Anion-Directed Self-Assembly of Unusual Discrete and One-Dimensional Copper(II) Complexes of 3,6-Bis(2′-pyridyl)pyridazine

The preparation and crystal structures of six new copper­(II) compounds of formula [Cu­(dppn)₂(ClO₄)]­ClO₄ (<b>1</b>), [Cu₂(dppn)­(OH)­(ClO₄)₃(H₂O)₃]·H₂O (<b>2</b>), [Cu₂(dppn)₂(H₂O)₂]­(ClO₄)₄ (<b>3</b>), [Cu₂(dppn)₂(ClO₄)₄] (<b>4</b>), {[Cu₂(dppn)­(N₃)₄]·H₂O/[Cu₂(dppn)­(N₃)₄(H₂O)]}_<i>n</i> (<b>5</b>) and {[Cu₂(dppn)­(OH)­(dca)₃]·H₂O}_<i>n</i> (<b>6</b>) [dppn = 3,6-bis­(2′-pyridyl)­pyridazine and dca = dicyanamide] are reported. <b>1</b> is a mononuclear complex where two bidentate dppn molecules and a monodentate perchlorate build an intermediate square pyramidal/trigonal bipyramidal (sp/tbp) five-coordinate environment around the copper­(II) ion, the overall positive charge being balanced by a free perchlorate anion. <b>2</b>–<b>4</b> are dinuclear complexes with either one (<b>2</b>) or two bis-bidentate dppn ligands (<b>3</b>, <b>4</b>) and a single hydroxo bridge (<b>2</b>). One (<b>2</b>) or two water molecules (<b>3</b>) and three (<b>2</b>) or four perchlorate groups (<b>4</b>) complete the metal coordination sphere, describing elongated octahedral (<b>2</b> and <b>4</b>) or intermediate sp/tbp environments (<b>3</b>). Free perchlorate anions neutralize the positive charge of the dicopper­(II) unit in <b>3</b>. <b>3</b> and <b>4</b> are noteworthy because 1:1 Cu­(II)-dppn complexes have never been reported. The simultaneous use of dppn and potentially bridging coligands such as azide and dca led to the chain compounds <b>5</b> and <b>6</b>. Two forms, {[Cu₂(dppn)­(N₃)₄]·H₂O}_<i>n</i> (<b>5A</b>) and {[Cu₂(dppn)­(N₃)₄(H₂O)]}_<i>n</i> (<b>5B</b>), were noted to coexist in the crystals of complex <b>5</b>, sharing a common [Cu₂(dppn)­(N₃)₄] dicopper­(II) fragment. <b>5A</b> consists of a step-like one-dimensional polymer in which the dinuclear entities are linked through single end-to-end azido bridges, while a supramolecular one-dimensional motif is present in <b>5B</b>, where the Cu–(μ_1,3-N₃)–Cu link is replaced by a Cu–Ow···(N₃)–Cu hydrogen-bonding interaction. Similarly, [Cu₂(dppn)­(μ-OH)­(dca)₂] dicopper­(II) fragments in <b>6</b> are connected via single μ_1,5-dca bridges. However an intrachain hydrogen bond is also present in this case, contributing to define a ladder-like motif instead. The variable-temperature magnetic study of <b>2</b>,<b> 3</b>, <b>5</b> and <b>6</b> reveals the occurrence of very strong antiferromagnetic interactions between the copper­(II) ions [<b>2</b>, <b>3</b> and <b>6</b> being practically diamagnetic at room temperature and <i>J</i> = −598(5) cm^–1 for <b>5</b>; <i><b>H</b></i> = −<i>J</i><b>S</b>_A · <b>S</b>_B]. The remarkable efficiency of the double (<b>3</b>) and single diazine (<b>2</b>, <b>5</b> and <b>6</b>) and single hydroxo (<b>2</b> and <b>6</b>) or end-on azido (<b>5</b>) groups to mediate electronic effects when acting as bridges between the copper­(II) ions [values of the copper–copper separation of 3.346(1) (<b>2</b>), 3.785(2) (<b>3</b>), 3.469(1) (<b>5</b>) and 3.368(1) Å (<b>6</b>)] accounts for the strong magnetic couplings observed in these compounds