Ancillary-Ligand-Assisted Variation in Nuclearities Leading to the Formation of Di-, Tri-, and Tetranuclear Copper(II) Complexes with Multifaceted Carboxylate Coordination Chemistry

Abstract

The self-assembly of a carboxylate-based dinucleating ligand, N,N′-bis[2-carboxybenzomethyl]-N,N′-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol (H3cpdp), and copper(II) ions in the presence of various exogenous ancillary ligands results in the formation of the new dinuclear complex [Cu2(cpdp)(μ-Hisophth)]4·2H2isophth·21H2O (1), trinuclear complex [Cu3(Hcpdp)(Cl)4] (2), and tetranuclear complex [Cu4(cpdp)(μ-Hphth)(μ4-phth)(piconol)(Cl)2]·3H2O (3) (H2phth = phthalic acid; H2isophth = isophthalic acid; piconol = 2-pyridinemethanol; Cl– = chloride). In methanol–water, the reaction of H3cpdp with CuCl2·2H2O at room temperature leads to the formation of 2. On the other hand, 1 and 3 have been obtained by carrying out the reaction of H3cpdp with CuCl2·2H2O/m-C6H4(CO2Na)2 and CuCl2·2H2O/o-C6H4(CO2Na)2/piconol, respectively, in methanol–water in the presence of NaOH at ambient temperature. All three complexes have been characterized by elemental analysis, molar electrical conductivity and magnetic moment measurements, FTIR, UV–vis spectroscopy, and PXRD, including single-crystal X-ray structural analyses. The molecular structure of 1 is based on a μ-alkoxide and μ-isophthalate-bridged dimeric [Cu2] core; the structure of 2 represents a trimeric [Cu3] core in which a μ-alcohol-bridged dinuclear [Cu2] unit is exclusively coupled with a [CuCl2] species by two μ:η1:η1-syn-anti carboxylate groups forming a triangular motif; the structure of 3 embodies a tetrameric [Cu4] core, with two copper(II) ions in a distorted-octahedral coordination environment, one copper(II) ion in a distorted-trigonal-bipyramidal coordination environment, and the other copper(II) ion in a square-planar coordination environment. In fact, 2 and 3 represent rare examples of copper(II)-based multinuclear complexes showing outstanding features of rich coordination chemistry: (i) using a symmetrical dinucleating ligand, trinuclear complex 2 is generated with four- and five-coordination environments around copper(II) ions; (ii) the unsymmetrical tetranuclear complex 3 is obtained by using the same ligand with four-, five- and six-coordination environments around copper(II) ions; (iii) tetracopper(II) complex 3 shows four different bridging modes of carboxylate groups simultaneously such as μ:η2, μ:η1:η1, μ3:η2:η1:η1, and μ4:η1:η1:η1:η1, the μ4:η1:η1:η1:η1 mode of phthalate being unprecedented. The formation of these [Cu2], [Cu3], and [Cu4] complexes can be controlled by changing the exogenous ancillary ligands and pH of the reaction solutions, thus allowing an effective tuning of the self-assembly. The magnetic susceptibility measurements suggest that the copper centers in all three complexes are antiferromagnetically coupled. The thermal properties of 1–3 have been investigated by thermogravimetric and differential thermal analytical (TGA and DTA) techniques, indicating that the decomposition of all three complexes proceeds via multistep processes.

Structures and Properties of a Series of High-Spin [CoII2] Complexes Supported by Ancillary Benzoate, Ortho-Hydroxybenzoate, and Para-Hydroxybenzoate Ligands

“…As depicted in Chart , the alkoxide and carboxylate groups of H 3 cpdp exhibit a number of coordination modes (A–F) during complexation with different metal ions. Among them, the coordination modes C, D, E, and F are very attractive resulting in the formation of Cu­(II)- and Zn­(II)-based tri-, tetra, hexa-, octa-, and decanuclear complexes with fascinating architectures. ,,, In view of that, dinuclear Co­(II) complexes 1–3 were synthesized following the routes outlined in Scheme . Indeed, complexes 1–3 were obtained directly by one-pot synthesis, starting from H 3 cpdp and Co­(BF 4 ) 2 ·6H 2 O in the presence of C 6 H 5 CO 2 Na, o -C 6 H 4 (OH)­CO 2 Na or p -C 6 H 4 (OH)­CO 2 Na as ancillary ligands under ambient conditions.…”

“…Among them, the coordination modes C, D, E, and F are very attractive resulting in the formation of Cu(II)-and Zn(II)-based tri-, tetra, hexa-, octa-, and decanuclear complexes with fascinating architectures. 57,62,64,65 In view of that, dinuclear Co(II) complexes 1−3 were synthesized following the routes outlined in Scheme 1. Indeed, complexes 1−3 were obtained directly by one-pot synthesis, starting from H − has very poor coordinating ability with metal ions, and hence, it can assemble mostly outside the coordination sphere.…”