Accessible Published by De Gruyter October 8, 2016

Synthesis, crystal structures and blue emission of zinc(II) halide complexes of 1-alkyl-imidazole and (–)-nicotine

Elnaz Hobbollahi, Barbora Veselkova, Manuela List, Günther Redhammer and Uwe Monkowius


Zn(II) halide complexes of the form L2ZnX2 (X=Cl, Br, I) containing bio-relevant or bio-related ligands like 1-alkyl-imidazoles (alkyl=methyl, ethyl and iso-propyl) or (–)-nicotine are presented. All complexes were characterized by 1H NMR spectroscopy, mass spectrometry and elemental analysis. The molecular structures of the majority of complexes were determined by single crystal X-ray diffraction. The zinc ion exists in a tetrahedral environment coordinated by two halide anions and two nitrogen atoms of the N-heterocycles. Upon photoexcitation the nicotine complexes feature a blue emission which we tentatively assign to phosphorescence.

1 Introduction

Zinc is an essential element and found in all forms of life [1]. On average, an adult human contains about 3 g of zinc and estimated 10% of all proteins may contain zinc ions [2], [3]. It is found in several enzymes where Zn(II) ions often function as a Lewis acid to facilitate hydroxylation reactions or further catalytic transformations [4]. In addition, zinc ions stabilize certain protein structures, e.g. in zinc fingers [5], [6]. Besides their catalytic and structural roles, Zn(II) complexes are found to be active against some cancer cells [7]. Hence, it is not surprising that Zn(II) influences several biological processes and is beneficial for the treatment of several diseases. In typical biological complexes, the Zn(II) atom is coordinated by nitrogen atoms of histidine or sulfur atoms of cysteine. Several model compounds have been synthesized to mimic enzymatic reactions [8]. Additionally, zinc complexes have also been investigated as homogeneous catalysts for organic transformations [9], [10].

In this contribution, we present Zn(II) halide complexes of the form L2ZnX2 (X=Cl, Br, I) which contain bio-relevant or bio-related ligands like 1-alkyl-imidazoles (alkyl=methyl, ethyl and iso-propyl) or (–)-nicotine. Many complexes bearing five-membered nitrogen heterocyclic ligands mimicking the heterocyclic side chain of histidine or the purine moiety of adenine or guanine have been reported. Indeed, metal complexes of N-substituted imidazole ligands have been synthesized before [11], [12], [13], [14]. However, structural studies particular on such Zn(II) complexes are rare [15], [16], [17], [18]. A comparable situation is found for (–)-nicotine: A small number of structurally characterized metal complexes have been reported so far [19], [20], [21], [22], [23], [24], [25]. They have been prepared for different reason, e.g. for biological studies [26], for use as caged nicotine [27], as a ligand in catalytic active [28] or emissive metal complexes [29]. Interestingly, there are a number of nicotine complexes with other d10 metals like Cu(I), Ag(I), Cd(II), Hg(II) known [29], [30], [31], [32], [33], [34], [35], but only a few crystal structures of nicotine coordinated to a Zn(II) ion have been published so far [36], [37], [38].

2 Results and discussion

2.1 Synthesis and characterisation

The Zn(II) complexes were synthesized from anhydrous Zn(II) halides and the N-heterocycles in methanol in a stoichiometric ratio under reflux conditions (Scheme 1). In general, the yields of the isolated complexes were low to moderate. Single crystals of almost all compounds could be obtained by crystallization from methanol. As reported recently, the zincate complex (HL)ZnCl3 bearing a protonated pyrrolidine nitrogen atom is formed under very similar reaction conditions (but in a stoichiometric ratio of 1:1 for nicotine to ZnCl2) [37].

Scheme 1: Synthesis of the Zn(II) complexes.

Scheme 1:

Synthesis of the Zn(II) complexes.

All complexes were characterized by 1H NMR and UV/Vis spectroscopy, mass spectrometry and elemental analysis. The 1H NMR spectra feature the signals expected for coordinated alkyl-imidazole and nicotine, respectively. In the ESI mass spectra, no peaks representing the molecular ion could be detected. However, complex ions like [LZnX]+, [L2ZnX]+ and [L3ZnX]+ were formed by ligand scrambling reactions. For chloride complexes also dimeric species of the form [L3Zn2Cl3]+ were detected.

2.2 Structural studies

With the exception of 3-Cl all Zn(II) complexes formed crystals suitable for single crystal X-ray diffraction. Table 1 contains selected structural parameters, Tables 2 and 3 summarize the crystallographic data.

Table 1:

Selected structural parameters (values of 1-Cl are taken from Ref. [16]).

Table 2:

Crystal data and data collection and structure refinement details for the imidazole complexes.

Empirical formulaC8H12Br2N4ZnC8H12I2N4ZnC10H16Cl2N4ZnC10H16Br2N4ZnC10H16I2N4ZnC12H20Br2N4ZnC12H20I2N4Zn
Size, mm0.24×0.16×0.150.39×0.30×0.200.11×0.08×0.070.24×0.16×0.150.11×0.09×0.070.22×0.18×0.110.45×0.12×0.11
Crystal systemMonoclinicMonoclinicMonoclinicMonoclinicMonoclinicMonoclinicMonoclinic
Space groupP21/nP21/nP21/nP21/cP21/aP21/cP21/c
a, Å8.2702(4)8.8507(12)11.503(3) Å15.089(2)8.765(2)8.578(2)8.8616(7)
b, Å12.8177(7)12.2685(15)10.082(3) Å11.979(2)12.237(3)12.656(3)12.5974(9)
c, Å12.9999(7)13.6860(17)13.545(4) Å8.5681(13)15.546(4)16.517(4)17.2889(13)
β, deg101.7993(7)99.892(3)109.057(5)95.92196.143(3)98.449(3)95.2667(9)
V, Å31353.6(2)1468.3(6)1484.7(13)1540.4(4)1657.8(8)1773.7(7)1921.9(4)
ρcalcd., g cm−31.912.191.471.802.051.671.86
μ(MoKα), mm−
T, K293293293293293293293
θ range, deg2.3–28.62.2–29.12.0–22.32.2–23.72.1–26.22.0–24.02.0–28.7
Measured reflections16941182271380313682176481632123966
Independent reflections3373368918822326331827944817
Reflections with I>2σ(I))2622320614821877264222543768
Absorption correctionMulti-scanMulti-scanMulti-scanMulti-scanMulti-scanMulti-scanMulti-scan
Refined parameters140140158156158177177
R1 (I>2 σ(I))0.0290.0270.0350.0330.0350.0330.032
ρfin (max/min), e Å−30.64/–0.500.47/–0.810.43/–0.300.52/–0.271.11/–0.390.57/–0.460.79/–0.36
CCDC no.1495476149548314954811495485149548214954841495477
Table 3:

Crystal data and data collection and structure refinement details for the nicotine complexes.

Empirical formulaC20H28Cl2N4ZnC20H27Br2N4ZnC20H28I2N4Zn
Size, mm30.69×0.17×0.090.81×0.20×0.160.57×0.27×0.26
Crystal systemOrthorhombicOrthorhombicOrthorhombic
Space groupP212121P212121P212121
a, Å5.6481(6)5.733(2)5.9419(7)
b, Å18.2912(18)18.357(9)19.093(2)
c, Å21.181 (2)20.992(9)21.140(3)
V, Å32188.2 (4)2209.2(17)2398.3(5)
ρcalcd., g cm−31.401.651.78
μ(MoKα), mm−
T, K300300300
θ range, deg2.2–23.92.2–23.12.2–26.3
Measured reflections232572057026268
Independent reflections367332684934
Reflections with I>2σ(I))309523483696
Absorption correctionMulti-scanMulti-scanMulti-scan
Refined parameters246247247
R1 (I>2 σ(I))0.0350.0770.064
ρfin (max/min), e Å−30.25/–0.361.26/–1.493.12/–2.72
x (Flack)0.01(1)0.04(4)0.01(6)
CCDC no.149547914954781495480

All alkyl-imidazole complexes crystallize in monoclinic space groups with similar size of their unit cells (Table 2). However, they do not crystallize isostructurally. All zinc atoms exist in a tetrahedral environment coordinated by two chlorine atoms and two nitrogen atoms (N1, N3) of two imidazole ligands. In all complexes the N–Zn distances are ~ 2.0 Å. The Zn–X distances are ~ 2.2 (Cl), ~ 2.4 (Br), and ~ 2.5 Å (I). The N–Zn–N angles are around the tetrahedral standard and vary from 104 to 110°. To the contrary, the X–Zn–X angles are considerably above the tetrahedral standard reaching values up to 120° for the bromides and iodides (Table 1). The most obvious difference is the mutual orientation of the imidazole rings – they are either pointing in the same or in opposite directions. No clear relation can be identified between the nature of the anions or of the alkyl groups and the orientation of the imidazole rings (compare molecular structures in Fig. 1). In all imidazole complexes, hydrogen atoms of the imidazole rings and rarely also those of the alkyl substituents participate in a network of intermolecular C–H···X hydrogen bonds. It should be noted that the molecular structure of 1-Cl has been reported previously. It is isostructural to 1-Br [16]. For completeness, the geometric parameters of 1-Cl are also included in Table 1.

Fig. 1: Molecular structures of all imidazole complexes and of 4-Cl. (Displacement ellipsoids are drawn at the 50% probability level, H atoms as spheres with arbitrary radii.)

Fig. 1:

Molecular structures of all imidazole complexes and of 4-Cl. (Displacement ellipsoids are drawn at the 50% probability level, H atoms as spheres with arbitrary radii.)

Contrary to the imidazole complexes, all nicotine complexes are isostructural (orthorhombic, P212121, Table 3) with very similar crystallographic metrics. Again, the N–Zn distances are ~2.0 Å. The Zn–X distances are ~2.22 (Cl), ~2.35 (Br), and ~2.56 Å (I). Interestingly, the angles X–Zn–X decrease with increasing atomic number from 125.1(4)° for the chloride to 123.6(9)° and 121.8(5) for the bromide and iodide, respectively – a trend which can be found less pronounced also for py2ZnX2 [39]. No intramolecular C–H···X hydrogen bonds are observed.

2.3 Spectroscopic studies

We have investigated the electronic properties of the nicotine complexes by UV/Vis and luminescence spectroscopy [40]. All complexes feature structured absorption bands around 260 nm (Table 4). Such absorptions are typical for π-π* excitations of the pyridine moiety of the nicotine ligand. Pure pyridine features similarly shaped absorbance bands at comparable wavelengths (λabs=246, 252, 258, and 264 nm) [41], [42], [43]. For the iodide complex an additional band can be observed at 220 nm which is caused by the absorption of the iodide coordinated to the Zn(II) ion [44]. We could not observe any emission of both the free nicotine ligand as well as of the zinc complexes 4-X in methanolic solution at r. t. or 77 K. Pyridine is considered to be almost non-emissive in various solvents. The negligible emission quantum yields are caused by quenching n-π* excited states. However, at 77 K pure crystalline pyridine as well as solutions of pyridine in various polar and nonpolar solvents feature weak dual emission with a broad, structureless phosphorescence band (360–540 nm, λmax=~430 nm) [45]. By blocking the n-π* transition by protonation, a broad phosphorescence band around 400 nm could be detected in a mixture of diluted hydrochloric acid and ethylene glycol at room temperature [46]. Both, the emission of the free pyridine as well as of the pyridinium cation were assigned to a 3π-π* excited state.

Table 4:

UV/Vis and emission data of 4-X.

CompoundAbsorption in MeOHEmission (solid): λmax (in nm)
λmax (in nm) (log ɛ)298 K77 K
(–)-nicotine256 (2.80), 261 (2.84), 268 (2.74)
4-Cl259 (2.90), 262 (2.95), 268 (2.80)453460
4-Br255 (2.79), 259 (2.81), 262 (2.85), 268 (2.73)458458
4-I220 (2.07), 256 (2.65), 262 (2.69), 268 (2.47)463464

The nicotine complexes show photo-luminescence in solid state. Neither temperature nor the nature of the anion has a huge influence on the energy or shape of the emission bands which are found from 453 to 463 nm at r. t. and from 458 to 464 nm at 77 K (Fig. 2). Usually, the emission of Zn(II) complexes bearing N-heterocycles can be assigned to fluorescence [47]. However, all emission bands are broad and structureless and the differences between the longest wavelength absorptions and emission maxima are relatively large [48]. Therefore, an emission based on a 1π-π* excited state (= fluorescence) is unlikely. Due to the similarity between the shape and energy of the phosphorescence of pyridine and pyridinium [45], [46], we tentatively assign this emission to an 3π-π* excited state.

Fig. 2: Absorption spectra of (–)-nicotine and 4-X (c≈0.2 mm in MeOH) and emission spectra of crystalline 4-X at r. t. (•) and 77 K (–).

Fig. 2:

Absorption spectra of (–)-nicotine and 4-X (c≈0.2 mm in MeOH) and emission spectra of crystalline 4-X at r. t. (•) and 77 K ().

3 Conclusion

We have prepared Zn(II) halide complexes of the form L2ZnX2 (X=Cl, Br, I) containing bio-relevant or bio-related ligands such as 1-alkyl-imidazoles (alkyl=methyl, ethyl and iso-propyl) or (–)-nicotine. Most complexes formed crystals suitable for X-ray diffraction. The zinc ions are coordinated by two halide anions and two nitrogen atoms of the two N-heterocycles in a tetrahedral geometry. Upon photoexcitation, the nicotine complexes feature a blue emission which is tentatively assigned to phosphorescence.

4 Experimental section

4.1 General

All solvents and other reagents were commercially obtained and used as received. N-ethylimidazole and N-isopropylimidazole were synthesized according to a published procedure from imidazole, KOH and the respective alkyl halide in DMSO [49]. NMR spectra were recorded on an Avance DRX 300 (300 MHz) spectrometer, and 1H shifts are reported in ppm relative to SiMe4, with the residual signal of the deuterated solvent as internal reference. UV/Vis spectra were recorded on a Cary 300 spectrophotometer. Mass spectra were collected on a Finnigan LCQ DecaXPPlus ion trap mass spectrometer with ESI ion source.

4.2 Syntheses

General Procedure: ZnX2 (X=Cl, Br, I) was dissolved in 20 mL methanol. Two equivalents of alkyl-imidazole or (–)-nicotine were added. The mixture was stirred overnight. After refluxing for 1 h the mixture was filtered. The complexes crystallize upon evaporation of methanol as colorless crystals which were washed with diethyl ether and dried in a vacuum.

4.3 Bis(N-methylimidazole)-dibromido-zinc(II), 1-Br

ZnBr2 (0.510 g, 2.26 mmol), N-methylimidazole (0.370 g, 4.52 mmol). Yield: 0.14 g (16%). – Elemental analysis for C8H12N4ZnBr2 (389.40 g mol−1): calcd. C 24.68, H 3.11, N 14.39; found: C 24.70, H 3.08, N 14.03. – ESI-MS (MeOH): m/z=227 [LZnBr]+, 309 [L2ZnBr]+, 390.8 [L3ZnBr]+. – 1H NMR (DMSO, 300 MHz): δ=3.74 (s, 3H), 7.03 (s, 1H), 7.35 (s, 1H), 8.01 (s, 1H).

4.4 Bis(N-methylimidazole)-diiodido-zinc(II), 1-I

ZnI2 (0.57 g, 1.8 mmol), N-methylimidazole (0.29 g, 3.6 mmol). Yield: 0.33 g (37%). – Elemental analysis for C8H12N4ZnI2 (483.42 g mol−1): calcd. C 19.88, H 2.05, N 11.59; found: C 19.93, H 2.48, N 11.23. – ESI-MS (MeOH): m/z=291 [LZnI+H2O]+, 337 [LZnI+2MeOH]+. – 1H NMR (CDCl3, 300 MHz): δ=3.76 (s, 3H), 6.99 (s, 1H), 7.21 (s, 1H), 8.01 (s, 1H).

4.5 Bis(N-ethylimidazole)-dichlorido-zinc(II), 2-Cl

ZnCl2 (0.55 g, 4.0 mmol), N-ethylimidazole (0.77 g, 8.1 mmol). Yield: 0.17 g (13%). – Elemental analysis for C10H16N4ZnCl2 (328.58 g mol−1): calcd. C 36.56, H 4.91, N 17.05; found: C 36.43, H 4.84, N 16.82. – ESI-MS (MeOH): m/z=195.13 [LZnCl]+, 291.13 [L2ZnCl]+, 386.58 [L3ZnCl]+, 524.80 [L3ZnCl3]+. – 1H NMR (CDCl3, 300 MHz): δ=1.48 (t, 3H), 4.06 (q, 2H), 7.00 (s, 1H), 7.16 (s, 1H), 8.01 (s, 1H).

4.6 Bis(N-ethylimidazole)-dibromido-zinc(II), 2-Br

ZnBr2 (0.51 g, 2.2 mmol), N-ethylimidazole (0.43 g, 4.5 mmol). Yield: 0.29 g (29%). – Elemental analysis for C10H16N4ZnBr2 (417.46 g mol−1): calcd. C 28.77, H 3.86, N 13.42; found: C 28.77, H 3.86, N 13.15. – ESI-MS (MeOH): m/z= 241.07 [LZnBr]+, 339.00 [L2ZnBrl]+, 432.80 [L3ZnBr]+. – 1H NMR (CDCl3, 300 MHz): δ=1.49 (t, 3H), 4.05 (q, 2H), 7.01 (s, 1H), 7.18 (s, 1H), 8.02 (s, 1H).

4.7 Bis(N-ethylimidazole)-diiodido-zinc(II), 2-I

ZnI2 (0.57 g, 1.8 mmol), N-ethylimidazole (0.34 g, 3.6 mmol). Yield: 0.22 g (27%). – Elemental analysis for C10H16N4ZnI2 (511.48 g mol−1): calcd. C 23.48, H 3.15, N 10.95; found: C 23.50, H 3.11, N 10.58. – ESI-MS (MeOH): m/z= 287.13 [LZnI]+, 383.07 [L2ZnI]+, 478.93 [L3ZnI]+. – 1H NMR (CDCl3, 300 MHz): δ=1.49 (t, 3H), 4.05 (q, 2H), 7.04 (s, 1H), 7.18 (s, 1H), 8.05 (s, 1H).

4.8 Bis(N-isopropylimidazole)-dichlorido-zinc(II), 3-Cl

ZnCl2 (0.55 g, 4.0 mmol), N-isopropylimidazole (0.88 g, 8.1 mmol). Yield: 0.53 g (37%). – Elemental analysis for C12H20N4ZnBr2 (356.60 g mol−1): calcd. C 40.42, H 5.65, N 15.71; found: C 40.23, H 5.51, N 15.62. – ESI-MS (MeOH): m/z=209.13 [LZnCl]+, 319.13 [L2ZnCl]+, 429.00 [L3ZnCl]+, 566.73 [L3Zn2Cl3]+. – 1H NMR (CDCl3, 300 MHz): δ=1.50 (d, 6H), 4.42 (sept, 1H), 7.05 (s, 1H), 7.17 (s, 1H), 8.06 (s, 1H).

4.9 Bis(N-isopropylimidazole)-dibromido-zinc(II), 3-Br

ZnBr2 (0.57 g, 3.0 mmol), N-isopropylimidazole (0.66 g, 6.0 mmol). Yield: 0.23 g (22%). – Elemental analysis for C12H20N4ZnBr2 (445.51 g mol−1): calcd. C 32.35, H 4.52, N 12.58; found: C 30.15, H 4.31, N 10.15. – ESI-MS (MeOH): m/z=255.07 [LZnBr]+, 365.07 [L2ZnBr]+, 474.80 [L3ZnBr]+. – 1H NMR (CDCl3, 300 MHz): δ=1.51 (d, 6H), 4.39 (sept, 1H), 7.04 (s, 1H), 7.19 (s, 1H), 8.04 (s, 1H).

4.10 Bis(N-isopropylimidazole)-diiodido-zinc(II), 3-I

ZnI2 (0.51 g, 1.6 mmol), N-isopropylimidazole (0.35 g, 3.2 mmol). Yield: 0.45 g (48%). – Elemental analysis for C12H20N4ZnI2 (539.534 g mol−1): calcd. C 26.72, H 3.74, N 10.38; found: C 26.70, H 3.74, N 10.11. – ESI-MS (MeOH): m/z=301.13 [LZnI]+, 411.07 [L2ZnI]+, 520.87 [L3ZnI]+. – 1H NMR (CDCl3, 300 MHz): δ=1.51 (d, 6H), 4.39 (sept, 1H), 7.05 (s, 1H), 7.21 (s, 1H), 8.07 (s, 1H).

4.11 Bis((–)-nicotine)-dichlorido-zinc(II), 4-Cl

ZnCl2 (0.50 g, 3.6 mmol), (–)-nicotine (1.2 g, 7.4 mmol). Yield: 0.92 g (54%). – Elemental analysis for C20H28N4ZnCl2 (460.73 g mol−1): calcd. C 52.14, H 6.13, N 12.16; found: C 52.30, H 6.14, N 11.92. – ESI-MS (MeOH): m/z=195.14 [L+MeOH], 423.12 [L2ZnCl]+, 585.24 [L3Zn Cl]+, 623.21 [L3ZnCl2]+, 723.11 [L3Zn2Cl3]+. – 1H NMR (DMSO, 300 MHz): δ=1.57 (m, 2H), 1.82 (m, 4H), 2.05 (s, 6H), 2.27 (m, 4H), 3.16 (m, 4H), 7.44 (m, 2H), 7.80 (dt, 2H), 8.45 (dd, 2H), 8.51 (d, 2H).

4.12 Bis((–)-nicotine)-dichlorido-zinc(II), 4-Br

ZnBr2 (0.5 g, 2.2 mmol), (–)-nicotine (0.72 g, 4.4 mmol). Yield: 0.88 g (73%). – Elemental analysis for C20H28N4ZnBr2 (548.65 g mol−1): calcd. C 43.70, H 5.13, N 10.19; found: C 43.90, H 5.13, N 9.96. – ESI-MS (MeOH): m/z=195.14 [L+MeOH], 257.06 [LZn+MeOH]+, 325.23 [LZnBr]+, 405.16 [LZnBr2+H2O]+, 469.07 [L2ZnBr]+, 631.19 [L3ZnBr]+, 713.11 [L3ZnBr2]+. – 1H NMR (DMSO, 300 MHz): δ=1.54 (m, 2H), 1.81 (m, 2H), 2.06 (s, 6H), 2.21 (m, 4H), 3.14 (m, 4H), 7.44 (m, 2H), 7.82 (dt, 2H), 8.47 (dd, 2H), 8.52 (d, 2H).

4.13 Bis((–)-nicotine)-diiodido-zinc(II), 4-I

(0.5 g, 1.56 mmol) ZnI2, (–)-nicotine (0.50 g, 3.1 mmol). Yield: 0.65 g (65%). – Elemental analysis for C20H28N4ZnI2 (643.63 g mol−1): calcd. C 37.32, H 4.38, N 8.70; found: C 37.81, H 4.44, N 8.51. – ESI-MS (MeOH): m/z=257.06 [LZn+MeOH]+, 352.94 [LZnI]+, 515.06 [L2ZnI]+, 677.17 [L3ZnI]+, 805.09 [L3ZnI2]+. – 1H NMR (DMSO, 300 MHz): δ=1.58 (m, 2H), 1.81 (m, 4H), 2.07 (s, 6H), 2.29 (m, 4H), 3.13 (m, 4H), 7.39 (m, 2H), 7.70 (dt, 2H), 8.45 (dd, 2H), 8.49 (d, 2H).

4.14 Crystal structure determinations

Single-crystal structure analyses was carried out on a Bruker SMART APEX and Bruker SMART X2S diffractometer with graphite-monochromatized MoKα radiation (λ=0.71073 Å). The structures were solved by Direct Methods (Shelxs-97, Sir-97) [50], [51] and refined by full-matrix least-squares on F2 (Shelxl-97) [52]. The H atoms were calculated geometrically, and a riding model was applied in the refinement process. Tables 2 and 3 summarize the most important crystallographic data.

CCDC 1495476–1495485 contain the supplementary crystallographic data for 1-Br, 1-I, 2-Cl, 2-Br, 2-I, 3-Br, 3-I, 4-Cl, 4-Br and 4-I, respectively. These data can be obtained free of charge from The Cambridge Crystallographic Data Center


We thank the JKU and Prof. Günther Knör (JKU) for his generous support of the experimental work. The NMR spectrometers were acquired in collaboration with the University of South Bohemia (CZ) with financial support from the European Union through the EFRE INTERREG IV ETC-AT-CZ programme (project M00146, “RERI-uasb”).


[1] W. Maret, Adv. Nutr.2013, 4, 82. Search in Google Scholar

[2] C. F. Mills, Zinc in Human Biology, Springer-Verlag, London, 1989. Search in Google Scholar

[3] M. Laitaoja, J. Valjakka, J. Jänis, Inorg. Chem.2013, 52, 10983. Search in Google Scholar

[4] G. Parkin, Chem. Rev.2004, 104, 699. Search in Google Scholar

[5] D. S. Auld, BioMetals2009, 22, 141. Search in Google Scholar

[6] K. A. Mccall, C. Huang, C. A. Fierke, J. Nutr.2000, 130, 1437S. Search in Google Scholar

[7] D. Magda, P. Lecane, Z. Wang, W. Hu, P. Thiemann, X. Ma, P. K. Dranchak, X. Wang, V. Lynch, W. Wei, V. Csokai, J. G. Hacia, J. L. Sessler, Cancer Res.2008, 68, 5318. Search in Google Scholar

[8] G. Parkin, Chem. Commun.2000, 1971. Search in Google Scholar

[9] S. Enthaler, ACS Catal.2013, 3, 150. Search in Google Scholar

[10] E. S. Donovan, B. M. Barry, C. A. Larsen, M. N. Wirtz, W. E. Geiger, R. A. Kemp, Chem. Commun.2016, 52, 1685. Search in Google Scholar

[11] J. A. Welleman, F. B. Hulsbergen, J. Verbiest, J. Reedijk, J. Inorg. Nucl.Chem.1978, 40, 143. Search in Google Scholar

[12] C. Pettinari, F. Marchetti, A. Cingolani, S. I. Troyanov, A. Drozdov, Polyhedron1998, 17, 1677. Search in Google Scholar

[13] D.M.L. Goodgame, M. Goodgame, G.W. Rayner-Canham, Inorg. Chim. Acta1969, 3, 399. Search in Google Scholar

[14] D. M. L. Goodgame, M. Goodgame, G. W. Rayner-Canham, Inorg. Chim. Acta1969, 3, 406. Search in Google Scholar

[15] P. Drożdżewski, B. Pawlak, T. Głowiak, Polyhedron2002, 21, 2819. Search in Google Scholar

[16] G. Musie, X. Li, D. R. Powell, Acta Crystallogr. 2004, E60, m471. Search in Google Scholar

[17] S. G. Baca, I. G. Filippova, N. V. Gerbeleu, Y. A. Simonov, M. Gdaniec, G. A. Timco, O. A. Gherco, Y. L. Malaestean, Inorg. Chim. Acta2003, 344, 109. Search in Google Scholar

[18] P. K. Bharadwaj, H. J. Schugar, J. A. Potenza, Acta Crystallogr.1991, C47, 754. Search in Google Scholar

[19] H. Haendler, Acta Crystallogr.1990, C46, 2054. Search in Google Scholar

[20] M. Strickler, B. M. Goldstein, K. Maxfield, L. Shireman, G. Kim, D. S. Matteson, J. P. Jones, Biochem.2003, 42, 11943. Search in Google Scholar

[21] M. O. Onani, R. A. Lalancette, N. T. Muriithi, E. A. Nyawade, B. V. Kgarebe, Acta Crystallogr. 2010, E66, m480. Search in Google Scholar

[22] J. Guan, R. D. Fischer, Eur. J. Inorg. Chem.2001, 2497. Search in Google Scholar

[23] Z. Jiang, G. Tang, L. Lu, Acta Crystallogr.2008, E64, m958. Search in Google Scholar

[24] T. Kawasaki, T. Nishimura, T. Kitazawa, Bull. Chem. Soc. Japan2010, 83, 1528. Search in Google Scholar

[25] S. Michalik, R. Kruszynski, K. Leszczyńska-Sejda, J. Kusz, S. Krompiec, J. Coord. Chem.2009, 62, 1232. Search in Google Scholar

[26] F.M. Albertí, J.J. Fiol, A. García-Raso, M. Torres, A. Terrón, M. Barceló-Oliver, M. J. Prieto, V. Moreno, E. Molins, Polyhedron2010, 29, 34. Search in Google Scholar

[27] O. Filevich, M. Salierno, R. Etchenique, J. Inorg. Biochem.2010, 104, 1248. Search in Google Scholar

[28] S. Jana, P. A. G. Cormack, A. R. Kennedy, D. C. Sherrington, J. Mater. Chem.2009, 19, 3427. Search in Google Scholar

[29] C. Hirtenlehner, U. Monkowius, Inorg. Chem. Commun.2012, 15, 109. Search in Google Scholar

[30] Z.-J. Jiang, Y. Zhang, G.-D. Tang, J.-Y. Zhao, L.-D. Lu, Z. Kristallogr. NCS2009, 224, 466. Search in Google Scholar

[31] G. Meyer, A. Berners, I. Pantenburg, Z. Anorg. Allg. Chem.2006, 632, 34. Search in Google Scholar

[32] M. R. Udupa, B. Krebs, Inorg. Chim. Acta1980, 40, 161. Search in Google Scholar

[33] Z.-J. Jiang, L.-T. An, J. Song, L.-D. Lu, Lu-De, Wuji Huaxue Xuebao (Chin. J. Inorg. Chem.) 2012, 28, 35. Search in Google Scholar

[34] W. Lewis, P. J. Steel, Supramol. Chem.2005, 17, 579. Search in Google Scholar

[35] Z. Jiang, G. Tang, Y. Zhang, J. Zhao, Acta Crystallogr. 2008, E64, m1319. Search in Google Scholar

[36] E. C. Escudero-Adán, J. Benet-Buchholz, A. W. Kleij, Inorg. Chem.2008, 47, 4256. Search in Google Scholar

[37] S. Soudani, V. Ferretti, C. Jelsch, F. Lefebvre, C. Ben Nasr, Inorg. Chem. Commun.2015, 61, 187. Search in Google Scholar

[38] Z.-J. Jiang, G.-D. Tang, Y. Zhang, J.-Y. Zhao, G. Wang, Z. Kristallogr. NCS2009, 224, 577. Search in Google Scholar

[39] G. A. Bowmaker, Effendy, Fariati, S. I. Rahajoe, B. W. Skelton, A. H. White, Z. Anorg. Allg. Chem.2011, 637, 1361. Search in Google Scholar

[40] The imidazole complexes absorbed below 220 nm. With our spectrometers it is not possible to get reliable luminescence data from compounds which have such high-energy absorptions. Hence, we did not include these complexes in our spectroscopic studies. Search in Google Scholar

[41] E. B. Hughes, H. H. G. Jellinek, B. A. Ambrose, J. Phys. Chem.1949, 53, 410. Search in Google Scholar

[42] M. Yamin, R. M. Fuoss, J. Am. Chem. Soc.1953, 75, 4860. Search in Google Scholar

[43] The absorption spectra of pyridine and other nitrogen bases can be downloaded from: (accessed August 2016). Search in Google Scholar

[44] Pure ZnI2 in methanol shows as the sole spectral feature an intense signal at 221 nm. Search in Google Scholar

[45] S. K. Ghoshal, A. K. Maiti, G.S. Kastha, J. Luminesc.1984, 31 & 32, 541. Search in Google Scholar

[46] A. G. Motten, A. L. Kwiram, Chem. Phys. Lett.1977, 45, 217. Search in Google Scholar

[47] A. Beitat, S. P. Foxon, Ch.-C. Brombach, H. Hausmann, F. W. Heinemann, F. Hampel, U. Monkowius, C. Hirtenlehner, G. Knör, S. Schindler, Dalton Trans.2011, 40, 5090. Search in Google Scholar

[48] It is not appropriate to call this energy difference Stokes’ shift because solution and solid state spectra are compared. Search in Google Scholar

[49] O. V. Starikova, G. V. Dolgushin, L. I. Larina, T. N. Komarova, V. A. Lopyrev, ARKIVOC2003, xiii, 119. Search in Google Scholar

[50] G. M. Sheldrick Acta Crystallogr.1990, A46, 467. Search in Google Scholar

[51] A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R. Spagna, J. Appl. Cryst.1999, 32, 115. Search in Google Scholar

[52] G. M. Sheldrick, Acta Crystallogr.2008, A64, 112. Search in Google Scholar

Received: 2016-7-25
Accepted: 2016-8-29
Published Online: 2016-10-8
Published in Print: 2016-12-1

©2016 Walter de Gruyter GmbH, Berlin/Boston