Reciprocal Metal-η 2-arene π-Interactions and Non Classical C − H ⋅ ⋅ ⋅ O Bonding : Synthesis and X-ray Characterization of a Bis Diaryl Symmetric-substituted Triazenide Complex Polymer of Hg ( II )

1,3-bis(4-etoxicarbonilfenil)triazeno desprotonado reage com Hg(CH 3 COO) 2 em tetraidrofurano para formar cristais amarelos de {[Hg(RC 6 H 4 NNNC 6 H 4 R) 2 Py] 2 } n [R = EtOC(O)]. Os téctons [Hg(RC 6 H 4 NNNC 6 H 4 R) 2 Py] encontram-se ligados aos pares como dímeros centro simétricos por meio de interações π recíprocas do tipo metal-η-areno. As unidades dímeras relacionadas entre si através de um plano de reflexão-translação diagonal n, são operadas ao longo da direção cristalográfica [101] originando cadeias através de ligações de hidrogênio não clássicas C−H⋅⋅⋅(O) COEt envolvendo o grupamento orto C−H do ligante piridina. Estas cadeias por sua vez, relacionamse entre si por translação na cela elementar através de um segundo tipo de ligação de hidrogênio não-clássica, esta envolvendo átomos de hidrogênio e oxigênio de grupos etoxicarbonilfenil adjacentes na direção cristalográfica [100], resultando um arranjo cristalino supramolecular (2D) estendido paralelo ao plano cristalográfico (011).


Introduction
Nowadays it is well known that secondary bonds or interactions can play a significant role in the structural assembling of a wide variety of compounds.These interactions present σ or π character, and have not been recognized in earlier works, in spite of their real existence.Organotellurium compounds, for example, in addition to secondary Te⋅⋅⋅halogen bonds, show mostly intermolecular bonds of the type Te⋅⋅⋅π-aryl. 1,2Crystallographic aspects of this complex type have been described in the literature, and although intermolecular interactions exist in almost all the reported cases, they have not been mentioned by the authors, [3][4][5][6] especially the hydrogen bonds and the metal⋅⋅⋅πaryl interactions.This could be explained by the fact that only in recent years the real chemical significance of these selective, directional and strongly attractive noncovalent interactions, which can induce the self-assembly of predictable supramolecular aggregates, has become evident.8][9] According to S. Simard and co-workers, 8 a tecton (from Greek, tekton, builder) is defined as "any molecule whose interactions are dominated by particular associative forces that induce the self-assembly of an organized network with specific architectural or functional features".Supramolecular synthesis would be the design and construction of multicomponent supermolecules or supramolecular arrays utilizing non-covalent bonding of tectons. 9][11] Recently we have shown 12,13 that triazenide complexes of Hg(II) are tectons with a remarkably good ability to self-assemble of different manners through metal-η-arene π-interactions: the synthesis of {Hg[PhN 3 C 6 H 4 N 3 (H) Ph] (NO 3 )} 14 − a rare Hg(II) complex containing two phenyltriazenide chains − was one of the first evidences that in this complex type besides Metal−N bonds also metal-arene π-interactions perform a significant role in the architecture (or self-assembling) of the crystal lattice, in as much as the mentioned organotellurium compounds.
Aiming at the study of new self-assembling possibilities of systems involving symmetrical substituted triazenide chains and Hg(II), we report here on the successful achievement of a new sort of Hg-η-arene dimerization by blocking one of the axial positions of the Hg(II) ion with pyridine, as well as the broadening of the supramolecular lattice through additional, non classical hydrogen bonding.Detailed analytical structural data, with emphasis on X-ray diffractometry of mono crystals will be also presented and discussed.

Experimental
A single crystal fixed on a glass fiber was used for the X-ray data collection.Data were collected with a Bruker APEX II CCD area-detector diffractometer and graphite-monochromatized Mo-K α radiation.The data reduction and the absorption correction were performed using SAINT 15 and SADABS 16 programs, respectively.The structure of [Hg II (RC 6 H 4 NNNC 6 H 4 R) 2 Py] [R = EtOC(O)] was solved by direct methods 17 and refined on F 2 with anisotropic temperature parameters for all non H atoms. 18 H atoms of the phenyl, methylene, and methyl groups were positioned geometrically (C−H = 0.93 Å for Csp 2 , 0.96 Å (CH 3 ) and 0.97 Å (CH 2 ) for Csp 3 atoms) and treated as riding on their respective C atoms, with U iso (H) values set at 1.2U eq Csp 2 ) and 1.5U eq Csp 3 ).The crystallographic parameters and details of data collection and refinement are given in Table 1.
To a solution prepared by dissolving 0.06g (0.15 mmol) of 1,3-bis(4-ethoxycarbonylphenyl)triazene in 20 mL of a mixture of tetrahydrofurane / methanol (1:3), three drops of a saturated solution of potassium methanolate were added under stirring turning the color orange.A solution of 0.023 g (0.07 mmol) of Hg(CH
(RC 6 H 4 NNNC 6 H 4 R) 2 Py] 2 } n [R = EtOC(O)] − like the early mentioned examples − allows to exclude the possibility of occurrence of intermolecular interactions of the type Hg---η 6 -arene.In conclusion we have observed a second kind of non classical intermolecular C−H⋅⋅⋅O bonds involving hydrogen and oxygen atoms of adjacent
Ta b l e 1 .C r y s t a l a n d s t r u c t u r e r e f i n e m e n t d a t a f o r [Hg II (RC 6 H 4 NNNC 6 H 4 R) 2 Py] [R = EtOC(O)] Hg II (RC 6 H 4 NNNC 6 H 4 R) 2 Py] 2 [R = C 2 H 5 OC(O)]: the N−H band is absent.n max /cm -1 2982 [m, n(C−H)], 1717 [vs, n(C=O)], 1599 [vs, n(C=C)], 1275 [vs, n as (NNN)], a mean value with respect to the N-N absorptions in the free ligand (average bond order), 863 [s, n(C−Ν)].Far infrared, FIR (CsI): n max /cm -1 591 [s, n(Hg−N)].