Formation of Coordination Polymers or Discrete Adducts via Reactions of Gadolinium(III)–Copper(II) 15-Metallacrown‑5 Complexes with Polycarboxylates: Synthesis, Structures and Magnetic Properties

Reactions of the copper(II)–gadolinium(III) 15-metallacrown-5 complex [GdCu5(Glyha)5(NO3)2(H2O)6](NO3) (Glyha2– = dianion of glycinehydroxamic acid) with different di/tricarboxylates (1,3-phthalate, 1,4-phthalate, biphenyl-4,4′-dicarboxylate, citrate) resulted in formation of different types of products: {[(GdCu5(Glyha)5(H2O)2)(GdCu5(Glyha)5(H2O)3)(1,3-bdc)3]·16H2O} n (1), {[(GdCu5(Glyha)5(H2O)3)2(1,4-bdc)2](1,4-bdc)·8H2O} n (2), {[(GdCu5(Glyha)5(H2O)4)2(1,4-bdc)3]·8H2O} n (3), [GdCu5(Glyha)5(Citr)(H2O)4]·7H2O (4), {[GdCu5(Glyha)5(H2O)5](μ2-CO3)[Cu(Fgg)]}·7H2O (5) and [Cu(Gly)2(H2O)] n (6) (where bdc2– is the corresponding phthalate (benzenedicarboxylate), Citr3– is citrate, Fgg3– is the trianion of [(N-formylaminoacetyl)amino]acetic acid and Gly– is glycinate). Complexes 1–5 contain the [GdCu5(Glyha)5]3+ cation. Complexes 2 and 3 possess the same composition but differ by the mode of p-phthalate coordination to the [GdCu5(Glyha)5]3+ unit. In compounds 1–3, metallacrown cations are linked by the corresponding phthalates in 1D, 1D and 2D polymers, respectively, whereas 4 and 5 are discrete molecules. Compound 5 is the product of a multistep reaction, which finally involves atmospheric CO2 capture. Hydrolysis of hydroxamate in this reaction is confirmed by isolation of a mononuclear copper glycine complex 6. The χM T vs T data for 1 were fitted using a model based on the Hamiltonian Ĥ (GdCu5) = −2J 1(S 1 × S Gd + S 2 × S Gd + S 3 × S Gd + S 4 × S Gd + S 5 × S Gd) – 2J 2(S 1 × S 2 + S 2 × S 3 + S 3 × S 4 + S 4 × S 1 + S 5 × S 1. The best fit corresponded to J 1 = +0.60(2) cm–1, J 2 = −61.0(5) cm–1 and zJ′ = −0.035(4) cm–1. Complex 1 is the first example of a 15-metallacrown-5 system, for which numerical values of exchange parameters have been reported. The isotherm for methanol absorption by compound 1 at 293 K was typical for microporous sorbents, whereas ethanol sorption was negligibly small.