Discrete Binuclear Cobalt(III) Bis-dioximates with Wheel-and-Axle

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Discrete Binuclear Co(III) bis-Dioximates with Wheel-and-axle Topology as Building Blocks to Afford Porous Supramolecular Metal-organic Frameworks Eduard Coropceanu, Andrei Rija, Vasile Lozan, Ion Bulhac, Gheorghe Duca, Victor Ch. Kravtsov, and Polina Bourosh Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b01402 • Publication Date (Web): 06 Jan 2016 Downloaded from http://pubs.acs.org on January 6, 2016

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Crystal Growth & Design

Discrete Binuclear Co(III) bis-Dioximates with Wheel-and-axle Topology as Building Blocks to Afford Porous Supramolecular Metal-organic Frameworks Eduard Coropceanu,a Andrei Rija,a Vasile Lozan,a Ion Bulhac,a Gheorghe Duca,a Victor Ch. Kravtsov,b,* and Paulina Bouroshb,* a

Institute of Chemistry, Academy of Sciences of Moldova, Academiei str. 3, MD2028 Chisinau, Republic of Moldova; b Institute of Applied Physics, Academy of Sciences of Moldova, Academiei str. 5, MD2028 Chisinau, Republic of Moldova

ABSTRACT Three binuclear and one mononuclear Co(III) dioximates with the compositions [Co2(dmgH)4(bpy)Cl2]·1.5dmf (1), [Co2(nioxH)4(bpy)Cl2]·0.5H2O (2), [Co2(dmgH)4(bpe)Cl2]·0.5H2O (3) and [Co(dmgH)2(bpy)Cl]·H2O (4) (where dmgH2 = dimethylglyoxime, nioxH2 = 1,2-cyclohexanedionedioxime, bpy = 4,4’−bipyridine, bpe = 1,2bis(4-pyridyl)ethane and dmf = N,N-dimethylformamide) were prepared by replacement of water molecule in Co(III) mononuclear dioximates by bpy and bpe ligands. All compounds were characterized by single-crystal X-ray diffraction and spectroscopic techniques. In all complexes Co(III) atoms have an identical octahedral N5Cl environment formulated by four nitrogen atoms of two monodeprotonated oxime ligands in a square planar mode, and the nitrogen atom of the bpy/bpe molecules and chloride atom in the axial positions. In 1 – 3 bpy/bpe exo-bidentate spacer ligands serve as bridging “rods” and unite two planar Co(III) bis-dioximates in binuclear complex with wheel-and-axle topology. The packing of bulky binuclear complexes results in formation of porous structure with hourglass-like channels of diameter ca 0.6 − 1.3 nm in the crystal of compound 1 and smaller cavities in 2. The sorption properties for 1 were also measured. The π···π stacking interaction between monodentate bpy ligands of mononuclear complexes 4 emulate supramolecular binuclear assembly with wheel-and-axle topology. INTRODUCTION Classic bis-dioximates of transition metals were widely studied1–5 generally for the well documented Co-C bond stability and because they were proposed as important simple model for understanding of elusive mechanisms of B12 dependent enzymatic processes6,7 as well due to a range of synthetic, analytical, catalysis and structural possibilities. Survey of Cambridge Structural Database (CSD)8 reveals a tremendous number of structurally characterized bisdioximate complexes, in majority of which (about eight hundred hits in CSD) two dioximes (dimethylglyoxime, 1,2-cyclohexanedionedioxime, alkyl, aryl-substituted and some other dioximes) chelate metal atom through nitrogen atoms and result in planar mononuclear entity [M(dioxH)2] (M=metal, dioxH2 = any dioxime) stabilized additionally by two strong O−H…O intramolecular H-bonds. The coordination surrounding in such complexes is completed by axial ligands of various kind including neutral base, inorganic and organic ligand, thus indicating possibility to manipulate with axial ligands in such complexes and their applicability as molecular building block for chemistry at the axial positions. Although chemistry of mononuclear bis-dioximates is rich and well documented they are still intensively studied, for example as cheap photocatalysts for light-driven hydrogen production9−12. Surprisingly not much data has been reported on the polymers13–15 and binuclear complexes16–24 based on [M(dioxH)2] building blocks linked by pyridine based rod-like bridges, though they also revealed photocatalytic properties19. Such binuclear complexes possess wheeland-axle topology and provide to be useful molecular building block for creating flexible metallorganic supramolecular networks and porous architectures in crystal25–27 because they that cannot pack efficiently without including solvent molecules. However, they have received little ACS Paragon Plus Environment


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attention as components of porous materials. The porous supramolecular network may be assembled from discrete coordination complexes through weak CN···π,28, C–H···O,29 π···π stacking30,31 supramolecular interactions or convolution of π···π stacking and lipophilic interactions.32 Here, we report the formation and porosity of a crystalline solvates by three discrete dinuclear cobalt complexes and mononuclear one which have been obtained by replacement of water molecule in mononuclear [Co(dmgH)2(H2O)Cl] and [Co(nioxH)2(H2O)Cl] complexes by 4,4'-bipyridine (bpy) or 1,2-bis(4-pyridyl)ethane (bpe). The aqua-chloride complexes have been chosen as starting building blocks to avoid the formation of polymeric chains. Previously we have reported a series of Сo(III) dioximates containing Сl- and Br- or N3- anions and various polyfunctional ligands, derivatives of sulfanilamide, isonicotinic hydrazide, which coordinate to the metal in monodentate mode with the formation of mononuclear complexes33,34. EXPERIMENTAL DETAILS Materials and Methods. All reagents and solvents were obtained from commercial sources and were used without further purification. Elemental analyses were performed on an Elementar Analysensysteme GmbH Vario El III elemental analyzer. The IR spectra were obtained on a Perkin Elmer Spectrum-100 FT IR spectrometer in a range of 4000 – 400 cm-1 in Nujol mulls and 4000 – 650 cm-1 ATR. NMR-spectra were recorded on a Bruker spectrometer at 400.13 MHz for 1H and 100.61 MHz for 13C in DMSO-d6 using TMS as an internal reference. Chemical shifts (δ) are reported in parts per million (ppm) and are referenced to the residual nondeuterated solvent peak (2.49 for 1H and 39.70 for 13C). Sorption properties for 1 were measured on a Quantachrome NOVA 4000e instrument; degassing was conducted at 110°C for 4 h. Synthesis of complexes. The mononuclear Co(III) dioximates were used as starting salts in all syntheses35,36. [Co2(dmgH)4(bpy)Cl2]·1.5dmf (1). A mixture of [CoCl(dmgH)2(H2O)] (0.35 g, 1.0 mmol) and bpy (0.08 g, 0.5 mmol) in CH3OH/dmf (2:1, 30 ml) was heated at 70 °C for 10 min. The solution was filtered and left to stand for crystallization at room temperature. The brown prismatic crystals of 1 suitable for X-ray analysis were filtered off and dried in air. The crystals were unstable in the air, soluble in alcohols, dmf, and partly in water. Yield: ~30% (0.14 g). Anal. Calc. for C30.5H46.5Cl2Co2N11.5O9.5, %: C, 40.03; H, 5.12; N, 17.61. Found C, 39.52; H, 4.79; N, 17.46. The IR (cm-1) ν=: 2863 (w), 2611 (m), 1693 (w), 1572 (v.s), 1468 (m), 1390 (m), 1360 (s), 1165 (m), 1122 (m), 1049 (s), 1019 (s), 971 (s), 898 (s), 874 (s), 761 (m), 712 (m). [Co2(nioxH)4(bpy)Cl2]·0.5H2O (2). A mixture of [Co(nioxH)2Cl(H2O)] (0.40 g, 1 mmol) and bpy (0.08 g, 0.5 mmol) dissolved in CH3OH:dmf (2:1, 40 ml) was heated at 70°C for 10 min. The solution is filtered off and left for slow evaporation at room temperature. The dark brown prismatic crystals of 2 suitable for X-ray analysis were filtered off and dried in air. The crystals were soluble in alcohols, dmf, and partly in water. Yield: ~10% (0.05 g). Anal. Calc. for C34H45Cl2Co2N10O8.5, %: C, 44.45; H, 4.94; N, 15.25. Found C, 44.32; H, 4.80; N, 15.13. The IR (cm-1) ν=: 3109(w), 3065(w), 2947(w), 2864(w), 1619(m), 1530(s), 1485(m), 1434(m), 1377(m), 1228(s), 1087(s), 1035(m), 976(m), 868(m), 813(m), 695(m). [Co2(dmgH)4(bpe)Cl2]·0.5H2O (3). A mixture of [Co(dmgH)2Cl(H2O)] (0.35 g, 1 mmol) and bpe (0.08 g, 0.5 mmol) dissolved in the mixture CH3OH:dmf (2:1, 30 ml) was heated at 70°C for 10 min. The solution is filtered off and left for slow evaporation at room temperature. The brown rectangular stick-shaped crystals of 3 suitable for X-ray analysis were filtered off and dried in air. The crystals were soluble in methanol, alcohols, dmf, and partly in water. Yield: ~50% (0.21 g). Anal. Calc. for C28H41Cl2Co2N10O8.5, %: C, 39.91; H, 4.90; N, 16.62. Found C, 39.83; H, 4.81; N, 16.53. The IR (cm-1) ν=: 1627(m), 1619(m), 1555(s), 1511(m), 1433(m), 1377(m), 1237(s), 1214 (m), 1087(s), 1035(m), 976(m), 868(m), 813(m), 739(m).

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[Co(dmgH)2(bpy)Cl]·H2O (4). A mixture of [Co(dmgH)2Cl(H2O)] (0.35 g, 1 mmol) and bpy (0.16 g, 1 mmol dissolved in the mixture CH3OH:dmf (2:1, 30 ml) was heated at 70°C for 10 min. The solution is filtered off and left for slow evaporation at room temperature. The brown flattened needles of 4 suitable for X-ray analysis were filtered off and dried in air. The crystals were soluble in methanol, alcohols, dmf, and partly in water. Yield: ~40% (0.19 g). Anal. Calc. C18H24ClCoN6O5, %: C, 43.34; H, 4.85; N, 16.85. Found C, 43.23; H, 4.76; N, 16.72. The IR (cm-1) ν=: 1615(m), 1594(m), 1559(m), 1411(s), 1370(m), 1237(s), 1089(s), 868(m), 813(m), 739(m). X-ray Crystallography. The unit cell parameters and the sets of reflections intensity were measured at 293 K on a Xcalibur E CCD diffractometer for crystals 1 and 4, and at 153 and 100 K on a STOE IPDS-2T and a Nonius Kappa CCD diffractometers for crystals 2 and 3, respectively (MoKα radiation, graphite monochromator). The structures of compounds 1–4 were solved by the direct methods and refined by least squares in the anisotropic full matrix approximation for non-hydrogen atoms (SHELX-97)37. Crystal of 1 partially loses solvent molecules and only one dmf position has been found and refined with s.o.f. 0.75. All available crystals of 2 were found to be poor diffracted and revealed twinning. For the best sample the only ~29% (1506 reflections with I > 2σ(I)) were marked as observed among 5176 independent reflections measured up to 2θ=45°. The only one partially occupied position with s.o.f. ca 0.5 in 2 and 0.25 in 3 have been found for solvent water molecule. The C, N, and O-bound H atoms were placed in calculated positions and were treated using a riding model approximation with Uiso(H) = 1.2Ueq(C) or Uiso(H) = 1.5Ueq(O, C(CH3). The crystallographic data and X-ray experiment details for structures 1–4 are presented in Table 1, and the geometric parameters of hydrogen bonds are given in Table 2 and 2S. Table 1. Crystal Data and Structure Refinement for 1 – 4 1 2 Empirical C30.5H46.5Cl2Co2N11.5 C34H45Cl2Co2N10 formula O9.5 O8.5 Formula weight 915.05 918.56 T /K 293(2) 153(2) Crystal system trigonal orthorhombic Space group R-3 Pccn Unit cell dimensions a /Å 34.037(3) 26.703(5) b /Å 34.037(3) 17.733(3) c /Å 11.4798(6) 17.730(3) β / deg. 90 90 V /Å3 11517.8(15) 8395(3) Z 9 8 3 1.187 1.453 D(calc.)/mg/m 0.804 0.978 µ /mm-1 F(000) 4266 3800 0.2 x 0.15 x 0.1 Crystal size /mm3 0.6 x 0.3 x 0.15 Reflections collected Independent reflections Refinement method Parameters

3 C28H41Cl2Co2N10 O8.5 842.47 100(2) monoclinic P21/n

4 C18H24ClCoN6 O5 498.81 293(2) monoclinic C2/m

8.0490(2) 15.7980(5) 14.7400(5) 99.904(2) 1846.38(10) 2 1.515 1.104 870 0.2 x 0.16 x 0.08

20.1616(8) 13.5271(6) 8.1714(3) 107.173(5) 2129.22(15) 4 1.556 0.975 1032 0.25 x 0.1 x 0.07 3427

7738

33562

4764 (R(int) = 0.0176)

5176 (R(int) = 3423 (R(int) = 0.1772) 0.0410) Full-matrix least-squares on F2

2063 (R(int) = 0.0197)

289

509

150


12253

236

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GOOF on F2 R1, wR2[I>2σ(I)]

1.004 0.0495, 0.1623

1.000 0.0633, 0.1228

1.0010 0.0352, 0.0800

R1, wR2(all data)

0.0783, 0.1723

0.1831, 0.1464

0.0414, 0.0828

Table 2. Hydrogen Bonds (Å) and Angles (°) for 1 – 4. D–H···A d(H...A) d(D···A) (DHA) 1 C3–H···Cl1 C23–H···O1D C34–H···O21 C2D–H···O11 C2D–H···Cl1 2 O1W–H2···O11B С15A–H···O21B С16B–H···Cl1 3 O1W–H1···O11 O1W–H2···O22 C24–H···Cl1 C31–H···O1W C32–H···Cl1 C34–H···Cl1 4 O1W–H1···Cl1 C31–H···O22 C42–H···O1W

1.011 0.0367, 0.0852 0.0545, 0.0879

Symmetry transformation for acceptor

2.75 2.59 2.59 2.45 2.72

3.616(5) 3.36(1) 3.493(5) 3.27(1) 3.55(1)

151 137 165 144 145

–x+y+4/3, –x+2/3, z–1/3 x, y, z x–y+1/3, x–1/3, z+5/3 x, y, z–1 x–y+1/3, x–1/3, –z+5/3

2.08 2.57 2.93

2.93(2) 3.39(3) 3.59(2)

178 143 127

–x+1/2, –y+3/2, z –x+1/2, –y+1/2, z –x+1/2, y, z–1/2

1.90 1.93 2.86 2.41 2.74 2.85

2.779(7) 2.799(7) 3.640(3) 3.192(7) 3.550(3) 3.721(2)

165 163 139 142 146 157

x, y, z –x+1, –y, z+1 x–1, y, z x–1/2, –y+1/2, z+1/2 –x+1/2, y+1/2, –z+3/2 x–1/2, –y+1/2, z–1/2

2.60 2.38 2.57

3.344(3) 3.162(3) 3.324(4)

147 142 139

x, y, z –x+3/2, –y+3/2, –z+2 x+1/21, y–1/2, z

RESULTS AND DISCUSSION Spectroscopic characterization. IR spectra confirm the presence of organic ligands used in the syntheses through the typical vibrations of dioxime and/or pyridine aromatic rings38. The presence of dioximate anions in the complexes are documented by the oscillations ν(CH3) at 2930-3014 and 2781 cm-1, deformation vibrations δas(CH3) at ~1463-1481 cm-1 and δs(CH3) at 1370–1377 cm-1 and δas(N–O) at 1237 cm-1 and δs(N–O) at 1087–1090 cm-1. The band at 1614–1619 cm-1 can be ascribed to both ν(C–C) and ν(C=N) vibrations. The δ(CH) band at 680–739 cm-1, as well as the shape of this band (it is the characteristic shape of a para-substituted benzene ring) indicates the presence of bridging-ligand molecules in the complexes. In the region of 1493–1510 cm-1, the νs(C=C) band is observed. The presence of these bands in the IR spectra of the studied compounds confirms the coordination of bpy and bpe bridging-ligands to the central atom. The 1H NMR spectrum of 1 reveals characteristic signals for CH3 groups of dmgH ligand (δ(CH3)=2.32 ppm) and O–H groups that participates in O–H···hydrogen bond (18.45 ppm). Ligand bpy is characterized by two signals at 7.34 and 7.89 ppm. The 1H NMR spectrum of the [Co2(dmgH)4(bpe)Cl2]·0.5H2O (3) complex exhibits one singlet at 2.32 ppm that corresponds to the methyl groups of the dmgH ligand. The presence of a single sharp singlet indicates the chemical equivalence of all dmgH methyl groups. The signal at 18.45 ppm confirms the O– H···O intramolecular hydrogen bonds in the complex. The axial ligand bpe manifests the signals at 7.33 ppm (2H, d, J=6.18 Hz) and 7.90 ppm (2H, d, J=5.91 Hz) attributed to aromatic ring ACS Paragon Plus Environment

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protons and at 2.79 ppm (4H, s) attributed to CH2 groups. One signal for CH2 groups confirms their chemical equivalence. The 1H NMR spectra show a 4:1 ratio between dmgH and bpe ligands, which corresponds to the results of the elemental and X-ray analyses. The characteristic signals of the CH3 group (δ(CH3)=2.33 ppm) and hydrogen bonds O–H···O (18.47 ppm) protons were also observed in [Co(dmgH)2(bpy)Cl]·H2O (4) complex; which confirms the presence of dmgH ligand. The bpy ligand is characterized by four signals at 7.77–8.74 ppm. The presence of four signals instead of two for bpy, as well as the 2:1 ratio between dmgH and bpy means that bpy acts in the respective complex as a monodentate ligand. Structural Description. The coordination polyhedron of cobalt atom in all complexes 1– 4 is a distorted octahedron formed by N5Cl donor atoms: four nitrogen atoms from two coplanar dimethylglyoximato or 1,2-cyclohexanedionedioximato bidentate chelate ligands in the equatorial plane, and chloro and pyridyl ligands in trans-axial positions. The coplanar arrangement of the chelate ligands and the metal center is supported by a pair of strong intramolecular O–H···O hydrogen bonds (Table 2S). The metal coordination environment in equatorial plane represents an alteration of two five-membered chelate and two six-membered Hbonded cycles. Compound 1 crystallizes in trigonal R-3 space group and consists of a centrosymmetric binuclear [Co2(dmgH)4(bpy)Cl2] complexes, and dmf crystallization molecules located in the pockets of 1 (Figure 1). Although nominally stoichiometry complex : solvent dmf molecules should be 1 : 2, the refinement of site occupation factors for dmf molecule leaded to the value of 0.75(1), which indicate that crystal partially lost solvent molecules, so the stoichiometry obtained from X-ray data is 1:1.5. The non-hydrogen atoms of dmf molecules are located at the distances 3.75–4.05 Å from the plane of flat bpy ligand with the dmf/bpy dihedral angle equals 8.75°, thus indicating the absence any essential stacking like intermolecular interactions with the walls of the pockets in complex 1.

Figure 1. View of formula unit 1 with numbering scheme illustrates the mutual arrangement of centrosymmetric binuclear complex and dmf solvent molecules. Interatomic distances in the coordination polyhedron of the metal Co–Noxime 1.894(3) – 1.905(4), Co–Nbpy 1.960(3), Co–Cl 2.232(1) Å (Table 1S) are in good agreement with related compound [Co2(dmgH)4(bpy)Cl2] 3CH3OH 2H2O, which differs from 1 only by methanol/water solvent molecules19, also these complexes differ in conformation: [Co(dmgH)2] entities are parallel and pyridine moiety of bpy are coplanar in 1, but in cited complex [Co(dmgH)2] entities twisted on about 28° around Co···Co line and pyridine moieties form dihedral angle 38.9° in bpy ligand. The Co···Co separation equals 11.005 and 10.984 Å, accordingly. It should be noted, that although compound 1 and related one vary only by solvent the chemically equivalent binuclear complexes in crystals differ not only in conformation but also in molecular symmetry Ci in 1 and C2 in the related analogue. The dihedral angle between the N4 basal plane and bpy is 89.41° in 1. Since 1 is poor in functional groups able to form strong intermolecular hydrogen bonds, the only weak C–H···O and C–H···Cl hydrogen bonds were found in the solid-state structure ACS Paragon Plus Environment

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(Table 2). The packing of complexes and dmf molecules reveals hourglass-like open channels along the c axis with diameters of narrow neck ca 6.2 Å and biggest diameter of bulb ca 12.9 Å (Figure 2). No any reasonable electron density was found in these channels. The total potential solvent-accessible voids, (SAVs) of the channels, which can be occupied by small molecules, equals 2256.7 Å3 or 19.6% of the total unit cell volume 11517.8 Å3 as calculated by PLATON39. Upon removal of dmf molecules, which have been found of partial occupancy in the structure the SAVs increases up to 4812.9 Å3 or 41.8% of total unit cell volume. This large volume of channels and the lack of strong intermolecular interactions assume that this material can be used as a soft adsorptive material in contrast to non-porous methanol/water analog.

a b Figure 2. Fragments of crystal packing in 1. (a) View of channels along the crystallographic c axis. The dmf molecules are drawn in space filling mode for clarity. Contact surfaces are drawn by gold color; (b) Shape of hourglass channels is illustrated by using solvent accessible surface. Compound 2 [Co2(nioxH)4(bpy)Cl2]·0.5H2O crystallizes in orthorhombic Pccn space group and differs from 1 by 1,2-cyclohexanedionedioxime (nioxH2) as coordinated ligand instead of dimethylglyoxime. The asymmetric part of the unit cell contains two halves of two crystallographically independent Co(III) complexes: complex A resides around the two-fold axis, which passes through the middle of bpy ligand and thus having the C2 molecular symmetry, while complex B resides on an inversion center and possesses Ci molecular symmetry (Figure 3). The interatomic distances in the coordination polyhedra of cobalt for A are Co–Noxime 1.88(1) – 1.92(1), Co–Nbpy 1.914(9), Co–Cl 2.245(4) Å, for B Co–Noxime 1.839(11) – 1.883(10), Co–Nbpy 1.978(8), Co–Cl 2.234(3) Å (Table 1S) are in good agreement with those found in 1 and in related Co(III) complexes19-21. The cyclohexano rings of these ligands in both complexes have a flatten chair conformation with four almost coplanar carbon atoms and two others located from the different sides of their mean plane.


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a b Figure 3. View of two non-equivalent complexes in the structure 2 with numbering scheme: a) complex 2A resides on a two-fold axis; b) centrosymmetric complex 2B. The complexes A and B differ in conformation: in A planar [Co(nioxH)2] entities are about parallel and form the dihedral angle of 0.84°. They are slightly twisted on about 12° around Co···Co line, and pyridine moieties in bpy ligand form dihedral angle 23.2°; in B [Co(nioxH)2] entities are parallel, and the pyridine moieties of bpy are coplanar. The Co···Co separation equals 10.958(3) and 10.981(3) Å, in A and B, accordingly. The dihedral angle between the N4 basal plane and the pyridine plane of bpy in complexes A and B are 89.4 and 86.4°, respectively; therefore, the bpy only in the A complex is located almost perpendicular to the niox ligands donor atoms plane. The complexes A and B in 2 are bound in a crystal by hydrophobic interactions and weak hydrogen bonds, complexes A and B by C(15A)– H···O(21B)= 3.39(3) Å hydrogen bonds, complexes B by C16B–H···Cl1=3.59(2) Å hydrogen bonds. The crystal packing of 2 reveals isolated cylindrical cavities elongated along the a crystallographic axis, which accommodate water molecules bonded with complexes B by O1W– H···O11B=2.93(2)Å hydrogen bond (Figure 4, Table 2). The volume of the cavities which can be occupied by small molecules upon removal water molecules is 1139.7 Å3, which is 13.6 % of the total unit cell volume of 8395 Å3. Even with the presence of water molecules in the cavities the structure of 2 reveals SAVs of 734.5 Å3, or 8.7% of total unit cell volume, which actually is bigger taking in account the partial occupancy of water molecule position. The crystals of 2 were found to be more stable than 1, which may be related with closed cavities with solvent in 2 compare with open channels in 1.

a b Figure 4. Fragments of crystal packing in 2. (a) View of cavities along the crystallographic a axis accommodated water molecules. The H2O molecules are drawn in space filling mode; (b) Shape of cavities is illustrated by contact surface. Compound 3 [Co2(dmgH)4(bpe)Cl2]·0.5H2O crystallizes in monoclinic P21/n space group and differs from 1 by 1,2-bis(4-pyridyl)ethane bridging ligand. Survey of CSD8 does not reveal ACS Paragon Plus Environment

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Co(III) binuclear dioximates thus 3 is the first example of such compound, although Cu(II), Zn(II), and Cd(II) binuclear complexes with this bridging ligand are known22,40. The structure of 3 contains the [Co2(dmgH)4(bpe)Cl2] centrosymmetrical binuclear complexes (Figure 5) and a crystallization water molecules.

Figure 5. View of centrosymmetric complex 3 with numbering scheme. The geometry of complex 3 is quite similar to that in 1 and 2: Co–Noxime 1.896(2) – 1.904(2), Co–Nbpe=1.950(2), Co–Cl 2.2419(6) Å, Tab. 1S, but the Co···Co separation of 13.141(1) Å in this binuclear complex is essentially bigger than those ones in 1 and 2. The dihedral angle between the N4 plane and the pyridine aromatic ring of bpe is 82.8° and deviates from the right angle greater than in 1 and 2. Two water molecules double bridge neighboring complexes through O1W–H···O11= 2.779(7) and O1W–H···O22= 2.799(7) Å hydrogen bonds (Table 2) and result in formation of zigzag-like chains (Figure 6), which run along the [110] and [-110] directions. The chains are linked by the C31–H···O1W=3.192(7) and C32–H···Cl1=3.550(3) Å hydrogen bonds. Crystal structure of 3 reveals only negligible SAVs 78.1 Å3 or 4.2% of the total unit cell volume, which consist of very small closed cavities unsuitable for accommodation of any guest molecule. Actually, in crystal the total volume of pores should be bigger, as water molecule position is only partially occupied according with the X-ray data, thus crystal loses some water molecules.

Figure 6. H-bonded chain in the structure of 3, H-atoms on carbon atoms are omitted for clarity. Compound 4 [Co(dmgH)2(bpy)Cl]·H2O, where bpy acts as a monodentate ligand (Figure 7) crystallizes in monoclinic C2/m space group, and mononuclear complex resides on mirror plane thus having Cs symmetry. The interatomic distances in the coordination polyhedron are Co–Noxime 1.897(2) and 1.888(2), Co–Nbpy 1.960(3), and Co–Cl 2.223(1) Å (Table 1S). The bpy ligand and the equatorial N4 planes are almost perpendicular with the dihedral angle of 89.5°. The dihedral angle between the pyridine rings of bpy is 3.6°.


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Figure 7. View of complex 4 with numbering scheme and formation of supramolecular chain. In the crystal 4, the mononuclear complexes form centrosymmetric dimer by π···π faceto-face with offset stacking interactions between the pyridine rings of parallel bpy ligands. The centroid···centroid distance between overlapping rings is 3.723 Å and interplanar spacing between bpy ligands equals 3.547 Å (Figure 7). This π···π stacking interaction emulates binuclear assembly with wheel-and-axle topology. Two water molecules double bridge such binuclear assembly by O1W–H···Cl1=3.344(3) Å hydrogen bonds (Table 2), resulting in formation of supramolecular chain along the a crystallographic axis. The chains are bound in the ab plane via weak C42–H···O1W=3.324(4) Å hydrogen bonds which involved the –CH groups of two bpy ligands per one oxygen atom of water molecules and C31–H···O22=3.162(3) Å. The structure of 4 does not reveal any residual SAVs. 3.3. Sorption properties The fact that compound 1 (with a potential volume of cavities of 41.8%) exhibited open channel permanent porosity was confirmed using N2 gas sorption studies at 77.3 K. The sorption isotherm shown in Figure 8 exhibits a typical hysteresis, which is indicative of capillary condensation occurring in the pores. It can be inferred that there is a small permanent structural change in the crystal after N2 uptake. The molecular framework showed an N2 uptake of approximately 53 mL g-1, which is somewhat lower compared to other MOF structures41. The surface area calculated according to BET method42 is 95.88 m2 g-1 (Langmiur 137.619 m2 g-1) and the total pore volume is 7.29 x 10-2 mL g-1, indicating the mesoporous structure. 55 50 45

3 V, cm /g

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Figure 8. N2 ad-/desorption isotherm of compound 1.


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CONCLUSIONS The interaction of the Co(III) dioximate mononuclear molecular building block with bridging ligands, such as bpy or bpe, resulted in three novel compounds containing binuclear complexes with wheel-and-axle topology and the compositions: [Co2(dmgH)4(bpy)Cl2]·1.5dmf (1), [Co2(nioxH)4(bpy)Cl2]·0.5H2O (2), [Co2(dmgH)4(bpe)Cl2]·0.5H2O (3), and one mononuclear [Co(dmgH)2(bpy)Cl]·H2O (4). The porous structure of compound 1 reveals open channels and 2 – isolated cavities even in the presence of template solvent molecules. The biggest calculated volume of pores upon removal all solvent molecules is observed in 1, which sorption properties has been studied. More bulky chelate dioxime ligand nioxH2 instead of dmgH2 or longer bridging ligand bpe instead of bpy reduced the solvent accessible voids in structure that can be explained by more close packing of the complexes, which being in line with the results for relative Cu(II) complexes17. Comparison of structures 1 and 2 with the structures of similar compounds19 reveals the dramatic influence of solvent molecule on the final supramolecular architecture and formation of porous structures. The structures of 3 and 4 were found to be non-porous. ASSOCIATED CONTENT Supporting Information Crystallographic data for 1 – 4 have been deposited with the Cambridge Crystallographic Data Center, CCDC 996317–996320 (996319 – 1, 996320 – 2, 996317 – 3, 996318 – 4). Copies of this information may be obtained from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK(fax: +44-1233-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk ). Supplementary materials section contain selected bond distances and angles, table of hydrogen bonds, and ORTEP drawings with atom labeling schemes. AUTHOR INFORMATION Corresponding Author *E-mai: [email protected]; [email protected];tel: +373 22 738154; fax: 373 22 725887. Acknowledgements This work is financially supported from the State Program of R. Moldova (Project 14.518.02.04A). REFERENCES [1] Toscano, P.J.; Marzilli, L.G. Progress Inorg. Chem. 1984, 104–204. [2] Bresciani-Pahor, N.; Forcolin, M.; Marzilli, L.G.; Randaccio, L.; Summers, M.F.; Toscano, P.J. Coord. Chem. Rev. 1985, 63, 1–125. [3] Randaccio, L.; Bresciani-Pahor, N.; Zangrando, E.; Marzilli, L.G. Chem. Sos. Rev. 1989, 18, 225–250. [4] Randaccio, L. Comments Inorg. Chem. 1999, 21, 327–376. [5] Golding, B.T.; J. R. Neth. Chem. Soc. 1987, 106, 342–347. [6] Schrauzer, G.N.; Kohnie, J. J. Chem. Ber. 1964, 97, 3056–3063. [7] Schrauzer, G.N. Angew. Chem. Int. Ed. Engl. 1976, 15, 417–426. [8] Allen, F.H. Acta Crystallogr. 2002, B58, 380–388. [9] Luo, G.-G.; Fang, K.; Wu, J.-H.; Dai, J.-C.; Zhao Q.-H. Phys. Chem. Chem. Phys. 2014, 16, 23884–23894. ACS Paragon Plus Environment

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For Table of Contents Use Only Discrete Binuclear Co(III) bis-Dioximates with Wheel-and–axle Topology as Building Blocks to Afford Porous Supramolecular Metal−organic Frameworks Eduard Coropceanu, Andrei Rija, Vasile Lozan, Ion Bulhac, Gheorghe Duca, Victor Ch. Kravtsov, and Paulina Bourosh

Synopsis Porous supramolecular assembly have been generated from discrete binuclear Co(III) bis-dioximates with wheel-and-axle topology using C–H…O interactions, as well non porous structures have been obtained from the related bis- and monodioximate. The porous structures reveal open channels or isolated cavities even in the presence of template solvent molecules.


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Discrete Binuclear Cobalt(III) Bis-dioximates with Wheel-and-Axle

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