Crystal and Molecular Structure of Platinum(II) Complex with Bis(Diphenyl Phosphino)Methane

Introduction

Phosphine ligands have been intensively used in coordination chemistry because of their electron releasing capacity¹. The phosphine ligands can be organized based on the type of substituents bonded to the phosphorus atom². Trivalent phosphorus compound are commonly used as mono- and bi-dentate ligands in the organometallic and coordination compounds of the transition metals³.  Bisphosphanes are class of bidentate ligand that contain two phosphine atoms joined by a bridge⁴. The bridge, for instance, could involve only one or more methylene bridge or a few phenyl rings with heteroatoms joined⁵. The structure of the methylene bridge and the substituents joined to the phosphine atoms influence the chemical reactivity of the bisphosphanes ligand in coordination complexes by means of steric and electronic effects^6,7. Phosphanes ligands usually attached to the metal center through the pair of valence electrons on the phosphorus⁸. The ‘R’ group substituents bound to the phosphorus can then influence the behavior of the phosphine as a ligand bound to a metal center⁹. Phosphine ligands are usually strong σ-donor ligands and only weak π-acceptors¹⁰. This impact can be expanded with electron-donating groups in the rest R, although electron with-drawing groups in ‘R’ favor the π-acceptor back bonding¹¹. In the present work, the synthesized platinum complex has chlorine atom on the methylene group of dppm ligand that cause increase in the π-acceptor back bonding of dppm ligand and increase the stability of complex.

Experimental

Instrumentation and Materials

The FTIR spectra of complexes were recorded on a Shimadzu IRAffinity-1S FTIR Spectrophotometer in the range (4000-200 cm^-1) by using Caesium iodide disc, and IR spectra of the compound were recorded on Shimadzu, FT-IR spectroscopy Mod IR Affinity-1CE spectrophotometer in the region (4000-400 cm^-1) by using potassium bromide disc. Melting point of the complex were recorded by Melting Point-MPD-100 Pixel Technology CO apparatus.

The compounds platinum dichloride and bis(diphenylphosphino)methane were commercially valid and be valid from Yacoo chem. China. All solvents used in this research were commercial products and were used without further purification.

Synthesis of [PtC1₂(dppmCl)] complex

Bis(diphenylphosphino)methane (0.7687g, 2mmol) was dissolved in (20 cm³) dichloromethane and treated with a (20 cm³) solution of platinum dichloride (0.5319g, 3mmol) in a mixture of ethanol and concentrate hydrochloric acid in the same portion. The reaction mixture was stirred at 40 ^օC for 3 h, and allowed to evaporate slowly at 25 ^օC. The yellow precipitate was formed. The yellow Crystal was formed by slow evaporation of a dichloromethane solution of the complex after one week. Yield: 1.300 g (87%), m.p.: (310 °C). M.Wt: 650.378 g/mol.

Results and Discussion

X-ray data of [Pt(k²-dppmCl)Cl₂] complex were collected at 200 K in the Mo Kα radiation (0.71073 Å) on a Bruker Kappa Apex II diffractometer with graphite monochromated (λ= 0.71073 Å). The program APEX-Trak was utilized to data accumulation and SAINT for cell refinement and data reduction¹². The structure was carry out by straight manners applying SIR97¹³ and refined by smallest-squares procedures utilizing SHELXL-97¹⁴. The needle yellow crystals were obtained by slow evaporation of dichloromethane solution of the complex at room temperature after seven days, these crystals were sent to X-ray analysis. Figure 1 show the molecular geometry of the complex. The complex is composed of closely packed monoclinic molecule of [Pt(k²-dppmCl)Cl₂]. In the complex the Pt atom is surrounded to form square planer by two phosphorus atoms and two chlorine atoms. The bis(diphenylphosphino)methane contain two P as a donor atoms. The observed Pt-P1 and Pt-P2 length of 2.217(2) and 2.217(2) Ǻ. The Pt-Cl1 and PtCl2 length of 2.3661(19) and 2.3661 Ǻ respectively of [Pt(k²-dppmCl)Cl₂] metal complex¹⁵. A summary of crystal data, experimental details, and refinement outcomes is shown in Table 1.

Figure 1:  Molecular structure of [Pt(dppmCl)Cl2]complex Click here to view figure

Table 1: Crystallographic and structure refinement data for [Pt(dppmCl)Cl₂] complex

Compound                                                            [Pt(dppmCl)Cl2]
Empirical formula	C24.27H21.46Cl2P2Pt(Cl)0.729 (H) 0.54
Formula weight (g/mol)	667.43
R	0.03
Temperature (K)	200
Wave length (oA), Crystal system	0.71073, Monoclinic
space group	C2/c
a(oA)	16.2034(5)
b(oA)	7.8274(2)
c(o)	19.2496(6)
α(o)	90
β(o)	98.918(1)
γ(o)	90
Volume (A3)	2411.92(12)
Calculated density (mg/m3)	4, 1.838
Z	4
Crystal size	0.04 x  0.20 x  0.21 mm
Theta range for data collection	2.9,28.4 deg
Reflections collected / unique	16294,3007,[R(int)= 0.030]
Observed Data [I > 2.0 sigma(I)]	2930
R, wR2, S	R= 0.0478   wR2= 0.1178   S= 1.30
Min. and Max. Resd. Dens	[-1.71, 4.83] e/Ang^3

X-ray Crystal structure

Suitable crystals of the complex were produced by slow evaporation of a methylene chloride solution. A yellow Crystal with approximate dimensions 0.04 x 0.20 x 0.21 mm³ was formed and the crystal was sent to X-ray analysis. The molecular structure is given in   Figure 1. Crystals of complex are   monoclinic, space group C2/c with a= 16.2034(5), b= 7.8274(2), c=19.2496(6) A°, α=γ=90°, β=98.918(1)^ο, Z= 4. The R value is 0.03 (WR2=0.1178, S= 1.30).  The platinum center adopts a square planar geometry with Cl1-Pt1-P1 and Cl1-Pt1-P2 bonds angle of 98.10(7)° and 98.10(7)° respectively, the phosphine ligand is coordinated in bidentate fashion through two phosphorus atom, and the two chlorine atoms also coordinated to the metal center ^{16, 17, 18}. Table 2 gives the selected bond length and bond angles of metal complex.

Table 2: Selected Bond length [A] And Bond Angles [Degree] of [Pt(k²-dppmCl)Cl₂] Complex

Bond distance		Bond angle		Bond angle
Pt1-Cl1	2.3661(19)	Cl1-Pt1-P2	98.10(7)	C14-C13-H13	120.00
Pt1-P2	2.217(2)	Cl1-Pt1-P1	98.10(7)	C13-C14-H14	119.00
Pt1-P1	2.217(2)	Cl1-Pt1-Cl1_a	90.02(6)	C15-C14-H14	119.00
Pt1-Cl1_a	2.3661(19)	Cl1-Pt1-P2_a	171.58(7)	C14-C15-H15	121.00
Pt1-P2_a	2.217(2)	Cl1_a-Pt1-P2	171.58(7)	C16-C15-H15	121.00
P1-C21	1.816(7)	C14-C15-C16	118.6(9)	P2-C11-C16	122.9(6)
P1-C1	1.85(3)	C11-C16-C15	121.1(9)	C12-C11-C16	119.7(7)
P1-C11	1.808(8)	P2-C21-C22	121.9(6)	P1-C11-C12	117.5(6)
P2-C11	1.808(8)	P2-C21-C26	117.9(6)	P1-C11-C16	122.9(6)
P2-C21	1.816(7)	P1-C21-C22	121.9(6)	P2-C11-C12	117.5(6)
C21-C26	1.362(12)	P2-Pt1-P2_a	73.87(8)	C11-C12-C13	119.2(8)
C21-C22	1.386(12)	Cl1_a-Pt1-P1	171.58(7)	C11-C16-H16	119.00
C22-C23	1.381(13)	Cl1_a-Pt1-P2_a	98.10(7)	C15-C16-H16	119.00
C23-C24	1.387(14)	C1-P1-C11	107.4(5)	C21-C22-H22	120.00
C24-C25	1.358(17)	C1-P1-C21	108.0(5)	C23-C22 -H22	120.00
C25-C26	1.390(13)	P1-C21-C26	117.9(6)	C22 -C23-H23	120.00
C12-H12	0.9500	C22-C21-C26	120.2(7)	C24-C23-H23	120.00
C13-H13	0.9500	C21-C22-C23	120.2(8)	C12-C13-C14	119.8(9)
C14-H14	0.9500	C22-C23-C24	119.6(9)	C13-C14-C15	121.7(9)
C15-H15	0.9500	C23-C24-C25	119.5(9)	C24-C25-H25	119.00
P2-H2	1.0000	Pt1-P1-C1	97.0(9)	C26-C25-H25	119.00
C11-C12	1.388(11)	Pt1-P1-C11	117.7(3)	C23-C24-H24	120.00
C11-C16	1.391(12)	Pt1-P1-C21	117.2(3)	C25-C24-H24	120.00
C12-C13	1.394(12)	C11-P1-C21	108.1(3)	C21-C26-H26	120.00
C13-C14	1.364(16)	C11-P2-C21	108.1(3)	C25-C26-H26	120.00
C14-C15	1.384(15)	C24-C25-C26	121.4(10)
C15-C16	1.369(14)	C21-C26-C25	119.2(9)
C16-H16	0.9500	C11-C12-H12	120.00

Infrared spectral

The IR spectra of the metal complex are in agreement with X-ray analysis data with respect to the condition of coordination. The infrared spectrum of bis(diphenylphos phino)methane ligand have bands at 3064, 2899, 1431 and 511 cm^-1 are attributed to the stretching vibration of aromatic ν (C-H), aliphatic ν (C-H), ν (P-Ph) and aliphatic ν (P-C)  respectively^{19, 20, 21}. The IR spectrum of complex also shows stretching vibrations assigned to the Pt-P bond at 280 cm^-1 and Pt-Cl bond at 371 cm^{-1 22, 23}.

Conclusions

In conclusion, new Pt(II) metal complex of tertiarydiphosphine (dppm) can be readily obtained by the reaction of 1,1-Bis(diphenylphosphino)methane with Pt(II) chloride as given in the  Figure 1. The central platinum atom is bonded by two chlorine and two phosphorus atoms of 1,1-Bis(diphenylphosphino)methane ligand, thus forming the [Pt(k²-dppmCl)Cl₂] square planar compound. The chlorine atom bonded to methylene group of dppm ligand that make the complex new.

Acknowledgements

The authors wish to thank the chemistry Department. College of Education-Salahaddin University for their helping to finish our present study and the authors also thank the department of Physics, college of science, at Halabja University for their helps.

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