Tetrahedral CoII complexes with CoI2O2 and CoO2S2 cores - Crystal structures of [Co{HN(OPPh 2)(SPPh2)-O}2I2] and [Co{N(OPPh 2)(SPPh2)-O,S}2]

Article abstract of DOI:10.1002/ejic.200700441

The compound [Co^II{HN(OPPh₂)(SPPh₂)-O} ₂I₂] (1) was synthesised by the reaction of cobalt in powder with the iodine adduct of tetraphenylthiooxoimidodiphosphinic acid, HN(OPPh₂)(SPPh₂), in Et₂O; treatment of compound 1 with NaOH resulted in deprotonation of the ligands bound to the metal ion and a separation of [Co^II{N(OPPh₂)(SPPh ₂)-O,S}₂] (2). Molecular structures of complexes 1 and 2 were elucidated by X-ray diffraction analysis, which revealed a CoI ₂O₂ tetrahedral core for compound 1 in which two neutral ligands bind through the oxygen atoms the Co^II ion, and a tetrahedral CoO₂S₂ core for compound 2 with the oxygen and sulfur atoms of each anionic ligand chelating a Co^II centre. Variable-temperature magnetic susceptibility measurements are consistent with tetrahedral high-spin (S = 3/2) Co^II that possesses a ⁴A₂ ground state with best fit parameters g = 2.25, |D| = 12.0 cm^-1 and g = 2.37, |D| = 11.9 cm^-1 for complexes 1 and 2, respectively. The compounds were further characterised by UV/Vis and IR spectroscopy. DFT calculations were performed on model complexes [Co ^II{N(OPH₂)(SPH₂)-O,S}₂] (3) and [Co^II{N(SPH₂)₂-S,S′}₂] (4) to compare the electronic properties of the CoO₂S₂ and CoS₄ cores. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700441

FULL PAPER
DOI: 10.1002/ejic.200700441
Tetrahedral CoII Complexes with CoI2O2 and CoO2S2 Cores –
Crystal Structures of [Co{HN(OPPh2)(SPPh2)-O}2I2] and
[Co{N(OPPh2)(SPPh2)-O,S}2]
M. Carla Aragoni,[a] Massimiliano Arca,[a] M. Bonaria Carrea,[a] Alessandra Garau,[a]
Francesco A. Devillanova,[a] Francesco Isaia,*[a] Vito Lippolis,[a] Gian Luca Abbati,[b]
Francesco Demartin,[c] Cristian Silvestru,[d] Serhiy Demeshko,[e] and Franc Meyer[e]
Keywords: Cobalt / O,S ligands / Phosphanes / Sulfides / Density functional calculations / Magnetic properties
The compound [CoII{HN(OPPh2)(SPPh2)-O}2I2] (1) was syn-
thesised by the reaction of cobalt in powder with the iodine
able-temperature magnetic susceptibility measurements are
consistent with tetrahedral high-spin (S = 3/2) CoII that pos-
sesses a 4A2 ground state with best fit parameters g = 2.25,
|D| = 12.0 cm–1 and g = 2.37, |D| = 11.9 cm–1 for complexes 1
and 2, respectively. The compounds were further character-
ised by UV/Vis and IR spectroscopy. DFT calculations were
performed on model complexes [CoII{N(OPH2)(SPH2)-O,S}2]
(3) and [CoII{N(SPH2)2-S,SЈ}2] (4) to compare the electronic
properties of the CoO2S2 and CoS4 cores.
adduct
of
tetraphenylthiooxoimidodiphosphinic
acid,
HN(OPPh2)(SPPh2), in Et2O; treatment of compound 1 with
NaOH resulted in deprotonation of the ligands bound to the
metal ion and a separation of [CoII{N(OPPh2)(SPPh2)-O,S}2]
(2). Molecular structures of complexes 1 and 2 were eluci-
dated by X-ray diffraction analysis, which revealed a CoI2O2
tetrahedral core for compound 1 in which two neutral ligands
bind through the oxygen atoms the CoII ion, and a tetrahe-
dral CoO2S2 core for compound 2 with the oxygen and sulfur
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
atoms of each anionic ligand chelating a CoII centre. Vari- Germany, 2007)
cessful to date. Previous studies led us to consider that the
Introduction
overall oxidation/complexation reaction was composed of
two distinct processes in which the adduct was accountable
for the oxidation of the metal and the ligand/donor for the
complexation of the formed metal ion.[3] On the basis of
these considerations, the formation of the I2 adduct of
tetraphenyldithioimidodiphosphinic acid, HN(SPPh2)2,
HL(SS), represents a successful attempt to join together the
donor ability of the phosphane sulfide group and I2. The
result is a “robust” adduct, and the intrinsic ability of
HL(SS) and its deprotonated form [N(SPPh2)2]–, L(SS), to
adapt well to the preferred coordination geometries of the
metal ion results in a variety of coordination patterns
mainly involving S,SЈ sulfur chelation. In this respect, the
reaction in diethyl ether of the HL(SS)·I2 adduct with a vari-
ety of metal powders Ϫ Au, Co, Cu, In, Pd and Sb Ϫ and
liquid Hg allowed their oxidation and the formation of
complexes of the resulting metal ions with the ligand in its
anionic form.[1c–1e,4] In the reaction with Hg and Cu, it was
also possible to separate solid compounds whose crystal
The use of iodine or interhalogen charge-transfer ad-
ducts of chalcogen donor molecules as oxidising/complex-
ing agents towards zero-valent metals has been attracting
some interest in recent years because of their applications
both in the recovery of precious metals from waste indus-
trial materials and in the recovery of toxic metals for the
environment.[1] Because a great number of iodine adducts
with ligands containing sulfur donor atoms have been syn-
thesised, a wide choice of “reagents” is to be considered
potentially available for the oxidation/complexation of met-
als.[2] However, only a few of them have really proved suc-
[a] Dipartimento di Chimica Inorganica ed Analitica, Università
degli Studi di Cagliari,
S.S. 554 Bivio per Sestu, 09042 Cagliari, Italy
[b] Dipartimento di Chimica, Università di Modena e Reggio Emi-
lia,
Via G. Campi 183, 41100 Modena, Italy
[c] Dipartimento di Chimica Strutturale e Stereochimica Inor-
ganica, Università di Milano,
Via G. Venezian 21, 20133 Milano, Italy
[d] Facultatea de Chimie si Inginerie Chimica, Universitatea Babes- structures showed the unusual presence of HL(SS) in a
Bolyai,
S,SЈ-isobidentate coordinated fashion, i.e. complexes
400028 Cluj-Napoca, Romania
[Hg{HL(SS)}I2] and [Cu{HL(SS)}2]I3.[1d,5]
[e] Institut für Anorganische Chemie, Georg-August-Universität
Göttingen,
As a natural development of this synthetic route, we se-
lected the adduct HN(OPPh2)(SPPh2)·I2, HL(OS)·I2, as the
oxidising agent on the basis of the ligand containing mixed
Tammannstrasse 4, 37077 Göttingen, Germany
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2007, 4607–4614
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4607

F. Isaia et al.
FULL PAPER
hard (O) and soft (S) donor atoms for better ion-complex-
Because of the different bonding modes that are in-
ing adaptability. The chemistry of this ligand has been herently possible for HL(OS), and the unusual formulation
studied far less than that of HL(SS); according to the com- of complex 1, X-ray diffraction analysis was undertaken to
plexes reported in the literature, chelation as an O,S-biden- firmly establish the coordination pattern at the cobalt cen-
tate anionic ligand [L(OS); Scheme 1, structure I] is domi- tre.
nant, but not exclusive, with the S-monodentate coordina-
The molecular structure of 1 is reported in Figure 1; se-
tion mode (Scheme 1, structure II) being adopted in a vari- lected bond lengths and angles are given in Table 1. The
ety of complexes.[6] To date, no complexes of HL(OS) have complex contains a tetrahedral Co2+ ion surrounded by two
been characterised by X-ray crystallographic analysis.
iodide anions and by two HL(OS) monodentate ligands co-
ordinated to the metal atom through the oxygen atom. The
tetrahedral CoO2I2 core is slightly distorted with a Co(1)–
I(1)–I(1)/Co(1)–O(1)–O(2) dihedral angle of 84.21(7)°; the
X–Co–Y (X, Y = I, O) angles are in the range 100.94(11)–
Scheme 1.
This manuscript reports the reactivity of HL(OS) with co-
balt powder by using I2 as the activating agent; the struc-
tures of complexes [CoII{HN(OPPh2)(SPPh2)-O}2I2] (1)
and [CoII{N(OPPh2)(SPPh2)-O,S}2] (2), the latter obtained
by imido deprotonation of the ligands in 1, were deter-
mined by single-crystal X-ray diffraction analysis. Magnetic
parameters were also determined for both complexes. The
reactivity of complex 1 towards a few soft metal ions was
studied in an attempt to synthesise heterobinuclear com-
plexes; moreover, the protonation reaction of 2 by aqueous
hydroiodic acid is reported. In addition, the electronic na-
ture of the CoO2S2 and CoS4 cores was investigated by
DFT calculations on model compounds [CoII{N(OPH2)-
(SPH2)-O,S}2] and [CoII{N(SPH2)2-S,SЈ}2].
Figure 1. ORTEP drawing and atom-labelling scheme for
[CoII{HN(OPPh2)(SPPh2)-O}2I2] (1). Thermal ellipsoids are drawn
at 30% probability.
Table 1. Selected bond lengths [Å] and angles [°] for compounds 1
and 2.
Compound 1
Co–O(2)
Co–I(1)
S(1)–P(1)
O(2)–P(2)
P(1)–N(1)
P(3)–N(2)
I(1)–Co–I(2)
I(1)–Co–O(4)
I(2)–Co–O(2)
Co–O(2)–P(2)
S(1)–P(1)–N(1)
O(2)–P(2)–N(1)
P(1)–N(1)–P(2)
1.957(4)
2.5720(8)
1.941(2)
1.496(4)
1.693(4)
1.686(4)
118.93(3)
100.94(11)
102.76(11)
141.3(2)
115.6(2)
113.8(2)
131.2(3)
Co–O(4)
Co–I(2)
S(3)–P(3)
O(4)–P(4)
P(2)–N(1)
P(4)–N(2)
I(1)–Co–O(2)
O(2)–Co–O(4)
I(2)–Co–O(4)
Co–O(4)–P(4)
S(3)–P(3)–N(2)
O(4)–P(4)–N(2)
P(3)–N(2)–P(4)
1.975(4)
2.5704(8)
1.934(2)
1.510(4)
1.642(5)
1.657(5)
108.35(11)
113.19(15)
113.01(11)
144.4(2)
114.2(2)
114.4(2)
129.9(3)
Results and Discussion
Synthesis and Crystal Structure Determination of
[CoII{HN(OPPh2)(SPPh2)-O}2I2] (1)
The reaction between equimolar amounts of the adduct
HL(OS)·I2 and Co powder was carried out under a nitrogen
atmosphere in anhydrous diethyl ether. After three days
of stirring, 31P NMR spectroscopic resonances of the
HL(OS)·I2 species were not detectable any longer in the mix-
ture. In the course of the reaction, the initial dark-red col-
our of the solution, typical of the charge-transfer adduct
HL(OS)·I2 bearing the S–I–I group, turned to light emerald
green, and gradually, a light greenish powder separated
from the solution. Elemental analyses of the separated pow-
der agrees with the formed complex having stoichiometry
[CoII{HL(OS)}2I2] (1), and both ligand molecules are coor-
dinated, unprecedentedly, in their neutral form, in accord-
ance with the overall reaction in Equation (1).
Compound 2
Co(1)–O(1)
Co(1)–S(1)
S(1)–P(1)
O(1)–P(2)
P(1)–N(1)
P(2)–N(1)
S(1)···O(1)
S(1)···S(2)
S(1)···O(2)
O(1)–Co(1)–S(1)
O(2)–Co(1)–S(1)
O(2)–Co(1)–O(1) 105.86(17)
Co(1)–S(1)–P(1) 98.67(8)
Co(1)–O(1)–P(2) 122.0(3)
2.003(4)
2.3199(19)
2.012(2)
1.598(4)
1.584(5)
1.574(5)
3.553(5)
3.798(3)
3.612(4)
110.34(14)
115.03(14)
Co(1)–O(2)
Co(1)–S(2)
S(2)–P(3)
O(2)–P(4)
P(3)–N(2)
P(4)–N(2)
S(2)···O(2)
O(1)···O(2)
O(1)···S(2)
O(2)–Co(1)–S(2) 105.93(13)
O(1)–Co(1)–S(2) 110.46(13)
S(1)–Co(1)–S(2) 109.09(7)
Co(1)–S(2)–P(3) 95.82(8)
Co(1)–O(2)–P(4) 125.4(2)
1.956(4)
2.3426(19)
2.024(2)
1.526(4)
1.568(5)
1.591(5)
3.439(4)
3.159(5)
3.575(4)
S(1)–P(1)–N(1)
O(1)–P(2)–N(1)
P(1)–N(1)–P(2)
118.0(2)
118.9(2)
133.2(3)
S(2)–P(3)–N(2)
O(2)–P(4)–N(2)
P(3)–N(2)–P(4)
117.10(19)
116.8(2)
135.5(3)
(1)
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Eur. J. Inorg. Chem. 2007, 4607–4614

Tetrahedral CoII Complexes with CoI2O2 and CoO2S2 Cores
Figure 2. View of the hydrogen bonding pattern for the molecules of compound 1.
118.93(3)°, and the Co–I and Co–O average distances are
The reaction of 1 with an equimolar amount of mer-
2.5712(8) and 1.966(4) Å, respectively, (Table 1), which are cury(II) perchlorate or lead(II) nitrate, carried out in
very close to those reported for several monomeric CoII MeCN at room temperature, quickly led to the decol-
complexes displaying tetracoordination.[7] The O and S ouration of the solution with the formation of a mixture of
atoms of each HL(OS) ligand are on opposite sides with re- white and brown sticky powders. Conversely, in the reaction
spect to the P–N–P plane and are arranged so that the sul- with palladium(II) chloride the colour change was not ob-
fur atoms are involved in S···H–N hydrogen bonding with served, and complex 1 was recovered unreacted when the
adjacent complex molecules to form a polymeric array as solution was slowly concentrated in air. Interestingly, when
shown in Figure 2; the S(1)···N(2)Ј (Ј = x, 3/2 – y, 1/2 + z) the above reactions were carried out in the presence of
interaction is 3.365(5) Å and the N(1)···S(3)Ј is 3.306(4) Å; aqueous NaOH to obtain a 1/M/NaOH [M = HgII, PbII
the S1···HЈ–N(2)Ј and N(1)–H–S(3)Ј angles are 161.7 and and PdII ions] reaction molar ratio of 1:1:2, sticky oils in-
155.8°, respectively.
cluding a thin blue powder were observed in all cases. The
addition of aqueous NaOH to a solution of complex 1
(1/NaOH, 1:2) in CH3CN readily afforded a deep-blue solu-
tion along with a very thin brown powder.[9] From the con-
centration of the solution a blue powder was obtained, and
subsequent crystallisation from CH3CN/hexane yielded
well-shaped blue crystals with elemental analyses corre-
sponding to the formulation [Co{L(OS)}2] (2).
Solid complexes 1 and 2 and their MeCN solutions are
easily recognisable because of their green and blue colour,
respectively. Visible absorption spectra of these complexes
in the range 500–800 nm are reported in Figure 3; in both
compounds, the molar intensities of the d–d electronic tran-
sition bands [compound 1: UV/Vis (CH3CN): λmax (ε,
dm3 mol–1 cm–1) = 661 (172), 696 (346), 734 (432) nm; com-
Reactivity of Complex 1 and Crystal Structure of
[CoII{N(OPPh2)(SPPh2)-O,S}2] (2)
The X-ray crystal structure of 1 highlights two interest-
ing features not yet reported: (1) the neutral HL(OS) ligands
form units within the complex and (2) the O-monodentate
coordination mode at the CoII centre, which leaves the
–PPh2(S) groups in a dangling position. These aspects make
compound 1 attractive, as further coordination towards the
soft metal centre through the S donor atoms to form het-
erobinuclear complexes is, in principle, feasible. Moreover,
the mono- or dideprotonation of the coordinated ligands in
1 may increase the nucleophilicity of the sulfur donor atoms
as a consequence of the delocalisation of the negative
charge(s) over the complex. First, the reactivity of 1 was
tested towards a soft acceptor species such as molecular
iodine, as the formation/separation of 1:1 or 1:2 neutral ad-
ducts between 1 and I2 molecules would provide useful in-
formation for the bonding ability of the sulfur atoms. The
reaction of 1 with increasing amounts of molecular iodine
was carried out in MeCN and in the less polar solvent
CH2Cl2. In both cases, the formation of red oils, which
failed to crystallise on long standing, was observed. The
FT-Raman spectra recorded in the ν(I–I) region at 1/I2 mo-
lar ratios of 1:1 and 1:2 showed an intense peak at 113 cm–1
in MeCN and at 110 cm–1 in CH2Cl2 solution, which are
–
indicative of the formation/presence of the I3 species. A
further addition of I2, according to Raman peaks at 113,
146 and 169 cm–1 (MeCN) and 113, 146 and 169 cm–1
(CH2Cl2), led to the formation of complex mixtures.[8]
Figure 3. Visible absorption spectra in MeCN of complexes 1 [λmax
= 734, 696, 661 (sh) nm] and 2 (λmax = 715, 625, 566 nm).
Eur. J. Inorg. Chem. 2007, 4607–4614
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F. Isaia et al.
FULL PAPER
pound 2: UV/Vis (CH3CN): λmax (ε, dm3 mol–1 cm–1) 566 The Co(1)–S(2)–P(3)–N(2)–P(4)–O(2) ring in fact, is ar-
(319), 625 (331), 715 (205) nm] are consistent with CoII ranged in a pseudochair conformation with P(4) and S(2)
bound in a tetrahedral or distorted tetrahedral coordination in the apices and dihedral angles between the nearly planar
geometry.[10] The absorption spectra in the visible region, Co(1)–P(3)–N(2)–O(2) array [max. dev. from mean plane
taken after the addition of increasing amounts of aqueous Ϯ0.040(2) Å] and Co(1)–S(2)–P(3) and O(2)–P(4)–N(2)
NaOH to a solution of 1 in MeCN are reported in Figure 4; planes of 42.08(9) and 13.0(3)°, respectively. Co(1)–S(1)–
from the analysis of the bands at 734 and 566 nm, related P(1)–N(1)–P(2)–O(1) indeed shows a highly distorted pseu-
to complexes 1 and 2, respectively, it results that only a doboat geometry where S(1) and P(2) act as “bow” and
partial conversion of 1 into 2 occurs because of the ob- “stern” in comparison to the slightly twisted Co(1)–P(1)–
served concomitant formation of a thin brown powder.[9] N(1)–P(2) plane [max. dev. Ϯ0.119(2) Å], with P(1)–S(1)–
The inset to Figure 4 gives evidence of this fact and shows Co(1)–N(1)–P(1)–Co(1)–O(1) and N(1)–P(2)–O(1)–N(1)–
that a near sixfold excess of NaOH over the amount of 1 is P(1)–Co(1)–O(1) dihedral angles of 30.92(15) and 17.7(4)°,
necessary to obtain a 55% yield of 2.
respectively. As already observed in the related complex
[Co{N(SPPh2)}2], some degree of π-electron delocalisation
is present on the CoO(S)P2N rings, as shown by the P–X (X
= S, O) average bond lengths, which increase with respect to
[HN(OPPh2)(SPPh2)][14] by 0.071 Å (P–O) and 0.083 Å (P–
S), whereas the average N–P distances decrease by 0.104 Å.
Figure 4. Base-induced conversion of complex 1 into 2, as moni-
tored by Visible absorption spectroscopy. (a) [Co{HL(OS)}2I2] (1),
3.85ϫ10–3  in MeCN, 21 °C; and after the addition of NaOH
(1.0  in water) to realise a NaOH/[1] molar ratio of (b) 1.1; (c) 2.2;
(d) 3.3; (e) 4.4; (f) 5.5 and (g) 6.6. Inset: percent yield of complex 2,
which results from analysis of the bands at 566 and 734 nm, plotted
vs. [NaOH]/[1] molar ratios.
Figure 5. ORTEP drawing and atom-labelling scheme for
[CoII{N(OPPh2)(SPPh2)-O,S}2] (2). Thermal ellipsoids are drawn
at 50% probability.
The molecular structure of 2 (Figure 5 and Table 1) fea-
tures a CoII ion in a tetrahedral coordination geometry
linked through oxygen and sulfur atoms to two bidentate
anionic ligands [N(OPPh2)(SPPh2)]–. As a result, the metal
ion is surrounded by a spirobicyclic {NP2(S)O}Co{O(S)
P2N} system, with endocyclic S···O bites of 3.439(4)/
Reactivity of Complex 2
In previous papers it was demonstrated that in complexes
3.553(5) Å (see Table 1). The tetrahedral CoO2S2 core is of the formula M{L(SS)}2 (M = Pd, Cu)[4c,5] it was possible
slightly distorted and shows X–Co–Y (X, Y = S, O) angles to protonate the metal-bound ligands to form the corre-
in the range 105.86(17)–115.03(14)°, Co–O/Co–S average sponding cationic complexes in which the S,SЈ chelation of
distances of 1.980(6)/2.331(3) Å (Table 1) and a Co(1)– the ligands was preserved. As a result of the different set of
S(1)–O(1)/Co(1)–S(2)–O(2) dihedral angle of 86.28(10)°. donor atoms in complex 2, the protonation of the metal-
The Co–X (X = S, O) bond lengths are very close to those bound ligands may induce different coordination modes at
reported for various monomeric CoII complexes with tetra- the metal centre: complexes with CoO2X2 or CoS2X2 cores
or octahedral coordination geometry,[11] such as and with X being a cobalt-coordinating anion. The forma-
[Co{N(SPPh2)2}2][4b] [av. Co–S 2.335(2) Å], [Co(OAc)2- tion of the cationic complex [Co{HL(OS)}2]2+ in which the
(etu)2],[12a] [Co–S 2.328(3) Å, av. Co–O 1.957(7) Å; etu = CoO2S2 core is preserved cannot be excluded either. In this
ethylenthiourea] and [Co(acac)2(py)2][12b] [Co–O 2.034(3) Å; study the reactivity of 2 was only tested towards HI to ver-
acac = acethylacetonate]. As similarly observed in complexes ify the feasibility of this synthetic procedure and the nature
[Mn{N(OPPh2)(SPPh2)}2][13a] and [Ni{N(OPR2)(SPPh2)}2] of the formed complex. The reaction of 2 in MeCN with
(R = Ph, Me),[13b] no static disorder effects[13c] in the metal- increasing amounts of hydroiodic acid (55 wt.-% in water)
bonded donor-atom sites are present. Close inspection of to reach a 2/HI molar ratio of 1:4 results in the complete
the structure shows that the two chemically equivalent, disappearance of the visible band at 566 nm, which is char-
nonplanar CoO(S)P2N rings exhibit different geometries. acteristic of complex 2, and the formation of the pattern of
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Eur. J. Inorg. Chem. 2007, 4607–4614

Tetrahedral CoII Complexes with CoI2O2 and CoO2S2 Cores
bands related to the formation of complex 1. The diagram
reporting the conversion of 2 into complex 1 vs. the molar
ratios of HI/2 shows that such a conversion is almost stoi-
chiometric (ca. 92%) when starting with a HI/2 molar ratio
of 2 (Figure 6).
Figure 6. Percent conversion of compound 2 into 1 vs. [HI]/[2] mo-
lar ratios, which results from analysis of the bands at 566 and
734 nm. [Co{L(OS)}2] (2), 7.25ϫ10–4  in MeCN, HI (55% in
water), 21 °C. HI/[2] molar ratios: 0.00, 0.48, 0.97, 1.46, 1.95, 2.44,
2.93, 3.42, 3.91.
Figure 7. Plots of µeff (᭺) and χM–1(᭹) vs. temperature for 1 (top)
and 2 (bottom) at 5000 G; the solid lines represent the fitted calcu-
lated curve (see text).
Magnetic Studies and Theoretical Calculations
TIP = 1310ϫ10–6 cm3 mol–1 and Θ = 0.11 K for 1 and g =
2.37, |D| = 11.9 cm–1, TIP = 541ϫ10–6 cm3mol–1 and Θ =
0.66 K for 2. The |D| parameters for 1 and 2 are almost
identical and lie in the upper range of typical values for
many tetrahedral CoII compounds (7–12 cm–1).[15,17] ZFS
values around –9.5 cm–1 were recently found for two other
compounds with a tetrahedral [CoI2O2] core, whereas larger
values D = –12.4 cm–1 and D = –16.7 cm–1 were reported
for [CoCl2(PPh3)2] and [CoBr2(PPh3)2], respectively.[21] The
Weiss temperature Θ relates to intermolecular interactions
zJ of 0.03 cm–1 for 1 and 0.18 cm–1 for 2, where J is the
interaction parameter between two nearest neighbour mag-
netic centres and z is the number of nearest neighbours.[22]
Intermolecular interactions are apparently very weak if not
negligible for both complexes, and they appear to be even
smaller for 1 than for 2. This confirms that no significant
coupling occurs through the H-bonding linkages that con-
stitutes the 1D polymeric array in 1.
Electronic structures of the new complexes were probed
by SQUID measurements and DFT calculations. Magnetic
susceptibility measurements were carried out for both com-
plexes at two different magnetic fields in a temperature
range from 2.0 to 295 K. No significant field dependence
was observed for either of the complexes. The temperature
–1
dependence of χM and the effective magnetic moment µeff
are shown in Figure 7. The value of µeff is around 4.70 or
4.75 µB for 1 or 2, respectively, at room temperature, which
is in the range expected for high-spin (S = 3/2) CoII ions
that reside in a tetrahedral environment.[15] The value of µeff
remains almost constant over a large temperature range but
drops to around 3.5 µB at very low temperatures. This may
be attributed to zero-field splitting (ZFS) of the 4A2 ground
state, which can be quite large for tetrahedral CoII (al-
though smaller than for five- or six-coordinate CoII
ions).[15–18] Magnetic parameters were determined by using
a fitting procedure to the spin Hamiltonian for axial ZFS
and Zeeman interaction as shown in Equation (2).[19]
DFT calculations (see Experimental Section) were per-
formed on the anionic model ligands [N(OPH2)(SPH2)]–,
LЈ(OS), and [N(SPH2)2]–, LЈ(SS), and on the corresponding
neutral CoII complexes [Co{N(OPH2)(SPH2)-O,S}2] (3)
and [Co{N(SPH2)2-S,SЈ}2] (4). The geometry optimisation
(2)
Temperature-independent paramagnetism (TIP) was in- of these complexes in their quartet electron configuration
cluded according to χcalcd. = χ + TIP. For both complexes with the use of the UB3LYP hybrid functional yields bond
slightly better agreement with experimental data was ob- lengths and angles very close to the structural ones
tained when intermolecular interactions were considered in (Tables S1 and S2, Supporting Information). As regards
a mean field approach by using a Weiss temperature Θ.[20,21] LЈ(SS), the optimised bond lengths and angles are repro-
Best simulation parameters are g = 2.25, |D| = 12.0 cm–1, duced well relative to those previously reported with
Eur. J. Inorg. Chem. 2007, 4607–4614
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4611

F. Isaia et al.
FULL PAPER
Gaussian 94 at the same level of theory.[4b] In Figure 8, the
HOMO and LUMO computed for LЈ(OS) and LЈ(SS) are de-
picted. In both compounds, the HOMO is mainly built of
the in-plane p atomic orbitals of the sulfur donor atoms,
which are negatively charged; the calculated Mulliken
charge for LЈ(OS) are QS = –0.582 e, QO = –0.578 e and for
LЈ(SS) the calculated charge QS = –0.561 e. It is noteworthy
that the calculated QS charges show similar values, which
suggests a similar bonding ability for the P–S groups in the
related anionic ligands; the acidity constant values deter-
mined experimentally for the HL(OS) and HL(SS) ligands
(pKa = 5.42 and 5.61, respectively) further support this
view. The Mulliken charge calculated on the metal centre
at the fully relaxed geometry (Figure 9) shows a marked
difference in the CoIIO2S2 and CoIIS4 cores (QCo = 0.436
and 0.023 e in 3 and 4, respectively), which might be the
basis for the different reactivities of the two complexes. This
is reflected in a different charge distribution on the S–P–
N–P–O and S–P–N–P–S elements that constitute the back-
bones of complexes 3 and 4, which show markedly different
values, mostly related to the P=O and P=S groups.
Conclusions
The CoII complex [Co{[HN(OPPh2)(SPPh2)-O]2}I2] (1)
was synthesised in a single step from the oxidation of cobalt
powder by the adduct HL(OS)·I2 in Et2O prepared in situ.
The X-ray crystal structure of this complex shows a CoII
ion in a tetrahedral coordination environment with the li-
gands in a neutral form, which has not been previously ob-
served, and the metal ion is bound through the oxygen
atoms and two iodide ions, which completes the CoI2O2
core. This mode of ligation leaves the –PPh2(S) groups in a
dangling position, which we were unsuccessful in involving
in further coordination activity towards “soft” centres. The
treatment of 1, dissolved in MeCN, with NaOH caused the
deprotonation of the imido group in the ligands and the
formation of [Co{[N(OPPh2)(SPPh2)-O,S]2}] (2), in which
the CoII ion is found to occupy a tetrahedral coordination
environment with a CoO2S2 core. The magnetic behaviour
of 1 and 2 is consistent with tetrahedral high-spin (S = 3/2)
CoII possessing a A2 ground state with appreciable ZFS
4
(|D| ≈ 12 cm–1). When complex 2 is treated with hydroiodic
acid, complex 1 is almost quantitatively reobtained. Com-
parison of the Mulliken charges at the CoII centres in the
CoO2S2 and CoS4 cores reveals that the metal in the latter
core is markedly less electropositive (0.437 and 0.023 e,
respectively) than the former, which instills different intrin-
sic reactivity towards nucleophilic agents.
Experimental Section
Materials and instrumentation: Reagents were used as purchased
from Aldrich. Diethyl ether was distilled from LiAlH4 shortly be-
fore use. IR spectra were measured as KBr (4000–400 cm–1) pellets
with a Bruker Equinox 55 FTIR spectrometer. FT-Raman spectra
were recorded with a Bruker FRS 100/S Fourier transform Raman
spectrometer operating with a diode-pumped Nd:YAG exciting la-
ser emitting at 1064 nm. 31P NMR spectra were recorded with a
Varian Unity 300 MHz spectrometer. The pKa values of the HL(OS)
and HL(SS) ligands were determined by NMR spectroscopic mea-
surements according to the guidelines reported in the IUPAC Tech-
nical Report.[23] The 31P NMR spectra of 19 different solutions in
MeCN/H2O, 4:1 (5.12ϫ10–3 ) and 0.1  [(Bu)4N(NO3)], as sup-
porting electrolyte, at (25.0Ϯ0.2) °C were recorded in the pH range
2.5–12.0. The pH values were adjusted by the addition of HCl or
NaOH (0.1 or 0.5 ). Peak positions are reported relative to H3PO4
(85%) at δ = 0.00 ppm used as external reference in a sealed coaxial
tube. pH values were measured with a glass electrode. The experi-
mental data were fitted by a sigmoidal equation with the SigmaPlot
software (see Supporting Information, section S3). Visible absorp-
tion spectra were measured with a Nicolet Evolution 300 spectro-
photometer. Susceptibility measurements were carried out with a
Quantum-Design MPMS-5S SQUID magnetometer equipped with
a 5 T magnet in the range from 295 to 2 K. The powdered samples
were contained in a gel bucket and fixed in a nonmagnetic sample
holder. Each raw data file for the measured magnetic moment was
corrected for the diamagnetic contribution of the sample holder
and the gel bucket. Experimental data were corrected for the under-
lying diamagnetism by using tabulated Pascal constants (incremen-
tal method). Simulations of the experimental magnetic data were
performed with full-matrix diagonalisation of zero-field splitting
Figure 8. HOMO (bottom row) and LUMO (top row) drawings in
LЈ(OS) (left) and LЈ(SS) (right). Optimised selected bond lengths and
angles: LЈ(OS): P–S 1.984, P–O 1.504, N–P(O) 1.621, N–P(S)
1.619 Å; P–N–P 128.14°;·LЈ(SS): P–S 1.980, P–N 1.623 Å; P–N–P
128.20°.
Figure 9. Mulliken charge distribution (e) in model complexes 4 (a)
and 3 (b). Hydrogen atoms are omitted for clarity.
4612
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 4607–4614

Tetrahedral CoII Complexes with CoI2O2 and CoO2S2 Cores
and Zeeman interaction according to the appropriate Hamiltonian
(see text) and including temperature-independent paramagnetism
(TIP).[24] The ligand HN(OPPh2)(SPPh2), HL(OS), was prepared ac-
cording to ref.[25] Quantum chemical calculations were carried out
at the density functional theory (DFT) level by using the
NWChem. 4.7 program[26,27] and ECCE 3.2.5.[28] DFT calculations
were attempted on [Co{[HN(OPH2)(SPH2)-O]2}I2], [Co{[HN-
(SPH2)(OPH2)-S]2}I2], [Co{N(OPH2)(SPH2)-O,S}2] (3) and
[Co{N(SPH2)2-S,SЈ}2] (4) by adopting different functionals and ba-
sis sets. Unfortunately, notwithstanding the numerous attempts and
different types of SCF convergence methods, a combination of
functional and basis set capable to allow SCF convergence for all
compounds was not found. We report here the results obtained for
3 and 4 by using Schafer, Horn and Ahlrichs all-electron double-ζ
basis sets with polarisation function[29] for the ligand atoms, the
LanL2DZ basis set along with effective core potentials[30] for Co,[31]
with the three-parameter[32] hybrid B3LYP functional (based on the
gradient corrected Becke exchange functional[33] along with the
Lee, Yang and Parr correlation functional[34]). All calculations were
performed on a Pentium 4 workstation running on a Linux Mand-
riva One 2006 operating system.
∆F map are 1.344 and –1.050 eÅ–3, respectively for compound 1
and 0.527 and –0.447 eÅ–3 for compound 2.
CCDC-641240 and -641241 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Crystal data for 1: C48H42CoI2N2O2P4S2, M = 1179.57, ortho-
rhombic, a = 21.892(2) Å, b = 18.590(2) Å, c = 24.046(2) Å, U =
9786.1(16) Å3, T = 294(2) K, space group Pbca (no. 61), Z = 8, µ
= (Mo-Kα) 1.868 mm–1. 85740 reflections (9660 unique) were col-
lected at room temperature in the range 3.22Յ2θՅ52.20° by em-
ploying a 0.10ϫ0.10ϫ0.05 mm crystal mounted on a Siemens
SMART CCD diffractometer. 5768 reflections (Rint = 0.0807), final
R1 [wR2] values of 0.0506 [0.1306] on IϾ2σ(I) [all data], with GoF
= 0.954 for 550 parameters.
Crystal data for 2: C48H40CoN2O2P4S2, M = 923.75, monoclinic, a
= 12.511(2) Å, b = 18.272(5) Å, c = 19.599(3) Å, β = 100.495(10)°,
U = 4405.3(16) Å3, T = 298(2) K, space group P21/c (no. 14), Z =
4, µ = (Mo-Kα) 0.671 mm–1. 7551 reflections (6064 unique) were
collected at room temperature in the range 4.22Յ2θՅ46.00° by
employing a 0.26ϫ0.22ϫ0.08 mm crystal mounted on a P4RA
Siemens automatic diffractometer. 7548 reflections (Rint = 0.0563),
final R1 [wR2] values of 0.0606 [0.1471] on IϾ2σ(I) [all data], with
GoF = 1.020 for 692 parameters and 4 restraints.
[Co{HN(OPPh2)(SPPh2)-O}2I2] (1). A mixture of HL(OS) (0.100 g,
0.230 mmol) and I2 (0.058 g, 0.230 mmol) in diethyl ether (200 mL)
was stirred at 25 °C under an atmosphere of N2 until the reagents
were completely dissolved. Cobalt metal powder (Ͻ 2 µ; 0.014 g,
0.237 mmol) was added while stirring. This was continued at room
temperature for ca. 4 d. The resulting emerald green solid was col-
lected by suction filtration, washed with a mixture of CH2Cl2/
n-hexane (1:5) and dried in vacuo. Yield: 0.074 g (26.4%). M.p. Ͼ
Supporting Information (see footnote on the first page of this arti-
cle): Optimised geometries of complexes 3 and 4 in Cartesian or-
thogonal coordinate format, as derived from DFT calculations, and
pKa determination of HN(OPPh2)(SPPh2) and HN(SPPh2)(SPPh2).
250 °C. IR (KBr): ν = 2632 (w), 1436 (vs), 1328 (m), 1312 (s), 1172
˜
(s), 1151 (s), 1129 (s), 1099 (s), 1026 (w), 998 (w), 998 (s), 944 (s),
789 (s), 747 (s), 728 (s), 688 (s), 646 (s), 614 (w), 569 (m), 523 (m), Acknowledgments
487 (m) cm–1. UV/Vis (CH3CN): λmax (ε, dm3 mol–1 cm–1) = 661
(172), 696 (346), 734 (432) nm. C48H42CoI2N2O2P4S2 (1179.57):
calcd. C 48.87, H 3.59, N 2.37, S 5.44; found C 49.1, H 3.7, N 2.4,
S 5.2.
Thanks are expressed to Prof. Antonio C. Fabretti (Dipartimento
di Chimica, Università di Modena) for helpful discussions and to
the “Centro Interdipartimentale Grandi Strumenti (C.I.G.S.)” of
the University of Reggio Emilia for providing P4-RA Siemens X-
ray equipment. Financial support from the National University Re-
search Council (CNCSIS, Romania; Research project No. A-1456/
2007) is greatly appreciated.
[Co{N(OPPh2)(SPPh2)-O,S}2] (2). To a stirred solution of com-
pound 1 (0,100 g, 0.084 mmol) dissolved in CH3CN (25 mL) was
slowly added NaOH (1 , 180 µL, 0.180 mmol). The deep-blue
solution was concentrated to separate well-shaped blue crystals that
were washed with CH2Cl2/n-hexane (1:5) and dried in vacuo. Yield:
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˜
1482 (w), 1436 (s), 1236 (vs), 1233 (vs), 1178 (s), 1121 (s), 1045 (vs),
1025 (s), 998 (m), 799 (w), 745 (s), 725 (vs), 692 (vs), 618 (w), 575
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chelating ligands were carefully tested, but led to unphysical varia-
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The maximum and minimum residual electron density on the final
Eur. J. Inorg. Chem. 2007, 4607–4614
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4613

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FULL PAPER
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Published Online: August 20, 2007
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Eur. J. Inorg. Chem. 2007, 4607–4614