOMO–LUMO energy gap and hardness value,
complex 3 and the model compound M5 demands only 0.6 and is expected to be the most stable amongst the [Cu(μ-
and 0.4 kcalmol–1, respectively, thus indicating a very flat X)(dpbz)]2 (X = Cl, Br, or I) complexes.
potential energy surface for both complexes. Therefore, fac-
No significant differences could be observed between the
tors such as the 4.298-Å π-stacking interaction between two natural and net atomic charges on the CuI bridging halide
almost parallel phenyl groups of the dppbz ligand could and phosphorus donor atoms of M4, M5 and M6 (Table 4).
enforce the bending of the Cu2Br2 core in the real complex The CuI metal centres acquire positive natural charges of
3. It should be noted that in an analogous dinuclear AgI about 0.6–0.8 |e|, while the halide bridging ligands acquire
complex containing bulky diphosphane or diarsane ligands negative natural charges of around –0.7 |e|. According to
the folding of the Ag(μ-Br)2Ag core has been attributed to the natural electron configurations, the electron density is
steric strain in the crystal.[13] The intermetallic Cu···Cu dis- mainly transferred from the valence p atomic orbitals of the
tance follows the order M4 Ͼ M5 Ͼ M6, in line with our bridging halide ligands to the 4s orbitals of the CuI metal
previous results[7a] on analogous systems with general for- centres.
mula [Cu(μ-X)(PH3)2]2 (X = Cl, Br or I), as well to the
The most important MOs of the [Cu(μ-X)(dpbz)]2 di-
observations made by Soloveichic et al.[14] in the framework mers are depicted in Scheme 3. The HOMO corresponding
of EHMO theory for the complexes [LnCu(μ-X)CuLn] (n = to π* antibonding Cu–X interactions is polarized towards
1 or 2, L = PR3). Alvarez et al.[15] have also found from the bridging halide ligands, while the LUMO is delocalised
MP2 and B3LYP calculations that the Cu···Cu distance in over the benzene rings of the diphosphane ligands. There
Eur. J. Inorg. Chem. 2006, 334–344
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339

P. Aslanidis, P. J. Cox, A. Kaltzoglou, A. C. Tsipis
FULL PAPER
Scheme 3. The most important molecular orbitals of the dinuclear complex [Cu(μ-Br)(dppbz)]2 (isodensity contours of 0.03 a.u.). The
relevant MOs for [Cu(μ-Cl)(dppbz)]2 and [Cu(μ-I)(dppbz)]2 are analogous.
are σ-type MOs (HOMO–17 and HOMO–18) delocalised
The complexes are four-coordinate with a tetrahedral co-
over the entire four-membered Cu(μ-X)2Cu ring. The de- ordination environment. The calculated structural param-
localisation of the σ-electron density over the Cu(μ-X)2Cu eters of M8 are in excellent agreement with those obtained
rhombus having eight framework electrons[16] could proba- from the X-ray structural analysis of the “real” complex 2.
bly account for the almost equivalent Cu–X bonds. Interest- The most remarkable structural difference between M8 and
ingly, all [Cu(μ-X)(dpbz)]2 dimers exhibit a σ-type MO 2 is the orientation of the 2,4-dithiouracil ring − in M7, M8
(HOMO–10), which suggests the existence of weak inter- and M9 the plane of the 2,4-dithiouracil ring is perpendicu-
metallic Cu···Cu interactions.
lar to the plane of the diphosphane ligand and bisects the
P–Cu–P bond angle. The 2,4-dithiouracil ligand in M7, M8
and M9 is further stabilized by a hydrogen bond between
the halide ligand and an H atom of the 2,4-dithiouracil.
The calculated X···H distances are predicted to be 2.113,
2.302 and 2.597 Å for M7, M8 and M9, respectively. The
H-bond formation is reflected in the computed X···H bop
values, which were found to be 0.16, 0.14 and 0.12 for M7,
M8 and M9, respectively, as well as in the existence of a
MO, with a σ component (Scheme 4, b), describing the
Equilibrium Geometries, Electronic Structure and Bonding
Mechanism of Mononuclear [CuX(dpbz)(2,4-dtucH2)]
(X = Cl, Br or I) Complexes
Selected structural parameters and electronic properties
of the model compounds mononuclear [CuCl(dpbz)(2,4-
dtucH2)] (M7), [CuBr(dpbz)(2,4-dtucH2)] (M8) and [Cu-
I(dpbz)(2,4-dtucH2)] (M9) computed at the B3LYP/
DGDZVP level of theory are summarised in Table 5.
Table 5. Selected structural parameters and electronic properties of the mononuclear model compounds [CuX(dpbz)(2,4-dtucH2)] (X =
Cl, Br or I) computed at the B3LYP/DGDZVP level.
Property
[CuCl(dpbz)(2,4-dtucH2)] (M7)
[CuBr(dpbz)(2,4-dtucH2)] (M8) [CuI(dpbz)(2,4-dtucH2)] (M9)
Re(Cu–X) [Å]
Re(Cu–P1) [Å]
Re(Cu–S) [Å]
θe(P–Cu–X) [°]
θe(P–Cu–P) [°]
θe(P–Cu–S) [°]
θe(S–Cu–X) [°]
μe [D]
2.324
2.341
2.336
105.2
88.0
120.0
114.6
6.62
2.451
2.348
2.346
105.4
87.8
118.8
116.7
7.14
2.647
2.356
2.349
105.7
87.4
116.3
120.3
8.11
η [eV][a]
3.31
0.71
3.12
0.69
2.77
0.65
[b]
qCu
qX
qP
–0.77
0.23
–0.75
0.24
–0.71
0.23
qS
–0.21
0.17
0.15
0.20
–0.20
0.19
0.15
0.21
–0.20
0.21
0.15
0.20
bop(Cu–X)[c]
bop(Cu–P)
bop(Cu–S)
nec(Cu)[d]
nec(X)
nec(P)
4s0.373d9.86
3s1.963p5.80
3s1.463p3.23
3s1.733p4.44
4s0.393d9.87
4s1.964p5.78
3s1.463p3.22
3s1.733p4.44
4s0.413d9.88
5s1.965p5.75
3s1.463p3.23
3s1.733p4.43
nec(S)
[a] Hardness η = (εLUMO – εHOMO)/2. [b] Natural charges. [c] Mulliken bond-overlap population. [d] Natural electron configuration.
340 Eur. J. Inorg. Chem. 2006, 334–344
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Copper(i) Complexes of 2,4-Dithiouracil (2,4-dtucH2)
FULL PAPER
Scheme 4. The most important molecular orbitals of 2,4-dithiouracil (a) and the mononuclear compound [CuBr(dpbz)(2,4-dtucH2)] (b)
(isodensity contours of 0.03 a.u.). the relevant MOs for [CuCl(dpbz)(2,4-dtucH2)] and [CuI(dpbz)(2,4-dtucH2)] are analogous.
X···H interaction. The latter introduces an elongation to the σ and π components, as can be seen from the corresponding
N–H bond only about 0.03–0.02 Å in the 2,4-dithiouracil MOs shown in Scheme 4b. The electron density is transfer-
ligand with respect to that of the “free” ligand.
red from the HOMO of the 2,4-dithiouracil ligand, which
The computed unscaled ν(N–H) stretching vibrational is a non-bonding (lone pair) p-type MO localised mainly
frequencies appear at 3002, 3068 and 3160 cm–1 for M7, M8 on the S donor atom at the 4-position and to a lesser extent
and M9, respectively, while in the “free” 2,4-dithiouracil li- on the S atom at the 2-position (Scheme 4a), to a vacant
gand it appears at 3564 cm–1. The strong shift of the ν(N– orbital of the CuI metal centre, thus forming the σ(CuǟS)
H) stretching vibrational band towards lower frequencies dative coordination bond. Obviously, the nature of the
upon coordination of the 2,4-dithiouracil ligand to the CuI HOMO accounts well for the inability of the S atom at the
centre is indicative of the involvement of the H atom in H- 2-position to act as a second donor atom coordinated to
bond formation with the halide ligand. In all another CuI metal centre. In addition, there is π back-bond-
[CuX(dpbz)(2,4-dtucH2)] (X = Cl, Br, or I) complexes the ing through the interaction of an occupied orbital of the
X···H–N moiety is almost linear, the calculated X···H–N CuI centre with the LUMO of the 2,4-dithiouracil ligand,
bond angle being equal to 175–177°. On the other hand, which is a delocalised π*-type MO having a high contri-
the S–Cu–X and Cu–S–C bond angles were found to be bution from the 3p orbitals of the S(4) acceptor atom
smaller, ranging from 114–120° and 110–114°, respectively. (Scheme 4a). The Cu–S coordination bond is relatively
Coordination of 2,4-dithiouracil to the CuI centre does not weak, with a predicted bond-dissociation energy (BDE) of
alter its structure significantly. However, in the 16.2, 14.8 and 13.2 kcalmol–1 for M7, M8 and M9, respec-
[CuX(dpbz)(2,4-dtucH2)] (X = Cl, Br, or I) complexes the tively, at the B3LYP/DGDZVP level.
coordination of the 2,4-dithiouracil through the S donor
Upon coordination of the 2,4-dithiouracil ligand to the
atom in the 4-position lengthens the C=S bond by about [CuX(dpbz)] (X = Cl, Br, or I) fragment the Cu–X bond is
0.03 Å. This could be attributed to electron-density transfer elongated by about 0.14–0.15 Å. This elongation is ac-
from the C=S group of the 2,4-dithiouracil ligand to the companied by a decrease of the bop values compared to
CuI centre, leading to formation of the Cu–S coordination those found for the [CuX(dpbz)] fragments. The coordina-
bond. The latter has a composite nature and exhibits both tion of the 2,4-dithiouracil to the CuI centre of the
Eur. J. Inorg. Chem. 2006, 334–344
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341

P. Aslanidis, P. J. Cox, A. Kaltzoglou, A. C. Tsipis
FULL PAPER
KBr discs with a Perkin–Elmer 1430 spectrophotometer, while a
Perkin–Elmer–Hitachi 200 spectrophotometer was used to obtain
the electronic absorption spectra. Melting points were measured in
open tubes with a STUART scientific instrument and are uncor-
rected. Molar conductivities, magnetic susceptibility measurements
and elemental analyses for carbon, nitrogen and hydrogen were per-
formed as described elsewhere.[17]
[CuX(dpbz)] fragments does not affect the natural atomic
charges significantly, while the same holds true for the natu-
ral electron configurations of the respective atoms.
Conclusions
We have described the synthesis and structural character- Computational Details: The structural, electronic and energetic
properties of all compounds were computed with Becke’s three-
parameter hybrid functional[18] combined with the Lee–Yang–Parr
correlation functional,[19] abbreviated as B3LYP, using the
DGDZVP basis set.[20] We used the all-electron, double-zeta val-
ence DGDZVP basis set, which is comparable with the 6-31G(d)
level,[21] because it has been found previously[22] that it provides a
satisfactory description of the structural and energetic properties
of analogous CuI complexes (overall closer to the experiment) but
it is less time consuming for computations with such big-sized tran-
sition metal complexes than the larger 6-31G(d,p) basis set. No
isation of copper(i) coordination compounds bearing 1,2-
bis(diphenylphosphanyl)benzene (dppbz) and/or 2,4-dithio-
uracil (2,4-dtucH2) as ligands. The reaction of 1,2-bis(di-
phenylphosphanyl)benzene (dppbz) with copper(i) halides
yields [CuX(dppbz)] adducts, which for X = Br corresponds
to a dimer of the formula [Cu(μ-Br)(dppbz)]2 containing a
non-symmetrical, bent Cu2Br2 core structure. The Cu···Cu
separation distance of 2.8410(6) Å is indicative of weak in-
termetallic interactions. The latter is further corroborated
by DFT calculations on the model dinuclear compound constraints were imposed on the geometry in any of the calcual-
tions. Full geometry optimisation was performed for each structure
using Schlegel’s analytical gradient method[23] and the attainment
of the energy minimum was verified by calculating the vibrational
frequencies that result in an absence of imaginary eigenvalues. All
calculations were performed using the Gaussian 03 suite of pro-
grams.[24]
[Cu(μ-Br)(dpbz)]2, which exhibits a characteristic σ-type
MO (HOMO-10) describing these weak intermetallic
Cu···Cu interactions. However, the non-planarity of the
central Cu2Br2 core is not observed for the Cu2X2 core in
the optimised model structures, thus indicating that π-
stacking interactions between the two almost parallel
phenyl groups of the diphosphane ligand are probably re-
sponsible for the Cu2Br2 folding across the Br···Br axis. The
presence of σ-type MOs delocalised over the entire four-
membered Cu(μ-X)2Cu ring containing eight framework
electrons accounts for the equivalent Cu–X bonds of the
rhombus. The dimerisation energy of the [Cu(μ-X)(dpbz)]2
(X = Cl, Br, or I) dimers is predicted to be 25–26 kcalmol–1
at the B3LYP/DGDZVP level. The [CuBr(dppbz)]2 dimer
and its chloride and iodide analogues prove to be good pre-
cursors for the preparation of other derivatives and are
used, in the course of the present study, for the synthesis of
heteroleptic complexes which contain, besides the chelating
dppbz, a 2,4-dithiouracil ligand. In line with theoretical
predictions, the 2,4-dithiouracil ligand, which adopts the di-
Crystal Structure Determination: Single crystals suitable for crystal-
structure analysis were obtained by slow evaporation of acetoni-
trile/methanol solutions of the complexes at room temperature. X-
ray diffraction data were collected on an Enraf–Nonius Kappa
CCD area-detector diffractometer. The programs DENZO[25] and
COLLECT[26] were used for data collection and cell refinement,
respectively. Details of crystal and structure refinement are shown
in Table 6. The structures were solved using the program SIR97[27]
and refined with SHELX-97.[28] Molecular plots were obtained
with the program ORTEP-3.[29]
CCDC-243707 (for 2) and -269670 (for 3) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Synthesis of Complexes 1 and 2: 1,2-Bis(diphenylphosphanyl)ben-
thione form as its stable conformation, acts as a mono- zene (223.2 mg, 0.1 mmol) was added to a suspension of CuCl or
CuBr (0.5 mmol) in 30 mL of dry acetonitrile and the mixture was
stirred for 2 h at 50 °C, during which time a greenish precipitate
was formed. A solution of pyrimidine-2,4-dithione (0.5 mmol) in a
small amount (Ϸ20 mL) of methanol was then added and the reac-
tion mixture was stirred under reflux for two hours, whereupon the
precipitate gradually disappeared. The resulting clear solution was
filtered off and left to evaporate at ambient temperature. The
microcrystalline solid, which was deposited upon standing for se-
veral days, was filtered off and dried in vacuo.
dentate ligand that is coordinated to the metal ion exclu-
sively through its thione-S atom at the 4-position. The na-
ture of the HOMO − a non-bonding, lone-pair, π-type MO
localised mainly on the S donor atom at the 4-position −
accounts well for the inability of the S atom at the 2-posi-
tion to act as a second donor to another CuI centre. More-
over, the 2,4-dithiouracil ligand in the [CuX(dpbz)(dtucH2)]
complexes is predicted to be loosely associated with the CuI
centre, the interaction energies being 13–16 kcalmol–1 at the
B3LYP/DGDZVP level.
[CuCl(dppbz)(2,4-dtucH2)] (1): Orange-red solid (125 mg, 70%),
m.p. 261 °C. C34H28ClCuN2P2S2 (689.70): calcd. C 59.21, H 4.09,
N 4.06; found C 59.75, H 4.05, N 3.93. IR: ν = 3446m, 3050m,
˜
1599s, 1570vs, 1532vs, 1480m, 1435m, 1342s, 1215s, 1198s, 1100s,
859m, 741s, 692s, 520s, 493s, 467m cm–1. UV/Vis (CHCl3): λmax
(log ε) = 262 nm (3.68), 298 (3.69), 392 (3.31).
Experimental Section
Materials and Instrumentation: Commercially available copper(i)
chloride, bromide and iodide, and 1,2-bis(diphenylphosphanyl)ben-
zene were used as received, while pyrimidine-2,4-dithione (Aldrich)
was recrystallised from hot ethanol prior to use. All the solvents
were purified by standard methods and stored over molecular
sieves. IR spectra in the region of 4000–200 cm–1 were obtained in
[CuBr(dppbz)(2,4-dtucH2)] (2): Orange-red crystals (130 mg, 70%),
m.p. 265 °C. C34H28BrCuN2P2S2 (734.15): calcd. C 55.63, H 3.84,
N 3.82; found C 55.91, H 3.88, N 3.79. IR: ν = 3457m, 3147w,
˜
3070m, 1618m, 1599vs, 1531vs, 1479s, 1435s, 1341m, 1215s,
1196vs,1099vs, 1068m, 768s, 740s, 692vs, 519vs, 492s, 441s cm–1.
342
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Copper(i) Complexes of 2,4-Dithiouracil (2,4-dtucH2)
FULL PAPER
Table 6. Crystal data and structure refinements for 2 and 3.
2
3
Molecular formula
Formula weight
Temperature [K]
Wavelength [Å]
Crystal system
C34H28BrCuN2P2S2
734.09
120(2)
0.71073
monoclinic
P21/c
C60H48Br2Cu2P4
1179.76
120(2)
0.71073
monoclinic
P21
Space group
Unit cell dimensions
a = 13.5328(4) Å, α = 90°
b = 14.4864(5) Å, β = 92.407(2)°
c = 16.3381(4) Å, γ = 90°
3200.12(17)
a = 11.2105(3) Å, α = 90°
b = 18.7290(6) Å, β = 97.6364(17)°
c = 12.1317(2) Å, γ = 90°
2524.60 (11)
Volume [Å3]
Z
4
2
Density (calculated) [Mgm–3]
Absorpt. coefficient [mm–1]
F(000)
1.524
2.189
1488
1.552
2.592
1192
Crystal size [mm]
θ range for data collection [°]
Index ranges
0.52×0.45×0.10
2.97 to 27.47°
–17 Յ h Յ 17
–18 Յ k Յ 18
–21 Յ l Յ 19
46486
0.10×0.10×0.08
3.39 to 27.48
–14 Յ h Յ 14
–22 Յ k Յ 24
–15 Յ l Յ 15
Reflections collected
30939
Independent reflections
Completeness to θ
7284 [R(int) = 0.0538]
99.4% (θ = 27.47°)
7284 / 0 / 380
0.8108 and 0.3957
Full-matrix least-squares on F2
1.025
R1 = 0.0313, wR2 = 0.0680
R1 = 0.0530, wR2 = 0.0739[a]
0.355 and –0.415
10626 [R(int) = 0.0571]
99.7% (θ = 27.48°)
10626 / 1 / 613
0.8195 and 0.7816
Full-matrix least-squares on F2
0.973
R1 = 0.0374, wR2 = 0.0613
R1 = 0.0569, wR2 = 0.0666[b]
0.428 and –0.610
Data / restraints / parameters
Max. and min. transmission
Refinement method
Goodness-of-fit on F2
Final R indices [I Ͼ 2σ(I)]
R indices (all data)
Largest diff peak and hole [eÅ3]
2
2
2
2
[a] w = 1/[σ2(Fo2) + (0.0379P)2 + 0.3987P], where P = (Fo + 2Fc )/3. [b] w = 1/[σ2(Fo2) + (0.0184P)2], where P = (Fo + 2Fc )/3.
UV/Vis (CHCl3): λmax (log ε) = 248 nm (4.09), 284 (4.31), 358
692vs, 518vs, 496s, 480m cm–1. UV/Vis (CHCl3): λmax (log ε) =
(3.94).
248 (4.36), 330 (4.04).
Synthesis of Complexes 3 and 4: 1,2-Bis(diphenylphosphanyl)ben-
zene (446.5 mg, 1 mmol) was added to a suspension of copper(i)
bromide or iodide (1 mmol) in 50 mL of dry acetonitrile, and the
mixture was heated under reflux for 4 h. Slow evaporation of the
resulting light-green solution at room temperature gave a crystal-
line solid, which was filtered off and dried in vacuo.
Synthesis of Complexes 6 and 7: A solution of 2,4-dithiouracil
(144 mg, 1 mmol) in a small amount (Ϸ20 mL) of methanol was
added to a suspension of CuI or CuBr (0.5 mmol) in 30 mL of dry
acetonitrile and the mixture was stirred for 2 h. The orange-yellow
precipitate that deposited upon cooling was filtered off, washed
with small amounts of THF and dried in vacuo.
[Cu(μ2-Br)(dppbz)]2 (3): Light-green powder (550 mg, 93%), m.p.
295 °C. C30H24BrCuP2 (589.93): calcd. C 61.08, H 4.10; found C
[CuI(2,4-dtucH2)]x (6): Orange-red powder (155 mg, 93%), m.p.
295 °C. C4H4CuIN2S2 (334.68): calcd. C 14.36, H 1.20, N 8.37;
60.86, H 3.97. IR: ν = 3415m, 3049w, 1637w, 1585m, 1480m,
˜
found C 14.23, H 1.12, N 7.85. IR: ν = 3212m, 3096w, 2975w,
˜
1435s, 1184m, 1096m, 1027m, 750m, 744s, 695s, 518s, 497m,
482m cm–1. UV/Vis (CHCl3): λmax (log ε) = 258 nm (3.71), 293
(3.68), 351 (3.63).
1609vs, 1528vs, 1466m, 1260s, 1220s, 1195s, 1110vs, 983m, 856m,
789m, 692m, 671m, 462m, 395w cm–1 UV/Vis (DMF): λmax (log ε)
= 284 (4.07), 352 (3.75), 397 (3.04).
[CuI(dppbz)]x (4): Light-green powder (541 mg, 85%), m.p. 298 °C.
C30H24CuIP2 (636.94): calcd. C 61.08, H 4.10; found C 56.15, H
[CuBr(2,4-dtucH2)]x (7): Orange-red powder (120 mg, 84%), m.p.
280 °C. C4H4BrCuN2S2 (287.67): calcd. C 16.70, H 1.40, N 9.74;
3.89. IR: ν = 3437m, 3048w, 1637m, 1585w, 1480m, 1434s, 1184w,
˜
found C 17.62, H 1.49, N 9.50. IR: ν = 3198w, 3070m, 2985m,
˜
1156w, 1094m, 1027w, 759m, 741s, 691vs, 518vs, 496m, 480m
cm–1 UV/Vis (CHCl3): λmax (log ε) = 248 nm (4.35), 293 (4.16), 328
(4.07).
2883m, 1616s, 1575s, 1551vs, 1481m, 1220m, 1125s, 744w, 693m,
518w cm–1 UV/Vis (DMF): λmax (log ε) = 284 (4.18), 354 (3.88),
403 (3.45).
Synthesis of [CuI(dppbz)(2,4-dtucH2)] (5): 1,2-Bis(diphenylphos-
phanyl)benzene (112 mg, 0.25 mmol) was added in small portions
to a suspension of 4 (83 mg, 0.25 mmol) in 60 mL of dry acetone
and the mixture was stirred for 1 h at 50 °C. The resulting clear
solution was filtered and left to evaporate at ambient. The micro-
crystalline solid that was deposited upon standing for several days
was filtered off and dried in vacuo. Orange powder (105 mg, 53%),
m.p. 305 °C. C34H28CuIN2P2S2 (781.16): calcd. C 52.28, H 3.61, N
Acknowledgments
We thank the EPSRC X-ray crystallography service at the Univer-
sity of Southampton for collecting the X-ray data.
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3.59; found C 52.47, H 3.59, N 3.46. IR: ν = 3216w, 3048m,
˜
1610m, 1531s, 1480s, 1435s, 1185m, 1112m, 1095vs, 759m, 742vs,
Eur. J. Inorg. Chem. 2006, 334–344
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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Received: August 15, 2005
Published Online: December 5, 2005
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