Effects of Metal Doping on the Spin-Crossover Properties of an Iron(II) Complex with Extended π-Conjugated Schiff-Base Ligand Having an N4O2 Donor Set

Abstract

The spin-crossover (SCO) complex [Fe(qnal) 2 ]¢CH 2 Cl 2 (1), (Hqnal: N-(8¤-quinolyl)-2-hydroxy-1-naphthaldimine) with an N 4 O 2 donor set, has been synthesized and characterized. Investigation of magnetic properties shows that the complex exhibits an abrupt and complete spin transition with a 5 K wide thermal hysteresis loop. The X-ray diffraction analysis of complex 1 reveals that the molecules are connected into a quasi one-dimensional chain through extended ³³ interactions between aromatic rings of ligands. The effects of metal doping on SCO properties have been investigated in the mixed-metal system [Fe 1¹x M x (qnal) 2 ]¢CH 2 Cl 2 (M = zinc(II) and nickel(II)). The results reveal that metal doping increases the gradual character of spin transition, and no marked differences found between zinc and nickel doping, which suggest the dominant effect of the doping-degree (concentration) rather than metal species on cooperativity. However, the metal doping shows different effects on critical temperature (T 1/2 ), where a more pronounced descending of T 1/2 is observed in response to increased Zn-doping than in Ni-doping, indicating the noticeable consequence of internal pressure due to the different radii of doping metal ions.Since the discovery of the first spin-crossover (SCO) compound, 1,2 such complexes have aroused more and more attention for potential applications in molecular switches or in data storage devices.37 SCO is not only induced by external stimulus (temperature, pressure, light irradiation, or magnetic field) but is altered by internal constraints such as structural changes of molecules and crystal lattices. In the solid state, SCO behavior can be understood as an entropically driven phenomenon, 8 which is favored by large structural changes during the process. Because of the large change in metalligand bond lengths between the HS and LS states, iron(II)/N-ligand combinations have the possibility to induce large cooperative spin transition between spin centers.9 Hence SCO is frequently observed in complexes containing iron(II) with an N 6 coordination sphere but rare for compounds with N 4 O 2 1013 or N 4 S 2 14 donor sets. In the solid state, spin transitions between LS and HS states depend strongly on cooperativity, which is sensitive to the coupling between the adjacent spin centers, metaldonor bond length, and the crystal lattice vibrations. 15 Hence, it is possible for these complexes to affect a spin transition in a certain range by variation of the intermolecular interaction of compounds. Metal doping is an available strategy to control and adjust these interactions. Although a number of studies have examined metal-doping behaviors in iron(II) complexes exhibiting thermal spin crossover, 1624 few studies have investigated SCO iron(II) species with N 4 O 2 donors.In the present work, we investigate experimentally metaldoping effects on the SCO properties of [Fe(qnal) 2 ]¢CH 2 Cl 2 , which we reported previously as an iron(II) complex with an N 4 O 2 donor set. 25 This complex exhibited com...

High-Temperature Cooperative Spin Crossover Transitions and Single-Crystal Reflection Spectra of [FeIII(qsal)2](CH3OSO3) and Related Compounds

“…A number of multifunctional materials from the [Fe(qsal) 2 ] cation have been reported to date [24][25][26][27][28][29][30][31][32][33]. Recently, heteroleptic Fe(III) compounds [34][35][36][37] as well as Fe(II) compounds [38][39][40][41][42][43][44] from the qsal and its derivatives, were also reported.…”

Metal Doping Effects on the Spin Transition properties of the Two-Dimensional Coordination Polymer {Fe^II_<i>x</i>M^II_1-<i>x</i>(3-Fluoropyridine)₂[Au^I(CN)₂]₂} (M = Mn, Co)

“…In terms of the critical temperature, the downward shift of Tc for doped samples can be explained as the chemical pressure to the Fe center. Similar ionic radius to Fe II (HS) act as growth constraint of the domain for LS state [19] because ionic radius of Fe II (LS) is the smallest in the crystal structure. (Mn II (HS) > Fe II (HS) > Co II (HS) > Fe II (LS)).…”

“…In just the past decade we reported the series of novel Hofmann-like compounds {Fe II (L)2[Au I (CN)2]2} (L = pyridine derivatives) which shows the various SCO behaviors [9][10][11][12][13][14][15][16]. In terms of the controlling of cooperativity, the metal doping effect have been proposed [17][18][19][20][21]. While many studies of the doping effect in SCO monomeric complexes have been reported, polymeric complexes have been investigated little [17].…”

Palladium complexes of NO type Schiff bases: synthesis, characterization and antioxidant activities

“…Among its various features, bioactivity of Schiff bases especially comes to the forefront in consequence of interactions and hydrogen bonds between the azomethine group and certain sites in the cell structure beside structural factors like solubility, dipole moment and cell permeability [14]. Also, electrons in sp 2 hybrid orbitals of azomethine nitrogen play a crucial role in biological applications [15].…”