Syntheses,Spectroscopic Properties and Terahertz Time Domain Spectroscopy of Two Copper（Ⅰ）Complexes Based on Diphosphine Ligands and N-Donor Ligands

LI Zi-Xi HU Cong SUN Zhen-Zhou LI Xiao-Qi HAN Hong-Liang YANG Yu-PingXIN Xiu-LanJIN Qiong-Hua＊,

（1Department of Chemistry,Capital Normal University,Beijing 100048,China）

（2School of Science,Minzu University of China,Beijing 100081,China）

（3School of Food and Health,Beijing Technology and Business University,Beijing 100048,China）

Abstract:Two nove1 Cu（Ⅰ） comp1exes,[Cu（dppp）（Bphen）]C1·1.8CH3OH（1）and[Cu2（CN）2（dppp）（dmp）2]·2.5CH3OH（2）（dppp=1,3-bis（dipheny1phosphany1）propane,Bphen=4,7-dipheny1-1,10-diazaphenanthrene,dmp=2,9-dimethy1-1,10-phenanthro1ine）,have been synthesized in a mixture of CH3OH and CH2C12and characterized by sing1e-crysta1 X-ray diffraction,e1ementa1 ana1ysis,IR,1H NMR and31P NMR spectroscopy,f1uorescence spectra and terahertz time-domain spectroscopy（THz-TDS）.The sing1e crysta1 X-ray diffraction shows that comp1ex 1 is a distorted tetra-hedra1 structure with copper as the center,Bphen and dppp as the che1ating 1igands.Comp1ex 2 is obtained by mixing CuCN,dppp and dmp in a ratio of 2∶1∶2.The two phosphates of comp1ex 2 form coordination bonds with two Cu（Ⅰ）,and each copper coordinates with a cyanogen and a dmp,respective1y.The 1uminescent spectra show that the emission mechanism of comp1exes 1 and 2 are meta1-to-1igand charge transfer（MLCT）.The app1ication of THz-TDS a1so supports to the study of both the comp1exes.CCDC:2071597,1;2071598,2.

Keywords:copper（Ⅰ）comp1ex;diimine;diphosphine;1uminescent spectra;terahertz techno1ogy

0 Introduction

Over the 1ast few years,there are p1entifu1 researches of 1uminescence meta1 comp1exes that are expected to be used in materia1s science,1ight-emitting diodes and Nixie tubes[1-3].Cu （Ⅰ） comp1exes,compared with precious meta1 comp1exes such as Os（Ⅲ） comp1ex-es,Ir（Ⅲ） comp1exes and Pt（Ⅳ） comp1exes,have wide sources,1ow toxicity and 1ow price,and are wide1y regarded as a reasonab1e substitute for precious meta1 comp1exes[4-10].Up to now,p1enty of mixed-1igand Cu（Ⅰ）diphosphine diimine comp1exes such as[Cu（N^N）（P^P）]+system have been reported and usua11y have good 1uminescence properties[11-12].

1,3-Bis（dipheny1phosphany1）propane （dppp）,a diphosphine 1igand,can coordinate as either bridged 1igand or che1ating 1igand.According to the hard-soft-acid-base（HSAB）theory,dppp can easi1y coordinate with Cu（Ⅰ）to he1p improving crysta1 qua1ity.The dii-mine 1igands,due to their strong che1ate coordination abi1ity,1,10-phenanthro1ine（phen）and its derivatives usua11y have been used as che1ating 1igands to coordi-nate with Cu（Ⅰ）[13-15].1,10-phenanthro1ine and its deriva-tives have 1ow π*orbita1 energy,and often show meta1-to-1igand charge transfer（MLCT）characteristics.As for[Cu（N^N）（P^P）]+comp1exes,since the work of McMi11in et a1.,Cu（Ⅰ）hetero1eptic comp1exes constructed by phen and its derivatives are too numerous to enumerate.Peo-p1e have found that function groups at 2-position or 9-position of phen can efficient1y reduce the distortion of configuration of meta1 center,therefore improving the photo1uminescence quantum yie1d（PLQY）of comp1ex-es.Besides,function groups in other positions a1so have an impact on the property of comp1exes[11-13,26].Herein,2,9-dimethy1-1,10-phenanthro1ine（dmp）and 4,7-dipheny1-1,10-diazaphenanthrene（Bphen）were cho-sen to synthesize two comp1exes to make a comparsion of their properties（Scheme 1）.

Scheme 1 Structures of the 1igands

In our previous studies,we have reported some Cu（Ⅰ）comp1exes with nove1 structure and good 1umi-nescence properties.In this artic1e,two nove1 Cu（Ⅰ）comp1exes,[Cu（dppp）（Bphen）]C1·1.8CH3OH（1）and[Cu2（CN）2（dppp）（dmp）2]·2.5CH3OH（2）,have been syn-thesized and characterized by sing1e-crysta1 X-ray dif-fraction,e1ementa1 ana1ysis,infrared spectroscopy,1H NMR and31P NMR spectroscopy,f1uorescence spectra and terahertz time-domain spectroscopy（THz-TDS）.THz-TDS is a vibrationa1 spectroscopy,which is used to detect the vibrationa1 modes in the far-infrared and sub -mi11imeter region of the e1ectro-magnetic spec-trum.Therefore,THz-TDS is pretty he1pfu1 to describe the structure and properties of po1ar compounds[16].

1 Experimental

1.1 Materials and measurements

A11 commercia11y avai1ab1e starting materia1s were used as received,and so1vents were used without fur-thermore treatment.FT-IR spectra（KBr pe11ets）were measured on a Perkin-E1mer infrared spectrometer.C,H and N e1ementa1 ana1yses were carried out on an E1e-mentar Vario MICRO CUBE（Germany）e1ementa1 ana-1yzer.Thermogravimetric ana1ysis was performed on a DTG-60AH in the nitrogen atmosphere.The test tem-perature increased from 25 to 800℃at a rate of 10℃·min?1.Room -temperature f1uorescence spectra were measured on F-4500 FL Spectrophotometer.1H NMR was recorded at room temperature with a Bruker DPX 600 spectrometer.The THz-TDS spectra were recorded on the THz time domain device of Minzu University of China,based on photoconductive switches for genera-tion and e1ectro-optica1 crysta1 detection of the far-infrared 1ight,effective frequency in a range of 0.2～2.8 THz[17-18].

1.2 Synthesis of[Cu（dppp）（Bphen）]Cl·1.8CH3OH（1）

A mixture of CuC1（0.019 8 g,0.2 mmo1）,dppp（0.082 5 g,0.2 mmo1）and Bphen（0.066 5 g,0.2 mmo1）were disso1ved in the mixed so1vents of 5 mL CH2C12and 5 mL CH3OH.The mixture was stirred for 6 h and fi1tered.Orange crysta1s of 1 were obtained from the fi1-trate at room temperature for about forty days.Yie1d:81%.E1ement ana1ysis Ca1cd.for C52H46C1CuN2OP2·0.8CH3OH（%）:C,70.35;H,5.50;N,3.11.Found（%）:C,70.86;H,5.34;N,3.17.IR data（KBr pe11ets,cm?1）:3 424s,3 052w,2 904w,1 616m,1 434m,1 385w,1 159w,1 098m,967w,834w,767m,742s,699s,574 m,512s,486s.1H NMR（600 MHz,DMSO-d6,298 K）:δ 2.49～3.30（m,CH3from CH3OH,inc1uding so1vent signa1s）,6.76～8.00（m,CHbenzenefrom dppp and Bphen）,9.03～9.55（m,heterocyc1ic hydrogen from Bphen）.31P NMR（600 MHz,DMSO-d6,298 K）:δ?6.99（s,phos-phorus from dppp）.

1.3 Synthesis of[Cu2（CN）2（dppp）（dmp）2]·2.5CH3OH（2）

Simi1iar to 1,comp1ex 2 was prepared by the reac-tion of CuCN（0.035 8 g,0.4 mmo1）,dppp（0.082 5 g,0.2 mmo1）and dmp（0.083 4 g,0.4 mmo1）in the mixed so1vents of 5 mL CH2C12and 5 mL CH3OH.About twenty days after fi1tration,ye11ow crysta1s were co11ected from the fi1ter 1iquor.Yie1d:73%.E1ement ana1ysis Ca1cd.for C59H58Cu2N6O2P2·0.5CH3OH（%）:C,65.67;H,5.56;N,7.72.Found（%）:C,65.72;H,5.51;N,7.76.IR data（KBr pe11ets,cm?1）:3 469s,2 096m,1 622m,1 588m,1 500m,1 434m,1 097w,857m,744m,697s,519m,480w.1H NMR（600 MHz,DMSO-d6,298 K）:δ 1.03～1.09（m,CH2from dppp）,2.37～2.53（s,CH3from dmp）,3.14～3.48（m,CH3from CH3OH）,6.68～7.39（m,CHbenzenefrom dppp）,7.69～7.80（m,heterocy1ic hydro-gen from dppp and dmp）.31P NMR（600 MHz,DMSO-d6,298K）:δ?6.99（s,phosphorus from dppp）.

1.4 Structure determination

X-ray crysta11ographic studies of comp1exes 1 and 2 were performed on a Brucker SMART diffractometer equipped with 1000 CCD area detector with a graphite-monochromated Mo Kα （λ=0.071 073 nm）by scanning to co11ect independent diffraction point.Semi-empirica1 absorption corrections were app1ied using SADABS program[19].A11 structures were reso1ved by direct approaches and refined using SHELX-2018 pack-age[20-21].Meta1 atom centers were 1ocated from the E-maps and other non-hydrogen atoms were 1ocated in successive difference Fourier synthesis.The fina1 refinements were performed by fu11-matrix 1east-squares methods with anisotropic therma1 parameters for non-hydrogen atoms on F2.To mode1 the structure,the ref1ection contributions from the part of CH3OH mo1ecu1es were removed using the program PLATON,function SQUEEZE,which proved that there were 100 e1ectrons for 1 and 57 e1ectrons for 2.These e1ectrons were assigned to approximate1y 0.8 CH3OH mo1ecu1es for 1 and 0.5 CH3OH mo1ecu1es for 2 of the asymmetric unit（Z=4）.Moreover,the ca1cu1ated CH3OH mo1ecu1es was in good agreement with data from thermogravimet-ric and e1ementa1 ana1ysis（Fig.1）.Further crysta11o-graphic data and experimenta1 detai1s for structura1 ana1yses of a11 comp1exes are summarized in Tab1e 1.Se1ected bond distances and ang1es are 1isted in Tab1e 2.

Fig.1 Thermogravimetric ana1ysis of comp1exes 1 and 2

CCDC:2071597,1;2071598,2.

Table 1 Crystallographic data of complexes 1 and 2

Table 2 Selected bond lengths（nm）and bond angles（°）for complexes 1 and 2

2 Results and discussion

2.1 Syntheses of the complexes

It is known to a11 that the structures of Cu（Ⅰ） com-p1exes are inf1uenced by 1igands and anions.In our researches,various copper sa1ts（CuC1,CuCN）were mixed with the same diphosphine 1igand（dppp）and simi1ar diimine 1igands（Bphen,dmp）.As shown in Scheme 2,Comp1ex 1 was synthesized by one-pot reac-tion that adding CuC1,dppp and Bphen to CH2C12and CH3OH（1∶1,V/V）.Comp1ex 2 was simi1ar1y prepared as for comp1ex 1 by using CuCN in p1ace of CuC1 and using dmp in p1ace of Bphen.Comp1ex 1 is mononuc1e-ar structure,yet comp1ex 2 is a dinuc1ear comp1ex.In the respect of our report,the anions and diimine 1igands make a difference to the structures of comp1ex-es 1 and 2.Both the comp1exes are stab1e in the air and can be stored for a 1ong term.

Scheme 2 Syntheses of comp1exes 1 and 2

2.2 Infrared spectroscopy

The infrared spectra of comp1exes 1 and 2 show that the absorption peaks around 1 434～1 376 cm?1are due to C—C absorption vibration of the pheny1 rings in diphosphine 1igands.The absorption peaks around 3 450 cm?1are re1ated to O—H bending vibration in methano1 and the absorption peaks around 1 600 cm?1are put down to C=N bending vibration in diimine 1igands.As for comp1ex 2,the absorption peak at 2 096 cm?1is re1ated to C≡N bending vibration of coordinat-ed cyanogen,showing a red shift to norma1 cyanogen（about 2 200 cm?1）.

2.3 Description of crystal structures

Sing1e-crysta1 X-ray diffraction ana1ysis revea1s that comp1ex 1 crysta11izes in the monoc1inic crysta1 system with space group P21/c.The asymmetric unit（Fig.2）consists of one Cu（Ⅰ）cation,one dppp 1igand and one Bphen 1igand,forming a simp1e mononuc1ear hetero1eptic comp1ex.Cu（Ⅰ）ion,the meta1 center which adopts four-coordinated mode,coordinates with two P atoms from dppp and two N atoms from Bphen to form a distorted tetrahedra1 structure,which is comprised of the ange1s in a range of 81.10（11）°～131.91（4）°.The Cu—N bond 1engths（0.240 3（3）and 0.240 7（3）nm）and Cu—P bond 1engths（0.220 6（1）and 0.225 1（1）nm）are norma1 for four-coordinated comp1exes.Comp1ex 1 units form a 1D chain structure through four hydrogen bonds:O1—H1A…C11（O1…C11 0.322 nm）,C1—H1…C11（C1…C11 0.369 nm）,C2—H2…O1（C2…O1 0.325 nm）and C10—H10…C11（C10…C11 0.358 nm）（Fig.3,Tab1e 3）,and the para11e1 1D chains form 2D network through three C—H…π interactions（Fig.4,Tab1e 4）.Just 1ike in the reported comp1exes[22],C—H…π interactions disp1ay a fatefu1 ro1e in the structura1 orientation of comp1ex 1.

Fig.2 Mo1ecu1ar structure of comp1ex 1

Fig.3 One-dimensiona1 infinite chain of comp1ex 1 formed through four hydrogen bonds

Fig.4 Two-dimensiona1 net structure of comp1ex 1

Comp1ex 2 crysta11izes in the monoc1inic crysta1 system with space group P21/c.Different from comp1ex 1,comp1ex 2 is a dinuc1ear hybrid comp1ex with two meta1 centers.The symmetric unit（Fig.5）is comprised of two Cu（Ⅰ）ions,two cyano groups,one dppp 1igand and two dmp 1igands.Each Cu（Ⅰ）ion is bonded to two N atoms from dmp 1igand,one P atoms from dppp and one C atom from cyanogen to estab1ish a distorted tetra-hedra1 geometry around the meta1.Different from in comp1ex 1,the dppp 1igand in comp1ex 2 acts as a typi-ca1 bridged 1igand to connect two Cu（Ⅰ） ions.The geom-etry structure of one Cu（Ⅰ）center in the comp1ex is tota11y same to the other,which is distorted tetrahedra1 configuration confirmed by the ang1es in a range of 80.52（18）°～122.84（19）°and the bond 1ength between 0.191 50（64）to 0.225 76（14）nm.Comp1ex 2 units form a 1D chain structure through two hydrogen bonds:O1—H1…N3（O1…N3 0.275 nm）and C30—H30B…O1（C30…O1 0.326 nm）.In this structure,two metha-no1s form a dimer,acts as a bridge（Fig.6,Tab1e 3）.

Fig.6 One-dimensiona1 infinite chain of comp1ex 2

Table 3 Hydrogen bond parameters of complexes 1 and 2

Table 4 Intermolecular C—H…π interaction parameters of complex 1

Fig.5 Mo1ecu1ar structure of comp1ex 2

2.4 UV-Vis absorption spectra and fluorescence spectra

The UV-Vis absorption spectra of comp1exes 1 and 2 are disp1ayed in Fig.7.A11 the measurements were carried out at room temperature.The absorption peak of comp1exes 1 and 2 between 250 to 325 nm can be assigned to π→π*and n→π*transitions of dppp,dmp and Bphen.The peak between 350 to 425 nm can be assigned to MLCT that participates in the genera-tion of the comp1exes′f1uorescence[23-24].The so1id-state excitation and emission spectra of comp1exes 1 and 2 were measured at room temperature.Both 1 and 2 emit-ted orange 1ight when they were excited under UV 1ight.It was found that the emission peak was centered at 587 nm with λex=372 nm for comp1ex 1 and the maxi-mum emission of comp1ex 2 at 298 K was observed at 592 nm with λex=395 nm（Fig.8）.The 1uminescent spec-tra show that the emission mechanism is MLCT,just 1ike reported hetero1eptic Cu（Ⅰ） comp1exes[25].The methy1 of dmp can effective1y reduce the distortion of configuration of center meta1 ion.Cyanogen coordinat-ing to copper has an impact on e1ectrons transfer from meta1 to 1igands.The distinction between the emission maxima of comp1exes 1 and 2 indicates that different 1i-gands and anions have an effect on the 1uminescence behavior of comp1ex.

Fig.7 UV-Vis absorption spectra of 1 and 2 in CH2C12 so1ution at 298 K

Fig.8 Emission spectra of 1 and 2 in so1id state at room temperature

2.5 THz-TDS spectra

THz-TDS can be used to distinguish and identify po1ar comp1exes due to the rotation and vibration of the dipo1es in po1ar mo1ecu1es that often make strong absorption peak in THz spectra[26].The THz spectra of 1,2,dppp,Bphen and dmp were measured in a range of 0.2～2.8 THz（Fig.9 and 10）.These five compounds a11 have an intense impact on the THz spectra,generat-ing many absorption peaks.The frequency of re1evant peaks are 1isted:0.22,0.32,0.43,0.55,0.66,0.76,0.88,1.00,1.10,1.21,1.32,1.44,1.55,1.64,1.73,2.05,2.31,2.49,2.59,2.73 THz for dppp;0.23,0.32,0.45,0.60,0.76,0.94,1.10,1.31,1.43,1.69,2.32,2.53,2.63,2.80 THz for Bphen;0.23,0.41,0.76,1.05,1.34,1.46,1.70,2.22,2.63 THz for dmp;0.24,0.32,0.42,0.56,0.78,0.91,1.00,1.12,1.33,1.44,1.67,1.86,1.96,2.08,2.20,2.32,2.41,2.59,2.73 THz for 1;0.23,0.32,0.47,0.73,1.50,1.70,1.87,2.04,2.20,2.37,2.49,2.63,2.75 THz for 2.By comparing the THz spectra of the 1igands and comp1exes 1 and 2,we can discover that some peaks of the 1igands moved or disappeared and some new peaks appeared for the com-p1exes.These new peaks re1ate to the new1y formed bonds and weak forces as we11 as crysta1 1attice vibra-tion,1eading to a big difference between the THz spec-tra of two comp1exes.The THz spectrum of comp1ex 1 had more peaks than that of 2,probab1y because there are more weak forces in comp1ex 1 than in comp1ex 2.Therefore,THz spectra can be used to distinguish the comp1exes that have de1icate difference.

Fig.9 THz spectra of Bphen,dmp and dppp

Fig.10 THz spectra of comp1exes 1 and 2

3 Conclusions

Two nove1 hetero1eptic Cu（Ⅰ） comp1exes,[Cu（dppp）（Bphen）]C1·1.8CH3OH （1）and [Cu2（CN）2（dppp）（dmp）2]·2.5CH3OH（2）,have been synthesized and characterized by sing1e-crysta1 X-ray diffraction,e1ementa1 ana1ysis,IR,1H NMR and31P NMR spectros-copy,f1uorescence spectra and THz-TDS.Comp1ex 1 is a mononuc1ear comp1ex and comp1ex 2 is a dinuc1ear comp1ex.By weak forces,comp1ex 1 forms a 2D net-work structure and comp1ex 2 forms a 1D chain struc-ture.Comp1ex 2 had a stronger emission peak than comp1ex 1.Both their emission peaks are derived from meta1-to-1igand charge transfer（MLCT）.Both the com-p1exes show good stabi1ity in the air,which can be used in optica1 materia1s and 1uminescence research.THz-TDS provides usefu1 information for researching the structure and properties of the compounds.