Synthesis, Crystal Structure, and Spectroscopic Characterization of <i>trans</i>-Bis[(μ-1,3-bis(4-pyridyl)propane)(μ-(3-thiopheneacetate-<i>O</i>))(3-thiopheneacetate-<i>O</i>)]dicopper(II), {[Cu<sub>2</sub>(O<sub>2</sub>CCH<sub>2</sub>C<sub>4</sub>H<sub>3</sub>S)<sub>4</sub>μ-(BPP)<sub>2</sub>]}<i><sub>n</sub></i>: From a Dinuclear Paddle-Wheel Copper(II) Unit to a 2-D Coordination Polymer Involving Monatomic Carboxylate Bridges
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From the reaction between a dinuclear paddle-wheel carboxylate, namely [Cu2μ-(O2CCH2C4H3S)4] (1), and the flexible ligand 1,3-bis(4-pyridyl)propane (BPP) a neutral 2-D coordination polymer {[Cu2(O2CCH2C4H3S)4μ-(BPP)2]}n (2) was obtained. Compounds 1 and 2 were characterized by means of elemental analysis, thermal analysis (TG/DSC), vibrational spectroscopy, and electron paramagnetic resonance (EPR). The crystal structure of 2 reveals that each CuII is coordinated by two nitrogen atoms from different BPP ligands and two 3-thiopheneacetate groups within a distorted square planar geometry in a trans-{N, N, O, O} arrangement. The BPP ligand adopts a TG conformation bridging two copper centers giving rise to a 1-D sinusoidal polymeric chain along the crystallographic c axis. Adjacent 1-D chains are extended into a 2-D coordination network through pairs of monatomic carboxylate bridges in direction of the b axis. This bridging mode affords centrosymmetric dimeric units Cu2O2, and therefore, the copper ions are involved in a CuN2O2O‘ chromophore displaying a (4 + 1) square pyramidal coordination in the resultant 2-D polymeric network. The polycrystalline X-band EPR spectrum of 2 at room temperature is characteristic of a triplet state with nonnegligible zero-field splitting in agreement with the crystal structure. Crystal data for 2: monoclinic, space group P21/c, a = 9.4253(10) Å, b = 10.9373(10) Å, c = 23.6378(10) Å, β = 98.733(4)°, Z = 2.
