Spectroscopic, Thermal, and Magnetic Properties of Metal/TCNQ Network Polymers with Extensive Supramolecular Interactions between Layers

Reactions of [M(MeCN)<i><sub>n</sub></i>][BF<sub>4</sub>]<sub>2</sub> salts with Bu<sub>4</sub>N(TCNQ) in MeOH yield M(TCNQ)<sub>2</sub>(MeOH)<i><sub>x</sub></i> (M = Mn, <b>1</b>; Fe, <b>2</b>; Co, <b>3</b>; Ni, <b>4</b>, <i>x</i> = 2−4), and reactions of MnCl<sub>2</sub>, FeSO<sub>4</sub>·7H<sub>2</sub>O, CoSO<sub>4</sub>·7H<sub>2</sub>O and NiCl<sub>2</sub>·6H<sub>2</sub>O in H<sub>2</sub>O produce M(TCNQ)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub> (M = Mn, <b>5</b>; Fe, <b>6</b>; Co, <b>7</b>; Ni, <b>8</b>). Infrared spectroscopy, powder X-ray diffraction and thermogravimetric analyses of <b>1</b><b>−</b><b>8</b> indicate that the products prepared in the same solvent constitute isostructural families of compounds. [Mn(TCNQ−TCNQ)(MeOH)<sub>4</sub>]<sub>∞</sub> (<b>9</b>) crystallizes in the triclinic space group <i>P</i>1̄, <i>a</i> = 7.2966(8) Å, <i>b</i> = 7.4289(8) Å, <i>c</i> = 14.060(2) Å, α = 76.112(2)° <i>β</i> = 87.242(2)°, <i>γ</i> = 71.891(2)°, <i>V</i> = 702.91(13) Å<sup>3</sup>, <i>Z</i> = 1; [Mn(TCNQ)(TCNQ−TCNQ)<sub>0.5</sub>(MeOH)<sub>2</sub>]<sub>∞</sub> (<b>10</b>) crystallizes in the monoclinic space group <i>C</i>2/<i>c</i>, <i>a</i> = 14.4378(5) Å, <i>b</i> = 27.3067(11) Å, <i>c</i> = 13.1238(5) Å, β = 90.057(1)°, <i>V</i> = 5174.0(3) Å<sup>3</sup>, <i>Z</i> = 8. Compound <b>9</b> contains TCNQ<sup>-</sup> ligands that have undergone an unusual σ-dimerization to [TCNQ−TCNQ]<sup>2-</sup> that acts as a tetradentate ligand to Mn(II) ions to give a 2-D staircase polymeric motif. The layers are connected by hydrogen-bonds between axially coordinated MeOH from adjacent layers and MeOH located between the layers. Compound <b>10</b> exhibits a zigzag polymeric motif with equatorially bound TCNQ-derived ligands of two types; the edges of the layers consist of cis-μ-TCNQ<sup>-</sup> molecules involved in π-stacking with TCNQ<sup>-</sup> units from another layer and σ-[TCNQ−TCNQ]<sup>2-</sup> acting as a tetradentate bridging ligand. Axial MeOH ligands are hydrogen-bonded to dangling nitrile groups of <i>cis</i>-μ-TCNQ<sup>-</sup> ligands in the next layer. Mn(TCNQ)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub> (<b>11</b>) crystallizes in the monoclinic space group <i>I</i>2/<i>a</i>, <i>a</i> = 12.5843(7) Å, <i>b</i> = 13.7147(7) Å, <i>c</i> = 13.3525(70 Å, β = 92.887(1)°, <i>V</i> = 2301.58 Å<sup>3</sup>, <i>Z</i> = 4. This material adopts a double-layer motif consisting of Mn(II) ions bonded to <i>syn</i>-μ<sub>2</sub>-TCNQ<sup>-</sup> equatorial ligands and axial H<sub>2</sub>O molecules. Compounds <b>1</b><b>−</b><b>11</b> exhibit Curie−Weiss behavior with weak antiferromagnetic coupling being observed at low temperatures. The Zn(II) analogue of <b>10</b>, [Zn(TCNQ)(TCNQ−TCNQ)<sub>0.5</sub>(MeOH)<sub>2</sub>]<sub>∞</sub> (<b>12</b>) was also prepared:  space group <i>C</i>2/<i>c</i>, <i>a</i> = 14.2252(1) Å, <i>b</i> = 27.3290(4) Å, <i>c</i> = 13.1177(2) Å, β = 90.074(1)°, <i>V</i> = 5099.64(11) Å<sup>3</sup>, <i>Z</i> = 8. Powder X-ray diffraction was used to probe structures <b>1</b>−<b>11</b>, and it was found that <b>9</b> converts to a new phase with heating or exposure to X-rays that is related to disruption of the σ-dimer (TCNQ−TCNQ)<sup>2-</sup> ligands and loss of MeOH. The new phase, whose powder pattern is identical with that of a phase prepared from MeCN, exhibits ferromagnetic behavior.