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Self-Assembly of Electroactive Thiacrown Ruthenium(II) Complexes into Hydrogen-Bonded Chain and Tape Networks

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posted on 2008-12-15, 00:00 authored by Naz Shan, Samuel M. Hawxwell, Harry Adams, Lee Brammer, Jim A. Thomas
A family of coordination complexes has been synthesized, each comprising a ruthenium(II) center ligated by a thiacrown macrocycle, [9]aneS3, [12]aneS4, or [14]aneS4, and a pair of cis-coordinated ligands, niotinamide (nic), isonicotinamide (isonic), or p-cyanobenzamide (cbza), that provide the complexes with peripherally situated amide groups capable of hydrogen bond formation. The complexes [Ru([9]aneS3)(nic)2Cl]PF6, 1(PF6); [Ru([9]aneS3)(isonic)2Cl]PF6, 2(PF6); [Ru([12]aneS4)(nic)2](PF6)2, 3(PF6)2; [Ru([12]aneS4)(isonic)2](PF6)2, 4(PF6)2; [Ru([12]aneS4)(cbza)2](PF6)2, 5(PF6)2; [Ru([14]aneS4)(nic)2](PF6)2, 6(PF6)2; [Ru([14]aneS4)(isonic)2](PF6)2, 7(PF6)2; and [Ru([14]aneS4)(cbza)2](PF6)2, 8(PF6)2 have been characterized by NMR spectroscopy, mass spectrometry, and elemental analysis. UV/visible spectroscopy shows that each complex exhibits an intense high-energy band (230−255 nm) assigned to a π−π* transition and a lower energy band (297−355 nm) assigned to metal-to-ligand charge-transfer transitions. Electrochemical studies indicate good reversibility for the oxidations of complexes with nic and isonic ligands (|Ia/Ic| = 1; ΔEp < 100 mV), In contrast, complexes 5 and 8, which incorporate cbza ligands, display oxidations that are not fully electrochemically reversible (|Ia/Ic| = 1, ΔEp ≥ 100 mV). Metal-based oxidation couples between 1.32 and 1.93 V versus Ag/AgCl can be rationalized in term of the acceptor capabilities of the thiacrown ligands and the amide-bearing ligands, as well as the π-donor capacity of the chloride ligands in compounds 1 and 2. The potential to use these electroactive metal complexes as building blocks for hydrogen-bonded crystalline materials has been explored. Crystal structures of compounds 1(PF6)·H2O, 1(BF4)·2H2O, 2(PF6), 3(PF6)2, 6(PF6)2·CH3NO2, and 8(PF6)2 are reported. Four of the six form amide−amide N−H···O hydrogen bonds leading to networks constructed from amide C(4) chains or tapes containing R22 (8) hydrogen-bonded rings. The other two, 2(PF6) and 8(PF6), form networks linked through amide−anion N−H···F hydrogen bonds. The role of counterions and solvent in interrupting or augmenting direct amide−amide network propagation is explored, and the systematic relationship between the hydrogen-bonded networks formed across the series of structures is presented, showing the relationship between chain and tape arrangements and the progression from 1D to 2D networks. The scope for future systematic development of electroactive tectons into network materials is discussed.