Structural Diversity in Metal−Organic Frameworks Derived from

Feb 9, 2008 - ... Cu1B···Cu2B = 2.954(2) Å confirm that the metrics of the two types of grids ...... Belcher , W. J.; Longstaff , C. A.; Neckenig ...
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Structural Diversity in Metal-Organic Frameworks Derived from Binuclear Alkoxo-Bridged Copper(II) Nodes and Pyridyl Linkers Geanina Marin,† Marius Andruh,*,† Augustin M. Madalan,† Alexander J. Blake,‡ Claire Wilson,‡ Neil R. Champness,‡ and Martin Schröder*,‡

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 3 964–975

Inorganic Chemistry Laboratory, Faculty of Chemistry, UniVersity of Bucharest, Str. DumbraVa Rosie nr. 23, 020464-Bucharest, Romania, and School of Chemistry, UniVersity of Nottingham, UniVersity Park, Nottingham, NG7 2RD, U.K. ReceiVed September 13, 2007; ReVised Manuscript ReceiVed October 16, 2007

ABSTRACT: New coordination polymers have been obtained by reaction of alkoxo-bridged copper(II) dimers [Cu2(mea)2]2+ and [Cu2(pa)2]2+ (Hmea ) monoethanolamine; Hpa ) propanolamine) with divergent pyridyl-containing ligands that act as rigid linear exo-bidentate linkers [p-bis(4-pyridyl)benzene, bpbenz, bis(4-pyridyl)acetylene, bpac, 9,10-bis(4-pyridyl)anthracene, bpanth], as a flexible angular exo-bidentate ligand [bis-(4-pyridyl)disulfide, bpds] or as an exo-tridentate connector [tris(3pyridyl)benzene, tpyb]. The single crystal X-ray structures of [Cu2(mea)2(bpbenz)(NO3)](NO3) · 2.75CH3OH (1), [Cu2(mea)2(bpbenz)2](CF3SO3)2 · 0.5(bpbenz) · 3CH3OH (2), [Cu2(pa)2(bpac)2](ClO4)2 (3), [Cu2(mea)2(bpanth)](CF3SO3)2] (5), [Cu2(mea)2(bpanth)2](ClO4)2 · 2.5CH3OH (4), [Cu2(mea)2(CH3OH)(H2O)(bpanth)(NO3)2] · CH3OH · H2O (6), [Cu2(mea)2(bpds)2](CF3SO3)2 · 2CH3OH (7), [Cu2(pa)2(bpds)2](BF4)2 (8), [Cu2(mea)2(tpyb)(ONO2)](NO3) · CH3OH (9), and [Cu2(mea)2(tpyb)(FBF3)](BF4) · CH3OH (10) are reported. Compound 4 exhibits a linear chain structure, while compounds 1, 2, 3, 5, 6, 7, and 8 incorporate extended two-dimensional (2-D) grids. In compound 2 the 2-D networks are disposed parallel to each other, while in compounds 3 and 6 interlocked three-dimensional (3-D) structures resulting from inclined interpenetration of the 2-D sheets are observed. Compounds 7 and 8 consist of layers that pack to give channels running through the solid-state structure. In 9 and 10, the tris(3-pyridyl)benzene ligand interacts with the binuclear nodes to give channels. The role of hydrogen-bonding and stacking interactions in sustaining the supramolecular solid-state architectures in these materials is discussed.

1. Introduction The crystal engineering of hybrid inorganic–organic framework materials lies at the interface of coordination and supramolecular chemistry and is currently a hot topic in chemical research.1 The construction of one-, two-, or three-dimensional (1-D, 2-D, or 3-D) coordination polymers with various architectures is based upon the directionality and control of metal–ligand interactions. Thus, the coordination and stereochemical algorithm of metal center nodes coupled to the structural features and directionality of exo-dentate ligands, which act as spacers and linkers, are crucial factors in the assembly of these materials.2 Over the past 15 years, careful analysis of coordination polymers has led to coherent classifications of their network topologies,3 and these are constantly being expanded with the discovery of new materials incorporating novel and intriguing structures.4 Noncovalent interactions such as hydrogen-bonds, π-π, or d10-d10 (aurophilic/argentophilic) interactions also play an important role in sustaining these supramolecular solid-state architectures,5 and the understanding and appreciation of these interactions coupled to metal–ligand coordinate bonding allow the synthesis and development, in a deliberate way, of materials with potentially interesting properties and function. These include magnetic, luminescent and conducting materials, porous hosts for guest storage and separation, and catalytic systems.6 The “node and spacer” approach7 is by far the most common procedure for constructing coordination polymers. Recently, several papers have shown that this strategy can be developed using stable bi- or oligonuclear complexes as nodes where the metal centers interact with a divergent ligand through readily * To whom correspondence should be addressed. E-mail: [email protected] (M.A.); [email protected] (M.S.). † University of Bucharest. ‡ University of Nottingham.

accessible coordination sites. Such nodes can comprise (i) binuclear species with metal ions connected through metal-metal bonds with or without additional bridging ligands;8 (ii) paddlewheel species incorporating two metal ions bridged by syn-syn carboxylato groups;9 (iii) bis(hydroxo)-bridged copper(II) species;10 (iv) homobinuclear species with metal ions held within a compartmental ligand;11 and (v) heterobinuclear species combining the electronic and stereochemical features of different metal ions.12 Many other extended structures based on oligonuclear nodes have been reported,13 and their synthetic and structural rationalization gives valuable synthetic principles to crystal engineering and paves the way to the rational design of new materials. The presence of two or more metal ions within a node can confer higher geometrical flexibility, and moreover, the metal-metal intra- and internode interactions may lead to potential new redox, electrical, or magnetic properties. We report herein a study of alkoxo-bridged binuclear Cu(II) species incorporating monoethanolamine (Hmea) and monopropanolamine (Hpa) that act as nodes in the design of framework polymers. These centers have been coupled to additional ligand spacers such as p-bis(4-pyridyl)benzene (bpbenz), bis(4-pyridyl)acetylene (bpac), 9,10-bis(4-pyridyl)anthracene (bpanth), bis-(4-pyridyl)disulfide (bpds), and tris(3pyridyl)benzene (tpyb). We now extend our previous work on coordination polymers constructed from alkoxo-bridged nodes14 by employing various spacer amine ligands with a range of interesting features. These latter ligands can sustain solid-state supramolecular architectures through π-π stacking interactions (bpbenz and bpanth), high flexibility (bpds), and via higher denticity (tpyb). To monitor and establish the role played by the anion accompanying the Cu(II) ions in the self-assembly processes we have employed as starting materials various Cu(II) perchlorate, nitrate, triflate, and tetrafluoroborate salts.

10.1021/cg700879q CCC: $40.75  2008 American Chemical Society Published on Web 02/09/2008

0.98, -0.46 0.48, -0.41 0.94, -0.86 0.58, -0.40 0.92, -0.72

1.61, -1.07

0.67, -0.74

1.44, -0.43

1.85, -1.07

0.53, -0.28

0.0759, 0.0997 0.0394, 0.0858 0.143, 0.250 0.0512, 0.102 0.106, 0.200

0.0686, 0.154

0.0783, 0.137

0.0636, 0.135

0.113, 0.217

0.0384, 0.0897

0.0409, 0.0848 0.0318, 0.0818 0.0777, 0.210 0.0344, 0.0872 0.0350, 0.0894 0.0682, 0.186

0.0524, 0.139

0.0599, 0.128

0.0530, 0.129

0.0833, 0.199

889.52 120(2) 0.71073 monoclinic P21/c 12.2429(7) 10.4943(5) 20.5980(12) 90 125.020(4) 90 2167.3(2) 2 1.363 1.238 900 1.05 1222.19 150(2) 0.71073 monoclinic P21/c 18.2394(12) 15.8743(11) 19.9582(13) 90 110.019(1) 90 5429.5(6) 4 1.495 0.945 2516 0.95

834.60 150(2) 0.71073 monoclinic P21/c 10.4247(11) 11.9967(13) 14.591(2) 90 96.623(2) 90 1812.6(4) 2 1.529 1.382 852 1.07

877.76 150(2) 0.71073 triclinic P1j 7.943(2) 9.083(2) 11.287(3) 88.694(4) 83.983(4) 84.686(5) 806.3(3) 1 1.808 1.542 444 1.08

803.76 150(2) 0.71073 monoclinic Cc 28.583(3) 12.9499(13) 9.4865(9) 90 96.586(2) 90 3488.2(6) 4 1.530 1.289 1664 1.08

1191.02 150(2) 0.71073 triclinic P1j 16.775(2) 17.697(2) 19.447(2) 105.702(2) 106.851(2) 92.785(2) 5268.3(10) 4 1.502 0.979 2460 1.05

1050.07 150(2) 0.71073 monoclinic P21/n 12.3642(13) 10.5636(11) 16.322(2) 90 90.054(2) 90 2131.8(4) 2 1.636 1.374 1068 1.04

712.66 150(2) 0.71073 triclinic P1j 10.4113(10) 11.0951(10) 14.1050(13) 76.808(2) 71.915(2) 72.846(2) 1463.1(2) 2 1.618 1.518 732 1.01

762.26 150(2) 0.71073 triclinic P1j 10.4254(9) 11.7087(10) 14.5120(12) 75.823(1) 70.211(1) 69.733(1) 1547.2(2) 2 1.636 1.461 772 1.04

Scheme 1

691.65 150(2) 0.71073 monoclinic P21/c 15.295(2) 14.351(2) 26.579(3) 90 97.514(2) 90 5784.0(13) 8 1.589 1.537 2860 1.07

10 9 8 7 6 5 4 3 2

Table 1. Crystallographic Data, Details of Data Collection, and Structure Refinement Parameters for Compounds 1–10

Crystal Growth & Design, Vol. 8, No. 3, 2008 965

chemical formula M (g mol-1) temp, (K) wavelength, (Å) crystal system space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Z Dc (g cm-3) µ (mm-1) F(000) goodness-of-fit on F2 final R1, wR2 [I > 2σ(I)] R1, wR2 (all data) largest diff peak and hole (e Å-3)

1 compound

C22.75H35Cu2N6O10.75 C49H54Cu2F6N7O11S2 C30H32Cl2Cu2N6O10 C30H28Cu2F6N4O8S2 C30H40Cu2N6O12 C54.5H54Cl2Cu4N6O12.5 C28H36Cu2F6N6O10S6 C26H32B2Cu2F8N6O2S4 C26H31Cu2N7O9 C26H31B2Cu2F8N5O3

MOFs from Binuclear Alkoxo-Bridged Cu(II) Nodes

2. Experimental Procedures Synthesis. The ligands bpbenz and bpanth were prepared by Suzuki coupling15 of 4-pyridylboronic acid pinacol ester with the dibromo compounds 1,4-dibromobenzene and 9,10-dibromoanthracene, respectively. Tris(3-pyridyl)-1,3,5-benzene (tpyb) was prepared by Suzuki coupling of 1,3,5-tribromobenzene with 3-pyridylboronic acid pinacol ester, and bis(4-pyridyl)acetylene was obtained from trans-4,4′-bispyridylethylene, which was converted to its perbromide via bromination with HBr. Subsequent dehydrobromination leads to bis(4-pyridyl)acetylene in high yield.16 Bis-(4-pyridyl)disulfide (bpds) was used as purchased. Complexes 1, 2, 4, 5, and 6 were prepared following the same procedure in which a methanolic solution (20 mL) of copper salt (0.3 mmol) was added with stirring to a methanolic solution (10 mL) containing monoethanolamine (0.9 mmol). To the resultant blue solution (15 mL) of bidentate pyridyl ligand (0.3 mmol) in CH2Cl2 was added. Slow evaporation of the reaction mixtures gave crystalline products after a few days. Complexes 3, 7, 8, 9, and 10 were prepared in an analogous manner, but with all the reagents dissolved in MeOH. The complexes 2, 6, and 7 are green in the solid state, while all other complexes reported herein are blue. IR data (KBr, cm-1) (1): 432w, 496w, 700w, 808w, 887w, 1065s, 1122w, 1382vs, 1590s, 2845m, 2936m, 3119s, 3206s, 3279s, 3428s; (2): 493m, 574w, 634m, 725m, 800s, 864w, 1027s, 1071m, 1153m, 1222m, 1271s, 1398m, 1430s, 1487s, 1550w, 1543w, 1612vs, 2840w, 2911w, 3055m, 3445vs; (3): 436w, 470w, 541s, 591m, 624s, 835s, 866m, 933m, 1024s, 1080vs, 1115vs, 1165s, 1218m, 1321w, 1370w, 1414m, 1502w, 1543w, 1609vs, 2708w, 2817m, 2886m, 2936m, 3093m, 3177m, 3257s, 3300s, 3442m, 3514m; (4): 510m, 535m, 575m, 611s, 633vs, 676w, 748m, 773s, 805w, 827m, 877w, 1022vs, 1066vs, 1144s, 1165s, 1219s, 1244vs, 1273vs, 1389m, 1426m, 1516w, 1539w, 1588m, 1613s, 2855m, 2930m, 2974w, 3044w, 3073w, 3154w, 3266m, 3338m, 3442m, 3482m, 3735w; (5): 508w, 538w, 609w, 645w, 675w, 744w, 771m, 813w, 884w, 1029w, 1066s, 1219w, 1383vs, 1583w, 1613m, 2841w, 2914w, 2928w, 3127m, 3220s, 3419s; (6): 410w, 497w, 539m, 624s, 677m, 742m, 770s, 812m, 885w, 949w, 1030m, 1064vs, 1084vs, 1117vs, 1214m, 1262w, 1416m, 1441m, 1609w, 1541s, 2886w, 2943w, 3063m, 3273s, 3324s, 3413s, 3434s, 3735w; (7): 444w, 496m, 517m, 575w, 638s, 704m, 721m, 757w, 812m, 936m, 1007w, 1030vs, 1058s, 1167s, 1223s, 1253vs, 1370w, 1420m, 1485m, 1544w, 1577s, 1599s, 2724w, 2884m, 2962m, 3168s, 3267s, 3320s; (8): 438w, 500m, 599w, 704m, 718m, 813s, 935m, 1058vs, 1163m, 1220m, 1284w, 1320w, 1372w, 1416m, 1484m, 1543w, 1577s, 1596vs, 1949vw, 2713w, 2836m, 2883m, 2939m, 3100w, 3176w, 3279s, 3327s, 3438s, 3738w; (9): 497w, 704w, 809w, 887w, 1030w, 1062w, 1117vw, 1194vw, 1383vs, 1448w, 1485w, 1603w, 2852w, 2935w, 3122w, 3212m, 3420m; (10): 521m, 658m, 707s, 809m, 885m, 1033vs, 1062vs, 1078vs, 1120vs, 1197m, 1335w, 1390m, 1449w, 1485w, 1605m, 2848w, 2884w, 2940w, 3125m, 3230m, 3302s, 3360s, 3415s.

10

Cu1-N1 1.9764(19) Cu1-N1A 1.9811(18) Cu1-O1 1.9413(15) Cu1-O2 1.8965(16) Cu1-F4A 2.695(2) Cu2-N2 2.016(2) Cu2-N2A 2.0073(19) Cu2-N3A 2.3506(19) Cu2-O1 1.9828(15) Cu2-O2 1.9411(16)

9

Cu1-N1 1.981(3) Cu1-N1A 1.981(3) Cu1-O1 1.954(2) Cu1-O2 1.923(2) Cu1-O32S 2.456(4) Cu2-N2 2.021(3) Cu2-N2A 2.009(3) Cu2-N3A 2.346(3) Cu2-O1 1.984(2) Cu2-O2 1.933(2)

Crystal Structure Determination. Details of data collection and solution refinement are summarized in Table 1. X-ray diffraction measurements were performed on a Bruker SMART 1000 diffractometer for 1-7, 9, and 10, and on a Nonius Kappa CCD diffractometer for 8, both operating with a Mo KR (λ ) 0.71073 Å) X-ray tube with a graphite monochromator. The structures were solved (SHELXS-97) by direct methods and refined (SHELXL-97) by full-matrix least-squares procedures on F2. All ordered non-H atoms were refined anisotropically. Selected bond distances for compounds 1–10 are given in Table 2. CCDC reference nos.: 647126–647135.

3. Results and Discussion

Cu1-N3 1.990(7) Cu1-N2 2.002(6) Cu1-N1 2.346(7) Cu1-O1 1.940(5) Cu1-O1ii 1.949(6)

ii: -x, -y, -z.. b ii: 1 - x, 1 - y, -z. c ii: 1 - x, -y, 2 - z; iii: -0.5 + x, 0.5 - y, 0.5 + z. d ii: -x, 1 - y, -z. a

8d 7c

Marin et al.

Cu1-N1 1.9799(16) Cu1-N2iii 2.2934(17) Cu1-N101 2.0157(17) Cu1-O1 1.9289(13) Cu1-O1ii 1.9611(14) Cu1A-N01A 2.030(6) Cu1A-N1A 2.250(6) Cu1A-N2D 1.999(5) Cu1A-O1A 1.945(4) Cu1A-O1B 1.955(5) Cu2A-N01B 2.018(6) Cu2A-N1C 2.231(6) Cu2A-N1D 2.025(5) Cu2A-O1A 1.945(5) Cu2A-O1B 1.948(4) Cu1B-N01E 2.015(7) Cu1B-N1E 2.240(6) Cu1B-N1F 2.047(6) Cu1B-O1E 1.961(5) Cu1B-O1G 1.942(5) Cu2B-N01G 2.055(7) Cu2B-N1G 1.996(5) Cu2B-N1H 2.243(6) Cu2B-O1E 1.972(5) Cu2B-O1G 1.936(4)

6 5

Cu1-N1 2.007(5) Cu1-N1A 2.003(5) Cu1-O1 1.912(4) Cu1-O2 1.955(4) Cu1-O1W 2.641(6) Cu1-O1P 2.646(7) Cu2-N2 2.017(5) Cu2-N2A 1.976(5) Cu2-O1 1.926(4) Cu2-O2 1.935(4) Cu2-O3W 2.434(6) Cu2-O3Q 2.732(4) Cu1-N1 2.025(5) Cu1-N1A 1.982(4) Cu1-O1 1.914(4) Cu1-O1ii 1.934(4) Cu1-O1S 2.469(7) Cu1-O3Sii 2.858(8)

4b 3a

Cu1-N1B 1.9977(16) Cu1-N1 2.0320(18) Cu1-N1A 2.2270(18) Cu1-O1 1.9398(13) Cu1-O2 1.9707(14) Cu2-N2B 1.9888(16) Cu2-N2 2.0217(18) Cu2-N2A 2.2500(18) Cu2-O1 1.9742(14) Cu2-O2 1.9467(13) Cu1-N1 1.998(6) Cu1-N1A 2.009(5) Cu1-O1 1.947(4) Cu1-O2 1.936(4) Cu1-O2R 2.421(5) Cu2-N2 1.989(5) Cu2-N2B 2.000(6) Cu2-O1 1.933(5) Cu2-O2 1.939(4) Cu2-O3R 2.522(5) Cu3-N2A 1.975(5) Cu3-N3 2.008(6) Cu3-O3 1.930(4) Cu3-O4 1.936(5) Cu3-O2Q 2.523(5) Cu4-N1B 1.991(5) Cu4-N4 1.996(5) Cu4-O3 1.938(5) Cu4-O4 1.950(4) Cu4-O3Q 2.505(6)

Cu1-N1 2.007(4) Cu1-N1B 2.010(4) Cu1-N1A 2.323(4) Cu1-O1 1.934(3) Cu1-O1ii 1.947 (3)

2 1

Table 2. Selected Bond Lengths (Å) for Coordination Environments of the Copper(II) Centers in Compounds 1–10

966 Crystal Growth & Design, Vol. 8, No. 3, 2008

The binuclear bis(alkoxo)-bridged nodes, [Cu2(mea)2]2+ and [Cu2(pa)2]2+, are formed spontaneously from the reaction of Cu(II) salts with monoethanolamine and propanolamine, respectively, in the presence of the exo-dentate ligands. The following spacer ligands were employed in this study: (a) the rigid linear exo-bidentate ligands p-bis(4-pyridyl)benzene (bpbenz), bis(4-pyridyl)acetylene (bpac), 9,10-bis(4-pyridyl)anthracene (bpanth); (b) the flexible angular exo-bidentate ligand bis-(4-pyridyl)disulfide (bpds), and; (c) the exo-tridentate ligand 1,3,5-tris(3-pyridyl)benzene (tpyb) (Scheme 1). Thus, the nature of these ligand spacers (length, denticity, flexibility) has been varied to investigate the effect on the network topologies in the isolated products. In the case of the exo-bidentate ligands, reactions using 1:1 ligand-to-node ratios led to the formation of 1-D coordination polymers, while altering the stoichiometry by increasing the ligand-to-node ratio, led to the formation of higher dimensional networks. The denticity of the aminoalcohol employed within the binuclear nodes also influences the dimensionality of the resultant coordination polymers. In principle, binuclear complexes of monoethanolamine and propanolamine should generate 4,4-networks with an appropriate divergent ligand (Scheme 2). However, lower dimensionality for the resultant polymers is anticipated if the anion accompanying the Cu(II) starting material binds to the binuclear node. We report herein 10 new coordination polymers constructed from [Cu2(mea)2] and [Cu2(pa)2] nodes and appropriate bridging ligands. Coordination Polymers from Linear exo-Bidentate Ligands: p-Bis(4-pyridyl)benzene (bpbenz), Bis(4-pyridyl)acetylene (bpac), and 9,10-Bis(4pyridyl)anthracene (bpanth). Because of their extended length (bpac: 9.6 Å; bpbenz and bpanth: 11.4 Å), these ligands have been used to design molecular materials with large pores.17 In this study, the complexes [Cu2(mea)2(bpbenz)(NO3)](NO3) · 2.75CH3OH (1) and [Cu2(mea)2(bpbenz)2](CF3SO3)2 · 0.5(bpbenz) · 3CH3OH (2) were obtained by reaction of monoethanolamine and bpbenz with Cu(NO3)2 and Cu(CF3SO3)2, respectively. Each Cu(II) ion in 1 displays a slightly distorted square pyramidal geometry (Figure 1a) with the basal plane defined by two alkoxo oxygen atoms, one amino nitrogen, and one nitrogen atom from the bpbenz ligand. The fifth coordination site is occupied by the oxygen atom from the nitrato group [Cu1-O2R ) 2.421(5); Cu2-O3R ) 2.522(5); Cu3-O2Q ) 2.523(5); Cu4-O3Q ) 2.505(6) Å]. A measure of trigonal distortion for a square-pyramidal geometry can be described using the parameter τ, defined as [(θ φ)/60] × 100, where θ and φ are the angles between the donor atoms and the Cu(II) ion forming the diagonals of the basal plane in a square-pyramidal geometry.18 The values of τ for the coordination polyhedra of the Cu(II) ions in 1 are τCu1 ) 12.5; τCu2 ) 4.9; τCu3 ) 2.0; τCu4 ) 15.3%, indicating small distortions from the square-pyramidal geometry. In 1 there are four crystallographically independent Cu(II) centers within the

MOFs from Binuclear Alkoxo-Bridged Cu(II) Nodes

Crystal Growth & Design, Vol. 8, No. 3, 2008 967

Figure 1. (a) A view of the asymmetric unit in 1 showing the atom numbering scheme, with displacement ellipsoids drawn at the 30% probability level and atoms identified by color as follows: Cu, orange; oxygen, red; N, blue; carbon, grey; H, small white spheres; (b) a view of a chain formed by covalent and coordination bonds which runs parallel to the [111j] direction; the view is approximately along the crystallographic b axis [in Figure 1b,c only those H atoms involved in hydrogen-bonding are shown, and counteranions and solvent molecules are also omitted for clarity]; (c) a space-filling plot viewed approximately along the a axis showing hydrogen-bonding between the chains forming a 2-D sheet in the (100) plane; (d) a view along the a axis showing hydrogen-bonding involving the chains and some counteranions and solvents which generates a 3-D lattice with base vectors [101j], [010], and [201j]: only those H atoms involved in hydrogen-bonding are shown, and channels containing uncoordinated anions and solvent molecules are clearly visible; (e) details of π-π interactions between bpbenz moieties from different chains within the layer (fragments A and A′) and between the neighboring layers (fragments A′ and B).

Scheme 2

chain with Cu · · · Cu intranode separations of Cu1 · · · Cu2 ) 2.879(2), Cu3 · · · Cu4 ) 2.858(2) Å. Complex 1 exhibits a 1-D chain structure with bpbenz ligands connecting the binuclear nodes (Figure 1b) with a nitrato ion bridging Cu(II) centers within the node. The distance between the Cu(II) ions bridged by the bpbenz ligand is 15.420(3) Å, and analysis of the packing in this structure shows chains running in two different directions,

the chains running in the same [111j] direction being grouped into pairs (Figure 1b). The angle between two chains running in different directions is 41.4°. N-H · · · O hydrogen-bonds link the chains into a 2-D sheet with base vectors [010] and [001] lying in the (100) plane (Figure 1c). Hydrogen-bonding involving the chains and some of the counteranions and solvents generates a 3-D lattice (Figure 1d). Chains with the same

968 Crystal Growth & Design, Vol. 8, No. 3, 2008

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Figure 2. (a) A view of node and spacers in 2 with the atom numbering scheme; (b) view of a layer in 2 along the crystallographic c axis; (c) packing diagram showing the superposition of two layers (one guest bpbenz molecule is drawn in green); (d) view of uncoordinated bpbenz molecules (green) within adjacent layers.

orientation form layers and interact with those from adjacent layers through long-range π-π contacts (3.4–3.9 Å) between the phenyl rings of the bpbenz ligands (ligands A′ and B in Figure 1e). Stacking interactions (3.07–3.67 Å) are also observed between chains (ligands A and A′ in Figure 1e), and this superposition of layers generates infinite channels that host uncoordinated anions and solvent molecules (Figure 1d). In complex 2 the triflate anion does not bind to the metal centers and, consequently, the Cu(II) ions are available for coordination to more than one pyridyl ligand and expansion of the structure in two directions is observed (Figure 2a). The

geometry at each Cu(II) ion is distorted square-pyramidal with the basal positions for the two crystallographically inequivalent Cu(II) ions occupied by two oxygen atoms from the alkoxo bridges, one nitrogen from the amino group, and one nitrogen from the bridging ligand. The Cu-N distances are slightly longer than Cu-O, and the apical position is occupied by the nitrogen center from another heterocyclic ligand [Cu1-N1A ) 2.2270(18); Cu2-N2A ) 2.2504(18) Å]. The values of the τ parameter for the two Cu(II) ions are τCu1 ) 31.5 and τCu2 ) 25%, higher than those found with complex 1. The distance between the Cu(II) centers within a node is 2.958 Å, with a

MOFs from Binuclear Alkoxo-Bridged Cu(II) Nodes

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Figure 3. (a) A view of a layer in 3 with the atom numbering scheme; (b) a packing diagram showing the inclined interpenetration mode in 3.

Cu · · · Cu internode separation of 15.32 and 15.75 Å. The [Cu2(mea)2]2+ cores are interconnected through bpbenz molecules, resulting in 4,4 grid-like layers with rhombic meshes (Figure 2b) with layers disposed in the crystal parallel to each other (Figure 2c,d). Interestingly, these grids are interconnected at the supramolecular level through uncoordinated bpbenz molecules, which interact through π-π contacts (3.5–3.7 Å) with the p-phenylene moieties from two bpbenz linkers from adjacent layers (Figure 2c,d). In addition, hydrogen-bond interactions are observed between the nitrogen atoms of the uncoordinated bpbenz and methanol molecules (N1C · · · O3w ) 2.831 Å). Reaction of Cu(ClO4)2, propanolamine, and bis(4-pyridyl)acetylene affords the complex [Cu2(pa)2(bpac)2](ClO4)2 (3)

(Figure 3a), which has an overall topology similar to that found for complex 2. The distance between the alkoxo-bridged Cu(II) ions within the node is 3.044(2) Å, while the distances between the Cu(II) ions connected by bpac are 14.23 and 13.63 Å. The metal ions are pentacoordinated in a square-pyramidal geometry [basal plane: Cu-N(ave) ) 2.006(2) Å; Cu-O(ave) ) 1.940(2) Å; apical coordination: Cu1-N1A ) 2.323(4) Å; τCu1 ) 1.7%]. The analysis of the packing diagram reveals an interlocked 3-D architecture with every square having two networks passing through it (Figure 3b). Thus, the 3-D structure comprises inclined catenated p-p (parallel-parallel) (4,4) layers with a Doc (2/2) motif.3a Three complexes [Cu2(mea)2(bpanth)](CF3SO3)2] (4), [Cu2(mea)2(CH3OH)(H2O)(bpanth) (NO3)2] · CH3OH · H2O (5),

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Figure 4. (a) A view of 1-D coordination polymer in 4 with the atom numbering scheme; (b) a packing diagram for 4.

[Cu2(mea)2(bpanth)2](ClO4)2 · 2.5(CH3OH) (6) have been obtained using the bpanth spacer. Compounds 4 and 5 both contain chains of coordination polymers, similar to those in compound 1, but with the Cu(II) ions exhibiting an elongated octahedral stereochemistry. In 5, however, hydrogen-bonding between the chains and the anions and solvent molecules leads to the formation of extended sheets (see below). The equatorial plane is defined by two oxygen atoms from the alkoxo bridges, one amino nitrogen from the mea ligand, and one nitrogen from bpanth. The apical positions are occupied by the oxygen atoms from the triflate ions [Cu1-O1S ) 2.469(7); Cu1-O3Sii ) 2.858(8) Å; ii: 1-x, 1-y, -z], which bridge metal ions in the binuclear node (Figure 4a). The intranode Cu · · · Cu distance is 2.902(5) Å, and the distance between Cu(II) ions connected by the bpanth ligand is 15.36 Å. The packing diagram for compound 4 confirms that all polymeric strands lie parallel to each other (Figure 4b). The binuclear nodes in 5 comprise Cu(II) ions with an elongated octahedral stereochemistry, which are coordinated in the equatorial plane by two alkoxo-oxygens, one amino nitrogen, and one nitrogen arising from the bpanth ligand (Figure 5a). The axial positions of one Cu(II) ion in the node are occupied by a methanol molecule [Cu1-O1W ) 2.641(6) Å] and by a nitrate ion [Cu1-O1P ) 2.646(7) Å], while for the other Cu(II) ion, the axial positions are occupied by an aqua ligand [Cu2-O3W ) 2.434(6) Å] and a weakly coordinated nitrate ion [Cu2-O3Q ) 2.732(4) Å]. The intranode Cu1 · · · Cu2 distance is 2.984(3) Å, while the distance between the Cu(II) ions bridged by the bpanth ligand is 15.34 Å. Covalent and coordinate bonding leads to the formation of chains that run parallel to the [112] direction (Figure 5b). These chains are linked in extended sheets (Figure 5c) lying in the (11j 0) plane by hydrogen-bonding between the chains, the counter-anions, and the solvent

molecules. The bpanth spacers belonging to chains from one layer interact with those from adjacent layers via long-range face-to-face π-π stacking interactions (3.5–4.0 Å) between the peripheral rings of the anthracene moieties (Figure 5d). The packing diagram is similar to that observed for 1, that is, chains running in two directions to generate layers. However, in the case of 5 the chains running in the same direction are not grouped in pairs. Interestingly, the bpanth moieties within chains in one layer interact with those from adjacent layers via face-to-face π-π stacking contacts established between the peripheral rings of the anthracene moieties (3.5–4.0 Å) and by point-to-face (C-H · · · π) interaction (C-H21A · · · π ) 2.75 and C-H4AA · · · π ) 2.77 Å; Figure 5d). The superposition of chains running in different orientations generates infinite channels running along the crystallographic c axis, and these are filled with solvent (Figure 5e). The chemical composition of 6 suggests the formation of a 2-D gridlike coordination polymer, and this is confirmed by a crystallographic study (Figure 6a). In 6 there are four crystallographically independent copper ions, Cu1A and Cu2A, which form one type of 4,4 layer, and Cu1B and Cu2B forming another. The stereochemistry of all the Cu(II) ions is distorted square-pyramidal (τCu1A ) 40.4; τCu2A ) 22.3; τCu1B ) 28.9; τCu2B) 59.5%) with the nitrogen centers of the bpanth ligand bound at apical positions. The intranode copper-copper distances Cu1A · · · Cu2A ) 2.955(3), Cu1B · · · Cu2B ) 2.954(2) Å confirm that the metrics of the two types of grids are similar within this structure. The most interesting feature of the solid-state architecture of compound 6 is its interlocked structure resulting from the inclined interpenetration of gridlike sheets in which every square incorporates one net passing through it (Figure 6b). Thus, the 3-D supramolecular architecture comprises of inclined catenated

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Figure 5. (a) A view of the asymmetric unit in 5 showing the atom numbering scheme, with displacement ellipsoids drawn at the 30% probability level and atoms identified by color as follows: Cu, orange; oxygen, red; N, blue; carbon, grey; H, small white spheres; (b) a view of part of a chain formed by covalent and coordination bonds that runs parallel to the [112] direction; the view is approximately along the crystallographic b axis, with H atoms, counteranions, and solvent molecules are omitted for clarity; (c) a space-filling view along the c axis showing part of a sheet formed by hydrogen-bonding between the chains and the anions and solvent molecules; only those H atoms involved in hydrogen-bonding are shown; (d) details of the packing of 5 showing the interactions between bpang between different chains; (e) packing diagram showing the formation of the channels in 5.

p-p (parallel-parallel) (4,4) layers with a Doc (1/1) motif.3a Point-to-face (C-H · · · π) interactions are observed between the pyridyl group from one bpanth bridge belonging to one layer and the peripheral aromatic ring from the anthracene moiety from another (C-H23A · · · π ) 2.43, C-H24A · · · π ) 2.85, C-H1GA · · · π ) 2.58, and C-H2GA · · · π ) 2.53 Å; Figure 6c). These interactions between ligands are enhanced by π-π contacts between the phenyl rings of the anthracene fragments (3.6–3.9 Å; Figure 6c), and this feature favors the interpenetration of layers. Coordination Polymers from an Angular exo-Dentate Ligand, Bis(4-pyridyl)disulfide. The prediction of structures for networks derived from flexible divergent ligands such as bis(4-pyridyl)ethane, bis(4-pyridyl)propane, bis(4-pyridyl)disulfide is less precise than for more rigid linkers. However, this flexibility has afforded interesting solid-state architectures.19 Two complexes have been obtained in the present work, [Cu2(mea)2(bpds)2](CF3SO3)2 · 2CH3OH (7) prepared from

[Cu(CF3SO3)2], monoethanolamine, and bpds, and [Cu2(pa)2(bpds)2](BF4)2 (8) from [Cu(BF4)2], propanolamine, and bpds. The structure of 7 is built from centrosymmetric [Cu2(mea)2] nodes and angular bpds spacers (Figure 7a) with a C-S-S-C torsion angle of 87.49°. The Cu(II) ions are pentacoordinate with a slightly distorted square-pyramidal geometry (τCu1 ) 14.3%). The basal plane is formed by two alkoxo oxygens [Cu1-O1 ) 1.9289(13); Cu1-O1ii ) 1.9611(14) Å; ii: 1 - x, -y, 2 - z], one amino nitrogen [Cu1-N101 ) 2.0157(17) Å], and a nitrogen atom arising from the pyridine moiety of bpds [Cu1-N1 ) 1.9799(16) Å]. The apical position is occupied by the nitrogen atom from another bpds [Cu1-N2iii ) 2.2934(17) Å; iii: -0.5 + x, 0.5 - y, 0.5 + z] with an intranode Cu · · · Cu distance of 3.037 Å and S-S ) 2.027(1) Å. Alternatively, the structure can be viewed as comprising Cu(II) centers connected by the bpds ligands in helicoidal chains, which are then interconnected by the alkoxo bridges to form

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Figure 6. (a) A view of structure of 6; (b) detail of the packing diagram of 6 showing interpenetration of layers; (c) detail of the intermolecular π-π and C-H · · · π interactions in 6.

layers. A view through each layer along the b axis reveals nanosized channels of 10 × 10 Å (Figure 7b) filled with methanol molecules. Analysis of the channels confirms that each one is constructed exclusively either from left- or right-handed helices with each layer containing alternating helices of opposite chirality (Figure 7c). The complex 8 exhibits the same network topology. The fluorine atoms from the BF4- ions are disordered

over two positions (occupation factor 0.5). In both complexes 7 and 8, the anions are located between the layers. Interaction of the Tridentate exo-Dentate Ligand, 1,3,5-Tris(3-pyridyl)benzene (tpyb), with Binuclear Nodes. Tris(4-pyridyl) derivatives of benzene and triazine have a rich coordination chemistry,20 but surprisingly few examples of networks derived from the 3-pyridyl analogues have been

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Figure 7. (a) A view of a layer in 7 with atom numbering scheme; (b) a view of layered structure and channels in 7; (c) two views of helices of opposite chirality resulting from binding of Cu(II) with bpds in 7.

reported.21 1,3,5-Tris(3-pyridyl)benzene was obtained by Suzuki coupling of 1,3,5-tribrombenzene with 3-pyridylboronic acid pinacol ester. Reaction of monoethanolamine and tpyb with [Cu(NO3)2] or [Cu(BF4)2] affords the isomorphous complexes [Cu2(mea)2(tpyb)(ONO2)](NO3) · CH3OH (9) and [Cu2(mea)2(tpyb)(FBF3)](BF4) · CH3OH (10), respectively. In 9 and 10, both Cu(II) ions in the binuclear node are pentacoordinate, but their coordination spheres differ. Cu1 is coordinated in the basal plane by two bridging alkoxo oxygens [Cu1-O1 ) 1.954(2) Cu1-O2 ) 1.923(2) Å], one amino [Cu1-N1 ) 1.981(3) Å], and one pyridyl nitrogen [Cu1-N1A ) 1.981(3)

Å], with the nitrato group coordinated at the apical position [Cu1-O32S ) 2.456(4) Å]. The other Cu(II) ion is bound in the basal plane to two alkoxo oxygens [Cu2-O1 )1.984(2); Cu2-O2 ) 1.933(2) Å] and two nitrogen atoms from the amino [Cu2-N2 ) 2.021(3) Å], and pyridyl groups [Cu2-N2A ) 2.009(3) Å], while the apical position is occupied by a pyridyl nitrogen atom [Cu2-N3A ) 2.346(3) Å] (Figure 8a). The values for the τ parameter for the two Cu(II) ions are τCu1 ) 27.9 and τCu2 ) 39.3% with an intranode Cu · · · Cu distance of 2.946(3) Å. The tpyb ligand is coordinated to three copper ions belonging to three different nodes, and this results in a double

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Figure 8. (a) A view of the structure of 9 showing a ladder of cations that run parallel to [101j]; (b) an alternative view of 9 showing the channels, with the anions and solvent molecules omitted for clarity.

chain or ladder with alternating small and large metallacycles. Since the pyridyl moieties of the tpyb ligand are not coplanar with the central phenyl ring, the resultant framework coordination shows a structure with channels (Figure 8b) in which anions and solvent molecules reside. Conclusions The results reported herein illustrate the versatility of the alkoxo-bridged binuclear units in the generation of framework polymers with various dimensionalities and architectures. The originality of the network topologies arises from the combination of two types of bridges (alkoxide and heterocyclic polyamines) that impose both short and long Cu · · · Cu separations. The binuclear alkoxo-bridged nodes result spontaneously when reacting Cu(II) salts with the amino-alcohol and the exo-dentate ligand, as shown here and in preceding papers.14 Previous studies have shown that in the absence of the spacer amine ligands, supramolecular hydrogen-bonded Cu(II) dimers are formed.22 The two nodes encountered in the present study, [Cu2(mea)2]2+ and [Cu2(pa)2]2+, generate 2-D coordination polymers, provided that the anions do not coordinate to the Cu(II) centers. In this respect, copper(II) perchlorate is more appropriate as a starting material to form polydimensional products, and conversely, with copper(II) nitrate, the dimensionality of the resulting coordination polymers is reduced due to coordination of the nitrato ions to the metal centers thus preventing the binding of a second and further linker molecules. The primary structure of these coordination polymers is governed by the denticity and by the relative position of the donor atoms within the ligand spacer, and by secondary interactions, particularly hydrogen-bonding, which stabilize and

further decorate the overall solid-state architectures. In the present work, two out of the five ligands used, bpbenz and bpanth, show abilities in sustaining supramolecular architectures by means of π-π and/or C-H · · · π stacking interactions. Acknowledgment. Financial support from the CERES Program is gratefully acknowledged. G.M. is grateful to the European Community for a Marie Curie Fellowship. M.S. gratefully acknowledges receipt of a Royal Society Wolfson Merit Award and of a Royal Society Leverhulme Trust Senior Research Fellowship. We thank EPSRC (UK) for the provision of instrumentation, and the EPSRC National Crystallography Service for data collection on compound 8.

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CG700879Q