Heterometallic 3d-4f Single Molecule Magnets: Experiment and Theory Kuduva R Vignesh , Stuart K Langley, Keith S Murray and G Rajaraman Email: [email protected] 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 {Co 2 Ln 2 } based SMMs Co(NO 3 ) 2 .6H 2 O + Ln(NO 3 ) 3 .6H 2 O + N HO HO + COOH Et 3 N MeCN 8 8 U eff =87K τ QTM =0.16s 1 Single Molecule Magnets U eff = S 2 D Magnetic Refrigerants Information Storage Devices Spintronics Q-bits Mn(NO 3 ) 2 .6H 2 O + Ln(NO 3 ) 3 .6H 2 O + N HO HO + COOH R Et 3 N MeCN 1 Red block crystals Computational Details MOLCAS 7.8 Code, Gaussian 09 CASSCF+RASSI calculations Active Space (9,7) for Dy III ANO…RCC TZVP Dy & ANO…RCC VDZP (C, N,O) DFT calculation CSDZ Basis Set for Y & TZVP for rest = −2 1 2 S=16 & J = 0.43 cm -1 Ln= Dy(1), Ho(2&5), Y(3&6) , Yb(4) and Er(7) R= -H or –CH 3 1 zig-zag arrangement of two ions up and two ions down. The Mn III centres →Jahn-Teller octahedral distortions with a {NO 5 } sphere & The Dy III ions → distorted triangular dodecahedron geometries. Overall void volume of approximately 43% of the unit cell. No uptake of N 2 at 77K in the range 0 – 0.99 atm. Similarly, the uptake of CO 2 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 M T / cm 3 K mol -1 Exp data DFT-sim a) From room T to 1.8 K is indicative of the depopulation of the excited m J Stark levels of the Ln III ions. Dy1 Dy2 Dy3 Dy4 Dy5 Dy6 Dy7 Dy8 g x 0.3101 0.1414 0.3236 0.1636 0.3624 0.1482 0.3442 0.1480 g y 0.8721 0.3421 0.9181 0.4073 1.0564 0.3628 0.9942 0.3624 g z 18.5386 19.1346 18.4936 19.0719 18.4212 19.1533 18.4683 19.1282 No SMM behavior was observed for {Mn III 8 Ho III 8 } (2), {Mn III 8 Yb III 8 } (4), {Mn III 8 Ho III 8 } (5) and {Mn III 8 Er III 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 50 100 150 200 250 300 10 20 30 40 50 60 70 80 T/K M T/cm 3 K mol -1 J = - 0.1 cm -1 Poly-aniso fit Exp data The fast QTM and weak SMM behaviour in {Mn 8 Dy 8 } 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 Ln III ions occupying the body positions and the Co III 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 {Mn III 8 Dy III 8 } (1) & {Mn III 8 Y III 8 }(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 Dy III ,(8,7) for Tb III , (10,7) for Ho III ANO…RCC TZVP for Dy, Tb & Ho g x g y g z U eff {Dy 2 Co 2 }(8) 0.0 0.0 39.8612 112.2 K {Tb 2 Co 2 }(9) 0.0 0.0 34.4534 4.8 K {Ho 2 Co 2 }(10) 0.0 0.0 21.1565 8.7 K The QTM is lower in the {Co 2 Dy 2 } 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 χ M T product (at H = 1 T) for 8- 10 from room temperature to 1.8 K is indicative of the presence of AF interactions.