Konkol_ACSENY UGR POSTER 2014
1
Synthesis and Characteriza0on of Thermochromic Metal Complexes with a Near Room Temperature Spin Crossover Alexandria Konkol and Jesse W. Karr* Department of Chemistry and Biochemistry Siena College, Loudonville, NY 12211 Discussion and Future Work Thermochromic complexes have a color change associated with the shi5 from high spin7to7low spin caused by temperature change, thus crea<ng a physical indica<on of the spin crossover. It appears that both the solvent and counter ion iden<ty effect the thermodynamic parameters for changing the spin state of the [Fe(pybimH) 3 ] 2+ complex synthesized. These iron(II) complexes exhibi<ng a SCO behavior are easily synthesized and characterized making them ideal for integra<on into an undergraduate laboratory curriculum. Future analysis of the complexes will include inves<ga<ng the temperature dependence on the magne<c suscep<bility of these complexes using mangne<c resonance spectroscopy (i.e. the Evans NMR or EPR spectroscopy) Acknowledgements • Dr. John Caradonna and Ellen Matson of Boston University • Dr. John Miecznikowski of Fairfield University • Dr. Jodi O’Donnell of Siena College • Siena College Department of Chemistry and Biochemistry for use of it’s facili<es References • Cambi, L.; Cagnasso, A., A" Accad. Naz. Lincei 1931, 13, 809713; Cambi, L.; Szegö, L., Ber.Dtsch. Chem. Ges. 1931, 64, 259178. • Baker, W. A.; Bobonich, H. M., Inorg. Chem. 1964, 3, 1184788. • Hauser, A., Top. Curr. Chem. 2004, 234, 1557198. • Létard, J.; Guionneau, P.; Coux7Capes, L., Top. Curr. Chem. 2004, 235, 221749. • Telfer, S. G.; Bocquet, B.; Williams, A. F., Inorg. Chem. 2001, 40, 4818720; Chabonnière, L. J.; Williams, A. F.; Piguet, C.; Bernardinelli, G.; Rivara7Minten, E., Chem. Eur. J. 1998, 4, 485793. • Wolsey, W. C., J. Chem. Educ. 1973, 50, A33577. • Bain, G. A.; Berry, J. F., J. Chem. Educ. 2008, 85, 5327536. • Sams, J.R.; Tsin, T.B., 5 T 2g ⟶ 1 A 1g Spin crossover in tris[27(27pyridyl)benzimidazole]iron(II) complexes Inorganic Chemistry. 1976, 15, 154471550. Determina0on of Thermodynamic Parameters of the SCO Process • The KSCO was defined as the ra<o of A 466 /A 494 =ε ls [LS]/ε hs [HS] • This allowed for the use of a van’t Hoff plot to determine ΔH, ΔS, and T SCO for the SCO process. van’t Hoff plot of [Fe(pybimH) 3 ](PF 6 ) 2 in methanol. The K SCO , found using data from the absorp<on spectra, was plooed against the inverse temperature Abstract It is widely known that the valance electrons of a compound are responsible for its observed color. Thermochromic metal compounds will change color with temperature because of a change in the occupancy of their valence molecular orbitals. Tradi<onal inorganic texts teach that for transi<on metal complexes the distribu<on of valence electrons is the result of the metal’s oxida<on state along with the nature of its coordina<ng ligands; implying that this electronic arrangement is a sta<c phenomenon. However, according to the Maxwell7 Boltzmann theory the electronic distribu<on will also be temperature dependent, meaning that for a given metal complex the distribu<on of valence electrons, and resul<ng color, will also depend on temperature. This changing of the electronic distribu<on is referred to as a spin crossover (SCO) process. Here we present the synthesis and characteriza<on of a small library of tris[27(27 pyridyl)benzimidazole]iron(II), [Fe(pybimH) 3 ] 2+ , complexes which exhibit thermochromic proper<es due to having a near room temperature SCO point. Using absorp<on spectroscopy we examined the thermodynamic parameters of this spin crossover for the various [Fe(pybimH) 3 ] 2+ salts. Also we show preliminary data to suggest this spin crossover process is solvent dependent. Ul<mately these compounds can be used as an introductory laboratory experiment demonstra<ng the SCO process. Introduc0on • Octahedral metal complexes have electrons constrained to MOs that have approximately the same energy as the atomic d7orbitals • Energy difference between the t 2g and e g * is referred to as ligand field strength (Δ o ) • Low spin is produced by strong field ligands, conversely high spin complexes are produced by weak field ligands. • External perturba<on resul<ng in a change in magnitude of Δ o can cause a metal ion to change spin state Octahedral Ligand Field Spli`ng Adapted from Hauser, 2004. • SCO complexes exist in a ground state and have a accessible excited spin state. • Excita<ons to this higher energy spin states can thermally, photoly<cally, or pressure induced. • Electrons in these complexes can be excited from the HOMO to the LUMO giving rise to a spectroscopic signal. • This spectroscopic signal provides a useful way of monitoring the SCO process. s T = 0, Low Spin G.S. Term Symbol: 1 A 1g t 2g e g * Δ o >Π c t 2g e g * s T = 2, High Spin G.S. Term Symbol: 5 T 2g Δ o <Π c Δ o Synthe0c Approach • Approximately three molar equivalents of pybimH were combined with one molar equivalent of iron chloride in a minimal amount of methanol. • The reddish solu<on was then added to an aqueous solu<on of the desired ammonium counter ion salt causing the [Fe(pybimH) 3 ]X 2 complex to precipitate. • The red crystals were isolated via vacuum filtra<on. FeCl 2 + 3 (pybimH) Fe(pybimH) 3 X 2 27(27pyridyl)benzimidazole Fe(II) + 3 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 300 350 400 450 500 550 600 650 700 Absobance (ABS) Wavelength (nm) Temperature dependent absorp0on of [Fe(pybimH) 3 ](PF 6 ) 2 !nH 2 O in Methanol. A methanol solu<on with a concentra<on of 1mg/mL was analyzed using the UV7Vis between temperatures of 10°765°C at 5° increments. Absorp0on Spectroscopy of [Fe(pybimH) 3 ](PF 6 ) 2 Temperature dependent absorp0on of [Fe(pybimH) 3 ](PF 6 ) 2 !nH 2 O in Acetonitrile. An acetonitrile solu<on with a concentra<on of 1mg/mL was analyzed using the UV7Vis between temperature of 10°750°C at 10° increments. [Fe(pybimH) 3 ](PF 6 ) 2 in methanol at low, high, and room temperature. Aliquots of the same 1mg/mL [Fe(pybimH) 3 ](PF 6 ) 2 complex at 793°C, 25°C, and 65°C (from le5 to right, respec<vely). NH 4 X • As the complex is heated, there is a blue shi5 in the visible peak from 494nm to 466nm.
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Transcript of Konkol_ACSENY UGR POSTER 2014
Synthesis)and)Characteriza0on)of)Thermochromic)Metal)Complexes)with)a)Near)Room)
Temperature)Spin)Crossover))
Alexandria)Konkol)and)Jesse)W.)Karr*)
Department)of)Chemistry)and)Biochemistry)
Siena)College,)Loudonville,)NY)12211)
Discussion)and)Future)Work!
Thermochromic!complexes!have!a!color!change!associated!with!the!shi5!from!high!spin7to7low!spin!caused!by!temperature!change,!thus!crea<ng!a!physical!indica<on!of! the! spin! crossover.! It! appears! that! both! the! solvent! and! counter! ion! iden<ty!effect! the! thermodynamic! parameters! for! changing! the! spin! state! of! the![Fe(pybimH)3]
2+! complex! synthesized.! ! These! iron(II)! complexes! exhibi<ng! a! SCO!behavior! are! easily! synthesized! and! characterized! making! them! ideal! for!integra<on!into!an!undergraduate!laboratory!curriculum.!
Future! analysis! of! the! complexes! will! include! inves<ga<ng! the! temperature!dependence! on! the!magne<c! suscep<bility! of! these! complexes! using!mangne<c!resonance!spectroscopy!(i.e.!the!Evans!NMR!or!EPR!spectroscopy)!!
Acknowledgements!• Dr.!John!Caradonna!and!Ellen!Matson!of!!Boston!University!
• Dr.!John!Miecznikowski!of!Fairfield!University!
• Dr.!Jodi!O’Donnell!of!Siena!College!
• Siena!College!Department!of!Chemistry!and!Biochemistry!for!use!of!it’s!facili<es!
References!• Cambi,!L.;!Cagnasso,!A.,!A"#Accad.#Naz.#Lincei#1931,!13,!809713;!Cambi,!L.;!Szegö,!L.,!
Ber.Dtsch.#Chem.#Ges.#1931,!64,!259178.!• Baker,!W.!A.;!Bobonich,!H.!M.,!Inorg.#Chem.#1964,!3,!1184788.!• Hauser,!A.,!Top.#Curr.#Chem.#2004,)234,!1557198.!• Létard,!J.;!Guionneau,!P.;!Coux7Capes,!L.,!Top.#Curr.#Chem.#2004,!235,!221749.!• Telfer,!S.!G.;!Bocquet,!B.;!Williams,!A.!F.,!Inorg.#Chem.#2001,!40,!4818720;!Chabonnière,!
L.!J.;!Williams,!A.!F.;!Piguet,!C.;!Bernardinelli,!G.;!Rivara7Minten,!E.,!Chem.#Eur.#J.#1998,!4,!485793.!
• Wolsey,!W.!C.,!J.#Chem.#Educ.#1973,!50,!A33577.!• Bain,!G.!A.;!Berry,!J.!F.,!J.#Chem.#Educ.#2008,!85,!5327536.!• Sams,!J.R.;!Tsin,!T.B.,!5T2g⟶1A1g!Spin!crossover!in!tris[27(27pyridyl)benzimidazole]iron(II)!
complexes!!Inorganic#Chemistry.#1976,!15,!154471550.!
Determina0on)of)Thermodynamic)Parameters)
of)the)SCO)Process)• The!KSCO!was!defined!as!the!ra<o!of!A466/A494!=!εls[LS]/εhs[HS]!
• This!allowed!for!the!use!of!a!van’t!Hoff!plot!to!determine!ΔH,!ΔS,!and!TSCO!for!the!SCO!process.!
van’t) Hoff) plot) of) [Fe(pybimH)3](PF6)2) in)
methanol.)The!KSCO,! found!using!data!from!the!absorp<on!spectra,!was!plooed!against!the!inverse!temperature)
Abstract!It!is!widely!known!that!the!valance!electrons!of!a!compound!are!responsible!for!its!observed! color.! Thermochromic! metal! compounds! will! change! color! with!temperature! because! of! a! change! in! the! occupancy! of! their! valence! molecular!orbitals.!Tradi<onal! inorganic! texts! teach!that! for! transi<on!metal!complexes! the!distribu<on!of!valence!electrons! is!the!result!of!the!metal’s!oxida<on!state!along!with! the! nature! of! its! coordina<ng! ligands;! implying! that! this! electronic!arrangement! is! a! sta<c! phenomenon.! However,! according! to! the! Maxwell7Boltzmann!theory!the!electronic!distribu<on!will!also!be!temperature!dependent,!meaning!that!for!a!given!metal!complex!the!distribu<on!of!valence!electrons,!and!resul<ng! color,!will! also!depend!on! temperature.! This! changing!of! the!electronic!distribu<on!is!referred!to!as!a!spin!crossover!(SCO)!process.!Here!we!present!the!synthes is! and! character i za<on! of! a! smal l! l ibrary! of! t r i s [27 (27pyridyl)benzimidazole]iron(II),! [Fe(pybimH)3]
2+,! complexes! which! exhibit!thermochromic! proper<es! due! to! having! a! near! room! temperature! SCO! point.!Using! absorp<on! spectroscopy! we! examined! the! thermodynamic! parameters! of!this!spin!crossover!for!the!various![Fe(pybimH)3]
2+!salts.!Also!we!show!preliminary!data!to!suggest!this!spin!crossover!process!is!solvent!dependent.!Ul<mately!these!compounds!can!be!used!as!an!introductory!laboratory!experiment!demonstra<ng!the!SCO!process.!
Introduc0on!• Octahedral!metal!complexes!have!electrons!constrained!to!MOs!that!have!approximately!the!same!energy!as!the!atomic!d7orbitals!!
• Energy!difference!between!the!t2g!and!eg*!is!referred!to!as!ligand!field!strength!(Δo)!
• Low!spin!is!produced!by!strong!field!ligands,!conversely!high!spin!complexes!are!produced!by!weak!field!ligands.!!
• External!perturba<on!resul<ng!in!a!change!in!magnitude!of!Δo!can!cause!a!metal!ion!to!change!spin!state!
!Octahedral)Ligand)Field)Spli`ng)
Adapted#from#Hauser,#2004.#
• SCO!complexes!exist!in!a!ground!state!and!have!a!accessible!excited!spin!state.!
• Excita<ons!to!this!higher!energy!spin!states!can!thermally,!photoly<cally,!or!pressure!induced.!
• Electrons!in!these!complexes!can!be!excited!from!the!HOMO!to!the!LUMO!giving!rise!to!a!spectroscopic!signal.!
• This!spectroscopic!signal!provides!a!useful!way!of!monitoring!the!SCO!process.!
sT)=)0,)Low)Spin)
G.S.)Term)Symbol:)1A1g)
t2g)
eg*)
Δo)>)Πc)
t2g)
eg*)
sT)=)2,)High)Spin)
G.S.)Term)Symbol:)5T2g)
Δo)<)Πc)
Δo)
Synthe0c)Approach!• Approximately!three!molar!equivalents!of!pybimH!were!combined!with!one!molar!equivalent!of!iron!chloride!in!a!minimal!amount!of!methanol.!
• The!reddish!solu<on!was!then!added!to!an!aqueous!solu<on!of!the!desired!ammonium!counter!ion!salt!causing!the![Fe(pybimH)3]X2!complex!to!precipitate.!
• The!red!crystals!were!isolated!via!vacuum!filtra<on.!
FeCl2+!3!(pybimH)!!!!!!!!!!!!!!!!!!Fe(pybimH)3X2!!
27(27pyridyl)benzimidazole!
Fe(II)!+!3!
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
300 350 400 450 500 550 600 650 700
Abs
oban
ce (A
BS)
Wavelength (nm)
Temperature) dependent) absorp0on) of)[Fe(pybimH)3](PF6)2!nH2O) in) Methanol.) A!methanol! solu<on! with! a! concentra<on! of!1mg/mL! was! analyzed! using! the! UV7Vis!between! temperatures! of! 10°765°C! at! 5°!increments.!
Absorp0on)Spectroscopy)of)[Fe(pybimH)3](PF6)2)
Temperature) dependent) absorp0on) of)[Fe(pybimH)3](PF6)2!nH2O)in)Acetonitrile.!An! ace ton i t r i l e! so lu<on! w i th! a!concentra<on! of! 1mg/mL! was! analyzed!using!the!UV7Vis!between!temperature!of!10°750°C!at!10°!increments.!
[Fe(pybimH)3](PF6)2) in) methanol) at)
low,) high,) and) room) temperature.)
Aliquots! of! the! same! 1mg/mL2! complex! at!793°C,! 25°C,! and! 65°C! (from! le5! to!right,!respec<vely).)
NH4X!
• As! the! complex! is! heated,! there! is! a! blue! shi5! in! the! visible! peak! from! 494nm! to!466nm.!!
