thermo and pressure induced valence tautomerism in layered ......n. bélanger desmarais,c l....

Thermo and pressure induced valence tautomerism in layered Mn(II) – nitronyl nitroxide radical compounds:

Synthesis, structure, magnetism and Raman spectroscopyConstance Lecourt,a,* C. Desroches,a R. Chiriac,a F. Toche,a K. Inoue,b K. Maryunina,b C. Reber,c

N. Bélanger Desmarais,c L. Khrouz,d D. Luneaua

aUniv Lyon, Université Claude Bernard Lyon 1, CNRS, Laboratoire des Multimatériaux et Interfaces, F-69622 Villeurbanne, FrancebHiroshima University, Center for Chiral Science, Higashi-Hiroshima 739-8526, Japan

cUniversité de Montréal, Département de Chimie, Montréal, CanadadUniv Lyon, ENS de Lyon, CNRS UMR 5182, Université Claude Bernard Lyon 1, Laboratoire de Chimie F69342, Lyon, France

*[email protected]

INTRODUCTION SYNTHESIS AND X-RAY STRUCTURE

MAGNETIC PROPERTIES – VALENCE TAUTOMERISM

CONCLUSION REFERENCES & ACKNOWLEDGMENT

▪ Switchable ferrimagnetic compounds: thermo-induced valence tautomeric conversion

▪ Structural modification with different counter-anions: modification of transition

temperature and inter-layered interactions

▪ Raman spectroscopy: new band at 1620 cm-1 (NO. reduction)

▪ Pressure favorizes VT phenomenon

Future: conductivity measurement, X-ray under pressure, new anions… ❖ Japan Society for the Promotion of Science - Summer Program 2017

▪ Luneau D., Rey P., Coord. Chem. Rev., 2005, 249, 2591

▪ Lannes A., Suffren Y., Tommasino J.B., Chiriac R., Toche F., Khrouz L., Molton F., Duboc C., Kieffer I., Hazemann J.L., Reber C.,

Hauser A., Luneau D., JACS, 2016, 138, 16493

▪ Artiukhova N. A., Romanenko G. V., Bogomyakov A.S., Barskaya I. Yu., Veber S.L., Fedin M. V., Maryunina K. Yu., Inoue K.,

Ovcharenko V. I., J. Mater. Chem. C, 2016, 4, 11157

▪ Beaulac R., Bussière G., Reber C., Lescop C., Luneau D., New J. Chem., 2003, 27, 1200

▪ Roux C., Adamas D.M., Itié J. P., Polian A., Hendrickson D. N;, Verdaguer M., Inorg. Chem., 1995, 35, 2846

▪ Stable: delocalization unpaired electron on two NO

▪ Chelating and bridging ligand

▪ Non-innocent: spin carrier

▪ Redox active species

S=0 S=0S=1/2

SMn=5/2 SMn=5/2 Srad= ½ Srad= ½

Nitronyl

nitroxyde

Nitronyl

nitroxydeMn2+ Mn2+

Asymmetric unit

Mn1

Mn2

Mn1

Mn1

N1

N2

N3

O1

O2O3

▪ 2D-coordination polymers of {[Mn2(NITIm)3]ClO4}n▪ Honeycomb structure along a axis

▪ Variable counter-anions

ClO4-

BF4-

PF6-

Isostructural compounds

b

c

a=d100

: anion X

d100

BF4-

10,17 Å 10,21 Å 11,40 Å

a

PF6-ClO4

-

▪ 1/3 of the radicals are delocalized at low T

▪ Middle interactions between polymers

➢ Thermo-induced electrons transfer: Valence tautomeric conversion

➢ Transfer from metallic cations to radicals

Legend:

{[MnII2(NITIm)3]X}n {[MnIII

2 (NITImred)2(NITIm)]X}nT

T

➢ Oxidation: Mn2+Mn3+ and reduction: NITIm- NITImred (2/3 of the radicals)

MAGNETISM AND RAMAN SPECTROSCOPY UNDER P

1 bar

3 kbar

4 kbar

11 kbar

16 kbar

22 kbar

33 kbar

Pressure favorizes the valence tautomerism conversion

PVMn2+-rad= 2037,5 Å3 VMn3+-rad reduced= 1974,1 Å

3X-ray at variable T:

▪ Hydrostatic high pressure CuBe cell

▪ Transition shifts to higher temperature

▪ Hysteresis loop is compressed

▪ Diamond anvil cell

▪ Transition at 4 kbar: 1560 1610 cm-1

▪ Reversible

1 bar

1 kbar

➢ Anisotropic pressure on {[Mn2(NITIm)3]ClO4}n powder

▪ 1/3 of the radicals are delocalized at low T

▪ Strong interactions between polymers

▪ 1/3 of the radicals are localized at low T

▪ Weak interactions between polymers

RAMAN SPECTROSCOPY AT VARIABLE T

➢ Objective: Following the transition by modification of NO bond with temperature

Elongation

u=1500-1600 cm-1

NITImH Raman

signature

▪ u(NO.) = 1570 cm-1 at 293 K

▪ Broadband between 200 K and 130 K

▪ 2nd peak at 80 K: u = 1620 cm-1

Delocalization and strong interactions

➢ For X = BF4- and ClO4

-:

▪ u(NO.)= 1570 cm-1 at 323 K

▪ 2nd peak at u = 1620 cm-1 increases

and decreases clearly with T

Localization and weak interactions

➢ For X = PF6-:

250 K

203 K

130 K

170 K

323 K

X = PF6-

210 K

200 K

130 K

80 K

293 K

X = ClO4-

293 K

170 K

150 K

130 K

80 K

X = BF4-

➢ Elaboration of molecule-based magnets: magnetic molecular entities

➢ Alternation of different spin with antiferromagnetic interactions: non-zero magnetization

➢ Metal – radical synthesis approach:

➢ Mn2+: 5 free e-, high spin

➢ Free radical:

NaX

exo

280 K

276 K

ELECTRON PARAMAGNETIC RESONANCE

▪ X = BF4-and PF6

-:

two dependent peaks two successive Mn2+ oxidation

▪ In agreement with magnetic susceptibility

{[MnII2(NITIm)3]PF6}n

{[MnII2(NITImred)2(NITIm)]PF6}n

375 K

cT400K=7,14 emu.K.mol-1

350 K

287 K

275 K

exo

348 K

343 K

360 K

365 K

exo

{[MnII2(NITIm)3]BF4}n

{[MnII2(NITImred)2(NITIm)]BF4}n

290 K265 K


➢ Counter-anion X impacts on transition temperature and mechanism: modification of interlayered

interactions and radical delocalization

{[MnII2(NITIm)3]ClO4}n

{[MnII2(NITImred)2(NITIm)]ClO4}n

276 K296 K


1000 Oe 1000 Oe1000 Oe

: Mn2+

: Mn3+ : NITImred

: NITIm-

dotted: delocalized

X = BF4-

X = ClO4-

X = PF6-

▪ Heating: Mn3+ Mn2+ ▪ Double hysteresis

DIFFERENTIAL SCANNING CALORIMETRY

350 K

290 K

260 K

180 K

➢ {[Mn2(NITIm)3]BF4}n

300 K

280 K

thermo and pressure induced valence tautomerism in layered ......n. bélanger desmarais,c l....

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