The Case of a Cu₄ Rhombus in Molecular Magnetism:  Preparation, Crystal Structure, and Magnetic Properties of [Cu₄(dpk·CH₃O)₄(CH₃O)₂](ClO₄)₂ (dpk·CH₃OH = Monomethylated Diol of Di-2-pyridyl Ketone), an Example of a Cluster Allowing the Determination of All Its Exchange Parameters, Ranging from Very Strong to Very Weak

Abstract

Treatment of [Cu2(O2CCH3)4(H2O)2] with 2 equiv of di-2-pyridyl ketone (dpk) in methanol followed by addition of 1 equiv of NaClO4 yields [Cu4(dpk·CH3O)4(CH3O)2] (ClO4)2 (1) in ∼75% yield (dpk·CH3O- = the monoanion of the monomethylated diol of dpk). The same complex has also been isolated from the 1:2:2 and 1:4:4 stoichiometries. The 1:2 reaction of Cu(ClO4)·6H2O with dpk in methanol affords the mononuclear complex [Cu(dpk·CH3OH)2](ClO4)2·2CH3OH (2) in ∼70% yield. Complex 1, C50H50Cl2Cu4N8O18, crystallizes in the tetragonal space group I41/acd with a = b = 15.551(1) Å, c = 48.938(3) Å, and Z = 8. Crystal data for 2: C26H32Cl2CuN4O14, monoclinic, space group P21/a, a = 12.923(1) Å, b = 12.969(2) Å, c = 9.655(1) Å, β = 92.78(1)°, Z = 2. The four CuII atoms in the cation of 1 are all coplanar, exhibiting a rhombic arrangement. The dpk·CH3O- ion behaves as a η1:η2:η1:μ2 ligand. In the cation of 2, the dpk·CH3OH ligand functions as a tridentate chelate toward the copper center, with the pyridyl nitrogens and the methylated oxygen being the ligated atoms. The magnetic properties of compound 1 are characteristic of prevailing antiferromagnetic interactions. The susceptibility data of 1 were fitted with a 3-J magnetic model, affording a very strong antiferromagnetic interaction (J 2 = −490(9) cm-1), a weak ferromagnetic interaction (J 1 = +22(4) cm-1), and a very weak antiferromagnetic interaction (J 3 = −0.36(1) cm-1). The energy spectrum of the states, the magnetization, and the EPR data of complex 1 are in line with an almost degenerate ground state with a magnetic component. An investigation of this degeneration is attempted.

Di(2‐pyridyl) Ketone Complexes of CuI‐ and CuII‐Containing Iodide and Thiocyanate Ligands: An Unusual Case of a Mixed‐Aldol Condensation

“…At ambient temperature, 3 was found to be paramagnetic with an isotropic g factor (g = 1.97), which is similar when compared to other copper complexes with dpk derivatives, where isotropic factors varied from g = 2.00-2.06. [32,33] An effective magnetic moment of 1.81 μ B per Cu II ion, as expected for non-interacting Cu II d 9 ions. [25] The magnetic moment increased to 1.96 μ B at 40 K. The μ eff vs. T (K) plot shows an increase in μ eff as the temperature is lowered, followed by a steep drop at low temperatures (40 K) which is characteristic of ferromagnetic coupling [34] and is confirmed by the positive J value of +45.2 cm -1 .…”

Structural and Magnetic Characterization of a Linear Trinuclear Copper Complex Formed through Ligand Sharing

“…The resulting expression of the molar magnetic susceptibility in the βH/k B T ϽϽ 1 approximation, with an additional term to take into account a Temperature-Independent Paramagnetism (TIP), is given in Equation (2). (2) The best set of parameters obtained (full line in Figure 3) was J 1 ϭ Ϫ511(2) cm…”

Di-μ-iodido-bis{[hydroxy(methoxy)bis(2-pyridyl)methane-κ3N,O,N′]iodidocadmium(II)}

“…For general background to metal complexes with bis(2pyridyl)ketone or derivative ligands, see: Bandoli et al (1994); Breeze et al (1996); Crowder et al (2004); Hemmert et al (1999); Katsoulakou et al (2002); Kavounis et al (1996); Padhi & Sahu (2008); Papadopoulos et al (1996); Rattanaphani & McWhinnie (1974); Serna et al (2001); Sommerer et al (1993); Tangoulis et al (1997). Table 1 Selected bond lengths (Å ).…”