Heterometallic 3d–4f Complexes as Single‐Molecule Magnets

Abstract

Heterometallic 3d-4fc omplexes are being investigated, for some time, as being useful in molecular magnetism, particularly as single-molecule magnets (SMMs). This interest is primarily because of the possibility of an increased ligand-mediated super-exchange phenomenon between the 3d and 4f metal ions. Such an interaction, apart from bestowing af avorable ground-state spin to the complex, also assists in reducing quantum tunneling of magnetization that is widely prevalenti nS MMs making them to lose magnetization. However,a ssembling both 3d as well as 4f ions using same ligand system is challenging and involves the design of multi-site coordination ligandsw ith specific coordination compartments for the 3d and the 4f metal ions while at the same time allowing these disparate metal ions to be linked to each other through ab ridging ligatinga tom. This review presents as ummary of the 3d-4f complexes primarily derived from the author's work while alluding to importante xamplesf rom the literature. We also provide an outlookf or the future design of such complexes.[a] Dr.A .Dey, Prof. V. Chandrasekhar 4434Minireview dro-imidazol-2-ylidenea nd DmpN 3 = 2,6-dimesitylphenyl azide] which exhibit slow magnetic relaxation with U eff values of 450 and 413 cm À1 respectively. [13][14][15] Similarly,t here have been reports on mononuclear lanthanide complexes [12a, 16] ever since the seminalp aper on the first lanthanide based SMM in 2003, (Bu 4 N)[Ln III (Pc) 2 ] [17] [Ln III = Tb III (7)a nd Dy III (8); Pc = phthalocyaninato].R ecently,t he complexes [(Cp ttt ) 2 Dy III ][B(C 6 F 5 ) 4 ] [18] (9) (Cp ttt [19] (10)h ave been reported with blockingt emperatures of 60 and 80 Kr espectively.C omplex 10 holds the record for the highest reported energy barrier U eff = 1541 cm À1 for the reversal of magnetization.One of the problemsa ssociated with SMMs is that the magnetization can be lost by av ariety of ways including quantum tunneling mechanism (QTM) which shortcuts the energy barriers of relaxation. [6b] This is an important impediment and progress in this field is dependent on minimizing or eliminating QTM. There are many strategies to do this including assembling mononuclear complexes possessing point-group symmetries such as C 1v , D 1h , S 8 (I 4 ), D 4d , D 5d and D 5h[12a] or by increasing the ferromagnetic coupling between the adjacent lanthanide centers,a ne xample of this being the dinuclearc omplex [K(18crown-6)]{[((Me 3 Si) 2 n) 2 (THF)Dy III ] 2 (m-h 2 :h 2 -N 2 )} (11)w here the radicall igand, N 2 3À , [20] facilitates af erromagnetic exchange between the two lanthanide centers. [21] Another strategy is to involve heterometallic transition metal/lanthanide complexes where as uper-exchange ferromagnetic interaction between the lanthanide and transition metal ion can mitigate QTM. [22] Accordingly,t he first 3d-4fb ased SMM, a[ Cu II 2 Tb III 2 ]( 12) complex, was reported by Osa and co-workers in 2004. [23] Murray and co-workers have successfully utilized this strategy for av ariety of complexes with {Cr II...

Trinuclear NiII-LnIII-NiII Complexes with Schiff Base Ligands: Synthesis, Structure, and Magnetic Properties

“…Complexes [(NiL 1 ) 2 Ln](ClO 4 ) (H 3 L 1 = (S)P[N(Me)N=CH-C 6 H 3 -2-OH-3-OMe] 3 , Ln III = La-Er, except Pm) [11,12], [(NiL 2 ) 2 Gd](NO 3 ) (H 3 L 2 = 6,6 -((1E)-((2-(((E)-(2-hydroxy-3-methoxybenzylidene)amino)methyl)-2-methylpropane-1,3-diyl)bis(azanylylidene))bis(methanyl ylidene))bis(2-methoxyphenol) [13], [(NiL 3 ) 2 Ln](NO 3 ) (Ln III = Gd, Tb, Dy) and [(NiL 3 ) 2 Dy](ClO 4 ) (H 3 L 3 = 6,6 ,6"-((1E,1 E)((nitrilotris(ethane-2,1-diyl))tris(azanylylidene))tris(methanylylidene))tris(2methoxyphenol) [14], [(NiL 4 ) 2 Ln(H 2 O) 1/0 ](ClO 4 ) (H 3 L 4 = 6,6 ,6"-((1,4,7-triazonane-1,4,7-triyl)tris(methyl ene))tris(2-methoxy-3-methylphenol), Ln III = Y, La, Ce-Lu, except Pr, Pm, Yb) [15], [(NiL 5 )Tb](ClO 4 ) (H 3 L 5 = 6,6 ,6"-((1,4,7-triazonane-1,4,7-triyl)tris(methylene)) tris (2,3-dimethylphenol) [16], [(NiL 6…”

“…3 ) 2 Ln](NO 3 ) (HL 6 = (Z)-2-methoxy-6-((phenylimino)methyl)phenol, Ln III = La, Pr, Gd, Tb) [17,18], and [{Ni{L 7 ) 1.5 } 2 Ln(OH)] (H 2 L 7 = 7,7 -(ethane-1,1-diyl)bis(quinolin-8-ol), Ln III = Eu, Tb, Gd) [19] Each of the terminal Ni II ions in the above complexes [11][12][13][14][15][16][17][18][19][20][21][22][23][24] is coordinated to three phenolato oxygen atoms and three nitrogen atoms, consisting of in situ formed (NiL) − metalloligand. The coordination geometry around the Ni II ions is distorted octahedral except in the case of [{Ni{L 7 ) 1.5 } 2 Ln(OH)] [19] in which the N 3 O 3 atoms create a regular trigonal-antiprismatic geometry around the Ni II ions.…”

Hexanuclear Co4Dy2, Zn4Dy2, and Co4Y2 Complexes with Defect Tetracubane Cores: Syntheses, Structures, and Magnetic Properties

“…Recent development in SMMs reveals that the aggregation of 4f and 3d metals in a molecular entity is a promising strategy for assembling SMMs with higher energy barriers [31–33] . The heavy lanthanide ions like Dy III and Tb III possess large angular momentum in the ground multiplet state and strong magnetic anisotropy [34–37] .…”

Effect of the Alkaline Metal Ion on the Crystal Structure and Magnetic Properties of Heterometallic GdIII-VIV Complexes Based on Cyclobutane-1,1-Dicarboxylate Anions

“…The interest in the directed synthesis of heterometallic compounds where 3d and 4f metal ions are combined in a single molecule is caused by the wide range of physicochemical properties they exhibit, including luminescent properties [1,2], molecular magnetism [3,4], magnetocaloric effect [5][6][7][8][9], and catalytic activity [10][11][12]. In addition, studies on such heterometallic compounds are of fundamental concern in order to elucidate the exchange interactions between paramagnetic centers of different nature, 3d and 4f metal ions, and the effect of these interactions on the dynamic characteristics of a single-molecule magnet (SMM), for example, the magnitude of the energy barrier to magnetization reversal ∆ eff .…”