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B. Copper Polymers Assembled by Aromatic Dithioether Ligands

B. Copper Polymers Assembled by Aromatic Dithioether Ligands

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106



Luminescent Oligomeric and Polymeric Copper Coordination



preferred for n 5 2 or 3. Some representative examples for that chelating

coordination mode are cis-[PtCl2{PhS(CH2)nSPh}2] (n 5 2,3), tetrahedral [Cu

{PhS(CH2)nSPh}2][BF4] (n 5 2,3), octahedral [SnCl4{PhS(CH2)3SPh}2], and

[(η5-C5Me5)Rh(H2O){PhS(CH2)2SPh)}][triflate]2.136À139 However, a significant change is noticed when the number of methylene units reaches n 5 4,

5, and 6. A relationship between ligand chain length and structure about a

PdCl2 fragment has been established by Sanger et al. Based on IR data, the

formation of ligand-bridged palladium complexes of trans-geometry have

been proposed for n 5 4À6.140 Recently, an X-ray diffraction study on [Pd

{PhS(CH2)5SPh}Cl2]n confirmed that 1,5-bis(phenylthio)pentane indeed

spans the Pd-centers, generating a polymeric chain complex.141 The crystal

engineering with the ligand 1,4-bis(phenylthio)butane on Ag(I) salts under

different conditions (varying the solvent, metal to ligand ratios, and counterions) gave rise to a number of 2D frameworks with fascinating structural

motifs.142 Very recently, luminescent gold polymers spanned by this flexible

ligand have been synthesized by Brisse et al.143 We have previously shown

that the complexation of PhS(CH2)4SPh on HgX2 (X 5 Cl, Br) in a 1:2 ratio

allows the assembly of 2D coordination polymers of the type [{PhS

(CH2)4SPh}Hg2X4]n (X 5 Cl, Br).144

With the objective to elaborate low-cost luminescent CuX coordination

polymers with easily accessible dithioether ligands of the type ArS(CH2)nSAr,

our group embarked on a project to construct CuX metal-organic polymers

assembled by such dithioether ligands with varying spacer lengths and -SAr

aromatic groups to evaluate the impact of these systematic variations on the

luminescence properties, dimensionality, and cluster nuclearity of the resulting

hybrid organic-inorganic materials. Furthermore, the influence of the halide

ion on the architecture was studied.

Reaction of CuI with bis(phenylthio)methane in acetonitrile in a 2:1 molar

ratio gave air-stable colorless crystals of general formula [{Cu4(μ3-I)4}

{μ-PhSCH2SPh}2]n 9 (Scheme 8). Modification of the molar ratio—for example,

a 1:1 or 1:2 molar ratio—had no influence on the composition of the resulting

material and only compound 9 was formed.145 The crystal structure of 9 (Fig. 13)

consists of cubane-like Cu4I4 clusters linked by bridging dithioether ligands to



S



S

I



S



Cu



Cu I

S Cu I

I Cu

S



TolS



STol

MeCN



CuI



PhS



SPh

MeCN



S

I



Cu



Cu I

S Cu I

I Cu

S

1D [Cu4I4{␮-PhSCH2SPh}2]n



1D [Cu4I4{␮-TolSCH2STol}2]n

10



9



SCHEME 8



Luminescent Copper Polymers Assembled by Thioether Ligands



107



form an infinite chain with CuÀS distances of 2.292(2) and 2.301(2) A˚.

The CuÀI bond lengths fall in the range of 2.6077(11)À2.7704(11) A˚. The

CuÀCu distances [2.6173(18)À2.7864(14) A˚] are somewhat below to the sum of

the Van der Waals radii (2.8 A˚) and lie clearly below those observed for

[(Et2S)3{Cu4(μ3-I)4}]n 1. In contrast to single-bridged 1, two adjacent Cu4I4 cores

are linked by two flexible dithioether ligands, thus leading to the formation of a

1D necklace structure. All phenyl substituents adopt a parallel orientation with a

short Cipso-Cipso distance of 3.502 A˚.

Despite the fact that the phenyl groups of neighboring ribbons are

somewhat interpenetrated, there are no close interribbon interactions between

the 1D chains of coordination polymer 9, the separation between the midpoints

of two adjacent Cu4I4 units being 11.64 A˚ (Fig. 14).

In order to evaluate the influence of additional methyl groups at the paraposition of the ÀSAr groups, we also reacted CuI under analogous conditions

with bis(p-tolylthio)methane in acetonitrile in a 2:1 molar ratio (Scheme 8). An

X-ray diffraction study revealed that colorless polymer 10 of general formula

[{Cu4(μ3-I)4}{μ-p-TolSCH2STol}2]n is isostructural with 9, crystallizing in the

monoclinic space group C2/c.

Figure 15 illustrates that again tetranuclear Cu4(μ3-I)4 units are doubly

bridged by the dithioether ligand to form a 1D ribbon. Within the tetranuclear

cluster, the CuÀCu distances range between 2.652(3) and 2.829(2) A˚, the mean

separation of 10 being somewhat superior to that encountered in 9 (2.730 vs.

2.678 A˚ at 173 K). Also the CuÀS distances of 2.320(3) and 2.328(3) A˚ are

slightly elongated compared to 9, the CuÀI bond lengths fall in the range of

2.634(2)À2.756(2) A˚.

As expected, both materials 9 and 10 exhibit interesting luminescence

properties. The superposed solid-state emission spectra of 9 and 10 are depicted



FIGURE 13. View on the 1D chain of polymer 9 along the c axis. H atoms are omitted

for clarity.



108



Luminescent Oligomeric and Polymeric Copper Coordination



FIGURE 14. View of packing of [Cu4I4{μ-PhSCH2SPh}2]n 9 on the ab plane.



FIGURE 15. View of the parallel arrangement of the 1D chains of [{Cu4(μ3-I)4}

{μ-p-TolSCH2STol}2]n 10 along the c axis. H atoms are omitted for clarity.



Luminescent Copper Polymers Assembled by Thioether Ligands



Normalized Emission Intensity



1.2



109



CuI/PhS-CH2-SPh

CuI/p-TolS-CH2-STol-p



1

0.8

0.6

0.4

0.2

0

400



450



500



550



600



650



700



Wavelength (nm)



FIGURE 16. Normalized superimposed solid-state emission spectra recorded at room

temperature for isostructural compounds 9 (solid line) and 10 (dotted line) after excitation at 360 nm.



in Figure 16. Upon excitation at 360 nm, a very strong unstructured emission

band was observed for the tetranuclear dithioether-adduct 9 with a maximum

at 532 nm, whereas isostructural 10 displays a blueshifted maximum at B508

nm. At present, it remains speculative to discuss the shift of the maxima

noticed between 9 and 10. The bis(p-tolylthio)methane ligand should behave as

a slightly stronger donor ligand compared to bis(phenylthio)methane; however,

it seems difficult to differentiate between the impact of electronic effects and

packing forces on the subtle diverging CuÀCu and CuÀS bond lengths

between polymers 9 and 10. Emissions in a similar spectral range have been

observed for nitrogen-substituted Cu4I4L4 clusters and were attributed to an

emission from a triplet cluster-centered excited state (3CC). As discussed for

[(Me2S)3{Cu4(μ-I)4}]n 4 and suggested for [(Et2S)3{Cu4(μ3-I)4}]n 1, these broad

emissions of CC-excited states have a mixed character with equal contributions

of iodine to copper charge transfer (XMCT) and centered copper orbital (d-s)

transitions. Lifetime measurement performed on 10 yielded for τ 1.39 6 0.05 μs

at 298 K and 1.43 6 0.03 μs at 77 K.

The colorless crystals obtained from the reaction of CuI with the 1,2-bis

(tolylthio)ethane ligand in acetonitrile in a 1:1 molar ratio were identified by

an X-ray study as the coordination polymer [(CuI)2{μ-PhS(CH2)2SPh}2]n 11.

The framework consists of centrosymmetric Cu2(μ2-I)2 rhomboid dimers,

connected to an adjacent unit via one μ2-bridging dithioether ligand (Fig. 17).

Each Cu atom is in a distorted tetrahedral environment, coordinated by two

bridging iodo ligands and two thioether groups of two distinct ligands. The 2D

network resulting from this coordination mode includes centrosymmetric

24-membered metallomacrocycles constituted by four dithioether ligands, six



110



Luminescent Oligomeric and Polymeric Copper Coordination



FIGURE 17. View of the core structure of 11 on the ab plane. H atoms and phenyl

groups are omitted for clarity.



Cu atoms, and two iodo ligands (Fig. 16). The average distance of the two Cu-S

bonds (2.3000(11) and 2.3855(10) A˚) is just somewhat longer than the value in

9. However, the Cu?Cu separation of 2.8058(11) A˚ is markedly longer than

those observed in the earlier mentioned Cu4I4 unit of 9.145

In contrast to 9 and 10, the emission spectrum recorded for polymeric 11

containing the dinuclear Cu2I2 unit exhibits under similar experimental conditions a much weaker emission centered at 413 nm with a shoulder at 438 nm

(Fig. 18). Although less studied than the tetranuclear systems, photophysical

properties of some dinuclear Cu2X2 compounds have been reported in the

literature but are currently limited to N-heterocyclic and phosphoros-donor

ligands.79 The observation of a shoulder suggests a different contribution originating from an XMCT and a Cu (d-s) transition. Solution measurements

carried out in acetonitrile at room temperature show the disappearance of the

luminescence properties for 9, 10, and 11. This is probably due to a disassembly

of the cluster units by this strongly coordinating solvent.

In contrast to the observation that substitution of -SPh by STol-p in

ArSCH2SAr has no impact on the dimensionality and nuclearity of isostructural polymers 9 and 10, replacement of phenyl substituents of PhS

(CH2)2SPh by p-tolyl groups causes a profound change of the framework

on reaction with copper iodide. Independently of the metal to ligand



Luminescent Copper Polymers Assembled by Thioether Ligands



111



1200000



I (a.u)



800000



400000



0

380



430



480



530



580



630



680



Wavelength (nm)



FIGURE 18. Superimposition of the solid-state luminescence spectra recorded at room

temperature for compounds 9 (solid line) and 11 (dotted line).



ratio employed, a colorless material of composition [(Cu2I2){μ-p-TolS

(CH2)2STol}2]n 12, crystallizing in the monoclinic space group P2(1)/c, was

isolated. Figure 19a shows that the unusual inorganic core motif is best

described as a corrugated 1D ribbon assembled by Cu(μ2-I)2Cu rhomboids

with Cu?Cu interactions of 2.9073(11) A˚, which are interconnected to the

adjacent rhomboids through week Cu?Cu contacts of 2.9511(11) A˚ and two

μ3 bridging iodo ligands. In addition, each second Cu(μ2-I)2Cu unit is μ2spanned by a 1,2 bis(tolylthio)ethane ligand (Fig. 19b).

To probe the influence of the halide on the architecture of the network,

1,2-bis(phenylthio)ethane was also reacted with CuBr, according Scheme 9.

Unexpectedly and regardless of the CuBr to ligand ratio, only the dinuclear

complex [Cu(μ-Br){p-TolS(CH2)2STol}]2 13 was produced. As corroborated by

an X-ray diffraction study, the dithioether ligand is bound in a chelating

manner on CuBr, forming a five-membered ring. The Cu?Cu separation of 13

is even more pronounced than that of 12 and reaches 3.0111(14) A˚.

Polymeric material 12 is only weakly emissive compared to the Cu4I4

containing 1D chains of polymers 1, 9, and 10, most probably due to the

absence of strong Cu?Cu interactions. Upon excitation at 360 nm, a structured emission with maxima at 416 and 434 nm is observed (Fig. 20). The

strong resemblance with the emission spectrum of the free ligand depicted in

Figure 21 suggests that the luminescence of the polymer chain is essentially due

to the dithioether ligand. The fact that the emission spectrum of [Cu(μ-Br){pTolS(CH2)2STol}]2 13 also displays two maxima in the same spectral range at

an 419 and 430 nm ( λexcit 360 nm) indicates that the luminescence properties

are mostly originating from the ligand.



112



Luminescent Oligomeric and Polymeric Copper Coordination



FIGURE 19. (a) View of the inorganic core 1D ribbon of 12 along the c axis. (b) View

of the metal-organic framework of 12. The H atoms are omitted for clarity.

I



S



Cu



Cu

S



S



S



I



SPh

PhS



S



STol

CuI



TolS



MeCN



I



Cu



I



S

Cu



Cu



S

I



I



Cu



Cu

Cu

I

I

I

S

S

S

S

1D [(CuI)2{␮-TolS(CH2)2STol}2]n



Cu

MeCN



2D [(CuI)2{␮-PhS(CH2)2SPh}2]n



11



12

STol

CuBr



Br



S



TolS



S



MeCN



S

Cu



Cu

Br



S



0D [CuBr{TolS(CH2)2STol}]2



13



SCHEME 9



Upon treatment of a solution of 1,3-bis(phenylthio)propane in MeCN

with an equimolar amount of CuI at ambient temperature, colorless crystals

were formed. X-ray diffraction determination revealed the organization of

coordination polymer [(CuI)2{μ-PhS(CH2)3SPh}2]n 14 in form of a 2D sheet



Luminescent Copper Polymers Assembled by Thioether Ligands



113



CuI/p-TolS(CH2)2STol-p



Normalizes Intensity



1.2



Excitation at 360 nm

Emission at 416, 434 nm



1

0.8

0.6

0.4

0.2

0

290



340



390



440



490



540



590



640



690



Wavelength (nm)



FIGURE 20. Excitation (left) and emission (right) of solid [(Cu2I2){μ-p-TolS-p

(CH)2STol-p}2]n 12 at 298K.



Normalized Intensity



1.2



Excitation at 360 nm

Emission at 412, 436 nm



p-TolS(CH2)2STol-p



1

0.8

0.6

0.4

0.2

0

290



340



390



440



490



540



590



640



690



Wavelength (nm)



FIGURE 21. Excitation (left) and emission (right) of solid ligand p-TolS(CH2)2STol-p

at 298 K.



structure. The framework consists of centrosymmetric Cu2(μ2-I)2 rhomboid

dimers connected to an adjacent unit via one μ2-bridging dithioether ligand

(Fig. 22). Each Cu atom is in a distorted tetrahedral environment, coordinated

by two bridging iodo ligands and two thioether groups of two distinct ligands.

The 2D network resulting from this coordination mode includes centrosymmetric 28-membered metallomacrocycles constituted by four dithioether

ligands, six Cu atoms, and two iodo ligands. Overall, the coordination mode is

quite reminiscent of that encountered in coordination polymer [(CuI)2{μ-PhS

(CH2)2SPh}2]n 11. The Cu?Cu separation of 14 is similar to that observed in

[(CuI)2{μ-PhS(CH2)2SPh}2]n [2.826(10) vs. 2.8058(11) A˚].



114



Luminescent Oligomeric and Polymeric Copper Coordination



FIGURE 22. View of the core structure of 14 on the ab plane. H atoms and phenyl

groups are omitted for clarity.



Changing the molar CuI to ligand ratio to 2:1 (using the same experimental conditions) has a dramatic effect on the composition of the colorless

crystalline material 15. Now elemental analyses were in accordance with the

ligation of two CuI units per dithioether. Unfortunately, we failed to obtain

X-ray-suitable crystals to elucidate the solid-state structure of this compound.

However, comparison of the emission spectra of this extremely luminescent

material with those of polymers 1, 9, 10, 16, and 21 (see below), for which the

occurrence of Cu4(μ3-I)4 clusters has been crystallographically established,

suggests the existence of cubane-like Cu4(μ3-I)4 units in compound 15.

It is not surprising that the emission spectrum of 14 resembles that of 11.

After excitation at 360 nm, it displays two emission maxima of medium

intensity at 414 and 435 nm. In contrast, material 15 is strongly luminescent.

In the solid state after excitation at 360 nm, it displays a broad featureless

emission with λmax at about 550 nm (Fig. 23).

Reaction of CuI with 1,4-bis(phenylthio)butane in acetonitrile in a 2:1

molar ratio gave air-stable crystals of the general formula [Cu4I4{μ-PhS

(CH2)4SPh}2]n 16 (Scheme 10). Modification of the molar ratio to 1:1 had, in

this case, no influence on the composition of the resulting material and only



Luminescent Copper Polymers Assembled by Thioether Ligands



115



(a)

1.2



Normalized Intensity



1

0.8

0.6

0.4

0.2

0

390



440



490

540

590

Wavelength (nm)



640



690



440



490



640



690



(b)

1.2



Normalized Intensity



1

0.8

0.6

0.4

0.2

0

390



X

540



590



Wavelength (nm)



FIGURE 23. Normalized solid-state emission spectra of 14 (a) and 15 (b) recorded at

ambient temperature, featuring maxima at 414, 435, and 550 nm, respectively

(λexcit 5 360 nm). X denotes an emission at 414 nm due to some traces of compound 14

as impurity in the sample of 15.



colorless material 16 was formed, crystallizing in the triclinic space group P1. Its

crystal structure consists of cubane-like Cu4I4 clusters linked by bridging

dithioethers, forming (in contrast to 9 and 10) an infinite 2D network (Fig. 24).

Its (4,4) topology can be described as undulated square grids, in which Cu4I4

clusters as secondary building units (SBUs) define the corners and the dithioether

ligands, the edges. The side length of each 32-membered square-like macrocycle is

B10.6 A˚. Two of these grids are interpenetrated in such a manner that the square

centers of a net plane are approximately located on the middle of the edges of

the second one (Fig. 25). Each SBU is connected to four dithioether ligands, with



116



Luminescent Oligomeric and Polymeric Copper Coordination

S

S



I



Cu



Cu

I

I

S Cu

I

Cu

S



SPh

PhS

CuI

MeCN



16



2D [Cu4I4{␮-PhSCH4SPh}2]n

S



S

Cu



Cu

I

PhS



SPh



CuI



Cu



S



MeCN



I

Cu

I I

I S Cu

S

I

Cu



17

S



3D [Cu6I6{␮-PhSCH2C=CCH2SPh}]n



S

I



STol

p-TolS

CuI



Cu



Cu

MeCN



S



S

I



Cu



Cu



I

S



I



Cu



Cu



I



S



I



S



18



2D [(CuI)2{␮-p-TolS(CH2)4STol-p}2]n



STol

p-TolS



Br



S



CuBr



S



S

Cu



Cu

MeCN



19

S



Br



2D [(CuBr)2{␮-p-TolS(CH2)4STol-p}2]n



STol

o-TolS



I



S



CuI



S

MeCN



S

Cu



Cu

I



20

S



2D [(CuI)2{␮-o-TolS(CH2)4STol-o}2]n



SCHEME 10



averaged CuÀS bond distances of 2.299(2) A˚. The CuÀI bond lengths range

between 2.6391(12) and 2.7745(14) A˚. The Cu?Cu distances between the four

nonequivalent Cu(I) centers [2.6505(16)À2.7431(16) A˚] have at 173 K a mean

value of 2.6942 A˚, almost identical to that of the 1D polymer 9.146

The photophysics of strongly luminescent 16 have been examined in

detail in collaboration with the Harvey group.146 After excitation at 360 nm, a



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B. Copper Polymers Assembled by Aromatic Dithioether Ligands

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