Heterometallic 3d-4f Single Molecule Magnets: Experiment and Theory

Kuduva R Vignesh, Stuart K Langley, Keith S Murray and G Rajaraman Email: rajaraman@chem.iitb.ac.in

Department of Chemistry, IITB-Monash Research Academy, IIT Bombay, Mumbai-400076

References:

Acknowledgement IITB-Monash Research Academy

1) R. Sessoli, D.Gatteschi, A. Caneshi, M. A. Novak, Nature 1993, 365, 141. 2) D. Gatteschi, Angew. Chem., Int. Ed. 2003, 42, 246. 3) D. Gatteschi, R. Sessoli, J. Villain, Molecular Nanomagnets, Oxford University Press, Oxford, 2006. 4) Bagoni, L, Wernsdorfer, W. Nature Materials, 2008, 7, 179-186. 5) Murray et. al. Chem. Commun. 2010, 46, 7787. 7) Powell et. al. Coor. Chem. Rev. 2009, 232, 8) Rajraman et. al. Chem. Eur. J. 2015, accepted. 9) Aquilante et.al. WIREs Comput. Mol. Sci. 2013, 3, 143-149. 10) Cirera et.al. Chem. Eur. J., 2006, 12, 3162.11) Chibotaru et.al. Angew. Chem. Int. Ed., 2008, 47, 4126-4129. 12) Gaussian 09, Revision A.02, Gaussian,Inc., Wallingford CT, 2009.

Generic Mechanism of {Co2Ln2} based SMMs

Co(NO3)2.6H2O

+

Ln(NO3)3.6H2O

+ N

HO

HO

+

COOH

Et3N

MeCN8

8

Ueff=87K

τQTM =0.16s

1

Single Molecule Magnets Ueff = S

2D

Magnetic Refrigerants

Information Storage Devices

Spintronics

Q-bits

Mn(NO3)2.6H2O

+

Ln(NO3)3.6H2O

+ N

HO

HO

+

COOH

REt3N

MeCN

1

Red block

crystals

Computational Details MOLCAS 7.8 Code, Gaussian 09

CASSCF+RASSI calculations

Active Space (9,7) for DyIII

ANO…RCC TZVP Dy & ANO…RCC VDZP (C, N,O)

DFT calculation CSDZ Basis Set for Y & TZVP for rest

𝐻 = −2𝐽 𝑆𝑀𝑛1 𝑆𝑀𝑛2

S=16 & J = 0.43 cm-1

Ln= Dy(1), Ho(2&5), Y(3&6) , Yb(4) and Er(7)

R= -H or –CH3

1

zig-zag

arrangement of

two ions up

and two ions

down.

The MnIII centres →Jahn-Teller octahedral distortions

with a {NO5} sphere & The DyIII ions → distorted

triangular dodecahedron geometries.

Overall void volume of approximately 43% of

the unit cell.

No uptake of N2 at 77K in the range 0 – 0.99 atm.

Similarly, the uptake of CO2 at 273K was lower.

0 50 100 150 200 250 300

2

4

6

8

10

12

14

16

18

20

22

24

26

T / K

MT

/ c

m3 K

mo

l-1

Exp data

DFT-sim

1 2 3 4 5 6 7 8

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

50Hz

100Hz

250Hz

500 Hz

997 Hz

M"

/ cm

3 K

mo

l-1

T / K

a) b)

From room T to

1.8 K is

indicative of the

depopulation of

the excited mJ

Stark levels of

the LnIII ions. Dy1 Dy2 Dy3 Dy4 Dy5 Dy6 Dy7 Dy8

gx 0.3101 0.1414 0.3236 0.1636 0.3624 0.1482 0.3442 0.1480

gy 0.8721 0.3421 0.9181 0.4073 1.0564 0.3628 0.9942 0.3624

gz 18.5386 19.1346 18.4936 19.0719 18.4212 19.1533 18.4683 19.1282

No SMM behavior was observed for

{MnIII8HoIII

8} (2), {MnIII8YbIII

8} (4),

{MnIII8HoIII

8} (5) and {MnIII8ErIII

8} (7).

3

8

9

10

zJ= -0.01 cm-1

The S = 16 GS & very small J explains

the fast magnetic relaxation rate and

weak SMM behaviour observed for 3. POLY_ANISO

Mn(III)-Dy(III) interactions.

0 50 100 150 200 250 30010

20

30

40

50

60

70

80

T/K

MT

/cm

3 K

mo

l-1

J = - 0.1 cm-1

Poly-aniso fit

Exp data

The fast QTM and

weak SMM behaviour

in {Mn8Dy8} wheel → very weak Mn(III)-

Dy(III) coupling &

unfavourable

Dy(III)/Mn(III)

anisotropy.

Green Crystals

{Ln= Dy(8), Tb(9),Ho(10)}

9

10

A planar butterfly motif, with the LnIII ions occupying the body positions and the CoIII ions the outer wing.

At 2 K the relaxation becomes

independent of T, indicating a

QTM of relaxation.

Tb & Ho analogues showed

susceptibility peaks in 5000 Oe and

2000 Oe dc field respectively. This

behavior is due to very fast QTM at

zero field.

Poly_Aniso Fit

Origin of Anisotropic Exchange

For {MnIII8DyIII

8} (1)

& {MnIII8Y

III8}(3&6),

indicating SMM

behavior but with fast

QTM.

SHAPE Analysis → Two type of Dy ions

8 9 10

Computational Details Active Space (9,7) for DyIII,(8,7) for TbIII, (10,7) for HoIII

ANO…RCC TZVP for Dy, Tb & Ho

gx gy gz Ueff

{Dy2Co2}(8) 0.0 0.0 39.8612 112.2 K

{Tb2Co2}(9) 0.0 0.0 34.4534 4.8 K

{Ho2Co2}(10) 0.0 0.0 21.1565 8.7 K

The QTM is lower in the {Co2Dy2} because of weak

AF coupling.

The nonmagnetic KDs are a fingerprint of

polynuclear complexes of strongly anisotropic

Ln’s. KDs → the design of qubits for

quantum computation.

8

The decrease of

the χMT product

(at H = 1 T) for 8-

10 from room

temperature to 1.8

K is indicative of

the presence of

AF interactions.