Inorganic Chemistry, Vol.47, No.24, 11551-11560, 2008
Self-Assembly of Electroactive Thiacrown Ruthenium(II) Complexes into Hydrogen-Bonded Chain and Tape Networks
A family of coordination complexes has been synthesized, each comprising a ruthenium(II) center ligated by a thiacrown macrocycle, aneS(3), aneS(4), or aneS(4), 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(aneS(3))(nic)(2)Cl]PF6, 1(PF6); [Ru(aneS(3)) (isonic)(2)Cl]PF6, 2(PF6); [Ru(aneS(4))(nic)(2)](PF6)(2), 3(PF6)(2); [Ru(aneS(4))(isonic)(2)](PF6)(2), 4(PF6)(2); [Ru(aneS(4)) (cbza)2](PF6)2, 5(PF6)2; [Ru(aneS4)(nic)2](PF6)2, 6(PF6)2; [Ru(aneS4)(isonic)2](PF6)2, 7(PF6)2; and [Ru(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 pi-pi* transition and a lower energy band (297-355 nm) assigned to metal-to-ligand chargetransfer transitions. Electrochemical studies indicate good reversibility for the oxidations of complexes with nic and isonic ligands (vertical bar I-a/I-c vertical bar = 1; Delta E-p < 100 mV), In contrast, complexes 5 and 8, which incorporate cbza ligands, display oxidations that are not fully electrochemically reversible (vertical bar I-a/I-c vertical bar = 1, Delta Ep >= 100 mV). Metal-based oxidation couples between 1.32 and 1.93 V versus Ag/AgCI can be rationalized in term of the acceptor capabilities of the thiacrown ligands and the amide-bearing ligands, as well as the pi-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) center dot H2O, 1(BF4) center dot 2H(2)O, 2(PF6), 3(PF6)(2), 6(PF6)(2) center dot CH3NO2, and 8(PF6)(2) are reported. Four of the six form amide-amide N-H center dot center dot center dot O hydrogen bonds leading to networks constructed from amide C(4) chains or tapes containing R-2(2) (8) hydrogen-bonded rings. The other two, 2(PF6) and 8(PF6), form networks linked through amide-anion N-H center dot center dot center dot 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 1 D to 21) networks. The scope for future systematic development of electroactive tectons into network materials is discussed.