Effect of pH on the formation of complex compounds with Schiff ...

Nov.2011-Jan.2012, Vol.2.No.1, 6-13 E- ISSN: 2249 –1929Journal <strong>of</strong> Chemical, Biological and Physical SciencesAn International Peer Review E-3 Journal <strong>of</strong> SciencesResearch ArticleAvailable online at www.jcbsc.orgSection A: Chemical Science<strong>Effect</strong> <strong>of</strong> <strong>pH</strong> on the formation <strong>of</strong> complex compoundswith Schiff bases derived from 3-aldehydosalicylic acidwith 7-amino-4-methyl coumarinBasavaraj M. Kalshetty 1 *, S.S.Suvarnakhandi1, R.C.Sheth 1 and M.B.Kalashetti 21 Comm. BHS Arts and TGP science College Jamkhandi, Dist: Bagalkot.2 P.G.Studies in Department <strong>of</strong> Chemistry, Karnatak University Dharwad.Received: 19 September 2011; Revised: 15 October 2011, Accepted: 12 November 2011ABSTRACTThe complex compounds <strong>of</strong> metal ions like Cu (II), Ni (II), Co (II), Cd (II), with the Schiff base ligand LH 2have been synthesized at different <strong>pH</strong> ranges. The synthesized complex compounds have beencharacterized on the basis <strong>of</strong> elemental analysis, molar mass and IR spectral studies. Hence, the studyreveals that the ligand LH 2 (Scheme 1) behaves as a monobasic bidentate ON donor where the twostructures suggest the non-involvement <strong>of</strong> carboxylic oxygen atom in coordination at <strong>pH</strong>= 3-4. The ligandLH 2 behaves as dibasic tridentate OON donor, suggesting the non-involvement <strong>of</strong> carbonyl oxygen atom <strong>of</strong>coumarin in the complex compounds at <strong>pH</strong>= 7. The ligand LH 2 behaves as a dibasic tetra dentate OONOdonor at <strong>pH</strong>=8, suggesting the coordination <strong>of</strong> coumarin carbonyl oxygen atom to the metal ions in thecomplex compounds.Key words: 3-aldehydosalicylicacid, 7-amino-4-methyl coumarin, <strong>pH</strong> effect, Schiff basesINTRODUCTIONThe biological activities <strong>of</strong> coumarin derivatives so far reported as anti-inflammatory 1 , anti-oxidant 2 ,vasorelant 3 , cytotoxic 4 , anti-HIV 5 , anti-tubercular 6 and anti-microbial 7 . The literature survey revealed thatcompounds with coumarin derivatives and thiazolidinone ring have been reported to use a wide range <strong>of</strong>pharmacological activities, such as antibacterial, antifungal, anticonvulsant anddevelop effective therapies 8 .Among the coumarin derivatives 7-Amino-4-methyl coumarin is known to be biologically active molecule,it has been used as a marker in the study <strong>of</strong> bio-transformations <strong>of</strong> drugs in the human body. Also itsmetabolites are reported to exhibit correlation with plasma fibronectin level in monitoring patients withchronic liver illness 8 .It is a desired liver corrective, aimed to provide therapeutic benefits in liver diseases anddisorders by virtue <strong>of</strong> vital activities incorporated in it. It provides required benefits to restore the liverfunction parameters and bringing the Serum Glutamic oxaloacetic Transiminase (SGOT), Serum Glutamic6 J. Chem. Bio. Phy. Sci. Sec. A. Nov. 2011- Jan. 2012, Vol.2, N0.1, 6-13

<strong>Effect</strong> <strong>of</strong> <strong>pH</strong>....B. M. Kalshetty et al.Pyruic acid Transuminase (SGPT) to normal condition, and it helps to restore the liver functioning byproviding multidimensional approach by showing anti-viral, anti-oxidant, anti-inflammatory, immunomodulatory,choleretic and anti-cholestatic activity 8 .The metal complexes are still a major line <strong>of</strong> approach to develop new drugs. It involves efforts to combinethe separate pharmacophoric groups <strong>of</strong> similar activity into one compound. Thus making structural changes inthe biological activity. As reported earlier the thiazolidine ring present in a large number <strong>of</strong> biologically activecompounds exhibiting different activities. The development <strong>of</strong> penicillin which shows the thiozoline ring.The present developments <strong>of</strong> 7-Amino-4-methyl coumarin compounds with metal ions are most fascinatingand useful areas in medical chemistry. The discovery <strong>of</strong> coumarin as therapeutic agents in 1820’s was thebeginning <strong>of</strong> the coumarin drug development. Due to the diversified nature <strong>of</strong> coumarin and is completely safewhich renders as useful substance in drug research.Keeping in view the above importance <strong>of</strong> 7-Amino-4methyl coumarin and the continuation <strong>of</strong> work on thesynthesis <strong>of</strong> Schiff base derived from 3-Aldehydosalicylic acid and its complex compounds with metal ionssuch as Cu (II), Zn (II), Ni (II), Co (II), and Cd (II) at different <strong>pH</strong>. The Schiff base compound (Scheme 1)synthesized followed by standard procedures 9,10 contains the acidic groups such as –COOH and –OH(phenolic), it is predicted that the coordination behavior <strong>of</strong> ligand would be developed on <strong>pH</strong> using differentreaction conditions and are remarkably different from those reported by Nag et al 11 .,COOHCH 3OHHCNOOScheme-1: Schiff base ligand (LH2) 2-hydroxy-3-((4-methyl-2-oxo-2H-chromen-7-ylimino)methyl)benzoic acidResults and DiscussionSchiff base ligands LH 2 (Scheme 1) was synthesized by the standard methods 9, 10 . It is dark yellow incolor; it is sparingly soluble in water, in aqueous sodium hydroxide solution. But, readily soluble in alcohol(owing to the possession <strong>of</strong> the phenolic and carboxylic groups).The synthesis <strong>of</strong> coordination compoundswith metal ions at various <strong>pH</strong> ranges reported as follows:(I) At <strong>pH</strong>= 3-4: An aqueous or water-ethanol solution <strong>of</strong> the ligand LH 2 (Scheme 1) reacts with metal ions in2:1 molar ratio forming metal complex compounds <strong>of</strong> the types [M(LH) 2 ] where M= Cu(II), Zn(II), Cd(II)(Scheme 2) and [M(LH) 2 (OH) 2 ] where M= Co(II), Ni(II) (Scheme 3). The formations <strong>of</strong> the complexcompounds at this <strong>pH</strong> range are shown below:MCl 2 (aq) + 2LH 2 (aq)[M (LH) 2 ] + 2 HCl...1Wher as M= Cu (II), Zn (II), Cd (II).andMCl 2 (aq) + 2LH 2 (aq) [M (LH) 2(H 2 O) 2 ]...2wher as M= Co (II), Ni (II).7J. Chem. Bio. Phy. Sci. Sec. A. Nov. 2011- Jan. 2012, Vol.2, N0.1, 6-13

<strong>Effect</strong> <strong>of</strong> <strong>pH</strong>....B. M. Kalshetty et al.(II). At <strong>pH</strong>= 7: the water-ethanol [50% (v/v)] solution <strong>of</strong> ligand LH 2 (Scheme 1) refluxed with alcoholicsolution <strong>of</strong> copper metal ion in 1:1 molar ration, forming the complex compound <strong>of</strong> the type [CuL] 2 (Scheme4) at this <strong>pH</strong> range, shown below:CuCl 2 + 2LH 2 (aq)EtOHReflux[CuL]2 + 4HCl ...3In the same <strong>pH</strong> condition, a ethanolic solution <strong>of</strong> ligand LH 2 reacts with alcoholic solution <strong>of</strong> metal ions in 1:1molar ratio, forming the complex compound <strong>of</strong> the types [ML(EtOH)] where M= Zn(II), Cd(II) (Scheme 5),the formation <strong>of</strong> the complex compounds at this <strong>pH</strong> range are shown below:MCl 2 (aq) + 2LH 2 (aq)EtOHReflux[ML(EtOH)] + HCl ...4M= Zn(II), Cd(II).a. At <strong>pH</strong>=8: the alcoholic solution <strong>of</strong> metal ions react with an alcoholic solution <strong>of</strong> LH 2 (Scheme1) in 1:1molar ratio in the presence <strong>of</strong> sodium-ethoxide and forming the bimetallic complex compounds <strong>of</strong> thetypes [ML(EtOH)] 2 where M= Cu(II), Zn(II),Co(II),Ni(II), Cd(II) (Scheme 6).EtOH2 MCl 2 +2 LH 2 (aq)[ML(EtOH)] 2 + 4 HCl. ...5RefluxM= Cu(II), Zn(II),Ni(II),Co(II), Cd(II).All the synthesized complex compounds were sparingly soluble in water but are fairly soluble in absolutealcohol.The analytical, molecular weight and other characterization data <strong>of</strong> the ligand LH 2 (Scheme 1) and itscomplex compounds with metal ions formed at various <strong>pH</strong> conditions reported in Table 1. The molecularmeasurements indicate the monomeric nature <strong>of</strong> complex compounds (Scheme 2) and (Scheme 3) at <strong>pH</strong> 3-4,the complex compounds (Scheme 4), (Scheme 5) formed at <strong>pH</strong>=7 and the complex compounds (Scheme 6)formed at <strong>pH</strong>=8 showed dimeric nature. The synthesized complex compounds remained stable up to certaintemperatures recorded in the Table 2.Table 1: Analytical, Molecular weight and other characterization data <strong>of</strong> complex compound between LH 2 (1)and Metal ions Observed and calculated:No1234567Compound Mol. FormulaLH 2 C 18 H 15 NO 5[Cu(LH) 2 ] CuC 36 H 28 N 2 O 10[Zn(LH) 2 ] ZnC 36 H 28 N 2 O 10[Cd(LH) 2 ] CdC 36 H 28 N 2 O 10[Co(LH) 2 (H 2 O) 2 CoC 36 H 32 N 2 O 12[Ni(LH)2(H2O) 2 NiC 36 H 32 N 2 O 12[CuL] 2 Cu 2 C 36 H 26 N 2 O 10Mol.Wt(Obs.)(Calcd.)320.0320.0705.3711.6743.5713.4762.7760.4731.2742.9761.6742.7725.8709.6MetalIonC(Obs)(Calcd.)__ 67.567.59.02 61.258.94 60.718.80 58.109.17 60.6614.36 55.1914.78 56.818.06 59.087.90 58.157.71 56.727.90 58.1617.53 59.5217.93 60.88H(Obs)(Calcd.)4.694.693.973.943.773.933.583.684.384.314.204.313.583.66N(Obs)(Calcd.)4.384.383.973.933.773.933.583.683.833.773.683.773.863.958J. Chem. Bio. Phy. Sci. Sec. A. Nov. 2011- Jan. 2012, Vol.2, N0.1, 6-13

<strong>Effect</strong> <strong>of</strong> <strong>pH</strong>....B. M. Kalshetty et al.Table 2: Nature <strong>of</strong> Coordination in complex compounds.Scheme <strong>pH</strong> Complex types Nature<strong>of</strong>complex1 3-4 [M(LH) 2 ] Monomeric 2502 “ [M(LH) 2 (H 2 O) 2 ] Monomeric 1403 8-9 [CuL] 2 Dimeric 844 “ [ML(EtOH)] Dimeric 2505 10-11 [ML(EtOH)] 2 Dimeric 85Stable uptotempareture inoCThe IR spectra <strong>of</strong> the Schiff base ligand (Scheme 1) and its complex compounds were recorded in KBrpellets. The ligand LH 2 (Scheme 1) exhibits intra molecular H- bonded (carboxylic COOH and phenolic OHgroup) stretches at 2900cm -1 , intermolecular H- bonded (phenolic OH group) stretches at 2700cm -1 , γ(C=O)(carboxylic) stretches at 1690 cm -1 , γ(C=O) (cumarin) stretches at 1680 cm -1 and γ(C-O) (phenolic) stretchesat 1570cm -1 .The appearance <strong>of</strong> γ(C=O) (carboxylic) stretches at the same energy in the ligand and its coordinationcompounds formed at <strong>pH</strong> 3-4 suggests the non-involvement <strong>of</strong> carboxylic O atom(s) in coordination. Thecoordination compounds formed at <strong>pH</strong>=7 and <strong>pH</strong>=8 exhibit the γ as (COO) and γ s (COO) stretches <strong>of</strong> thecarboxylates group in the range 1560-1650 cm -1 (i.e.,1600cm-1) and 1340-1430 cm -1 (i.e.,1400cm-1)respectively. The energy difference between γ as (COO) and γ s (COO) is more than 200cm -1 which indicatesthe monodentate nature <strong>of</strong> carboxalate moiety 12 .OOHCNOOH 3 CCOOHMHOOCCH 3OONCHHCONCOOHH 3 CO H 2 OMOH 2CHHOOC3ONOCHO(Scheme 2)[M (LH) 2 ]: M= Cu (II), Zn (II), Cd (II).All are ON-donor at <strong>pH</strong>= 3-4.O(Scheme3)[M (LH) 2 (H 2 O) 2 ]: M= Co (II), Ni (II).Both are ON-donor at <strong>pH</strong>=3-4.9J. Chem. Bio. Phy. Sci. Sec. A. Nov. 2011- Jan. 2012, Vol.2, N0.1, 6-13

<strong>Effect</strong> <strong>of</strong> <strong>pH</strong>....B. M. Kalshetty et al.HCNOOOC OOCuCuH 3 COCH 3 O CO(Scheme 4)[CuL] 2: OON-donor at <strong>pH</strong>=7.OONCHOC OHC OMNOO CH 3O(Scheme 5)[ML (EtOH) ]: M= Zn (II), Cd (II).Both are OON-donor at <strong>pH</strong>= 7.HEtAll the coordination compounds, exhibits a medium intensity and broad band at 3350 cm -1 indicatingpresence <strong>of</strong> OH group which may be due to coordinated water molecules or unionized COOH group. Theγ(C=O) (coumarin) stretch <strong>of</strong> the ligand occurring at 1690cm -1 . It does not undergo a considerable change inthe coordination compounds. The complex compounds (Scheme 2), (Scheme 3) formed at <strong>pH</strong>= 3-4 andcomplex compound (Scheme 4), (Scheme 5) formed at <strong>pH</strong>= 7 suggesting the non-involvement <strong>of</strong> (C=O)carbonyl oxygen atom <strong>of</strong> coumarin towards coordination in these complex compounds. But, in the complexcompound (Scheme 6) formed at <strong>pH</strong>= 8 suggesting the coordination <strong>of</strong> cumarin carbonyl oxygen atom to themetal ions in the coordination compound.OOHCNOCOEtOMHOCH 3MNOOCH 3 COEtHOCHOO(Sheme 6)[ML (EtOH) ] 2 : M= Cu (II), Zn (II), Ni (II), Co (II), Cd (II).All are OONO-donor at <strong>pH</strong>=8.10J. Chem. Bio. Phy. Sci. Sec. A. Nov. 2011- Jan. 2012, Vol.2, N0.1, 6-13

<strong>Effect</strong> <strong>of</strong> <strong>pH</strong>....B. M. Kalshetty et al.The γ(C-O) (phenolic) stretch <strong>of</strong> (Scheme 1) occurring at 1562 cm -1 shifts to higher frequency by 10cm -1 in(Scheme 2), (Scheme 3) formed at <strong>pH</strong>=3-4 and complex compounds (Scheme 4), (Scheme 5) formed at <strong>pH</strong>=7 suggesting the non-involvement <strong>of</strong> (C=O) (coumarin) O atom towards coordination in these complexcompounds. But, the complex compound (Scheme 6) formed at <strong>pH</strong>= 8 suggesting the coordination <strong>of</strong>coumarin carbonyl O atom to the metal ions in the coordination compound.The γ(C-O (phenolic) stretch <strong>of</strong> (Scheme 1) occurring at 1581 cm -1 shifts to higher frequency by 10 cm -1in complex compounds (Scheme 2),(Scheme 3) formed at <strong>pH</strong>= 3-4 supports the involvement <strong>of</strong> phenolic Oatom in coordination 13 . However, the γ(C-O) (phenolic) stretch <strong>of</strong> (Scheme 1) shifts to higher frequency bymore than 10 cm -1 in (Scheme 4), (Scheme 5) formed at <strong>pH</strong>= 7 and complex compounds (Scheme 6) formedat <strong>pH</strong>= 8 indicates the presence <strong>of</strong> the oxo bridge in these bimetallic coordination compounds.The magnitude<strong>of</strong> the shift (

<strong>Effect</strong> <strong>of</strong> <strong>pH</strong>....B. M. Kalshetty et al.analytical R grade were used and the sodium hydroxide solutions were prepared in double distilled water andit is standardized by the usual method.(i). Synthesis <strong>of</strong> Ligand compound LH 2 (Scheme 1) and metal complexes: The ligand (LH 2 ) wasprepared by the method reported by Nag et al 11 . The metal complexes [M(LH 2 )] where M= Cu(II),Zn(II),Cd(II) ,[M(LH) 2 (H 2 O) 2 ] where M= Co(II),Ni(II) , [CuL] 2, [ML(EtOH)] where M= Zn(II), Cd(II) and[ML(EtOH)] 2 where M= Cu(II), Zn(II), Ni(II), Co(II), Cd(II) where prepared by following the methodreported by Kumar et al 16 .(ii).Synthesis <strong>of</strong> [M(LH) 2 ] M= Cu(II), Cd(II) (Scheme 2) and [M(LH) 2 (H 2 O) 2 ] M= Co(II),Ni(II) (Scheme 3): Ligand LH 2 (2.10g) was dissolved in aqueous NaOH solution (0.5 g in 10 ml), yellowcoloured solution was obtained. After then 30-50 ml <strong>of</strong> an aqueous solution <strong>of</strong> metal chloride was added. Themixture was stirred magnetically for 10 minutes. Glacial acetic acid or hydrochloric acid (1:1) was then addeddrop wise to above solution till <strong>pH</strong> <strong>of</strong> solution becomes 3-4. The resulting turbid mixture was refluxed for twohours. The coloured solids formed on cooling, filtered, washed and recrystalized from water followed bywashing with ether. M.P. 250 o C. Yield =40%.(iii).Synthesis <strong>of</strong> [CuL] 2 (Scheme 4):A ethanol solution (30 ml) <strong>of</strong> LH 2 (1.05g) was added to ethyl alcoholsolution (35ml) <strong>of</strong> appropriate metal chloride and the mixture was heated under reflux for 3 hours on a waterbath and then cooled to room temperature. The solid product formed were filtered, washed with andrecrystallized from ethyl alcohol followed by washing with ether. M.P. 248 o C, yield= 60%.(iv).Synthesis <strong>of</strong> [ML(EtOH)] 2 M= Cu(II), Zn(II), Ni(II),Co(II),Cd(II) (Scheme 5): A ethylalcohol solution (30ml) <strong>of</strong> LH 2 (1.05g) was added to a EtOH solution (35ml) <strong>of</strong> appropriate metal chloridesand the mixture was stirred magnetically for 10 minutes. A 10% ethyl alcohol solution <strong>of</strong> EtONa was thenadded drop wise to the above solution till the <strong>pH</strong> <strong>of</strong> the solution becomes 8. The resulting mixture wasrefluxed for 3 hours on a water bath, coloured solids formed on cooling, filtered, washed with EtOH followedby washing with ether. M.P. 86 o C, yield=70%.CONCLUSIONSThe different types <strong>of</strong> complex compounds <strong>of</strong> same ligand with metal ions have been obtained by varying<strong>pH</strong> and solvent during their synthesis. The basicity and denticity <strong>of</strong> the Schiff base (Scheme 1) derived from3-Aldehydosalicylic acid and 7-Amino-4-methyl coumarin changes considerably with the role <strong>of</strong> <strong>pH</strong> from 3-8.The basicity and denticity <strong>of</strong> ligand increase with the increase in <strong>pH</strong>. The ligand at <strong>pH</strong> 3-4 acts as monobasicbidentate ON-donor ligand forms monometallic complex compounds [M(LH) 2 ] where M= Cu(II),Zn(II),Cd(II) (Scheme 2) and [M(LH) 2 (H 2 O) 2 ] where M= Co(II), Ni(II) (Scheme 3). At the <strong>pH</strong>= 7, the ligand acts asa dibasic tridentate OON-donor ligand forming the monometallic complex compound <strong>of</strong> the type [ML(EtOH)] where M= Zn (II), Cd (II), (Scheme 5) and at the same <strong>pH</strong> = 7 the ligand formed dimetalic complexcompound <strong>of</strong> the type [(CuL) 2 ] with copper metal ion (Scheme 4). While at <strong>pH</strong>= 8 the ligand acts as a dibasictetradentate OONO-donor ligand in EtOH and forms dimetalic compound <strong>of</strong> the type[ML(EtOH)]2 where M=Cu(II),Zn(II),Ni(II), Co(II), Cd(II) (Scheme 6).The basicity and denticity confirmed by the various methods , the IR spectra <strong>of</strong> the Schiff base (Scheme 1)and other metal complexes (Scheme 2 ) reveals that the non-involvement <strong>of</strong> carboxylic atom in coordinationat <strong>pH</strong>=3-4. However, the coordination formed at <strong>pH</strong>=7 and <strong>pH</strong>=8 the carboxylic O atom involved in thecoordination (Schemes 3 to 6) by exhibiting the γ as (COO) and γ s (COO) stretches <strong>of</strong> carboxylate group in theranges: 1560-1650 cm -1 (i.e.,1600cm -1 ) and 1340-1430 cm -1 (i.e.,1400cm -1 ) respectively. The energydifference between γ as (COO) and γ s (COO) is more than 200 cm -1 indicates the monodentate nature <strong>of</strong> thecarboxylate moiety 12 .12J. Chem. Bio. Phy. Sci. Sec. A. Nov. 2011- Jan. 2012, Vol.2, N0.1, 6-13

<strong>Effect</strong> <strong>of</strong> <strong>pH</strong>....B. M. Kalshetty et al.ACKNOWLEDGEMENTSThe authors are highly indebted to the administrative <strong>of</strong>ficer Pr<strong>of</strong>. S.H.Lagali, B.L.D.E’s AssociationBijapur, providing financial support for this work. Author takes this opportunity to extend their heartfeltthanks to chairman, P, G.Department <strong>of</strong> studies in Chemistry, Karnatak University Dharwad for cooperationand facilities given for getting IR-Spectra and analytical data from the Department <strong>of</strong> Chemistry.REFERENCES1. P.M.Ronad,R.D.Hunshi, D.Satayanarayana, V.S.Maddi, Pharm.Chem.life science, 2008, 341 696.2. Y.K.Tyagi, A.Kumar, H.G.Raja, P.Vohra, G.Gupta, R.K.Gupta, Eur. J. Med. Chem.2005, 40, 413.3. S.Vilar, E. Quezada, L.Santana, E. Uriarte, M. Yanez, Fraiz. Bio org. Med. Chem. Lett. 2006.16, 257.4. J.Nawrot-Modranka, E. Nowrot, J. Graczik, . Eur.J.Med.Chem. 2006, 41, 1301.5. D. Yu, M.Suzuki, I.Xie, S.I.Netschke, K.H.Lee, Med- Res. Reiv., 2003, 23, 322.6. N.Korali, A. Kocabalkanli, A. Gursoy, O. Ates, Formica, 2002, 57, 589.7. K.B.Gudasi, M.S. Patil, R.S. Vadavi, Eur.J.Med.Che.,2008, 43, 2436..8. K. Coleman, Drug Discov. Toay ther. Strateg. 2004, 1, 455.9. J.C.Duff and E.J.Bills, J.Chem. Soc., 1932,1987,; D. Kumar, P.K.Gupta and A. Syamal, Indian J.Chem. Sect. A, 2002,41,2494.; G.J.Chen, J.W. McDonald and W.E.Newton, Inorg. Chem., 1976, 15,2612.10. S.N.Poddar, Anorg. Allg. Chem., 1963,322, 326.11. J.K.Nag, s. Pal and C. sinha, Trans. Met. Chem., 2005,30,523.12. F.E.Smith, L.E.Khoo, N.K.Goh, R.C.Hynes and G.Eng. Can. J.Chem. 1996,74,2041.13. A.Syamal and O.P.Singal, Trans.Met. Chem., 1979, 4,179.14. I.I.Grandberg, L.K. Denisov, and O.A.Popova, Khim. Geterotsikl. Soedin., No.2, 147 (1987).15. H.Pechmann and O. Schwarz, Berichte, 32, 3696 (1899).16. D,Kumar, A.Syamal, Anju Gupta, Mukesh Rani and P.K.Gupta J. Indian Chemical Society, 2010,. 87,10.*Correspondence Author: Basavaraj M. Kalshetty, Comm.BHS Arts and TGP science College Jamkhandi, Dist: Bagalkot13J. Chem. Bio. Phy. Sci. Sec. A. Nov. 2011- Jan. 2012, Vol.2, N0.1, 6-13