‘Simple’ Oligopyridine Complexes – Sources of Unexpected Structural Diversity

Abstract

The simple formulae often presented for main-group metal complexes of oligopyridines (typically 2,2′-bipyridine, 1,10-phenanthroline, and 2,2′:6′,2″-terpyridine) hide a wide variety of polymeric solid-state structures. We present an overview of these structures and reveal a plethora of 1D chains, including ladder assemblies, and 2D networks. In most assemblies, the polymeric backbone or network is defined by the metal atoms and bridging ligands other than oligopyridines. The heterocyclic ligands typically feature as peripheral decorations, often engaging in face-to-face supramolecular π-stacking interactions which define the assembly of the crystal. In 1D coordination polymers, three types of decoration predominate which we have defined as Type 1 (all the oligopyridines on the same side and π-stacked), Type 2 (alternating arrangement of oligopyridines), and Type 3 (a pairwise alternating structure).

Stoichiometrically Controlled Assembly of Lanthanide Molecular Complexes of the Heteroditopic Divergent Ligand 4′-(4-Pyridyl)-2,2′:6′,2″-terpyridine N-Oxide in Hypodentate or Bridging Coordination Modes. Structural, Magnetic, and Photoluminescence Studies

“…A terpyridyl unit is often used in the design of new organic linkers for the relatively easy synthesis and functionalization, for the strong bond with d transition metals, and for the interesting redox, photoluminescent, and magnetic properties. − The divergent ligand 4′-(4″′-pyridyl)-2:2′,6′:2″-terpyridine (pyterpy) is well-known in the literature, forming a large number of molecular and extended structure compounds for d metals − but a limited number of examples for lanthanide metals. − Furthermore, very little attention has been paid in the literature to the analogue N-oxidated ligand 4′-(4″′-pyridyl- N -oxide)-2:2′,6′:2″-terpyridine (pyterpyNO) (Scheme ); a single paper reported the synthesis of a mononuclear iron­(II) complex, [Fe­(pyterpyNO) 2 ]­(BF 4 ) 2 , where the metal is coordinated to only the terpyridine unit . Nevertheless, this rigid aromatic ligand with two different binding sites is expected to have a rich coordination chemistry, to be able to control the selective and spontaneous organization of molecular units into ordered structures, and to be potentially useful for the synthesis of heterometallic complexes, a hot topic in the development of polynuclear molecular materials based on lanthanide systems, as previously shown for the analogous 4,4′-bipyridine N -oxide ligand. ,− …”

Functionalised Terpyridines and Their Metal Complexes—Solid-State Interactions

“…In the totality of the interactions exceeding dispersion (Figure 4), there is no evidence for nucleophile addition to C-atoms adjacent to N, so it can be said at this point that M(II) cations seem to be distinguishable from M(V) and M(VI) cations in this respect. Interactions of the cations with the counteranions and lattice solvents occur along with aromatic-aromatic interactions, and even in only the eight cases considered, there are variations in both the coun- The vast majority of the structural studies of complexes of 2,2 :6 ,2 -terpyridine and its derivatives concern metal(II) and metal(III) species, and the present work largely complements such investigations, which range, for Co(II), for example, from early determinations on a single compound for which H-atom coordinates are not available, e.g., [65], to those of several complexes of various derivatives with full coordinates, e.g., [66], such variations reflecting, in part, major advances in the ease of the synthesis of the ligands [1][2][3][4][5][6][7] and in crystallographic equipment. The complexes 2-6 of the tptpy ligand add Fe(II), Ni(II) and Ru(II) to the series, with Co(II), Cu(II), Zn(II) and Cd(II) studied earlier [34,37], and form part of a rather large family of structurally characterised complexes of 4 derivatives of 2,2 :6 ,2 -terpyridine, where the substituent is an apolar aromatic unit.…”

“…While much of the interest in 2,2 :6 ,2 -terpyridine chemistry has been focused on metalion complexes in low oxidation states [1][2][3][4][5][6][7], complexes of high-oxidation-state metal ions are also known, with vanadium(V) [59] and uranium(VI) (as the uranyl ion, UO 2 2+ ) [60][61][62][63] providing examples of extremes. In that the formation of a coordinate bond is formally a process where the metal ion gains electrons and the ligand loses them, such extreme cases might be expected to be associated with charge redistribution favouring the appreciable interaction of the bound ligand with nucleophiles, akin to the addition to an imine bond.…”

“…Ligands based on the 2,2 :6 ,2 -terpyridine (tpy) substructure have been employed in an extraordinary variety of studies concerning their metal-ion coordination chemistry [1][2][3][4][5][6][7]. Much of this chemistry has concerned condensed phases-crystals, liquid crystals, monolayers on surfaces, intercalation complexes, and films-where interactions between complex ion units and between them and their environment can be particularly important, as is well-known for 2,2 :6 ,2 -terpyridine itself [8].…”

Halide Ion Embraces in Tris(2,2′-bipyridine)metal Complexes

“…There is a large body of crystallographic data for metal complexes of these ligands in the Cambridge Structural Database (using version 5.41) and we have, in general, restricted our coverage to complexes containing the parent compound 2,2'-bipyridine in order to eliminate the influence of other interactions between the halogen and substituents on the ligand. Furthermore, the chemistry of these ligands and their complexes is exceptionally well documented [23][24][25][26][27][28][29][30][31][32][33][34][35][36], facilitating correlations between the solid-state features and chemical behaviour.…”