Coordination Diversity in Mono- and Oligonuclear Copper(II) Complexes of Pyridine-2-Hydroxamic and Pyridine-2,6-Dihydroxamic Acids

Abstract

Solution and solid state studies on Cu(II) complexes of pyridine-2-hydroxamic acid (HPicHA) and pyridine-2,6-dihydroxamic acid (H2PyDHA) were carried out. The use of methanol/water solvent allowed us to investigate the Cu(II)-HPicHA equilibria under homogeneous conditions between pH 1 and 11. In agreement with ESI-MS indication, the potentiometric data fitted very well with the model usually reported for copper(II) complexes of α-aminohydroxamate complexes ([CuL](+), [Cu5(LH-1)4](2+), [CuL2], [CuL2H-1](-)), however with much higher stability of the 12-MC-4 species. A series of copper(II) complexes has been isolated in the solid state and characterized by a variety of spectroscopic methods, X-ray structure analysis, and magnetic susceptibility measurements. The ligands show the tendency to form bi- and trinuclear species with copper(II) ions due to the {(N,N'); (O,O')} bis-(bidentate) chelating-and-bridging mode involving (O,O')-hydroxamate chelate formation combined with (N,N') chelating with participation of the pyridine and hydroxamic nitrogen atoms, so that the hydroxamate groups play a μ2-(N,O)-bridging role. Molecular and crystal structures of three synthesized complexes [Cu3(PicHA-H)2(dipy)2](ClO4)2·4/3DMSO·2/3H2O (1), [Cu2(PyDHA)(dipy)2(ClO4)2]·DMF·H2O (4), and [Cu3(PyDHA-2H)(tmeda)3](ClO4)2 (5) (dipy, 2,2'-dipyridyl; tmeda, N,N,N',N'-tetramethyl-1,2-diaminoethane) have been determined by single crystal X-ray analysis. In 1, two trans-situated doubly deprotonated hydroxamic ligands play a {(O,O')(N,N')}-(bis)bidentate-bridging function forming bridges between the medial, Cu(2) (CuN4), and the terminal, Cu(1) and Cu(3) (CuN2O2), copper(II) ions; the chelating dipy ligands are coordinated to the latter. In 4, the ligand is coordinated in a classical (O,O')-hydroxamate chelating mode with the help of two separate hydroxamic groups while the central tridentate donor compartment remains vacant. In 5, the hydroxamate ligand is coordinated by the {(O,O');(N,N',N″);(O″,O"')}-tridentate-(bis)bidentate mode, bridging three copper(II) ions, while the chelating tmeda ligands are coordinated to all three copper(II) ions. Magnetic susceptibility measurements (1.7-300 K) of powdered samples of the trinuclear complexes 1 and 5 revealed strong antiferromagnetic coupling between the copper(II) ions mediated by the hydroxamate bridges.

Synthesis and Molecular Structures of CuII 15‐Metallacrown‐5 Complexes with Encapsulated CaII, PrIII and NdIII Ions

“…In contrast, the Ca II complex 1 is almost planar and the metal ion fits ideally to the size of the metallacrown cavity (the calculated ionic radius is 1.126 Å, r cavity = 1.127 Å). This fact determines high affinity of Cu II o ‐PicHA‐15‐MC‐5 framework towards Ca II ions, which is reflected, in particular, in persisting observations of the corresponding complex in ESI mass spectra of Cu II ‐ o ‐PicHA solutions (registered even in the presence of only trace quantities of calcium) 3a,12a. In 2 and 3 all the axial positions of Cu II and one axial position of Ln III ions appear to be occupied by pyridine molecules, what prevents, typical for metallacrowns, aggregation of the hexanuclear complexes into larger assemblies.…”

“…A prerequisite for the choice of the lanthanide ions was a limited structural data available on Ln ‐o‐picHA‐containing 15‐MC‐5 complexes, if compared with MC species of other ligands, like glycine hydroxamic acid (GlyHA) or phenylalanine hydrioxamic acid (PheHA) 12c,22. Interest to Ca II complexes is due to high affinity of Cu II o ‐PicHA‐15‐MC‐5 framework towards Ca II ions 3a,12a. Note, that only one X‐ray single crystal study of Ca II 15‐MC‐5 has been reported up to date 21.…”

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

“…The calculated pK a = 9.54 corresponds to the ionization of hydroxamic unit and it is in good agreement with the literature data obtained for similar systems. 1, 22,26 The phosphonic proton dissociation occurs much below pH 2 and the constant corresponding to this process could not be determined under our experimental conditions. [38][39][40] The potentiometric studies of Cu(II) (oxygen) Cu(II) CT transitions, 41,42 (Table 1, Figure S1).…”

“…Taking into account the possible applications of MCs in a number of research fields (in particular, synthesis of porous MOFs for selective absorption of guest molecules, luminescent materials, selective molecular recognition agents) [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] over the last two decades their chemistry has largely expanded, revealing that a key aspect in the control of the MCs scaffolds' topology and geometry is a proper match between the metal ion and the ligand. 3,[20][21][22] Apart numerous hydroxamate ligands functionalized in α-or β-position by NH 2 -group (e.g. glycinehydroxamic acid, Glyha, α-alaninehydroxamic acid, α-Alaha, leucinehydroxamic acid, Leuha, β-alaninehydroxamic acid, β-Alaha, Scheme 1), there are only a few examples of hydroxamic acids able to form MCs while having donor groups other than the amino group, and these include picolinehydroxamic acid, Picha, quinaldinehydroxamic acid, Quinha, salicylhydroxamic acid, Shi, and malonomonohydroxamic acid, MACZ (Scheme 1).…”

Crystal structure of N-hydroxyquinoline-2-carboxamide monohydrate

“…They are widely used in the preparation of metallacrowns (Golenya et al, 2012a;Gumienna-Kontecka et al, 2013;Safyanova et al, 2015) and as building blocks for synthesis of metal-organic frameworks and coordination polymers (Gumienna-Kontecka et al, 2007;Golenya et al, 2014;Pavlishchuk et al, 2010Pavlishchuk et al, , 2011.…”