Synthesis, magnetic properties, and STM spectroscopy of an unprecedented octanuclear chloro-bridged nickel(ii) double cubane

Abstract

Reaction of nickel(II) chloride hexahydrate with N-n-butyldiethanolamine H(2)L (3) in the presence of LiH in anhydrous THF leads to the formation of the unique octanuclear chloro-bridged nickel(II) double cubane [({Ni(II)(4)(μ(3)-OH)Cl(3)(HL)(3)}μ(2)-Cl)(2)] (4) in 57% yield. According to single crystal X-ray structure analysis, complex 4·4CH(2)Cl(2) possesses a [({Ni(4)(μ(3)-OH)(μ(3)-O)(3)(OH)(3)(N)(3)(Cl)(3)}μ(2)-Cl)(2)] core and crystallizes in the monoclinic space group P2(1)/c with a = 18.292(2), b = 19.8972(5), c = 23.295(2) Å, β = 98.408(6)°, V = 8387.3(8) Å(3), and four molecules in the unit cell. The analysis of the SQUID magnetic susceptibility data identified 4 as a weakly coupled dimer (J(1) = 14.5 K, J(2) = -0.6 K) with a ground state of S = 0, resulting from two S = 4 states of each {Ni(4)} subunits. Although complex 4 does not show an ac out-of-phase signal in a zero dc field at temperatures of 1.8 K and higher, low-temperature magnetization measurements revealed that complex 4 is a single-molecule magnet and shows hysteretic magnetization characteristics with typical temperature and sweep-rate dependencies. The eye-catching feature of complex 4 is the presence of two different blocking temperatures (0.9 K around zero field and 1.3 K at higher fields). The origin of this highly unusual behavior can be assigned to the dimer-nature of the interaction between the two S = 4 units. Furthermore STM and current imaging tunnelling spectroscopy (CITS) were performed on aggregates of 4 drop-coated on highly oriented pyrolytic graphite (HOPG) surfaces. CITS measurements show a strong contrast in the area of the nickel centers and a HOMO-LUMO gap of approximately 0.8 V.

Topological insights in polynuclear Ni/Na coordination clusters derived from a schiff base ligand

“…The interest in polynuclear Ni(II) coordination chemistry was first captured when the first Ni(II)-based SMM, a Ni 12 complex, was reported in 2001 by Cadiou et al [24]. Ever since, there have been a number of homometallic polynuclear Ni II CCs with high nuclearities including, Ni 5 [7,25], Ni 6 [26], Ni 7 [27,28], Ni 8 [29][30][31][32], Ni 9 [33,34], Ni 11 [35], Ni 12 [7], Ni 13 [36], Ni 14 [37], Ni 20 [38], Ni 21 [39], Ni 24 [40] and Ni 26 [41], and many of these display interesting magnetic properties including ferromagnetic, ferrimagnetic coupling, diamagnetism and SMM behaviour.…”

A Database of Topological Representations of Polynuclear Nickel Compounds

“…The user can also search for a given topological motif within more complicated cluster skeletons by using the TOPOS subgraph search procedure. Recently reported high nuclearity Ni clusters such as Ni 8 ,52 Ni 8 ,53 Ni 9 ,54 Ni 13 ,55 and Ni 20 56 suggest that Ni chemistry has started to receive more attention; it is thus anticipated that several compounds will be reported so that the need for this database is imperative. With the knowledge gained by analyzing and classifying the coordination compounds of Mn, Co, and Ni, our next target is to extend this classification to Fe chemistry.…”

Synthesis, Magnetic Properties, and X‐ray Spectroscopy of Divalent Cobalt(II) and Nickel(II) Cubanes [MII4(HL2)4(OAc)4]

“…In previous work, we demonstrated that N ‐substituted diethanolamines8,9 are an important class of ligands that stabilize supramolecular aggregates with fascinating structural diversities. In this context, we recently reported on the synthesis of the octanuclear dichloro‐bridged nickel(II) double cubane [({Ni II 4 (μ 3 ‐OH)Cl 3 (HL 1 ) 3 }μ 2 ‐Cl) 2 ] ( 1 ; Figure 1)7e and the tetranuclear cobalt(II) cubanes [Co II 4 Cl 4 (HL 1 ) 4 ] (not shown)7c starting from N ‐ n ‐butyldiethanolamine (H 2 L 1 , 2 ) and an appropriate metal source.…”