Construction of copper chains with new fluorescent guanidino-functionalized naphthyridine ligands

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Construction of copper chains with new

ﬂuorescent guanidino-functionalized

naphthyridine ligands†

Cite this: DOI: 10.1039/c6dt03166h

Christoph Krämer, Simone Leingang, Olaf Hübner, Elisabeth Kaifer,

Hubert Wadepohl and Hans-Jörg Himmel*

The three new blue-ﬂuorescent ligands 2,7-bis(tetramethylguanidino)-1,8-naphthyridine (1), 2,7-bis(N,N’-

dimethylethylene-guanidino)-1,8-naphthyridine (2) and 2,7-bis(N,N’-diisopropylguanidino)-1,8-naphthyri-

dine (3) are synthesized, and their optical properties (electronic absorption and emission spectroscopy)

studied. Reactions of 1 or 2 with [Cu(CH

3

CN)

4

]BF

4

yield the Cu

4

chain compounds [Cu

4 2 4 4

(1) ](BF )

(

that crystallizes as [Cu (1) (CH CN) ](BF ·2CH

4

2

3

2

4

)

4

2

Cl

2

) and [Cu

4

(2) ](BF

2

)

4

. The variations of the optical pro-

perties upon coordination are evaluated, and the electronic transitions identiﬁed by time-dependent DFT

TD-DFT) calculations. Then the redox properties of the new Cu chain complexes are studied. In the

course of these experiments, the new Cu complex [Cu (1) (CuCl

ordinate to the Cu₄chain in [Cu (1) ] , was fully characterized. In addition, the Cu₃chain complexes

(

4

2

+

−

6

4

2

)

2

]

, in which two CuCl

2

units co-

4

+

Received 9th August 2016,

Accepted 26th September 2016

4

2

3+

3

[Cu (1)

3

]

3

and [Cu (1)

2

]

were isolated as products of redox-induced degradation processes. Finally, we

4+

DOI: 10.1039/c6dt03166h

show by quantum chemical calculations that in [M

(1)

4 2

]

complexes (M = coinage metal), the HOMO

www.rsc.org/dalton

changes from a ligand-centered to a metal-centered orbital for replacement of M = Cu by Au.

Introduction

The design of new multidentate ligands that trigger metal

atoms to assemble in 1D chains is of high interest. Such 1D

chains exhibit interesting electronic properties and, in the

case of metals with unpaired electrons, magnetic properties.

In addition to several infinite metal chains, such as

1

Krogmann’s salt K [Pt(CN) ]Br ·3H O, or mixed-valent

2

4

0.3

2

,3

Pt complexes with dithiocarboxylato ligands (“MMX chains”),

which fascinate due to their high electrical conductivity, a

number of oligomeric metal chains have been synthesized.

Scheme 1 (a) The ligand bis(diphenylphosphanylmethyl)phenyl-

The combination of the special electronic structure and the phosphane (dpmp) used for the synthesis of tri- and hexanuclear chain

generally low coordination number of the metals in the chains complexes. (b) The tetraphosphine ligand dpmppm (meso-bis[(diphenyl-

phosphinomethyl)-phenylphosphino]-methane), used for the synthesis

makes these compounds attractive for photo-catalytic appli-

8

of a Pd chain. (c) The ligand pmf (anion of N,N’-bis(pyrimidyl-2-yl)

cations. For the directed synthesis of such metal chain com-

plexes, a careful ligand design is required. For example, Pt

4

formamidine) used to construct Cu chains.

3

and Pt Pd chain complexes of the bis(diphenylphosphanyl-

2

4

methyl)phenylphosphane ligand (dpmp, see Scheme 1a) were

5

chain complexes. Using the tetraphosphine (meso-bis[(diphenyl-

phosphinomethyl)-phenylphosphino]-methane (dpmppm), see

6 2 2 2

linked to redoxactive hexanuclear Pt respectively Pt Pd Pt

4

+

Scheme 1b), Pd₈chain complexes [Pd (dpmppm) ]

[Pd (dpmppm) L ]

8 4 2

and

8

4

+

Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg,

Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.

(L = 2,6-xylyl isocyanide, acetonitrile or

6

N,N-dimethylformamide (dmf)) were synthesized.

The

E-mail: hans-jorg.himmel@aci.uni-heidelberg.de; http://www.uni-heidelberg.de/

fakultaeten/chemgeo/aci/himmel; Fax: +49-6221-545707

−

complex [Cu (pmf) (SCN) ] (where pmf is the anion of N,N′-

4

3

2

bis(pyrimidyl-2-yl)formamidine, see Scheme 1c) is the first

†

Electronic supplementary information (ESI) available. CCDC 1498071–1498080.

For ESI and crystallographic data in CIF or other electronic format see DOI:

0.1039/c6dt03166h

I 7

example for a Cu chain featuring exclusively Cu . Using the

4

II

2+

1

same ligand, the linear trinuclear Cu complex [Cu (pmf) ]

3 4

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(

ref. 8 and 9) and the mixed-valence complex [Cu

4

(pmf)

4 2

X ]

9

(X = Cl or Br) were obtained. An early example of a Cu chain

3

with very short Cu⋯Cu distances (2.348(2) and 2.358(2) Å) is

the complex [Cu(p-tolyl-N,N,N,N,N-p-tolyl)] , in which all three

copper atoms are trigonal-planar coordinated.

Naphthyridine ligands were also used in the past decades

3

1

0

Scheme 3 Lewis structures of the new ﬂuorescent guanidino-substi-

tuted aromatic compounds 2,7-bis(tetramethylguanidino)-1,8-naphthyr-

to assemble metal atoms to chains. Using naphthyridine and idine (1), 2,7-bis(N,N’-dimethylethylene-guanidino)-1,8-naphthyridine

I

(

2) and 2,7-bis(N,N’-diisopropylguanidino)-1,8-naphthyridine (3).

derivatives, dinuclear Cu (ref. 11) and mixed-valence copper

1

2

complexes have been synthesized (see Scheme 2a). Already

such dinuclear complexes show interesting chemical pro-

perties. Very recently, bis(5,7-dimethyl-1,8-naphthyridine-2-yl) connected by nitrogen atoms (see Scheme 2b for two

I

18

amine was used to synthesize dinuclear Cu complexes which examples).

catalyze the azide–alkyne cycloaddition reaction (“click” reac-

Recently we reported on fluorescent 2,3-bis(guanidino)

tion). The complex [Cu (napy)(PPh ) I ] (see Scheme 2a), phenazine and 2,3,7,8-tetrakis(guanidino)phenazine com-

13

2

3 2 2

1

9

with a Cu⋯Cu distance of 2.6123(5) Å, shows red phosphor- pounds. The substitution of the phenazine system with gua-

1

4

escence at room temperature in the solid state. Special 1,8- nidino groups increases the Lewis basicity of the ligand and

naphthyridine derivatives were synthesized and used as enhances fluorescence, as also shown for fluorescent guani-

II 15

20

fluorescent sensors for transition metals including Cu .

dine–pyridine and guanidine–quinoline hybrid ligands.

II

Moreover, pentanuclear Cu chains stabilized by a hexadentate Herein we report the synthesis of the three new naphthyridine

N-donor ligand containing a 1,8-naphthyridine building block, derivatives 1, 2 and 3 (see Scheme 3), that are intensely yellow-

show dynamic rearrangement of the copper ions triggered by colored compounds showing blue fluorescence. Their coordi-

coordination and elimination of halide ions.

nation chemistry will be discussed, and it will be shown that

Dinuclear nickel complexes with 1,8-naphthyridine (napy) compounds 1 and 2 are suitable for the preparation of tetra-

1

6

+

II

ligands of the formula [Ni

2

(napy)

4

X

2

] , that resemble Cu

nuclear copper complexes, in which the four copper atoms are

acetate in their structure, were already synthesized in 1973 and arranged in a chain and exhibit a low coordination number.

1

7

the Ni⋯Ni bonding intensively studied.

More recently, In such complexes, ligands that promote light-induced metal–

mixed-valence) nickel chains (with up to 11 nickel atoms in a ligand charge transfer are interesting for applications in the

(

4

+

4 2

row, in [Ni11(tentra) Cl

] ) were synthesized by use of field of photo-redox catalysis. To provide a basis for future

extended ligand systems, in which naphthyridine units are research in this area, the optical properties and the redox

chemistry of these compounds are evaluated, and the experi-

mental results are accompanied by quantum chemical

calculations.

Results and discussion

We first discuss the synthesis and properties of the free

ligands, before turning to the copper chain complexes and

their chemistry.

Ligand synthesis and characterization

The new ligands 1 and 2 featuring per-alkylated guanidino

groups are obtained by reaction of 2-chloro-1,1′,3,3′-tetra-

methylformamidium chloride respectively 2-chloro-1,3,-

dimethylimidazolidinium chloride with 2,7-diamino-1,8-

naphthyridine, followed by deprotonation with NaOH.

Compound 3 with partially alkylated guanidino groups is syn-

thesized by reacting di(isopropyl)carbodiimide with 2,7-

diamino-1,8-naphthyridine in the presence of sub-stoichio-

metric amounts of AlClMe (see Scheme 4), following the pre-

2

viously reported protocols for the guanidinylation of aromatic

2

1

amines. Compounds 1 and 2 are obtained in pure form, but

elemental analysis shows that 3 contains some trace impurities

that are not completely removed (see Experimental details).

Scheme 2 (a) Three dinuclear copper complexes with naphthyridine

3

Crystals of 1 and 2 are obtained from CH CN solution at room

ligands. (b) Two ligand systems with naphthyridine units used for the

construction of Ni

5

, Ni

7

, Ni

9

, and Ni11 chains.

temperature, and the molecular structures of both compounds

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With 1.312(2)/1.316(2) Å for 1 and 1.314(2)/1.300(2) Å for 2, the

two imino NvC bond lengths within the guanidino groups

fall into a typical region. Due to the σ- and π-contributions to

2

the metal–guanidine bonding in complexes, these distances

are expected to increase significantly upon coordination. The

small C–N–C angles (C1–N3–C9 and C7–N6–C14) at the imino

N atoms and the conformation of the guanidino groups seem

at first glance to be unfavorable for metal coordination with

both the imino N atom and the N atom of the naphthyridine

ring system. However, facile rotation around the C1–N3 and

C7–N6 bonds, as confirmed by NMR spectroscopy, allows the

ligands to adopt a more favorable conformation upon co-

ordination (see below).

The UV/Vis spectra of the three new compounds in CH CN

3

solution are compared in Fig. 2a. Intense bands appear at 235,

2

64 (with a shoulder at 290) and 373 nm for 1. The bands at

35, 264 and 290 nm are in good accordance with the pub-

lished absorption maxima for unsubstituted 1,8-naphthyri-

2

3

dine. Hence, the band at 373 nm can be assigned to a tran-

sition involving the guanidino groups. This low energy tran-

sition is further red-shifted to 381 nm for 2 and 399 nm for 3

Scheme 4 Synthesis of the new 2,7-bisguanidino-1,8-naphthyridine

derivatives 1, 2 and 3 starting with 2,7-diamino-1,8-naphthyridine.

(

see ESI, Fig. S3,† for UV/Vis spectra in Et

showing complex vibrational fine structures).

To achieve an understanding of the observed transitions,

2

O solutions,

are visualized in Fig. 1a and b. Compound 3 crystallizes only the electronic excitations of 1 and 3 are calculated by time-

in its di-protonated form under similar conditions (see dependent density functional theory (TD-DFT), relying on the

Fig. 1c). Crystals of 3 are obtained from toluene solution, but B3LYP functional and the def2-SV(P) basis set. The calculated

are unfortunately not suitable for X-ray diﬀraction analysis. spectra are displayed in Fig. 3a. Compound 1 has a low-lying

2 2

Fig. 1 Molecular structures of (a) 1, (b) 2, and (c) (3H )Cl . Vibrational ellipsoids drawn at the 50% probability level. Hydrogen atoms omitted.

Selected bond distances (in Å) and angles (in °): for 1: N1–C1 1.3339(15), N1–C8 1.3654(15), N2–C7 1.3312(15), N2–C8 1.3654(14), N3–C1 1.3852(15),

N3–C9 1.3121(16), N4–C9 1.3765(16), N5–C9 1.3653(15), N6–C7 1.3881(15), N6–C14 1.3163(15), N7–C14 1.3741(15), N8–C14 1.3652(15). For 2: N1–

C1 1.3364(18), N1–C8 1.3647(18), N2–C7 1.3349(18), N2–C8 1.3683(18), N3–C1 1.3705(18), N3–C9 1.3138(18), N4–C9 1.3557(19), N5–C9 1.3636(19),

N6–C7 1.3806(19), N6–C14 1.3004(19), N7–C14 1.361(2), N8–C14 1.352(2). For (3H

.328(3), N4–C1 1.317(3), N4–C5 1.365(2), N3⋯N4 2.644(3), N3–H⋯N4 1.837.

2

)Cl

2

: N1–C1 1.406(3), N1–C6 1.366(3), N2–C6 1.333(3), N3–C6

1

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Fig. 3 (a) Theoretical UV/Vis spectrum from TD-DFT calculations

(B3LYP/def2-SV(P)) for 1 and 3. Data was ﬁtted as Gaussian curve with a

Fig. 2 (a) UV/Vis absorption spectra of the new ligands 1 (c = 2.0 ×

half-width of 20 nm. (b) Visualization of the isodensity surfaces for

HOMO and LUMO of 1 (left) and 3 (right).

−5

1

0

M), 2 (c = 1.7 × 10 M) and 3 (c = 2.0 × 10 M) in CH

3

CN solution.

(

2

b) Normalized emission spectra of compounds 1 (λex = 373 nm, c =

−5

.0 × 10 M), 2 (λex = 381 nm, c = 1.7 × 10 M) and 3 (λex = 399 nm, c =

−5

3

.0 × 10 M) in CH CN.

pounds, the maximum of fluorescence is reached at

4

00–430 nm (blue emission), with moderate solvent shifts.

strong transition at 321 nm and further strong transitions at Table 1 summarizes the wavelengths of the emission maxima

39 and 227 nm. For compound 3, the transitions are and the fluorescence quantum yields. The highest quantum

red-shifted with respect to 1, the strong lowest-lying transition yields are measured for compounds 2 and 3 in CH OH solu-

is located at 363 nm and further transitions located at 280 and tion (0.26 and 0.27, respectively). For comparison, the fluo-

54 nm. The lowest-lying transitions of the two substances rescence quantum yield of unsubstituted 1,8-naphthyridine is

diﬀer from the experimental band maxima of 373 nm (1) and determined to be 0.04 ± 0.02 (in THF) relative to benzo-

2

3

2

24

3

99 nm (3) by 52 and 36 nm, but the shift between the two phenone. Hence, substitution of 1,8-naphthyridine with guani-

compounds is found to be qualitatively correct. These tran- dino groups greatly enhances the fluorescence quantum yield.

sitions are HOMO → LUMO transitions, the corresponding

Finally, the redox properties of the new compounds 1, 2

orbitals are shown in Fig. 3b.

and 3 are accessed by CV measurements in CH CN solutions.

3

For 3, the experimental UV/Vis spectrum shows two pro- The CV curves (see Fig. S5–S7 in the ESI†) reveal that the three

nounced maxima (399 and 379 nm), which in principle could ligands can be oxidized at relatively low potentials, but the

be due to diﬀerent electronic transitions. However, according redox-processes are not reversible. For 1, the measured curve

to the calculations, there is only a single electronic excitation contains two oxidation waves centered at +0.38 and +0.67 V vs.

+

in this region. Therefore, the structure resolved in the observed Fc/Fc (Fc = ferrocene). The CV curve of 2 shows oxidation

+

spectra has to be assigned to a vibrational fine structure.

waves at +0.23 and +0.63 V vs. Fc/Fc , and that of 3 at +0.38

+

All compounds emit blue light when irradiated with a UV and +0.73 V vs. Fc/Fc . Hence, in line with results on guani-

2

5

lamp. The fluorescence spectra in CH

3

CN solutions are repro- dino-functionalized aromatic compounds (GFAs),

substi-

duced in Fig. 2b (see ESI† for more spectra). For all three com- tution with N,N′-dimethylethylene-guanidino groups leads to a

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Table 1 Comparison of absorption and emission wavelengths (in nm), stokes shift (in cm⁻¹) and quantum yield Φ for ligands 1, 2, 3 and complexes

Cu (1) ](BF and [Cu (2) ](BF

[

4

2

4

)

4

2

4 4

)

Compound

Solvent

MeOH

λ

max, abs

λ

max, em

Stokes shift

Φ

1

228, 260, 378

235, 264, 373

404

401

410

429

402

446

442

1703

2057

1289

1309

1120

672

1690

187

2641

2067

0.17 ± 0.03

0.11 ± 0.02

0.26 ± 0.02

0.18 ± 0.02

CH

MeOH

CH CN

MeOH

3

CN

2

3

210, 233, 249, 260, 384

215, 267, 381

257, 294, 378, 392

261, 298, 379, 389, 399

252, 296, 379, 389, 400

262, 299, 358, 368, 377, 386, 399

208, 384, 399

3

0.27 ± 0.03

a

CH

3

CN

Cl

a

2

Et O

[

Cu

4

(1)

(2)

2

](BF

4

)

4

CH

3

CN

0.15 ± 0.02

0.08 ± 0.02

4

2

4

3

208, 267, 385, 405

a

Not determined.

1

stronger electron donor than substitution with tetramethyl- (see Introduction, Scheme 2a) is slightly longer (2.506(2) Å).

guanidino groups. As previous experiments with the GFAs The two copper atoms at both ends of the chain are only co-

showed, substitution of aromatic compounds with guanidino ordinated to two ligand imino nitrogen atoms (with Cu–N dis-

groups increases the HOMO energy and decreases the HOMO– tances of 1.865(2) Å). The inner two copper atoms are co-

LUMO gap. This is also the case for naphthyridine and its ordinated to two naphthyridine nitrogen atoms, giving rise to

guanidino substituted derivatives presented in this work. slightly longer Cu–N distances (1.997(2) and 2.001(2) Å), and

According to B3LYP/def2-SV(P) calculations, the HOMO energy in addition to two CH

increases from −6.74 eV for unsubstituted naphthyridine to As expected, coordination leads to an increase of the imino

5.33 eV for 1, while the HOMO–LUMO gap is lowered from NvC bond distances from 1.312(2)/1.316(2) Å in free 1 to

.83 eV for unsubstituted naphthyridine to 4.36 eV for 1. 1.376(2)/1.374(2) Å in [Cu (1) (CH CN) ](BF ·2CH Cl , while

3

CN solvent molecules.

−

4

2

3

2

4

)

4

2

all other N–C bond lengths involving the guanidino nitrogen

atoms decrease. The increase of the imino NvC bond dis-

Copper coordination

Reaction of 1 with [Cu(CH CN) ]BF aﬀords the tetranuclear tances upon coordination can be explained by the σ- and

3

4

+

−

22

complex [Cu

CH

CN together with two solvent molecules, which coordinate recorded in d

to the central two copper atoms, and the structure derived of the two coordinating CH

from X-ray diﬀraction is reproduced in Fig. 4 from two perspec- Fig. S8 in the ESI†). Hence the H NMR spectrum contained

tives. The four copper atoms are arranged in a zig-zag chain only a signal of free CH CN (at δ = 2.07 ppm), but not a second

4

(1)

2

] (BF

4

)

4

(see Scheme 5). It crystallizes from π-contributions to the metal–ligand bonding. NMR spectra

-DMSO solution are in line with the dissociation

CN molecules in solution (see

3

6

3

1

3

1

(

see Fig. 4b) with relatively short Cu⋯Cu distances of 2.4910(8) one assignable to coordinated CH

Cu1–Cu1′) and 2.4857(10) (Cu1–Cu2) Å. For comparison, the of CD CN solutions show the appearance of a new signal at

(napy) ](ClO

1.99 ppm upon cooling to −35 °C indicating coordination of

3

CN. H NMR measurements

3

Cu⋯Cu distance in the dinuclear complex [Cu

2

4 2

)

Scheme 5 Synthesis of the two compounds [Cu

cules) and [Cu (1) Br )]Br.

4

(1)

2

](BF

4

)

4

(crystals grown from CH

3

CN solution contain two weakly coordinating solvent (L) mole-

3

2

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dine, as well as benzonitrile (for details see ESI†). Addition of

two equivalents of pydridine to

a CH CN solution of

3

4

+

1

[Cu

4

(1)

2

]

reveals only small shifts in the H NMR spectrum at

lower temperature (see ESI, Fig. S10†). In the case of benzo-

nitrile, crystals are obtained from CH Cl solution, but a struc-

2

tural characterization by X-ray diﬀraction (see ESI, Fig. S11†)

shows that the unit cell contains a mixture of the three

complexes [Cu (1) ](BF ) , [Cu (1) (CH Cl ) ](BF )

and

4

2

4 4

4

2

2 2

4 4

[Cu

4

(1)

2

(CuCl

2

)

2

](BF

4

)

2

(this diamagnetic hexanuclear copper

complex will be discussed below), that cannot be separated by

chemical or physical methods. Nevertheless, the character-

4

+

ization of a [Cu

4

(1)

2

]

ion, in which the copper atoms are only

coordinated to two naphthyridine ligands, again indicates that

the CH CN co-ligands are only weakly bount and eliminated in

3

solution.

4

Coordination of halides to the Cu chain might alter the

electronic structure of the metal chain (see, for example, the

discussion in ref. 16). However, addition of halides, e.g. in the

form of PPNCl (bis(triphenylphosphoranylidene)ammonium

4

+

chloride), to a solution of [Cu (1) ] in CH CN shows no reac-

4

2

3

tion (for details see ESI, Fig. S12†). Therefore we tried to incor-

I

porate the halides by directly reacting ligand 1 with Cu

halides. Reaction with CuCl results in a mixture of com-

pounds, from which it is not possible to isolate a clean

product. Reaction with CuBr does not lead to a tetranuclear

complex, but instead we obtained the trinuclear complex

3 2 2

[Cu (1) Br )]Br (see Scheme 5) as reaction product. In this cat-

ionic complex (displayed in Fig. 5) three copper atoms are co-

ordinated to two ligands, which are displaced with respect to

their position relative to the metal chain axis. The central

in copper atom is coordinated to two naphthyridine nitrogen

4+

4 2 3 2

Fig. 4 Structure of the tetracationic complex [Cu (1) (CH CN) ]

the salt [Cu

4

(1)

2

(CH

3

CN)

2

](BF

4

)

4

·2CH

2

Cl

2

from two perspectives. atoms, whereas each terminal copper atom is coordinated to

Vibrational ellipsoids drawn at the 50% probability level. All hydrogen

atoms omitted. Selected bond distances (in Å) and angles (in °):

Cu1⋯Cu1’ 2.4910(8), Cu1⋯Cu2 2.4857(10), Cu1–N1 1.9965(15), Cu1–N2

one naphthyridine nitrogen atom and one imino nitrogen

atom. The terminal copper atoms are additionally stabilized by

2.0005(15), Cu1’–N9 2.0284(17), Cu2–N3 1.8652(15), Cu2–N6 1.8647(15),

N1–C1 1.352(2), N2–C7 1.354(2), N3–C1 1.366(2), N3–C9 1.376(2),

N4–C9 1.342(2), N5–C9 1.334(2), N6–C7 1.375(2), N6–C14 1.374(2),

N7–C14 1.340(2), N8–C14 1.331(2), Cu2⋯Cu1⋯Cu1’ 140.65(2), N1–

Cu1–N2 150.93(6), Cu2⋯Cu1–N1 86.59(5), Cu2⋯Cu1–N2 84.31(5), N3–

Cu2–N6 175.67(6), Cu1⋯Cu2–N3 87.42(6), Cu1⋯Cu2–N6 88.65(6).

3

CH CN to the copper chain at low temperatures (see ESI,

Fig. S9†). This assumption is supported by the appearance of

two additional signals at 6.54 and 8.01 ppm for the aromatic

protons.

As shown below, the coordination of neutral Lewis bases

3 4

such as CH CN to the Cu chain alters its structure (linear

without coordination and zig-zag with coordination).

Therefore we tried to attach Lewis bases that more strongly

+

Fig. 5 Molecular structure of the monocation [Cu

(1) Br ]Br·2CH Cl

3

(1)

2

Br

2

]

in

bind to the Cu

4

chain than CH

3

CN, so that the possible influ- [Cu

3

2

. Vibrational ellipsoids drawn at the 50% prob-

ability level. All hydrogen atoms omitted. Selected bond distances (in Å)

and angles (in °): Cu1⋯Cu2 2.5352(10), Cu1⋯Cu2’ 2.3232(11), Cu1–N1

ence of the structural changes on the electronic structure and

optical properties could be studied. However, further experi-

ments indicate that it is not possible to substitute the weakly

1

2

.939(2), Cu1–N3 2.737, Cu1–N6 1.935(2), Cu1–Br1 2.731(4), Cu1–Br11

.6160(12), Cu2–Br1’ 2.652(3), Cu2⋯Br11’ 3.016(3), N3–C9 1.325(3), N6–

C14 1.366(3), N1–Cu1–N6 154.12(9), N2–Cu2–N2’ 160.03(4),

and its derivatives 4-(dimethlyamino)pyridine and 2-nitropyri- Cu1⋯Cu2⋯Cu1’ 164.66(3), Cu1–Br1–Cu2’ 51.12(5).

3

bound CH CN molecules by other neutral ligands like pyridine

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a weak coordination to a second imino nitrogen atom adjacent

to the coordinating naphthyridine nitrogen atom. The two

bromido ligands bridge the central and terminal copper

atoms. The Cu–Br–Cu angles measure 51.12(5)°, and the

Cu⋯Cu distances 2.3232(11)/2.5352(10) Å. The three copper

atoms are arranged in an approximately linear chain with a

Cu1⋯Cu2⋯Cu1′ angle of 164.66(3)°. The Cu–N distances

between the terminal copper atom and the imino nitrogen

atom or the naphthyridine nitrogen atom vary only little

(1.939(2) and 1.935(2) Å, respectively). With 1.964(2) and

1

.967(2) Å, the Cu–N bond distances involving the central

copper atom are only slightly longer, but still shorter than for

the tetranuclear complexes. The imino bond lengths (N3–C9)

of 1.325(3) Å are in the region typical for non-coordinated

imino bonds, indicating weak interaction with the terminal

copper atoms. The N6–C14 bond distance is elongated to

1

.366(3) Å, signaling a stronger ligand–metal interaction. In the

UV/Vis spectrum, two separated absorption maxima appear at

84 and 401 nm. The emission maximum is reached at 446 nm,

thus being considerably red-shifted with respect to free 1.

3

Reaction of 2 with [Cu(CH

3

CN)

4

]BF

4

in CH

3

4

CN solution

+

−

yields the analogue Cu chain complex [Cu

4

(2)

2

] (BF

4

)

4

, the

structure of which is presented in Fig. 6. The absence of co-

ordinating solvent molecules confirms that the two inner

4

copper atoms in these Cu chains only weakly interact with

Lewis bases such as CH CN. With 2.4225(6) (Cu1⋯Cu1′) and

3

Fig. 6 Structure of [Cu (2) ](BF ) from two perspectives. Vibrational

4

2

4 4

2

.4594(6) Å (Cu1⋯Cu2), the Cu⋯Cu distances in [Cu

)

4 4

4

(2)

are short and might argue for some d –d interaction. omitted. Selected bond distances (in Å) and angles (in °): Cu1⋯Cu1’

.4225(6), Cu1⋯Cu2 2.4594(6), Cu1–N1 1.920(2), Cu1–N2 1.920(2),

2

]

ellipsoids drawn at the 50% probability level. All hydrogen atoms

1

0

10

(

BF

The arrangement of the two ligand units is similar to that in

Cu (1) ](BF , but (due to the absence of the CH CN mole-

cules) the copper atoms are almost arranged in a linear chain,

2

Cu2–N3 1.882(2), Cu2–N6 1.872(2), N1–C2 1.368(3), N2–C8 1.369(3),

N3–C2 1.364(3), N3–C9 1.388(3), N4–C9 1.323(3), N5–C9 1.323(3), N6–

C8 1.357(3), N6–C14 1.390(3), N7–C14 1.311(3), N8–C14 1.328(3), Cu1’

[

4

2

4

)

4

3

with Cu1′–Cu1–Cu2 angles close to 180° (173.99(2)°). In the ⋯Cu1⋯Cu2 173.99(2), N1–Cu1–N2 175.48(8), N3–Cu2–N6 169.93(8).

−

solid state, the BF

4

anions weakly interact through B–F⋯Cu

interactions (2.419 Å) with the two central copper atoms.

Similar to [Cu (1) ](BF ) ·2CH CN, the distances between the similar to that of 3. The fluorescence maximum is located at

4

2

4 4

3

inner copper atoms to the naphthyridine nitrogen atoms 408 nm, hence also varying only little from 3. Reaction of 3 with

1.9965(15) and 2.0005(15) Å) are slightly longer than the dis- one equivalent of ZnCl₂yields the mononuclear complex

(

tances between the terminal copper atoms and the ligand [(ZnCl )3]. Again, a structural characterization of the complex is

2

imino nitrogen atoms (with Cu–N bond distances of 1.882(2) unfortunately not possible, and the absorption and emission

and 1.872(2) Å). As a result of coordination, the imino NvC spectra show only small changes with respect to 3. The failure

bond distances within the guanidino groups are elongated to synthesize copper chain complexes with 3 might have two

substantially to 1.388(3)/1.390(3) Å.

reasons. First the steric demand of the isopropyl groups might

The coordination chemistry of 3 is very diﬀerent to that of 1 prevent formation of such complexes. Second, the N–H func-

and 2. Hence in the case of 3, only mono- and dinuclear com- tions of the ligand might be involved in hydrogen bonding inhi-

plexes are obtained, while 1 and 2 give rise to tetranuclear biting formation of complexes of higher nuclearity due to an

(and trinuclear) complexes. In contrast to 1 and 2, it is not unfavorable position of the imino nitrogen atoms. Quantum

possible to isolate a product from the reaction of 3 with chemical calculations on the complex [(CuCl) 3] (see Fig. S14 in

2

[

Cu(CH

3

CN)

4

]BF

4

or CuBr. From the manifold reactions the ESI†) do not find significant N–H⋯Cl interactions. Hence

carried out with ligand 3, two representative examples are in this case the formation of tri- or tetranuclear complexes of

briefly discussed here. Hence reaction of 3 with two equiva- 3 is inhibited by the steric demand of the isopropyl groups.

lents CuCl leads to the dinuclear complex [(CuCl)

2

3]. In the

3], signals appear at δ (ppm) =

.25, 4.02, 6.68 and 7.69 which are only slightly shifted com-

pared to free 3. Crystals grow from CH Cl solution, but are Coordination aﬀects the electronic absorption and emission

1

H NMR spectrum of [(CuCl)

2

4

Optical properties of the Cu chain complexes

1

2

unfortunately not suitable for structural characterization by spectra (see Table 1). As expected from the presence of two

X-ray diﬀraction. The absorption spectrum of [(CuCl) 3] is ligand units in the complex, the molar extinction coeﬃcients

2

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CN solution (c = 3.0 × 10⁻M). For comparison, the spectra for free 1 are also

(1) ](BF and 373 nm for 1. (b) UV/Vis and emission spectra of [Cu (2) ](BF in

CN solution (c = 1.1 × 10⁻M). For comparison, the spectra for free 2 are also included. The emission spectra were excited at 381 nm for

(2) ](BF and 385 nm for 2.

6

4 2 4 4 3

Fig. 7 (a) UV/Vis and emission spectra of [Cu (1) ](BF ) in CH

included. The emission spectra were excited at 384 nm for [Cu

4

2

4

)

4

2

4 4

)

5

CH

Cu

3

[

4

2

4 4

)

4

+

4+

of absorption bands due to [Cu (1) ] and [Cu (2) ] in explanation for the fluorescence quenching in CH OH is a sig-

4

2

4

2

3

CH

3

CN solution are much higher than for free 1 or 2 (see nificant interaction of the CH

3

OH solvent molecules with the

Fig. 7). The comparison with the spectrum of free 1 shows that complex in its electronically excited state, favoring a non-radia-

the molar extinction coeﬃcient of the lowest-energy band of tive electron relaxation pathway.

4

+

[

Cu

4

(1)

2

]

has approximately doubled, in agreement with the

Quantum chemical calculations are carried out to obtain

additional information about the electronic structure and elec-

presence of two ligand units in the complex.

In the case of [Cu (2) ] , the intensity gain is even larger tronic excitations of the new Cu chain complexes. First the

see Fig. 7). The lowest-energy bands in the absorption spec- structure of [Cu

4

+

4

2

4

+

(

4

(1)

2

]

is calculated. In the energy minimum

4

+

4+

trum of [Cu

4

(1)

2

]

and [Cu

4

(2)

2

]

are slightly red-shifted with structure, the Cu atoms are located almost in the naphthyri-

respect to free 1 (373 nm) and 2 (381 nm), and split in two con- dine aromatic planes of the two ligands (linear chain). The cal-

4

+

4+

tributions at 384/399 nm for [Cu

4

(1)

2

]

and 385/405 nm for culated Cu⋯Cu distances for [Cu

4

(1)

2

]

(2.426 and 2.449 Å)

4

+

4+

[Cu

4

(2)

2

] . The emission spectra (see Fig. 7) exhibit maximum are close to the experimental distances for [Cu

intensity at 446 nm for [Cu (1) ] and 442 nm for [Cu (2) ] , [Cu (2) ] . For [Cu (1) (CH CN) ] the calculated structure

4

(1)

2

]

and

4

+

4+

4

2

4

2

4

2

4

2

3

2

again red-shifted with respect to free 1 and 2 (404 nm). with two CH

3

CN molecules coordinated to the copper atoms

Lowering the temperature to −35 °C has no significant eﬀect results in a zig-zag arrangement of the copper atoms, in pleas-

4

+

on the absorption spectrum of [Cu (1) ] , thus coordination ing agreement with the experimental results (for more details

4

2

of CH

3

CN molecules to the copper chain only marginally see Table S1 in the ESI†).

The calculated UV/Vis spectrum of [Cu

Fluorescence for [Cu (1) ] and [Cu (2) ] is almost comple- Fig. 8a. The transitions at 360.5 nm and 347.9 nm are the

4

+

aﬀects the electronic transitions (see ESI, Fig. S15†).

4

(1)

2

]

is shown in

4

+

4+

4

2

4

2

4

+

tely quenched in CH

3

OH (Φ = 0.01 for [(1)

2 4

Cu ] , compared to HOMO → LUMO+1 and HOMO−2 → LUMO transitions. These

0

.17 in 1), while in CH

3

CN higher quantum yields of 0.15 for transitions fit pleasantly to the observed transitions at 399 and

4

+

4+

[Cu (1) ] and 0.08 for [Cu (2) ] are measured. A possible 384 nm. The involved orbitals are shown in Fig. 8b. HOMO

4 2 4 2

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4+

Fig. 8 (a) Theoretical UV/Vis spectrum from TD-DFT calculations (B3LYP/def2-SV(P)) for [Cu

(1)

4 2

]

. (b) Visualization of the isodensity surfaces for

4+

orbitals of [Cu

4

(1)

2

]

involved in the electronic transitions.

and HOMO−2 are combinations of the HOMO of the ligands, results are in line with the experimental UV/Vis spectra that

LUMO and LUMO+1 are combinations of the LUMO of the show only small changes upon coordination of CH CN at low

3

ligands. Thus both strong transitions are essentially ligand temperatures (see ESI, Fig. S15†).

HOMO → LUMO transitions, which are only slightly altered by

4

+

4 2

Chemical properties of [Cu (1) ]

coordination. The next electronic transition with sizable inten-

sity is located at 293.1 nm. It is a transition from HOMO−1 to The previous discussion shows that the copper atoms only

LUMO+5. HOMO−1 has its main contribution from all four Cu weakly interact with Lewis bases, despite of their low coordi-

3

d orbitals and from the coordinating N atoms and LUMO+5 nation number. To see if they display any reactivity, the coup-

from the two outer Cu atoms and from the guanidino groups. ling reaction between phenylacetylene and benzyl azide to give

Hence, the transition is related to a charge reorganization at 1-benzyl-4-phenyl-1H-1,2,3-triazole (azide–alkyne klick reac-

4

+

the Cu atoms and a charge transfer from the Cu atoms to the tion), catalyzed with 1.0 mol% of [Cu (1) ] in DMSO solution

4

2

ligand guanidino groups. We assign the band at 264 nm in the is tested (see ESI† for more details). The reaction mixture is

experimental spectrum to this transition. Hence for any poss- stirred at room temperature overnight, and NMR spectra show

ible application of the complexes for photo-redox catalysis this quantitative product formation. This result demonstrates that

band is very important. The coordination of two CH

cules leads to a shift of the corresponding charge transfer

band from 293.1 nm to 309.7 nm in the calculated UV/Vis cate that the HOMO and LUMO orbitals of [Cu (1) ] and

3

CN mole- the copper complex is indeed a suitable catalyst.

Next the redox properties are tested. The calculations indi-

4

+

4

2

4

+

4+

spectrum of [Cu

4

(1)

2

(CH

3

CN)

2

]

(see ESI, Fig. S16†), while the [Cu (2) ] are located at the ligand units rather than on the

4 2

ligand HOMO → LUMO transitions change slightly from 360.5 metal atoms. Therefore it seems unlikely that copper oxidation

I

to 364.3 nm and from 347.9 to 341.3 nm, respectively. These is possible, despite of the presence of four Cu atoms. To

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3

follow up this point, CV experiments are made in CH CN

solution (see ESI, Fig. S18 and S19†). As expected, both for

4

+

−

4+

−

[Cu

4 2 4 4 4 2 4 4

(1) ] (BF ) and [Cu (2) ] (BF ) , no oxidation wave is

observed up to ca. 1 V. On the other hand, reduction waves

+

4+

appear at −0.69 V and −1.07 V vs. Fc/Fc for [Cu (1) ] and

4

2

+

4+

−1.18 V vs. Fc/Fc for [Cu

4 2

(2) ] . After reduction of the

complex, strong oxidation waves occur at −0.71, −0.54 and

+

4+

0

.33 V vs. Fc/Fc for [Cu (1) ] and −0.76 and −0.55 V vs. Fc/

4

2

+

4+

Fc for [Cu

4 2

(2) ] . However, the redox-processes are not

reversible.

To obtain information about possible redox-induced

decomposition pathways, chemical oxidation and reduction of

4

+

[Cu

4

(1)

2

]

is examined. Various oxidation agents are tested. In

2+

Fig. 9 Structure of the hexanuclear complex [Cu

salt [Cu (1) (CuCl ](BF . Cu1⋯Cu1’ 2.4647(7), Cu1⋯Cu2 2.4686(5),

Cu1⋯Cu3 3.0950(6), Cu1–Cl1’ 2.5091(8), Cu2–Cl2 2.6441(8), Cu3–Cl1

.1167(8), Cu3–Cl2 2.1149(8), Cu1–N1 1.966(2), Cu1–N2 1.971(2), Cu2–

4

(1)

2

(CuCl

2

)

2

]

in the

line with the results of the CV experiments, ferrocenium tetra-

4

2

)

2

4 2

)

fluoroborate or p-benzoquinone are too weak for oxidation of

4

+

the tetracation [Cu

4 2

(1) ] , and no reaction takes place.

2

Reaction with AgBF or NOBF leads to decomposition without

4

N3 1.912(2), Cu2–N6 1.909(2), N1–C1 1.350(3), N1–C8 1.377(3), N2–C7

1.358(3), N2–C8’ 1.372(3), N3–C1 1.378(3), N3–C9 1.363(3), N4–C9

the possibility to identify the products.

On the other hand, reaction with 2 equivalents of the Cu

compound CuCl₂gives the hexanuclear Cu complex

II

1

.343(4), N5–C9 1.336(3), N6–C7 1.372(3), N6–C14 1.372(3), N7–C14

1.334(3), N8–C14 1.346(3), Cu1’⋯Cu1⋯Cu2 140.46(3), Cu1–Cl1’–Cu3’

3.53(3), Cu2–Cl2–Cu3 93.37(3), Cl1–Cu3–Cl2 167.31(4), N1–Cu1–N2

58.67(9), N3–Cu2–N6 152.67(10).

I

8

1

−

4 2 2 2 4 2 4 2

[Cu (1) (CuCl ) ](BF ) with a Cu -chain bridged by two CuCl

units in a yield of 40%. This diamagnetic product, which can

now be completely characterized, was already observed for

4

+

−

reaction of benzonitrile with [Cu

4

(1)

2

] (BF

4

)

4

(vide supra). In

are reduced the copper atoms. The structure of [Cu

to Cu . This is obviously only possible if some of the ized in Fig. 10a. The three copper atoms are aligned almost in

II

the course of the reaction, the Cu atoms of CuCl

2

3 2 5 2 3

(1) ](I ) (I ) is visual-

I

4

+

I

II

[

Cu

explaining the moderate product yield. Interestingly, it is not placed with respect to their position from the chain axis.

possible to synthesize this complex by reacting [Cu (1) ](BF )

Whereas the central copper atom is bound to two naphthyri-

with 2 equivalents of CuCl/KCl. In such experiments no reac- dine nitrogen atoms, the terminal copper atoms are each co-

tion takes place (see ESI† for details).

ordinated to one naphthyridine nitrogen atom and one imino

The structure of the dication [Cu (1) (CuCl ) ] is displayed nitrogen atom. Similar to [Cu

4

(1)

2

]

complexes decompose with oxidation of Cu to Cu , a linear chain and coordinated to two ligand units that are dis-

4

2

4 4

2

+

(1)

Br ] , the terminal copper

2 2

4

2

2 2

3

in Fig. 9. The Cu⋯Cu distances (2.4647(7)/2.4686(5) Å) are atoms are additionally weakly coordinated to a second imino

4

+

slightly shorter than in [Cu

4 2

(1)

] . The Cu–Cl distances in the nitrogen atom adjacent to the coordinating naphthyridine

CuCl₂⁻unit measure 2.1167(8) and 2.1148(8) Å, and are in a nitrogen atom. The Cu⋯Cu distances are in average 2.465 Å

−

II

region typical for CuCl

2

(e.g. 2.110(1) Å in [(Cu Cl

2 2

)

3 2 5 2 3

(tdipgb)] long. The absorption spectrum of [Cu (1) ](I ) (I ) shows

I

(Cu Cl )

2 2

, tdipgb = 1,2,4,5-tetrakis(N,N′-diisopropylguanidino) bands at 231, 290, 348, 370, 387 and 412 nm (see ESI,

benzene). The Cl–Cu–Cl angles in the CuCl₂units measure Fig. S21†). The bands at 231, 387 and 412 nm could be

67.31(4)°. The copper atom of the bridging CuCl

.165 Å away from the nearest Cu atom in the Cu

In the H NMR spectrum of [Cu (1) (CuCl ) ](BF ) , signals tion). The fluorescence maximum is red-shifted from 404 nm

appear at δ (ppm) = 3.05, 7.12 and 8.29. They are slightly in 1 to 450 nm in [(1)

shifted with respect to the tetranuclear complex [Cu (1) ](BF

Reduction of [Cu (1)

δ (ppm) = 2.99, 6.55, 8.03), indicating that the two CuCl₂

copper chain. Reaction with two equivalents of cobaltocene

2

6

−

1

2

unit is assigned to ligand transitions, whereas the bands at 290, 347

−

3

4

chain.

and 370 nm arise from I

3

and I

2

(I

5

decomposes in solu-

1

27

4

2

2 2

4 2

3

+

2

Cu

3

] .

)

4

2

](BF

4 4

) also leads to downsizing of the

4

2

4

−

(

units are also in solution bount to the copper chain. The gives the trinuclear copper complex [Cu

3

(1)

3

](BF

4

)

3

in 57%

−

coordination of two CuCl

2

units to the Cu

4

chain in yield. Cobaltocene is oxidized to the cobaltocenium ion, and

I

[

Cu (1) (CuCl ) ](BF ) only very slightly changes the band the elimination of a Cu atom and its reduction to elemental

4 2 2 2 4 2

maxima in the UV/Vis spectrum, but reduces their extinction copper (precipitating during reaction) complete the redox part

3

+

coeﬃcient. The maximum of emission occurs at 456 nm, of the reaction. The structure of the trication [Cu

3

(1)

played in Fig. 10b. The three ligands adopt a propeller-type

leads to the trinuclear arrangement around the central, almost linear Cu chain. The

) in a yield of 35%. In this reaction, I

terminal copper atoms are coordinated to two, respectively one

is reduced to I₃and I₅polyanions, respectively, whereas the naphthyridine nitrogen atom and one, respectively two imino

3

]

is dis-

4

+

slightly red-shifted with respect to [Cu (1) ] (446 nm).

4

2

Treatment of [Cu

complex [Cu (1) ](I

4

(1)

(I

2

](BF

4

)

4

with I

2

3

2

−

5

)

2

3

2

−

3

+

copper atoms in [Cu

3

(1)

2

]

are all in the oxidation state +I. nitrogen atoms. The central copper atom is exclusively co-

The low yield could then again be explained by decomposition ordinated by three naphthyridine nitrogen atoms with similar

4

+

of some of the [Cu (1) ] complexes induced by oxidation of Cu–N distances (1.969(3)–2.051(3) Å). The Cu⋯Cu distances

4

2

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Fig. 11 (a) Theoretical UV/Vis spectrum from TD-DFT calculations

4+

(B3LYP/def2-SV(P)) for [Au

4 2

(1) ] . Data was ﬁtted as Gaussian curve

with a half-width of 20 nm. (b) Visualization of the isodensity surfaces

Fig. 10 Illustration of the structures of (a) [Cu

3

(1)

2

](I

5

)

2

(I

3

) obtained by

4+

for orbitals of [Au

4

(1)

2

]

involved in the electronic transitions.

4 2 4 4 2

reaction of [Cu (1) ](BF ) with I (vibrational ellipsoids drawn at the 50%

3+

probability level) and (b) the trication [Cu

3

(1)

3

]

in the salt [Cu

3

(1)

3

]

(

BF

4

)

3

·[CoCp

2

](BF

4

), obtained by reaction of [Cu

4

(1) ](BF with CoCp

2

4

)

4

2

(

in this case a ball-and-stick representation was chosen for clarity). In Consequently, the Au⋯Au distances (2.684/2.633 Å) are shorter

both structures the hydrogen atoms were omitted for clarity. Both com- than in the Ag complex (for further information, see Table S2

4

pounds are diamagnetic trinuclear Cu(I) complexes.

in the ESI†). Of particular importance is the question if the

nature of the low-lying transitions is altered by metal

4

+

exchange. For [Ag (1) ] , the observed transitions remain

4

2

(

2.4606(7)/2.4679(7) Å) are similar to those in the other chain

located on HOMO and LUMO orbitals of the two ligands,

hence no metal orbitals are involved. These transitions can be

complexes. The absorption bands of [Cu (1) ](BF ) (at 224,

2

maximum is reached at 456 nm, red-shifted with respect to

free 1.

3

4 3

4

+

4+

62 and 384 nm) only slightly shift relative to 1. The emission

also found for [Au (1) ] . Additionally, for [Au (1) ] exists a

4

2

4

2

transition from HOMO to LUMO+5 at 328.5 nm involving the

Au d orbitals similar to the Cu complex (see Fig. 11 and ESI†).

4

+

4+

In contrast to [Cu (1) ] , the HOMO of [Au (1) ] is metal-

4

2

4

2

4

+

Variations of the electronic structure for [M (1) ] complexes

(

centered (see Fig. 11b), making this complex particularly

4

2

8

M = Cu, Ag or Au)

attractive for photo-redox catalytic applications. However, its

synthesis requires a careful choice of the Au reagent and is

beyond the scope of this work.

To study the influence of the metal atoms in the tetranuclear

complex on the structure and electronic excitations, calcu-

lations are also performed for the [Ag

4

+

4+

4

(1)

2

]

4 2

and [Au (1) ]

homologues. The calculated minimum structures are visual-

4

+

ized in Fig. S22 in the ESI.† In contrast to [Cu

metal atoms in [Ag (1) ]

4 2

4

(1)

2

] , the

Conclusions

4

+

are arranged in a zig-zag chain with

the central atoms being out of the ligand plane. The Ag⋯Ag In this work three new blue-fluorescent 2,7-bis-

distances are 2.696/2.664 Å. The calculated structure of guanidino-naphthyridine ligands are synthesized. Reaction of

4

+

[Au

4

(1)

2

]

is closer to that of the Cu homologue, as the Au 2,7-bis(tetramethylguanidino)-1,8-naphthyridine (1) or 2,7-bis

atoms are only slightly displaced from the ligand plane. (N,N′-dimethylethylene-guanidino)-1,8-naphthyridine (2) with

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4

+

[

(

[

Cu(CH

crystallizing

3

CN)

4

]BF

as

4

aﬀords tetranuclear complexes [Cu

[Cu (1) (CH CN) ](BF ) ·2CH Cl )

4

(1)

2

]

BIORAD Excalibur FTS 3000 spectrometer. Bruker ApexQe

and FT-ICR (high resolution electrospray ionisation, HR-ESI) and

Cu (2) ] , in which the four Cu atoms are aligned in a chain JEOL JMS-700 (fast atom bombardment, FAB) machines were

4 2

4

2

3

2

4 4

2

4

+

I

with short Cu⋯Cu distances in the range of 2.42–2.49 Å. The used for mass spectrometry (MS). UV/Vis measurements were

coordination number of each of the four copper atoms is only carried out on a Varian Cary 5000 UV/Vis/NIR spectrophoto-

two (Cu⋯Cu interactions not considered). Quantum chemical meter. Fluorescence spectra were recorded with a Varian Cary

calculations show that the HOMO and LUMO of the two com- Eclipse machine. Quantum yields were determined by the

plexes are ligand-centered. The coordination of copper atoms absolute method described by Resch-Genger using an Ulbricht

3

1

leads to a red-shift of the absorption bands and fluorescence sphere. An EG&G model 273A potentiostat/galvanostat was

signals. With the aid of TD-DFT calculations, the lowest-energy used for electrochemical studies at room temperature. The

bands in the UV/Vis spectra are assigned to ligand-centered reference electrode was an aqueous Ag/AgCl in 3 M KCl elec-

electronic excitations. Metal-to-ligand charge transfer (MLCT) trode. As auxiliary electrode a platinum wire was used and the

4 4 6

bands follow at higher energy. These Cu chain complexes working electrode was a glassy carbon disk. [n-Bu N][PF ] was

cannot be synthesized with copper halides. Hence the tri- used as supporting electrolyte. If not otherwise stated, the

+

−1

nuclear complex [Cu

3 2 2

(1) Br )] is obtained as product of the scan rate was 100 mV s .

reaction of 1 with CuBr.

Then the chemical properties of the tetracationic complex

4

+

2,7-Bis(tetramethylguanidino)-1,8-naphthyridine, 1

[

Cu

4

(1)

2

]

are studied. NMR experiments demonstrate that

4

+

is a suitable catalyst for the azide–alkyne klick reac- 0.30 ml (2.43 mmol, 3.0 eq.) N,N,N′,N′-tetramethylurea was dis-

4

+

tion. Redox reactions with [Cu (1) ] generally lead to redox- solved in dry CHCl (5 ml) and 1.04 ml (12.17 mmol, 15.0 eq.)

4

2

3

induced decomposition processes (with oxidation/reduction of oxalyl chloride was added. The reaction mixture was stirred for

some of the Cu atoms), but the isolated Cu–naphthyridine 17 h under reflux. After cooling to room temperature, the

I

complexes again are Cu complexes. The hexanuclear Cu

solvent was removed in vacuo. The remaining solid was washed

chain is bridged three times with 20 ml portions of Et O and dried under

vacuum. The activated urea was dissolved in 10 ml CH CN and

and finally added to a suspension of 115 mg (0.72 mmol, 1.0 eq.)

with I 2,7-bisamino-1,8-naphthyridine and 0.80 ml (5.73 mmol,

8.0 eq.) Et N in 10 ml CH CN. The reaction mixture was stirred

2

+

complex [Cu

4

(1)

2

(CuCl

2

)

2

] , in which the Cu

4

2

−

4+

by two CuCl

2

anions, is synthesized by reaction of [Cu

with Cu Cl . The trinuclear complexes [Cu (1) ]

4

3+

(1)

2

]

3

II

2

3

2

4+

3

+

[Cu

3

(1)

3

]

are formed in the reactions of [Cu

4

(1)

2

]

2

and CoCp

2

, respectively.

3

Preliminary quantum chemical calculations show that the for 3 h at 82 °C, during which it turned brown. The brown

HOMO changes its character from a ligand-centered orbital to solid obtained after removal of the solvent in vacuo was re-

4

+

4+

a metal-centered one if [Cu

Hence this complex should be particularly interesting for of 25% aqueous NaOH solution a yellow solid precipitated

photo-redox catalysis, and its synthesis will be attempted in which was extracted with Et O. The combined organic phases

, and the solvent was removed under

4

(1)

2

]

4 2

is replaced by [Au (1) ] . dissolved in a 10% aqueous HCl solution (5 ml). Upon addition

2

future work by our group.

2 3

were dried over K CO

vacuum to aﬀord a yellow solid which was purified by sublima-

tion (140 °C, 10⁻mbar). The product was obtained in a yield

of 0.145 g (0.406 mmol, 57%). Elemental analysis calcd (%) for

C H N , (356.48): C 60.65, H 7.92, N 31.43; found C 60.50,

2

Experimental section

1

8

28 8

1

All reactions were carried out under an inert gas atmosphere H 7.69, N 31.32. H NMR (600.13 MHz, CD

using standard Schlenk techniques. The solvents were dried 24 H, –CH ), 6.61 (d, J = 8.48 Hz, 2 H, CHar), 7.72 (d, J = 8.45

prior to use by standard methods. The following starting Hz, 2 H, CH ) ppm. C NMR (150.90 MHz, CD CN): δ = 40.12

3

CN): δ = 2.73 (s,

3

1

3

ar

3

materials and reagents were obtained commercially and used (–CH

as delivered: N,N,N′,N′-tetramethylurea, oxalyl chloride, Et N, 163.64 (Cguanidine), 165.90 (Car) ppm. IR (CsI): ν = 2999, 2941,

,3-dimethylimidazolidin-2-one, lithium diisopropyl-amide 2887, 1599, 1558, 1554, 1538, 1507, 1491, 1467, 1421, 1415,

2.0 M in hexane), N,N′-diisopropylcarbodiimide, AlClMe 1406, 1387, 1361, 1346, 1301, 1265, 1219, 1149, 1124, 1070,

1.0 M in hexane), 4-dimethylamino-pyridine, 2-nitropyridine, 1059, 1043, 1020, 918, 860, 828, 813, 788, 780, 723, 705, 622,

3

), 113.58 (Car), 116.11 (Car), 137.19 (Car), 158.27 (Car),

3

1

(

2

−

1

+

benzonitrile, phenyl acetylene, [Cu(CH CN) ]BF , CuBr, CuCl, 582, 559, 508, 448, 412 cm . MS (ESI ): m/z (%) = 356.4

3

4

+

−5

−1

Cp

2 4 4 4 2 2 2 2 3

FeBF , NOBF , AgBF , CuCl , I and ZnCl . CoCp and ([M + H] , 100). UV/Vis (CH OH, c = 2.0 × 10 mol l , d =

p-benzoquinone were sublimed prior to use. Benzyl azide was 1.0 cm): λ (ε, L mol⁻cm ) = 228 (34 439), 260 (39 007), 378

1

−1

2

9

−5

−1

synthesized according to the literature. The compound 2,7- (32 754) nm. UV/Vis (CH CN, c = 2.0 × 10 mol l , d =

3

−1

bisamino-1,8-naphthyridine was prepared as described pre- 1.0 cm): λ (ε, L mol⁻cm ) = 235 (26 337), 264 (32 736), 373

1

3

0

viously.

3

Elemental analyses were carried out at the (28 408) nm. Fluorescence spectrum (CH OH, λex. = 378 nm):

Microanalytical Laboratory of the University of Heidelberg. λ = 404 nm. Fluorescence spectrum (CH CN, λ = 373 nm): λ =

3

ex.

NMR spectra were measured on a BRUKER Avance III 600, a 404, 424 nm. Quantum yield: Φ375 nm (CH

3

OH) = 0.17 ± 0.03,

BRUKER Avance II 400 or on a BRUKER Avance DPX AC200

spectrometer. IR spectra were taken with the help of a FTIR vs. Fc/Fc .

Φ

375 nm (CH

3 2 2

CN) = 0.11 ± 0.02. CV (CH Cl ): Eox = 0.38, 0.67 V

+

Dalton Trans.

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Paper

2

,7-Bis(N,N′-dimethylethylene-guanidino)-1,8-naphthyridine, 2

C

22

H

36

N

8

(412.59): C 64.05, H 8.80, N 27.15; found C 63.42,

1

H 8.14, N 25.26. H NMR (600.13 MHz, CD Cl ): δ = 1.28 (d, J =

2

0.68 ml (6.25 mmol, 4.0 eq.) 1,3-dimethylimidazolidin-2-one

6.42 Hz, 24 H, –CH

3

), 3.99 (sept., 4 H, –CH–), 6.70 (d, J = 8.43

was dissolved in dry CHCl

1

stirred for 17 h under reflux. After cooling to room tempera-

ture, the solvent was removed in vacuo. The remaining solid

was washed three times with 20 ml portions of Et O and dried

under vacuum. The activated urea was redissolved in 20 ml

3

CH CN and 240 mg (1.51 mmol, 1.0 eq.) 2,7-bisamino-1,8-

naphthyridine and 1.91 ml Et N (13.79 mmol, 9.1 eq.) were

added. The reaction mixture was stirred for 1 h at 82 °C,

during which it turned brown. The brown solid obtained after

removal of the solvent in vacuo was redissolved in a 10%

aqueous HCl solution (5 ml). Upon addition of 25% aqueous

NaOH solution a yellow solid precipitated which was extracted

with CH Cl . The combined organic phases were dried over

2 3

K CO , and the solvent was removed under vacuum to aﬀord a

yellow solid which was washed with Et O and dried in vacuo.

The product was obtained in a yield of 259 mg (0.74 mmol,

3

(5 ml) and 2.64 ml (30.75 mmol,

5.0 eq.) oxalyl chloride was added. The reaction mixture was

1

3

Hz, 2 H, CHar), 7.59 (d, J = 8.51 Hz, 2 H, CHar) ppm. C NMR

(

150.90 MHz, CD Cl ): δ = 23.74 (–CH ), 43.06 (–CH–), 112.83

2 2 3

C

ar), 119.03 (Car), 136.06 (Car), 154.50 (Car), 154.62 (Cguanidine),

65.03 (Car) ppm. IR (CsI): ν = 3436, 3346, 2971, 2933, 2875,

624, 1603, 1560, 1506, 1494, 1465, 1437, 1399, 1366, 1341,

305, 1287, 1268, 1239, 1210, 1175, 1126, 1070, 1037, 979, 955,

23, 865, 847, 806, 750, 701, 690, 668, 649, 638, 599, 554, 526,

1

9

5

2

3

−

1

+

02, 488, 473, 419 cm . MS (HR-ESI ): m/z (%) = 413.31348

+

−5

−1

(

1

3

[M + H] , 100). UV/Vis (CH OH, c = 2.0 × 10 mol l , d =

.0 cm): λ (ε, L mol⁻cm ) = 257 (36 597), 294 (16 864), 378

1

−1

−

5

(

30 170), 392 (35 329) nm. UV/Vis (CH CN, c = 2.0 × 10 mol

3

−

1

−1

l

, d = 1.0 cm): λ (ε, L mol cm ) = 261 (39 515), 298

21 664), 379 (36 289), 389 (29 867), 399 (50 206) nm. UV/Vis

(

2

−

5

−1

(

CH Cl , c = 2.0 × 10 mol l , d = 1.0 cm): λ (ε, L mol cm )

2 2

=

252 (28 616), 296 (16 978), 379 (29 016), 389 (28 313), 400

2

O, c = 2.0 × 10⁻mol l , d = 1.0 cm):

5

−1

(

33 612) nm. UV/Vis (Et

2

−

1

−1

λ (ε, L mol cm ) = 262 (23 292), 299 (14 100), 358 (9621), 368

11 798), 377 (23 867), 386 (17 804), 399 (35 864) nm.

Fluorescence spectrum (CH OH, λex. = 392 nm): λ = 410,

30 nm. Fluorescence spectrum (CH CN, λ = 399 nm): λ =

4

24 8

9%). Elemental analysis calcd (%) for C18H N (352.45):

(

C 61.34, H 6.86, N 31.79; found C 60.88, H 7.00, N 31.70.

1

3

H NMR (200.13 MHz, CD Cl ): δ = 2.73 (s, 12 H, –CH ), 3.46

2

3

4

3

ex.

2

(s, 8 H, –CH –), 6.66 (d, J = 8.62 Hz, 2 H, CHar), 7.61 (d, J =

1

3

410, 428 nm. Fluorescence spectrum (CH

λ = 429 nm. Fluorescence spectrum (Et O, λex. = 377 nm): λ =

02, 412, 424, 428 nm. Quantum yield: Φ₃₇₅_n_m(CH OH) =

2 2

Cl , λex. = 379 nm):

8

.19 Hz, 2 H, CH ) ppm. C NMR (150.09 MHz, CD Cl ): δ =

ar 2 2

2

3

4.99 (–CH ), 48.61 (–CH –), 112.67 (C ), 115.88 (C ), 136.32

3

2

ar

4

0

3

(C

ar), 157.19 (Car), 159.46 (Cguanidine), 163.49 (Car) ppm.

+

.27 ± 0.03. CV (CH

2

Cl

2

): Eox = 0.38 V; 0.73 V vs. Fc/Fc .

IR (CsI): ν = 3049, 2932, 2864, 1631, 1588, 1555, 1495, 1474,

1

9

445, 1409, 1377, 1340, 1287, 1233, 1174, 1127, 1076, 1032,

[

Cu

To a solution of 182 mg (0.58 mmol, 2.0 eq.) [Cu(CH

in 5 ml CH CN a solution of 103 mg (0.29 mmol, 1.0 eq.) of

in 12 ml CH CN was added. The reaction mixture was stirred

4 2 4 4 3

(1) ](BF ) ·2CH

CN

−

1

72, 852, 803, 783, 748, 696, 631, 592, 545, 512, 476, 437 cm

.

+

3 4 4

CN) ]BF

MS (ESI ): m/z (%) = 353.4 ([M + H] , 100). UV/Vis (CH OH, c =

2

3

_.₀_×₁₀− mol l , d = 1.0 cm): λ (ε, L mol cm ) = 210

5

−1

3

1

3

(23 347), 233 (24 132), 249 (24 735), 260 (24 974), 384 (28 109)

−5

−1

for 1 h at room temperature. The solvent was removed in vacuo

receiving a yellow solid which was re-dissolved in CH Cl

Overnight yellow crystals were obtained. The isolated crystals

were washed with a small amount of CH Cl . Yield 92 mg

0.07 mmol, 46%). Elemental analysis calcd (%) for

nm. UV/Vis (CH CN, c = 1.7 × 10 mol l , d = 1.0 cm): λ (ε,

3

_L_m_o_l− cm ) = 215 (15 221), 267 (19 774), 381 (17 878) nm.

Fluorescence spectrum (CH OH, λex. = 384 nm): λ = 403, 423 nm.

Fluorescence spectrum (CH CN, λ = 381 nm): λ = 401, 421 nm.

1

−1

2

.

3

2

3

ex.

(

Quantum yield: Φ₃₇₅_n_m(CH OH) = 0.26 ± 0.02, Φ

(CH CN) =

3

375 nm

+

C H B Cu F N ·2CH Cl (1566.31):

N

(

–

C

32.21,

H

4.28,

NMR

4

0

62

4

16 18

2

0.18 ± 0.02. CV (CH

2

Cl

2

): Eox = 0.23, 0.63 V vs. Fc/Fc .

1

16.10; found

399.89 MHz, CD

CH ), 6.55 (d, J = 8.60 Hz, 4 H, CH ), 8.03 (d, J = 8.60 Hz, 4 H,

C

31.96,

H 4.28, N 16.68.

3

CN): δ = 1.96 (s, 6 H, CH

3

CN), 2.99 (s, 48 H,

2

,7-Bis(N,N′-diisopropylguanidino)-1,8-naphthyridine, 3

3

ar

1

3

To a suspension of 0.400 g (2.48 mmol, 1.0 eq.) 2,7-bisamino- CHar) ppm. C NMR (100.55 MHz, CD

1

2

3

CN): δ = 40.94 (–CH

,8-naphthyridine in 250 ml toluene a 2.0 M solution of 114.34 (Car), 114.47 (Car), 140.44 (Car), 154.70 (Car), 165.52

.10 ml (4.20 mmol, 1.7 eq.) lithium diisopropylamide in (C_g_u_a_n_i_d_i_n_e), 166.46 (C ) ppm. IR (CsI): ν = 2948, 1624, 1617,

3

),

ar

hexane was added. Subsequently 0.90 ml (11.78 mmol, 4.8 eq.) 1609, 1507, 1473, 1457, 1406, 1350, 1297, 1230, 1168, 1054,

−1

+

N,N′-diisopropylcarbodiimide and 0.70 ml (0.70 mmol, 28 mol 861, 849, 832, 791, 732, 678, 519, 503 cm . MS (FAB ): m/z (%)

+

%

) of a 1.0 M solution of AlClMe in hexane were added. The = 1226.8 ([M − 2CH CN − BF ] , 15). UV/Vis (CH CN, c = 3.0 ×

2

3

4

3

−

6

−1

reaction mixture was stirred at 100 °C over a period of 3 d, 10 mol l , d = 1.0 cm): λ (ε, L mol cm ) = 208 (121 597),

leading to a brown precipitate and a yellow-orange colored 384 (68 717), 399 (61 729) nm. Fluorescence spectrum (CH CN,

solution which was filtered oﬀ. The solvent was removed λ_e_x_.= 384 nm): λ = 446 nm. Quantum yield: Φ (CH CN) =

3

399 nm

3

under vacuum aﬀording a yellow solid which was washed with 0.15 ± 0.02. CV (CH

CN, 500 mV s⁻): Eox = −0.71 V; −0.54 V;

1

3

hexane (2 × 20 ml). After purification of the solid by column 0.33 V; Ered = −1.07 V; −0.69 V.

chromatography (SiO , gradient from EtOAc to EtOAc/CH OH

2

3

[

Cu (2) ](BF )

4 2 4 4

2

0

/1) the product was obtained as a yellow solid in a yield of

.640 g (1.55 mmol, 63%). Unfortunately, the purity of the To a solution of 71.5 mg (0.23 mmol, 2.0 eq.) [Cu(CH

3

4 4

CN) ]BF

compound was not satisfying. Elemental analysis calcd (%) for in 5 ml CH CN a solution of 40 mg (0.11 mmol, 1.0 eq.) of 2 in

3

This journal is © The Royal Society of Chemistry 2016

Dalton Trans.

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Paper

Dalton Transactions

5

1

ml CH

3

CN was added. The reaction mixture was stirred for CH

2

Cl

2

(2 × 4 ml). From this solution yellow crystals were

h at room temperature. The solvent was removed in vacuo obtained within 2 d. Yield 25.7 mg (0.02 mmol, 40%).

6 8 16

Cl Elemental analysis calcd (%) for Cl Cu F N

receiving a yellow solid which was re-dissolved in CH

2

.

C

36

H

56

B

2

4

Overnight yellow crystals were obtained. The isolated crystals (1409.64): C 30.67, H 4.00, N 15.90; found C 30.68, H 4.38,

1

were washed with a small amount of CH Cl . Yield 71 mg N 16.11. H NMR (199.87 MHz, CD CN): δ = 3.05 (s, 48 H,

2

3

(

C

0.05 mmol, 48%). Elemental analysis calcd (%) for –CH

Cu

C 32.76, H 3.70, N 16.67. H NMR (399.89 MHz, CD CN): δ =

3

), 7.12 (s, 4 H, CHar), 8.29 (s, 4 H, CHar) ppm. The low

F N16 (1306.29): C 33.10, H 3.70, N 17.16; found solubility hampered the detection of clear signals in the

4 16

36

H

48

B

4

1

13

C NMR spectrum. IR (CsI): ν = 2925, 2873, 2856, 1610, 1592,

3 2

), 3.72 (s, 16 H, –CH –), 6.60 (d, J = 8.80 Hz, 1559, 1507, 1472, 1407, 1350, 1301, 1246, 1228, 1210, 1154,

3

2

4

.87 (s, 24 H, –CH

H, CHar), 7.88 (d, J = 8.60 Hz, 4 H, CHar) ppm. C NMR 1057, 1034, 851, 801, 557, 527, 520, 503 cm . MS (HR-ESI ):

13

−1

+

(

150.90 MHz, CD CN): δ = 34.44 (–CH ), 48.62 (–CH –), 109.6 m/z (%) = 925.3494 ([(1) + 2Cu + BF ] , 3), 775.41649 ([(1) +

3 3 2 2 4 2

C

+

ar), 114.1 (Car), 139.4 (Car), 159.4 (Car), 165.3 (Cguanidine), Cu] , 1), 616.9678 ([1 + 2Cu + CuCl] , 2), 517.0712 ([1 + Cu +

+

1

7

=

2

68.5 (Car) ppm. IR (CsI): ν = 2964, 2931, 2895, 1617, 1560, CuCl] , 8), 455.1494 ([1 + CuCl + H] , 26), 419.1727 ([(1) +

2

+

521, 1473, 1458, 1444, 1404, 1360, 1308, 1300, 1262, 1236, 2Cu] , 7), 357.2509 ([1 + H] , 100). UV/Vis (CH CN, c =

3

−1

207, 1178, 1063, 1039, 980, 964, 901, 881, 857, 836, 802, 789, 1.2 × 10⁻mol l , d = 1.0 cm): λ (ε, L mol cm ) = 209

5

−1

+

66, 757, 702, 669, 657, 547, 522, 502 cm . MS (FAB ): m/z (%) (83 105), 380 (29 218), 399 (25 861) nm. Fluorescence spectrum

+

−5

−1

1218.6 ([M − BF ] , 16). UV/Vis: (CH CN, c = 1.1 × 10 mol (CH CN, λ = 380 nm): λ = 456 nm. CV (CH CN, 200 mV s ):

4

3

−1

3

ex.

3

−

1

, d = 1.0 cm): λ (ε, L mol⁻¹cm ) = 208 (80 945), 267

l

(

Eox = −0.55 V; 0.20 V; Ered = −1.35 V; −0.60 V.

47 999), 385 (68 996), 405 (51 137) nm. Fluorescence spectrum

[

Cu (1) ](I (I

3

2

5 2 3

) )

CH CN, λ = 385 nm): λ = 442 nm. Quantum yield: Φ

3

ex.

405 nm

−1

CH

3

CN) = 0.08 ± 0.02. CV (CH

3

CN, 500 mV s ): Eox = −0.76 V; A solution of 46.2 mg (0.18 mmol, 5.0 eq.) iodine in 4 ml

CH CN was added dropwise to a solution of 50.8 mg

0.04 mmol, 1.0 eq.) [Cu (1) ](BF ) ·2CH CN in 10 ml CH CN.

−

0.55 V; Ered = −1.18 V.

3

(

4

2

4 4

3

[Cu (1) Br ]Br

3

2

While stirring the solution for 19 h at room temperature, the

3

2

2.2 mg (0.09 mmol, 1.0 eq.) of 1 and 26.0 mg (0.18 mmol, color turned from red to brown. Thereafter the solvent was

.0 eq.) CuBr were suspended in 7 ml toluene. The reaction removed in vacuo receiving a brown solid which was extracted

2 2

mixture was stirred for a period of 2.5 h at 110 °C. During that with CH Cl . Finally, the solvent was removed under reduced

time a brown solid precipitated. The reaction mixture was pressure and a brown solid was obtained. Yield 17.1 mg

allowed to cool to room temperature and the precipitate (0.01 mmol, 35%). Elemental analysis calcd (%) for

removed by filtration. Subsequently the solvent was removed

under vacuum receiving an orange solid which was washed 16.72, H 2.18, N 8.46. H NMR (200.18 MHz, CD

with a small amount of Et O. Crystals of [Cu (1) Br ]Br were (s, 48 H, –CH ), 7.12 (d, J = 8.76 Hz, 4 H, CH ), 8.28 (d, J =

36 3 13

C H58Cu I N16 (2553.35): C 16.93, H 2.21, N 8.78; found C

1

3

CN): δ = 3.04

2

3

2

3

ar

1

3

obtained from CH

7.9 mg (0.02 mmol, 54%). Unfortunately, the purity of the by low solubility. IR (CsI): ν = 2954, 2928, 2856, 2814, 1654,

compound was not satisfying. Elemental analysis calcd (%) for 1648, 1617, 1595, 1540, 1508, 1468, 1420, 1406, 1379, 1344,

Cu 16 (1143.31): C 37.82, H 4.94, N 19.60; found C 1331, 1301, 1248, 1230, 1170, 1144, 1056, 1037, 924, 902, 850,

8.67, H 5.28, N 20.65. H NMR-Spektrum (200.13 MHz, 801, 764, 677, 623, 604, 558, 521, 451 cm . MS (HR-ESI ): m/z

2 2

Cl solution at room temperature. Yield 8.76 Hz, 4 H, CHar) ppm. The C NMR analysis was hampered

2

C

3

36

H

56Br

3

N

1

−1

+

2

+

CD Cl ): δ = 2.87 (s, 24 H, –CH ), 6.55 (d, J = 8.56 Hz, 2 H, (%) = 736.91895 ([1 + 2Cu + 2I + H] , 3), 547.08483 ([1 + Cu + I

2

3

2

13

+

3

CHar), 7.75 (d, J = 8.52 Hz, 2 H, CHar) ppm. C NMR: too low + H] , 11), 357.25080 ([1 + H] , 100). UV/Vis (CH CN, c =

solubility. IR (CsI): ν = 2933, 2871, 2801, 1611, 1577, 1540, 1.1 × 10⁻mol l , d = 1.0 cm): λ (ε, L mol cm ) = 231

5

−1

1

5

517, 1500, 1469, 1420, 1403, 1350, 1340, 1230, 1217, 1155, (138 239), 290 (73 823), 348 (68 867), 370 (61 571), 387 (64 102),

110, 1065, 1038, 1006, 961, 914, 848, 794, 776, 718, 700, 675, 412 (50 417) nm. Fluorescence spectrum (CH

3

CN, λex.

=

−

1

+

94, 556, 503, 430 cm . MS (ESI ): m/z (%) = 1068.73 387 nm): λ = 450 nm.

+

2+

+

([M − 2Br] , 6), 419.39 ([(1) + 2Cu] , 29), 357.25 ([1 + H] ,

2

−

5

−1

[Cu (1) ](BF ) ·[CoCp ](BF )

3 3 4 3 2 4

1

3

00). UV/Vis (CH CN, c = 1.0 × 10 mol l , d = 1.0 cm): λ (ε,

−

1

−1

L mol cm ) = 205 (96 842), 262 (48 353), 384 (54 639), 401 47.0 mg (0.03 mmol, 1.0 eq.) [Cu

4

(1)

2

](BF

4

)

4

·2CH

3

CN and

(52 723) nm. Fluorescence spectrum (CH CN, λ_e_x_.= 384 nm): 12.7 mg (0.07 mmol, 2.0 eq.) cobaltocene were dissolved in

3

λ = 446 nm. CV (CH

3

CN): Eox = −0.78 V; −0.34 V; 0.15 V; 0.76 V; 14 ml CH CN. While stirring the solution for 2 h at room

Ered = −1.34 V; −0.63 V; 0.27 V; 0.46 V.

temperature, a black solid precipitated which was removed by

filtration. The solution was removed in vacuo receiving a yellow

[

Cu (1) (CuCl ) ](BF )

4 2 2 2 4 2

solid. Yellow crystals were obtained from CH

at −20 °C within 2 d. Yield 37.4 mg (0.02 mmol, 57%).

BF ) ·2CH CN and 12.3 mg (0.09 mmol, 2.0 eq.) CuCl 5 ml Unfortunately, the purity of the compound was not satisfying.

3 2

CN/Et O solution

4 2

To a mixture of 64.2 mg (0.05 mmol, 1.0 eq.) [Cu (1) ]

(

4

3

2

CH

3

CN were added. The reaction mixture was stirred for 18 h Elemental analysis calcd (%) for C54

84 3 3 12 2

H B Cu F N24·[CoCp ]

at room temperature. Then the solvent was removed in vacuo (BF

receiving a yellow-brownish solid which was extracted with H 5.31, N 17.96. H NMR (200.13 MHz, CD CN): δ = 2.76 (s, 48

4

) (1796.41): C 42.79, H 5.27, N 18.71; found C 41.19,

1

3

Dalton Trans.

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Dalton Transactions

Paper

H, –CH

H, CH ) ppm. C NMR (150.90 MHz, CD CN): δ = 40.54 m/z (%) = 549.3 ([3 + ZnCl + H] , 2), 413.4 ([3 + H] , 50). UV/Vis

3

), 6.43 (d, J = 8.41 Hz, 4 H, CHar), 7.89 (d, J = 8.41 Hz, 1234, 1221, 1173, 1151, 959, 849, 796, 503 cm⁻. MS (FAB ):

1

+

1

3

+

4

ar

3

3 3

), 115.72 (Car), 139.00 (Car), 154.60 (Car), 164.81 (CH )

OH, c = 2.0 × 10⁻mol l , d = 1.0 cm): λ (ε, L mol cm

5

−1

(

–CH

guanidine), 165.86 (Car) ppm. IR (CsI): ν = 3118, 2956, 2939, = 257 (35 024), 294 (15 899), 379 (28 564), 392 (34 515) nm. UV/

C

−

5

−1

2

1

7

(

9

801, 1610, 1544, 1502, 1473, 1421, 1405, 1349, 1336, 1284, Vis (CH CN, c = 2.0 × 10 mol l , d = 1.0 cm): λ (ε, L mol

3

262, 1231, 1215, 1157, 1054, 1036, 915, 869, 852, 804, 772, cm ) = 261 (20 196), 295 (17 429), 379 (28 923), 388 (27 150),

20, 702, 674, 650, 642, 588, 554, 520, 464, 437 cm . MS 399 (36 516) nm. Fluorescence spectrum (CH OH, λex. =

3

HR-ESI ): m/z (%) = 1077.27937 ([(1) + 3Cu + 2BF ] , 6), 379 nm): λ = 410, 428 nm. Fluorescence spectrum (CH CN,

2 4 3

25.34915 ([(1)

19.17269 ([(1)

−

1

−

1

+

2

+ 2Cu + BF

4

] , 22), 775.41649 ([(1)

+ 2Cu] , 32), 357.25093 ([1 + H] , 100). UV/Vis

2

+ Cu] , 52),

λex. = 379 nm): λ = 409, 428 nm.

2

+

4

(

−5

−1

CH CN, c = 1.4 × 10 mol l , d = 0.2 cm): λ (ε, L mol cm )

3

=

224 (65 836), 262 (77 063), 384 (59 817) nm. Fluorescence

CN, λex. = 384 nm): λ = 456 nm.

X-ray crystallographic study

spectrum (CH

3

Suitable crystals were taken directly out of the mother liquor,

immersed in perfluorinated polyether oil and fixed on top of a

glass capillary. Measurements were made with a Nonius-Kappa

CCD diﬀractometer with a low-temperature unit using graph-

ite-monochromated MoKα radiation. The temperature was set

to 100 K. The data collected were processed using the standard

[

(CuCl) 3]

2

3

1.5 mg (0.08 mmol, 1.0 eq.) of 3 were added to a suspension

of 14.8 mg (0.15 mmol, 1.96 eq.) CuCl in 8 ml toluene. After

stirring the reaction mixture for 1 h at room temperature, CuCl

was completely dissolved and the solution turned orange.

Overnight an orange solid precipitated which was isolated and

3

2

Nonius software. All calculations were performed using the

SHELXT-PLUS software package. Structures were solved by

direct methods with the SHELXS-97/2014 program and refined

subsequently washed with Et

received as an orange solid in a yield of 25.7 mg (0.04 mmol,

5%). Crystals were obtained from a CH Cl solution, but were

2

O (3 × 5 ml). The product was

3

3,34

with the SHELXL-97/2014 program.

Graphical handing of

5

2

the structural data during solution and refinement was per-

not suitable for X-ray diﬀraction analysis. Elemental analysis

calcd (%) for C H Cl Cu N (610.58): C 43.28, H 5.94,

N

(

3

5

formed with XPMA. Atomic coordinates and anisotropic

thermal parameters of non-hydrogen atoms were refined by

full-matrix least-squares calculations. For 1 498 071 and

2

36

2

8

1

18.35; found

200.13 MHz, CD

.02 (m, 4 H, –CH–), 6.68 (d, J = 8.31 Hz, 2 H, CH ), 7.69 (d,

C

42.99,

H

6.23,

N

18.50.

H

NMR

2

3

CN): δ = 1.25 (d, J = 6.22 Hz, 2 H, –CH

3

),

1

498 072, full shells of intensity data were collected at low

temperature with an Agilent Technologies Supernova-E CCD

diﬀractometer (Mo- or Cu-K radiation, microfocus X-ray tube,

2

4

ar

2

13

J = 8.31 Hz, 2 H, CH ) ppm. C NMR: too low solubility.

ar

α

IR (CsI): ν = 3274, 2973, 2934, 2872, 1602, 1577, 1570, 1560,

1

multilayer mirror optics). Detector frames (typically ω-,

occasionally φ-scans, scan width 0.4–1°) were integrated by

556, 1507, 1461, 1438, 1411, 1381, 1374, 1343, 1233, 1154,

128, 1109, 1015, 962, 830, 783, 705, 555, 503 cm . MS (FAB ):

−

1

+

3

6,37

profile fitting.

Data were corrected for air and detector

+

2 3

m/z (%) = 573.17 ([3 + Cu Cl] , 40). UV/Vis (CH CN, c =

3

7

absorption, Lorentz and polarization eﬀects and scaled

.7 × 10⁻mol l⁻¹, d = 1.0 cm): λ (ε, L mol cm ) = 261

84 034), 299 (44 885), 379 (75 014), 389 (62 736), 399 (105 331)

nm. Fluorescence spectrum (CH CN, λex. = 379 nm): λ = 407,

28 nm.

5

−1

0

(

essentially by application of appropriate spherical harmonic

3

8,39

functions.

cally (Gaussian grid).

formed as part of the numerical absorption correction. The

Absorption by the crystal was treated numeri-

3

9,40

An illumination correction was per-

4

3

9

4

1

structures were solved by the charge flip procedure and

refined by full-matrix least squares methods based on

[(ZnCl )3]

2

42

6

6.0 mg (0.48 mmol, 1.0 eq.) ZnCl was suspended in 20 ml

F

against all unique reflections. All non-hydrogen atoms

2

CH

2

Cl

2

and 200 mg (0.48 mmol, 1.0 eq.) of 3 was added. The were given anisotropic displacement parameters. Hydrogen

reaction mixture was stirred at 50 °C for 3 h. While allowing atoms were input at calculated positions and refined with a

the reaction mixture to cool to room temperature an orange riding model. In the tetrafluoroborate anions B–F and F⋯F

solid precipitated. The precipitate was filtered oﬀ and the distances were restrained or constrained to sensible values

solvent was removed in vacuo aﬀording a yellow solid. The during refinement. Disorder was treated with split atom

solid was washed with hexane (3 × 10 ml) and dried in models whenever possible. Solvent of crystallization (dichloro-

vacuum. The product was obtained as a yellow solid. Yield: methane) was also subjected to suitable geometry and adp

1

95 mg (0.36 mmol, 73%). Elemental analysis calcd (%) for restraints. CCDC no. 1498080 for 1, 1498075 for 2, 1498073

C H Cl N Zn (548.87): C 48.14, H 6.61, N 20.42; found for [3H ]Cl , 1498076 for [Cu (1) ](BF ) ·2CH CN, 1498079

2

36

2

8

2

4

2

4 4

3

1

C 47.94, H 6.31, N 19.72. H NMR (200.13 MHz, CD

95.0 K): δ = 1.31 (d, J = 6.19 Hz, 24 H, –CH ), 4.04 (m, 4 H, for [Cu

2

Cl

2

,

for [Cu

4

(2)

(1)

2

](BF

(CuCl

4

)

4

,

1498074 for [Cu

](BF 1498077 for [Cu

3

(1)

2

Br

2

]Br, 1498072

(1) ](I (I ),

2

3

4

2

)

2

4

)

2

,

3

2

5 2 3

)

–

CH–), 6.85 (d, J = 8.57 Hz, 2 H, CH ), 7.68 (d, J = 8.33 Hz, 2 H, 1498078 for [Cu (1) ](BF ) ·[CoCp ](BF ) and 1498071 for

ar

3

4 3

2

4

1

3

CHar) ppm. C NMR hampered by low solubility. IR (CsI): ν = [Cu

4

(1)

2

(CuCl

2

)

2

](BF

4

)

2

/[Cu

4

(1)

2

(CHCl

2

)

2

4 4 4 2 4 4

](BF ) /[Cu (1) ](BF )

3

1

379, 3310, 2972, 2930, 2873, 1642, 1603, 1587, 1555, 1539, contain the supplementary crystallographic data for this

522, 1503, 1472, 1465, 1451, 1389, 1371, 1341, 1302, 1274, paper (see Table 2 for details).

Dalton Trans.

View Article Online

Paper

Dalton Transactions

Table 2 Crystallographic data and structure reﬁnement for 1, 2, [3H

2

]Cl

·[CoCp

2

·3.6CHCl

3 4 2 3 2 4 4 2 2 4 2 4 4

, [Cu (1) (CH CN) ](BF ) ·2CH Cl , [Cu (2) ](BF ) ,

[

Cu

3

(1)

2

Br

2

]Br·2CH

2

Cl

2

, [Cu

(1)

4 2

(CuCl

2

)

2

](BF

4

)

2

, [Cu

3

(1)

2

](I

5

)

2

(I

3

) and [Cu

3

(1)

3

](BF

4

)

3

2

](BF

4

)

1

2

2 2 3

[H 3]Cl ·3.6CHCl

Formula

C

18

H

28

N

8

C

18

H

24

N

8

25.60 8

C H41.60Cl12.80N

915.23

0.71073

Monoclinic

C2/c

−

1

M

r

(g mol

)

356.48

0.71073

Monoclinic

P2 /n

352.45

0.71073

Monoclinic

P2 /n

λ (Å)

Crystal system

Space group

1

θ

range (°)

2.11 to 30.05

12.442(3)

11.747(2)

13.211(3)

90

97.68(3)

90

1.95 to 30.04

12.567(3)

9.4180(19)

15.448(3)

90

98.81

90

2.18 to 30.10

23.191(5)

14.615(3)

16.702(3)

90

126.50(3)

90

a (Å)

b (Å)

c (Å)

α (°)

β (°)

γ (°)

3

V (Å )

Z

1913.6(7)

4

1806.8(6)

4

4550.8(16)

4

T (K)

100

1.237

0.080

100

1.296

0.084

100

1.336

0.805

−3

dcalc (Mg m

)

−1

µ (mm

)

F(000)

Crystal size (mm )

Reflections measured

768

752

1875

0.40 × 0.40 × 0.25

12 965

3

0.60 × 0.50 × 0.50

11 004

0.35 × 0.30 × 0.10

10 522

Independent reflections

Goodness-of-fit on F

R [I > 2σ(I)]

R (all data)

5581 [Rint = 0.0377]

2

1.040

2

F(R) = 0.0442, wR(F ) = 0.1187

2

F(R) = 0.0705, wR(F ) = 0.1379

[

Cu

4

2 3 2

(1) (CH CN) ](BF

) ·2CH Cl

4 4 2 2

[Cu (2) ](BF )

4 2 4 4

[Cu

3 2

(1) Br

2 2 2

]Br·2CH Cl

Formula

C

42

H

66

4 4

B Cl Cu

4

F

N

16 18

C

36

H

48

B

4

Cu F

N

16 16

C

38

H

60Br

3 4 3

Cl Cu N

16

−

1

M

r

(g mol

)

1566.33

0.71073

1306.30

0.71073

1313.17

0.71073

λ (Å)

Crystal system

Space group

Triclinic

Monoclinic

P2 /c

2.0 to 30.08

12.124(2)

13.969(3)

14.043(3)

90

95.19(3)

90

2368.6(8)

2

Monoclinic

P2 /n

2.28 to 30.04

9.4390(19)

17.862(4)

15.593(3)

90

103.57(3)

90

2555.5(9)

2

Pˉ1

1

θrange (°)

2.50 to 33.14

8.3220(17)

12.133(2)

16.453(3)

108.68(3)

100.32(3)

92.76(3)

1538.4(5)

1

a (Å)

b (Å)

c (Å)

α (°)

β (°)

γ (°)

3

V (Å )

Z

T (K)

100

1.691

1.635

100

1.832

1.885

100

1.707

3.838

−3

dcalc (Mg m

)

−1

µ (mm

)

F(000)

Crystal size (mm )

Reflections measured

Independent reflections

Goodness-of-fit on F

R [I > 2σ(I)]

R (all data)

792

1312

0.40 × 0.30 × 0.15

39 750

6926 [Rint = 0.0669]

1.014

F(R) = 0.0393, wR(F ) = 0.0804

F(R) = 0.0758, wR(F ) = 0.0923

1320

0.50 × 0.40 × 0.25

44 038

7478 [Rint = 0.0523]

1.029

F(R) = 0.0430, wR(F ) = 0.1037

F(R) = 0.0693, wR(F ) = 0.1160

3

0.40 × 0.25 × 0.25

21 391

11 687 [Rint = 0.0254]

2

1.032

2

F(R) = 0.0397, wR(F ) = 0.0973

F(R) = 0.0569, wR(F ) = 0.1056

2

[

4 2 2 2

Cu (1) (CuCl ) ](BF

)

4 2

3 2

[Cu (1) ](I

5 2 3 3

) (I )·CH CN

[Cu

3 3 4 3 2 4

(1) ](BF ) ·[CoCp ](BF )

Formula

C

36

H

56

B

2

Cl Cu

4

F

6 8

N

16

C

38

H

59Cu

I N

3 13 17

C

67.6

H

99.4

B

CoCu F N

4 3 16 25.8

−

1

M

r

(g mol

)

1409.62

1.54184

2594.34

0.71078

1870.32

0.71078

λ (Å)

Crystal system

Space group

Triclinic

Monoclinic

P2 /c

1.89 to 30.00

14.331(3)

28.599(6)

17.554(4)

90

111.43(3)

90

6697(2)

Triclinic

Pˉ1

1

θrange (°)

3.4 to 70.8

1.96 to 30.21

16.074(3)

16.837(3)

18.684(3)

93.06(3)

112.92(3)

108.97(3)

4309.5(15)

a (Å)

b (Å)

c (Å)

α (°)

β (°)

γ (°)

9.36083(19)

10.8067(2)

13.0128(2)

88.2314(16)

81.4761(16)

82.3836(17)

1290.26(4)

3

V (Å )

Dalton Trans.

View Article Online

Dalton Transactions

Paper

Table 2 (Contd.)

[

Cu

4 2 2 2

(1) (CuCl ) ](BF

)

4 2

[Cu

3 2

(1) ](I

5 2 3 3

) (I )·CH CN

[Cu

2

3 3 4 3 2 4

(1) ](BF ) ·[CoCp ](BF )

Z

T (K)

1

4

120(1)

1.814

5.262

708

0.11 × 0.07 × 0.05

79 658

4945 [Rint = 0.0336]

1.118

F(R) = 0.0306, wR(F ) = 0.0918

100

−3

dcalc (Mg m

)

2.573

6.978

4728

0.15 × 0.10 × 0.10

137 445

19 527 [Rint = 0.1486]

1.017

1.441

1.009

1927

0.40 × 0.10 × 0.10

73 717

25 288 [Rint = 0.0687]

0.946

−1

µ (mm

F(000)

Crystal size (mm )

Reflections measured

Independent reflections

Goodness-of-fit on F

R [I > 2σ(I)]

R (all data)

)

3

2

F(R) = 0.0548, wR(F ) = 0.0766

F(R) = 0.1588, wR(F ) = 0.0994

F(R) = 0.0628, wR(F ) = 0.1338

F(R) = 0.1408, wR(F ) = 0.1559

2

F(R) = 0.0319, wR(F ) = 0.0927

Details of quantum chemical calculations

9 Z.-K. Chan, C.-H. Lin, C.-C. Wang, J.-D. Chen, J.-C. Wang

and C. W. Liu, Dalton Trans., 2008, 16, 2183–2189.

10 J. Beck and J. Strähle, Angew. Chem., Int. Ed. Engl., 1985, 24,

409–410, (Angew. Chem., 1985, 97, 419–420).

The density functional calculations were carried out with the

4

3

TURBOMOLE program package and used the B3LYP func-

4

45

tional and the def2-SV(P) basis set. For the calculation of

the two-electron integrals, the approximate resolution-of-the-

1

1 M. Munakata, M. Maekawa, S. Kitagawa and M. Adachi,

Inorg. Chim. Acta, 1990, 167, 181–188.

2 D. Gatteschi, C. Mealli and L. Sacconi, Inorg. Chem., 1976,

4

6

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5, 2774–2778.

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4 H. Araki, K. Tsuge, Y. Sasaki, S. Ishizaka and N. Kitamura,

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Acknowledgements

The authors gratefully acknowledge continuous financial

support by the Deutsche Forschungsgemeinschaft (DFG). This

research was supported in part by the computational resources

provided by the bwForCluster JUSTUS, funded by the Ministry

of Science, Research and Arts and the Universities of the State

of Baden-Württemberg, Germany, within the framework

program bwHPC-C5.

2009, 1664–1666.

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7 (a) D. Gatteschi, C. Mealli and L. Sacconi, J. Am. Chem.

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3

Notes and references

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K. Krogmann and H.-D. Hausen, Z. Anorg. Allg. Chem.,

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Angew. Chem., Int. Ed., 2004, 43, 5029–5032, (Angew. Chem., 19 E. Bindewald, R. Lorenz, O. Hübner, D. Brox, D.-P. Herten,

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E. Kaifer and H.-J. Himmel, Dalton Trans., 2015, 44, 3467–

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K. Nakamae, Y. Takemura, B. Kure, T. Nakajima,

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8

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2

Dalton Trans.

View Article Online

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Dalton Transactions

2

3 P. Wormell and A. R. Lacey, Chem. Phys., 1987, 118, 71–89.

4 D. W. Boldridge, G. W. Scott and T. A. Spiglanin, J. Phys.

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36 K. Kabsch, in International Tables for Crystallography, ed.

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2

5 For a detailed discussion, see: (a) D. Emeljanenko, 37 CrysAlisPro, Agilent Technologies UK Ltd., Oxford, UK,

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Construction of copper chains with new fluorescent guanidino-functionalized naphthyridine ligands

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