Abstract
Reaction between NiCl2·6H2O, 2-hydroxy-4-methyl-6-phenyl-pyridine-3-amidoxime (H2L), benzoic acid, and M(NO3)3·6H2O (M = Gd, Y) in MeCN under basic conditions yields the complexes [NiII4GdIII5(PhCOO)10(HL)4(HLzw)4(OH)2(NO3)2]Cl·13.6MeCN·H2O (1·13.6MeCN·H2O) and [NiII4YIII5(PhCOO)10(HL)4(HLzw)4(OH)2(NO3)1.5(H2O)0.5]0.5Cl(NO3)·3H2O (2·3H2O). Both clusters display similar structures, consisting of a bell-shaped {NiII4MIII5} unit, in which a linear "zigzag" {Ni4} subunit bisects the central {MIII5} "ring". Direct (dc) and alternating current (ac) magnetic susceptibility measurements carried out in the 2-300 K temperature range for complexes 1 and 2 revealed ferromagnetic intermolecular interactions, while heat-capacity measurements for the Gd analogue suggest that complex 1 lowers its temperature from T = 9.6 K down to 2.3 K by adiabatically demagnetizing from Bi = 7 T to Bf = 0.
Highlights
The field of molecular magnetism has become a multidisciplinary, dynamic field of science for which a breadth of potential applications can be envisioned
Solid state magnetic measurements were carried out on freshly prepared samples of 1 and 2 on a Quantum design SQUID MPMS-XL magnetometer equipped with a 7 T DC magnet at the University of Edinburgh, while the observed paramagnetic susceptibilities were corrected using Pascal’s constants
The formation of the enneanuclear species 1 may be summarized in the following chemical eqn (1): 4 NiCl2·6H2O + 5 Gd(NO3)3·6H2O + 8 H2L + 10 PhCOOH [Ni4Gd5(PhCOO)10(HL)4(HLzw)4(OH)2(NO3)2]Cl + 13 NO3- + 7 Cl- + 20 H+ + 51 H2O (1)
Summary
The field of molecular magnetism has become a multidisciplinary, dynamic field of science for which a breadth of potential applications can be envisioned. Structural complexity leads to an increase in the number of intramolecular exchange pathways, and to obvious consequences for interpreting and understanding magnetic behavior Despite these difficulties, numerous examples of such large cages exist, including an {FeIII10GdIII10} cyclic complex with an S = 60 ground-state,[3] a giant {FeIII18FeII24} nanocluster with an S = 45 spin ground-state,[4] a {MnIII12MnII7} cluster with an S = 83/2 ground-state,[5] a {MnIII11MnII6} complex with an S = 37 ground-state,[6] and most recently a [Ni21Gd20] cage displaying a remarkable (field-induced) S = 91 ground state.[7] In this work, the isolation, characterization and investigation of the magnetic behavior of an enneanuclear [NiII4GdIII5] cluster are reported, built by employing the amidoxime ligand 2hydroxy-4-methyl-6-phenyl-pyridine-3-amidoxime, H2L (Scheme 1), which was previously employed succesfully in heterometallic chromium chemistry yielding two CrIII-centered heterometallic [MII6CrIII] (M= Ni, Co) wheels.11a The complex [NiII4GdIII5(PhCOO)10(HL)4(HLzw)4(OH)2(NO3)2]Cl·3.6MeCN·H2O (1.13.6MeCN·H2O; zw = zwitter ion) displays an unusual bell-shaped[8] metal-topology, and dominant ferromagnetic intramolecular exchange interactions
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