Supramolecular Maleate Adducts of Copper(II) 12‐Metallacrown‐4: Magnetism, EPR, and Alcohol Sorption Properties

Abstract

With maleate, [Cu5(ahpha)4]2+ gives two complexes, [Cu5(ahpha)4(DMF)2](MalH)2·2DMF (1) and [Cu5(ahpha)4(MalH)2] (2) (ahpha2– is 3‐amino‐3‐hydroximinopropane hydroxamate; MalH2 is maleic acid). Both 1 and 2 contain non‐oligomerized [Cu5(ahpha)4]2+ metallacrown blocks; in 1, two MalH– are bound to [Cu5(ahpha)4]2+ only via H‐bonds, while in 2, they coordinate to Cu2+. The X‐band EPR of 1 was observed at 20 K, 100 K, and 295 K. The EPR at 20 K was of an S = 1/2 ground state, while at room temperature anisotropic |ΔMs| = 1 and |ΔMs| = 2 resonances around 3200 G (g ≈ 2.19) and 1600 G (g ≈ 4.25) were observed for the Cu5 system, due to partial occupation of an S = 3/2 state. The room temperature EPR of 1 was simulated as the weighted sum of the spectra of its various S = 1/2, 3/2, and 5/2 states. Its magnetic behavior was fitted with a χMT vs. T model using a spin Hamiltonian accounting for central–peripheral (J1), peripheral–peripheral (J2) Cu2+–Cu2+ and intercrown (zJ′) spin interactions, yielding J1 = –156(4) cm–1, J2 = –63(1) cm–1, and zJ′ = –4.5(3) cm–1. For sorption of methanol and ethanol vapors at 293 K by a desolvated polycrystalline sample of 1, the shape of the adsorption and desorption isotherms indicated a “gates opening” phenomenon.

Complex formation of copper(ii), nickel(ii) and zinc(ii) with ethylophosphonoacetohydroxamic acid: solution speciation, synthesis and structural characterization

“…3), which strongly supports the model without the presence of any mononuclear Cu(II) complexes which are expected to be EPR active. A silencing of the EPR signal is typical for polynuclear Cu(II) species, and was earlier observed for the majority of Cu(II) 12-MC-4 complexes; 1, 22,25,26 to date only two 12-MC-4 were revealed not EPR-silent, but both measured at 4-6 K. 43,44 According to the potentiometric calculations, the species dominating in solution from pH 4 to 9 is [Cu 5 (LH -1 ) 4 ] 2-, and the EPR behaviour is consistent with this finding. The stability of the MC species formed by PAHEt is comparable to that reported for MACZ ligand 26 (Table 2), in which a carboxylate group was introduced in the β-position with respect to the hydroxamic function.…”

“…In its turn, this would result in the formation of extended polynuclear assemblies of higher nuclearity with MC core. Unlike numerous MC-based assemblies obtained with the use of axial binding of MC moieties, in particular, 1-, 2-and 3D-coordination polymers, including porous MOFs, [23][24][25] the possibility to obtain of discrete exchange clusters or layered assemblies through of in-plane exo-coordination to MC is still poorly explored.…”

Magnetic Properties of LnIII–CuII 15‐Metallacrown‐5 Dimers with Terephthalate (LnIII = Pr, Nd, Sm, Eu)

“…There is a putative correlation between J Cu–Cu and Cu–O–Cu angle in 9‐metallacrown‐3 systems, but there is no obvious relationship between any structural parameter and J Cu–Cu for 12‐metallacrown‐4 and 15‐metallacrown‐5 systems. However there is a modest trend for J Cu–Cu values decreasing from 9‐metallacrown‐3 to 15‐metallacrown‐5 systems , , , …”

“…In‐depth studies of the magnetic properties of metallamacrocyclic compounds have given widely spread typical values of exchange parameters for copper(II) and nickel(II) 12‐metallacrown‐4 complexes , . However, there is still a paucity of quantitative magnetochemical data for heteronuclear metallacrowns.…”

“…Information About Composition: There are minor differences (in the solvent composition) in the composition of 1 – 4 obtained from the X‐ray structure determination for a single crystal taken out from a mother liquor and from elemental analysis performed for a bulk polycrystalline air‐dried sample. Such differences are quite typical for complexes possessing large voids in their lattices,, , or that suffer from substantial disorder of the solvating molecules. The composition obtained from X‐ray analysis was used for crystal structure description, while the compositions obtained from elemental analysis for the polycrystalline samples were used for the description of their magnetic properties.…”