Iron Copper Complex LCuFeCl

2

, but the resulting omplex, most likely bearing a BF

4

as ounterion

instead of a hloride as an axial ligand, was prone to faster deomposition than the

hloride analog.

5.3 Iron Copper Complex LCuFeCl

With LH

2

FeCl in hand, the synthesis of the iron opper omplex LCuFeCl ould be

performedbyadditionofaopper(II)saltinapolarsolvent. Theresulting

heterobimetal-li omplex inorporates two redox ative metal ions, whih intheir redued states are

both potentiallysuitable forsmall moleule ativation, like moleular oxygen.

[59,162164℄

The rude reation mixture of LH

2

FeCl ould be used for further omplexation

rea-tions(Fig. 5.6),eventhoughremaining freebaseSiamese-twin porphyrin inthesolution

alsoledto theformationof the diopperomplex LCu

2

uponaddition of aoppersalt.

5.3.1 Synthesis of LCuFeCl

Cu(OAc) ₂

Sheme 5.6:SynthesisoftheheterobimetalliironopperomplexLCuFeCl.

Theresidueofthe synthesisof LH

2

Fe wasdissolved intoluene and addedto a solution

of opper aetate in MeOH. The reation mixture was stirred for 30 min at ambient

temperature and the solvent was removed under redued pressure. The residue was

redissolvedinCH

2 Cl

2

andlteredoveraplugofbasialuminumoxidetoremoveLCu

2 ,

whih was the only frationpassing. The remaining LCuFeCl was eluted with MeOH

andthesolventwasremoved underreduedpressure. Therudeprodutwaspuriedby

olumnhromatography (silia,n-hexane/EtOA 4:1)and rerystallized fromamixture

of CH

2 Cl

2

and n-hexane (1:1) to yield polyrystalline LCuFeCl. No suitable single

rystalsfor X-ray dirationouldbeobtained sofar.

5.3.2 Charaterization of LCuFeCl

The rystallization behavior and eletroni struture of the inorporated iron ion of

LCuFeCl is assumedto besimilar to thatof LNiFeCl,due to thesimilarityof Cu(II)

andNi(II)with regardsto theiroordinationenvironment,aswellaspreviously

enoun-tered similaritiesof the homobimetalli omplexesLCu

2

andLNi

2 .

The LCuFeCl ouldbe haraterized by HRMS,againas[M℄

+

speies(Fig. 5.17).

Figure5.17: HRMSESI

+

spetrumofLCuFeClinMeOH.Inset: Comparisonofthemeasured

(blak)and the alulated isotopi pattern (grey bars). [M℄

+

m/z =1415.5149

(ald.: 1415.5150).

TheoveralloptialspetrumofLCuFeCllookedsimilartothatofLNiFeCl(Fig. 5.18),

even thoughall three absorptionbandsareshifted.

Figure5.18: UV-visspetraof LCuFeCl(blue)andLNiFeCl(brown)inCH

2 Cl

2

atambient

temperature.

Withinthe error ofthemeasurement theredshiftedSoret like band(388nm) showed a

similar extintion oeient (

ǫ

^{= 72500). The rst Q-band appears at a wavelength of}

560 nm and is red shifted, whereas the seond Q-band (692 nm), whih is assumed to

have mainly some opperontribution, isslightly blue shifted.

EPR and Möÿbauer spetrosopy as well as magneti suseptibility measurements

were performed on LCuFeCl to ompare the iron ion's spin and oxidation state with

those of LNiFeCl. Even though opper(II), as a d

9

metal ion, has a spin of S = 1/2,

noEPR signalould be obtained at temperatures above 120 K. Thisisinontradition

to the previously synthesized opper omplexes LCu

2

and LNiCu, [53,55℄

but an be

explainedwiththepreseneoftheiron(III)ion. Exhange ouplingbetweentheiron(III)

and opper(II) metal ions an lead to an EPR silent spin ground state or an result in

signal broadening too large to resolve a signal in X-band EPR spetrosopy at higher

temperatures. Indeed,magnetisuseptibilitymeasurementsonsolidmaterialhavebeen

interpretedasanantiferromatiallyoupled twospinsystemwithspins ofS

1

^{=3/2 and}

S

2

^{=1/2 (Fig. 5.19).}

Figure5.19:Suseptibility measurement of LCuFeCl (blak irles) and its t (red) with

g

1

^=2.083,D

1

⁼

−

^6.81,g

²

^=2.050andJ=

−

^6.40m

^{− 1}

^.

Aneetivemagnetimomentof

µ _{ef f}

^=4.32attemperaturesover 100Kisindiative of aspinsystemofS

1

^{=3/2 andS}

2

^{=1/2,whose spin-onlyvaluewouldbe 4.25, assuming}

g-values of2.0023. Twospin enterswith S

1

^{=3/2 and S}

2

^{=1/2 areinagreement with}

anis-iron(III)(S=3/2)andaopper(II)(S=1/2)ion. Anintermediatespiniron(III)ion

wasexpetedfrompreviousresultsforLNiFeClandwasfurtheronrmedbyMöÿbauer

spetrosopy(Fig. 5.20).

A doublet (

δ _{F e}

^{= 0.55) with a quadrupol splitting of}

∆E Q

^{= 2.82, whih istypial for}

iron(III)intermediatespin, wasobservedin80%arearatio togetherwithadoubletwith

adistintsmallerquadrupolsplitting(

δ F e

^=0.54,

∆E Q

^{=1.36)in20%arearatio. Both}

doubletsarenearlyidential withthedoubletsobtainedfor LNiFeCl (Table 5.6). Even

thoughthesynthesisof LCuFeCland LNiFeClwaspartlydierent,theratiobetween

thetwoharateristi Möÿbauer doubletswasretained, however.

Figure5.20: Solid state Möÿbauer spetrum of LCuFeCl with

δ F e

^{= 0.54 and 0.55,}

∆E Q

^{=1.36and2.82at80K.}

Table5.6: Möÿbauerparametersof LCuFeClandLNiFeClinsolidstateat80K.

Complex

δ _{F e} ∆E _Q

^{rel. Int. / %}

LCuFeCl

0.54 1.36 20

0.55 2.82 80

LNiFeCl

0.53 1.20 20

0.58 2.70 80

Similar toLNiFeCl,theredoxhemistryof LCuFeCl wasstudied byyliand square

wavevoltammetry andshowedtheexpetedtwo reversibleligand-based oxidationevents

togetherwithfour irreversible redutionevents(Fig. 5.21).

(a) (b)

Figure5.21: (a)CV(top) and SWV(bottom)urveof LCuFeCl at asan rateof 100mV.

Thetworeversibleligand-based oxidationsare marked in blue and theassumed

iron(III)redutionin red. Half wavepotentials(E

1/2

^{)areindiatedin voltsand}

determinedfromsquarewavevoltammetry. (b)CVurveoftheeletrohemially

reversibleoxidationsofLCuFeClatdierentsanratesindiated. Both

measure-mentswereperformedin CH

2 Cl

2

at ambienttemperaturewith0.1m[Bu

4 N ℄PF

6

aseletrolytereferenedtotheredoxoupleF/F +

.

The two reversible ligand-based oxidation waves at

−

^0.28and

+

^{0.24V vs. F/F+ and}

theredutionevents at

−

^1.07and

−

^1.71or

−

^{1.85V areomparablewiththemeasured}

2

values forthe othermetalomplexesoftheSiamese-twin porphyrin (Tab. 5.7). The two

redutionwavesat

−

^{1.71and 1.85V interfereand annot be explained.}

Table 5.7:Potentialsoftherstredutionandthersttwooxidationsof LCuFeCl [a℄

in

om-parisonto theiron,nikelandopperomplexesoftheSTPvs. F/F +

[a℄ Values as determined by square wave voltammetry (in CH

2

Fig. 5.8. [b℄ Eletrohemially irreversible. [℄ The values reported previously [55℄

have been

inorretly referened beause of oniting data in literature.

[141℄

A potential of

−

^{0.48 V of}

deamethylferroenevs. ferroenewashoosen insteadof

−

^{0.59. Aorretion of}

−

^{0.11V was}

donein thistable.

Therst oxidation oftheSTPsaold of LCuFeCl oursat adistint lower potential

(

−

^{0.34 V)than therst oxidation in LNiFeCl (}

−

^{0.08 V)but is in thesame region as}

therstoxidation ofthe opperomplexes LCuNiand LCu

2

. Thisindiates, thatthe

rst oxidation of LCuFeCl takes plae at the dipyrromethene unitat the opper side.

Theiron-based redutionwave at

−

^{1.07V vs. F/F}

⁺

^{iswithin thesame region asitis}

forLNiFeCl(

−

^{1.12Vvs. F/F}

⁺

^{)andshouldthereforealsobe aessiblefor redution}

withCoCp

2

^{,to yieldthe ferrous omplex LCuFe . However, further} investigations have yetto bedoneto analyzethe redoxhemistryof LCuFeCl inmoredetail. Additionally,

otherheterobimetalli omplexesan be synthesizedstarting fromLH

2 FeCl .

Im Dokument New Derivatives and Iron Complexes of the Siamese-Twin Porphyrin (Seite 64-68)