dlf Complexes with Uniform Coordination Geometry:  Structural and Magnetic Properties of an LnNi2 Core Supported by a Heptadentate Amine Phenol Ligand

Abstract

The synthesis and physical characterization of a series of lanthanide (Ln(III)) and nickel (Ni(II)) mixed trimetallic complexes with the heptadentate (N(4)O(3)) amine phenol ligand H(3)trn [tris(2'-hydroxybenzylaminoethyl)amine] has been accomplished in order to extend our understanding of how amine phenol ligands can be used to coaggregate d- and f-block metal ions and to investigate further the magnetic interaction between these ions. The one-pot reaction in methanol of stoichiometric amounts of H(3)trn with NiX(2).6H(2)O (X = ClO(4), NO(3)) followed by addition of the corresponding LnX(3).6H(2)O salt, and then base, produces complexes of the general formula [LnNi(2)(trn)(2)]X.nH(2)O. The complexes were characterized by a variety of analytical techniques. Crystals of five of the complexes were grown from methanol solutions and their structures were determined by X-ray analysis: [PrNi(2)(trn)(2)(CH(3)OH)]ClO(4).4CH(3)OH.H(2)O, [SmNi(2)(trn)(2)(CH(3)OH)]NO(3).4CH(3)OH.2H(2)O, [TbNi(2)(trn)(2)(CH(3)OH)]NO(3).4CH(3)OH.3H(2)O, [ErNi(2)(trn)(2)(CH(3)OH)]NO(3).6CH(3)OH, and [LuNi(2)(trn)(2)(CH(3)OH)]NO(3).4.5CH(3)OH.1.5H(2)O. The [LnNi(2)(trn)(2)(CH(3)OH)](+) complex cation consists of two octahedral Ni(II) ions, each of which is encapsulated by the ligand trn(3)(-) in an N(4)O(2) coordination sphere with one phenolate O atom not bound to Ni(II). Each [Ni(trn)](-) unit acts as a tridentate ligand toward the Ln(III) ion via two bridging and one nonbridging phenolate donors. Remarkably, in all of the structurally characterized complexes, Ln(III) is seven-coordinate and has a flattened pentagonal bipyramidal geometry. Such uniform coordination behavior along the whole lanthanide series is rare and can perhaps be attributed to a mismatch between the geometric requirements of the bridging and nonbridging phenolate donors. Magnetic studies indicate that ferromagnetic exchange occurs in the Ni(II)/Ln(II) complexes where Ln = Gd, Tb, Dy, Ho, or Er.

Metal complexes as potential ligands: The deprotonation of aminephenolate metal complexes

“…The positioning of the pendant phenoxide in these complexes which coordinates solely to potassium facilitates the dimerisation of the motif. A similar result is observed for the lanthanoids [3][4][5][6]. However, here the lower charge of the potassium fulfils the charge balance on the metalloligand and aggregation thus takes place around a centrosymmetric di-potassium core.…”

“…The synthetic protocols employed to produce these compounds routinely use non-coordinating bases such as triethylamine to deprotonate the ligand during the reaction [3,4]. Our previous work on tris-(2-hydroxybenzyl)-aminoethylamine (H6TrenSal 1 ; Fig.…”

“…Our interest in this process stems not just from our desire to design and synthesise further multimetallic complexes but to try an understand why [(H6Tren-Sal)Cu] + and [(H6TrenSal)Zn] + (Fig. 1c) do not readily form trimetallic lanthanoid complexes similar to the corresponding nickel complex [3][4][5][6]. It is likely that the altered reaction pathway stems either from the nature of the uncoordinated phenolates or the manner in which the ligands deprotonate during reaction.…”

Magnetic molecular materials with paramagnetic lanthanide ions

“…It seems that the magnetic coupling properties are mainly governed by the nature of the chemical linker between the spin carriers, but not always right either. For example, ferromagnetic couplings happened for Mn( Ⅲ ) [61] , Fe( Ⅱ ) [62] , Co(Ⅱ) [63] and Ni(Ⅱ) [64][65][66] when the bridges between Gd(Ⅲ) and TM ions were oxygen atoms of a series of Schiff base derivatives. However, both ferro-and antiferromagnetic interactions were found for paramagnetic V(Ⅳ) ions [67,68] .…”

[GdNi6] and [LaNi6]: High‐Field EPR Spectroscopy and Magnetic Studies of Exchange‐Coupled Octahedral Clusters

“…The quasi-systematic ferromagnetic nature of the coupling between Cu II and Gd III has been corroborated by a considerable amount of experimental data, [16] and a recent report has established the theoretical grounds of this observation. [17] In contrast, the magnetic exchange between Ni II and Gd III -always found to be ferromagnetic so far [18][19][20][21][22][23] --has not been explored as extensively. The few systems where this coupling has been analyzed are almost all dinuclear compounds.…”