A Modified Synthetic Pathway for the Synthesis of so far Inaccessible N1-Functionalized Tetrazole Ligands - Synthesis and Characterization of the 1D Chain-Type Spin Crossover Compound [Fe(3ditz)3](BF4)2.

1 MB·English

by  Muller, Danny

FULL PAPER
DOI:10.1002/ejic.201201062
A Modified Synthetic Pathway for the Synthesis of so far
Inaccessible N1-Functionalized Tetrazole Ligands –
CLUSTER
Synthesisand Characterizationofthe 1D Chain-Type Spin ISSUE
CrossoverCompound[Fe(3ditz) ](BF )
3 4 2
Danny Müller,[a] Christian Knoll,[a] Berthold Stöger,[b,c]
Werner Artner,[b] Michael Reissner,[d] and Peter Weinberger*[a]
Keywords: Ligand design / N ligands / Spin crossover / Magnetic properties / Iron
A modified phase-transfer-catalyst-assisted synthetic path- thanforthosewithanoddnumber.Inlinewiththisobserva-
waywasdevelopedthatwidensthepoolofaccessible1-sub- tion,theshortestodd-numberedhomologuessuchas1,1-bis-
stituted tetrazoles, which are possible ligands for iron(II) (tetrazol-1-yl)methane (1ditz) and 1,3-bis(tetrazol-1-yl)prop-
spin-crossovercompounds.Withinthefamilyofα,ω-bis(tetra- ane(3ditz)wereinaccessiblesofar.Inthispaper,wereport
zol-1-yl)alkanes, a series of ligands and their respective thesuccessfulpreparationandcharacterisationoftheclassi-
iron(II) spin-crossover compounds were synthesized and callyinaccessible1,3-bis(tetrazol-1-yl)propane(3ditz)andof
structurally and spectroscopically characterized in the past. its spin-crossover complex [Fe(3ditz) ](BF ) , which features
3 42
The classical route to prepare these ligands is based on the anabruptandalmostcompletespintransitionatT =159K.
½
respective amino-precursors. Hence the pool of accessible The single-crystal X-ray structure of the low-spin and the
compoundsislimitedbythecommercialorsyntheticalavail- high-spin species is presented. The magnetic data are sup-
abilityofα,ω-diaminoalkanes.Furthermore,theconcomitant ported by variable-temperature IR, UV/Vis/NIR, and 57Fe
transformationtothetetrazolemoietiesturnsouttobeeasier Mössbauerspectra.
for diamino-alkanes with an even number of carbon atoms
Introduction abruptnessofthespinswitchingbetweenthehigh-spin(HS)
andthe low-spin(LS) species.[2]Therefore, intenseresearch
In the quest for technologically applicable iron(II) spin- effort is focused on the elucidation of a structure–property
crossover(SCO) compounds,a rationaldesignof thecoor- relationship. Despite of the existence of rare predictive
dinationcomplexeswithappropriatemagneto-opticalprop- models, for example, for 1D chain-type triazole-based FeII
erties[1] is of utmost importance. It is a matter of fact that coordinationpolymers,[3]itisimpossibletopredictthespin-
severalfactors(i.e.,ligandtype,solventused,synthesiscon- transitionbehaviorofalmostanynewSCOcompound,be-
ditions, etc.) govern the key properties of spin-crossover causethe empiricaltrends establishedthusfar aretypically
complexes,suchasthethermalspintransition(T )andthe specificforasingleclassofcompoundsonly.[4]Toshedlight
½
ontheimpactofthestructuraldetailsofanychosenligand
[a] InstituteofAppliedSyntheticChemistry,ViennaUniversityof on the imposed SCO properties, we prepared a homologue
Technology, series of ligands to derive trends within their SCO com-
Getreidemarkt9/163-AC,1060Vienna,Austria plexes.[5]Thesyntheticstrategy usuallyappliedwasderived
Fax:[phone]
E-mail:[email protected] from the classical tetrazole synthesis established by Franke
Homepage:http://www2.ias.tuwien.ac.at/iaspb/ et al.[6] This reaction scheme allows for the synthesis of
pers_e.php?pid=2094233 aryl- as well as alkyl-substituted mono-N1- or di-N1,N1(cid:2)-
[b] X-rayCenter,ViennaUniversityofTechnology,
Getreidemarkt9,1060Vienna,Austria tetrazoles.Thus,awholelibraryofligandscouldbesynthe-
[c] InstituteofChemicalTechnologiesandAnalytics,Vienna sized and was the basis for a series of mononuclear and
UniversityofTechnology,
Getreidemarkt9/164-SC,1060Vienna,Austria polynuclear iron(II) SCO compounds.[5,7] Especially, the
[d] InstituteofSolidStatePhysics,ViennaUniversityof class of bridging α,ω-bis(tetrazol-1-yl)alkanes (nditz; n is
Technology,
thenumberofcarbonatomsinthealkylspacer)wasofgreat
WiednerHauptstrasse8–10/138,1040Vienna,Austria
Supporting information for this article is available on the interest,becausethevariationofthespacerlengthbetween
WWWunderhttp://dx.doi.org/10.1002/ejic.201201062. the two coordinating tetrazole moieties created a fascinat-
Re-useofthisarticleispermittedinaccordancewiththeTerms
ing playground for the investigation of the impact of the
andConditionssetoutathttp://onlinelibrary.wiley.com/journal/
10.1002/(ISSN)1099-0682c/homepage/2005_onlineopen.html usedsolventandthecounteranionontheSCObehaviorof
Eur.J.Inorg.Chem.2013,984–991 984 ©2013Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim
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thecomplexes.[8]Theiron(II)complexesof1,2-bis(tetrazol- Molecular and Crystal Structure of 3ditz
1-yl)ethane (2ditz) and the 1,2-bis(tetrazol-1-yl)propane
3ditzcrystallizesinthespacegroupP2 /n,andonecrys-
(btzp) feature a chain-type coordination-polymer structure 1
tallographicallyuniquemoleculeislocatedonageneralpo-
with a rather weak cooperativity of the spin-switching
sition.Thetwotetrazoleunitsareinanti(C1,N1–N4)and
iron(II)coordinationcenters,[7]whereasthecoordinationof
in gauche conformation (C2, N5–N8) to the propyl group,
Fe(II) with 1,4-bis(tetrazol-1-yl)butane (4ditz) gives rise to
respectively (Figure1) .
threefold interpenetrated 3D networks, which show a two-
step abrupt spin-transition behavior. The latter compound
was studied in depth to show the impact of the size of the
counteranionaswellasofthesolvent,andthisstudyeluci-
dated the drastic effects these modifications have.[8] The
homologues with longer spacers (5ditz–9ditz) revealed an
unusualparityeffect,whichisduetothenumberandparity
of carbon atoms in the alkyl spacer. Because the flexibility
of these ligands increases with the spacer length, the mag-
Figure1.Ellipsoidplotofthemolecularstructureof3ditz.Cand
netic properties of their respective iron(II) complexes are
Natomsarerepresentedbylightanddarkgreyellipsoids,respec-
not promisingwith respect to applicablecompounds.[5c] As
tively,drawnat75%probabilitylevels.Hatomsarerepresentedby
thecooperativity ofthe spinswitching oftheiron(II) coor- whitespheresofarbitraryradius.
dination centers is a crucial prerequisite for abrupt spin
The 3ditz molecules are connected through nonclassic
transitions, the preparation of the shorter α,ω-bis(tetrazol-
C–H···Nhydrogenbonds,whichinvolvetheHatomsofthe
1-yl)alkanes, that is, the so far inaccessible 1,3-bis(tetrazol-
tetrazole units (Table1).
1-yl)propane (3ditz), was a synthetic challenge in recent
time. As this “missing link” in the series of bridging α,ω-
Table1. Nonclassic C–H···N hydrogen bonds in the crystal struc-
bis(tetrazol-1-yl)alkanes(nditz)wasinterestingwithrespect tureof3ditz,whichinvolvehydrogenatomsofthetetrazolerings.
to systematic variations of the ligand that shed light on its
Atoms C–H[Å] H···N[Å] C–N[Å] C–H···N[°]
influences on the spin-transition properties, we put effort
C1–H1···N8[a] 0.949(10) 2.385(10) 3.3016(10) 162.1(9)
into developing alternative synthetic strategies to prepare
C2–H2···N2[b] 0.968(10) 2.477(10) 3.3935(10) 157.7(9)
this compound. As this alternative protocol allows prepar-
[a]–x,1–y,–z.[b]3/2–x,y+1/2,1/2–z.
ing thetarget molecules from bromoprecursorsrather than
from aminoprecursors, the shortest bridging ligand (1ditz) Pairsof3ditzmoleculesthatarerelatedbyinversionsare
may become accessible as well, but this will be the subject connected by two C1–H1···N8 bonds. These pairs are con-
of further investigations that go beyond the scope of this nected by C2–H2···N2 bonds to infinite 2D sheets ex-
paper. tending parallel to (103¯) (Figure2).
Results and Discussion
As the classical synthetic pathway by Franke et al.,[6]
which starts from the corresponding 1,3-diaminopropane,
neveryieldedthedesiredproduct,anewsyntheticapproach
that starts from the 1,3-dibromopropane and makes use of
a phase-transfer catalyst was developed. In principle, the
useofphase-transfercatalystsforthesynthesisoftetrazoles
has been known for decades. The list of tetrazole com-
pounds prepared by this method ranges from industrial-
application compounds such as 5-(benzylmercapto)-1H-
tetrazole (synthesized with hexadecyltrimethylammonium
bromideasphase-transfercatalyst)[9],toseveralbiologically
active tetrazole compounds of the family of angiotensin-II
inhibitors (i.e., irbesartan, cardesartan, losartan, and val-
sartan),whichareC5-substituted,[10]toavarietyofC5,N1-
disubstituted tetrazoles.[11] However, on the basis of the
abovementionedsyntheticprotocols,thereisnoestablished
Figure2. Layers of hydrogen-bonded 3ditz molecules parallel to
synthetic pathway for the efficient synthesis of N1-substi-
(103¯)projectedonthelayerplane.
tutedtetrazolessuchastheN1-substituted1,3-bis(tetrazol-
1-yl)propane (3ditz). So far, only the N2-substituted and Thesheetsarestackedalong[103¯]andconnectedbyvan
the mixed N1,N2-substituted 1,3-bis(tetrazol-1-yl)propane der Waals interactions and possibly by weak hydrogen
were reported in the literature.[12] For synthetic details see bonds involving aliphatic hydrogen atoms. A packing di-
the Experimental Section. agram of the crystal structure is given in Figure3.
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Figure3.Packingdiagramofthecrystalstructureof3ditz.
Synthesis of the Complex [Fe(3ditz) ](BF ) ThecoordinationsphereoftheFe2+ionismadeupofsix
3 4 2
equivalent N4 atoms located at the corners of a practically
Astraightforwardcomplexationreactionyieldedthenew
regular octahedron (symmetry 3¯). The Fe–N bond lengths
spin-crossover coordination polymer [Fe(3ditz) ](BF ) ,
3 4 2 at100[6(cid:3)1.9947(14)Å]and200K[6(cid:3)2.180(2)Å]arein
which exhibits an almost complete and abrupt spin transi-
good agreement with Fe2+ in its low-spin and high-spin
tion at T = 159K (see the Exp. Section for synthetic de-
½ state, respectively.
tails). The obtained powder product was used for all
The aliphatic spacers of the 3ditz ligands are disordered
physicochemical characterizations, whereas single crystals
aroundtwofoldaxesparallelto(cid:4)100(cid:5).Thecentralmethyl-
were used for the X-ray crystal structure determination.
ene (–CH –) group had to be refined as a split position,
Calculatedpowderdiffractionpatternsderivedfromtheex- 2
whereas the disorder of the outer methylene groups is re-
perimental single-crystal X-ray diffraction data were com-
flectedbyenlargedatomicdisplacementparameters(ADP)
pared with measured XRPD (X-ray powder diffraction)
(Figure5).
data to prove that both, the crystals as well as the powder
product, were the same compound. For details, see Fig-
ureS1 in the Supporting Information.
Crystal Structure of [Fe(3ditz) ](BF )
3 4 2
Despite the spin transition at 159K, the structures of
[Fe(3ditz) ](BF ) at 100 and at 200K are crystallographi-
3 4 2
cally equivalent. The complex crystallizes in the space
groupP3¯c1,andthe structurefeaturesonecrystallographi-
cally unique Fe2+ ion located on a site with a 3¯ symmetry
Figure5.Disordered3ditzligandconnectingtwoFe2+ions.Color
and one unique 3ditz ligand. The Fe2+ centers are coordi-
code: C is represented by grey, N by blue and Fe by yellow ellip-
nated by six 3ditz molecules acting as bridging ligands. soids.Primedandnonprimedatomsarerelatedbyatwofoldaxis.
Thusinfinite[Fe(3ditz) ]2+chainsareformed,whichextend C3andC3(cid:2)arehalf-occupied.Hatomsareomittedforclarity.
3
along [001] with a p3¯1c symmetry (Figure4).
The space between the [Fe(3ditz) ]2+ chains is filled by
3
BF – anions located on a site with symmetry 3 (Figure6).
4
The BF – anions are disordered: Two different orienta-
4
tionsarerelatedbyapseudomirrorsymmetrywithaplane
parallelto (001).Theoccupationratio ofbothorientations
was determined as 0.742:0.258(5).
[Fe(3ditz) ](BF ) can be considered isostructural[13] to
3 4 2
thepositionalisomer[Fe(btzp) ](ClO ) [7a]and,irrespective
3 4 2
of disorder, likewise to the two-carbon homologue
[Fe(2ditz) ](BF ) .[7b]Asinthetitlecomplex,theligandsin
3 4 2
[Fe(btzp) ](ClO ) are disordered around the twofold axes
3 4 2
parallel to (cid:4)100(cid:5). In contrast, the ligands in [Fe(2ditz) ]-
3
(BF ) aredisorderedbypseudo-symmetry,namely,bymir-
4 2
roring at planes parallel to {100}. As a consequence, the
disorder affects only the aliphatic spacer in [Fe(3ditz) ]-
Figure4. Perspective projection of [Fe(3ditz) ](BF ) showing the 3
3 42 (BF ) and [Fe(btzp) ](ClO ) , but it affects the whole li-
1Dchainstructure.ColorcodesasinFigure1,Fe2+ionsarewhite. 4 2 3 4 2
Ellipsoidsaredrawn50%probabilitylevels.Hatomsandthedisor- gand in[Fe(2ditz)3](BF4)2. On theother hand,the disorder
deroftheligandsareomittedforclarity. of the BF – and ClO – anions is equivalent in all three
4 4
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due to thespace needed for the methyl groupof the ligand
andforthelargeranions.Intotalandasexpected,theunit
cellvolumeincreaseswiththesizeoftheligandsandofthe
anions: [Fe(2ditz) ](BF ) (1308.6Å3), [Fe(3ditz) ](BF )
3 4 2 3 4 2
[1471.88(14)Å3], [Fe(btzp) ](ClO ) [1532.6(4)Å3]. For the
3 4 2
crystal structure data of both the free 3ditz ligand and the
corresponding Fe2+ complex see Table2.
Magnetic and Spectroscopic Characterisation of
[Fe(3ditz) ](BF )
3 4 2
The magnetic susceptibility of [Fe(3ditz) ](BF ) was
3 4 2
measured between 50K and 300K, which revealed an al-
mostcompleteandabruptspin-transitionbehavioratT =
½
159K (see Figure7).
Figure6. View of the crystal structure of [Fe(3ditz) ](BF ) along
3 42
[001].ColorcodeasinFigure5;BisrepresentedbyredandFby
greenellipsoids.HatomsandthedisorderoftheligandsandBF –
4
anionsareomittedforclarity.
structures. In contrast to [Fe(2ditz) ](BF ) ,we did not ob-
3 4 2
serve any streaking or broadening of reflections in the dif-
fractionpatternof[Fe(3ditz) ](BF ) ,whichwouldpointto
3 4 2
correlateddisorderorsmalldomains.However,ithastobe
notedthatthecrystalunderinvestigationwastiny,anddif-
fusescatteringmayhavebeenunobservedbecauseofalack
of intensity.
Surprisingly,becauseofamorecorrugatedconformation Figure7. Molar magnetic susceptibility of [Fe(3ditz) ](BF ) be-
3 42
of the 3ditz ligand in comparison to the shorter ligands tween50Kand300KatanexternalfieldstrengthofH=1T.
2ditz and btzp, the Fe–Fe distances along the cationic
chains are significantly shorter in the 3ditz complex The astonishing abruptness of the spin transition is due
[7.1325(11)Å at 100K for 3ditz compared to 7.293(4) and to a strong cooperative effect among the spin-switching
7.273(1)Åfor2ditzandbtzp,respectively],whichtranslates iron(II) coordination centers, and it can be explained by
toashorterlatticeparameterc=2d(Fe–Fe).Theadditional thesignificantlyshorterFeII–FeIIdistancealongsidethe1D
space needed for the extra methylene group in 3ditz is pro- chain-type coordination polymer in comparison to the ho-
vided by a less dense packing of the cationic chains com- mologous compound [Fe(2ditz) ](BF ) (i.e., 7.13Å com-
3 4 2
paredtothe2ditzcomplex,whichalsoresultsinanincrease paredto7.29Å,respectively,at100K).[7a]Furthermore,the
ofthelatticeparametersa=b[10.9153(4)Åfor3ditzcom- three helically twisted bridging 3ditz ligands form a stiffer
pared to 10.178(2)Å for 2ditz]. The packing is even less packing motif than the shorter 2ditz ligands in the corre-
dense in [Fe(btzp) ](ClO ) [a = b = 11.030(2)Å], which is sponding[Fe(2ditz) ](BF ) compound,thuspreventingthe
3 4 2 3 4 2
Table2.Crystalanddiffractiondatafor3ditzand[Fe(3ditz) ](BF ) .
3 42
3ditz [Fe(3ditz) ](BF ) at100K [Fe(3ditz) ](BF ) at200K
3 42 3 42
Empiricalformula C H N FeC H N B F FeC H N B F
5 8 8 15 24 24 2 8 15 24 24 2 8
Formulaweight 180.2 770.0 770.0
Crystalsystem monoclinic trigonal trigonal
Spacegroup P2 /n P3¯c1 P3¯c1
1
a/Å 5.1113(2) 10.9153(4) 11.0529(3)
b/Å 15.0899(6) 10.9153(4) 11.0529(3)
c/Å 10.3860(4) 14.2650(11) 14.5434(5)
β/° 92.628(2) 120 120
V/Å3 800.22(5) 1471.88(14) 1538.68(8)
T/K 100 100 200
Z 4 2 2
μ/mm–1 0.110 0.621 0.594
Reflectionscollected 13026 32967 40179
Independentreflections 2929 1178 1192
R[I(cid:5)3σI],wR[all],GooF 0.0350(2464refl.),0.0462,2.42 0.0353(828refl.),0.0366,1.77 0.0502(888refl.),0.0753,3.56
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kind of shock-absorber effect of the bridging ligands that subtle changes of the absorption features of the octahedral
impairs the cooperativity of the iron(II) centers in the iron–nitrogen coordination sphere are observed in the FIR
[Fe(2ditz) ](BF ) compound.[14] Therefore, the title com- spectra (for a temperature-dependent representation of the
3 4 2
plexisanotherexampleforspin-crossovercompoundswith FIR spectra see FigureS2 in the Supporting Information).
per se flexible ligands that yield an abrupt spin transition- The two distinct iron(II) spin states can be easily iden-
behavior,whichismainlyduetopackingeffectsratherthan tified because of the different colors of the HS compound
to the stiffness of the ligand itself. (colorless) and the LS compound (purple), which corre-
Theresultsofthemagneticmeasurementsaresupported spond to different electronic d–d transitions. Therefore,
by independent spectroscopic measurements, such as vari- variable-temperatureUV/Vis/NIRspectroscopyofthesolid
able-temperaturefar-rangeIR(FIR),mid-rangeIR(MIR), powder sample with the diffuse-reflection technique allows
and UV/Vis/NIR spectroscopy. As the spin transition be- for a detection of the electronic absorptions. The HS com-
tween high-spin and low-spin iron(II) has a drastic impact pound shows no significant absorption in the visible range
on the bond strength of the Fe–N4 bond, it also has an 400–700nm, as the absorption corresponding to the
impact on the strengths of the neighboring N4–C1 bonds 5T (cid:2)5E transition, which is characteristic of FeII HS com-
2
andevenonthenext-neighboringC1–H1bonds.Especially, pounds,arisesaround850nm.Incontrast,thepurplecolor
thebond-strengthchangeofthetetrazoleC–Hgroupupon of the LS species is due to the 1A (cid:2)1T -transition band at
1 1
spin transition of the iron(II) can be detected by variable- 545nm, which is distinctive for LS FeII compounds. An-
temperature MIR spectroscopy.[15] The ν band is ob- other typical absorption feature at 383nm corresponds to
CH
served at 3152cm–1 at 93K for the low-spin compound, the 1A (cid:2)1T transition and can be found as a shoulder in
1 2
whereas the same absorption can be found at 3147cm–1 at thespectrumoftheLSspecies. Thecomparisonofthetwo
298Kforthehigh-spincompound(seeFigure8).Themore spectra is shown in Figure9.
Figure8.Variable-temperatureMIRspectra:acomparisonoftheν bandof[Fe(3ditz) ](BF ) at93K(black)andat298K(grey).
CH 3 42
Figure9.UV/Vis/NIRspectra:acomparisonof[Fe(3ditz) ](BF ) at138(black)and173K(red),showingthetypicald–dtransitionsfor
3 42
FeIIinthelow-spinandthehigh-spinstate,respectively.
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A temperature-dependent representation of the UV/Vis/ crossover coordination polymer [Fe(3ditz) ](BF ) . Unlike
3 4 2
NIR spectra is given in FigureS3 in the Supporting Infor- the isostructural 1D chain-type coordination polymers
mation. [Fe(2ditz) ](BF ) [7a]and[Fe(btzp) ](BF ) [7b],thetitlecom-
3 4 2 3 4 2
57Fe-Mössbauer spectroscopy is a direct method to de- poundfeatures analmost completeand abruptspin-transi-
termine the spin state of the FeII coordination centers. For tionbehavioratT =159K,whereastheformercomplexes
½
an analysis of the Mössbauer spectra (see Figure10), four showed gradual spin transitions around T = 140K and
½
subspectra are necessary. T = 130K, respectively. In most cases, an abrupt spin
½
transitioncanbeobservedbecauseofarigidligandsystems
used. Only in a few cases, per se flexible ligands like 3ditz
arepackedtightlyorestablisharigidcoordination-polymer
network.Insuchrarecases,theabruptnessofthespin-tran-
sition behavior is only due to the strong cooperativity en-
forcedbythewholemolecularpacking.Thetitlecompound
is a new example of exactly such a rather rare case.
Experimental Section
Warning:Tetrazolesandtheirderivativesarepotentiallyshock-sen-
sitiveorexplosivecompoundsandshouldthereforebehandledwith
greatcare.
Spectroscopic Characterization of 3ditz: 1H NMR and 13C NMR
spectra in [D ]Me CO were measured by using a Bruker 200 FS
6 2
FT-NMR spectrometer. 1H NMR chemical shifts are reported in
ppm against TMS. Mid-range IR spectra of the ligand were re-
corded with the attenuated-total-reflectance (ATR) technique
withintherange4000–450cm–1byusingaPerkin–ElmerSpectrum
TwoFTIRspectrometerwithaUATRaccessoryattached.
Synthesis of 1,3-Bis(tetrazol-1-yl)propane (3ditz): 1,3-Dibromo-
Figure10. 57Fe-Mössbauer spectra: a comparison of [Fe(3ditz) ]-
3 propane (3.54mL, 34.67mmol), sodium hydroxide (2.77g,
(BF ) at 4.2, 50, 100, 150, 200, and 294K shows the transitions
42 69.35mmol),and1H-tetrazole(4.86g,69.35mmol)wereheatedto
ofFeIIfromthelow-spintothehigh-spinstate.
refluxedinamixtureof30mLoftolueneand30mLofwaterfor
Athightemperature,thewholesampleisinthehigh-spin 20hwithtetrabutylammoniumbromide(10mol-%)asphase-trans-
fer catalyst. The solvents were removed in vacuo and the yellow
state.87%oftheFeatomshaveaquadrupolesplitting(QS)
eQV /4 = (0.77(cid:6)0.07)mm/s, the rest has a splitting of crudeoilwaspurifiedbycolumnchromatographyonsilicagelwith
zz ethylacetateasthemobilephase.Afterevaporationofthesolvent,
(1.1(cid:6)0.01)mm/s. The center shift (CS) for both compo-
the ligand was obtained as a white solid. Single crystals suitable
nents is (0.93(cid:6)0.03)mm/s at 294K. The transition to the
forX-raydiffractionanalysisweregrownbyslowevaporationfrom
low-spin state appears between 200 and 150K, which is in methanol, yield 0.66g (10.6%). C H N (180.17): calcd. C 33.33,
5 8 8
good agreement with the results of the magnetic measure- H 4.48, N 62.19; found C 33.84, H 4.42, N 61.40. 1H NMR
ments (see Figure7). At low temperatures, the high-spin (200MHz, [D ]Me CO, 298K): δ = 2.70 (m, J = 6.95Hz, CH ),
6 2 2
componentwithitshigherquadrupolesplittingisstillpres- 4.71(t,J=6.95Hz,CH ),9.19(s,CH)ppm.13CNMR(50MHz,
2
ent downto the lowesttemperatures measured. Therest of [D6]Me2CO, 298K): δ = 30.47 (CH2), 45.77 (CH2), 144.46 (CH)
the Fe centers changes to the low-spin state with QS = 0, ppm.IR:ν˜ =3144,3122,1568,1486,1428,1171,1112,1102,874,
664,642cm–1.
splitting into two components. The larger one (70%) has a
center shift CS = (0.386(cid:6)0.02)mm/s; the smaller compo- Characterizationof[Fe(3ditz) ](BF ) :Elementalanalyses(C,H,N)
3 42
nent exhibits CS = (1.102(cid:6)0.02)mm/s. wereperformedattheMikroanalytischesLaboratorium,University
ofVienna, Vienna,Austria. Mid-rangeIR spectraofthe complex
wererecordedbyusingKBrpelletswithintherange3400–600cm–1
Conclusions with a Perkin–Elmer 400 FIR/MIR FTIR spectrometer. Pellets
wereobtainedbypressingthepowderedmixtureofthesamplesin
The missing link [Fe(3ditz) ](BF ) between the complex KBr in vacuo by using a Carver 4350.L hydraulic press and by
3 4 2
[Fe(2ditz) ](BF ) andthecomplexes[Fe(nditz) ](BF ) with applyingapressureofapproximately10.000kg/cm2for5min.Far-
3 4 2 3 4 2
rangeIRspectrawererecordedwithintherange700–30cm–1with
n = 4–9 was only obtained after the strategy of the ligand
thesame Perkin–Elmer400 FIR/MIRFTIRspectrometer andby
synthesiswaschanged.Thewell-establishedsyntheticpath-
using polyethylene pellets. The variable-temperature IR spectra
way of Franke et al.[6] failed to produce the desired ligand
were recorded by using a Graseby Specac thermostatable sample
3ditz because of unclear problems. The modified approach
holder. Electronic spectra of the undiluted powder samples were
thatmakesuseofaphase-transfercatalystcouldfillthegap measured with a Perkin–Elmer Lambda 900 UV/Vis/NIR spec-
in the series of accessible ligands, and thus allowed for a trometerequippedwithathermostatablepowdersampleholderin
successfulpreparationandcharacterizationofthenewspin- diffuse reflection geometry (Praying Mantis accessory®) between
Eur.J.Inorg.Chem.2013,984–991 989 ©2013Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim
www.eurjic.org FULL PAPER
335 and 1200nm within the temperature range 138–173K. Mag- X-ray Powder Diffraction: As all spectroscopic and magnetic in-
neticmeasurementswereperformedbyusingacryogenicvibrating- vestigations have been performed on powder samples of the title
sample magnetometer (VSM) between 50 and 350K. For TGA/ compound,weverifiedthatthepowdersamplesofthecomplexare
DSC(TGA:thermogravimetricanalysis,DSC:differentialscanning identicaltothesinglecrystalsusedforthestructuredetermination.
calorimetry)analysesaNetzschSTA449F1Jupitersystemwitha TheX-raypowderdiffractionmeasurementswerecarriedoutwith
heating rate of 10K/min under N atmosphere was used between a Panalytical X’Pert diffractometer in Bragg–Brentano geometry
2
298 and 673K. 57Fe-Mössbauer measurements were performed by using Cu-K radiation, a X(cid:2)Celerator linear detector with a
α1,2
withastandardconstant-accelerationspectrometerintransmission Nifilter,samplespinningwithbackloadingsampleholders,and2θ
geometry.The57Co/Rhsourcewasmountedonthedrivingsystem = 5–70° at T = 297K. By using the structural data of the single
andkeptatroomtemperature.Allcentershiftdataaregivenrela- crystalsofthecomplex,Rietveldrefinementswerecarriedoutwith
tivetothissource.Thecalibrationofthevelocityscalewascarried the program TOPAS by using the fundamental parameter ap-
outwithaα-Fefoil.Forthetemperaturevariationbetween4.2K proach.[19] Apart from unit cell dimensions, instrumental param-
and room temperature, a continuous-flow cryostat was used, in eters, and a background polynomial coefficient, a texture param-
whichthesampleiskeptinHeexchangegas.Thetemperaturesta- eterwasrefined.ThecomparisonofthemeasuredXRPDwiththe
bility was (cid:6)0.5Kat temperatures above 77Kand (cid:6)0.2K below. calculated XRPD on the basis of the single crystal XRD data is
The spectra were analyzed by solving the full Hamiltonian with giveninFigureS1intheSupportingInformation.
bothmagneticandquadrupolehyperfineinteraction.
SupportingInformation(seefootnoteonthefirstpageofthisarti-
Synthesisofthe[Fe(3ditz)3](BF4)2:Forallmanipulationsofiron(II) cle):XRPDpatternof[Fe(3ditz)3](BF4)2incomparisontoacalcu-
salts, standard Schlenk techniques were used. Fe(BF ) ·6H O lated XRPD pattern; variable-temperature FIR spectra of
42 2
(236mg, 0.6mmol) and 3ditz (324mg, 1.8mmol) were heated in [Fe(3ditz)3](BF4)2; variable-temperature UV/Vis/NIR spectra of
10mL of methanol for 6h at 45°C. After the evaporation of the [Fe(3ditz)3](BF4)2; DSC during thermal decomposition of
solvent,thewhiteresiduewaswashedtwicewith3mLofdichloro- [Fe(3ditz)3](BF4)2; TGA during thermal decomposition of
methane.SinglecrystalssuitableforX-raydiffractionanalysiswere [Fe(3ditz)3](BF4)2.
grown by slow evaporation of a crude reaction mixture, yield
163mg (35.4%). C15H24B2F8FeN24 (769.97): calcd. C 23.40, H Acknowledgments
3.14,N43.66;foundC22.57,H3.11,N40.75.
SimultaneousThermalAnalysis:Explosivedecompositionat525K The authors are grateful for financial support from the Austrian
(727.6J/g), residual mass (673K) 33.3%. For detailed graphical Science Fund (FWF) (project number P24955-N28). The authors
representations of the DSC and TGA experiments see FiguresS4 also gratefully acknowledge the help of the X-ray center of the
andS5intheSupportingInformation. ViennaUniversityofTechnology(Dr.KlaudiaHradil).
Note: The perchlorate analogue was also prepared and showed
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