Greasy tails switch 1D-coordination [{Zn2(OAc)4(4′-(4-ROC6H4)-4,2′:6′,4′′-tpy)}n] polymers to discrete [Zn2(OAc)4(4′-(4-ROC6H4)-4,2′:6′,4′′-tpy)2] complexes

CrystEngComm This journal is © The Royal Society of Chemistry 2014 Department of Chemistry, University of Basel, Spitalstrasse 51, CH4056 Basel, Switzerland. E-mail: catherine.housecroft@unibas.ch; Fax: +41 61 267 1018; Tel: +41 61 267 1008 Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700 Fribourg, Switzerland. E-mail: aurelien.crochet@unifr.ch † Electronic supplementary information (ESI) available: Synthesis and characterization of precursors. Fig. S1–S11: H NMR and electronic spectra of ligands, structural figures and powder diffraction data. See DOI: 10.1039/ c4ce01422g Cite this: CrystEngComm, 2014, 16, 9915


Experimental
Electrospray mass spectra were measured on a Bruker Esquire 3000 instrument using MeCN solutions of samples. Absorption spectra were recorded on Varian Carry 5000 spectrometer, and IR spectra on a Shimadzu FTIR-8400S or Perkin Elmer UATR Two spectrophotometer. 1 H and 13 C NMR spectra were recorded using a Bruker Avance III-500 or 400 NMR spectrometers at 295 K; chemical shifts were referenced to residual solvent peaks with respect to δĲTMS) = 0 ppm.

Crystallography
Single crystal data were collected on a Bruker APEX-II diffractometer with data reduction, solution and refinement using the programs APEX 25 and SHELXL97 or SHELX-13. 26 ORTEP diagrams and structure analysis used Mercury v. 3.0.1 or 3.3. 27,28 Crystallographic data for all structures are given in Table 1. Powder diffractograms were measured on a STOE STADI P diffractometer equipped with a Cu Kα 1 radiation (λ = 1.540598 Å) and a Mythen1K detector.

Results and discussion
Ligand synthesis and characterization Compounds 1-9 were prepared using the one pot method of Wang and Hanan 29 summarized in Scheme 2, and were isolated in yields ranging from 47.3 to 63.1%. A convenient route to compound 10 proved to be the reaction of nucleophilic 4-Ĳĳ4,2′:6′,4″-terpyridin]-4′-yl)phenol (formed by deprotection of 1 with pyridinium chloride) with 1-bromodecane (Scheme 3); this strategy is analogous to that used for the preparation of polyethyleneoxy-functionalized tpy derivatives. 30 The electrospray mass spectrum of each compound exhibited a base peak corresponding to [M + H] + . The 1 H and 13 C{ 1 H} NMR spectra of 1-10 were assigned using COSY, NOESY, HMQC and HMBC methods, and representative 1 H NMR spectra are shown in Fig. S1. † The NOESY spectrum of 1 is shown in Fig. 1 and illustrates that crosspeaks between protons H A3 /H B3 , H B3 /H C2 and H C3 /H OMe (see Scheme 1 for labelling) allow unambiguous assignments of the aromatic protons in the A and C rings. The appearance of a triplet or multiplet around ∂ 4 ppm in the 1 H NMR spectrum of each compound along with an HMQC associated signal in the 13 C NMR spectrum at ∂ 55.6 ppm in 1 or in the range ∂ 64-69 ppm for 2-10 was consistent with the presence of the alkoxy substituent.   (7) 10.8959Ĳ6), 11.2529Ĳ7), 12.1372 (7) 8.0908 (9) absorption spectra of the ten 4'-Ĳ4-ROC 6 H 4 )-4,2′:6′,4″-tpy ligands. Each exhibits an intense absorption band around 270 nm with a shoulder at 305 nm. Dominant contributions to these bands come from π* ← π and π* ← n transitions. Single crystals of 6 and 7 suitable for X-ray analysis were serendipitously obtained from layer diffusion of solutions of 6 in CHCl 3 and ZnĲOAc) 2 ·2H 2 O in MeOH, or by slow evaporation of the solvent from a MeOH solution of 7, respectively. Fig. 2 and S3 † show the structures of these compounds and important bond parameters are given in the figure captions. All bond lengths and angles are as expected. At the molecular level, the two structures are similar with the alkyl chain in an extended conformation and the phenyltpy domain twisted. The angles between the rings containing atoms N1/N2, N2/N3 and N2/C16 are 17.6, 22.7 and 14.3°in 6, and 16.9, 27.9 and 20.0°in 7. Compounds 6 and 7 crystallize in the triclinic P1 and monoclinic Cc space groups, respectively, and the packing of molecules of 6 and 7 necessarily differs. In both structures, the primary assembly motif is a ribbon built up by translation (Fig. 3a) with CH⋯N short contacts (in 6, C14H14a⋯N1 i = 2.57 Å, symmetry code i = x, 1 + y, z; in 7, C2H2a⋯N3 i = 2.67 Å, symmetry code i = x, y, 2 + z). In 6, adjacent ribbons are related by inversion leading to interdigitation of hexoxy chains and the assembly of planar sheets (Fig. 3b). The packing, dictated by P1 symmetry, resembles that observed in 4′-Ĳ4-n butoxyphenyl)-4,2′:6′,4″-terpyridine (CSD 31 code ACUKAK), 32 4′-Ĳ4-dodecoxyphenyl)-4,2′:6′,4″-terpyridine (QATQEJ), 23 and 4′-Ĳ4-n octadecoxyphenyl)-2,2′:6′,2″-terpyridine (JERNUQ) 33 and 4′-Ĳ4-n octoxyphenyl)-2,2′:6′,2″-terpyridine (JERPAY). 33 A similar layer arrangement is also observed in 4′-Ĳ4-octoxyphenyl)-4,2′:6′,4″-terpyridine 34 (XAYPOC); each sheet is built up from centrosymmetric pairs of molecules but in this case, additional symmetry in the space group C2/c, affects the relationship between molecules in adjacent sheets. In 7, neighbouring ribbons are related by a glide plane giving rise to an off-axis interdigitation of heptoxy chains, all of which point in the same direction (Fig. 3c). The overall packing in 7 (Fig. 3d) involves a combination of π-stacking of aromatic rings, CH⋯π contacts and inter-chain van der Waals interactions, with no one type apparently predominant. It is likely that the energy difference between the two different molecular arrangements in the lattices of 6 and 7 is small, and that environmental effects influence the observed packing.
The compound ĳ{2Zn 2 (OAc) 4 Ĳ5)·2H 2 O} n ] crystallizes in the triclinic space group P1, with two independent {Zn 2 ĲOAc) 4 } and two independent ligands 5 in the asymmetric unit (Fig. 7). This contrasts with ĳ{Zn 2 (OAc) 4 Ĳ1)} n ], ĳ{Zn 2 (OAc) 4 Ĳ2)} n ] and ĳ{Zn 2 (OAc) 4 Ĳ3)} n ] Ĳmonoclinic, P2 1 /c and one independent ĳ{Zn 2 (OAc) 4 }ĲL)] unit). The second feature that distinguishes the polymer containing the pentoxy-tailed ligand 5 from those of containing the methoxy, ethoxy and n-propoxy-substituted ligands is the presence of solvent in the lattice (see later). As Fig. 7 shows, the 1D-chain in ĳ{2Zn 2 (OAc) 4 Ĳ5)·2H 2 O} n ] mimics that in the earlier polymers in the series and the bond parameters for the {Zn 2 ĲOAc) 4 } units are unexceptional. The tpy domains of the two independent ligands are more slightly twisted than in the complexes with shorter alkoxy chains; in ĳ{2Zn 2 (OAc) 4 Ĳ5)·2H 2 O} n ] the angles between the planes of the rings containing N1/N2 and N2/N3 are 4.5 and 9.1°, and between those with N4/N5 and N5/N6 are 5.5 and 10.4°. The phenyl rings in the two 4,2′:6′,4″-tpy ligands are twisted 26.3 and 27.4°with respect to each central pyridine ring. The most noticeable difference between the two independent ligands is the conformation of the pentoxy chain. The chain containing atom O2 is in an approximately extended conformation, and the maximum deviation of an alkyl C atom from the plane through the phenyl ring to which the chain is attached is 1.17 Å for C50; the terminal atom C52 lies 0.77 Å out of this plane. In contrast, the chain containing O1 is twisted out of the plane of the phenyl ring containing C16 (Fig. 7); the terminal atom C26 lies 3.02 Å away from the plane of the phenyl ring containing C16.
In contrast to ĳ{Zn 2 (OAc) 4 Ĳ1)} n ], ĳ{Zn 2 (OAc) 4 Ĳ2)} n ] and ĳ{Zn 2 (OAc) 4 Ĳ3)} n ], the change in packing associated with the longer alkyl chains in ĳ{Zn 2 (OAc) 4 Ĳ5)} n ] gives rise to cavities in the lattice that are occupied by H 2 O molecules Ĳmodelled as one full, one half and two quarter occupancies). The partial occupancies mean that detailed discussion of interactions involving these molecules is not meaningful. Solvent inclusion indicates that the packing of the 1-dimensional polymer chains is less efficient with n-pentoxy-substituted ligands than with the methoxy, ethoxy and n-propoxy-substituted ligands. Note that the elemental analytical data for the bulk material containing the n-butoxy-substituted ligand 4 are also consistent with the presence of water in the lattice.
Discrete complexes formed between ZnĲOAc) 2 ·2H 2 O and ligands 5 and 8-10 The molecular structure of ĳZn 2 (OAc) 4 Ĳ5) 2 ] ĲFig. 12) resembles that reported for ĳZn 2 (OAc) 4 ĲL) 2 ] where L = 4′-Ĳ4-dodecoxyphenyl)-4,2′:6′,4″-tpy. 23 ĳZn 2 (OAc) 4 Ĳ5) 2 ] crystallizes in the P1 space group with half of the molecule in the asymmetric unit; all bond metrics ĲFig. 12 caption) are unexceptional. Each ligand 5 is monodentate and binds through atom N1 to an axial site of the paddlewheel {Zn 2 ĲOAc) 4 } unit. The n-pentoxy group adopts an extended conformation (Fig. 12). The 4,2′:6′,4″-tpy domain is virtually planar (the angles between the planes of the rings containing N1/N2 an N2/N3 are 1.3 and 6.5°). The phenyl ring is twisted 25.0°out of the plane of the central pyridine ring, consistent with minimizing H⋯H interactions. The molecules pack into sheets (Fig. 13a) with the pendant pyridine ring containing N3 directed into the V-shaped cavity defined by the pyridine rings containing N1 ii and N2 ii and the phenyl ring with C16 ii (symmetry code ii = 1 + x, y, z) of an adjacent ligand 5; the shortest N⋯HC contact is 2.47 Å. Fig. 13a shows the interdigitation of the n-pentoxy chains, and also illustrates that the sheets contain voids between phenyl units of adjacent chains. These pockets accommodate the methyl groups of two of the four acetato-ligands from the next sheet (Fig. 13b).
Each polymer has a zigzag backbone and the chains nest together to generate planar sheets. The increasing length of the alkoxy substituent forces the polymer chains further apart Scheme 4 Defined here for ĳZn 2 (OAc) 4 Ĳ5) 2 ], the Zn⋯Zn separation, x, quantifies the effect of increasing the alkoxy chain Ĳsee text) within a sheet.
Scheme 5 Overview of the formation of crystallographically proven coordination polymers and discrete complexes as a function of alkoxy chain length.