Solvothermal Synthesis,Structure,and Fluorescence Properties of Four Organotin Complexes Based on m-Phthaloyl Bis(substituted salicylaldehyde acylhydrazone)

FENG Yong-Lan JIANG Wu-Jiu ZHANG Fu-Xing KUANG Dai-Zhi

(Key Laboratory of Functional Metal-Organic Compounds of Hunan Province,Key Laboratory of Organometallic New Materials of College of Hunan Province,College of Chemistry and Material Science,Hengyang Normal University,Hengyang,Hunan 421008,China)

Abstract:Four new organotin complexes based on m-phthaloyl bis(substituted salicylaldehyde acylhydrazone)(H4L),(SnR2)2L(1-4),were synthesized by solvothermal reaction of H4L with R23SnOH,or one-pot solvothermal reaction of m-phthaloyl hydrazide,3-tert-butyl salicylaldehyde,and tricyclohexyltin hydroxide,where H4L=m-Ph(CONH—N=CH(o-OH)PhR1)2;R1=NEt2,R2=Ph(1);R1=3,5-di-tert-butyl=3,5-t-2Bu,R2=Ph(2);R1=3,5-t-2Bu,R2=Cy(3);R1=3-tert-butyl=3-t-Bu,R2=Cy(4).And they were characterized by elemental analysis,IR,and(1H,13C,and 119Sn)NMR.The structures of complexes 1-4 were confirmed by X-ray diffraction.Three“inward E-type”complexes 1-3 were formed by the inward orientation oftwo substituted salicylaldehyde acylhydrazone chains of H4L and coordination with tin atoms.And two substituted salicylaldehyde acylhydrazone chains were oriented outward and coordinated with tin atoms to form an“outward E-type”complex 4.Complexes 1,2,and 4 belong to the triclinic P space group and complex 3 belongs to the monoclinic P21/c space group.The central tin and the coordination atom form a five-coordinate distorted triangular bipyramids configuration.The fluorescence properties of the ligands and the complexes-chloroform solution showed that when free ligand m-Ph(CONH—N=CH(o-OH)PhNEt2)2(H4L1)with weak fluorescence and ligand m-Ph(CONH—N=CH(o-OH)Ph(3,5-t-2Bu))2(H4L2)without fluorescence coordinated with phenyltin or cyclohexyltin,the chloroform solution of the complexes emitted strong fluorescence.CCDC:2111478,1;2111479,2;2111480,3;2111481,4.

Keywords:m-phthaloyl bis(substituted salicylaldehyde acylhydrazone);organotin complex;solvothermal synthesis;crystal structure;fluorescence properties

0 Introduction

Nucleophilic addition and dehydration of organic aldehydes or ketones with hydrazide result in acylhydrazone compounds containing amide Schiff base(R1C(O)—NH—N=CH(R)—R2).The acylhydrazone compounds not only have good bactericidal[1-2],antitumor[3-4],and optical properties[5-9]but also provide multiple coordination atoms such as oxygen and nitrogen.These—CH=N—,＞NH and—CONH— active groups have their respective chemical reactivity and cooperation interaction effect.The lone pair electrons of amino-group(＞NH)arep-πconjugated with adjacent carbonyl and double bond imine-groups,and the double bond producesZ-,E-isomerization[10].Therefore,acylhydrazone compounds have a variety of coordination modes with metals,providing a broad space for the synthesis of complexes with diverse structures and functions[11-13].Therefore,people are inspired to think that acylhydrazone compounds[14-15]containing bis(poly)-acylhydrazone X[NH—N=CHAr(OH)]2(X can be carbonyl＞C=O/S,aromatic polycarbonyl,and other bridge groups or atoms)have more active groups,more coordination modes than monoacylhydrazone,and are more prone to keto and enol conversion of acylhydrazone chain and deprotonation of amide nitrogen[16].The coordination of acylhydrazone compounds with metals to assemble complexes with various structures and properties[17]has attracted more interest.In this work,m-phthaloyl bis(substituted salicylaldehyde acylhydrazone)compounds(H4L)were prepared by condensation of 4-diethylaminosalicylaldehyde,3,5-di-tertbutyl salicylaldehyde and 3-tert-butyl salicylaldehyde withm-phthaloyl hydrazine,respectively.The triphenyltin hydroxide and tricyclohexyltin hydroxide reacted with H4L respectively to synthesize organotin diacylhydrazone complexes(SnR2)2L(1-4),where H4L=m-Ph(CONH—N=CH(o-OH)PhR1)2;R1=NEt2,R2=Ph(1);R1=3,5-di-tert-butyl=3,5-t-2Bu,R2=Ph(2);R1=3,5-t-2Bu,R2=Cy(3);R1=3-tert-butyl=3-t-Bu,R2=Cy(4).The fluorescence properties of the complexes were preliminarily evaluated.

1 Experimental

1.1 Material and instruments

FT-IR spectra were recorded on a Bruker TENSORⅡ Fourier infrared spectrometer with the samples prepared as KBr(400-4 000 cm-1)pellets.C,H,and N analyses were carried out with a PE-2400Ⅱelement analyzer.UV-Vis absorption spectra were recorded on a UV-2500PC spectrophotometer.1H,13C,and119Sn NMR spectra were determined by Bruker Avance 500 NMR(TMS as internal standard and CDCl3or DMSO-d6as solvent).Melting points were measured by an X-4 microscopic melting point apparatus made by Beijing Tech Instrument Co.,Ltd.and were uncorrected.Fluorescence spectra in the solution were recorded on a Hitachi F-7000 spectrometer.

4-Diethylaminosalicylaldehyde(99%)and 3-tertbutyl salicylaldehyde(CP)(Beijing,J&K Chemical Ltd.),m-phthaloyl hydrazide and 3,5-di-tert-butyl salicylaldehyde(CP)(Shanghai Shaoyuan Co.,Ltd.),tricyclohexyltin hydroxide (CP) (Hubei Jusheng Technology Co.,Ltd.),triphenyltin hydroxide(CP)(Shanghai Civi Chemical Technology Co.,Ltd.)were used without further purification.

1.2 Preparation of the ligands

A mixture ofm-phthaloyl hydrazide(3.890 g,0.020 mol),4-diethylaminosalicylaldehyde(7.732 g,0.040 mol),and 60 mL ethanol solution was placed in a flask.The reactant was stirred and refluxed until the solid was dissolved,and the reaction continued for 24 h.Then the mixture was cooled and filtered.The obtained solid was recrystallized and dried in a vacuum to obtain 8.420 g of orange powder ofm-phthaloyl bis(4-diethylaminosalicylaldehyde acylhydrazone)(H4L1),with a yield of 75.0%.m.p.300℃.Anal.Calcd.for C30H36N6O4(%):C,66.16;H,6.66;N,15.43.Found(%):C,66.20;H,6.68;N,15.38.FT-IR(KBr,cm-1):3 448(m,νO—H);3 292,3 239(m,νN—H);3 072,2 972,2 930,2 900(m,νAr—HandνC—H);1 648,1 628(vs,νC=OandνC=N);1 585,1 546(m,benzeneνC=C).1H NMR(500 MHz,DMSO-d6):δ12.02(s,2H),11.47(s,2H),8.50-6.15(m,12H),3.36(m,8H),1.13(s,12H).13C NMR(126 MHz,DMSO-d6):δ162.14,160.24(C=O);150.71(C=N);133.99,132.11,131.01,129.28,127.17,106.89,104.17,97.95(spectral line of benzene carbon);44.30,40.48,40.40,40.31,40.23,40.15,39.98,39.81,39.64,39.48(methylene carbon spectral line of ethylamine);13.00(methyl carbon of ethylamine).

m-Phthaloyl hydrazide(5.825 g,0.030 mol),3,5-di-tert-butyl salicylaldehyde(14.059 g,0.060 mol)and 50 mL of ethanol were added into the reaction flask.The reactant was stirred and refluxed for 48 h.Then the mixture was cooled and filter.The precipitate was dried in a vacuum.The yellow powder(8.961 g)ofm-phthaloyl bis(3,5-di-tert-butyl salicylaldehyde acylhydrazone)(H4L2)was obtained,with a yield of 69.1%.m.p.114℃.Anal.Calcd.for C38H50N4O4(%):C,72.81;H,8.04;N,8.94.Found(%):C,72.85;H,8.08;N,8.76.FT-IR(KBr,cm-1):3 476(m,νO—H);3 252(m,νN—H);3 062,2 960,2 909,2 870(m,νAr—HandνC—H);1 669,1 646(vs,νC=OandνC=N);1 622,1 589(m,benzeneνC=C).1H NMR(500 MHz,CDCl3):δ11.91(s,2H),8.76(s,2H),7.46-7.01(m,10H),1.57-1.20(m,36H).13C NMR(126 MHz):δ165.29(C=O);156.86(C=N);141.29,136.88,128.24,126.98,116.70 (spectral line of benzene carbon);35.15,34.21,31.45,29.45(tert-butyl carbon).

1.3 Synthesis of the complexes

H4L1(0.545 g,1 mmol),triphenyltin hydroxide(0.734 g,2 mmol),and 8 mL mixed solvent(3 mL methanol and 5 mL DMF)were mixed and heated to 120℃for 72 h,then the mixture was reduced to room temperature at 1℃·h-1and filtered.Complex 1 was obtained by recrystallization.

Complex 2 was synthesized by replacing H4L1with H4L2(0.433 g,1 mmol).Complex 3 was synthesized by replacing triphenyltin hydroxide with tricyclohexyltin hydroxide and reacting with H4L2.

One-pot solvothermal synthesis of complex 4:mphthaloyl hydrazide(0.194 g,1 mmol),3-tert-butyl salicylaldehyde(0.356 g,2 mmol),tricyclohexyltin hydroxide(0.771 g,2 mmol)and 8 mL methanol were added to the polytetrafluoroethylene reactor.Then,following the synthesis steps of complex 1,complex 4 was obtained.

Complex 1,orange crystal,0.869 g,Yield:80.0%.m.p.300℃.Anal.Calcd.for C54H52N6O4Sn2(%):C,59.70;H,4.82:N,7.74.Found(%):C,60.01;H,4.78:N,7.71.FT-IR(KBr,cm-1):3 065,3 047,2 971,2 928,2 902,2 809(m,νAr—HandνC—H);1 607,1 586(s,νC=O andνC=N);1 505,1 479(m,benzeneνC=C);546(w,νSn—O);500(w,νSn—N);451(w,νSn—C).1H NMR(500 MHz,CDCl3):δ8.97(s,2H),8.57-6.16(m,10H)3.40(m,8H),1.25(s,12H).13C NMR(126 MHz,CDCl3):δ169.16,166.57(C=O);160.05,153.87(C=N);140.02,136.57,136.40,136.35,136.14,133.99,130.12,129.38,129.00,128.67,128.32,128.02,126.30,107.18,103.99,100.98(carbon of benzene);44.63(methylene carbon of ethylamino);12.86(methyl carbon of ethylamino).119Sn NMR(SnMe4,187 MHz,CDCl3):δ-329.62.

Complex 2,orange red crystal,0.594 g,Yield:50.8%.m.p.253-255℃.Anal.Calcd.for C62H67N4O4Sn2(%):C,63.72;H,5.69;N,4.79.Found(%):C,63.68;H,5.75;N,4.75.FT-IR(KBr,cm-1):3 059,2 959,2 906,2867(s,νAr—HandνC—H);1 611,1 591(s,νC=OandνC=N);1 552,1 537,1 509,1 477,1 460(m,benzeneνC=C);694(w,νSn—O);443(w,νSn—N);407(w,νSn—C).1H NMR(500 MHz,CDCl3):δ9.00,8.87(s,2H),8.75-7.02(m,30H),1.53,1.47,1.32(m,36H).13C NMR(126 MHz,CDCl3):δ168.46,165.27,164.94,163.11(C=O);156.86(C=N);141.29,140.58,139.63,139.21,137.95,137.24,136.89,136.46,136.24,136.14,136.02,133.53,131.03,130.35,130.31,129.13,128.96,128.79,128.64,128.44,128.33,128.22,127.02,126.97,116.71,116.29(carbon of benzene);35.48,35.14,34.19,34.03,31.44,31.29,30.09,29.46(carbon oftert-butyl).119Sn NMR(SnMe4,187 MHz,CDCl3):δ-324.04.

Complex 3,orange flake crystal,0.476 g,Yield:39.9%.m.p.278℃.Anal.Calcd.for C62H92N4O4Sn2(%):C,62.32;H,7.76;N,4.69.Found(%):C,62.45;H,7.78;N,4.65.FT-IR(KBr,cm-1):3 014,2 950,2 920,2 848(s,νAr—HandνC—H);1 611,1 595(s,νC=OandνC=N);1 548,1 534,1 518(m,benzeneνC=C);525(w,νSn—O);484(w,νSn—N);459(w,νSn—C).1H NMR(500 MHz,CDCl3):δ9.07-8.63(m,2H),8.19-6.81(m,8H),1.96-1.30(m,80H).13C NMR(126 MHz,CDCl3):δ168.89,165.35,162.47(C=O);156.86(C=N);140.07,137.93,133.98,130.28,129.87,128.53,128.02,126.67,116.08(carbon of benzene);39.94,35.29,33.95,31.35,31.13,29.93,29.91,29.69,28.82,28.55,28.53,26.76,26.61(carbon oftert-butyl and cyclohexyl).119Sn NMR(SnMe4,187 MHz,CDCl3):δ-249.76.

Complex 4,yellow block crystal,0.26 g,Yield:24.1%.m.p.226℃.Anal.Calcd.for C54H74N4O4Sn2(%):C,60.02;H,6.90;N,5.18.Found(%):C,60.05;H,6.92:N,5.11.FT-IR(KBr,cm-1):3 053,3 017,2 996(s,νAr—HandνC—H);1 606(s,νC=OandνC=N);1 547,1 516,1 443(m,benzeneνC=C);534(w,νSn—O);497(w,νSn—N);455(w,νSn—C).1H NMR(500 MHz,CDCl3):δ8.79(m,2H),8.19-6.68(m,10H),2.13-1.21(m,62H).13C NMR(126 MHz,CDCl3):δ168.46,165.27,164.94,163.11(C=O);156.86,141.29,140.58,139.63,139.21,137.95,137.24,136.89,136.46,136.24,136.14,136.02,133.53,131.03,130.35,130.31,129.13,128.96,128.79,128.64,128.44,128.33,128.22,127.02,126.97,116.71,116.29(carbon of benzene);35.48,35.14,34.19,34.03,31.44,31.29,30.09,29.46(carbon oftert-butyl and cyclohexyl).119Sn NMR(SnMe4,187 MHz,CDCl3):δ-250.68.

1.4 X-ray data collection and refinement

The suitable crystals of the complexes were obtained by slow volatilization of methanol solvent.The single crystals of the complexes were mounted on a glass capillary of a Bruker SMART APEXⅡCCD X-ray diffractometer.Intensity data for the crystals were measured on a diffractometer with graphite-monochromatized MoKαradiation(λ=0.071 073 nm)by using theφ-ωscan technique and a certainθrange.Multiscan absorption correction was applied to the intensity data using the SAINT program.The structures were solved and refined by OLEX2 software[18]and SHELXS[19]program.All non-hydrogen atoms and their anisotropic thermal parameters were refined to convergence by the full-matrix least square method with the SHELXL program.Complexes 2 and 3 have a disorder oftert-butyl and cyclohexyl groups,respectively.After splitting and restraint,a chemically reasonable structural model and atomic displacement parameters were obtained.All hydrogen atoms were positioned geometrically and refined using a riding model.Details of the crystal data and structure refinement parameters for 1-4 are summarized in Table 1.

Table 1 Crystal data and structure refinement for complexes 1-4

Continued Table 1

CCDC:2111478,1;2111479,2;2111480,3;2111481,4.

2 Results and discussion

2.1 Crystal structure of complexes

The ligands,m-phthaloyl bis(substituted salicylaldehyde acylhydrazone)with diacylhydrazone chains contain multiple nitrogen and oxygen atoms that can coordinate with metals.Due to the double bond C=N,the arrangement of phenyl and acyl hydrazone chains producesE-,Z-isomerism.In solids,due to hydrogen bonding,it often exists in anE-type configuration[20-21],In addition,the acylhydrazone chain contains a rotatable single bond.The C1—N—N=CPh(OH)and C8—N—N=CPh(OH)chains on the central benzene ring can be oriented inward and outward by C1—C2 or C4—C8 bond rotation.Theoretical calculations show that the coplanar structure of benzene and acylhydrazone chain of ligands H4L1and H4L2is assumed as the initial conformation(α=0°)and the C1—C2 bond rotates 360°around space.Other configurations remain unchanged,and the system energy(E)changes with the rotation(α)was explored.The difference between the maximum energy barrier and the lowest energy conformation of the curve was found(ΔE=Emax-Emin)to be 20.15 kJ(H4L1)and 19.78 kJ(H4L2)respectively.It can be seen that the C1—C2 bond of H4L1and H4L2can rotate freely,and the two acylhydrazone chains of the ligand can coordinate with the metal in an inward orientation or outward orientation to construct mono-,poly-metal complexes.X-ray crystal structure analysis shows that complexes 1-3 form anE-type internal orientation coordination structure.In complex 4,the C1—C2 and C4—C8 bond rotate,the configuration of the benzoylacylhydrazone chain is reversed,and the ligand atom coordinates with cyclohextin to form anE-type outward orientation structure.The selected bond length and bond angle data are shown in Table 2 and the molecular structure is shown in Fig.1.Complexes 1,2,and 4 belong to the triclinicPspace group and complex 3 belongs to the monoclinicP21/cspace group.These two kinds of internally and externally oriented coordination structures areproduced bynitrogen,oxygen from ligand with tin,which coordinate with diphenyl(dicyclohexyl)tin to construct five coordinated diphenyl(dicyclohexyl)tin complexes,in which C1—O1 and C8—O2 bonds are 0.130 1(4)and 0.130 4(4)nm,respectively,and the bond length is between the normal carbon-oxygen single bond length(0.143 0 nm)and double bond length(0.122 4 nm)[22],indicating that the carbonyl group becomes enol type.Two phenyl groups(cyclohexyl)extend up and down the ligand“plane” to form ∠C—Sn—C: 119.39(15)° (1),115.98(15)°(2),134.7(6)°(3),and 127.97(16)°(4).It can be seen that cyclohexyl has a greater steric effect than phenyl.The bond parameters of the covalent bond composed of central tin and the nitrogen,oxygen,and carbon atoms of the ligand are different.O1 and O3 atoms are in the axial position at the top of the triangular bipyramid,the axial angles(∠O1—Sn1—O3)are 153°-159°,which deviates from the linear structure,and the cyclohexyltin of 3 and 4 deviates 180°morethan that of 1 and 2 phenyltin complexes,which further supports the influence of space effect.The bond angle between the equatorial carbon and nitrogen atoms and the axial position,such as ∠O1—Sn1—C(N),varies from 72°to 98°.It can be seen that the central tin and the coordination atom form a distorted triangular bipyramids configuration.

Table 2 Selected bond lengths(nm)and bond angles(°)of complexes 1-4

Fig.1 Molecular structures of complexes 1-4 with thermal ellipsoids drawn at the 30% probability level

Interestingly,for complexes 1-4,there are some interactions intermolecular in crystal stacking.For example,complex 1 has fourσ…πweak action of adjacent intermolecular:C23—H23A…C32i,C27—H27B…C8ii,C35—H35…C49iii,and C40—H40…C3iv(Symmetry codes:i2-x,-y,1-z;ii2-x,2-y,-z;iiix,1+y,-1+z;iv1-x,1-y,-1-z).The distances between the four H…C are 0.286 0,0.289 5,0.278 2,and 0.282 6 nm respectively,∠C—H…C are 146.26°,127.59°,153.97°,and 152.96°respectively.A 3D supramolecular structure is formed by these weak interactions.

2.2 Spectral characteristics of the complexes

The infrared spectra of the ligands had four groups of characteristic peaks:(1)3 400-3 500 cm-1for phenolic hydroxyl groupνO—Handca.3 300 cm-1for aminoνN—Hstretching vibration peak;(2)C—H vibrational absorption peaks of the benzene ring(ca.3 000 cm-1)and methyl and methylene(ca.2 800 cm-1);(3)carbonyl(ca.1 700 cm-1,νC=O)and imine(ca.1 600 cm-1,νC=N)characteristic peak;(4)benzene C=C vibration absorption peak of the skeleton.There are three groups of chemical shift signals in the NMR spectrum:(1)phenolic hydroxyl hydrogen and amino hydrogen signals appearing atδ=10-13 in the low field region;(2)δ=6-9 for benzene hydrogen(Ar—H)and methylene hydrogen(HC=N);(3)δ=1-3 for methyl and methylene hydrogen proton signals in high field.After phenyltin or cyclohexyltin is coordinated with the ligands,the characteristic infrared absorption peak of the phenolic hydroxyl groupνO—Hand aminoνN—H,and its NMR proton signal disappeared in the spectra of the complexes,and the weak peaks of O(N)→Sn and C—Sn[23-24]appeared in the low wavenumber region of the infrared spectrum of the complexes,indicating that the dehydrogenated ligand is coordinated with tin.The stretching peaks of the carbonyl group and the imine group of the ligands shifted towards the low wavenumber in the spectra of complexes,due to the carbonyl enol conversion and Schiff base imine coordination to tin weakening carbonyl and imine groups.After the ligands are coordinated to tin,the electron transfer occurs,and the characteristic lines of the13C NMR spectra of the complexes shift to the low field region and divide into more lines.In the119Sn NMR spectra,the chemical shifts of the complexes moved toca.330(1,2)andca.250(3,4)in the high field relative to SnMe4[25],which further indicates that the ligands coordinate with tin as an electron donor.

2.3 Fluorescence properties of ligands and their complexes

The ligands H4L1,H4L2,and the complexes(1-4)-chloroform solution with 50 μmol·L-1were prepared.The solution was scanned in 3D on a fluorescence spectrometer and the excitation wavelength of the test solution was determined by referring to the UV spectrum.Then,the fluorescence spectrum of the solution was measured in a range of 400-800 nm at room temperature with 430 nm(H4L1),290 nm(H4L2),370 nm(1),436 nm(2),330 nm(3),and 330 nm(4)as excitation wavelengths respectively.The results are shown in Fig.2.The H4L1-chloroform solution emitted weak fluorescence at 466 nm(I=282.2)and 494 nm(I=201.7).When complex 1 was formed by H4L1and diphenyltin,the 466 nm peak red-shifted to 476 nm and emitted strong yellow fluorescence.The intensity was 6 037,which was 21.4 times higher than that of H4L1;The strong fluorescence of complex-chloroform solution was 34.1 times higher than that of H4L1solution at 494 nm.No fluorescence was found in the H4L2-chloroform solution in a range of 400-800 nm.When coordinated with diphenyltin or dicyclohexyltin,complexes 2-and 3-chloroform solution produced strong fluorescence at 504 nm,and the fluorescence of solution 3 was 1.3 times that of solution 2.The luminescence property of complex 4 was similar to that of 3,with strong fluorescence at 490 nm.It can be seen that the ligand coordinates with diphenyl(dicyclohexyl)tin to form a planar conjugate rigid structure,which greatly increases the fluorescence intensity of the complex compared with the ligand[26].Especially when the benzene ring of salicylaldehyde contains color enhancers such as the diethylamine group,the complex produces strong fluorescence and becomes a substance with luminescent properties,which can be further studied as luminescent materials.

Fig.2 Fluorescence spectra of H4L1,H4L2,and their complexes 1-4 in CHCl3solution

3 Conclusions

Them-phthaloyl bis(substituted salicylaldehyde hydrazone)was prepared by reaction of substituted salicylaldehyde withm-phthaloyl hydrazine.m-phthaloyl bis(substituted salicylaldehyde hydrazone)tetraphenyl(tetracyclohexyl)ditin complexes were successfully synthesized by methanol solvothermal reaction of ligands with phenyl(cyclohexyl)tin hydroxide.In the preliminary test of the fluorescence properties of 50 μmol·L-1ligands,the complexes-chloroform solution shows that when the ligands with weak fluorescence(H4L1)and non-fluorescence(H4L2)coordinated with phenyl(cyclohexyl)tin,the chloroform solution of the complexes emitted strong fluorescence,which can be further studied as fluorescent materials.