Synthesis and magneto-structural studies on a new family of carbonato bridged 3d–4f complexes featuring a [CoII3LnIII3(CO₃)] (Ln = La, Gd, Tb, Dy and Ho) core: slow magnetic relaxation displayed by the cobalt(ii)–dysprosium(iii) analogue

Abstract

A new family of [3 + 3] hexanuclear 3d-4f complexes [(μ-CO){CoLnL(μ-OH)(OH)}]-(ClO)·mCHOH·nHO (1-5) [Ln = La (1), Gd (2), Tb (3), Dy (4), and Ho (5)] have been prepared in moderate to high yields (62-78%) following a self-assembly reaction between the ligand 6,6',6''-(nitrilotris(methylene))tris-(2-methoxy-4-methylphenol) (HL), Co(OAc)·4HO and the lanthanide ion precursors in the mandatory presence of tetrabutylammonium hydroxide. During the reaction, atmospheric carbon dioxide is fixed in the product molecule as a bridging carbonato ligand which connects all the three lanthanide centers of this molecular assembly through a rare η:η:η-μ mode of bridging as revealed from X-ray crystallography. The metal centers in all these compounds, except the Gd analogue (2), are coupled in antiferromagnetic manner while the nature of coupling in the CoGd complex is ferromagnetic. DFT calculations revealed that this ferromagnetic interaction occurs most likely by the Co-Gd superexchange, mediated via the bridging oxygen atoms. Only the Co-Dy compound (4) displayed a slow relaxation of the magnetization at a very low temperature as established by AC susceptibility measurements. The data provides an estimation of the activation energy U/k = 9.2 K and the relaxation time constant τ = 1.0 × 10 s.

Generalized Heisenberg-Type Magnetic Phenomena in Coordination Polymers with Nickel–Lanthanide Dinuclear Units

“…The above-inferred ferromagnetic character of interactions in complexes 2 – 5 is in agreement with that reported by others for similar, albeit discrete, LnNi complexes. , However, one should note that antiferromagnetic couplings have been reported for Ln 2 Ni 4 type of complexes , and that, in the strong-anisotropy limit, some striking maxima in the corresponding single-crystal χT products can be revealed in antiferromagnetic chains, too . The observed decrease of χ M T at extreme low temperatures is usually attributed to intermolecular antiferromagnetic interactions between spin carriers and thermal depopulation of Stark levels of the Tb III , Dy III , and Ho III centers, to the presence of zero-field splitting (ZFS), or to a combined effect of the above factors. ,,− ,,, …”

“…The measurements provide evidence for paramagnetic behavior in complex 1 and intra-unit ferromagnetic 3d–4f interactions in all other complexes. They also reveal a field-induced slow relaxation in compound 4 with embedded Ni–Dy units, previously observed in a handful of complexes containing Dy III ions ,− and in some one-dimensional compounds composed of Dy III monomers. , However, the binuclear units in 4 are subject to single-ion easy-plane anisotropy in analogy to S = 3 / 2 Co II ions, − showing an unexpected SMM behavior. This type of anisotropy favors the ground state with the lowest spin projection and is widely regarded as being antagonistic to magnetic bistability .…”

“…The design and synthesis of homo- and heterometallic coordination compounds has been attracting increasing research attention, owing to their potential as new magnetic materials, as well as their relevance to bioinorganic chemistry. − Among such materials, particularly important are compounds containing multiple metallic atoms − that may be single-molecule magnets (SMMs) or single-chain magnets (SCMs) and therefore useful for high-density information storage, spintronic devices, or quantum computation applications. − Since the initial report of a {Mn 12 }-based cluster compound as the first single-molecule magnet (SMM), , much effort has been devoted to seeking compounds with improved magnetic characteristics, resulting in the documentation of numerous SMMs and SCMs. − Many discrete SMMs are based exclusively on complexes comprising only 3d transition metals − or lanthanides, − but some are based on mixed 3d–4f heterometallic entities − and double phenoxo bridges. , …”

Highly water-soluble dimeric and trimeric lanthanide carbonates with ethylenediaminetetraacetates as precursors of catalysts for the oxidative coupling reaction of methane

“…26 Usually, lanthanide carbonates (K sp E 10 À20 -10 À35 ) 24 will form insoluble polymeric products at pH Z 6.0. [27][28][29][30] However, in these experiments, highly water-soluble products are formed by the reactions of CO 2 with lanthanide ethylenediaminetetraacetate compounds even in a strongly alkaline solution at pH 10.0. The formation of carbonato aggregates is inhibited by the strong coordination of ethylenediaminetetraacetate.…”

Spectrum of some arrow-bordered circulant matrix

“…For small systems some results have been obtained with simple calculus [55,59], but more general considerations need strictly proved properties, i.e., the results of this paper [see 60]. It is worth noting that for actually synthesized magnetic molecules [see, e.g., [61][62][63] there is needed analysis of some more general matrices (not regularly weighted graphs), e.g., alternating circulant matrices or arrow-bordered alternating circulant ones.…”