Unexpected Assembly of a Unique Cyano-Bridged Three-Dimensional Cu₃Cr₂ Ferromagnet

Abstract

Unexpected Assembly of a Unique Cyano-Bridged Three-Dimensional Cu 3 Cr 2 Ferromagnet.-The three-dimensional coordination polymer (III) crystallizes in the monoclinic space group P2/m with Z = 1. The asymmetric unit of the structure is composed of two independent [Cr(CN) 6 ] 3− units and two different types of Cu II centers. Each Cr(1) ion is connected to four [Cu(en)] 2+ groups and each Cr(2) is bonded to four Cu(EtOH) 2 and two Cu(en) moieties. The connectivity of the different building units leads to an unexpected 3D structure. Long-range ferromagnetic ordering is observed below 57 K as expected for a 3D system. (III) is the first Cu II -containing Prussian blue analogue with spontaneous magnetization.

Extended Structures and Magnetic Properties of Lanthanide–Copper Complexes with Picolinic Acids as Bridging Ligands

“…In order to construct such extended 3d-4f heterometallic structures, an assembly reaction is designed to have the Cu(pic) 2 Figure 1), which suggests that the Ln ions can be further coordinated by more Cu(pic) 2 ligands to form higher dimensional structures. On the basis of this idea, the mole ratio of Cu(pic) 2 to Ln- …”

“…There are four Cu(pic) 2 units around each Gd III , as shown in Figure 3. The Gd III atoms are linked by the unco-ordinated carboxylic O atoms of the Cu(4)(pic) 2 and the Cu(3)(pic) 2 moieties to form a pseudozigzag chain along the b direction. These chains are further bridged by Cu(2)(pic) 2 moieties through their two uncoordinated carboxylic O atoms along the c direction to form extended two-dimensional layers (Figure 4).…”

“…[2] Since the Ln and M (M = transition metal) ions may be connected through bidentate carboxylate groups, efforts have been made to use carboxylate acids and carboxylate-like betaines as ligands. Many such studies focused on discrete polynuclear complexes such as LnM, LnM 2 , Ln 2 M 2 , Ln 2 M 4 , Ln 2 M 8 etc.…”

“…[4b,9] In our laboratory, we have synthesized a series of polymeric 3d-4f complexes through the use of carboxylate groups as bridging units. [10] As an extension of this work, picolinic acid (Hpic) was used as a chelating ligand to make the [COH(NH 2 ) 2 ] 2 [Cu(pic) 2 (ClO 4 ) 2 ] precursor by reaction with Cu(ClO 4 ) 2 ; [11] The monomer Cu(pic) 2 can be used as a "metallo ligand" to bind lanthanide metal ions for the preparation of complexes containing rare earth and transition metals. We have successfully obtained three novel series of one-and two-dimensional 3d-4f coordination polymers, namely, [LnCu 2 (pic) 4 (11) (1D).…”

Stoichiometric Control of the Magnetic Properties in Copper(II) Cyano‐Bridged Bimetallic Complexes

“…However, not very many examples of these have been reported to date. Only two of such copper-containing compounds, [Cu(Et-OH) 2 ][Cu(en)] 2 [Cr(CN) 6 ] 2 (en ϭ 1,2-diaminoethane) [15] and [Cu(tn)] 3 [Cr(CN) 6 ] 2 ·3H 2 O (tn ϭ 1,3-diaminopropane), [18] have been structurally characterised and exhibit spontaneous magnetisation, with critical temperatures, T c , of 57 K and 9.5 K, respectively. To the best of our knowledge, no Cu II ϪFe III cyanide-bridged compounds showing magnetic ordering have been reported so far, as most of the Cu II ϪFe bimetallic systems are indeed formed by diamagnetic hexacyanoferrate(II) units.…”