Structure,optical and thermal properties of a new iodocuprate(I) complex stabilized by bis(isoquinoline)alkane cation

2.1 Materials and methods

The dications 1,3-bis(isoquinoline)propane were prepared as the bromide salt by direct alkylation of isoquinoline with 1,3-dibromoalkane and acetonitrile served as the solvent for the reaction. The reaction route was shown in (Scheme 1). Other chemicals were obtained from commercial sources and used as received without further purification. The IR spectrum was recorded on a Shimazu IR435 spectrometer as KBr disk (4000–400 cm^–1). Powder X-ray diffraction (PXRD) analyses were recorded on a Rigaku Dmax2500 diffractometer with Cu Kα radiation (λ= 1.54056Å) with a step size of 0.05°. A model NETZSCHTG209 thermal analyzer was used to record simultaneous TG curves in the flowing nitrogen atmosphere of 20 mL min^–1 at a heating rate of 5°C min^–1 in the temperature range r. t. –800°C using platinum crucibles. The photoluminescent spectra were performed on a Perkin–Elmer LS55 spectrofluorometer. The room-temperature optical diffuse reflectance spectrum of powder samples was obtained using a Shimadzu UV-2600 UV-vis spectrophotometer. The absorption spectrum was calculated from the diffuse reflectance spectrum by using the Kubelka-Munk function: a/S = (1–R)2/2R [17].

OPEN IN VIEWER

Scheme 1

Synthesis of the 1, 3-bip cation (n = 3).

[CuI ₃ ](1,3-bip) (1). To the mixed solution of CuI(0.5 g) in 5 ml DMF/H₂O, DMF solution of 1,3-bip·2Br(1 g) was added dropwise to obtain a clear yellow solution. The solution was then filtrated and slowly evaporated in a vial at room temperature. The light yellow crystals, which were suitable for X-ray single crystal diffraction analysis, were obtained after two days, dried in air. IR (KBr): 3037 (w), 2104(m), 1635(m), 1473(m), 1395(m), 1158(m), 823(s), 764(s), 476(m) cm^–1. Anal calcd for C₂₁H₁₉N₂CuI₃: C, 33.92; H, 2.57; N, 3.77. Found, % : C, 33.90; H, 2.55; N, 3.86.

2.3 X-ray crystallography study

X-ray diffraction data for 1 were collected by using a Bruker Nonius Kappa CCD diffractometer at 290(1) K equipped with graphite–monochro-matized Mo-Ka radiation (λ= 0.71073Å). The structure was solved by direct methods and expanded using Fourier techniques. A numerical absorption correction was applied [18] Hydrogen atoms were placed at calculated positions and refined using a riding model. All parameters were refined against F2. All non-hydrogen atoms were refined with anisotropic displacement parameters. Crystallographic data and structural refinement details for 1 were summarized in Table 1. Important bond lengths and angles were given in Table 2. The simulated PXRD spectra were from the single-crystal data and the Mercury (Hg) program obtained from the Web site at http://www.iucr.org. The PXRD patterns were conducted on crystalline samples to confirm the phase purities of complex 1. As shown in Fig. 1, the experimental PXRD patterns of as-synthesized samples agree well with their simulated ones, indicating the phase purities of the bulk samples.

OPEN IN VIEWER

Fig.1

Power X-ray diffraction (PXRD) of complex 1.

3.1 Description of crystal structure

3.1.1 Structure of (1,3-bip) [CuI₃] (1)

In the title compound, (1,3-bip)[CuI₃], the asymmetric unit contains a 1,3-bip cation and a CuI₃ anion (Fig. 2). In the anion, Cu-I bond distances lie in the range of 2.513–2.525Å. All of the atoms in the anion are essentially coplanar. In the crystal structure, an extensive network of C–HI hydrogen bonds links the cations and anions into an extended three-dimensional network, with the cations further aggregated through – stacking interactions (Fig. 1b). Other bond angle and lengths are compared with those found in the organic cation stabilized iodocuprate analogues [19, 20].

OPEN IN VIEWER

Fig.2

The perspective view and the C–HI hydrogen bonding of the structure of 1.

Figure 3a-b shows the absorption spectra of 1, 3-bip and 1 in 10^–5 mol/L DMF solution. Both compounds present an intense absorption band centered at ca. 270 nm (267 nm for 1) and 335 nm (338 nm for 1). Such bands can be tentatively assigned to the π⟶ π * charge transfer transition. The band gaps (Eg) was determined as the intersection point between the energy axis and the line extrapolated from the linear portion of the absorption edge in a plot of Kubelka-Munk function F against energy E. Kubelka-Munk function, F =  (1–R)2/2 R, was converted from the recorded diffuse reflectance data, where R is the reflectance of an infinitely thick layer at a given wavelength [21, 22]. Extrapolating the linear par of the rising curve to zero provides the onset of absorption at 2.50 eV for 1 as shown in Fig. 3c. The absorption lies in the energy range suitable for visible-light photocatalytic applications and shows that 1 can be regarded as semiconducting materials. The band gap of the title compound encouraged us to investigate its photocatalytic activity, which was evaluated for MB photodegradation under visible-light illumination.

OPEN IN VIEWER

Fig.3

Absorption spectra of 1,3-bip (a) and 1 (b) in DMF solution; (c) Diffuse reflectance UV-vis-NIR spectra of K–M functions vs. energy (eV) of compounds 1; (d) Photocatalytic degradation of MB solution under UV light irradiation with the use of compounds 1 and the control experiment without any catalyst.

To research the photocatalytic activity of complex 1 in detail, we selected aqueous solution of MB (methyl blue, 1.0×10^–5 M, 100 mL) as models of dye water. The compounds 1 (50 mg) were added into MB aqueous solution. Then magnetically stirred in the dark for 30 min to ensure the equilibrium of adsorption/desorption. Afterward, under the irradiation of a 500 W Xe lamp the solution was kept continuously stirring with the aid of a magnetic stirrer. 3.0 mL sample was taken for analysis. The photodegradation process of MB without any catalyst had also been studied for the control experiment. The characteristic absorption of MB at about 664 nm (MB) was chosen to monitor the photocatalytic degradation process. Besides, the concentrations of MB (C) versus reaction time (t) of complexes 1 are plotted in Fig. 3d (wherein, C₀ is the initial concentration of the MB and C is the concentration of the dye at any given time). As shown in Fig. 3d, the photolysis of MB itself under visible-light illumination was negligible. We can see that complexes 1 are vigorous for the decomposition of MB under the sunlight irradiation. Satisfyingly For complex 1, approximately 52% of MB have been decomposed after 100 min. illustrating an impressive photocatalytic activity of compound 1.