Heterometallic [MnPtn(L)2n]x+ Macrocycles from Dichloromethane

Publication Date (Web): August 18, 2016. Copyright © 2016 American Chemical .... J. Gałęzowska , P.J. Boratyński , R. Kowalczyk , K. Lipke , H. Cz...
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Heterometallic [MnPtn(L)2n]x+ Macrocycles from DichloromethaneDerived Bis-2-pyridyl-1,2,3-triazole Ligands Dan Preston,* Robert A. J. Tucker, Anna L. Garden, and James D. Crowley Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand S Supporting Information *

ABSTRACT: There is continued interest in the assembly of heterometallic metallosupramolecular assemblies due to the potential for new structural types and/or interesting chemical and physical properties. Two novel methylene-linked bis-2pyridyl-1,2,3-triazole ligands (1a, 1b) were synthesized through CuAAC “click” chemistry between dichloromethane (DCM), sodium azide, and the appropriate ethynylpyridine, giving the shortest possible “regular” bis-pyridyl-1,2,3-triazole. The first example of bis-coordination of two 2-pyridyl-1,2,3-triazoles (Rpytri) around one Pt(II) center is reported, giving exclusive formation of head-to-tail [Pt(Rpytri)2]2+ complexes with vacant binding sites suitable for complexation with other metals and the formation of heterometallic assemblies. The concentration-dependent formation of an equilibrium mixture of a heterometallic [Pd2Pt2(L)4]8+ [4 + 4] square and [Pd3Pt3(L)6]12+ [6 + 6] hexagon was observed, and at lower concentrations ([reactants] = 1.5 mM) hexamer formation was negligible. The [Pt(L)2]2+ building block could also be utilized in the synthesis of a concentrationindependent [Cu2Pt2(L)4]6+ metallomacrocyle. These compounds were characterized with 1H, 13C, and 1H DOSY NMR spectroscopies, elemental analysis, mass spectrometry, and in some cases X-ray crystallography.

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INTRODUCTION As metallosupramolecular chemistry1 evolves and matures, structures of ever-increasing complexity and functional diversity are produced. As greater control is attained over traditional systems utilizing a single ligand type and metal, more attention has been turned toward heteroleptic and/or heterometallic systems as a source of added variety. The interest in heterometallic species continues unabated due to the potential to access hitherto unavailable structural types of assembly1e,2 and the opportunity for interesting chemical2a,b,3 or photophysical properties.4 The formation of heterometallic species has usually been accomplished through low symmetry ligands, where the system has different orthogonal binding sites.1a,c,3d These sites might exhibit preference for one metal over another through exploiting the coordination preference of different metals,2f,g,5 or using a stepwise synthetic procedure where an inert metal is bound and then another binding site is added for coordination to a more labile metal.3b,4a,6 Far less common is the use of a ligand with a single binding mode at all sites for the controlled formation of heterometallic architectures. Ward and co-workers have utilized bisbidentate pyridyl-pyrazole ligands with one inert and one labile metal to give mixed metal species,2a−e,3c,7 forming tris inert metal complexes before addition of a metal to the second binding pocket, and have thus accessed a wide array of structures. They have utilized inert octahedral Ru(II) and Os(II) metal ions, forming [M(L)3]2+ metalloligands, generally in a 1:3 mer/fac ratio. These isomers are either separated prior to further use, or used as a mixture where one reacts preferentially. Labile metals used have been Co(II) and Cd(II) in octahedral geometry, or Ag(I) in a tetrahedral geometry. © XXXX American Chemical Society

While Pt(II) has been used together with cis-protecting strategies and monodentate ligands,3b it is yet to be utilized as the inert metal with bidentate ligands in this type of approach. In the synthesis of polybidentate ligands for metallosupramolecular systems (heterometallic or otherwise), the properties bestowed by the 2-pyridyl-1,2,3-triazole bidentate binding pocket are manifold. Such benefits include ready synthetic ease through the copper-catalyzed azide−alkyne cycloaddition (CuAAC) reaction, under mild reaction conditions and with varied functional scope.8 Additionally, a wide array of metals with various coordination geometries have been used in combination with this or related motifs.2d,5a,9 A large family of bis-pyridyl triazoles have been synthesized with aryl and alkyl linkers, with the smallest in size being the ethyl linkage.10 We and others are interested in “click” ligands and, in particular, 2-pyridyl-1,2,3-triazoles for the generation of a range of metallosupramolecular architectures, including cylinders,11 tetrahedra9c and other cages,5a and metallomacrocyles.7,10a,12 This latter class of cyclic assembly has exhibited, as a general class, properties such as luminescence,13 redox activity,14 cytotoxicity,15 and host−guest capabilities.12b,16 These systems have potential for diverse applications such as molecular scavenging,17 drug delivery,18 and catalysis,14b including the conversion of carbon dioxide to oxalate.12c However, a complication that may arise in the attempted synthesis of macrocycles is the possibility for the formation of equilibrium mixtures of different macrocycle size. The adage that the Received: June 15, 2016

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DOI: 10.1021/acs.inorgchem.6b01435 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 1. Synthesisa

thermodynamic product in metallosupramolecular assembly will adopt the smallest possible cyclic structure has always been subject to the constraints imposed by the geometry of the ligand and the coordination preference of the metal.1 Indeed, the palladium(II) “Fujita” squares archetypical of supramolecular macrocycles exist in equilibrium in solution beside the entropically favored triangle when the ligand possesses sufficient flexibility.19 The entropic gain of smaller assemblies can be offset by the enthalpic cost of bond strain and torsion or a reduced coordination sphere, and the position of the equilibrium between the smallest possible assembly and larger architectures has been demonstrated by Fujita and others to be concentration dependent, with lower concentrations favoring smaller assemblies.20 This behavior has been observed for a variety of ligand systems including those with polybidentate metal binding modes.20a−c We have demonstrated that [Pd(Rpytri)2]2+ complexes consistently form with the ligands in a head-to-tail arrangement, thereby avoiding steric clash and giving rise to favorable interligand hydrogen bonding.9b,21 The analogous Pt(II) complexes have not been synthesized. However, related platinum Rpytri compounds are known including [Pt(Rpytri)2Cl2] complexes,9b,22 heteroleptic [Pt(Rpytri)2(L)2]2+ complexes where L = phenylpyridine23 or diaminocyclohaxane,24 and bis-pyridyl-triazolato complexes.25 We herein report the synthesis of two new bis-2-pyridyl-1,2,3-triazole ligands (L) with methylene spacers, the shortest possible “regular” pyridyltriazole linkage, with the fewest possible degrees of freedom of any “hinged” bis-pyridyl-1,2,3-triazole. These were used to form the first examples of bis-pyridyl-triazole [Pt(L)2]4+ complexes, which assembled exclusively in the head-to-tail conformation. These Pt(II) metalloligands had vacant peripheral binding sites that could then be used in the generation of heterometallic species. Mixed Pd(II)/Pt(II) macrocycles ([4 + 4] or [6 + 6]) were formed in a concentration-dependent manner, while a mixed metal Cu(I)/Pt(II) [4 + 4] macrocycle was cleanly obtained independent of concentration (Scheme 1).

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RESULTS AND DISCUSSION While a wide range of bis-pyridyl-triazole ligands10 is known, we targeted the previously unreported methylene linked ligands, 1,1-bis(2-pyridyl-1,2,3-triazol-4-yl)methane (1a) and 1,1-bis((4-(5-(hexyloxy)pyridin-2-yl)-1H-1,2,3-triazol-1-yl)methane (1b), to reduce the number of degrees of freedom in the ligand architecture.26 Presumably these systems have not been examined before because their synthesis requires the use of the explosive diazidomethane.27 Bis-triazoles (and indeed, tris-triazoles) attached to a single carbon linker have been synthesized, but only through isolation of the azide intermediate.28 The ligands (1a, 1b) were synthesized in a single step through a CuAAC “click” reaction, generating the explosive diazide in situ from sodium azide and dichloromethane (DCM) in a microwave in dimethylformamide (DMF) up to 110 °C in the presence of carbonate and then “clicking” on 2 equiv of 2-ethynylpyridine (for 1a) or 2-(2(trimethylsilyl)ethynyl)-5-(hexyloxy)pyridine 29 (for 1b) (Scheme 1). Negligible monosubstitution occurred when making the ligands despite a 25-fold excess of DCM. The new ligands were characterized by NMR spectroscopy, elemental analysis, mass spectrometry, and, for 1a, X-ray crystallography (Supporting Information). In considering the macrocyclic self-assembly behavior of these ligands with four-coordinate metals, one can envisage

(i) NaN3, Na2CO3, DMF, 60 °C for 20 min then 110 °C for 20 min, 2-ethynylpyridine or 2-(2-(trimethylsilyl)ethynyl)-5-(hexyloxy)pyridine with Na2CO3, CuSO4·5H2O, sodium ascorbate, water, RT overnight; (ii) [Pt(DMSO)2Cl2], AgNO3, 1a or 1b, DMSO, 85 °C, [NH4]PF6 or [N(Bu)4]BF4; (iii) 1:1 equiv of [Pd(CH3CN)4](BF4)2 and [Pt(1b)2](BF4)2 in nitromethane; (iv) 1:1 equiv of [Cu(CH3CN)4](BF4)4 and [Pt(1b)2](BF4)2 in nitromethane or CH3CN. a

binding of two ligands around each metal center, to give [n + n] macrocycles of many sizes. Indeed, the attempted formation of homonuclear macrocycles using a selection of metals resulted in either untidy spectra indicative of multiple cyclic/oligomeric species or precipitation, presumably of the same.30 It was reasoned that the 2:1 combination of ligand to Pt(II) might give a [Pt(Rpytri)2]2+ metalloligand capable of being then combined with Pd(II), thereby confining the available macroB

DOI: 10.1021/acs.inorgchem.6b01435 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry cycle sizes to [n + n] where n is an even number ≥4, thus decreasing the number of possible competing permutations, with the [4 + 4] and [6 + 6] macrocycles predicted to predominate due to entropic considerations. It was anticipated that complications with isomers potentially present with inert octahedral metal ions (e.g., mer and fac and optical isomers thereof) would here be avoided due to the square planar geometry of the metal in conjunction with the head-to-tail preference of the ligand, seen exclusively with analogous [Pd(Rpytri)2]2+ complexes.9b,21 Density functional theory (DFT) calculations (B3LYP, LanL2DZ basis set for metal ions, 6-31G(d) for other atoms, dimethyl sulfoxide (DMSO) solvent field) comparing the free energies of head-totail and head-to-head mononuclear [Pt(Bnpytri)2]2+ complexes, where Bnpytri = 2-(1-benzyl-1H-1,2,3-triazol-4-yl)pyridine), revealed the head-to-tail configuration or isomer being significantly thermodynamically favored, by 28.6 kJ mol−1 (a similar value, 28.7 kJ mol−1, was obtained for the corresponding palladium(II) analogue), and it was envisaged that, despite the more inert nature of Pt(II) compared to Pd(II), the head-to-tail configuration or isomer would nonetheless prevail under conditions allowing formation of the thermodynamic product. The synthesis of the mononuclear [Pt(Bnpytri)2](PF6)2 model complex was first attempted to confirm the preferential formation of the head-to-tail isomer. Reaction of [Pt(DMSO)2Cl2]31 (1 equiv), Bnpytri (2 equiv), and AgNO3 (2 equiv) in DMSO at 85 °C overnight, followed by precipitation with [NH4]PF6, provided the complex [Pt(Bnpytri)2](PF6)2 as a colorless solid in 52% yield. The resulting complex was characterized using NMR spectroscopy, elemental analysis, and mass spectrometry, and the solid state structure was confirmed using X-ray crystallography (P21/c). The complex displayed the expected head-to-tail arrangement of the ligands around the Pt(II) ions (Supporting Information, Figure 1a). Pleasingly, the equivalent [Pt(L)2]2+ complexes could be formed using 2 equiv of the bisbidentate ligands 1a or 1b, using similar procedures, giving [Pt(1a)2](PF6)2 and the far more soluble [Pt(1b)2]-

(BF4)2 (Scheme 1), despite the potential complications introduced by the additional binding sites. The 1H NMR spectra of these products showed the desymmetrization of the ligands consistent with complexation in a single pyridyl-triazole

Figure 2. Partial stacked 1H NMR spectra (500 MHz, d3-nitromethane, 298 K) of (a) 1b, (b) [Pt(1b)2](BF4)2, (c) combined 1:1 [Pd(CH3CN)4](BF4)2 (27 mM) and [Pt(1b)2](BF4)2, (d) combined 1:1 [Pd(CH3CN)4](BF4)2 (5.5 mM) and [Pt(1b)2](BF4)2, (e) combined 1:1 [Pd(CH3CN)4](BF4)2 (1.5 mM) and [Pt(1b)2](BF4)2, and (f) [Cu2Pt2(1b)4](BF4)6. ∗ = trace impurity in d3-nitromethane.

pocket of each ligand (Figure 2b and Supporting Information). 1 H DOSY NMR spectroscopy confirmed the creation of larger architectures diffusing at slower rates through solution (1a and [Pt(1a)2](PF6)2, 500 MHz, d6-DMSO, D = 2.81 × 10−10 or 1.46 × 10−10 m2 s−1, respectively, and 1b and [Pt(1b)2](BF4)2, 500 MHz, d3-nitromethane, D = 6.23 × 10−10 or 4.04 × 10−10 m2 s−1, respectively).32 Despite repeated efforts, crystals grown of [Pt(1b)2](BF4)2 were of poor quality, were small, and gave poor diffraction, but those from vapor diffusion of diethyl ether into acetonitrile (P1̅) gave a structure which was sufficient to establish connectivity and showed a head-to-tail conformation at the metal with the desired free pyridyl-triazole pockets at either end (Figure 1b). The combination of a 1:1 ratio of [Pt(1b)2](BF4)2 (chosen over [Pt(1a)2](PF6)2 due to the extremely low solubility of the latter) with [Pd(CH3CN)4](BF4)2 in d3-nitromethane gave an 1 H NMR spectrum that still displayed low symmetry but showed downfield shifts of the peaks associated with the previously unoccupied pyridyl-triazole moiety (Figure 2c−e), consistent with coordination to the palladium(II) ions. At a concentration of 27 mM for both reactants, the upper limit of solubility, peaks consistent with the formation of two distinct species were observed at a 5:2 ratio. As the concentration of the mixture was lowered, the percentage of the more prevalent species (at higher chemical shift) decreased until it was negligible at a concentration of 1.5 mM. 1H DOSY NMR spectroscopy confirmed that there were two distinct species

Figure 1. Ellipsoid plots of (a) [Pt(Bnpytri)2](PF6)2 (bond lengths Pt1−N1 = 2.048(9) Å, Pt1−N2 = 1.997(9) Å; bond angle N1−Pt1− N2 = 79.4°) and (b) [Pt(1b)2](BF4)2 (one of the three molecules present in the unit cell; bond lengths Pt1−N1 = 2.06(9) Å, Pt1−N2 = 1.96(9) Å; bond angle N1−Pt1−Pt2 = 78.3°). Ellipsoids are shown at the 50% probability level. Color scheme: carbon, gray; hydrogen, white; nitrogen, blue; platinum, purple. Counterions and solvent molecules are omitted for clarity. C

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Inorganic Chemistry present in solution; the species with more upfield 1H NMR chemical shifts displayed a diffusion coefficient (D = 2.87 × 10−10 m2 s−1) consistent with a [Pd2Pt2(1b)4](BF4)8 [4 + 4] metallomacrocyle, while the species with further downfield chemical shifts diffused (D = 1.83 × 10−10 m2 s−1) more slowly in solution, consistent with the formation of the [Pd3Pt3(1b)6](BF4)12 hexamer (Figure 3).

Figure 3. Plot of log(D) against log(MW) for 1b, [Pt(1b)2](BF4)2, [Pd2Pt2(1b)4](BF4)8, [Pd3Pt3(1b)6](BF4)12, and [Cu2Pt2(1b)4](BF4)6. (500 MHz, d3-nitromethane, 298 K. Units: D, ×10−10 m2 s−1; Mw, g mol−1.)

Figure 4. HR ESI-MS (CH3NO2 or CH3NO2/CH3CN): observed versus calculated isotopic distribution for (a) [Pd2Pt2(1b)4](BF4)(Cl)(CHOO)24+ and (b) [Pd2Pt2(1b)4](BF4)2(Cl)(CHOO)23+. (c) Partial mass spectrum of [Cu2Pt2(1b)4](BF4)6.

The movement of the equilibrium toward the tetramer at lower concentrations is consistent with previously described behavior in related systems.20a−c High resolution electrospray ionization (HR-ESI) mass spectrometry under pseudocold spray conditions of a mixed sample gave a highly fragmented spectrum. Analysis was further complicated by overlaid peaks of different charge, and mixtures of counterions associated with the charged species, but ions consistent with the intact tetramer could be identified (m/z = 973.3247, calc [Pd2Pt2(1b)4](BF4)2(Cl)(CHOO)23+ = 973.2980; m/z = 708.2430, calc [Pd2Pt2(1b)4](BF4)(Cl)(CHOO)24+ = 708.2224) (Figure 4a,b). The tetramer was cleanly prepared at a low concentration (1.5 mM for reactants), and isolated by precipitation in a poor yield (33%) due to the high dilution required, resulting in difficulties with complete precipitation and collection. Unfortunately, efforts to crystallize either the tetramer or the hexamer were unsuccessful. The DFT optimized structure of [Pd2Pt2(1b)4]8+ (and also [Cu2Pt2(1b)4]6+, vide infra, both structures calculated using B3LYP with a LanL2DZ basis set for metal ions, 6-31G(d) for other atoms, nitromethane solvent field, calculated without hexyloxy chains for computational simplicity, Supporting Information) was successfully determined. The [Pd2Pt2(1b)4]8+ tetramer exhibited the expected boxlike geometry (also MMFF modeling, Figure 5a), while the calculations for the larger hexamer did not converge on a minimum. MMFF modeling (with hexyloxy chains) for the hexamer gave the expected geometry (Figure 5b). While the use of square planar Pd(II) gave a concentrationdependent assembly, it was anticipated that the use of a labile metal with tetrahedral geometry might have less scope for the formation of larger macrocycles, in addition to bringing the Pt(II) centers closer together, and stabilize the tetramer

through platinum−platinum and π-stacking interactions. Diamagnetic Cu(I) and Ag(I) [M(Rpytri)2]+ complexes have both previously been reported.9a,10a,22e,33 Despite the normative preference of Ag(I) for tetrahedral geometry over square planar,34 it has shown a tendency to adopt a head-to-tail square planar geometry with bispyridyl-triazoles.10a,22e,35 In contrast, previously reported four-coordinate Rpytri Cu(I) complexes have consistently demonstrated tetrahedral geometry, both crystallographically and through DFT calculations.9a,22e,33 [Cu2Pt2(L)4]6+ macrocycles have previously been reported, but only through the use of asymmetric ligands with orthogonal binding sites, in combination with cis-protecting directional bonding strategies at the Pt(II) centers.3b,5d The addition of [Cu(CH3CN)4](BF4) (1 equiv) to a CH3CN solution [Pt(1b)2](BF4)2 (1 equiv) resulted in the clean formation of a single assembly. The 1H NMR spectrum exhibited a single set of peaks downfield-shifted from free 1b ([Cu(I)] from 1.5 to 8 mM) (Figure 2f), and DOSY NMR spectra showed that this species was diffusing at a rate similar to the [Pd2Pt2(1b)4]4+ tetramer (Figure 3, D = 2.80 × 10−10 m2 s−1) . Mass spectrometry of the sample showed, in addition to the peaks pertaining to free [Pt(1b)2]2+, the macrocycle [Cu2Pt2(1b)4](BF4)22+ overlaid with [CuPt(1b)2](BF4)2+ (m/z = 1441.5066, calc = 1441.4940 and 1441.4937), as well as other Cu(I) containing fragments (Figure 4c). The formation of a single discrete architecture rather than an equilibrium mixture seems likely to be due to the tetrahedral Cu(I) “corners” favoring the tetramer over larger macrocycles. The use of Cu(I) has shown that it is possible to controllably incorporate metal ions of varied coordination geometry into a single structure using this strategy. D

DOI: 10.1021/acs.inorgchem.6b01435 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

reported as proof of concept in this work exhibited no host− guest capabilities with commonly used guests,16a,17b,36 but cavity size and character could be readily tuned through ligand choice to enable guest encapsulation. In this manner, the Pt(II) metalloligand could be combined with other metals of numerous geometries to access multitudinous novel structural types and interesting new functionalities.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01435. MMFF and DFT calculated structures (XYZ) Crystallographic information (including CIF files, CCDC numbers 1482854−1482858) (CIF) Experimental section, 1H, 13C and DOSY NMR spectral information, DFT calculation details, and calculated structures (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +64 3 479 7910. Tel.: +64 3 479 7910. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Figure 5. MMFF models of (a) [Pd2Pt2(1b)4]8+, (b) [Pd3Pt3(1b)6]12+, and (c) [Cu2Pt2(1b)4]6+. Colors: carbon, gray; hydrogen, white; copper, copper; nitrogen, blue; oxygen, red; palladium, magenta; platinum, purple.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Dr. Synøve Scottwell for assistance. D.P. and R.A.J.T. thank the University of Otago for a Ph.D. scholarship and summer studentship, respectively. A.L.G. thanks the MacDiarmid Institute for Advanced Materials and Nanotechnology for financial support. The authors thank the University of Otago for additional funding. The authors acknowledge the contribution of the NeSI high performance computing facilities to the results of this research. New Zealand’s national facilities are provided by the New Zealand eScience Infrastructure and funded jointly by NeSI’s collaborator institutions and through the Ministry of Business, Innovation & Employment’s Research Infrastructure program. URL: https://www.nesi.org.nz.

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CONCLUSIONS The ligands 1,1-bis(2-pyridyl-1,2,3-triazol-4-yl)methane (1a) and 1,1-bis((4-(5-(hexyloxy)pyridin-2-yl)-1H-1,2,3-triazol-1yl)methane (1b) were safely synthesized in a single step through a CuAAC “click” reaction, generating the potentially explosive diazide in situ from sodium azide and dichloromethane. These ligands have a single methylene carbon linker, the shortest possible regular bis-2-pyridyl-1,2,3-triazole. Presumably this in situ azide formation method could be exploited for the generation of other methylene-linked bis-triazole compounds. The first examples of bis-pyridyl-1,2,3-triazole [Pt(L)2]2+ complexes were formed, exclusively as the head-to-tail isomer. A bis-pyridyl-1,2,3-triazole platinum(II) metalloligand was generated with two vacant peripheral bidentate sites. These metalloligands were used for formation of larger heterometallic macrocyclic assemblies. Concentration-dependent [PdnPtn(L)2n]4n+ tetrameric and hexameric macrocycles were obtained when the platinum(II) metalloligand was treated with palladium(II) ions. A concentration independent tetrameric [Cu2Pt2(L)4]6+ macrocycle was formed when copper(I) ions were added to the metalloligand. These or related metallomacrocycles have potential for integration into larger interlocked architectures, and work in this direction is underway. In addition, this strategy for synthesis of mixed metal architectures could be used either with novel polypyridyl-triazoles, or from drawing from the extensive library of already synthesized ligands of this sort, or even with lower symmetry ligands with orthogonal binding sites. The assemblies

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REFERENCES

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Inorganic Chemistry

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DOI: 10.1021/acs.inorgchem.6b01435 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry DMF or DMSO due to oxidation of the metal. A 1:1 combination of Pt(II) with [Pt(1b)2](BF4)2 or the free ligands gave numerous kinetically trapped intermediates that could not be purified. (31) Allampally, N. K.; Bredol, M.; Strassert, C. A.; De Cola, L. Chem. - Eur. J. 2014, 20, 16863−16868. (32) Molecular weights showed good correlation to both molecular volumes and molecular radii (calculated from MMFF models, Supporting Information) and in this case any of the three could be used interchangeably. (33) Thongkam, P.; Jindabot, S.; Prabpai, S.; Kongsaeree, P.; Wititsuwannakul, T.; Surawatanawong, P.; Sangtrirutnugul, P. RSC Adv. 2015, 5, 55847−55855. (34) Young, A. G.; Hanton, L. R. Coord. Chem. Rev. 2008, 252, 1346−1386. (35) This promiscuity of Ag(I) toward square planar geometry with 2-pyridyl-1,2,3-triazoles was demonstrated again during the course of this work. Vapor diffusion of diethyl ether in a DMF solution with a 1:1 ratio of 1a with AgSbF6 gave crystals of two different morphologies from different crystallizations, with both resulting structures (Pmc/21 and P1̅) revealing a square planar [Ag(1a)]∞ linear coordination polymer (Supporting Information). (36) Kishi, N.; Akita, M.; Yoshizawa, M. Angew. Chem., Int. Ed. 2014, 53, 3604−3607.

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DOI: 10.1021/acs.inorgchem.6b01435 Inorg. Chem. XXXX, XXX, XXX−XXX