Turning {M(tpy)2}n+ embraces and CH⋯π interactions on and off in homoleptic cobalt(ii) and cobalt(iii) bis(2,2′:6′,2″-terpyridine) complexes

Abstract

We present a structural investigation of thirteen homoleptic complexes containing {Co(tpy) 2 } 2+ or {Co(tpy) 2 } 3+ cores and tpy, Cltpy, MeOtpy, EtOtpy or PrOtpy ligands (Cltpy ¼ 4 0 -chloro-2,2 0 :6 0 ,2 00terpyridine, MeOtpy ¼ 4 0 -methoxy-2,2 0 :6 0 ,2 00 -terpyridine, EtOtpy ¼ 4 0 -ethoxy-2,2 0 :6 0 ,2 00 -terpyridine, PrOtpy ¼ 4 0 -propoxy-2,2 0 :6 0 ,2 00 -terpyridine). For the twelve hexafluoridophosphate salts, several trends in the ways in which the cations pack in the solid state emerge. In [Co(tpy) 2 ][PF 6 ] 2 $2MeCN and [Co(Cltpy) 2 ][PF 6 ] 2 , two-dimensional grids of cations assemble through tpy embraces. Oxidation of cobalt(II) to cobalt(III) results in a loss of the grid, consistent with the presence of an increased number of anions and the need to minimize cation/cation repulsions. In the solid state, the cobalt(II) complexes containing MeOtpy or EtOtpy ligands exhibit face-to-face ROtpy/tpyOR embraces supported by CH alkoxy /p interactions. These are the dominant packing interactions in [Co(MeOtpy) 2 ][PF 6 ] 2 and [Co(EtOtpy) 2 ][PF 6 ] 2 $2MeCN. The transition from [Co(MeOtpy) 2 ][PF 6 ] 2 to [Co(MeOtpy) 2 ][PF 6 ] 2 $MeCN causes the packing to revert to a two-dimensional grid with tpy embraces; the MeCN solvent molecules produce periodic dislocations in the grid-like array. On going from ethoxy to propoxy derivatives, we observe a reversion to assemblies dependent upon tpy embraces. Onedimensional chains are favoured in [Co(PrOtpy) 2 ][PF 6 ] 2 $MeCN and [Co(PrOtpy) 2 ][PF 6 ] 2 $MeCN$Et 2 O, with the degree of solvation influencing the packing motifs. Oxidation of each of [Co(ROtpy) 2 ][PF 6 ] 2 (R ¼ Me, Et, Pr) results in increased separation of the cations. The crystal packing in [Co(Xtpy) 2 ][PF 6 ] 3 $MeCN for X ¼ Cl and MeO is virtually superimposable, and the [Co(Xtpy) 2 ] 3+ cation only has to undergo a slight twist within its lattice cavity to accommodate the Cl or MeO substituent. On going from [Co(PrOtpy) 2 ][PF 6 ] 2 $MeCN or [Co(PrOtpy) 2 ][PF 6 ] 2 $MeCN$Et 2 O to 2{[Co(PrOtpy) 2 ][PF 6 ] 3 }$5MeCN, oxidation of the metal tips the balance between tpy embraces and CH alkoxy /p interactions, and pairing of cations through the latter interactions is favoured. In [Co(EtOtpy) 2 ]Br 3 $MeCN$H 2 O, the [Co(EtOtpy) 2 ] 3+ cations assemble into one-dimensional chains through CH alkoxy /p interactions.Scheme 1 Ligands and numbering scheme for NMR assignments (tpy ¼ 2,2 0 :6 0 ,2 00 -terpyridine).

Tailoring of the Frontier Orbital Character in Co2+/3+ Complexes with Triarylamine Substituted Terpyridine Ligands

“…As is generally observed in complexes of meridional ligands,, , also in [Co 2+ ( 3 ) 2 ] 2+ the distances to the inner pyridyl donor nitrogen atoms are shorter (Co1–N2/N6: 2.043/2.043 Å) than the distances to the distal pyridyl donor nitrogen atoms. Different from C 2 v ‐symmetric ligands, there is additional “left‐right” anisotropy in [Co 2+ ( 3 ) 2 ] 2+ (XRD) and [Co 2+ ( 1 ) 2 ] 2+ (DFT) (Co1–N1/N5: 2.167/2.184 Å and Co1–N3/N7: 2.190/2.197 Å) with elongated Co–N bonds corresponding to ortho ‐substituted pyridine donors.…”

Structure and Electronic Properties of an Expanded Terpyridine Complex of Nickel(II) [Ni(ddpd)2](BF4)2

“…On the other hand they deviate stronger from the ideal octahedral values of 90° and 180° than those of the low‐spin [Fe(ddpd) 2 ] 2+ complex . The packing of the cations in [Ni(ddpd) 2 ](BF 4 ) 2 · 2MeCN can be described with intermolecular π interactions with one offset face‐to‐face ( off ) and two edge‐to‐face ( ef ) interactions between ligands of two neighboring complex cations (Figure b), typical for meridional complexes with aromatic N ‐donor ligands …”

“…[6] The packing of the cations in [Ni(ddpd) 2 ](BF 4 ) 2 ·2MeCN can be described with intermolecular π interactions with one offset face-to-face (off) and two edge-to-face (ef) interactions between ligands of two neighboring complex cations (Figure 2b), typical for meridional complexes with aromatic N-donor ligands. [44][45][46] Density functional theory calculations (CPCM(acetonitrile)-RIJCOSX-B3LYP-D3BJ-ZORA/def2-SVP) essentially reproduce the Ni-N distances (2.070-2.093 Å) and N-Ni-N bond angles (85.7-171.3°) of the structure determined in the solid state.…”

Systematic investigation of the antiproliferative activity of a series of ruthenium terpyridine complexes

“…The Ru(II) precursor Ru(terpy)Cl3 was synthesised as previously published. [36] The substituted 2,2':6',2"-terpyridine ligands (terpy-X): 4'-chloro-2,2':6',2"-terpyridine (terpy-Cl), [37] 4'-bromo-2,2':6',2"-terpyridine (terpy-Br), [38] 4'-methoxy-2,2':6',2"-terpyridine (terpy-OMe), [39] 4'-carboxy-2,2':6',2"-terpyridine (terpy-COOH), [40] 4'-methylcarboxy-2,2':6',2"-terpyridine (terpy-COOMe), [40] 4'dimethylamino-2,2':6',2"-terpyridine (terpy-NMe2) [41] were synthesised as previously reported.…”