Novel Bis(4,4′-dipyridylamine) Ligand with a Flexible Butadiyne Linker: Syntheses, Structures, and Photoluminescence of d¹⁰ Metal Coordination Polymers

The design and syntheses of novel ligands are essential for developing coordination compounds with novel structures and interesting properties. In this work, we designed and synthesized a novel ligand bis­(4,4′-dipyridylaminophenylene)­butadiyne (<b>L</b>) by attaching two 4,4′-dipyridylamine moieties to a flexible butadiyne linker. Starting from this novel ligand, seven coordination polymers [Zn₂L­(HCOO)₃(OH)]_<i>n</i> (<b>1</b>), [Cd₂L₂Cl₄]_<i>n</i>·3<i>n</i>DMF·3<i>n</i>H₂O (<b>2</b>), [CdLBr₂]_<i>n</i> (<b>3</b>), [Cd₆L₃(SO₄)₆]_<i>n</i>·4<i>n</i>MeCN (<b>4</b>), [Hg₂LBr₄]_<i>n</i>·3<i>n</i>CH₂Cl₂·<i>n</i>H₂O (<b>5</b>), [Cu₂LI₂]_<i>n</i>·0.5<i>n</i>CH₂Cl₂ (<b>6</b>), and [Ag₂L­(H₂O)₂]_<i>n</i>(NO₃)_2<i>n</i>·2<i>n</i>H₂O (<b>7</b>) were synthesized. Single-crystal X-ray diffraction analyses revealed that two forms of the ligand crystals, <b>L</b> and <b>L·0.5DMF</b> present straight and bent conformations, respectively, because of the flexibility of the butadiyne unit. A rich structural diversity was observed for its d¹⁰ metal complexes. Complexes <b>1</b> and <b>5</b> present ladder-like structures. In complexes <b>2</b> and <b>4</b>, the ligand molecules are linked by metal atoms to afford 3D supramolecular structures. It is noteworthy that the 3D structure of complex <b>4</b> consists of interesting infinite {Cd₆(SO₄)₆}_∞ chains, whereas complexes <b>3</b>, <b>6</b>, and <b>7</b> exhibit 2D network structures. Interestingly, in the crystal of complex <b>7</b>, each ligand links four metal ions and each Ag ion bridges two ligands, leading to the formation of undulated 2D sheets with large cavities composed of 66-membered metallomacrocycles, which are interpenetrated by three other such 2D sheets, affording a 4-fold interpenetrated structure. In summary, the complex structures are dependent on the metal ions and the anions. In addition, the flexibility of the butadiyne moiety provides additional means for modulating the structures. Solid state photoluminescence of the free ligand and the complexes shows emission maxima within the range of 420–515 nm, which can be modulated by the conformations of the ligand in addition to the variation of the metal ions and anions, and the introduction of the butadiyne unit has a bathochromic effect