Synthesis, magnetic properties, and STM spectroscopy of an unprecedented octanuclear chloro-bridged nickel(ii) double cubaneCCDC reference number 850029. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c2dt12007kDedicated to Professor Rudi van Eldik on the occasion of his 65th birthday

• Main Authors: Scheurer, Andreas, Gieb, Klaus, Alam, Mohammad S, Heinemann, Frank W, Saalfrank, Rolf W, Kroener, Wolfgang, Petukhov, Konstantin, Stocker, Michael, Mller, Paul
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c2dt12007k

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 ( 3 -OH)Cl 3 (HL) 3 } 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 ( 3 -OH)( 3 -O) 3 (OH) 3 (N) 3 (Cl) 3 } 2 -Cl) 2 ] core and crystallizes in the monoclinic space group P 2 1 / c with a = 18.292(2), b = 19.8972(5), c = 23.295(2) , = 98.408(6), V = 8387.3(8) 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 HOMOLUMO gap of approximately 0.8 V. The octanuclear chloro-bridged nickel( ii ) double cubane [({Ni II 4 ( 3 -OH)Cl 3 (HL) 3 } 2 -Cl) 2 ] ( 4 ) (R = n -butyl) shows an easy-axis type SMM behavior with two different blocking temperatures due to the interactions between the two {Ni4} subunits.