Geometrical Aspects of Trinuclear Tetra-µ-Chloro-Cadmium Complex with 5-Methyl-4H-1,2,4-Triazole-3,4-Diamine

Introduction

Amongst five-membered ring systems available, the presence of the three nitrogens in triazoles provides an interesting class of compounds. Triazoles in particular, substituted-1,2,4-triazole are among various heterocycles that have received the most attention during last two decades as potential antimicrobial agents, antifungal, antitubercular, anti-HIV, antiinflammatory, CNS stimulants, sedatives, antianxiety¹. A larger variety of 1,2,4-triazole-based ligands have been used for preparation of polymeric coordination networks² and synthesis of nitrogen-rich energetic materials³.

In the past few years we have studied complexation of multi N-donor ligands⁴⁻⁷. In continuation of our previous studies, in this work the preparation of cadmium(II) complex, [Cd₃(L)₂(HL)₂(μ-Cl)₄Cl₄] (1), with 5-methyl-4H-1,2,4-triazole-3,4-diamine (L, scheme 1) was described. This complex was characterized by elemental analysis, IR spectroscopy and X-ray crystallography.

Scheme 1: The structure of ligand. Click here to View scheme

Material and Methods

General methods

All starting chemicals and solvents were reagent or analytical grade and used as received. The infrared spectrum of a KBr pellet was recorded in the range 4000–400 cm⁻¹ using a FT-IR 8400-Shimadzu spectrometer. The carbon, hydrogen and nitrogen contents were determined in a Thermo Finnigan Flash Elemental Analyzer 1112 EA. Melting point was determined using a Barnsted Electrothermal 9200 electrically heated apparatus.

Synthesis of [Cd₃(L)₂(HL)₂(μ-Cl)₄Cl₄], 1.

A solution of L. HCl (1.3 mmol, 0.19 g), dissolved in 10 mL EtOH, were added to a 10 mL ethanolic solution of CdI₂ (1 mmol, 0.36 g). The reaction mixture was stirred at 60 °C for 2 h and a white precipitate was formed and then filtrated. The resulting solution was left at room temperature for several days and colorless crystals suitable for X-ray diffraction were collected. The results of melting point, CHN analysis and IR spectroscopy of the crystals were identical to those of the initial precipitate. Yield (0.25 g) 83%; Decomposed > 270 °C. Anal. Calcd for C₁₂H₃₀Cd₃Cl₈N₂₀ (%): C, 13.40; H, 2.81; N, 26.05. Found: C, 13.42; H, 2.81; N, 25.88. IR (KBr, cm⁻¹): 3317 s (ν_as NH₂), 3240 m (ν_s NH₂), 3183 m (ν NH), 1697 s (ν C=N), 1643 m (δ NH₂),1435 w (δ_as CH₃), 1381 w (δ_s CH₃), 1281 w (ν CN), 1092 w (ν NN).

Crystal structure determination and refinement

Intensity data were collected on a Bruker APEX-II CCD area detector diffractometer with graphite monochromated Mo K_a radiation (50 kV, 30 mA) using the APEX-II⁸ data collection software. The collection method involved w-scans of width 0.5° and 512 × 512 bit data frames. Data reduction was carried out using the program SAINT+⁹ and face indexed absorption corrections were made using the program XPREP⁹. The crystal structure was solved by direct methods using SHELXTL¹⁰. Non-hydrogen atoms were first refined isotropically followed by anisotropic refinement by full matrix least-squares calculations based on F² using SHELXTL. Hydrogen atoms were first located in the difference map then positioned geometrically and allowed to ride on their respective parent atoms. Crystallographic data and details of the data collection and structure refinement are listed in table 1. Selected bond lengths and angles are listed in table 2.

Table 1. Crystal data and structure refinement for 1.

Empirical formula	C12H30Cd3Cl8N20
Formula weight (g mol−1)	1075.36
Temperature (K)	173(2)
Crystal system	Monoclinic
Space group	P21/n
Unit cell dimensions (Å, °)
a	9.1524(2)
b	9.3816(2)
c	18.8619(3)
β	101.5050(10)
Volume (Å3), Z	1587.02(5), 2
Calculated density (g cm−3)	2.25
Absorption coefficient (mm−1)	2.7
F(000)	1044
Crystal size (mm3)	0.27 × 0.23 × 0.11
θ range for data collection (°)	2.20–28.00
h, k, l ranges	−12:12, −12:12, −24:24
Reflections collected	24192
Independent reflections	3833
Rint	0.0528
Data / restraints / parameters	3833 / 8 / 226
Goodness-of-fit on F2	1.051
Final R indices [I>2σ(I)]	R1 = 0.0284, wR2 = 0.0713
R indices (all data)	R1 = 0.0341, wR2 = 0.0734
Largest diff. peak and hole (e.Å−3)	0.68 and −1.22

 

Table 2. Selected bond lengths (Å) and angles (°) for 1.

Bond lengths (Å)		Angles (°)
Cd1−N1	2.358(3)	N1−Cd1−N6	177.20(9)
Cd1−N6	2.477(3)	N1−Cd1−Cl1	92.67(7)
Cd1−Cl1	2.5578(8)	N1−Cd1−Cl2	94.69(7)
Cd1−Cl2	2.5743(8)	N1−Cd1−Cl3	88.78(7)
Cd1−Cl3	2.6379(8)	Cl1−Cd1−Cl2	96.41(3)
Cd1−Cl4	2.6666(8)	Cl1−Cd1−Cl4	92.82(3)
Cd2−N2	2.277(3)	N2−Cd2−N2i	180.0
Cd2−Cl3	2.7182(7)	N2−Cd2−Cl3	84.61(7)
Cd2−Cl4	2.6724(8)	N2−Cd2−Cl4	89.17(8)

Symmetry code: (i) – x + 1, − y + 1, − z + 1.

Results and Discussion

Reactions between L.HCl and ethanolic solution of cadmium(II) iodide provided colorless crystals of 1. This complex was characterized by IR, Raman, ¹H NMR spectroscopy and X-ray crystallography. This complex is air-stable and soluble in DMSO and DMF.

Presence of the RNH₂ group in 1 affect IR spectrum in two regions including 3317 and 3240 cm^–1 for asymmetric and symmetric NH₂ stretches and 1643 cm^–1 for NH₂ bending. The bands at 1697, 1281 and 1092 cm^–1 which were assigned to the ν (C=N), ν (CN) and ν (NN), respectively,confirm the presence of the triazole ring.

Description of the crystal structure

The crystal structure of 1 was determined by X-ray single-crystal diffraction. The molecular graphic was drawn with ORTEP-III¹¹.

Figure 1: The ORTEP-III diagram of the molecular structure of 1. The ellipsoids are drawn at the 50% probability level. Click here to View figure

In the crystal structure of 1 (figure. 1), the three cadmium atoms have a distorted octahedral coordination environment. Four sites are occupied by chloride ions with the Cd–Cl bond lengths in the range of 2.5578(8)–2.7182(7) Å. The two other sites are occupied by two nitrogen atoms of L. The ligand L coordinated by two different coordination modes. Two chloride and a N–N bridges connect two adjacent cadmium atoms. The complex has a center of inversion on the copper atom and C_i symmetry.

Supplementary material

CCDC 913232 for [Cd₃(L)₂(HL)₂(μ-Cl)₄Cl₄] contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html.

Acknowledgement

We are grateful to Payame Noor University of I. R. Iran for financial support.

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