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Korelacje magnetyczno-strukturalne dla układów molekularnych Cu-pikolinian oraz Cu-chinaldynian

Żurowska B.

Wiadomości Chemiczne

2008

[Z] 62, 1-2

9-48

This article concerns information on a synthesis, and structural and magnetic characterization of copper(II) compounds based on two classes of carboxylate ligands containing heterocyclic nitrogen atom of pyridine and quinoline i.e. pyridylo-2-carboxylate (2-picolinate, 2-pic) and quinolilo-2-carboxylate (2-chinaldynate, 2-qic), (Fig. 1, Tab. 1). Such compounds are products of a direct reaction of picolinate or chinaldynate acids with copper(II) salts [19, 37, 45, 48, 50, 51] and the hydrolytic [20, 52] and non hydrolytic [53] decomposition of ligands. Picolinate ion forms compounds of the general formula Cu(2-pic)2ź2H2O (1) or [Cu(2-pic)2Br2][(2-picH)2] (2). The compound of the formula Cu(pyridylo-2-carboxylate)2 exists in three polymorphic forms: monomeric (Cu(N2O2) chromophore) (3), and two (4 and 5) polymeric (1D) (Cu(N2O4) chromophore). With halide ions isostructural polymeric (2D) compounds of the formula Cu(2-pic)X, X= Cl (6) or Br (10) are formed (Cu(N2O2X) chromophore). However, with chinaldynate ion exist compounds of the stoichiometries: two isomeric forms of Cu(2-qic)2źH2O (7 and 8), which involve the same CuN2O3 chromophore (distortion isomers), and Cu(2-qic)X, X = Cl (9) and Br (11) compounds. The chloride and bromide (9 and 11) polymeric (2D) Cu(2-qic)X compounds, which crystal structure consists of two different chromophore Cu(N2O2X) and Cu(O2X2) are isostructural. Crystal structure of these copper-picolinate and copper-quinaldinate systems indicate, that carboxylate group in both ligands offers a variety of coordination modes leading to the formation of mononuclear and polynuclear compounds. The monomeric form of Cu(2-pic)2 (3) is an example of a square-planar copper(II) compound in which structure is achieved by important ?-? stacking intermolecular interaction. This interaction leads to antiferromagnetic coupling (J = -0.76 cm-1) [129]. The polymeric compounds of the formula Cu(2-pic)2 (4 and 5) are an example of an out-of-plane double carboxylato-bridged copper(II) compound resulting in the formation of an infinite chain. The magnetic properties revealed a weak intrachain antiferromagnetic coupling in both compounds (J = -0.73 and -1.04 cm-1 for 4 [48] and 5 [49], respectively). The structures of Cu(2-pic)X (6 and 10) and Cu(2-qic)X (9 and 11) compounds are based on syn-anti carboxylate bridge and additionally on halido-bridge. The carboxylate bridges transmit a weak ferromagnetic exchange (J < 0.5 cm-1) in both compounds [46, 47, 50]. For Cu(2-pic)X observed ferromagnetic coupling through dichloro-bridge (J = 15 cm-1) [46] is stronger than that through dibromo-bridge in bromide analog (J = 8.31 cm-1) [50]. For Cu(2-qic)X observed strong antiferromagnetic coupling through the single chloro-bridge (J = -57 cm-1) [47] is much weaker than that transmitted by the single bromo-bridge (J = -102.5 cm-1) [50]. The magnitude of the magnetic coupling through the non-covalent interactions (hydrogen bonds and ?-? stacking) is also discussed on the basis of the structural data [48, 49, 129, 130]. The magnitude of the exchange interactions between copper(II) ions are discussed on the basis of the molecular and crystal structures, in terms of bond properties and known theory of exchange [62-65, 100-104]. Keywords: copper(II), carboxylate ligands, halide ligands, structure, magnetism