Polymeric Networks of Copper(II) Phenylmalonate with Heteroaromatic N-donor Ligands: Synthesis, Crystal Structure, and Magnetic Properties

Two new phenylmalonate-bridged copper(II) complexes with the formulas [Cu(4,4‘-bpy)(Phmal)]n·2nH2O (1) and
[Cu(2,4‘-bpy)(Phmal)(H2O)]n (2) (Phmal = phenylmalonate dianion, 4,4‘-bpy = 4,4‘-bipyridine, 2,4‘-bpy = 2,4‘-bipyridine) have been synthesized and characterized by X-ray diffraction. Complex 1 crystallizes in monoclinic
space group P21, Z = 4, with unit cell parameters of a = 9.0837(6) Å, b = 9.3514(4) Å, c = 11.0831(8) Å, and
β = 107.807(6)°, whereas complex 2 crystallizes in orthorhombic space group C2cb, Z = 8, with unit cell parameters
of a = 10.1579(7) Å, b = 10.3640(8) Å, and c = 33.313(4) Å. The structures of 1 and 2 consist of layers of
copper(II) ions with bridging bis-monodentate phenylmalonate (1 and 2) and 4,4‘-bpy (1) ligands and terminal
monodentate 2,4‘-bpy (2) groups. Each layer in 1 contains rectangles with dimensions of 11.08 × 4.99 Å2, the
edges being defined by the Phmal and 4,4‘-bpy ligands. The intralayer copper−copper separations in 1 through
the anti−syn equatorial−apical carboxylate-bridge and the 4,4‘-bpy molecule are 4.9922(4) and 11.083(1) Å,
respectively. The anti−syn equatorial−equatorial carboxylate bridge links the copper(II) atoms in complex 2 within
each layer with a mean copper−copper separation of 5.3709(8) Å. The presence of 2,4‘-bpy as a terminal ligand
accounts for the large interlayer separation of 15.22 Å. The copper(II) environment presents a static pseudo-Jahn−Teller disorder which has been studied by EPR and low-temperature X-ray diffraction. Magnetic susceptibility
measurements of both compounds in the temperature range 2−290 K show the occurrence of weak antiferromagnetic
[J = −0.59(1) cm-1 (1)] and ferromagnetic [J = +0.77(1) cm-1 (2)] interactions between the copper(II) ions. The
conformation of the phenylmalonate−carboxylate bridge and other structural factors, such as the planarity of the
exchange pathway in 1, account for the different nature of the magnetic interaction.