Temperature induced spin crossover behaviour in mononuclear cobalt(II) bis terpyridine complexes
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.166
Temperature induced spin crossover behaviour in mononuclear cobalt(II) bis terpyridine complexes Venkata Nikhil Raj M.,1 Kishalay Bhar,1 Tanveer A. Khan,1 Surbhi Jain,1 Franc Perdih,2 Partha Mitra,3 Anuj K. Sharma1,* 1
Department of Chemistry, School of Chemical Sciences and Pharmacy, Central University of Rajasthan, NH-8, Bandarsindri-305817, Ajmer, Rajasthan, India
2
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, PO Box 537, SI-1000 Ljubljana, Slovenia
3 Department of Central Scientific Service (CSS), Indian Association for the Cultivation of Science, Kolkata 700 032, India
In Memory of Dr. Sunil G. Naik
Abstract
Dicationic cobalt(II) complexes of the type [Co(fterpy)2]c(X)2·nH2O·mCH3OH (fterpy = 4′-(2furyl)-2,2′:6′,2″-terpyridine; 1: X = PF6-, n = 1.5, m = 0; 2: X = ClO4-, n = 1, m = 1) have been isolated using self-assembly method and characterized by various spectroscopic techniques. In crystalline states both compounds exhibit gradual and incomplete spin crossover (SCO) behaviour in the temperature range 2-320 K. Various spin states of cobalt(II) in 1 have been confirmed by crystallographic evidences at 150 K and 293 K. A variation in counter anions and solvent molecules from 1 to 2 substantially improves the cooperativity among the spin active metal centres and thereby changing the nature of SCO behaviour.
*Corresponding author: Dr. Anuj K. Sharma (Email: [email protected])
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INTRODUCTION Spin crossover (SCO) materials1 which exhibit the bistable spin states2 have several practical applications like display3 and memory devices,4 nanoelectronic and spintronic devices,5 and pressure and temperature sensors.6 Moreover, switchable liquid crystals,7 nanoparticles,8 and thin films9 of SCO materials have also been realized. SCO phenomenon primarily exhibited by molecules containing an octahedrally coordinated transition metal ion with 3dn (n = 4-7) electronic configuration are capable of switching10 the spin states reversibly i.e., low spin (LS) l high spin (HS), by external stimuli like temperature,2 pressure11 or light irradiation.12 Molecular bistability or hysteresis2, 4, 13, 14 in SCO systems can be achieved via strong cooperativity among the spin active metal centres by supramolecular interactions2, 10, 13 and/or covalent bridges.4, 15 Iron(II)13, 16-20 and iron(III)21-23 have been by far the most studied metal ions in SCO, which is primarily due to their bistability features associated with drastic modification of physical properties like colour,4, 24 magnetic moment,1 and electrical resistance.8 In contrast, less attention has been paid to cobalt(II), 15, 25-29 perhaps owing to more gradual transitions. However, a handful number of cobal
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