Design of High-Dimensional Copper(II) Malonate Complexes with Exo-Polydentate N-Donor Ligands

Two polymeric malonato-bridged copper(II) complexes of formulas {(H2bpe)[Cu(mal)2]}n·4nH2O (1) and [Cu4(mal)4(bpe)3]n·6nH2O (2) [mal = malonate dianion; bpe = 1,2-bis(4-pyridyl)ethylene] have been synthesized and
characterized by X-ray diffraction. Complex 1 crystallizes in triclinic space group P1̄, Z = 1, with unit cell parameters
a = 4.8831(10) Å, b = 9.585(2) Å, c = 11.813(2) Å, α = 77.29(3)°, β = 82.18(3)°, and γ = 84.92(3)°, whereas
complex 2 crystallizes in the monoclinic space group P21/n, Z = 4, with unit cell parameters a = 13.462(3) Å, b
= 10.275(5) Å, c = 19.579(4) Å, and β = 105.21(3)°. The structure of 1 consists of anionic malonato-bridged
uniform copper(II) chains which are connected through hydrogen bonds involving malonate-oxygen atoms,
noncoordinated water molecules, and H2bpe2+ cations. The intrachain copper−copper separation through carboxylate-malonate bridge in the anti−syn conformation is 4.8831(10) Å. Complex 2 possesses a three-dimensional structure
made up of neutral corrugated malonated-bridged copper(II) layers linked through bis-monodentate bpe molecules.
The copper(II) atoms within each layer are bridged by a double μ-oxo and four carboxylato-malonate bridges with
copper−copper separations of 3.4095(7) Å (through oxo) and 4.9488(11)−6.5268(13) Å (through carboxylato). The
shortest interlayer copper−copper separation across bridging bpe is 13.434(3) Å. Variable-temperature magnetic
measurements (2−290 K) show an overall ferromagnetic behavior for both compounds. The magnetic pathway of
complex 1 is through a single carboxylate−malonate bridge connecting apical and equatorial positions of adjacent
copper(II) atoms, and the value of the magnetic coupling (J) for 1 through a numerical expression for a ferromagnetic
uniform chain of interacting local doublets is J = +0.049(1) cm-1. The values for the magnetic couplings through
the main intralayer exchange pathways in 2 which correspond to carboxylate−malonate bridges connecting equatorial−equatorial (J1) and equatorial−apical (J2) coordination sites and to the double μ-oxo bridge linking equatorial−apical (J5) positions have been determined through a simplified model. The three magnetic couplings are weak,
two of them being ferromagnetic (J1 = +23(1) cm-1 and J2 = +6.5(1) cm-1) and the other one antiferromagnetic
[zJ‘ = −1.0(1) cm-1]. The values of the magnetic couplings in 1 and 2 compare well with those previously reported
for similar malonato-bridged copper(II) complexes of different dimensionalities.