Competition in Coordination Assemblies: 1D-Coordination Polymer or 2D-Nets Based on Co(NCS)2 and 4′-(4-methoxyphenyl)-3,2′:6′,3″-terpyridine

Abstract

The synthesis and characterization of 4′-(4-methoxyphenyl)-3,2′:6′,3″-terpyridine (2) (IUPAC PIN 24-(4-methoxyphenyl)-12,22:26,32-terpyridine) are described, and its coordination behaviour with cobalt(II) thiocyanate has been investigated. In a series of experiments, crystals were grown at room temperature by layering a MeOH solution of Co(NCS)2 over a CHCl3 solution of 2 using 1:1, 1:2 or 2:1 molar ratios of metal salt-to-ligand. Crystals harvested within 2–3 weeks proved to be the 1D-coordination polymer [Co(2)(NCS)2(MeOH)2]n and powder X-ray diffraction (PXRD) confirmed that the crystals selected for single-crystal X-ray diffraction were representative of the bulk samples. Longer crystallization times with a Co(NCS)2 to 2 molar ratio of 1:1 yielded crystals of [Co(2)(NCS)2(MeOH)2]n (1D-chain) and the pseudopolymorphs [{Co(2)2(NCS)2}·3MeOH]n and [{Co(2)2(NCS)2}·2.2CHCl3]n ((4,4)-nets), each type of crystal originating from a different zone in the crystallization tube. PXRD for this last experiment confirmed that the dominant product in the bulk sample was the 1D-coordination polymer.

Directing 2D-Coordination Networks: Combined Effects of a Conformationally Flexible 3,2′:6′,3″-Terpyridine and Chain Length Variation in 4′-(4-n-Alkyloxyphenyl) Substituents

“…We note that π-stacking interactions play no role in the assembly. The network common to the compounds with ligands 2, 3 and 4 differs from that observed for the analogous compound containing ligand 1 with a methoxy substituent [19]. In the pseudopolymorphs [{Co(1) 2 (NCS) 2 } .…”

“…Figures S2-S6 in the supporting information display the 1 H, 13 C{ 1 H} NMR and solid-state IR spectra of 3, and NMR assignments (see Section 3.2) were made using 2D methods. The solution absorption spectrum of 3 ( Figure 2) is reminiscent of the spectra of other members of the homologous series of ligands shown in Scheme 2 [11,19,20], and the absorptions are assigned to a combination of spin-allowed π*←n and π*←π transitions.…”

“…A well-established route to 4 -aryl functionalized 2,2 :6 ,2"-terpyridines is the one-pot strategy of Wang and Hanan [8], and this methodology has also been used to prepare the 3,2 :6 ,3"-terpyridines 1 [19], 2 [20] and 4-6 [11,20,21]. However, in the case of compound 3, this strategy failed [20] and led instead to the cyclic product 3a (Scheme 3).…”

“…In a continuation of our investigations of the coordination of 4 -(4-alkyloxyphenyl)-3,2 :6 ,3"-tpy ligands [11,19], we now explore the effects of increasing the length of the alkyloxy substituent from methoxy to n hexyloxy (ligands 1-6, Scheme 2).…”

“…, depending on the crystallization conditions. However, powder X-ray diffraction (PXRD) revealed that in experiments where crystals selected for single crystal X-ray diffraction proved to be the (4,4)-nets, the 1D-polymer [Co(1)(NCS) 2 (MeOH) 2 ] n was always the dominant product [19].…”