Supramolecular Construction of Cyanide-Bridged ReI Diimine Multichromophores

Article abstract of DOI:10.1021/acs.inorgchem.8b02974

The reactions of labile [Re(diimine)(CO)₃(H₂O)]⁺ precursors (diimine = 2,2′-bipyridine, bpy; 1,10-phenanthroline, phen) with dicyanoargentate anion produce the dirhenium cyanide-bridged compounds [{Re(diimine)(CO)₃

Full text of DOI:10.1021/acs.inorgchem.8b02974

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Supramolecular Construction of Cyanide-Bridged ReI Diimine
Multichromophores
Kristina S. Kisel,†,‡ Alexei S. Melnikov,§ Elena V. Grachova,† Antti J. Karttunen,*,∥
⊥
Antonio Domenech-Carbo, Kirill Yu. Monakhov,# Valentin G. Semenov,† Sergey P. Tunik,†
́
́
and Igor O. Koshevoy*,‡
†Institute of Chemistry, St. Petersburg State University, Universitetskiy pr. 26, Petergof, St. Petersburg 198504, Russia
‡Department of Chemistry, University of Eastern Finland, 80101 Joensuu, Finland
§Peter the Great St. Petersburg Polytechnic University, Polytechnicheskaya, 29, St. Petersburg 195251, Russia
∥Department of Chemistry and Materials Science, Aalto University, 00076 Aalto, Finland
⊥Universidad de Valencia, Dr. Moliner 50, 46100 Burjassot, Valencia Spain
#Leibniz Institute of Surface Engineering (IOM), Permoserstraße 15, 04318 Leipzig, Germany
S
* Supporting Information
ABSTRACT: The reactions of labile [Re(diimine)-
(CO)3(H2O)]+ precursors (diimine = 2,2′-bipyridine, bpy;
1,10-phenanthroline, phen) with dicyanoargentate anion
produce the dirhenium cyanide-bridged compounds [{Re-
(diimine)(CO)3}2CN)]+ (1 and 2). Substitution of the axial
carbonyl ligands in 2 for triphenylphosphine gives the
derivative [{Re(phen)(CO)2(PPh3)}2CN]+ (3), while the
employment of a neutral metalloligand [Au(PPh3)(CN)]
affords heterobimetallic complex [{Re(phen)(CO)3}NCAu-
(PPh3)]+ (4). Furthermore, the utilization of [Au(CN)2]−,
[Pt(CN)4]2−, and [Fe(CN)6]4−/3− cyanometallates leads to
the higher nuclearity aggregates [{Re(diimine)-
(CO)3NC}xM]m+ (M = Au, x = 2, 5 and 6; Pt, x = 4, 7
and 8; Fe, x = 6, 9 and 10). All novel compounds were characterized crystallographically. Assemblies 1−8 are phosphorescent
both in solution and in the solid state; according to the DFT analysis, the optical properties are mainly associated with charge
transfer from Re tricarbonyl motif to the diimine fragment. The energy of this process can be substantially modified by the
properties of the ancillary ligands that allows to attain near-IR emission for 3 (λem = 737 nm in CH2Cl2). The Re−FeII/III
complexes 9 and 10 are not luminescent but exhibit low energy absorptions, reaching 846 nm (10) due to ReI → FeIII
transition.
with appealing optical and redox characteristics, resulting from
donor−acceptor (intervalence) charge transfer.5−10 In con-
trast, cyanometallate coordination polymers, particularly those
built of relatively flexible [M(CN)2]− (M = Au, Ag),
[AuX2(CN)2]− or [PtX2(CN)4]2− motifs, which simultane-
ously comprise weak noncovalent bonding, can exhibit
unconventional thermo- and piezo-mechanical features.11−15
Furthermore, dicyanometallates [M(CN)2]− of coinage
metal ions (M = Au, Ag, Cu) and tetracyanoplatinate
[Pt(CN)4]2− have been actively employed for the development
of birefringent16,17 and photoluminescent18−28 homo- and
heterobimetallic materials, including sensory systems with
distinct optical response to some volatile donor mole-
cules.29−32
INTRODUCTION
■
Anionic cyanometallates [M(CN)x]n−/[MLz(CN)y]m− occupy
a prominent position in the field of coordination-driven
supramolecular construction. Chemical stability and high
directionality of coordination bonding along with general
availability determines their wide utilization as metalloligands
in the design of a variety of multinuclear cyano-bridged arrays,
which span from the bimetallic complexes to ordered three-
dimensional frameworks.1−4 Depending on the electronic
properties of the constituting metal ions, the resulting
compounds exhibit an impressive diversity of physical and
chemical behavior. Thus, the inclusion of paramagnetic centers
(CrIII, FeIII, RuIII, CoII, etc.) is an established approach to the
magnetic polymeric and molecular materials.2−4 Combining
the metals in different oxidation states (reduced and oxidized),
which are capable to communicate electronically via the
cyanide linker, leads to the family of mixed-valence species
Received: October 19, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b02974
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
yellow-greenish crystals (29 mg, 67%). IR (CH2Cl2, ν(CO), cm−1):
2037s, 2028s, 1931s. IR (KBr, ν(CN), cm−1): 2151m. 1H NMR
(acetone-d6, 298 K; δ): 9.15 (dd, JHH = 5.1 and 1.3 Hz, 2H, 2,9-H
phen), 9.07 (dd, JHH = 5.1 and 1.3 Hz, 2H, 2,9-H phen′), 8.95 (dd,
2H, JHH = 8.3 and 1.3 Hz, 4,7-H phen), 8.90 (dd, JHH = 8.3 and 1.3
Hz, 2H, 4,7-H phen′), 8.38 (s, 2H, 5,6-H phen), 8.30 (s, 2H, 5,6-H
phen′), 7.97 (m, 4H, 3,8-H phen and 3,8-H phen′). ESI+ MS (m/z):
[M]+ 926.02 (calcd 926.02). Anal. Calcd for C32H16F3N5O9Re2S: C,
35.72; H, 1.50; N, 6.51; S, 2.98. Found: C, 35.93; H, 1.69; N, 6.58; S,
3.05.
[{Re(phen)(CO)2(PPh3)}2CN](CF3SO3) (3). Preparation of [Re-
(phen)(CO)2(PPh3)(NCMe)](CF3SO3). An acetonitrile solution (4 mL)
of [Re(phen)(CO)3(PPh3)](CF3SO3) (100 mg, 0.116 mmol) was
irradiated using a 351 nm pulsed laser (50 mW) for 2.5 h. Then, the
solvent was evaporated, and the orange solid was recrystallized by a
gas phase diffusion of diethyl ether into its acetone/methanol solution
at room temperature to give red crystalline material (71 mg, 70%). IR
(CH2Cl2, ν(CO), cm−1): 1956s, 1889s. 1H NMR (acetone-d6, 298 K;
δ): 9.10 (d, JHH = 5.1 Hz, 2H, 2,9-H phen), 8.82 (dd, 2H, JHH = 8.3
A notable though less explored route to the cyanometallate-
based photofunctional complexes relies on the incorporation of
chromophore fragments as constituting elements into the
target assemblies. For example, coupling the cyclometalated
33
anions [IrLz(CN)y]m−10,
with ReI(diimine) or
RuII(polypyridine) moieties induces efficient intermolecular
Ir → Re/Ru energy transfer in the excited state. A similar
scenario of Re → Ru excitation transfer has been described for
ReI(diimine)−RuII(diimine)2 CN-bridged dyads.5 On the
contrary, linking the RuII(polypyridine) centers with LnIII or
CrIII units having energetically lower lying excited states
sensitizes the MIII-centered emission.34,35
Taking into account that the decoration of [M(CN)x]n−
anions with luminogen components to generate discrete
molecular aggregates has been poorly investigated and is
mostly focused on the d−f coordination polymers, we intended
to prepare a series of heterometallic multichromophore
molecules using homoleptic cyanometallates of Au, Pt and
Fe as assembling metalloligands. To address this goal, we have
chosen [Re(diimine)(CO)3]+ (diimine = phenanthroline,
bipyridine) photoactive centers as terminal building blocks
for supramolecular construction due to their superior and well-
studied photophysical properties together with quite facile
coordination chemistry.36−38
and 1.2 Hz, 4,7-H phen), 8.29 (s, 2H, 5,6-H phen), 7.86 (dd, JHH
=
8.2 and 5.1 Hz, 2H, 3,8-H phen), 7.33−7.30 (m, 3H, para-H Ph),
7.26−7.21 (m, 6H, meta-H Ph), 7.17−7.12 (m, 6H, ortho-H Ph).
31P{1H} NMR (acetone-d6, 298 K; δ): 7.2 (s, 1P, PPh3).
Preparation of [{Re(phen)(CO)2(PPh3)}2CN](CF3SO3). [Re(phen)-
(CO)2(PPh3)(NCMe)](CF3SO3) (50 mg, 0.057 mmol) was
dissolved in acetone (5 mL) and treated with a solution of
K[Ag(CN)2] (6 mg, 0.029 mmol) in methanol (1 mL), causing an
immediate precipitation of AgCN. The suspension was stirred
overnight at room temperature in the absence of light. Then, the
solids were removed by filtration. Evaporation of the solvents
produced a bright red solid, which was recrystallized by a gas-phase
diffusion of diethyl ether into its acetone solution at 298 K to give red
crystalline material (29 mg, 65%). IR (CH2Cl2, ν(CO), cm−1): 1933s,
1865s. IR (KBr, ν(CN), cm−1): 2120m. 1H NMR (acetone-d6, 298 K;
δ): 8.54−8.48 (m, 6H, 2,9-H phen, 2,9-H phen′ and 4,7-H phen),
8.44 (d, JHH = 8.2 Hz, 2H, 4,7-H phen′), 8.09 (m, 2H, 5,6-H phen),
8.00 (m, 2H, 5,6-H phen′), 7.47 (dd, JHH = 8.2 and 5.1 Hz, 2H, 3,8-H
phen), 7.43 (dd, JHH = 8.2 and 5.1 Hz, 2H, 3,8-H phen′), 7.21−7.16
(m, 6H, para-H Ph and para-H Ph′), 7.10−7.06 (m, 12H, meta-H Ph
and meta-H Ph′), 6.98−6.93 (m, 6H, ortho-H Ph), 6.91−6.87 (m, 6H,
ortho-H Ph′). 31P{1H} NMR (acetone-d6, 298 K; δ): 31.3 (s, 1P,
PPh3), 26.6 (s, 1P, PPh3′). ESI+ MS (m/z): [M]+ 1396.21 (calcd
1396.21). Anal. Calcd for C66H46F3N5O7P2Re2S: C, 51.32; H, 3.00;
N, 4.53; S, 2.08. Found: C, 51.22; H, 3.27; N, 4.57; S, 2.15.
[{Re(phen)(CO)3}NCAu(PPh3)](CF3SO3) (4). A solution of [Au-
(PPh3)(CN)] (50 mg, 0.103 mmol) in dichloromethane (4 mL) was
added to a suspension of [Re(phen)(CO)3(H2O)](CF3SO3) (64 mg,
0.103 mmol) in dichloromethane (4 mL). The reaction mixture was
stirred at room temperature overnight in the absence of light. Then,
some precipitate was removed by filtration. Evaporation of the solvent
produced a yellow solid, which was recrystallized by a gas-phase
diffusion of diethyl ether into its ethanol/dichloromethane solution at
298 K to give green-yellow crystals (64 mg, 59%). IR (KBr, ν, cm−1):
(CN) 2183m; (CO) 2033s, 1935s. ESI+ MS (m/z): [M]+ 936.07
( c a l c d 9 3 6 . 0 7 ) , [ A u ( P P h 3 ) 2 ] + 7 2 1 . 1 5 , [ ( R e -
(CO)3 (phen))2 (NC)2 Au]+ 1148.99. Anal. Calcd for
C35H23AuF3N3O6PReS: C, 38.75; H, 2.14; N, 3.87; S, 2.96. Found:
C, 38.41; H, 2.36; N, 4.07; S, 2.89.
EXPERIMENTAL SECTION
■
General Comments. All manipulations were carried out under
aerobic conditions, except the synthesis of complex 9. Starting
materials from commercial sources were used as received. [Re(phen)-
(CO)3(H2O)](CF3SO3) and [Re(bpy)(CO)3(H2O)](CF3SO3) were
prepared in a manner similar to that used for the related
complexes39,40 by treating [Re(diimine)(CO)3Cl] with AgCF3SO3
in acetone.41 The resultant crude materials were recrystallized by a
gas-phase diffusion of diethyl ether into the solutions of titled
compounds in wet acetone to afford bright yellow crystalline
materials.42 [Re(phen)(CO)3(PPh3)](CF3SO3)43 was obtained by
treating [Re(phen)(CO)3(H2O)](CF3SO3) with PPh3 in refluxing
toluene under a nitrogen atmosphere. [Au(PPh3)(CN)]44 was
1
synthesized according to the reported procedures. The solution H
and 31P{1H} NMR spectra were recorded on a Bruker 400 MHz
Avance spectrometer. Mass spectra were determined on a LC/MS
hybrid ultrahigh resolution electrospray quadrupole time-of-flight
(UHR ESI-q-TOF) mass spectrometer Bruker MaXis 4G in the ESI+
mode. Infrared (IR) spectra were measured on a Bruker Vertex 70
spectrometer. Microanalyses were carried out at the analytical
laboratory of the University of Eastern Finland.
[{Re(bpy)(CO)3}2CN](CF3SO3) (1).5 Prepared by a modified
procedure. [Re(bpy)(CO)3(H2O)](CF3SO3) (50 mg, 0.084 mmol)
was dissolved in acetone (4 mL) and treated with a solution of
K[Ag(CN)2] (8.3 mg, 0.042 mmol) in methanol (1 mL), causing an
immediate precipitation of AgCN. The suspension was stirred
overnight in the absence of light. Then, the solids were removed by
filtration. Evaporation of the solvent produced a bright yellow-
greenish residue, which was recrystallized by a gas-phase diffusion of
diethyl ether into its acetone solution at 298 K to give yellow-greenish
crystalline material (32 mg, 74%). IR (CH2Cl2, ν(CO), cm−1): 2037s,
2027s, 1931s. IR (KBr, ν(CN), cm−1): 2151m. 1H NMR (acetone-d6,
298 K; δ): 8.91 (dd, JHH = 5.4 and 1.4 Hz, 2H, 2,9-H bpy), 8.85 (dd,
[{Re(bpy)(CO)3NC}2Au](CF3SO3) (5). [Re(bpy)(CO)3(H2O)]-
(CF3SO3) (50 mg, 0.084 mmol) and K[Au(CN)2] (12 mg, 0.040
mmol) were dissolved in a mixture of acetone (5 mL) and methanol
(1 mL), and the reaction mixture was stirred overnight at room
temperature in the absence of light. Evaporation of the solvents
produced a yellow solid, which was recrystallized by a gas-phase
diffusion of diethyl ether into its acetone/methanol solution at 298 K
to give light yellow crystalline material (42 mg, 81%). IR (CH2Cl2,
J
HH = 5.4 and 1.4 Hz, 2H, 2,9-H bpy′), 8.69 (d, JHH = 8.1 Hz, 2H, 5,6-
H bpy), 8.63 (d, JHH = 8.1 Hz, 2H, 5,6-H bpy′), 8.42 (m, 4H, 4,7-H
bpy and 4,7-H bpy′), 7.75 (m, 4H, 3,8-H bpy and 3,8-H bpy′). ESI+
MS (m/z): [M]+ 878.02 (calcd 878.02). Anal. Calcd for
C28H16F3N5O9Re2S: C, 32.72; H, 1.57; N, 6.81; S, 3.20. Found: C,
32.85; H, 1.73; N, 6.94; S, 3.27.
1
ν(CO), cm−1): 2035s, 1933s. IR (KBr, ν(CN), cm−1): 2183m. H
[{Re(phen)(CO)3}2CN](CF3SO3) (2). Prepared in a manner
analogous to that for 1 from [Re(phen)(CO)3(H2O)](CF3SO3)
(50 mg, 0.081 mmol) and K[Ag(CN)2] (8.2 mg, 0.041 mmol);
NMR (acetone-d6, 298 K; δ): 9.16 (dd, JHH = 5.4 and 1.4 Hz, 4H, 2,9-
H bpy), 8.81 (d, JHH = 8.1 Hz, 4H, 5,6-H bpy), 8.46 (td, JHH = 8.1
and 1.4 Hz, 4H, 4,7-H bpy), 7.90 (ddd, JHH = 8.1, 5.4, and 1.3 Hz,
B
DOI: 10.1021/acs.inorgchem.8b02974
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
4H, 3,8-H bpy). ESI+ MS (m/z): [M]+ 1100.99 (calcd 1100.99).
Anal. Calcd for C29H16AuF3N6O9Re2S: C, 27.84; H, 1.29; N, 6.72; S,
2.56. Found: C, 28.01; H, 1.42; N, 6.80; S, 2.61.
[{Re(phen)(CO)3NC}2Au](CF3SO3) (6). Prepared in a manner
analogous to that for 5 from [Re(phen)(CO)3(H2O)](CF3SO3) (50
mg, 0.081 mmol) and K[Au(CN)2] (12 mg, 0.041 mmol); yellow
crystalline material (38 mg, 72%). IR (CH2Cl2, ν(CO), cm−1): 2036s,
1934s. IR (KBr, ν(CN), cm−1): 2187m. 1H NMR (acetone-d6, 298 K;
The crystallization solvent in 2−4 and 6−10 was partially lost from
the crystal and could not be resolved unambiguously. The
contribution of the missing solvent to the calculated structure factors
was taken into account by using a SQUEEZE routine of PLATON.49
The missing solvent was not taken into account in the unit cell
content.
All hydrogen atoms in 2−10 were positioned geometrically and
constrained to ride on their parent atoms, with C−H = 0.95−0.99 Å
and Uiso = 1.2−1.5Ueq (parent atom). The crystallographic details are
summarized in Table S1. Selected structural parameters are listed in
Tables S2 and S3.
Photophysical Measurements. The photophysical measure-
ments were performed in dichloromethane and methanol solutions,
which were carefully deaerated by three “freeze−pump−thaw” cycles.
UV/vis absorption spectra were measured on a Shimadzu UV-1800
spectrophotometer; excitation and emission spectra in solution and in
the solid state were recorded with a HORIBA FluoroMax-4
spectrofluorometer. Lifetime and emission quantum yields in the
solid phase were performed on a HORIBA Scientific FluoroLog-3
spectrofluorometer. The uncertainty of the quantum yield measure-
ment was in the range of 5% (an average of three replications, which
correspond to different orientations of the sample). The emission
quantum yield in solutions was determined by the comparative
method using coumarin 102 in ethanol (Φr = 0.764)50 with refraction
indexes of dichloromethane and ethanol equal to 1.42 and 1.36,
respectively.
Electrochemical Studies. Electrochemical experiments were
performed at 298 1 K in a CH cell using a CH I660 potentiostat
(Cambria Scientific, Llwynhendy, Llanelli UK). A BAS MF2012 glassy
carbon working electrode (GCE) (geometrical area 0.071 cm2), a
platinum mesh auxiliary electrode and a platinum wire pseudorefer-
ence electrode were used in a conventional three-electrode arrange-
ment. Potentials are provided relative to the Fc/Fc+ couple, adding
ferrocene (Aldrich) as an internal standard during electrochemical
runs. The electrochemistry of complexes 9 and 10 in acetone
solutions (HPLC-grade, Carlo Erba reagents) containing 0.10 M
Bu4NPF6 (Fluka) as a supporting electrolyte was studied after
degassing by bubbling Ar for 10 min.
δ): 9.54 (dd, JHH = 5.1 and 1.3 Hz, 4H, 2,9-H phen), 9.05 (dd, JHH
=
8.3 and 1.3 Hz, 4H, 4,7-H phen), 8.38 (s, 4H, 5,6-H phen), 8.22 (dd,
JHH = 8.3 and 5.1 Hz, 4H, 3,8-H phen). ESI+ MS (m/z): [M]+
1148.99 (calcd 1148.99). Anal. Calcd for C33H16AuF3N6O9Re2S: C,
30.51; H, 1.24; N, 6.47; S, 2.47. Found: C, 30.69; H, 1.50; N, 6.56; S,
2.56.
[{Re(bpy)(CO)3NC}4Pt](CF3SO3)2 (7). Prepared in a manner
analogous to that for 5 from [Re(bpy)(CO)3(H2O)](CF3SO3) (50
mg, 0.084 mmol) and K2[Pt(CN)4] (8 mg, 0.021 mmol); yellow
crystalline material (39 mg, 81%). IR (CH2Cl2, ν(CO), cm−1): 2034s,
1932s. IR (KBr, ν(CN), cm−1): 2176m. 1H NMR (acetone-d6, 298 K;
δ): 9.06 (dd, JHH = 5.4 and 1.4 Hz, 8H, 2,9-H bpy), 8.81 (d, JHH = 8.1
Hz, 8H, 5,6-H bpy), 8.52 (td, JHH = 8.1 and 1.4 Hz, 8H, 4,7-H bpy),
8.02 (ddd, JHH = 8.1, 5.4, and 1.3 Hz, 8H, 3,8-H bpy). ESI+ MS (m/
z): [M]2+ 1002.00 (calcd 1002.00), [{Re(CO)3(bpy)}3(NC)3Pt-
(CN)]+ 1579.00. Anal. Calcd for C58H32F6N12O18PtRe4S2: C, 30.25;
H, 1.40; N, 7.30; S, 2.78. Found: C, 30.37; H, 1.52; N, 7.43; S, 2.95.
[{Re(phen)(CO)3NC}4Pt](CF3SO3)2 (8). Prepared in a manner
analogous to that for 5 from [Re(phen)(CO)3(H2O)](CF3SO3) (50
mg, 0.081 mmol) and K2[Pt(CN)4] (7.7 mg, 0.020 mmol); bright
yellow crystalline material (38 mg, 79%). IR (CH2Cl2, ν(CO), cm−1):
2034s, 1932s. IR (KBr, ν(CN) cm−1): 2178m. 1H NMR (acetone-d6,
298 K; δ): 9.39 (dd, JHH = 5.1 and 1.3 Hz, 8H, 2,9-H phen), 9.12 (dd,
JHH = 8.3 and 1.3 Hz, 8H, 4,7-H phen), 8.42 (s, 8H, 5,6-H phen), 8.34
(dd, JHH = 8.3 and 5.1 Hz, 8H, 3,8-H phen). ESI+ MS (m/z): [M]2+
1050.00 (calcd 1050.00), [(Re(CO)3(phen))3(NC)3Pt(CN)]+
1651.00. Anal. Calcd for C66H32F6N12O18PtRe4S2: C, 33.04; H,
1.34; N, 7.00; S, 2.67. Found: C, 33.27; H, 1.55; N, 7.11; S, 2.72.
[{Re(bpy)(CO)3NC}6Fe](CF3SO3)2 (9). [Re(bpy)(CO)3(H2O)]-
(CF3SO3) (50 mg, 0.084 mmol) was dissolved in acetone (7 mL),
and a suspension of K4[Fe(CN)6] (5 mg, 0.014 mmol) in methanol
(3 mL) was added. The mixture was stirred at room temperature for
12 h in the absence of light under nitrogen atmosphere to give a light-
brown solution. Evaporation of the solvents produced a brown oil,
which was recrystallized by a gas-phase diffusion of diethyl ether into
its acetone/methanol solution at 298 K to give brick-red crystalline
material (22 mg, 51%). IR (CH2Cl2, ν(CO), cm−1): 2021s, 1906s. IR
Solid-state experiments were performed at microparticulate films of
9 and 10 prepared by evaporation at air of a drop of an ethanolic
solution of the corresponding complex (1 mg/mL) deposited onto
the surface of a freshly polished GCE. 0.50 M NaCl aqueous solution
was used as a supporting electrolyte.
Computational Details. Compounds 1−10 were studied using
the hybrid PBE0 density functional method (DFT-PBE0).51,52 All
atoms were described by a triple-ζ-valence quality basis set with
polarization functions (def-TZVP).53 Multipole-accelerated resolu-
tion-of-the-identity technique was used to speed up the calcula-
tions.54,55 Point group symmetry was used to speed up the
calculations (1−4: Cs; 5, 6: C2h; 7, 8; C4h; 9, 10: S6). The used
symmetries are lower than the ideal symmetries observed in the NMR
experiments because the calculations at 0 K lack the rotational degrees
of freedom present at solution state. The geometries of all complexes
were first fully optimized within the applied point group using the
DFT-PBE0 method. The optimized geometries of the compounds are
in good agreement with the available X-ray structures (comparisons of
the structural parameters and the XYZ coordinates of the optimized
structures are included as Supporting Information, Table S4). The
excited states were investigated using the time-dependent DFT
formalism.56,57 The singlet excitations were determined at the
optimized ground-state S0 geometries, while the lowest energy triplet
emissions were determined at the optimized T1 geometry. In the case
of 4 and 7−10, the TD-DFT calculation of the T1 state could not be
converged due to numerical issues. The calculated excitation and
emission wavelengths are strongly red-shifted in comparison to the
experiment (Table S5), but the observed trends are reproduced well.
All electronic structure calculations were carried out with the
TURBOMOLE program package (version 7.3).58,59
1
(KBr, ν(CN) cm−1): 2089m. H NMR (acetone-d6, 298 K; δ): 8.84
(m, JHH = 5.4 Hz, 12H, 2,9-H bpy), 8.63 (m, JHH = 8.1 Hz, 12H, 5,6-
H bpy), 8.41 (m, 12H, 4,7-H bpy), 7.87 (m, 12H, 3,8-H bpy). ESI+
MS (m/z): [M]2+ 1385.00 (calcd 1385.00). Anal. Calcd for
C86H48F6FeN18O24Re6S2: C, 33.66; H, 1.58; N, 8.22; S, 2.10.
Found: C, 33.73; H, 1.62; N, 8.28; S, 2.14.
[{Re(bpy)(CO)3NC}6Fe](CF3SO3)3 (10). Prepared in a manner
analogous to that for 5 from [Re(bpy)(CO)3(H2O)](CF3SO3) (50
mg, 0.084 mmol) and K3[Fe(CN)6] (5 mg, 0.014 mmol); dark green
crystalline material (28 mg, 62%). IR (CH2Cl2, ν(CO), cm−1): 2028s,
1914s. IR (KBr, ν(CN), cm−1): 2154m. 1H NMR (acetone-d6, 298 K;
δ): 8.66 (d, JHH = 5.4 Hz, 12H, 2,9-H bpy), 8.40 (m, 2H, JHH = 8.1
Hz, 12H, 5,6-H bpy), 8.15 (m, 12H, 4,7-H bpy), 7.77 (m, 12H, 3,8-H
bpy). Anal. Calcd for C87H48F9FeN18O27Re6S3: C, 32.48; H, 1.50; N,
7.84; S, 2.99. Found: C, 32.71; H, 1.76; N, 7.87; S, 2.97.
X-ray Structure Determinations. The crystals of 2−10 were
immersed in cryo-oil, mounted in a Nylon loop, and measured at a
temperature of 150 K. The X-ray diffraction data were collected with
Bruker Kappa Apex II, Bruker Smart Apex II, and Bruker Kappa Apex
II Duo diffractometers using Mo Kα radiation (λ = 0.71073 Å). The
APEX245 program package was used for cell refinements and data
reductions. The structures were solved by direct methods using the
SHELXS-201446 program with the WinGX47 graphical user interface.
A numerical absorption correction (SADABS)48 was applied to all
data. Structural refinements were carried out using SHELXL-2014.46
Magnetic Susceptibility Measurements. Magnetic data for
compound 10 were recorded on a Quantum Design MPMS-5XL
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a
Scheme 1. Syntheses of Complexes 1−4
a
Reaction conditions: (i) acetone/methanol, room temperature, 12 h; (ii) toluene, 130°C, 16 h, N2; (iii) 351 nm pulsed laser, 2.5 h; (iv):
−
dichloromethane, room temperature, 12 h; counterion CF3SO3 .
a
Scheme 2. Syntheses of Complexes 5−10 ( )
a
−
Conditions: acetone/methanol, room temperature, 12 h; counterion CF3SO3 .
SQUID magnetometer. The polycrystalline sample was compacted
and immobilized into a cylindrical PTFE capsule. The data were
acquired as a function of the field (0.1−5.0 T) and temperature (2−
290 K) and were corrected for diamagnetic contributions of the
sample holder (PTFE capsule) and the compound 10 (χdia = −1.61×
10−3 cm3 mol−1).
The starting complexes [Re(diimine)(CO)3(H2O)]-
(CF3SO3) (diimine = 2,2′-bipyridine, bpy; 1,10-phenanthro-
line, phen) were readily prepared by the abstraction of Cl−
from the parent [Re(diimine)(CO)3Cl] compounds40 with
AgCF3SO3 in wet acetone. Subsequent treatment of the triflate
derivatives with 0.5 mol equiv of NaCN however results in a
mixture of products and gives the expected bridged species
[{Re(diimine)(CO)3}2CN)](CF3SO3) (diimine = bpy 1,5
phen 2) in small yields. Alternatively, reacting K[Ag(CN)2]
instead of sodium cyanide with 2 equiv of [Re(diimine)-
(CO)3(H2O)](CF3SO3) in acetone/methanol solution leads
to the formation of 1 and 2 as the dominant products (Scheme
1).
In order to vary the ligand environment of the dirhenium
motif in 2, the [Re(phen)(CO)3(H2O)](CF3SO3) precursor
was conventionally converted into the phosphine complex
[Re(phen)(CO)3PPh3](CF3SO3) in toluene at 130 °C.
Further photochemical substitution of the carbonyl group for
a labile acetonitrile ligand was achieved by employing a 351
RESULTS AND DISCUSSION
■
Synthesis and Characterization. The rhenium(I)
diimine complexes containing cyanide ligands are not excessive
and only a few polynuclear compounds built of the
cyanometalated units have been described.5,6,60 The available
reports though confirm the possibility of using the rigid −C
N− linker for the construction of multimetallic assemblies
containing Re(I) chromophore motifs. The ability of Re(I) ion
to bind both carbon and nitrogen atoms of the CN group
offers substantial synthetic flexibility and allows combining the
{Re(diimine)(CO)3} motif with a range of metal centers
irrespectively of their affinity to coordinating atoms of the
cyanide.
D
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nm pulsed laser (50 mW) under ambient conditions. This mild
protocol afforded an intermediate dicarbonyl compound
[Re(phen)(CO)2(PPh3)(NCMe)](CF3SO3)61 in good yield
(70%), but in contrast to commonly used high-pressure
mercury lamp irradiation62−64 does not require an inert
atmosphere and extensive cooling of the system. The
formation of the cyano-bridged dinuclear rhenium complex
[{Re(phen)(CO)2(PPh3)}2CN](CF3SO3) (3) was accom-
plished by means of similar to the synthesis of compound 2,
using K[Ag(CN)2] as a source of the cyanide linker (Scheme
1). The successful synthesis of 1−3, in which the [Re-
(diimine)(CO)3(CN)] unit may be considered as a neutral
metalloligand, prompted us to extend the methodology to the
heterometallic species. Indeed, the dinuclear rhenium(I)−
gold(I) complex [{Re(phen)(CO)3}NCAu(PPh3)](CF3SO3)
(4) was obtained by coupling the [Re(phen)(CO)3(H2O)]-
(CF3SO3) and [Au(PPh3)(CN)]44 constituents at room
temperature in the absence of light.
Moreover, decorating the anionic cyanometallates with
several cationic {Re(diimine)(CO)3}+ units has proven to be
a facile strategy to attain aggregates of higher nuclearity
(Scheme 2). Thus, the reaction of K[Au(CN)2] with
[Re(diimine)(CO)3(H2O)](CF3SO3) in 1:2 molar ratio
efficiently generated the trinuclear [{Re(diimine)-
(CO)3NC}2Au](CF3SO3) complexes (diimine = bpy 5, phen
6), though no congener compounds were observed in the case
of dicyanoargentate anion as described above (Scheme 1).
Pentametallic assemblies [{Re(diimine)(CO)3NC}4Pt]-
(CF3SO3)2 (diimine = bpy 7, phen 8) were constructed
from tetracyanoplatinate(II) dianion and 4 equiv of the
corresponding rhenium precursors. Finally, the heptanuclear
aggregates [{Re(bpy)(CO)3NC}6Fe](CF3SO3)n 9 (n = 2) and
10 (n = 3) were prepared by adding the {Re(diimine)(CO)3}+
blocks to ferro- and ferricyanide salts. The phen analogues of 9
and 10 were not observed presumably due to the steric
hindrance caused by the bulkier phenanthroline ligand. Further
physical data for each complex was provided through NMR
and IR spectroscopies, mass spectrometry, by elemental and X-
ray analysis, thus corroborating the attainment of the synthesis
of the homo- and heterometallic assemblies.
symmetrical structures depicted in Schemes 1 and 2. The
NMR data for complex 4 are compatible with ESI-MS result
and point to the existence of several species in solution (Figure
S6), which comprise compounds 4, 6, and [Au(PPh3)2]+; the
latter is also formed in the course of disproportionation
described for the parent [(PPh3)AuCN] complex.66
The IR spectra of all titled complexes in the CO stretching
region are very much alike and correspond to the
indistinguishable rhenium carbonyl motifs with rather minor
alterations of the vibrational frequencies. Compounds 9 and 10
with {Fe(CN)6}n− (n = 3 and 4) coordinating anion
demonstrate visibly lower energies of vibrations conceivably
due to a polyanionic character of the central motif that results
in enhanced π-back-donation dπ(Re) → π*(CO) and is
pronounced for the ferricyanide aggregate 9. In general, the
observed profiles are typical for other diimine di- (3) and
tricarbonyl (1, 2, and 4−10) rhenium species. In contrast, the
CN vibrations are sensitive to the nature of the central metal
atom M and vary from 2089 cm−1 (9, M = Fe2+) to 2187 cm−1
(6, M = Au+) that is comparable with the values found for
other cyanometallate-bridged species.67 Expectedly, the CN
frequencies for 9 and 10 differ substantially (2089 and 2154
cm−1) because of a higher π-basicity of the Fe2+ center.
The results of crystallographic analysis of 2−10 are shown in
Figures 1−3 and S7; Tables S2 and S3 contain selected bond
The ESI+ mass spectra of the studied complexes reveal the
dominating signals corresponding to singly (2−6) and doubly
(7−9) charged molecular ions, whose m/z values and isotopic
patterns are in complete agreement with the calculated ones
(Figure S1 and S2). In the case of 4, in addition to the
molecular cation (m/z [4]+ = 936.1) the signals of [Au-
(PPh3)2]+ and [(Re(CO)3(phen))2(NC)2Au]+, i.e., [6]+,
species are also observed, indicative of a reversible dissociation
and rearrangement of 4 in solution also confirmed by the
NMR spectroscopy (see below). The triply charged cation 10
Figure 1. Molecular views of complexes 2 and 3. Counter ions and
hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown
at the 50% probability level.
lengths and angles. In all complexes, rhenium ions are
hexacoordinated and adopt slightly distorted octahedral
environment, formed by the chelating diimine ligand, terminal
carbonyl (also phosphine in the case of 3) and the bridging
CN groups. The dirhenium compounds 2 and 3 belong to the
same structural type as 1, which was determined previously68
and comprises two {Re(diimine)} fragments linked by an axial
cyanide. In both complexes 2 and 3, the angles Re−NCN−CCN
and Re−CCN−NCN are in the range from 174.4 to 176.9°
(Table S2) that gives a nearly linear arrangement of the cyano-
bimetallic motif. Analogous to 1, phenanthroline congener 2
adopts the same eclipsed conformation with torsion angles
NNN−Re−Re−NNN of less than 3°. Introducing sterically and
electronically different PPh3 ligands in the axial positions in 3
was not detected evidently due to the reduction Fe3+
→
Fe2+that occurs under the conditions of ESI-MS experiment
and has been noted for other iron(III) compounds.65
The 1H NMR spectra of dirhenium compounds 1−3
demonstrate two similar sets of signals, which belong to the
nonequivalent {Re(diimine)} fragments (Figure S3). The
given patterns can be attributed to the electronic effect of a
nonsymmetrical cyanide bridge. In accordance with this
observation, two singlet resonances of 1:1 integral intensities
are found in the 31P NMR spectrum of 3. On the contrary, 5−
10 display 1H spectroscopic profiles, indicating that in solution
these compounds possess only one type of {Re(diimine)-
(CO)3} units (Figures S4 and S5) in compliance with idealized
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causes slight shortening of Re−CCN/NCN distances compared
to 2 and results in visible geometry distortions. The latter
involves the change of the NNN−Re−Re−NNN torsion to ca.
27° and an increase of the angle between the planes of the
phen ligands from 19° (2) to 23° (3).
Two independent molecules are found in the unit cell of
gold−rhenium complex 4, both having similar structural
parameters, which are not exceptional (Table S2). The
intermolecular Au···Au separation (3.509 Å) exceeds the sum
of van der Waals radii that implies no aurophilic interaction.
Though in solution 4 exists as a mixture of several species, its
crystallization gives phase pure material, which contains only
the bimetallic complex, shown in Figure 2, as confirmed by
PXRD analysis (Figure S8).
Figure 3. Molecular views of complexes 7 and 9. Counter ions and
hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown
at the 50% probability level.
Figure 2. Molecular views of complexes 4 and 6. Counter ions and
hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown
at the 50% probability level.
octahedral shape of the resultant heptanuclear species (Figures
3 and S7). The molecular symmetry of 9 and 10 in the crystals
is lower than that in solution, where all the pendant {Re(bpy)}
groups become indistinguishable. Nevertheless, the deviation
of the structural parameters among three crystallographically
inequivalent groups of metalloligands [Re(bpy)(CO)3NC] in
each of the complex are quite minor (Table S3) supporting
their easy symmetrization in the fluid medium. The change of
the oxidation state of the Fe ion (+2 in 9, +3 in 10) does not
have a significant impact on the molecular arrangement. For
example, the Fe−C bond lengths remain virtually unaffected
(average distances are 1.924 and 1.929 Å for 9 and 10), while
the Re−N contacts experience slight elongation in 10 (avg
2.135 Å vs 2.122 Å in 9) that might be attributed to the less
favorable electrostatics upon increase of the overall positive
charge. The structural data for 9 and 10 in general agree well
with those reported for the congener neutral molecule
[Re(dmb)(CO)3]3[Fe(CN)6] (dmb = 4,4′-dimethyl-2,2′-
bipyridine).6 The latter compound and its di/trinuclear
congeners represent virtually the only examples of cyanome-
tallate linkers furnished with {Re(diimine)} chromophores.
Moreover, complexes [M(CN)x][M′Ly]x (M = Pt, x = 4; Fe, x
Dicyanoaurate-bridged compounds 5 and 6 demonstrate
different molecular packings, which evidently determine their
solid-state molecular geometries (Figures 2 and S7). Thus, 5
has an eclipsed configuration, resembling that of 2, and a
substantial deviation of Re−NC−Au−CN−Re chain from
linearity (∠Re−Au−Re = 165.4°). Conversely, phenanthroline
complex 6 has a staggered conformation of {Re(phen)} units
and Re−Au−Re angle of 175.4°.
Both pentanuclear complexes 7 and 8 feature the expected
square-planar cyanoplatinate core, which holds four {Re-
(diimine)(CO)3} fragments (Figures 3 and S7). Their mutual
orientation is apparently defined by the steric requirements of
the diimine ligands, which determine the distortion of
structure 7 from the idealized square shape. The packings of
complexes 6−8 show non-negligible intermolecular π−π
stacking interactions between the diimine ligands of adjacent
molecules with interplanar distances of 3.60, 3.30, and 3.55 Å,
respectively (Figure S9).
The rhenium−iron assemblies 9 and 10 consist of the
central six-coordinated FeII and FeIII ions, respectively, which
are surrounded by six rhenium units giving nearly regular
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= 6) with all bridging cyanide ligands represent as a quite
limited class of molecular aggregates.69−72
Photophysical Properties. The electronic absorption
spectra of complexes 1, 2, and 5−8 (Figure 4 and Table 1)
from {Re(CO)3} fragment to the diimine ligand. Computa-
tional analysis confirms the proposed nature of the lowest
energy excitations S0 → S1 (Figures S10−S12), which also
involve cyanide groups in the case of 1 and 3. High molar
absorptivities of the charge transfer bands (350−370 nm, ε >
104 M−1 cm−1) indicate their certain mixing with IL character
and are also consistent with the presence of several
chromophores in the same molecular entity.76,77 In the case
of 3, the substitution of carbonyl groups in trans-position to
the cyanide bridge for triphenylphospine ligands results in a
considerable redshift of the longest wavelength absorption
band (λabs = 456 nm) compared to the tricarbonyl compounds.
This behavior is evidently related to a weaker π-accepting
ability of PPh3 with respect to carbonyl group that destabilizes
the dπ(Re) orbitals in 3 and, consequently, lowers the
HOMO−LUMO gap.62,76,78 Recently, even a more pro-
nounced decrease of the energy gap has been described for
[Re(deeb)(CO)2(PMe3)Cl] (deeb = 4,4′-diethylester-2,2′-
bipyridine) complex.79 Interestingly, in 1−3, the excited state
is predicted to engage the ReI blocks connected to the N atom
of the cyanide spacer (Figure S10).
The Re−Fe compounds display additional features which
are associated with iron hexacyanide motif. Thus, a relatively
weak band at ca. 480 nm, identified in the spectrum of 9 is not
80
observed for the individual components [Fe(CN)6]4− and
[Re(bpy)(CO)3CN].5 Therefore, it is likely to originate from
electronic transitions localized within the [FeII(CN)6]4−
coordinating anion perturbed by {Re(diimine)(CO)3} groups
and mixed with some FeII → bpy charge transfer (Figure S12).
Complex 10, which is derived from 9 via one-electron
oxidation of the iron center, exhibits a rather intense broad
near-infrared band at 846 nm (ε = 7 × 103 M−1 cm−1 in
methanol, Figure 4) that can be assigned to a MM′CT ReI →
6
FeIII transition by analogy with ReI−FeIII and the related
RuII−FeIII mixed-valence compounds.7,9 In line with the trend
observed for [ReI(dmb)(CO)3]n[FeIII(CN)6]n−3 (n = 1−3)
congeners, which absorb in methanol at 578, 610, and 649 nm,
respectively,6 increasing the number of peripheral {Re(bipy)}
fragments in aggregate 10 to n = 6 substantially decreases the
energy of the MM′CT band and simultaneously enhances the
molar absorptivity.
Figure 4. Electronic absorption spectra of complexes 1−3, 5−8
(CH2Cl2) and 9 and 10 (MeOH), 298 K.
are determined by the {Re(diimine)(CO)3} chromophores
and thus are reminiscent to those of a variety of previously
studied rhenium(I) compounds;5,40,73−75 the optical properties
of 4 were investigated only in the solid state due to the
aforementioned dissociation in solution. Analogously to the
earlier assignments, the intense high-energy absorption bands
in the region of 220−320 nm for the title compounds likely
correspond to the intraligand π−π* transitions. The lower
energy bands, which are centered around 350 nm with tails
extending up to 450 nm, are ascribed to the charge transfer
Complexes 1−8 display photoluminescence in solution and
in the solid state under ambient conditions; the relevant data
are provided in Tables 1 and 2. Re−Fe assemblies 9 and 10 are
not emissive as their lowest energy excited states are
dominated by the [Fe(CN)6]4−/3− fragments (see Figure
S12), which can accept higher energy excitation from the
Table 1. Photophysical Properties of Complexes 1−3 and 5−10 in Solution
a
b
c
d
λabs, nm (ε,·104 M−1 cm−1
)
λem (nm)
Φ (aer/deg) (%)
τobs (μs)
kr (s−1
)
knr (s−1
)
e
1
2
3
5
6
7
8
9
287 (4.6), 315 (2.4), 368 (1.0)
260 (8.8), 287 (4.4), 355 (1.2)
267 (9.8), 321 (2.5), 456 (1.2)
246 (8.4), 281 (4.7), 317 (2.9), 359 (1.1)
249 (9.6), 254 (9.5), 273 (7.7), 330 (1.6)
246 (10.3), 281 (9.0), 305 (5.7), 318 (5.1), 355 (1.8)
257 (12.5), 274 (12.5), 338 (2.2)
239 (17.6), 281 (14.0), 315 (8.8), 352 (3.1), 480 (0.4)
243 (15.0), 280 (11.9), 316 (8.0), 351 (2.8), 846 (0.7)
571 (515)
564 (515)
737 (606)
554 (504)
543 (505)
560 (519)
549 (516)
7/10
12/30
−/<1
11/19
15/48
10/21
12/42
0.4
1.6
0.023
0.6
1.9
2.5 × 105
1.9 × 105
2.2 × 106
4.4 × 105
3.2 × 105
2.5 × 105
4.2 × 105
1.9 × 105
1.4 × 106
2.7 × 105
1.6 × 106
2.6 × 105
0.5
2.2
10
a
b
c
d
e
Values in parentheses correspond to frozen solutions at 77 K. λex = 365 nm; kr = Φ/τobs. knr = kobs − kr = (1−Φ)/τobs. CH2Cl2 for 1−3 and 5−
8; methanol for 9 and 10.
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indicates fast energy transfer (diimine)Re → CN → Re-
(diimine) in these dirhenium systems.
Table 2. Solid-State Photophysical Properties of Complexes
1−8 at 298 K
The replacement of the bpy ligand (in 1, 5, and 7) for phen
(2, 6, and 8) in rhenium fragments conceivably alters the
energetics of MLCT and results in some hypsochromic shifts
of the emission maxima that has been noted earlier for other
[Re(diimine)(CO)3L] luminophores85−87 and qualitatively
reproduced computationally (Table S5). Furthermore, the
phosphorescence quenching of phenanthroline-based com-
pounds 2, 6, and 8 by molecular oxygen is higher than for the
bipyridyl-containing chromophores, because in the former case
the collisional quenching by O2 is evidently more effective due
to greater spatial accessibility of the phenanthroline aromatic
system and longer lifetime of the corresponding excited state.
In contrast, the cyanometallate bridges, [Au(CN)2]− and
[Pt(CN)4]2−, have a very small contribution into the frontier
molecular orbitals participating in the electronic transitions
and therefore show a negligible effect on the photophysical
properties of the studied multimetallic assemblies. The DFT
excited state density difference plots in Figure S11 clearly
illustrate that the orbitals of the Au atoms are not implicated at
all into the T1 → S0 emission of 5/6. Despite the calculation of
the T1 state for 7/8 did not converge, the S0 → S1 excitations
for these Re−Pt species involve only the rhenium fragments
(Figure S12), meaning that their lowest lying triplet states
likely are also localized on {Re(diimine)(CO)3} motifs. The
similarity of the emission characteristics for 5/6 and 7/8
supports this conclusion.
a
b
c
λem (nm)
Φ (%)
τ (μs)
kr (s−1
)
knr (s−1
)
1
2
3
4
5
6
7
8
523
528
637
534
522
562
547
19
22
2
25
31
3
1.0
2.5
0.1
2.4
1.0
0.6
0.5
1.5
1.9 × 105
8.8 × 104
2.0 × 105
1.0 × 105
3.1 × 105
5.0 × 105
2.8 × 105
1.3 × 105
8.1 × 105
3.1 × 105
9.8 × 106
3.1 × 105
6.9 × 105
1.2 × 106
1.7 × 106
5.4 × 105
14
19
549
a
b
c
λex = 340 nm. kr = Φ/τobs. knr = kobs − kr = (1 − Φ)/τobs
.
Re(bpy) fragments and then relax nonradiatively. In degassed
dichloromethane, complexes 1, 2, and 5−8 bearing tricarbonyl
rhenium motifs exhibit greenish to yellow photoemission
(Figure 5) with quantum yields ranging from 10% (1) to 48%
(6), which are systematically higher for phen-containing
compounds. The structureless profiles of the bands, their
wavelengths, and long lifetimes (τobs = 0.4−2.2 μs) are
compatible with the triplet nature of the emissive excited state
(3MLCT, where M actually represents the entire Re(CO)3
unit), which is typical for rhenium tricarbonyl species with bpy
and phen ligands.40,73,81,82 DFT calculations clearly support
the 3MLCT assignment (Figures S10−S12). In comparison to
the reported [Re(bpy)(CO)3CN]5,83,84 (λem = 591 nm in
CH2Cl2), the emissions of bpy-containing compounds 1 (λem
=
On the basis of the absorption data analysis, the emission of
complex 3, substituted with triphenylphosphine ligands, is
571 nm), 5 (λem = 554 nm), and 7 (λem = 560 nm) are found
at visibly shorter wavelengths and demonstrate longer observed
lifetimes. This eventually reflects the electronic effect of M−
CN → Re coordination in multimetallic species versus terminal
NC → Re bonding in the mononuclear predecessor.
expectedly redshifted in comparison to its predecessor 2 (λem
=
564 nm) and appears in the near-IR (NIR) region (λem = 737
nm, Figure 5). Such dramatic decrease in emission energy with
respect to 2 (Δν = 4162 cm−1) arises from introducing the less
π-acidic phosphine ligand instead of the carbonyl group that
In the case of complexes 1 and 2, which contain two
chemically nonequivalent {Re(diimine)(CO)3} fragments, i.e.,
C- and N-bound chromophores, we were not able to detect
dual emission under steady-state conditions. Using different
excitation wavelengths and monitoring the excitation spectra at
high and low energy sides of the emission bands produced
identical spectroscopic profiles (Figure S13). The lifetime
measurements at 500 and 680 nm gave virtually the same
values of τobs for each complex 1 and 2 (within an experimental
error) and confirmed the monoexponential decay. This
surveillance likely suggests that there is one emissive excited
state, which is localized on the N-coordinated rhenium
fragment according to the DTF analysis (Figure S10) and
eventually rises the energy of the ground state.79
A
substantially shorter observed lifetime for 3 (τobs = 23 ns)
results from much lower quantum efficiency (Φem < 1%) that is
a natural consequence of the “energy gap law”.88 The cases of
fast nonradiative relaxation were described for some other
dicarbonyl Re(I) compounds having axial substituents with a
weak ligand field.62,79 Although 3 shows low quantum yield in
solution of less than 1%, it illustrates that NIR phosphor-
escence, which is still rare among rhenium(I) diimine
species,82,89−91 can be achieved without demanding mod-
ification of the diimine fragment but through adjusting the
Figure 5. Normalized excitation (dotted lines) and emission spectra of complexes 1−3 and 5−8 in dichloromethane solution (solid lines); dashed
lines correspond to solid-state emission at 298 K.
H
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energy of the d orbitals via modification of the electronic
properties of the ancillary ligands. The given trend in energies
is also reproduced theoretically (Table S5), though the
predicted wavelengths for 1−3 are visibly underestimated.
These spectroscopic features contrast with luminescence
characteristics of diisocyanide-linked congeners [{Re(phen)-
that is increased progressively and likely indicates the chemical
oxidation of FeII leading to the degradation of 9. These features
can be interpreted on assuming that there are differences
between the coordinative arrangement of the hexacyanoferrate-
(II/III) centers in complexes 9 and 10 in solution, possibly
involving some dissociation of the pendant {Re(bpy)}
fragments and solvent interaction101 in the case of complex 9.
The voltammetry of microparticulate films of both
complexes are essentially very similar in the solid state after
one or two potential cycles. As can be seen in Figure S16, in
contact with air-saturated 0.50 M NaCl a one-electron
reversible couple is recorded at +0.71 V vs Ag/AgCl in both
cases with no apparent interaction with dissolved oxygen,
which displays a cathodic wave at −0.60 V. This signal can be
interpreted in the light of our previous studies on some Fc-
functionalized complexes,98,99 on the assumption that
assemblies 9 and 10 display solid-state electrochemical
reduction/oxidation processes involving the insertion/dein-
(CO)2(PPh3)}2(CN−R−NC)]2+ (λem = 564−566 nm, Φem
=
13−17%)76 pointing to the crucial role of electron density on
the rhenium atoms, modulated by the bridging unit. In frozen
solution at 77 K, the emission bands for all compounds 1−3
and 5−8 demonstrate substantial blue shift with respect to the
values obtained at 298 K (Table 1 and Figure S14); the
energies for tricarbonyl complexes become nearly identical.
Such rigidochromic effect is often encountered for rhenium
3
diimine luminophores with MLCT excited state, which can
get destabilized in a rigid environment.92−94
The difference between the solution and the solid-state
emissions at 298 K gradually diminishes with the growth of the
number of {Re(diimine)} fragments and becomes virtually
negligible for Re−Pt complexes 7 and 8 (Figure 5, Table 2),
which probably reflects an increasing intramolecular rigidity
due to steric confinements. Otherwise, the emission profiles,
lifetimes, and the radiative rate constants obtained for the
crystalline samples are very close to those found in solution,
meaning that in both phases the emissive excited state has the
same origin, i.e., predominantly 3MLCT, and very similar
environment properties.
Heterometallic Re−Au complex 4, which was investigated in
the crystalline form only, features green luminescence band of
moderate intensity (Φem = 25%) maximized at 534 nm (Figure
S15). The photophysical parameters for 2 and 4 are nearly the
same, including the identity of their excitation spectra 4
(Figure S15). These experimental data are in line with DFT
results (Figure S10) and suggest no appreciable contribution of
phosphino-gold cyanide motif to the observed emission of 4,
which originates exclusively from the {Re(phen)} fragment,
similarly to other rhenium(I)−gold(I) phosphine com-
plexes.74,95
−
sertion of CF3SO3 ions:
[Re(CO)3(bpy)]6[Fe(CN)6][CFSO3]3 (solid) + e−
3
→ [Re(CO)3(bipy)]6[Fe(CN)6][CFSO3]2 (solid)
3
+ CFSO3− (aqueous)
3
The relevant point to emphasize is that the overall reaction
proceeds reversibly and virtually the same way for complexes 9
and 10 thus denoting that there are no substantial coordinative
differences between them in the solid state.
The hexacyanoferrate(II/III) compounds are known to
contain low-spin FeII/III ions. To confirm that coordination of
{Re(bpy)} fragments did not change substantially the ligand
field strength and retained the spin state of the central ion, the
magnetic data for compound 10 were measured and are
presented in Figure S17A as χmT versus T curve at 0.1 T and as
Mm versus B curve at 2.0 K. The χmT curve reaches a value at
290 K of 0.794 cm3 K mol−1, which is typical for low-spin FeIII
2
centers due to the T2g ground term that generates distinct
contributions from orbital momentum. Thus, χmT is
considerably larger than the spin-only contribution of a S =
1/2 system (0.375 cm3 K mol−1 assuming g = 2.0). The purity
of complex 10 with respect to ferro- or ferrimagnetic impurities
has been checked by measurements at different magnetic
fields; the corresponding χmT versus T curve at 0.1−3.0 T is
illustrated in Figure S17B. Since we do not observe any notable
divergence of the χmT curves at T > 200 K, potential impurities
can be excluded. By lowering the temperature, χmT
continuously decreases to a minimum at 2.0 K and reaches a
value of 0.385 cm3 K mol−1, which is close to the expected
value for a S = 1/2 single ion. The magnetization curve at 2.0 K
shows a magnetization of Mm ≈ 0.9 NAμB at 5.0 T. Although
Mm is not saturated, the slope of Mm hints at a saturation value
of ca. 1 NA μB indicating a ground state of S = 1/2 derived
from the equation Mm,sat = gSNAμB.
Electrochemical and Magnetic Properties of 9 and
10. The electrochemical response of complexes 9 and 10,
containing redox active iron centers, has been studied in
acetone solution and in the solid state in contact with aqueous
electrolytes in order to provide complementary electro-
chemical information, using the voltammetry of microparticles
methodology96,97 previously employed for characterizing a
series of polymetallic compounds.98,99
The cyclic voltammograms of 9 and 10 in acetone solution
(Figure S16) show that in both cases a quasi-reversible one-
electron couple (as judged by the cathodic-to-anodic peak
potential separation approaching 60 mV at low scan rates) was
recorded at potentials near to that of the Fc/Fc+ couple
accompanied by a prominent irreversible oxidation process at
ca. +1.0 V. The latter process can be attributed to the oxidation
of ReI ions, while the reversible couple is assigned to the
oxidation/reduction of the hexacyanoferrate(II/III) groups
that correlates with the literature data.5,6,79,100 Remarkably, the
formal electrode potential (calculated as the half-sum of the
cathodic and anodic peak potentials) of complex 9 (−0.050 V
vs Fc/Fc+) differs significantly from that of complex 10
(−0.280 V vs Fc+/Fc), as shownn in Figure S16. No changes in
the voltammetric response of 10 were detected upon aeration
of its solution, whereas under the exposure to air 9 gives rise to
an additional reversible couple centered at +0.230 vs Fc/Fc+
CONCLUSIONS
■
We described the supramolecular construction of a series of
homo- and heterometallic complexes composed of rhenium(I)
diimine tricarbonyl chromophores along with linking cyanide
(1−4) and cyanometallate (5−10) anions. The polydentate
nature of the central fragments [M(CN)x]n− allows to vary the
nuclearity of the target assemblies and therefore the decoration
of [Au(CN)2]−, [Pt(CN)4]2−, and [Fe(CN)6]3−/4− motifs with
I
DOI: 10.1021/acs.inorgchem.8b02974
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Notes
{Re(diimine)} blocks affords tri- (5, 6), penta- (7, 8), and
heptametallic (9, 10) species, respectively. The spectroscopic
investigations of 1−8 reveal that their optical properties are
governed by the rhenium(I) constituents with negligible
contribution of the heterometals into the lowest lying excited
state. The luminescence of complexes 1−8 is associated with
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research has been supported by grant of the Russian
Science Foundation (16-13-10064, E.V.G., spectroscopic and
photophysical studies) and the Finnish National Agency for
Education (CIMO fellowship to K.S.K., synthesis and
structural characterization). The work was performed using
the equipment of the Analytical Centre for Nano- and
Biotechnologies (Peter the Great St Petersburg Polytechnic
University with financial support from the Ministry of
Education and Science of Russian Federation); Centers for
Magnetic Resonance, for Optical and Laser Materials Research,
for Chemical Analysis and Materials Research, Research Park
of St. Petersburg State University. We thank Dr. Jan van
3
electronic transitions predominantly of MLCT character; the
assignment is supported by theoretical analysis. In solution, the
yellow emission of bpy-containing compounds 1, 5, and 7 (λem
= 554−571 nm) is systematically red-shifted with respect to
phen congeners 2, 6, and 8 (λem = 543−564 nm), which also
demonstrate higher intensity with maximum quantum yield of
48% (Re−Au complex 6) and a more pronounced quenching
by molecular oxygen. In contrast, axially PPh3-substituted
dirhenium compound 3 shows NIR phosphorescence (λem
=
737 nm) that is attributed to the destabilizing effect of the
phosphine ligand on the d orbitals of the metal. The lack of
luminescence in the case of heptanuclear Re−Fe aggregates 9
and 10 is related to the active role of [Fe(CN)6]4−/3−
polyanions in the lowest lying excited state. In particular, the
presence of FeIII center induces intermetallic ReI → FeIII
charge transfer that results in the intense NIR absorption
(λabs = 846 nm, ε = 7 × 103 M−1 cm−1). The electrochemical
behavior of these compounds shows essentially irreversible
oxidation of the ReI ions that is accompanied by a quasi-
reversible one-electron redox process of the
[FeII/III(CN)6]4−/3− groups. The magnetic susceptibility
measurement of 10 confirms the low-spin configuration of
the iron(III), which is retained upon binding to the
rhenium(I) fragments. Overall, the titled cyano-bridged
aggregates illustrate a simple but efficient synthetic approach
to discrete supramolecular coordination complexes with
versatile physical properties.
Leusen (Institut fur Anorganische Chemie, RWTH Aachen
̈
University) for helpful discussions and suggestions.
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Accession Codes
CCDC 1873812−1873820 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail: igor.koshevoy@uef.fi (I.O.K.).
*E-mail: antti.karttunen@aalto.fi (A.J.K.).
ORCID
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