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Synthesis)and)Characteriza0on)of)Thermochromic)Metal)Complexes)with)a)Near)Room)
Temperature)Spin)Crossover))
Alexandria)K...
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Decay of Metastable States in Spin-Crossover Solids
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Konkol_ACSENY UGR POSTER 2014

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Konkol_ACSENY UGR POSTER 2014

  1. 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.,!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! 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!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 Absobance(ABS) 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! 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](PF6)2) in) methanol) at) low,) high,) and) room) temperature.) Aliquots! of! the! same! 1mg/mL! [Fe(pybimH)3](PF6)2! 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.!!

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