Structural studies of copper(ii) complexes with 2-(2-aminoethyl)pyridine derived Schiff bases and application as precursors of thin organic-inorganic layers

Article abstract of DOI:10.1039/c4dt00654b

Cu(ii) complexes with Schiff bases derived from 2-pyridin-2-ylethanamine were obtained and characterized by UV-Vis, fluorescence, and IR spectra. The X-ray crystal structures determined for [Cu(ii)(epy(di-t-Buba))Cl] × 0.042H₂O and [Cu(ii)(epy(di-t-Buba))O₂CCH₃] revealed tetrahedral distortion of the Cu(ii) coordination sphere in the solid phase. For both molecules the Cu(ii) ions were found in tetragonal environments, as was confirmed by the values of EPR g-matrix diagonal components. The thermal properties of the complexes and the gas phase composition were studied by TG/IR techniques. Thin layers of the studied copper(ii) complexes were deposited on Si(111) by a spin coating method and characterized by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM) and fluorescence spectra. For copper(ii) layers the most intensive fluorescence band from intra-ligand transition was observed between 498 and 588 nm. The layers' fluorescence intensity was related to the rotation speed and deposition time.

Full text of DOI:10.1039/c4dt00654b

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Structural studies of copper(II) complexes with
2-(2-aminoethyl)pyridine derived Schiff bases
and application as precursors of thin
organic–inorganic layers†
Cite this: Dalton Trans., 2014, 43,
9924
Magdalena Barwiolek,*a Edward Szlyk,a Andrzej Berg,a Andrzej Wojtczak,a
Tadeusz Muziola and Julia Jezierskab
Cu(II) complexes with Schiff bases derived from 2-pyridin-2-ylethanamine were obtained and character-
ized by UV-Vis, fluorescence, and IR spectra. The X-ray crystal structures determined for [Cu(II)(epy(di-t-
Buba))Cl] × 0.042H2O and [Cu(II)(epy(di-t-Buba))O2CCH3] revealed tetrahedral distortion of the Cu(II)
coordination sphere in the solid phase. For both molecules the Cu(II) ions were found in tetragonal environ-
ments, as was confirmed by the values of EPR g-matrix diagonal components. The thermal properties of
the complexes and the gas phase composition were studied by TG/IR techniques. Thin layers of the studied
copper(II) complexes were deposited on Si(111) by a spin coating method and characterized by scanning
electron microscopy (SEM/EDS), atomic force microscopy (AFM) and fluorescence spectra. For copper(II)
layers the most intensive fluorescence band from intra-ligand transition was observed between 498 and
588 nm. The layers’ fluorescence intensity was related to the rotation speed and deposition time.
Received 4th March 2014,
Accepted 29th April 2014
DOI: 10.1039/c4dt00654b
www.rsc.org/dalton
and their copper(II) complexes were also studied.9 It has been
stated that these complexes effectively interact with CT-DNA
Introduction
Study of copper(II) complexes with Schiff-base ligands has through the groove binding mode, resulting in strong confor-
become a point of interest owing to their intriguing structural mational changes of the CT-DNA. Copper(II) complexes with
features and potential application in various fields. These imine ligands containing imidazolate bridging groups (e.g.
compounds are known for their biological role and fluo- N,N′-bis(2-substituted-imidazol-4-ylmethylidene)-1,4-diamino-
rescence properties. Schiff base derivatives incorporating a butane) have been used as precursors of highly ordered
fluorescent moiety are a useful tool for optical sensing of structures.10–12 Imidazole and oxadiazole-type materials have
metal ions.1 Synthesis of Schiff bases and their complexes as been used as ETMs in the blue fluorescent OLEDs.13 As a
fluorescent materials have also received extensive concern.2
result, highly efficient amplified spontaneous emission as well
Pyridine ligands have been used in coordination chemistry as blue and white organic light-emitting diodes (OLEDs) were
for a variety of metals,3–7 and it has been stated that they play demonstrated with these imidazole derivatives. As a result,
a unique role in synthesis of the biologically active com- highly efficient amplified spontaneous emission as well as
pounds.8 The fluorescence properties and interaction with blue and white organic light-emitting diodes (OLEDs) could be
DNA of the Schiff bases obtained from imidazole derivatives demonstrated with these imidazole derivatives.14 Thin organic
(N-((1H-imidazole-2-yl)methyl)-2-(pyridine-2-yl)ethanamine, and organometallic films have attracted research interest due
N-((1-methyl-1H-imidazole-2-yl)methyl)-2-(pyridine-2-yl)ethana- to their technologically important optical and electronic pro-
mine; 2-(pyridine-2-yl)-N-((pyridine-2-yl)methyl)ethanamine) perties.15 These materials exhibit luminescence; they are used
as conductors, semi-conductors, organic light emitting diodes
(OLED) and drug transporters.16,17 Also many thin films of
metal complexes, such as Zn(II), Pt(II), Cu(II) or Ag(I) with Schiff
bases (e.g. N,N′-bis(salicylidene)-1,2-ethylenediamine, bis(2-
(2-hydroxyphenyl)benzothiazole), were synthesised and their
luminescence properties have been employed in organic
optoelectronics.18–22 Some of those films were spin coated
or vacuum deposited (4,4′-bis(9-carbazolyl)biphenyl and 2(4-
biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole).23 However,
aChemistry Department, Nicholas Copernicus University, 87-100 Torun, Poland.
E-mail: madzia@chem.umk.pl, mbarwiolek@umk.pl; Fax: +48 (56) 654 24 77;
Tel: +48 (56) 611 45 16
bFaculty of Chemistry, University of Wroclaw, 50-137 Wroclaw, Poland.
E-mail: julia.jezierska@chem.uni.wroc.pl; Fax: +48 71 328-23-48;
Tel: +48 (71) 3757330
†CCDC 950557 and 986880. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4dt00654b
9924 | Dalton Trans., 2014, 43, 9924–9933
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there are only a few reports on copper(II) compound materials. pentane-2,4-dione (acacH) (97%) were purchased from Aldrich.
Some of them were obtained by laser ablation, cathodolumi- Copper(II) chloride dihydrate and copper(II) acetate hydrate
nescence or by spin coating.13,24–27
(analytical grade) were supplied by POCH (Gliwice Poland) and
The optical and structural properties of the thin copper(II) used as received.
layers were also studied. In the case of CuPc (Pc – tetra-tricarb-
ethoxyethyl substituted phthalocyanine), the absorption
Methods and instrumentation
increase was noted at higher copper concentration in the UV-Vis absorption spectra were recorded on a Milton Roy Spec-
layers.24
tronic 1201 in CH3CN (1 × 10−5 M) solution and with a
Thin layers of the copper(II) complexes [Cu3(opba)(pmdta)2]- Specord M-40 (Carl Zeiss Jena) spectrophotometer as Nujol
(NO3)2 (pmdta 1,1,4,7,7-pentamethyl-diethylenetriamine, mulls. IR spectral experiments were performed on a Spectrum
opba = orthophenylenebis(oxamato)) on SiO2/Si by the spin 2000 Perkin/Elmer FT IR using KBr discs in the range
coating technique were obtained. The materials exhibited 400–4000 cm−1 and PE discs in the range 400–70 cm−1 1H,
=
.
results pointing out that spin coating is a promising method 13C, 15N NMR spectra of ligand were collected with a Bruker
for deposition of thin layers of transition metal complexes. 400 MHz in CDCl3, against the TMS standard. Elemental ana-
The obtained films were thin and homogeneous with small lysis of C, H and N was performed on a Vario Macro CHN ana-
crystallites on the surface.13 Also the spin coating technique lyser (Elementar Analysensysteme GmbH), whereas copper
was used for [(nBu3P)3Cu–O2CCH2CO2–Cu(PnBu3)3] and elemental analysis was carried by Atomic Absorption Spec-
[(nBu3P)3Cu–O2C(CH2)2CO2–Cu(PnBu3)3] on SiO2/TiN/Cu depo- troscopy (AAS) as Cu2+ salt on an atomic absorption spectro-
sition. The obtained layers were then heated up to 450 °C, meter (Carl Zeiss-Jena). Thermal analysis (TG, DTG, DTA) was
resulting in the complexes’ layers undergoing CuO decompo- performed on an SDT 2960 TA analyzer at nitrogen flow 60 ml
sition. The CuO layers exhibited some cracks.28 SEM results of min−1, heating rate 5 °C min−1 and heating range up to
these films showed not completely homogeneous layers and 1200 °C. Gaseous products of thermal decomposition were
defects. This was explained by the different film thicknesses detected by a FT IR Bio-Rad Excalibur spectrophotometer
obtained during the spin coating process, which upon heating equipped with a thermal connector heated to 200 °C for gases
produced defects due to unequal evaporation leading to par- evolved from an SDT 2960 TA analyser. Powder X-ray diffrac-
tially cracked copper films. However, these results indicated tion data for the thermal analysis residues were obtained with
that the spin coating technique could be used instead of the a Philips X’PERT diffractometer using Cu Kα radiation.
CVD method for non-volatile compounds to obtain thin
The EPR spectra were measured using a Bruker ELEXYS
metallic materials.
E500 spectrometer equipped with an NMR teslameter (ER
Previously, copper(II) and nickel(II) complexes with optically 036TM) and a frequency counter (E 41 FC) at X- and Q-band.
active Schiff bases derived from (1R,2R)(–)cyclohexanediamine The experimental spectra were simulated using the program
were deposited by us on silicon or glass using the spin coating Dublet (S = 1/2) written by Dr Ozarowski from NHMFL, Univer-
method.29,30 The obtained materials exhibited luminescence, sity of Florida, with resonance field calculated by full diagona-
which depends on the spin coating parameters and the struc- lization of the energy matrix.
ture of the complex.
The films were deposited by the spin coating technique on
The facts mentioned above: the fluorescence properties of Si(111) wafers (10\10 mm), glass and ITO. Precursors were dis-
the pyridine derivatives and their complexes, the possibility of solved in tetrahydrofuran and deposited on Si using a spin
using the spin coating technique for deposition of the coater (Laurell 650SZ). The morphology and composition of
copper(II) complexes on different substrates and the likely fluo- the obtained layers were analyzed with a scanning electron
rescence behaviour of the obtained layers prompted us to syn- microscope (SEM; LEO Electron Microscopy Ltd, England,
thesize a series of copper(II) complexes with new Schiff bases model 1430 VP) equipped with detectors of secondary elec-
derived from 2-(2-aminoethyl)pyridine and several aldehydes. trons (SE), and an energy dispersive X-ray spectrometer (EDS;
These complexes were characterized by X-ray crystallography Quantax) with an XFlash 4010 detector (Bruker AXS microana-
and spectroscopically, their fluorescence properties were also lysis GmbH). The atomic force microscopy (AFM) studies in
studied. The new copper(II) complexes were used as precursors the tapping mode were performed on a Veeco (Digital Instru-
of thin layers in the spin coating technique. The morphology ment) microscope (type: MultiMode NanoScope IIIa). The
of layers was analyzed by AFM and SEM microscopy, and the fluorescence spectra were recorded on an F-7000 spectrofluo-
fluorescence properties of the layers were also studied.
rometer (HITACHI) in the range 900–180 nm (5 × 10−4 mol
dm−3 MeCN solution).
X-ray crystallography
Experimental
Materials
The X-ray diffraction data of [Cu(II)(epy(di-t-Buba))Cl]
0.042H2O (1a) and of [Cu(II)(epy(di-t-Buba))O2CCH3] (1b) were
×
2-Pyridin-2-ylethanamine (epy) (95%), 3,5-di-tert-butyl-4-hydro- collected at room temperature using an Oxford Sapphire CCD
xybenzaldehyde (di-t-Buba) (99%), pyridine-2-carbaldehyde diffractometer, Mo Kα radiation λ = 0.71073 Å. The reflections
(pyca) (99%), 1H-imidazole-5-carbaldehyde (4Him) (98%), and were measured with the ω-2θ method and the analytical
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Table 1 Crystal data and structure refinement for [Cu(II)(epy(di-t-Buba))Cl] × 0.042H2O (1a) and [Cu(II)(epy(di-t-Buba))O2CCH3] (1b)
Identification code
(1a)
(1b)
Empirical formula
Formula weight
Temperature [K]
Wavelength [Å]
Crystal system, space group
Unit cell dimensions [Å] and [°]
C
22H29.08ClCuN2O1.04
C24H32CuN2O3
460.06
293(2)
437.21
293(2)
0.71073
Trigonal, R3
a = b = c = 15.8718(2)
α = β = γ = 106.6390(10)
0.71073
ˉ
Monoclinic, P21/c
a = 17.296(2)
b = 11.9783(9)
c = 12.1930(11)
β = 105.196(12)
2437.8(4)
4, 1.253
0.921
972
Volume [Å3]
3362.10(7)
6, 1.296
1.107
1377
Z, Calculated density [Mg m−3
]
]
Absorption coefficient [mm−1
F(000)
Crystal size [mm]
Theta range for data collection [°]
Limiting indices
0.63 × 0.49 × 0.18
2.45 to 27.09
0.36 × 0.34 × 0.05
2.09 to 28.16
−21 ≤ h ≤ 20
−15 ≤ k ≤ 13
−10 ≤ l ≤ 16
16 433/5400 [R(int) = 0.0812]
25° [100.0%]
0.9577 and 0.7354
5400/0/298
−20 ≤ h ≤ 10
−20 ≤ k ≤ 20
−18 ≤ l ≤ 20
Reflections collected/unique
Completeness to theta [%]
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
22 072/4873 [R(int) = 0.0839]
26.00° [99.9%]
0.8256 and 0.5423
4873/0/250
0.9671.000
0.863
Final R indices [I > 2sigma(I)]
R indices (all data)
R1 = 0.0368, wR2 = 0.0956
R1 = 0.0518, wR2 = 0.0990
0.364 and −0.228
R1 = 0.0527, wR2 = 0.1065
R1 = 0.1424, wR2 = 0.1293
0.549 and −0.518
Largest diff. peak and hole [e Å−3
]
absorption correction was applied for the studied crystals
(RED171 package of programs, Oxford Diffraction, 200031).
Both structures were solved by direct methods and refined
with the full-matrix least-squares procedure on F2 (package
SHELX-9732). All heavy atoms were refined with anisotropic
thermal displacement parameters. Hydrogen atoms were
located from the electron density maps and their positions
were constrained in the refinement. In (1a) the disordered
water molecule is found on the C3i axis and its total occupancy
is 0.25. However, this molecule was unstable during the refine-
ment and the thermal parameter was high. Therefore we mod-
elled the solvent disorder in SQUEEZY33 and subsequently the
refinement in SHELXL-97 was repeated resulting in slightly
better R factors and a smooth difference electron density map.
Fig. 1 Structural formula and atom numbering referring to the NMR
signals for epy(di-t-Buba) (1) (Z)-2,4-di-tert-butyl-6-((2-(pyridin-2-yl)-
ethylimino)methyl)phenol, epy(pyca) (2) 2-(4,5-dihydropyridin-2-yl)-N-
(pyridin-2-ylmethyl)ethanamine, (epy)2acacH (3) (2Z,4E)-N-(2-(pyridin-
For (1b) the geometric restraints have been used to ensure the
t
proper geometry of the disordered Bu group. All figures were 2-yl)ethyl)-4-(2-(pyridin-2-yl)ethylimino)pent-2-en-2-amine, epy(4Him)
prepared in DIAMOND34 and ORTEP-3.35 The results of the
(4) (E)-N-((1H-imidazol-4-yl)methylene)-2-(pyridin-2-yl)ethanamine.
data collections and refinement are listed in Table 1. The
CCDC 950557 and 986880 entries contain the crystallographic
1H [ppm]: 1.32 (s, 9H) CH3, 1.46 (s, 9H) CH3, 3.21 (t, 2H)
data for (1a) and (1b), respectively.
CH2−, 4.02 (t, 2H) CH2, 7.045 (d 1H), 7.13–7.21 (m, 2H) Ar–H;
7.28 (s, 1H), 7.38 (d, 1H), 7.59–7.63 (m, 1H) Ar–H; 8.58–8.59
(m, 1H) Ar–H; 8.34 (s, 1H) –NvCH–; 13.76 (s, 1H) –OH.36
Synthesis
Synthesis of ligands. Ligands (1–4) were prepared by a pro-
cedure described in detail for (1) and their structural formulae 117.83 (C15), 121.47 (C2), 123.70 (C4), 125.83 (C14), 126.83
are presented in Fig. 1.
(C3), 136.43 (C11), 136.63 (C12), 139.93 (C13), 149.45 (C1),
pen(di-t-Buba) (1) Schiff base was prepared in the reaction 158.10 (C5), 159.27 (C10), 166.39 (C8).
13C [ppm]: 29.42 (C6), 31.5 (C7), 34.1 (C17), 35.03 (C18),
of 2-hydroxy-3,5-di-tert-butyl-benzaldehyde (2.34 g; 10 mmol in
UV-Vis 209 nm π→ π*, 261 nm π→ π*, 329 nm π→ π*NvC,
15 ml MeOH) with 2-(2-aminoethyl)pyridine (1.19 ml; 409 nm n→π*.37–40
10 mmol). The mixture was stirred at r.t. for 5 h and the
epy(pyca) (2) 1H [ppm]: 2.24 (s, 1H); 3.07 (m, 2H), 3.96
solvent was removed on a rotary evaporator. The product was (s, 1H), 7.15 (m, 1H); 7.20 (d, 1H), 7.62 (m, 1H); 8.54 (m, 1H),
dried under air. Yield 3.10 g (92.1%).
8.34 (s, 1H) –NvCH–;36,41
9926 | Dalton Trans., 2014, 43, 9924–9933
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13C [ppm]: 38.58 (C7), 49.01 (C6), 121.24 (C10), 121.88 (C2),
[Cu(II)(epy(4Him))O2CCH3]
(4a)
Yield:
68.2%.
122.21 (C4), 123.29 (C12), 136.35 (C3), 136.43 (C11), 149.25 C13H15CuN4O2 calc./found %: Cu 19.86/19.40, C 48.82/49.19,
(C1), 149.31 (C13), 159.81 (C9), 160.21 (C5), 55.14 (C8).
15N NMR [ppm]: −69.90 (–NvC), −342.47 (NH).
UV-Vis: 211 nm π→ π*, 256 nm π→ π*, 324 nm π→ π*NvC
400 nm n→π*.37–40
N 17.52/17.42, H 4.68/4.24.
UV-Vis: 205 nm IL, 258 nm IL, 313 nm LMCT.37–40
,
(epy)2acacH (3) 1H NMR [ppm]: 1.85 –CH3 (s, 3H), 1.98 CH3
(s, 3H), 3.04 (t, 4H), CH2–Ar, 3.67 (q, 4H), CH2–N, 4.92 (s, 1H),
CvCH–C, 7.09–7.19 (4H), 7.62 (t, 2H), ArH, 8.55 (d, 2H), ArH,
10.90 (br s, 1H), NH–.36
Results and discussion
Structure of [Cu(II)(epy(di-t-Buba))Cl] × 0.042H2O (1a)
The [Cu(II)(epy(di-t-Buba))Cl] × 0.042H2O (1a) crystallized in
13C NMR [ppm]: 18.76 (C1), 28.77 (C2), 38.83 (C6), 42.73
(C7), 95.33 (C3), 121.75 (C11), 123.73 (C9), 136.60 (C10), 149.60
(C12), 158.25 (C8), 162.97 (C4), 194.86 (C5). Fig. 1.
15N NMR [ppm]: N(3) –NvC amine −266.3, −355.9 N(2) NH
equals N(1) NvC, −68.7.42
ˉ
the rhombohedral R3 space group with the whole molecule in
the asymmetric unit. However, the disordered and relatively
poorly refined water molecule is excluded from the final model
as was mentioned in the Experimental part. The copper(II)
coordination sphere is composed of two nitrogen atoms and
one oxygen from the Schiff base and chloride (Fig. 2). It adopts
the strongly distorted square planar environment with angles
in two ranges from 145.23(8) (O1–Cu1–N17) to 150.98(5) (N9–
Cu1–Cl2) and from 93.12(7) (N9–Cu1–N17) to 96.03(5)° (N17–
Cu1–Cl2). In the coordination sphere, the pyridine nitrogen
occupies the cis position relative to N9 and Cl atoms. The O1
(phenol) atom is trans to the N17 (pyridine) atom, whereas the
aliphatic N9 (azomethine) atom is trans to chloride. All Cu–X
(X = N, O, Cl) bonds differ significantly with the shortest
values observed for the Cu–O1 (phenol) bond (1.8724(15) Å)
and the biggest ones for Cu–Cl (2.2187(6) Å). The Cu–N(aryl) is
much longer (by approximately 0.05 Å) than N(alkyl). The
phenyl and pyridyl rings remain flat with an r.m.s. of 0.006 Å.
Two chelate rings differ significantly in their conformation:
the Cu1–O1–C2–C7–C8–N9 ring is flat with an r.m.s. of
0.016 Å, whereas the Cu1–N17–C12–C11–C10–N9 ring is
strongly folded with an r.m.s. of 0.296 Å and the largest devi-
ation of 0.493(2) Å observed for C11.
UV-Vis: 262 nm π→ π*, 307 nm π→ π*, 311 nm π→ π*NvC
,
410 nm n→π*.37–40
The presence of signals at the 1H, 13C and 15N spectra of (3)
confirm the tautomeric structure of the isolated compound
(3).42–44
1
epy(4Him) (4) H NMR [ppm]: 3.11 (t, 2H) –CH2–Nv, 3.42
(s, 1H) –NH–, 3.92 (t, 2H) –CH2–Ar, 7.08–8.48 (m, 6H) CHAr,
9.78 ppm (s, 1H) –NvCH–.36
13C NMR [ppm]: 39.4 (C6), 60.5 (C7), 119.8 (C10), 121.6
(C2), 122.3 (C9), 123.7 (C4), 136.6 (C3), 137.7 (C11), 149.1 (C1),
152.6 (C8), 159.3 (C5).
UV-Vis: 257 nm π→ π*, 341 nm π→ π*NvC, 406 nm
n→π*.37–40
Synthesis of complexes
[Cu(II)(epy(di-t-Buba))Cl] (1a). Copper(II) chloride dihydrate
(1.70 g; 10 mmol) in EtOH (10 ml) was added to an ethanolic
solution (10 ml) of the ligand (1) (3.39 g; 10 mmol). The
mixture was stirred for 4 h at r.t. Dark green crystals suitable
for X-ray diffraction from C2H5OH–C6H6 were isolated. Yield:
3.600 g (79.3%), C22H29.08ClCuN2O1.04 (calc./found %): Cu
14.55/14.20, C 60.53/60.81, N 6.41/6.34, H 6.69/7.08.
UV-Vis: 255 nm IL, 285 nm LMCT, 348 nm LMCT, 406 nm
LMCT.37–40
[Cu(II)(epy(di-t-Buba))O2CCH3] (1b). The compound was
prepared in a similar way as (1a) using copper(II) acetate
hydrate (1.990 g, 10 mmol). Dark green single crystals of (1b)
suitable for X-ray analysis were obtained from CH3Cl–C6H6
solution. Yield: 3.340 g (72.7%). C24H32CuN2O3, calc./found %:
Cu 13.81/13.55, C 62.65/62.30, N 6.08/6.23, H 7.01/6.78.
UV-Vis: 238 nm LMCT, 308 nm LMCT, 390 nm
LMCT.37–40
The phenyl and pyridine ring systems form a dihedral angle
of 49.34(13)°. The phenyl and Cu1–O1–C2–C7–C8–N9 chelate
rings are coplanar with an angle of 2.57(9)°, whereas Cu1–
N17–C12–C11–C10–N9 chelate and pyridine rings are inclined
by 27.54(12)°. Both chelate rings form an angle of 21.62(9)°.
Hence, the Schiff base exhibits a bowl shape with the copper(II)
ion on its top and shows a shift by 0.51 Å from the plane
defined by the coordinating O1, N9 and N17 atoms. Such an
Complexes (2a), (3a), (4a) were synthesised in the way
described above. Results of C, H, and N analysis are as follows:
[Cu(II)(epy(pyca))Cl2] (2a) Yield: 80.6%. C13H13CuN3Cl2 calc./
found %: Cu 18.38/18.27, C 45.36/45.71, N 12.15/12.11,
H 3.79/3.99.
UV-Vis: 202 nm IL, 260 nm IL, 309 nm LMCT.37–40
[Cu(II)((epy)2acacH))O2CCH3]
(3a)
Yield:
82.7%.
C21H25CuN4O2 calc./found %: Cu 14.81/14.97, C 58.79/58.46,
N 13.06/12.95, H 5.87/5.84.
Fig. 2 Molecule of [Cu(II)(epy(di-t-Buba))Cl] × 0.042H2O (1a) with the
numbering scheme and thermal ellipsoids at 30% probability.
UV-Vis: 205 nm IL, 254 nm IL, 316 nm LMCT.37–40
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orientation of aromatic rings is assured by conformation of
the –CHvN–CH2–CH2– linker and the most important impact
reveals dihedral angles around C10–C11 and C11–C12 bonds
from the folded N17 chelate rings showing values of −62.1(3)
and 61.4(3)°, respectively. The geometry of the Schiff base
motif is described by a C8–N9 distance of 1.283(3) and C7–C8–
N9 and C8–N9–C10 angles of 128.03(19) and 115.66(17)°,
respectively. The C2–C7–C8–C9 torsion angle describing the
geometry of the O1 chelate ring is −0.7(3)° indicating that this
ring is flat as was shown also by r.m.s. deviation.
The structure of 1a reveals the porous nature with channels
running along the c-axis filled with water molecules. Every
channel is encompassed by six adjacent channels. They are
surrounded by six complex molecules arranged in two inverted Fig. 3 Perspective view of (1a) along the [111] direction revealing chan-
nels of 5.2 Å diameter filled with partially occupied water molecules.
triangles forming the ⋯–AB–AB–⋯ pattern of layers. The dash
indicates large separation between triangles. It can be esti-
mated as Cu–Cu distance being 6.551 Å inside –AB– and (pyridine) 1.989(3) Å, which is similar to that found in (1a).
15.249 Å between B–A pairs of triangles. In the former case six The axial bond Cu1–O3 of 2.517(3) Å is formed by the acetate
molecules form a single pore. The diameter of these channels oxygen. Different C23–O bond lengths for the carboxylate
is approximately 5.2 Å. Hence, the water molecule located in anion (Table 3) were noted, indicating that O2 is a carboxylate
this position could not interact with walls of the pore and atom, while O3 forms a double bond to C23.
should be easily removed. Therefore, it was unstable in the
The CuN2O2 equatorial plane exhibits a significant tetra-
refinement and revealed a high thermal parameter. Six mole- hedral deformation with the atom displacement from the best
cules forming walls of the pore coming from –AB– layers are plane ranging from O1 0.440(2) Å to O2 −0.399(1) Å. Atoms N1
connected due to C10–H10⋯Cl2 (−z, 1 − x, 1 − y) hydrogen and O2 are displaced from the CuN2O2 plane towards axial O3,
bonds. Additionally, there are numerous π–π interactions, while O1 and N2 are displaced in an opposite direction. A
mainly between strongly inclined rings of the molecules similar geometry of the square-planar coordination sphere was
forming the pore and C15–H15⋯π interactions with the O1 reported for [{(2-etpy(sal))Cu}{μ-[Ag(CN)2]}] and [{(2-etpy(sal))-
chelate ring. Interactions between adjacent –AB– modules in Cu}{μ-[Cu(CN)2]}] complexes.45 In the equatorial plane, the
the channel, translated along the c-axis, do not exist due to sig- pairs of atoms positioned trans define N1–Cu1–O2 and O1–
nificant separations between molecules. However, there are Cu1–N2 angles of 159.90(11) and 151.58(11)°, respectively,
interactions between adjacent modules from different chan- values larger than those reported for (1a). The angles formed
nels. They concern two closest copper(II) ions separated by by the atoms in the cis positions range from 90.10(11) to
5.078 Å and are formed due to C11–H11⋯π interactions with 94.87(14) and are significantly smaller than those found in (1a).
the phenyl ring and numerous π–π interactions, including That seems to reflect the difference caused by the bulk of chlor-
stacking interactions between close, well-oriented and reveal- ide ligand in (1a). The angles between equatorial bonds formed
ing small slippage two O1 chelate rings (Table 2).
by O1, N1 and N2 and axial Cu1–O3 are 97.44(11), 103.36(10)
and 107.25(10)°, respectively. The O2–Cu1–O3 angle involving
both oxygen atoms of the acetate ligand equals is 56.54(9)°.
The dihedral angle between the phenolate and pyridyl rings
of the Schiff base ligand is 13.6(2)° and is much smaller than
that reported for (1a). Such a flat environment may be coupled
to the position of the acetate ligand, almost perpendicular to
the plane defined by both these rings, with the dihedral angles
between phenolate and pyridyl rings and the plane Cu1–O2–
C23–O3 being 79.46(12) and 76.54(10)°, respectively. The
torsion angle Cu1–O2–C23–O3 describing the rotation of acetate
around the coordination Cu1–O2 bond is 8.2(5)°. The acetate
ligand is slightly tilted relative to the equatorial CuN2O2 plane,
with the dihedral angle between these planes being 80.41(15)°.
The valence geometry of the Schiff base ligands is typical
for such systems. The C7–N1 distance is 1.280(5) Å, C6–C7–N1
and C7–N1–C8 angles are 127.0(4) and 117.8(3)°, respectively,
and are similar to those observed in (1a). The phenolate-Schiff
base moiety of the ligand is almost flat, with the torsion
angles C1–C6–C7–N1 and C6–C7–N1–C8 being 8.9(6)° and
Table 2 Selected interactions bond lengths [Å] and angles [°] for [Cu(II)-
(epy(di-t-Buba))Cl] (1a)
Bonds
Cu1–O1
Cu1–N9
1.8724(15)
1.9351(17)
Cu1–N17
Cu1–Cl2
1.9892(19)
2.2187(6)
Angles
O1–Cu1–N17
N9–Cu1–N17
O1–Cu1–N9
145.23(8)
93.12(7)
94.16(6)
N9–Cu1–Cl2
N17–Cu1–Cl2
O1–Cu1–Cl2
150.98(5)
96.03(5)
93.85(5)
X-ray crystal structure of [Cu(II)(epy(di-t-Buba))O2CCH3] (1b)
In (1b), the Cu(II) ion is coordinated by the asymmetric Schiff
base and the acetate ligand (Fig. 4) resulting in CuN2O3 square
pyramidal geometry. Among the equatorial bonds, the Cu1–O1
(phenolate) distance of 1.878(3) Å is much shorter than that
for Cu1–O2 (acetate) of 1.960(2) Å. There is a significant differ-
ence between Cu1–N1 (benzaldehyde) 1.937(3) and Cu1–N2
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Table 3 Selected bond lengths [Å] and angles [°] for [Cu(II)(epy(di-t-
Buba))O2CCH3] (1b)
Cu1–O1
Cu1–N1
Cu1–O2
Cu1–N2
Cu1–O3
1.878(3)
1.937(3)
1.960(2)
1.989(3)
2.517(3)
O1–Cu1–N1
O1–Cu1–O2
N1–Cu1–O2
O1–Cu1–N2
N1–Cu1–N2
O2–Cu1–N2
O3–Cu1–O1
O3–Cu1–O2
O3–Cu1–N1
O3–Cu1–N2
C1–O1–Cu1
C7–N1–Cu1
C8–N1–Cu1
C10–N2–Cu1
C14–N2–Cu1
C23–O2–Cu1
92.84(13)
90.10(11)
159.90(11)
151.58(11)
94.87(14)
91.92(11)
97.44(11)
56.54(9)
103.36(10)
107.25(10)
126.5(2)
Fig. 5 Packing of (1b) viewed along the c-axis.
121.9(3)
119.8(3)
122.8(3)
118.6(3)
102.7(2)
Both reported structures have different counterions that
heavily influence the packing and absorption properties. Only
the (1a) structure is porous (Fig. 3). Moreover, at the molecular
level the counterions affect the coordination number. In (1a),
the coordination sphere adopts a strongly distorted square
planar environment, whereas in (1b) it is a strongly elongated
tetragonal pyramid. In both cases the valence geometry of the
Schiff base is similar. However, some conformational differ-
ences are detected, of which the most important occurs for the
C8–N9–C10–C11 angle, being −171.98(19)° in (1a) and
−140.6(3)° in (1b) structure.
EPR analysis. The EPR spectra at the Q-band of polycrystal-
line compounds [Cu(II)(epy(di-t-Buba))Cl] (1a) and [Cu(II)(epy-
(di-t-Buba))O2CCH3] (1b) exhibit a much better resolution of
two signals for (1a) and three signals for (1b) (Table 4) than
those measured at X-band (Fig. 6). Although the EPR spectra
could be treated as showing axial and orthorhombic symmetry
of the Cu(II) centers, respectively, the values of g1 parameters
are too small considering: (a) a type of donors coordinated in
the Cu(II) plane, (NON)Cl and (NON)O, and (b) a significant
deviation of planar to tetrahedral geometry, which imposes the
increase of g-matrix diagonal components.46
−178.0(3)°. However, the ethylaminepyridil fragment is signifi-
cantly folded with consecutive torsion angles C7–N1–C8–C9,
N1–C8–C9–C10 and C8–C9–C10–N2 being −140.6(3), −72.8(5)
and 54.9(5)°. The C19 Bu group reveals a rotational disorder
with two equally populated rotamers (50/50%).
The six-membered chelate rings Cu1–O1–C1–C6–C7–N1
and Cu1–N1–C8–C9–C10–N2 are an envelope on Cu1 and a
boat, respectively. In the four-membered ring Cu1–O2–C23–O3
the torsion angles have alternating negative and positive
values ranging from −6.4(4) to 8.2(5)°.
t
Analysis of crystal packing revealed the π–π interaction
between the C1–C6 phenyl ring and pyridine C10–N2[1 − x,
−y, −z] with the angle between two rings of 13.57° and the dis-
tance between their gravity centers Cg–Cg of 3.885(3) Å. There
is an intermolecular C7–H7A…O3[x, −1/2 − y, −1/2 + z] inter-
action involving the Schiff base C–H and acetate oxygen, with
the C⋯O distance of 3.398(4) Å (Fig. 5). Two methyl groups of
t
C15 Bu are involved in the intramolecular interactions C16–
H16C…O1 and C17–H17B…O1, with C⋯O distances being
2.958(6) and 2.958(7) Å, respectively.
Fig. 6 EPR of polycrystalline compounds (1a) and (1b) (a) at X-band
(about 9.7 GHz) at room temperature and (b) at Q-band (about 36 GHz)
at room temperature. The weak signals for (1b) in the middle of the
spectrum at the Q-band correspond to the resonance transitions due to
differently oriented crystallites.
Fig. 4 Molecule of [Cu(II)(epy(di-t-Buba))O2CCH3] (1b) with the num-
bering scheme and thermal ellipsoids at 30% probability. For clarity,
H atoms for the disordered tBu were omitted.
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Table 4 EPR spectra of coupled and molecular g-matrix parameters and crystal structure data for (1a) and (1b)
c
gav
Cu–Cu [Å]
Canting angle [°]
Cu(salgly)diPhTu × H2O
Cu(salval)P × P
gc1 = 2.145
gz = 2.228a
gc2 = 2.145
gc3 = 2.042
2.111
2.111
90a
47
48
gy = ∼2.065a
gx = ∼2.04a
gc1 = 2.179
gz = 2.247a
gc2 = 2.127
gy = 2.066a
gc3 = 2.050
gx = 2.045a
2.119
2.119
6.131
74.0
[Cu(II)(epy(di-t-Buba))Cl] (1a)
[Cu(II)(epy(di-t-Buba))O2CCH3] (1b)
gc1 = 2.146
gc1 = 2.180
gc2 = 2.146
gc2 = 2.115
gc3 = 2.047
g3 = 2.059
2.113
2.118
6.550
6.352
60.41
76.23
This work
This work
a Calculated on the basis of EPR data.
Hence, the spectra can be considered to be a result of co- spectrum of epy(di-t-BubaH) (1) exhibits the Ph–O stretching
operative effects due to the magnetic exchange between the vibration band at 1235 cm−1, whereas the –OH stretching
non-equivalent paramagnetic centers. The observed values of vibration band was noted at 3467 cm−1. Upon complexation,
the g components are caused by the coupling of g matrixes the Ph–O stretching vibration band was shifted towards higher
giving gc1, gc2 and gc3 parameters (Table 4). The crystal structure frequencies (1256 cm−1 for (1a) and 1251 cm−1 for (1b)), while
reveals that for [Cu(II)(epy(di-t-Buba))Cl] (1a) the interactions –OH stretching vibration bands have disappeared.51–53
may arise at the shortest Cu⋯Cu distance of 6.550 Å for non-
Moreover, the band from azomethine stretching vibrations
parallel coordination polyhedra, whose planes Cl2–O1–N17–N9 in (2a) was noted at 1608 cm−1 for [Cu(II)(epy(pyca))Cl2], Δcoord
are canted by 60.41°. The monomeric units are joined by C10– = Δcomp − Δlig = 17 cm−1 for (2a), which confirms the copper
H10⋯Cl2 interactions and numerous π–π interactions, mainly binding by the –NvCH– group. Also, the stretching vibrations
between strongly inclined rings of the molecules. For [Cu(II)- of –NH– for (2a) were observed at 3446 cm−1 (Δ = 12 cm−1) for
(epy(di-t-Buba))O2CCH3] (1b) the dihedral angle between Cu1– (2a), which confirms the coordination via the pyridine nitro-
O2–O1–N1–N2 planes is 76.23° for the Cu(II) centers separated gen atom. In the spectrum of [Cu(epy(di-t-Buba))Cl]
×
by 6.352 Å. There are also intermolecular C7–H7A⋯O3 inter- 0.042H2O (1a) at 3436 cm−1 a band from stretching vibrations
actions involving the Schiff base C–H and acetate oxygen as of the –OH group was registered.
well as π–π interactions between inclined phenyl and pyridine
rings.
In the spectra of [Cu(II)(epy(4Him))O2CCH3] (4a), (1b) and
[Cu(II)((epy)2acacH)O2CCH3)] (3a), the bands from symmetrical
The Q-band spectra of [Cu(II)(epy(di-t-Buba))Cl] (1a) and and asymmetrical stretching vibrations of the carboxylate group
[Cu(II)(epy(di-t-Buba))O2CCH3] (1b) are similar to those in the region 1403–1474 cm−1 νsCOO− and 1628–1742 cm−1
reported47,48 for Cu(II) complexes with tridentate ONO Schiff νasCOO− were registered,54 suggesting the monodentate
bases and monodentate X ligands, Cu(salgly)diPhTuxH2O coordination.
where salgly = N-salicylidene-glycine and diPhTu = N,N′-diphe-
Moreover, the band from Cu–N vibrations was noted at
nylthiourea and Cu(salval)P × P where salval = N-salicylidene- 428 cm−1 (2a), whereas the band from Cu–O stretching
(R,S)-valine, P = pyrazole. The molecular EPR parameters were vibrations was registered at 507cm−1 (4a), at 543 cm−1 (1a), at
calculated for those complexes using the approximate relations 588 cm−1 (1b), and at 526 cm−1 (3a).55 Additionally, the band
between the canting angles (the angles formed by the tetra- from Cu–Cl stretching vibrations appears at: 309 cm−1 [Cu(II)-
gonal axis of magnetically non-equivalent chromophores)47 (epy(pyca))Cl2] (2a) and 352 cm−1 (1a).54 The presence of the
and the coupled gc components. Although the coupled g com- bands from Cu–O, Cu–N and Cu–Cl stretching vibrations con-
ponents listed in Table 4 have very close values, the molecular firms the coordination via Ph–O, N and Cl atoms respectively.
g tensor components of individual [Cu(II)(epy(di-t-Buba))Cl]
Summarizing IR results for the studied complexes it is
(1a) and [Cu(II)(epy(di-t-Buba))O2CCH3] (1b) complexes should evident that the copper(II) ions coordinate with the ligand via
exhibit stronger rhombicity than the parameters calculated for N or O atoms and Cl− or CH3COO− ions.
Cu(II) complexes with ONO Schiff bases. The latter can be
Thermal analysis of the complexes
caused by significant tetrahedral distortion in the Cu(II) plane
in [Cu(II)(epy(di-t-Buba))Cl] (1a) and [Cu(II)(epy(di-t-Buba))-
O2CCH3] (1b). Also a higher value of gz should be expected,
close to 2.26 according to the parameters observed for Cu(II)
complexes with different tridentate ONN49 and ONN50 Schiff
bases and polar solvents.
The DTA curve of [Cu(II)(epy(di-t-Buba))Cl] (1a) revealed an
endothermic process between 38 and 998 °C. Analysis of the
DTG curve indicates one process corresponding to the detach-
ment of the organic ligand (TG mass loss 71.24%). The final
product of decomposition was CuCl (calc. 16.83%,
exp. 16.34%), as was confirmed by the XRD analysis.
Infrared spectroscopy
The decomposition of [Cu(II)(epy(di-t-Buba))O2CCH3] (1b) is
The IR spectra of free ligands exhibit bands from –NvCH– also a one step endothermic process (Fig. 7). On the DTG peak
stretching vibrations in the region 1591–1623 cm−1 37,54
.
The (Tmax = 266 °C, 77.85% sample mass loss) corresponding to
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the Schiff base, detachment was observed. The final product of speed to 900, 1000, 1100 and 2000 rpm. The layers’ mor-
decomposition was the mixture of CuO with carbon phology was studied by SEM/EDX.
impurities.
The SEM images revealed that silicon surfaces are uni-
formly covered by the Cu(II) complex. The layers are amor-
phous, but sporadically crystalline structures appeared. The
calculated dimensions of these crystallites ranged from 0.5 to
2.0 μm. The latter can be caused by non-completed solidifica-
tion of the complex solution during the spin coating process.
The EDS results indicated that the copper contents decrease in
the layers obtained at higher rotation speed. The latter corres-
ponds to thinner layer formation upon the increase of the
rotation speed. For the majority of complexes, the best cover-
age and smooth layers were obtained at 1100 rpm and time
30 s. The obtained surfaces, in particular their roughness and
thickness, were analyzed by AFM measurements and results
are presented in Fig. 8.
Fig. 7 Thermogram of [Cu(II)(epy(di-t-Buba))O2CCH3] (1b).
The thermal decomposition of the [Cu(II)((epy)2acacH))-
O2CCH3] (3a) is an exothermic process (Ti = 145 °C, Tmax
=
191 °C and Tf = 1190 °C). As for (1a) and (1b), the final product
of decomposition was CuO (mass of residue calc. 18.94%;
exp. 18.32%).
Fig. 8 AFM images of the [Cu(II)(epy(pyca))Cl2] (2a)/Si(111) layers:
(a) 900 rpm min−1, (b) (2a)/glass 1000 rpm min−1, and (c) (2a)/ITO
1000 rpm min−1
.
In the case of [Cu(II)(epy(pyca))Cl2] (2a) the decomposition
is a multistage process (Ti = 26 °C and Tf = 964 °C). On the
DTG curve seven exothermic processes with maxima at: 58 °C,
163 °C, 175 °C, 249 °C, 329 °C, 437 °C and 1010 °C were
observed, which can be assigned to the detachment of chlorine
and partial decomposition of the Schiff base (total mass loss
81.40%). The final product of the decomposition process was
metallic Cu (calc. 18.6%, exp. 18.6%).
The thermogram of [Cu(II)(epy(4Him))O2CCH3] (4a) exhibits
four DTG peaks with maxima at 314, 394, 505 and 642 °C, and
the TG curve reveals four stages with 3.68, 7.75, 29.27 and
11.30% sample mass loss. The first step with a maximum at
184 °C at the DTA curve can be related to the detachment of
the acetic acid molecule (mass loss 18.66%, calc. 18.69%). The
assignment was confirmed by the IR spectra of gases evolved
during measurement, where the bands at 1394 and 1774 cm−1
from vCOO–sym and vCOO–asym vibrations were observed.39 After-
wards the partial dissociation of the Schiff base occurs leaving
the metallic copper (the % mass of residue 17.42% calc.,
exp. 19.78%). In the studied cases, the final product of the
thermal decomposition of copper(II) complexes was copper
oxide or metallic copper. The [Cu(II)(epy(4imH))O2CCH3] (4a)
complex is thermally more stable than others because it was
not completely decomposed below 1200 °C.
The images in Fig. 8 reveal that the smallest and most
uniform particles are on the Si surface, whereas on ITO there
are the highest dimensions of the complex particle. On the
glass substrate, particles revealed the biggest dissipation of
variation in size and did not cover the substrate surface uni-
formly. The complex [Cu(II)(epy(pyca))Cl2] (2a) forms layers
uniformly covering the silicon surfaces at all the used spin
speeds. Deposition of compound (2a) on the glass slides and
ITO was also performed (Fig. 8). The highest value of Rq and
Ra (average of image data without application of the surface
height deviations measured from the mean plane) parameters
were registered for the layers covering the glass slides. These
measurements indicated that the type of the substrate also
affects the morphology of the obtained layer. In the case of 2a)
the layers deposited on glass are rougher than those obtained
on silicon or on ITO substrates. The uniformly covered materials
were received at 900, 1000, 2000 rpm min−1 spin speed.
In the case of (1a)/Si and [Cu(II)(epy(di-t-Buba))O2CCH3]
(1b)/Si, homogeneous layers without significant differences in
roughness were obtained. The optimal spin speed was
1100 rpm min−1 (Rq and Ra parameters equal 35.1 and
24.9 nm for (1a)/Si and 103 and 70.1 nm for (1b)/Si). For (1a)/
Si, doubling of the spin speed and repetition of this process
(time 10 s) lead to a smoother layer with: Rq = 0.572 nm and
Ra = 0.842 nm. The depth of the layer equals 6 nm. For (4a)/Si,
the optimal spin speed giving a smooth layer with equally
spread compounds was 2000 rpm min−1 (Ra = 15.3 nm). The
content of Cu in this layer equals 3.11%.
Thin layer studies
The copper(II) organic–inorganic layers on a silicon substrate
were deposited by the spin coating technique. Because the
parameters of the layers depended on the spin speed and time
of coating for all experiments, time was set to 30 s and spin
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The above discussion suggests that the quality of the layer registered in solution revealed a much lower intensity of the
(uniformity, roughness) can be optimized by the variation of fluorescence bands than the bands of complex layers.
spin speed and deposition time. Concluding, the obtained These studies suggest that better smoothness of layers and
layers are thin and homogeneous with equally spread com- higher complex concentration result in higher fluorescence
plexes over the substrate surface.
intensity.
Fluorescence properties of the layers
Conclusions
The Schiff bases are known for their fluorescence properties and
their varied applications.56 Therefore, we studied the lumines-
cence properties of the obtained compounds and layers.
In the case of (1a) and (1b), the highest fluorescence band
intensities were observed for λex = 269 nm and 280 nm for
[Cu(II)(epy(di-t-Buba))Cl] (1a) and [Cu(II)(epy(di-t-Buba))-
O2CCH3] (1b) respectively. The emission band from intraligand
π*→π transitions was observed at 538 nm for (1a) and 560 nm
for (1b).37–39 The highest fluorescence intensity of the layers
(1a)/Si and (1b)/Si was noted when the rotation speed was set
to 2000 rpm min−1. These layers revealed the best smoothness
and uniformity. Besides, EDX results indicated that these
layers exhibited the highest content of copper (12.48% for (1a)
and 6.84% for (1b)).
The series of Schiff bases and their copper(II) complexes were
obtained. The X-ray crystal data for copper(II) complexes indi-
cated that the planar environment strongly distorted towards
tetrahedral geometry in the case of the [Cu(II)(epy(di-t-Buba))-
Cl] × 0.042H2O (1a). This structure reveals porous nature with
channels filled with water molecules running along the c-axis.
In the complex [Cu(II)(epy(di-t-Buba))O2CCH3] (1b), the Cu(II)
ion is coordinated in CuN2O3 square pyramidal geometry by
Schiff base and acetate ligands. The X-ray analysis results
suggested a significant influence of the anion on the geometry
of the coordination sphere. The EPR studies revealed the co-
operative effects due to magnetic interactions between Cu(II)
ions forming non-parallel coordination polyhedra. The final
products of the thermal decomposition were either copper
oxide or metallic copper and even a mixture of the copper
oxide with carbon. The thin layers containing copper(II) Schiff
base complexes exhibited fluorescence. The highest intensity
of the fluorescence was noted for the smooth layers obtained
at 1100 rpm min−1 or 2000 rpm min−1 which revealed the
highest copper content. The emission was observed at
490–560 nm and is connected to the intraligand π*→π tran-
sitions. The fluorescence emission of the layers makes these
materials potentially suitable for application in light emitting
devices.
Fig. 9 Fluorescence spectra of [Cu(II)(epy(pyca))Cl2] (2a)/Si, –––
Acknowledgements
900 rpm min−1
,
1000 rpm min−1
,
1100 rpm min−1, λex = 280 nm,
λem = 560 nm.
Authors would like to thank the National Science Centre
(NCN), Poland for financial support (grant no. 2013/09/B/ST5/
03509).
The [Cu(II)(epy(4Him))O2CCH3] (4a)/Si, [Cu(II)((epy)2acacH)-
O2CCH3] (3a)/Si materials also exhibit fluorescence λem = 552
and 588 nm (λex = 277 (4a)/Si and 295 nm (3a)/Si). These layers
were obtained at 1100 rpm min−1 (Ra = 19.7 nm (4a)), respect-
ively. Again they revealed the highest content of copper.
When the spin speed was set to 2000 rpm min−1, the
highest intensity of the fluorescence (λem = 560 nm) was
observed for (2a)/Si material (λex = 280 nm) (Fig. 9). However,
the hybrid layers of (2a) on the glass slides exhibit lower inten-
sity than on the silicon wafers. The optimal spin speed for
(2a)/ITO was 1000 rpm min−1 when the excitation was set at
250 nm and λem = 498 nm.
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9932 | Dalton Trans., 2014, 43, 9924–9933
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