基于 3，6-二（2-（4-氧化苯并吡嗪基））-4，5-二氮雜-3，5-辛二烯配體的兩個(gè)離散型Agガ配合物的合成與晶體結(jié)構(gòu)

任秀輝 王 鵬 蘇 劍 程軍妍＊,

（1山東師范大學(xué)化學(xué)化工與材料科學(xué)學(xué)院，濟(jì)南 250014）

（2山東科技大學(xué)化學(xué)與環(huán)境工程學(xué)院，青島 266590）

（3南京大學(xué)化學(xué)化工學(xué)院，南京 210023）

0 Introduction

Due to their novel structural topologies and potential applications in gas storage[1-2],adsorption and separation[3-4], luminescence[5-7], catalysis[8-10]and magnetic properties[11],pronounced interest has been focused on new discrete compounds and coordination polymers based on polydentate organic ligands.Of all factors in the process of constructing coordination compounds,such as coordination orientation of metal ions,counter-anions,template effect of solvent,the most important is the coordination ability,length,geometry and conformation of the organic ligands[12].Therefore,for a long time,a variety of organic ligands have been synthesized and used as building blocks to construct CPs with novel topological structures.One of continuing project in our laboratory has been the development of organometallic coordination compounds generated from double Schiff-base ligands with pyridine,pyrazine,and quinoxaline diazene as the terminal binding groups[13]. Our previous research demonstrated that such types of ligands were very useful to construct novel polymeric and discrete complexes due to their zigzag conformation of the spacer moiety （-RC=N-N=CR-）between two terminal coordination groups[14].Moreover,Agガ,as a soft Lewis acid,may adopt various coordination modes such as linear,trigonal planar,trigonal pyramidal,and tetrahedral coordination geometries[15].In this context,we design a double Schiff-base ligand,3,6-bis（2-（4-oxide-quinoxaline）-yl）-4,5-diaza-3,5-octadiene （L）（Scheme 1）[15].More novel coordination compounds may be obtained with the quinoxaline-N-oxide as the terminal binding groups.Additionally,the O atoms of quinoxaline-N-oxide can serve as potential binding sites and H-bond acceptors forming hydrogen bonds with solvent molecules.In this paper,based on this novel functional ligand,two silver complexes,[Ag8（L）8]（BF4）8·CH2Cl2·3CH3OH （1）and[Ag4（L）4]（PF6）4·CH2Cl2（2）,are successfully synthesized and the crystal structures are determined.As reported in other articles[16],the complex hydrogen bonding systems exist in the above two complexes.

Scheme 1 Schiff-base ligand used in the construction of coordination compounds

1 Experimental

1.1 M aterials and measurements

AgBF4and AgPF6（Acros）were purchased and used as obtained without further purification.The ligand L was synthesized according to the literature[15].Infrared （IR）samples were prepared as KBr pellets,and spectra were obtained in the 400～4 000 cm-1range using a Perkin-Elmer 1600 FT-IR spectrometer.Elemental analyses were performed on a Perkin-Elmer model 2400 analyzer.

1.2 Synthesis of 1

A solution of AgBF4（23.1 mg,0.12 mmol）in CH3OH （8 mL）was slowly diffused into a solution of L （12.0 mg,0.03 mmol）in CH2Cl2（8 mL）.Yellow crystals are formed in about 7 days in 50.7%yield（based on AgBF4）.Anal.Calcd.for C180H174B8N48O19F32Ag8Cl2（%）:C,43.70;H,3.52;N,13.60.Found（%）:C,43.26;H,3.45;N,13.79.IR （KBr pellet,cm-1）:3 449（s）,1 636 （m）,1 575 （w）,1 524 （w）,1 490 （w）,1 457（w）,1 401 （s）,1 249 （w）,1 218 （w）,1 085 （m）,910（w）,856 （w）,771 （w）,625 （w）.

1.3 Synthesis of 2

A solution of AgPF6（30.3 mg,0.12 mmol）in CH3OH （8 mL）was slowly diffused into a solution of L （12.0 mg,0.03 mmol）in CH2Cl2（8 mL）.Yellow crystals were formed in about 7 days in 24.3%yield（based on AgPF6）.Anal.Calcd.for C89H82N24O8F24P4Ag4Cl2（%）:C,39.58;H,3.04;N,12.45.Found（%）:C,38.65;H,3.15;N,11.61.IR （KBr pellet,cm-1）:3 417（s）,3 120 （w）,1 638 （m）,1 617 （m）,1 578 （m）,1 522（w）,1 492 （m）,1 459 （w）,1 400 （s）,1 375 （s）,1 277（w）,1 250 （w）,1 216 （w）,1 136 （w）,1 098 （w）,1 050（w）,982 （w）,942 （w）,910 （w）,838 （s）,771 （m）,557 （m）.

1.4 Determ ination of crystal structure

Suitable single crystals of 1 and 2 were selected and mounted in air onto thin glass fibers.X-ray intensity data were measured at 298（2）K on a Bruker SMART APEX CCD-based diffractometer （Mo Kα radiation,λ=0.071 073 nm）.The raw frame data for 1 and 2 were integrated into SHELX-format reflection files and corrected for Lorentz and polarization effects using SAINT[17].Corrections for incident and diffracted beam adsorption effects were applied using SADABS[18].None of the crystals showed evidence of crystal decay during data collection.The structures were solved by a combination of direct methods and difference Fourier syntheses and structural analysis refined against F2by the full-matrix least squares technique.Crystallographic data for 1 and 2 are listed in Table 1.Selected bond lengths and bond angles are listed in Table 2.Hydrogen bond lengths and bond angles are listed in Table 3.

CCDC:1838857,1;1838858,2.

Table 1 Crystallographic data for 1 and 2

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

Continued Table 2

Table 3 Structural parameters of hydrogen bonds for com plexes 1 and 2

Continued Table 3

2 Results and discussion

2.1 Structural analysis of[Ag8（L）8]（BF4）8·CH 2Cl2·3CH 3OH （1）

Complex 1 was obtained as yellow crystals in CH2Cl2/CH3OH mixed solvent system using combination of L and AgBF4（metal-to-ligand molar ratio 4∶1）at room temperature.The X-ray single-crystal analysis reveals that 1 crystallizes in the orthorhombic space group Pbca and exists as a dimer.Complex 1 possesses a dinuclear chiral double-helical structure with the Ag…Ag distance of 0.439 6 nm.As indicated in Fig.1,the asymmetric unit contains two crystallographic Agガcenters,two L ligands,two BF4-anions,a quarter CH2Cl2,and 0.75 CH3OH molecule.Each Agガcenter lies in a distorted tetrahedral coordination environment defined by two quinoxaline N-donors and two Schiff-base N-donors from two quadridentate ligands,respectively.The dihedral angle between two terminal benzene rings is 79.94°.BF4-anions are bonded to the[Ag2L2]2+unit through weak F…H-C bonds （F（3）…H（35A）-C（35）,F（3）…H（35A）0.260 nm,F（5）…H（11F）-C（11′）,F（5）…H（11F）0.262 nm,Fig.2）.In the solid state,through three sets of hydrogenbonding systems,the dinuclear subunits are linked together to give one-dimensional helical chains extending along the crystallographic c axis,which arrange in the crystallographic bc plane in parallel（Fig.3）.

Fig.1 ORTEP figure （left）and space-filling model （right）of 1

Fig.2 Hydrogen-bonds （dotted lines）between BF4-anions and[Ag2L2]2+unit

Fig.3 One-dimensional helical chains of 1 （left）and crystal packing of 1 （right）

2.2 Structural analysis of[Ag4（L）4]（PF6）4·CH 2Cl2（2）

The reaction of L with AgPF6in methanol/methylene chloride at room temperature afforded discrete complex 2 in 24.3% yield.Single-crystal analysis reveals that complex 2 contains four types of crystallographic independent Agガ ions （Fig.4）.Each Agガion is four-coordinated in an approximately tetrahedral coordination environment,which is defined by two quinoxaline N-donors and two Schiff-base N-donors from two quadridentate ligands.The Ag-N bond distancesare in a range of 0.220 8 （5）～0.247 3（4）nm,all of which are within the range of those reported for other Agガcomplexes with N donors[19].The dihedral angles between two terminal benzene rings are 60°and 75°,respectively.Additionally,the complex features diverse non-clsssical hydrogen bonding interactions （Fig.5）.PF6-anions are bonded to the [Ag2L2]2+units through weak F…H-C bonds（Table 3）.As shown in Fig.6,the dinuclear subunits are linked together into a two-dimensional net extending in the crystallographic bc plane through complicated hydrogen-bonding systems. These networks stack in an-ABAB-sequence along the crystallographic a axis （Fig.7）.

Fig.4 ORTEP figure （top）and space-filling model（below）of 2

Fig.5 Hydrogen-bonding systems between PF6-anions and[Ag2L2]2+unit

Fig.6 Two dimensional hydrogen-bonded nets found in 2

Fig.7 Two dimensional nets stack parallel to crystallographic ab plane

3 Conclusions

In summary,a double Schiff-base ligand,namely 3,6-bis（2-（4-oxide-quinoxaline）-yl）-4,5-diaza-3,5-octadiene （L）,was used as a polydentate ligand to coordinate with transition metal ions.Two novel discrete complexes with Agガcenters have been synthesized and structurally characterized.Both complexes exist as dimers and the frameworks were formed via hydrogen bonding interactions between uncoordinated counter ions and the discrete building blocks.Further investigations on supramolecular compounds based on the double Schiff-base ligand with new structures and multifunctional properties are ongoing in our group.