Manipulating the Conformation of 3,2 (cid:48) :6 ,3 -Terpyridine in [Cu 2 ( µ -OAc) 4 (3,2 ,3 -tpy)] n 1D-Polymers and with copper(II) Single-crystal structures of

: We report the preparation and characterization of 4 (cid:48) -([1,1 (cid:48) -biphenyl]-4-yl)-3,2 (cid:48) :6 (cid:48) ,3 (cid:48)(cid:48) -terpyridine ( 1 ), 4 (cid:48) -(4 (cid:48) -fluoro-[1,1 (cid:48) -biphenyl]-4-yl)-3,2 (cid:48) :6 (cid:48) ,3 (cid:48)(cid:48) -terpyridine ( 2 ), 4 (cid:48) -(4 (cid:48) -chloro-[1,1 (cid:48) -biphenyl]-4-yl)-3,2 (cid:48) :6 (cid:48) ,3 (cid:48)(cid:48) terpyridine ( 3 ), 4 (cid:48) -(4 (cid:48) -bromo-[1,1 (cid:48) -biphenyl]-4-yl)-3,2 (cid:48) :6 (cid:48) ,3 (cid:48)(cid:48) -terpyridine ( 4 ), and 4 (cid:48) -(4 (cid:48) -methyl-[1,1 (cid:48) -biphenyl]-4-yl)-3,2 (cid:48) :6 (cid:48) ,3 (cid:48)(cid:48) -terpyridine 4 L] n 1D-coordination polymers with L = 1 – 5 have been determined, and powder X-ray diffraction conﬁrms that the single crystal structures are representative of the bulk samples. [Cu 2 ( µ -OAc) 4 ( 1 )] n and [Cu 2 ( µ -OAc) 4 ( 2 )] n are isostructural, and zigzag polymer chains are present which engage in π -stacking interactions between [1,1 (cid:48) -biphenyl]pyridine units. 1D-chains nest into one another to give 2D-sheets; replacing the peripheral H in 1 by an F substituent in 2 has no effect on the solid-state structure, indicating that bifurcated contacts (H...H for 1 or H...F for 2 ) are only secondary packing interactions. Upon going from [Cu 2 ( µ -OAc) 4 ( 1 )] n and [Cu 2 ( µ -OAc) 4 ( 2 )] n to [Cu 2 ( µ -OAc) 4 ( 3 )] n , [Cu 2 ( µ -OAc) 4 ( 4 )] n , and [Cu 2 ( µ -OAc) 4 ( 5 )] n · n MeOH, the increased steric demands of the Cl, Br, or Me substituent induces a switch in the conformation of the 3,2 (cid:48) :6 (cid:48) ,3 (cid:48)(cid:48) -tpy metal-binding domain, and a concomitant change in dominant packing interactions to py–py and py–biphenyl face-to-face π -stacking. The study underlines how the 3,2 (cid:48) :6 (cid:48) ,3 (cid:48)(cid:48) -tpy domain can adapt to different steric demands of substituents through its conformational ﬂexibility.

In the [Cu 2 (µ-OAc) 4 {4 -(4-n-alkyloxyphenyl)-3,2 :6 ,3 -tpy}] n 1D-polymers with alkyloxy groups being methoxy, butyloxy, pentyloxy, hexyloxy, or heptyloxy [13,26], the conformational variation is more complex than a switch from I to II [13]. With the ligand in conformation II, the arrangement in the two axial sites of the {Cu 2 (µ-OAc) 4 } paddlewheel [27] can follow one of three assembly algorithms as shown in Scheme 3. The labels in and out refer to the orientation of the lone pair of each coordinating N atom with respect to the central N atom of the 3,2 :6 ,3 -tpy unit. Both in/out/in/out... and out/out/in/in... sequences are observed in [Cu 2 (µ-OAc) 4 {4 -(4-n-alkyloxyphenyl)-3,2 :6 ,3 -tpy}] n chains, and we have proposed that this is related to the growing importance of inter-chain van der Waals forces as the length of the alkyloxy chain increases. These interactions complement π-stacking interactions between phenyl/pyridine and pyridine/pyridine rings [13]. Following from these results, we were interested in exploring the effects of replacing the alkyloxy tails by substituents in which π-stacking interactions would be dominant.
All single-crystal growth experiments were carried out under ambient conditions using identical crystallization tubes (i.d. = 13.6 mm, 24 mL).
A blue solution of Cu 2 (OAc) 4 ·2H 2 O (79.9 mg, 0.200 mmol) in MeOH (30 mL) was added to a colorless CHCl 3 solution (10 mL) of 1 (77.1 mg, 0.200 mmol) in a round-bottomed flask. The blue solution was stirred at room temperature and after 1 h, a fine light-green suspension had formed. After 2 h, the suspension was centrifuged, and the solid was collected and dried in vacuo until it was a constant weight (6 h). [Cu 2 (µ-OAc) 4 (1)] n (24 mg, 0.032 mmol, 16%) was isolated as a light green powder. Found C 56. 11 4 (2)] n and Preparative Scale Reaction the crystals were washed with MeOH and CHCl 3 , dried in vacuo, and were analyzed by PXRD and FT-IR spectroscopy.
A blue solution of Cu 2 (OAc) 4 ·2H 2 O (79.9 mg, 0.200 mmol) in MeOH (30 mL) was added to a colorless CHCl 3 solution (15 mL) of 2 (80.7 mg, 0.200 mmol) in a round-bottomed flask. The blue solution was stirred at room temperature, and after 1 h, a fine light green suspension had formed. After 2 h, the solid was collected using a centrifuge and was dried in vacuo until a constant weight was achieved (6 h). [Cu 2 (µ-OAc) 4 (2)] n (101 mg, 0.132 mmol, 66.0%) was isolated as a light-green solid. Found C 54. 43 4

(3)] n and Preparative Scale Reaction
A MeOH (4 mL) solution of Cu 2 (OAc) 4 ·2H 2 O (12.0 mg, 0.030 mmol) was layered over a CHCl 3 solution (4 mL) of 3 (12.6 mg, 0.030 mmol). After eight days, X-ray quality green plate-like crystals had grown. One crystal was selected for single-crystal X-ray diffraction, and the remaining crystals were washed with MeOH and CHCl 3 , dried under vacuum, and analyzed by PXRD and FT-IR spectroscopy.
A solution of Cu 2 (OAc) 4 ·2H 2 O (79.9 mg, 0.200 mmol) in MeOH (30 mL) was added to a solution of 3 (84.0 mg, 0.200 mmol) in CHCl 3 (15 mL) in a round-bottomed flask. The blue solution was stirred at room temperature, and after about 5 min, a fine light green suspension had formed. After 2 h, the suspension was centrifuged, and the solid was dried in vacuo until it was a constant weight (6 h

Crystal Growth of [Cu 2 (µ-OAc) 4 (4)] n and Preparative Scale Reaction
Cu 2 (OAc) 4 ·2H 2 O (12.0 mg, 0.030 mmol) was dissolved in MeOH (4 mL), and the solution was layered over a CHCl 3 solution (4 mL) of 4 (13.9 mg, 0.030 mmol). Green plate-like crystals had grown after 20 days, and a single crystal was selected for X-ray diffraction. The remaining crystals were washed with MeOH and CHCl 3 , dried under vacuum, and analyzed by PXRD and FT-IR spectroscopy.
A solution of Cu 2 (OAc) 4 ·2H 2 O (79.9 mg, 0.200 mmol) in MeOH (30 mL) was added to a CHCl 3 solution (15 mL) of 4 (92.9 mg, 0.200 mmol) in a round-bottomed flask. The blue solution was stirred at room temperature, and a light-green suspension was observed after about 5 min. After 2 h, the suspension was centrifuged, and the solid was dried in vacuo to a constant weight (6 h

Crystal Growth of [Cu 2 (µ-OAc) 4 (5)] n ·nMeOH and Preparative Scale Reaction
Cu 2 (OAc) 4 ·2H 2 O (12.0 mg, 0.030 mmol) was dissolved in MeOH (4 mL), and the solution was layered over a CHCl 3 solution (4 mL) of 5 (11.9 mg, 0.030 mmol). After 25 days, X-ray quality green plates had grown, and a single crystal was selected for X-ray diffraction. The rest of the crystals were washed with MeOH and CHCl 3 , dried in vacuo, and analyzed by PXRD and FT-IR spectroscopy.
A solution of Cu 2 (OAc) 4 ·2H 2 O (79.9 mg, 0.200 mmol) in MeOH (30 mL) was added to a CHCl 3 solution (10 mL) of 5 (79.9 mg, 0.200 mmol) in a round-bottomed flask. The blue solution was stirred at room temperature, and a light-green suspension was observed after about 10 min. After 2 h, the suspension was centrifuged, and the solid was dried under vacuum until the weight was constant (6 h). [Cu 2 (µ-OAc) 4
Powder X-Ray diffraction (PXRD) patterns were collected at room temperature in transmission mode using a Stoe Stadi P diffractometer equipped with a Cu Kα1 radiation (Ge(111) monochromator) and a DECTRIS MYTHEN 1K detector. Whole-pattern decomposition (profile matching) analysis [37][38][39] of the diffraction patterns was performed with the package FULLPROF SUITE [39,40] (version July-2019) using a previously determined instrument resolution function based on a NIST640d standard. The structural models were taken from the single crystal X-Ray diffraction refinements. Refined parameters in Rietveld were scale factor, zero shift, lattice parameters, Cu and halogen atomic positions, background points, and peaks shapes as a Thompson-Cox-Hastings pseudo-Voigt function. Preferred orientations as a March-Dollase multi-axial phenomenological model were incorporated into the analysis.

Density Functional Theory (DFT) Calculations
DFT calculations on ligands 2-4 were carried out using Spartan'18 [41] with a B3LYP 6-31G* basis set with geometry optimization first carried out at the semi-empirical PM3 level.

Ligand Synthesis and Characterization
Compounds 1-5 were prepared using the one-pot method of Hanan [10] as shown in Scheme 5. The products precipitated from the reaction mixtures and were isolated in yields varying from 32.9% (for 5) to 44.8% (for 4). No attempts were made to optimize the reaction conditions. In the electrospray mass spectrum of each compound, the base peak arose from the [M + H] + ion (Figures S1-S5 in the Supporting Material) with characteristic isotope patterns observed for compounds 3 (chloro derivative) and 4 (bromo substituent).
The 1 H and 13 C{ 1 H} NMR spectra of compounds 1-5 were assigned with the aid of COSY, NOESY, HMQC, and HMBC techniques, and 1 H NMR, NOESY, HMQC, and HMBC spectra are shown in Figures S6-S25 in the Supporting Material. Figure 1

Density Functional Theory (DFT) Calculations
DFT calculations on ligands 2-4 were carried out using Spartan'18 [41] with a B3 6-31G* basis set with geometry optimization first carried out at the semi-empirical level.

Ligand Synthesis and Characterization
Compounds 1-5 were prepared using the one-pot method of Hanan [10] as show Scheme 5. The products precipitated from the reaction mixtures and were isolate yields varying from 32.9% (for 5) to 44.8% (for 4). No attempts were made to optimize reaction conditions. In the electrospray mass spectrum of each compound, the base p arose from the [M + H] + ion (Figures S1-S5 in the Supporting Material) with character isotope patterns observed for compounds 3 (chloro derivative) and 4 (bromo substitu Scheme 5. Synthetic route to compounds 1-5. Conditions: (i) KOH, EtOH; NH3 (aqueous), roo temperature, ca. 15 h. Atom numbering for the NMR spectroscopic assignments is given.
The 1 H and 13 C{ 1 H} NMR spectra of compounds 1-5 were assigned with the ai COSY, NOESY, HMQC, and HMBC techniques, and 1 H NMR, NOESY, HMQC, HMBC spectra are shown in Figures S6-S25 in the Supporting Material. Figure 1 disp a comparison of the 1 H NMR spectra of 1-5. The signals arising from the protons in r A, B, and C (see Scheme 5 for ring labels) are unaffected by the change in the substit in ring D. Assignments of the signals for H D2 and H D3 (Figure 1) were confirmed from Scheme 5. Synthetic route to compounds 1-5. Conditions: (i) KOH, EtOH; NH 3 (aqueous), room temperature, ca. 15 h. Atom numbering for the NMR spectroscopic assignments is given.   The absorption spectra of acetonitrile solutions of compounds 1-5 are shown inFigure 2a. Each spectrum is dominated by a broad and intense band arising principally from π*←π transitions. For the three halogen-substituted compounds, the value of λ max shifts from 284 nm (F) to 288 nm (Cl) to 292 nm (Br), consistent with a stabilization of the highestoccupied molecular orbital(s) for the more electron-withdrawing substituent. DFT calculations on ligands 2, 3, and 4 revealed that the highest occupied molecular orbital (HOMO) of each complex is localized on the 4 -halo-[1,1 -biphenyl] domain, while the lowest unoccupied molecular orbital (LUMO) manifold is largely localized on the 3,2 :6 ,3 -tpy unit (Figure 2b). The HOMO-1 is, in each case, localized on the 3,2 :6 ,3 -tpy.

Reactions of Copper(II) Acetate and Ligands 1-5
Ligands 1-5 were allowed to react with copper(II) acetate under ambient conditions by layering a methanol solution of Cu 2 (OAc) 4 ·2H 2 O over a chloroform solution of the appropriate ligand. Single crystals grew within days or several weeks, and after selection of crystals for single crystal X-ray analysis, the remaining crystals were washed with MeOH and CHCl 3 , dried, and analyzed by PXRD to confirm that the single crystals were representative of the bulk sample (see Section 3.4). The solid-state IR spectra of the bulk materials are all similar and are presented in Figures S31-S35 in the Supporting Material. Yields of the products from the single-crystal growth experiments were not optimized, and were in the range 20-30% if crystal growth was allowed to continue for a month.
The reactions were also carried out on a preparative scale by combining a methanol solution of Cu 2 (OAc) 4 ·2H 2 O with a chloroform solution of the respective ligand. The precipitate that formed was separated by centrifugation, dried, and analyzed by elemental analysis and PXRD. Elemental analytical data were in accord with the compositions [Cu 2 (µ-OAc) 4 (L)] n with L = 1-5. The PXRD data are discussed in Section 3.4.
In each of [Cu 2 (µ-OAc) 4 (3)] n , [Cu 2 (µ-OAc) 4 (4)] n , and [Cu 2 (µ-OAc) 4 (5)] n ·nMeOH, the 3,2 :6 ,3 -tpy adopts conformation II (Scheme 2), and the coordination arrangement at the paddle-wheel units (defined in Scheme 3) is in/in/out/out... Figure 8a illustrates part of one coordination polymer chain in [Cu 2 (µ-OAc) 4 (3)] n , and this structure is replicated in [Cu 2 (µ-OAc) 4 (4)] n and [Cu 2 (µ-OAc) 4 (5)] n ·nMeOH, as are the packing motifs described below. Figure 8b illustrates the interdigitation of 1D-polymer chains to produce 2D-sheets. The profile of the chain in Figure 8a contrasts with the zigzag nature of the polymers in Figure 7, and packing interactions are necessarily different. The near planarity of the 3,2 :6 ,3 -tpy unit ( Table 2) reflects the involvement of this domain in crystal packing. Centrosymmetric pairs of pyridine rings containing N3 (N3 and N3 iii , symmetry code iii = 1 − x, 1 − y, 1 − z) stack with an interplane distance of 3.34 Å and inter-centroid separation of 3.68 Å. The pyridine ring with N1 engages in a face-to-face contact with the phenyl ring containing C22 iv (symmetry code iv = 1 + x, 1 + y, z) with a centroid...centroid distance of 3.94 Å and an angle between the ring planes of 11.1 o . In addition, the pyridine ring containing N1 also sits over a biphenyl unit, thereby extending the stack of arene rings. The projection shown in Figure 8c illustrates how the layers comprise domains of π-stacked arene rings and columns of {Cu 2 (µ-OAc) 4 } paddle-wheel units (see also Figure S36 in the Supporting Material).
x, 1 − y, 1 − z) stack with an interplane distance of 3.34 Å and inter-centroid separation of 3.68 Å . The pyridine ring with N1 engages in a face-to-face contact with the phenyl ring containing C22 iv (symmetry code iv = 1 + x, 1 + y, z) with a centroid...centroid distance of 3.94 Å and an angle between the ring planes of 11.1 o . In addition, the pyridine ring containing N1 also sits over a biphenyl unit, thereby extending the stack of arene rings. The projection shown in Figure 8c illustrates how the layers comprise domains of π-stacked arene rings and columns of {Cu2(μ-OAc)4} paddle-wheel units (see also Figure S36 in the Supporting Material).

Characterization by PXRD
To ensure that the single crystal structures were representative of the bulk materials, powder X-ray diffraction patterns were determined for crystals remaining in the crystallization tubes after single crystals had been selected. The refinements ( Figures S37-S41) confirmed that the bulk materials of all the compounds were representative of the analyzed single crystals. Each peak in the experimental plots has a corresponding peak in the fitted spectra, and the differences in the intensities can be rationalized in terms of differences in the preferred orientations. Only [Cu2(μ-OAc)4(2)]n ( Figure S38) shows minor impurities (ca. 10%). A comparison of Figure S38 with PXRD patterns for the precursors 2 and Cu2(OAc)4·2H2O did not reveal matching peaks.
PXRD was also carried out on the materials obtained from the preparative scale reactions. The powder patterns matched those of the materials obtained from the singlecrystal growth experiments. Figure 9 displays the data for [Cu2(μ-OAc)4(1)]n as a representative example, and the superimpositions of the powder patterns for the remaining four coordination polymers are shown in Figures S42-S45 in the Supporting Materials.

Characterization by PXRD
To ensure that the single crystal structures were representative of the bulk materials, powder X-ray diffraction patterns were determined for crystals remaining in the crystallization tubes after single crystals had been selected. The refinements (Figures S37-S41) confirmed that the bulk materials of all the compounds were representative of the analyzed single crystals. Each peak in the experimental plots has a corresponding peak in the fitted spectra, and the differences in the intensities can be rationalized in terms of differences in the preferred orientations. Only [Cu 2 (µ-OAc) 4 (2)] n ( Figure S38) shows minor impurities (ca. 10%). A comparison of Figure S38 with PXRD patterns for the precursors 2 and Cu 2 (OAc) 4 ·2H 2 O did not reveal matching peaks.
PXRD was also carried out on the materials obtained from the preparative scale reactions. The powder patterns matched those of the materials obtained from the single-crystal growth experiments. Figure 9 displays the data for [Cu 2 (µ-OAc) 4 (1)] n as a representative example, and the superimpositions of the powder patterns for the remaining four coordination polymers are shown in Figures S42-S45 in the Supporting Materials.

Conclusions
We   4 (1)] n obtained from a preparative scale reaction (blue) and from the single-crystal growth experiment (red).