Heterotrimetallic 4f−3d Coordination Polymers: Synthesis, Crystal Structure, and Magnetic Properties

A series of cyano-bridged heterotrimetallic complexes [CuL]2Ln(H2O)2M(CN)6·7H2O have been synthesized by the
reactions of CuL (L2- = dianion of 1,4,8,11-tetraazacyclotradecane-2,3-dione), Ln3+ (Ln = Gd or La), and [M(CN)6]3-
(M = Co, Fe, or Cr). X-ray diffraction analysis reveals that these complexes are isostructural and have a novel
chain structure. The Ln3+ ion is eight-coordinated by six oxygen atoms of two CuL and two water molecules and
two nitrogen atoms of the bridging cyano ligands of two [M(CN)6]3-, while the [M(CN)6]3- anion connects two Ln3+
using two trans-CN- ligands giving rise to a chainlike structure. In the chain, every CuL group tilts toward the CN-
ligand of adjacent [M(CN)6]3- with the Cu−Ncyano contacts ranging from 2.864(6) to 2.930(6) Å. Magnetic studies
on the CuGdCo complex (1) indicate the presence of ferromagnetic coupling between Cu(II) and Gd(III). The
CuLaCr (5) and CuLaFe (2) complexes exhibit ferromagnetic interaction between paramagnetic Cu(II) and Cr(III)/Fe(III) ions through the weak cyano bridges (Cu−Ncyano = 2.930(6) Å for 2). A global ferromagnetic interaction is
operative in the CuGdFe complex (3) with the concurrence of dominant ferromagnetic Cu(II)−Gd(III) and minor
antiferromagnetic Gd(III)−Fe(III) as well as the ferromagnetic Cu(II)−Fe(III) interaction. For the CuGdCr complex
(4), an overall antiferromagnetic behavior was observed, which is attributed to the presence of dominant
antiferromagnetic CrIII−GdIII coupling and the minor ferromagnetic CuII−GdIII and CuII−CrIII interaction. Moreover, a
spin frustration phenomenon was found in complex 4, which results from the ferro−ferro−antiferromagnetic exchanges
in the trigonal Cu−Gd−Cr units. The magnetic susceptibilities of these complexes were simulated using suitable
models. The magneto−structural correlation was investigated. These complexes did not show a magnetic phase
transition down to 1.8 K.