Reactivity of the metalloligand [Pt2(μ-S)2(PPh3)4] toward tellurium(II) thiourea complexes: synthesis and structural characterization of the ditellurium(I) derivative [{Pt2(μ-S)2(PPh3<

Article abstract of DOI:10.1080/00958972.2018.1531285

Reaction of the platinum(II) sulfide metalloligand [Pt₂(μ-S)₂(PPh₃)₄] with the tellurium(II) source TeCl₂(tu)₂ (tu = thiourea) is dependent on reaction conditions employed. In the presence

Full text of DOI:10.1080/00958972.2018.1531285

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Reactivity of the metalloligand [Pt2(µ-S)2(PPh3)4]
toward tellurium(II) thiourea complexes:
synthesis and structural characterization of the
ditellurium(I) derivative [{Pt2(µ-S)2(PPh3)4}2Te2]2+
Ryland G. Fortney-Zirker, William Henderson, Joseph R. Lane & Edward R. T.
Tiekink
To cite this article: Ryland G. Fortney-Zirker, William Henderson, Joseph R. Lane & Edward R.
T. Tiekink (2018): Reactivity of the metalloligand [Pt2(µ-S)2(PPh3)4] toward tellurium(II) thiourea
complexes: synthesis and structural characterization of the ditellurium(I) derivative [{Pt2(µ-
S)2(PPh3)4}2Te2]2+, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2018.1531285
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JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2018.1531285
Reactivity of the metalloligand [Pt2(m-S)2(PPh3)4] toward
tellurium(II) thiourea complexes: synthesis and structural
characterization of the ditellurium(I) derivative
[{Pt2(m-S)2(PPh3)4}2Te2]2þ
Ryland G. Fortney-Zirkera, William Hendersona, Joseph R. Lanea and
Edward R. T. Tiekinkb
b
aChemistry, School of Science, University of Waikato, Hamilton, New Zealand; Research Centre for
Crystalline Materials, School of Science and Technology, Sunway University, Bandar
Sunway, Malaysia
ABSTRACT
ARTICLE HISTORY
Received 28 May 2018
Accepted 24 August 2018
Reaction of the platinum(II) sulfide metalloligand [Pt2(m-
S)2(PPh3)4] with the tellurium(II) source TeCl2(tu)2 (tu ¼ thiourea)
is dependent on reaction conditions employed. In the presence
of added acid, the dominant species observed in the electro-
KEYWORDS
Platinum complexes; ESI
mass spectrometry;
tellurium; DFT; DORI
spray ionization (ESI) mass spectrum is the tetraplatinum spe-
cies [{Pt2(m-S)2(PPh3)4}2Te2]2þ. This contains the Te2
moiety
2þ
and is related to the previously reported tellurium(I) dithiophos-
phinate analog [(Ph2PS2)2Te2]. However, in the absence of acid,
considerable degradation of the {Pt2S2} metalloligand occurs as
evidenced by the formation of the mononuclear complex
[Pt{SC(NH2)NH}(PPh3)2]þ containing a deprotonated thiourea lig-
and, together with other thiourea-containing ions, identified by
ESI MS. Likewise, attempted use of a fully substituted thiourea,
viz. Me2NC(S)NMe2 (tmtu) in TeCl2(tmtu)2, also resulted in deg-
radation of the {Pt2S2} core and detection of the known com-
plex [(Ph3P)2PtCl{SC(NMe2)2}]þ. The [{Pt2(m-S)2(PPh3)4}2Te2]2þ
cation was isolated with several anions, and unequivocal con-
firmation of the structure of the complex was obtained by an
-
X-ray structure determination on the BF4 salt, which shows the
2þ
presence of the Te2
unit, with the Te–Te bond bridged by
two {Pt2S2} metalloligands. Density functional theory was used
2þ
to further probe the Te2
bonding interactions in [{Pt2(l-
S)2(PPh3)4}2Te2]2þ and the previously reported [(Ph2PS2)2Te2].
CONTACT William Henderson
w.henderson@waikato.ac.nz
Chemistry, School of Science, University of Waikato,
Private Bag 3105, Hamilton 3240, New Zealand
Supplemental Material
ß 2018 Informa UK Limited, trading as Taylor & Francis Group

2
R. G. FORTNEY-ZIRKER ET AL.
1. Introduction
The platinum(II) sulfido complex [Pt2(m-S)2(PPh3)4] (1) has been known for many years,
yet continues to offer surprises: it is a potent metalloligand, and coordinates to metal
centers across the Periodic Table [1]. In contrast to the well-developed coordination
chemistry with metals, adducts with non-metals or semi-metals are far less well-
described. As part of our ongoing investigations into the chemistry of 1 we recently
described the reactivity of 1 and the selenide analogue [Pt2(m-Se)2(PPh3)4] toward a
variety of chalcogen sources (including the elemental chalcogens S8 and Se, as well as
diaryl dichalcogenides R2E2, where E ¼ S, Se and Te) with the intention of synthesizing
complexes containing mixed-chalcogenide ligands [2].
In this contribution, we describe investigations into the reactivity of 1 toward
tellurium(II) sources, with the intention of synthesizing complexes containing Te–S
bonds. The oxidation states of tellurium in compounds with sulfur ligands are com-
monly II and IV [3] with Te(II) being preferred, typically having four-coordinate square
planar [4], T-shaped [5], and trapezoidal planar geometries. Tellurium(II) forms a wide
range of complexes with bidentate chelating sulfur and selenium ligands such as
dithiocarboxylates [6], dithiocarbamates [7, 8] and [R2P(E)NP(E)R’2]– (E = S, Se) [5, 9, 10].
In this way, tellurium is acting as a pseudo-metal showing coordination chemistry-like
behavior. Accordingly, we reasoned that [Pt2(m-S)2(PPh3)4], being a well-known biden-
tate sulfur metalloligand, should also form complexes with Te(II). Although such com-
pounds are not expected to find any practical applications, they are of fundamental
interest in developing the pseudo-metallic chemistry of tellurium, and provide a com-
parison with the known complexes of [Pt2S2(PPh3)4] with neighboring metalloidal ele-
ments in the Periodic Table; although there are no antimony adducts, its heavier
analogue bismuth provides a number of examples [11–13].
Our methodology of choice uses Electrospray Ionization Mass Spectrometry (ESI MS) [14]
as a convenient and sensitive tool for identification of reaction products of 1. We have previ-
ously used ESI MS to explore the chemistry of [Pt2(m-S)2(PPh3)4] and the related selenide com-
plex, and our investigations in this area have been summarized in a review [15]. In this study,
we extend this methodology to the identification and subsequent synthesis and characteriza-
tion of the interesting tellurium(I) complex [{Pt2(m-S)2(PPh3)4}2Te2]2þ. The structures of the
compounds described in this article are shown in Scheme 1.

JOURNAL OF COORDINATION CHEMISTRY
3
Scheme 1. Structures of compounds described herein.
2. Results and discussion
2.1. Reactivity of [Pt2(m-S)2(PPh3)4] (1) toward TeCl2(tu)2 in acidic solution
The thiourea complex TeCl2(tu)2 was used as a convenient source of Te(II) in these
experiments, which were initially explored on a microscale, with reaction monitoring
using positive-ion ESI MS. In this study, the ligand abbreviation tu represents a neutral,
non-deprotonated thiourea ligand, viz. SC(NH2)2. Tellurium(II) thiourea complexes, par-
ticularly [Te(tu)4]Cl2, have been used as precursors for preparation of coordination
complexes containing the Te(II) center [5, 9, 10, 16, 17].
When [Pt2(m-S)2(PPh3)4] (1) was reacted with TeCl2(tu)2 in neutral solution, complex
spectra were obtained, vide infra. However, when reactions were carried out in the
presence of added acid (either acetic acid or hydrochloric acid), which protonate
[Pt2(m-S)2(PPh3)4] [18], reactions with TeCl2(tu)2 proceeded much more smoothly, giv-
ing a single dominant product. Thus, addition of hydrochloric acid to a light-orange
suspension of [Pt2(m-S)2(PPh3)4] (1) in methanol gave a transparent yellow solution,
which was reacted with TeCl2(tu)2, immediately forming a clear red solution. The solu-
tion was examined by ESI MS (Figure 1) and showed a dominant dicationic species at
m/z 1630.88, which was assigned on the basis of the m/z value and isotope pattern
matching (Figure 1 inset) to the ditellurium species [{Pt2(m-S)2(PPh3)4}2Te2]2þ (2). This
species, and its isolated salts described below, are air stable both as solids and
in solution.
Addition of NH4PF6 or Li[N(SO2C2F5)2] to filtered reaction solutions containing the
[{Pt2(m-S)2(PPh3)4}2Te2]2þ ion gave precipitates of the respective salts as red powders.
[{Pt2(m-S)2(PPh3)4}2Te2][N(SO2C2F5)2]2 gave satisfactory elemental analytical data. The
31P{1H} NMR spectrum of the [N(SO2C2F5)2]– salt showed the expected features, namely

4
R. G. FORTNEY-ZIRKER ET AL.
Figure 1. The positive-ion ESI mass spectrum of [Pt2(m-S)2(PPh3)4] (1) and TeCl2(tu)2 in methanol
with added HCl, after 10 min. The inset shows an isotope pattern comparison of (a) the observed
dication at m/z 1630.88 and (b) the calculated isotope pattern for [{Pt2(m-S)2(PPh3)4}2Te2]2þ (m/
z 1631.14).
a single 31P NMR resonance at d 20.9 with satellites due to coupling to 195Pt [1J(PtP)
2959 Hz], however, the peaks were surprisingly somewhat broader than are normally
obtained with diamagnetic adducts of [Pt2(m-S)2(PPh3)4]. Although the 31P NMR param-
eters of the starting [Pt2S2(PPh3)4] (1) do not appear to have been reported, due to its
insolubility in all common solvents, and reactivity with chlorinated solvents, the
closely-related complex [Pt2S2{P(p-tolyl)3}4] is soluble in C6D6, giving d 31P 27.3 and
1J(PtP) 2795 Hz [19]. The larger 1J(PtP) in [{Pt2(m-S)2(PPh3)4}2Te2]2þ is consistent with
coordination of sulfur to tellurium producing a concomitant decrease in trans-influ-
ence of the sulfido ligands.
All attempts at growing single crystals of the PF6 or [N(SO2C2F5)2]- salts suitable for
-
-
an X-ray diffraction study were unsuccessful. The BF4 salt was obtained in an analo-
gous method using NaBF4, and vapor diffusion of diethyl ether into an acetone solu-
tion gave dark brown prismatic crystals suitable for X-ray diffraction. The X-ray
structure determination unequivocally confirms the identity of the cation as [{Pt2(m-
S)2(PPh3)4}2Te2]2þ (2). The structure of the cation is shown in Figure 2.
The structure contains two bidentate [Pt2(m-S)2(PPh3)4] metalloligands spanning the
2þ
Te–Te bond of a formally Te2 unit. The dication is disposed about a point of sym-
metry 22. Thus, both Te atoms lie on a 2-fold axis and the Te–Te vector is bisected by
a second 2-fold axis perpendicular to the original axis. This implies the crystallographic
asymmetric unit comprises one quarter of a dication as indicated in the top view of
Figure 2. The Te–Te bond length is 2.7978(16) Å and, from symmetry, there is a unique
Te–S1 bond length of 2.676(3) Å. The resultant Te2S4 rectangle is close to planar and
the Te atom has a T-shaped coordination geometry defined by a S2Te donor set, the
S1–Te–S1i angle being 175.56(10)ꢀ; symmetry operation i: x, 1/2 – y, 1/2 – z.
As neither the Pt nor S1 atoms lie on an axis, there are two independent but, simi-
i
1
lar Pt–S1, S1 bond lengths, i.e. 2.343(2) and 2.339(2) Å; symmetry operation i: = – x,
2
1
y, = – z. The Pt S atoms adopt a folded configuration with the dihedral angle
2
2 2
between the two S2Pt residues being 44.16(10)ꢀ. The Pt coordination geometry is com-
pleted by two Ph3P ligands and the resulting cis-P2S2 donor set defines an approxi-
mate square planar geometry.

JOURNAL OF COORDINATION CHEMISTRY
5
-
Figure 2. Two views of [{Pt2(m-S)2(PPh3)4}2Te2]2þ (2) as its BF4 salt, showing the core structure (all
but the ipso-C atoms of the phenyl groups being removed) with atom labeling and displacement
ellipsoids at the 35% probability level (upper view) and the full dication, showing idealized spheres
(lower view). Selected bond lengths (Å) and angles (ꢀ): Pt–S1 2.343(2), Pt–S1i 2.339(2), Te–S1
2.676(3), Pt–P1 2.281(3), Pt–P2 2.303(3), Te–Te 2.7978(16), S1–Pt–P1 91.3(1), S1–Pt–P2 167.1(1),
S1–Pt–S1i 80.3(1), P1–Pt–P2 100.1(1), P1–Pt–S1i 171.5(1), P2–Pt–S1i 88.4(1), S1–Te–S1ii 175.6(1),
Pt–S1–Pti 90.2(1), Te–S1–Pti 107.0(1).
Related Te(I) complexes with Te–Te bonds and sulfide ligands have been previously
described in the literature, and the chemistry of tellurium complexes with sulfur donor
ligands has been reviewed [20]. These complexes predominantly have a T-shaped
coordination geometry, with long range contacts or secondary bonds sometimes
found at an axial position where a square–planar ligand would be; such secondary
bonds are common in tellurium chemistry [8, 21]. [(Ph2PS2)2Te2] (3) is a close analogue
of 2; complex 3 was originally prepared (and crystallized as the benzene solvate) by
2þ
reduction of TeO2 with Ph2PS2H [22]. This compound has a Te2 group spanned by

6
R. G. FORTNEY-ZIRKER ET AL.
Figure 3. A comparison of ESI mass spectra of [{Pt2(m-S)2(PPh3)4}2Te2][N(SO2C2F5)2]2 showing frag-
mentation at increasing capillary exit voltages of (a) 120 V, (b) 150 V, and (c) 180 V. The top inset is an
isotope pattern comparison of (a1) the observed peak at m/z 1502.06 and (a1a) an mMass-modeled
peak of [Pt2(m-S)2(PPh3)4]þ: [Pt2(m-S)2(PPh3)3Te2]þ 7:1 (m/z 1502.24). The lower inset follows the iso-
tope pattern of [{Pt2(m-S)2(PPh3)4}2Te2]2þ at capillary exit voltages of (b1) 150 V, (b2) 165 V, (b3) 174 V,
and (b4) 180 V. (b1a) is a calculated isotope pattern for [{Pt2(m-S)2(PPh3)4}2Te2]2þ (m/z 1631.14). (b4a) is
a modeled isotope pattern for [{Pt2(m-S)2(PPh3)4}2Te2]2þ: [Pt2(m-S)2(PPh3)4Te]þ 3:1 (m/z 1631.14).
two bidentate, bridging diphenyldithiophosphinate anions, although the ligand binds
the two Te centers somewhat asymmetrically. The same compound has also been pre-
pared by reaction of the tellurium(II) complex [Te(tu)4]Cl2 with Ph2P(S)NC(S)pip
(pip ¼ piperidyl) and KOtBu [23]. In the solid-state 3 forms long-range intermolecular
TeꢁꢁꢁTe contacts in the benzene solvate [22] or in the unsolvated compound (crystal-
lized from CH2Cl2–hexane); TeꢁꢁꢁS contacts result in long intermolecular chains [23].
The structural chemistry of this system has been summarized by Bandeira et al. [24]
who carried out a computational study (using DFT) on the nature of TeꢁꢁꢁTe interac-
2þ
tions in such species. In the case of the formal Te2 species reported herein, it is pos-
sible that reduction of Te(II) to Te(I) is facilitated by oxidation of the thiourea [to the

JOURNAL OF COORDINATION CHEMISTRY
7
formamidine disulfide cation, (H2N)2CSSC(NH2)2]2þ] [25, 26]. No attempts were made
to identify such oxidized thiourea by-products.
Complex 2 also resembles silver(I) [27–29] and gold(I) [18, 30] complexes 4, where
two d10 metal ions are spanned by two [Pt2(m-S)2(PPh3)4] metalloligands, and a signifi-
cant interaction is proposed to occur between the metals in them.
Detailed characterization of [{Pt2(m-S)2(PPh3)4}2Te2][N(SO2C2F5)2]2 has been carried
out using ESI MS, specifically with a view to exploring the fragmentation of the com-
plex cation. Figure 3 shows spectra of the compound at a range of capillary exit vol-
tages. At a relatively low voltage (120 V, Figure 3a) the spectrum is dominated by the
parent [{Pt2(m-S)2(PPh3)4}2Te2]2þ cation at m/z 1630.95, together with two partly over-
lapping ions around m/z 1502. An expansion of these is shown in the top inset to
Figure 3, which shows the observed isotope patterns, together with the excellent
agreement with an mMass-modeled pattern comprising [Pt2(m-S)2(PPh3)4]þ and [Pt2(m-
S)2(PPh3)3Te2]þ in a 7:1 ratio. The major ion [Pt2(m-S)2(PPh3)4]þ is formed by oxidation
of [Pt2(m-S)2(PPh3)4] and represents one of the fragment ions of 2. This ion has been
observed as a fragment ion previously, for example in the fragmentation of cobalt(III)
[31] and iron(III) [32] derivatives of [Pt2(m-S)2(PPh3)4], where the [Pt2(m-S)2(PPh3)4] cen-
ter undergoes oxidation, with concomitant reduction and loss of the Fe or Co. It is
noteworthy that non-redox active adducts such as indium(III) derivatives [31] do not
show the same behavior. The observation of this ion in the current tellurium(I) system
is therefore suggestive of possible electron transfer forming reduced tellurium-contain-
ing species. Indeed, the other observed ion, [Pt2(m-S)2(PPh3)3Te2]þ, formed by loss of a
PPh3 ligand, formally contains tellurium in the þ0.5 oxidation state (i.e. reduction from
Te in the þ1 oxidation state in 2, to þ0.5). At higher capillary exit voltages of 150 and
180 V (Figure 3b and 3c, respectively), the parent ion undergoes successively more
complete fragmentation to [Pt2(m-S)2(PPh3)4]þ and [Pt2(m-S)2(PPh3)3Te2]þ. However,
there is an additional fragmentation process operating under these conditions, which
is elucidated by examination of the high-resolution isotope patterns of the m/z 1631
ion, shown in the lower inset to Figure 3. At a relatively low voltage of 150 V, the
observed isotope pattern (spectrum b1) shows good agreement with the calculated
pattern for [{Pt2(m-S)2(PPh3)4}2Te2]2þ (spectrum b1a). On increasing the capillary exit
voltage, the isotope pattern progressively changes (through spectrum b2 at 165 V and
spectrum b3 at 174 V) to spectrum b4 at 180 V, which can be modeled (spectrum b4a)
as an overlap of [{Pt2(m-S)2(PPh3)4}2Te2]2þ with the mono-tellurium species [Pt2(m-
S)2(PPh3)4Te]þ (which would nominally have the same m/z value) in a 3:1 ratio. This
latter ion is formed by homolytic fragmentation of the dimer [{Pt2(m-S)2(PPh3)4}2Te2]2þ
.
2.2. Investigation of the effect of added acetic acid on the reaction between
[Pt2(m-S)2(PPh3)4] (1) and TeCl2(tu)2
As described in the preceding section, added acid was found to promote the forma-
tion of the ditellurium complex [{Pt2(m-S)2(PPh3)4}2Te2]2þ when [Pt2(m-S)2(PPh3)4] is
reacted with TeCl2(tu)2. Accordingly, we have carried out a detailed investigation of
the effect of different amounts of added acid on the product speciation using ESI MS
to monitor reactions.

8
R. G. FORTNEY-ZIRKER ET AL.
Figure 4. A comparison of reaction solutions of [Pt2(m-S)2(PPh3)4] (1) and TeCl2(tu)2 in methanol
containing (a) no glacial acetic acid, (b) one drop (ca 0.05 mL) glacial acetic acid and (c) three
drops (ca 0.15 mL) glacial acetic acid. Spectra were acquired after mixing 12 h at room temperature.
Capillary exit voltage 20 V.
When TeCl2(tu)2 is reacted, in the absence of added acid, with a stirred, light-orange
suspension of [Pt2(m-S)2(PPh3)4] (1) in methanol, a clear red solution was immediately
formed, which after stirring for 24 h changed from red to a clear, very dark-green solu-
tion. A trace amount of dark insoluble residue (possibly elemental tellurium) was pre-
sent. To assess the effect of different amounts of added acetic acid on the reaction
between [Pt2(m-S)2(PPh3)4] and TeCl2(tu)2 three parallel microscale reactions of 1 and
TeCl2(tu)2 in methanol were carried out and analyzed by ESI MS (Figure 4). A reaction
solution without acetic acid (Figure 4a) was compared with reaction solutions contain-
ing 0.05 mL (Figure 4b) and 0.15 mL (Figure 4c) of glacial acetic acid. The spectra were
acquired after mixing for 12 h at room temperature, and a very low capillary exit volt-
age of 20 V was employed to minimize fragmentation. In the absence of acid, a signifi-
cant ion at m/z 794.15 is observed, assigned as [(Ph3P)2Pt{SC(=NH2)NH}]þ (5)
(calculated m/z 794.15), while in the presence of acid, this ion is less significant.
Complex 5 has been reported on two previous occasions [33, 34] and contains an N,S-
chelated thiourea monoanion. Thus, the effect of added acetic acid appears to be to
suppress the deprotonation of thiourea, and hence reduce its nucleophilicity.
Other detected ions containing a deprotonated thiourea ligand are the trinuclear
species [Pt3(m3-S)2(PPh3)5{SC(=NH2)NH}]þ (m/z 2035.65) together with the thiourea-sub-
stituted ion [(Ph3P)Pt{SC(=NH2)NH}(tu)]þ at m/z 608.12. These ions, together with

JOURNAL OF COORDINATION CHEMISTRY
9
dications at m/z 1018.15, assigned as [Pt3(m3-S)2(PPh3)5(tu)]2þ and m/z 925.12, assigned
as [Pt3(m3-S)2(PPh3)4(tu)2]2þ with neutral thiourea ligands, are clearly indicative of sub-
stantial degradation of the [Pt2(m-S)2(PPh3)4] core.
The reactivity of [Pt2(m-S)2(PPh3)4] (1) toward TeCl2(tu)2 in neutral solution was
explored by following the reaction over time using ESI MS at a capillary exit voltage
of 150 V. After ca 5 min the spectrum displayed a prominent base peak at m/z
1503.13, which is indicative of an incomplete reaction. The assignment of this ion as
the oxidized parent complex [1]þ was made after a close examination of the isotope
pattern, as described previously [15]. After 12 h, the now green reaction solution gave
a similar spectrum, but with some notable changes. The base peak of the spectrum
was now m/z 794.16, due to 5, and the mono-oxidized ion [1]þ is of significant relative
intensity at m/z 1503.25 with partial overlapping with [Pt2(m-S)2(PPh3)3Te2]þ (m/z
1495.97). Low mass ions at m/z 532.07 and m/z 608.08 due to [(Ph3P)Pt{SC(=NH2)NH}]þ
(calculated m/z 532.06) and [(Ph3P)Pt{SC(=NH2)NH}(tu)]þ (calculated m/z 608.07),
respectively, were also observed. After 24 h, the mass spectrum showed a prominent
base peak due to 5 with no ions observed above m/z 780. Two lower intensity ions
[(Ph3P)Pt{SC(=NH2)NH}]þ and [(Ph3P)Pt(tu){SC(=NH2)NH}]þ are still present at m/z
532.07 and m/z 608.08, respectively.
2.3. Reaction of [Pt2(m-S)2(PPh3)4] and TeCl2(tmtu)2 (tmtu ¼ tetramethylthiourea)
Another approach at minimizing attack of platinum by liberated thiourea used a more pro-
tected thiourea with a decreased tendency to coordinate anionically; tetramethylthiourea
(tmtu) was chosen due to the absence of NH protons which are readily deprotonated.
Using a similar methodology to the previous reactions, 0.05 mL of glacial acetic acid was
added to a suspension of [Pt2(m-S)2(PPh3)4] (1) in methanol and stirred for 10 min. Upon
addition of TeCl2(tmtu)2, the reaction solution immediately turned clear red and the ESI
mass spectrum of the reaction solution was acquired after 1 h. Using gentle ionization con-
ditions (capillary exit voltage 20 V), a clean spectrum was observed with a base peak at m/
z 887.16 assigned as the mononuclear complex [(Ph3P)2PtCl{SC(NMe2)2}]þ (6, calculated
m/z 887.19), whose isotope pattern agreed closely with the calculated pattern. This com-
plex has been previously synthesized and structurally characterized, and a study by ESI MS
indicated that the tmtu ligand was easily lost, predicating the necessity for a low capillary
exit voltage for its successful observation [35]. Despite the absence of deprotonatable
N–H groups, it is likely that the strong sulfur-based nucleophilicity of the tmtu ligand is
responsible for its inability to suppress degradation of the {Pt2S2} core. No further investi-
gations were carried out using tmtu–Te complexes.
2.4. Computational investigation of [{Pt2(l-S)2(PPh3)4}2Te2]2þ and [(Ph2PS2)2Te2]
2þ
To further investigate the unusual Te2 unit, density functional theory (DFT) calcula-
tions were undertaken for [{Pt2(l-S)2(PPh3)4}2Te2]2þ and [(Ph2PS2)2Te2] using the corre-
sponding structures determined from X-ray crystallography. The resulting electron
densities were analyzed using the density overlap regions indicator (DORI) [36, 37] to
simultaneously elucidate areas of covalent and non-covalent character. As DORI is

10
R. G. FORTNEY-ZIRKER ET AL.
Figure 5. A DORI contour map of the {(l-S)2Te2(l-S)2} core of [{Pt2(m-S)2(PPh3)4}2Te2]2þ in the xz
plane. Values in the range from 0 (blue) to 1 (red).
2þ
Figure 6. A DORI contour map of the Te2 unit of [{Pt2(m-S)2(PPh3)4}2Te2]2þ in the yz plane.
Values in the range from 0 (blue) to 1 (red).
related to the geometric deformation of electron density, it is worth noting the vol-
ume of a DORI isosurface does not necessarily correspond to the strength of a particu-
lar interaction. DORI contour maps (Figures 5 and 6) of the Te–Te axis display overlap
regions of electron density mapped from 0 (blue, at the nuclei and far from the mol-
ecule) to 1 (red, strong overlap of electron density). The Te–Te axis is bisected by a
red lenticular region with small noticeable blue areas either side on the tellurium
atomic boundaries. Comparisons can be made with DORI contour plots of both O2
and F2 [36], the latter being a very weak covalent interaction [38]. The four Te–S inter-
actions, which display a more compressed shape to the Te–Te interaction, are merged
with the larger atomic regions of tellurium.

JOURNAL OF COORDINATION CHEMISTRY
11
Figure 7. DORI ¼0.97 isosurfaces of [{Pt2(m-S)2(PPh3)4}2Te2]2þ using a blue–green–red color map
of –0.08 < sign(k2)q < 0.08. Phenyl rings of triphenylphosphine ligands omitted for clarity.
Figure 8. DORI ¼0.97 isosurface of [(Ph2PS2)2Te2] using a blue–green–red color map of
–0.08 < sign(k2)q< þ0.08.

12
R. G. FORTNEY-ZIRKER ET AL.
As DORI itself provides no information on the attractive/repulsive nature or strength of
2
the bonding interaction, the electron density Laplacian (r q) can be used in combination
to reveal such properties [36]. Specifically, the sign(k2)q scalar field was used to color-map
(blue–green–red) a DORI isosurface (s= 0.97) (Figure 7) with negative (blue) and positive
(red) magnitudes corresponding to attractive and repulsive interactions, respectively.
The isosurfaces between {Pt2S2} rings and Te–Te–S–Pt–S cycles can now be identi-
fied as regions of mild repulsion; non-covalent interactions typical for loci of cyclic sys-
tems [39]. The blue–green lenticular isosurface bisecting the Te–Te axis is indicative of
a bonding interaction with covalent character, with the four isosurfaces in the Te–S
regions less cylindrical and greener in color suggesting weaker bonding interactions.
The blue isosurfaces around the square–planar platinum centers show the stronger
valence interfaces of the coordinated sulfides.
2þ
A DORI examination of a similar complex with a Te2
unit, [(Ph2PS2)2Te2] [23]
(Figure 8), reveals a similar blue–green lenticular isosurface bisecting the Te–Te axis
which is slightly separated from the atomic Te regions. Interestingly, there is notice-
able asymmetry in the molecular geometry and accordingly two distinct Te–S bonding
interactions can be identified, one strong bonding interaction and trans to this a
much weaker bonding interaction.
Overall, the areas of electron density overlap in [{Pt2(l-S)2(PPh3)4}2Te2]2þ as revealed
by DORI support the expected bonding interactions. The unusual separation of some
DORI isosurfaces displayed has been described as a numerical artifact attributed to the
nonphysical behavior of finite atomic orbital basis set expansion in areas of fringe
electronic density [36, 40].
3. Conclusion
The tellurium(II) complex TeCl2(tu)2 is a convenient source of low-valent inorganic tel-
lurium and gives the formally tellurium(I) complex [{Pt2(m-S)2(PPh3)4}2Te2]2þ on reaction
with [Pt2(m-S)2(PPh3)4]. Fragmentation of the {Pt2S2} core by thiourea leads to forma-
tion of the mononuclear platinum(II) thiourea complex [(Ph3P)2Pt{SC(=NH2)NH}]þ, how-
ever, this was successfully suppressed by addition of acid to the reaction mixture. The
tetra-platinum complex [{Pt2(m-S)2(PPh3)4}2Te2]2þ has a similar structure to the known
dithiophosphinate-bridged tellurium(I) species [Te2(S2PPh2)2] and to the silver(I) and
gold(I) adducts [{Pt2(m-S)2(PPh3)4}2M2]2þ
.
4. Experimental
4.1. Instrumentation
Mass spectra were obtained using a high-resolution Bruker MicrOTOF spectrometer that
was periodically calibrated with methanolic sodium formate. For reaction solutions, a drop
of the reaction mixture was diluted to ca 1.5 mL with methanol. Solutions were centri-
fuged prior to analysis and the sample introduced by a microliter syringe and syringe
pump. Typically a Capillary Exit voltage of 150 V and a Skimmer 1 voltage of 50 V were
used, though this was varied to investigate fragmentation behavior of observed ions (see
text). Ions were assigned by m/z value and comparison of experimental and theoretical

JOURNAL OF COORDINATION CHEMISTRY
13
isotope patterns. Theoretical patterns were obtained using Bruker instrument-based soft-
ware, and mass spectrometry data were further analyzed and prepared for presentation
with the open-source mass spectrometry tool mMass [41, 42].
Elemental analyses were carried out by the Campbell Microanalytical Laboratory,
University of Otago, Dunedin, New Zealand. 31P{1H} NMR spectra were recorded on a
Bruker AVIII-400 spectrometer in CDCl3 solution.
4.2. Materials
[Pt2(m-S)2(PPh3)4] (1) was prepared by the literature procedure [43]. Tetramethylthiourea
(tmtu, Aldrich) was used as supplied. TeCl2(tu)2 was from either a commercial source
(Aldrich) or was prepared by a literature procedure [44]. TeCl2(tmtu)2 was prepared by the
literature procedure [45]. NH4PF6 (Aldrich), NaBF4 (Aldrich) and Li[N(SO2C2F5)2] (3M) were
used as obtained. Other chemicals were at least of reagent grade.
4.3. Synthesis of [{Pt2(m-S)2(PPh3)4}2Te2][N(SO2C2F5)2]2
[Pt2(m-S)2(PPh3)4] (1) (101.8 mg, 0.067 mmol) was suspended in methanol (25 mL), 37%
aqueous HCl (0.1 mL) added, and the mixture stirred at room temperature for 3 h. The
resulting clear yellow solution was filtered to remove a trace amount of insoluble mat-
ter, and to the resulting filtrate was added TeCl2(tu)2 (23.6 mg, 0.067 mmol). The clear
red solution was stirred at room temperature for 10 min, filtered to remove insoluble
matter, and the filtrate examined by ESI MS. To the filtrate was added excess
Li[N(SO2C2F5)2] (150 mg, 0.387 mmol) and the red solution stirred for 30 min resulting
in the formation of a dark red precipitate. The solid was collected by vacuum filtration,
washed with water (10 mL ꢂ2) and diethyl ether (5 mL), and dried under vacuum to
give 29.3 mg (21.7%) of product as a red powder. Anal. Found: C, 45.65; H, 3.05; N,
0.86. C152H120F20N2O8P8Pt4S8Te2 requires: C, 45.39; H, 3.00; N, 0.70%. 31P{1H} NMR
(162 MHz), d 20.9 [br s, 1J(PtP) 2959 Hz]. ESI MS (capillary exit voltage 45 V) m/z
1630.88 [{Pt2(m-S)2(PPh3)4}2Te2]2þ (100%).
-
-
The other salts containing PF6 or BF4 ions were prepared by analogous proce-
dures, substituting Li[N(SO2C2F5)2] by excess NaBF4 or NH4PF6.
4.4. Reaction of [Pt2(m-S)2(PPh3)4] (1) with TeCl2(tu)2 in methanol
[Pt2(m-S)2(PPh3)4] (49 mg, 0.033 mmol) was suspended in methanol (20 mL) with
TeCl2(tu)2 (6 mg, 0.017 mmol) and the clear red mixture was stirred at room tempera-
ture for 24 h, with monitoring by positive-ion ESI MS. After 24 h a clear, dark green
solution was observed.
4.5. Comparison of reactions of [Pt2(m-S)2(PPh3)4] (1) with TeCl2(tu)2 in
methanol with varying amounts of acetic acid
In three parallel reaction vessels, [Pt2(m-S)2(PPh3)4] (20 mg, 0.0133 mmol) was sus-
pended in methanol (10 mL) and stirred. Reaction (a): the orange mixture was stirred

14
R. G. FORTNEY-ZIRKER ET AL.
at room temperature for 10 min. Reaction (b): same as (a), with glacial acetic acid
(0.05 mL) added. Reaction (c): same as (a) with glacial acetic acid (0.15 mL) added.
After 10 min, TeCl2(tu)2 (4.7 mg, 0.0134 mmol) was added to each reaction, with the
resulting clear red mixtures stirred at room temperature for 12 h. Reaction (a): the dark
green solution was filtered to remove insoluble matter and the filtrate analyzed by ESI
MS. Reactions (b, c): the clear red solutions were filtered to remove any insoluble mat-
ter and the filtrates were analyzed by ESI MS.
4.6. X-ray crystal structure determination of [{Pt2(m-S)2(PPh3)4}2Te2][BF4]2
Dark-brown prismatic crystals of the complex suitable for an X-ray diffraction study
were obtained by diffusion of diethyl ether into an acetone solution of the complex.
Intensity data were measured at T = 100(2) K on a SuperNova Dual AtlasS2 diffractom-
eter fitted with Cu Ka radiation so that hmax was 73.8ꢀ. Data reduction, including ana-
lytical absorption correction, was accomplished with CrysAlisPro [46]. Of the 29,343
measured reflections, 6512 were unique (Rint=0.057) and of these, 4621 data satisfied
the I ꢃ 2r(I) criterion of observability. The structure was solved by direct methods [47]
and refined (anisotropic displacement parameters, C-bound H atoms in the riding
model approximation, and a weighting scheme w = 1/[r2(Fo ) þ 0.086P2þ82.709P]
2
where P= (Fo þ2Fc )/3) on F2 [48]. For charge balance, half a BF4 is required. However,
this assignment was quite ambiguous. While a possible position for the B atom was
found, being located on a site of symmetry 222 implied multiple positions for the F
atoms which were not resolved in the X-ray experiment. Accordingly, the routine
2
2
-
-
SQUEEZE [49] was employed to model the unresolved electron density due to the BF4
anions. Even with this treatment, there was considerable atomic motion in the struc-
ture despite the low temperature of the X-ray experiment. In keeping with this, the
C61–C66 phenyl ring was found to be badly disordered and was modeled isotropically
as an idealized phenyl ring with C–C bond lengths fixed at 1.39 Å. Despite the difficul-
ties encountered in the refinement, the molecular structure of the cation has been
determined unambiguously. Based on the refinement of 324 parameters, the final val-
ues of R and wR (all data) were 0.070 and 0.207, respectively. The molecular structure
diagram was generated with DIAMOND [50].
Crystal data for C144H120B2F8P8Pt4S4Te2: M = 3435.57, orthorhombic space group
Pnnn, a = 18.4717(2), b = 18.5907(3), c = 19.0659(3) Å, V = 6547.26(16) Å3, Z = 2,
Dx=1.743 g cm–3, F(000) ¼ 3332, m=13.276 mm–1. CCDC deposition number: 1811863.
4.7. Computational details
Single point energy DFT calculations were performed using molecular geometry
obtained from crystal structures of [{Pt2(l-S)2(PPh3)4}2Te2](BF4)2 and [(Ph2PS2)2Te2] [23]
with the Q-Chem 4.2 [51] software package using the xB97X [52] functional with DFT-
D3 long-range dispersion correction by Grimme et al. [53]. The LANL2DZ [54] effective
core potential and basis set was used for platinum and tellurium atoms, the Dunning
double-f augmented correlation-consistent polarized basis set aug-cc-pV(D þ d)Z [55]
used for sulfur atoms, and the Pople double-f polarized basis set 6-31G(d) [56] used

JOURNAL OF COORDINATION CHEMISTRY
15
for the treatment of all other atoms. Wave function analysis was performed using
Multiwfn [57]. Visual Molecular Dynamics [58] and Tachyon [59] ray tracer were used
to render isosurfaces and Python was used to generate contour images.
Acknowledgements
We thank the University of Waikato and Sunway University for financial support of this work,
and Pat Gread and Wendy Jackson for technical assistance. We also thank New Zealand
eScience Infrastructure (NeSI) for providing access to high performance computing facilities.
Supplementary material
CCDC 1811863 contains the supplementary crystallographic data for this article. These data can
be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif. Supplementary data to this article can be found online.
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