New Network Structures from Cu(II) Complexes of ... - ACS Publications

New Network Structures from Cu(II) Complexes of Chelating Ligands with Appended Hydrogen Bonding Sites Maria D. Stephenson,† Timothy J. Prior,‡,§ and Michaele J. Hardie*,†

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 2 643–653

School of Chemistry, UniVersity of Leeds, Leeds LS2 9JT, U.K., and CCLRC Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, U.K. ReceiVed August 30, 2007; ReVised Manuscript ReceiVed October 2, 2007

ABSTRACT: Complexes [Cu(phenpyzda)Cl2(H2O)] · H2O (1) and [Cu(phenpyzda)Br2(H2O)] · 2H2O (2), where phenpyzda ) pyrazino[2,3-f][1,10]phenanthroline-2,3-diamide, show similar molecular structures with square planar Cu(II). Each complex has a complicated three-dimensional (3D) hydrogen bonding network with 1 having an unusual 3,9-connectivity. Use of the corresponding carboxylic acid, pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarboxylic acid, results in the unexpected conversion of the ligand to 1H,3H-imidazol[2,3-f][1,10]phenanthroline () imiphen) in the complex [CuCl3(imiphenH)] · 2H2O, which has a 3D hydrogen bonded network structure of 3,6-connectivity. The more extended phenanthroline-based ligand 1,10-phenanthroline-5,6-[pteridine-2,4-diamine] was also synthesized, but no crystalline complexes of it were isolated. [Cu(bpy4diol)2](NO3)2 · H2O (4), where bpy4diol ) 2,2′bipyridine-4,4′-diol, shows a two-dimensional (2D) hydrogen bonded network with hexagonal topology. [Cu(bpy4da)(NO3)2] (5) where bpy4da ) 2,2′-bipyridine-4,4′-diamine has a 3D 2-fold interpenetrating R-Po related hydrogen bonded structure. Complexes [Cu(bpy4da)Cl2] (6) and [Cu(bpy5dmol)Cl2] (7) where bpy5dmol ) 2,2′-bipyridine-5,5′-bis(hydroxymethyl) have similar chloro bridged coordination chains that hydrogen bond together into 3D and 2D networks, respectively. Despite their different hydrogen bonding patterns, complexes 6 and 7 are isomorphic. Introduction Supramolecular and other labile interactions can be used to manipulate the way in which molecules are arranged in crystal lattices in order to create network materials with infinite one-, two-, or three-dimensional (1D, 2D, or 3D) structural motifs.1–3 The major approaches to such materials that have emerged thus far include the use of hydrogen bonding interactions between organic molecules,1 hydrogen bonding between discrete transition metal complexes,2 and the construction of polymeric coordination networks referred to as coordination polymers or metal-organic frameworks.3 Such materials have garnered widespread interest due to their strong potential for a variety of applications including gas storage,4 as nanospace reaction vessels,5 as catalysts,6 and in magnetism.7 One approach to forming networks of discrete transition metal complexes is to use a chelating ligand that has additional interactional functionality attached to its backbone, such as additional coordination sites or hydrogen bonding groups, or extended π-functionality. The majority of such studies of this type have involved biscarboxylic acid derivatives of 2,2′bipyridine, which can form extended hydrogen bonded networks of discrete coordination complexes,8–10 or coordination polymers when deprotonation to the carboxylate occurs.10,11 2,2′-Bipyridine derivatives with other types of hydrogen bonding groups such as alcohols,12 amides,13 and amines14 have seen less investigation. Ligands based on 1,10-phenanthroline are excellent candidates for studies on π-π stacking effects, noting that complexes of 1,10-phenanthroline itself form networks through such interactions.15 The π-system of 1,10-phenanthroline can be extended by forming planar polypyridyl ligands, and metal * Fax: +44 113 343 6565; Tel: +44 113 343 6458; E-mail: [email protected]. † University of Leeds. ‡ CCLRC Daresbury Laboratory. § Current address: Department of Chemistry, The University of Hull, Kingston upon Hull, HU6 7RX, U.K.

complexes containing two or more such ligands should show significant π-π stacking interactions. There are, however, few examples of such systems.16,17 Combining the two approaches, by appending strong hydrogen bond donor/acceptor groups to extended 1,10-phenanthroline ligands, has been even less explored with the only examples being complexes of the ligand pyrazino[2,3-f][1,10]phenanthroline-2,3-dinitrile, where, in some cases, along with extensive π-π stacking interactions between metal complexes, the nitrile groups were involved in weak C-H · · · NC hydrogen bonding.17 In this study, we report our investigation of three new 1,10phenanthroline-based ligands that have both extended π-systems and strong hydrogen bonding donor and acceptor groups, namely, ligands 1,10-phenanthroline-5,6-[pteridine-2,4-diamine] () phenpte), pyrazino[2,3-f][1,10]phenanthroline-2,3-diamide () phenpyzda), and pyrazino[2,3-f][1,10]phenanthroline-2,3dicarboxylic acid () phenpyzdc). We also report metal complexes of some previously known 2,2′-bipyridine ligands that that have alcohol and amine hydrogen bonding groups, namely, 2,2′-bipyridine-4,4′-diol () bpy4diol),18 2,2′-bipyridine-4,4′diamine () bpy4da),19 and 2,2′-bipyridine-5,5′-bis(hydroxymethyl) () bpy5dmol).20 A handful of other ligands were also investigated in this context, including 1,10-phenanthroline-4,7diol, 1,10-phenanthroline-5,6-diamine,21 and 5,5′-bis(dihydroxymethyl)-2,2′-bipyridine, but these did not result in the isolation of any crystalline coordination complexes and will not be further discussed. While transition metal complexes of bpy4da and bpy5dmol have been reported,22 there have been no structural studies to date. There is one structurally authenticated complex of bpy4diol, namely, [RuCl(C6Me6)(bpy4diol)]Cl(CH3OH), which forms a hydrogen bonded dimer in the solid state through interactions between the diol groups and chloride counteranion.23 Structural studies have been undertaken of transition metal complexes of an isomer of bpy4da, namely, 2,2′-bipyridine-5,5-diamine () bpy5da).14 In this study, numerous discrete and 1D polymeric transition metal complexes of

10.1021/cg700820d CCC: $40.75  2008 American Chemical Society Published on Web 12/01/2007

644 Crystal Growth & Design, Vol. 8, No. 2, 2008

bpy5da were characterized that formed associations into more extended structures through hydrogen bonding interactions with each other, or to counteranions and/or solvent molecules, and through π-π stacking interactions.

Experimental Section General. Ligands 2,2′-bipyridine-4,4′-diol,18 2,2′-bipyridine-4,4′diamine,19 and 2,2′-bipyridine-5,5′-bis(hydroxymethyl)20 were prepared by literature methods. Other chemicals were obtained from commercial sources and used without further purification. NMR spectra were recorded by automated procedures on either a Bruker DPX 300 or a Bruker ARX 250 NMR spectrometer. Infrared spectra were recorded as solid phase samples on a Perkin-Elmer spectrometer, ultraviolet (visible) spectra were recorded on a Jasco V-530, and ESR spectra were recorded on a Bruker EMX ECO-8/2.7. Melting points were determined on a Bippy melting point apparatus and were recorded uncorrected. 1,10-Phenanthroline-5,6-[pteridine-2,4-diamine] (phenpte). 2,4,5,6Tetraaminopyrimidine tetrahydrosulfate (0.57 g, 2.4 mmol) and sodium hydroxide (0.28 g, 7.1 mmol) in water (10 mL) were heated at reflux for 30 min, then 1,10-phenanthroline-5,6-dione (0.50 g, 2.4 mmol) in hot ethanol (200 mL) was added, and the mixture was heated at reflux for 12 h. After cooling, a green solid was collected and washed with cold ethanol. Yield 0.73 g (97%). Melting point >350 °C. Microanalysis calculated for C16H10N8.4H2SO4: C 33.22, H 3.14, N 19.38; found C 32.70, H 2.90, N 18.90. IR V max(solid phase)/cm-1: 3316 s br, 2161 m, 1630 s, 1444 m, 1337 s, 996 m, 876 m, 859 w, 808 m, 781 m, 758 w, 739 m, 694 w, 618 s. 1H NMR (250 MHz; [D6]DMSO): δ 9.52 (dd 1H, JHH ) 6.5, 1.6 Hz, H4or7), 9.19 (dd, 1H, JHH ) 6.4, 1.8 Hz, H4or7), 9.00 (dd, 1H, JHH ) 4.5, 1.6 Hz, H2or9), 8.93 (dd, 1H, JHH ) 4.4, 1.8 Hz, H2or9) 7.69 (m, 2H, H3and8).13C{1H} NMR (250 MHz; [D6]DMSO): δ 164.2 (CNH2), 163.4 (CNH2), 155.4 (Cq), 152.6 (CH), 150.9 (CH), 148.1 (Cq), 146.1(Cq), 144.8, (Cq) 142.1 (CH), 133.9 (Cq), 133.6 (CH), 133.0 (CH), 127.7 (Cq), 126.9 (Cq), 125.0 (Cq), 124.4 (CH). ESI-MS Calculated accurate mass for (C16H11N8)+315.1107, found 315.1104. Pyrazino[2,3-f][1,10]phenanthroline-2,3-diamide (phenpyzda). 6,7Dicyanodipyridoquinoxaline (200 mg, 0.71 mmol) was dissolved in 5 mL of concentrated sulfuric acid and stirred for 5 days. The solution was carefully added dropwise to 20 mL of water/ice while stirring, then neutralized with 10 M NaOH. The beige precipitate was filtered washed with cold water, acetone, and Et2O and dried in a vacuum at 100 °C. Yield 0.154 g (68%). Melting point >350 °C. Microanalysis calculated for C16H10N6O2.1.5H2O: C 57.91, H 3.50, N 25.33%; found C 58.30, H 3.50, N 24.85%. IR V max(solid phase)/cm-1: 3387 m br, 3142 m, 2116 w, 1667 s (CdO stretch), 1591 s, 1535 m, 1509 w, 1488 m, 1450 m, 1363 m, 1268 m, 1206 m, 1103 m, 1035 m, 1008 w, 877 w, 830 m, 706 m, 706 m, 565 m. ESI-MS calculated accurate mass for (C16H11N6O2)+ 319.0943, found 319.0944. Pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarboxylic acid (phenpyzdc). 6,7-Dicyanodipyridoquinoxaline (200 mg, 0.71 mmol) was dissolved in 20 mL of 50% sulfuric acid and heated to reflux for 24 h. The mixture was cooled to room temperature, and the pH was adjusted to 4 by the addition of 10 M NaOH. The product was precipitated by the addition of concentrated HCl and stirred for 20 min. The light yellow solid was filtered washed with cold water, acetone, and Et2O and dried in a vacuum at 100 °C. Yield 0.200 g (88%). Melting point >350 °C. Microanalysis calculated for

Stephenson et al. C16H8N4O4.0.3H2O: C 59.00, H 2.67, N 17.21; found C 58.85, H 2.65, N 17.50. IR V max(solid phase)/cm-1: 2923 s br (O-H stretch), 1743 s (CdO stretch), 1576 w, 1510 w and 1408 m, 1199 s, 929 s, 781 m, 729 s, 675 w, 630 w, 607 w cm-1. 1H NMR (250 MHz; DMSO-d6): δ 9.42 (dd, 2H, JHH ) 8.1, 1.6, H4,7), 9.25 (dd, 2H, JHH ) 4.4, 1.6, H2,9), 7.99 (dd, 2H, JHH ) 8.1, 4.4, H3,8). 13C{1H} NMR (250 MHz; [D6]DMSO): δ 166.3 (COOH), 153.1 (CH), 147.8 (Cq), 142.4 (Cq), 139.7 (Cq), 133.6 (CH), 126.2 (Cq), 124.9 (CH). ESI-MS calculated accurate mass for (C16H9N4O4)+ 321.0631, found 321.0624. [Cu(phenpyzda)(Cl)2(H2O)] · H2O, (1). CuCl2 · 6H2O (5.2 mg, 0.03 mmol) in methanol (1 mL) was added to a mixture of phenpyzda (10 mg, 0.03 mmol) in hot water (2 mL) with 20 drops of concentrated HCl. The mixture was left to evaporate, and pale green plate-like crystals of complex 1 (5.4 mg, 73%) were formed overnight. Microanalysis calculated for complex with loss of one H2O molecule: C16H16N6CuO5Cl2;C 37.91, H 3.19, N 16.59%; found C 37.65, H 3.05, N 16.50%. IR V max(solid phase)/cm-1: 3207 s br, 1581 s, 1513 m, 1368 s, 1225 s, 1100 s, 941 w, 824 m, 732 m, 635 m, 472 w. ESR (room temperature): g⊥ 2.237. [Cu(phenpyzda)(Br)2(H2O)] · 2H2O, (2). Cu(NO3)3 · 6H2O in methanol (1 mL) was added to a solution of phenpyzda (10 mg, 0.03 mmol) and 20 drops of concentrated HBr in hot water (2 mL). On evaporation, dark green needle-like crystals of complex 2 (6.1 mg, 68%) were formed overnight. Microanalysis: calculated for C16H16N6CuO5Br2;C 32.26, H 2.71 N 14.11%; found C 30.35, H 1.60, N 13.20%. IR V max(solid phase)/cm-1: 3131 s br (N-H stretch), 1576 s (N-H bend), 1370 s, 1047 s, 725 m, 595 m. ESR (room temperature): g⊥ 2.231. [CuCl3(imiphenH)] · 2H2O, (3). CuCl2 · 6H2O (10.0 mg, 0.05 mmol), phenpyzdc (32.0 mg, 0.10 mmol), 2 mL of water, and 2 mL of concentrated aqueous HCl were added to a 23 mL Parr acid digestion vessel which was heated at 200 °C for 5 days. The pressure vessel was then allowed to cool to room temperature while still in the oven. The resultant green solution was left to slowly evaporate to give green needles of complex 3 (16.8 mg, 78%) after two days. Microanalysis: calculated for C13H13N4O2CuCl3.1.4H2O;C 34.18, H 3.40, N 12.27%; found C 34.00, H 2.85, N 12.40%. UV(Vis): λmax(DMF)/nm 689 (ε/ dm3 mol-1 cm-1 147). IR V max(solid phase)/cm-1: 3394 s br, 3067 s, 1619 m, 1534 m, 1465 m, 1450 m, 1419 m, 1371 m, 1309 w, 1208 m, 1191 w, 1160 m, 1112 w, 1081 m, 965 m, 923 s, 822 w, 730 m, 708 m, 647 w, 628 m, 477 w. ESR(room temperature): g⊥ 2.074. Complex 2 can also be synthesized by adding phenpyzdc (20 mg, 0.06 mmol) to 2 mL of hot water and concentrated HCl added until the ligand dissolves, followed by addition of CuCl2 · 6H2O (5.2 mg, 0.03 mmol) in methanol (1 mL) and subsequent slow evaporation. [Cu(bpy4diol)2](NO3)2 · H2O, (4). Bpy4diol (50 mg, 0.27 mmol), Cu(NO3)2 · 6H2O (65.2 mg, 0.27 mmol) and water (4 mL) were added to a 23 mL Parr acid digestion vessel and heated for 3 days at 150 °C. The pressure vessel was allowed to cool to room temperature while still in the oven. The mixture was filtered and allowed to evaporate very slowly, giving small pale blue platelike crystals of complex 4 and some additional amorphous blue powder after four weeks. Bulk yield 59.8 mg (38%). Microanalysis was performed on the bulk mixture due to the difficulty of separation, calculated for C20H16N6CuO6.2H2O;C 40.03, H 3.37, N 14.01%; found C 40.50, H 3.00, N 12.70%. UV(Vis): λmax(DMF)/nm 732 (ε/dm3 mol-1 cm-1 183). IR V max(solid phase)/ cm-1: 3379 br, 3090 br, 1617 m, 1406 m, 1063 and 1021 s, 977 m, 876 s, 753 s, 583 m, 522 m, 478 w. ESR (room temperature): g⊥ 2.086. [Cu(bpy4da)(NO3)2] (5). Cu(NO3)2 · 6H2O (7.2 mg, 0.03 mmol) dissolved in methanol (1 mL) was added to a solution of bpy4da (5.0 mg, 0.03 mmol) in 2,2,2-trifluoroethanol (2 mL) to give a blue solution. After 3 weeks of very slow evaporation, the solution turned bright green, and green block-like crystals of complex 5 were formed, along with a green amorphous precipitate, overall yield 8.2 mg (73%). Microanalysis was performed on the bulk mixture due to the difficulty of separation, calculated for C10H10N6O6Cu;C 32.13, H 2.70, N 22.49%; found C 26.25, H 2.40, N 16.50%. UV(Vis): λmax(DMSO)/nm 735 (ε/dm3 mol-1 cm-1 170). IR V max(solid phase)/cm-1: 3466 s, 3236 s, 2643 m, 2355 m, 1953 w, 1727 w, 1615 s, 1556 m, 1508 m, 1365 s br, 1151 m, 1092 w, 1021 s, 863 w, 837 s, 749 m, 667 s. ESR (room temperature): g⊥ 2.088. [Cu(bpy4da)(Cl)2] (6). CuCl2 · 6H2O (5.1 mg, 0.03 mmol) and bpy4da (5.0 mg, 0.03 mmol) were treated as for complex 5, giving green block-like crystals of complex 6 (5.7 mg, 59%) after one week of evaporation. Microanalysis: calculated for C10H10N4CuCl2; C 37.45, H 3.15, N 17.47%; found C 37.65, H 2.65, N 16.75%. IR V max(solid

Network Structures from Cu(II) Complexes of Chelating Ligands

Crystal Growth & Design, Vol. 8, No. 2, 2008 645

Table 1. Details of Data Collections and Structure Refinements for Complexes 1–7

formula Mr crystal color and shape crystal size (mm) crystal system space group a (Å) b (Å) c (Å) a ( o) β (o) γ (o) U (Å3) Z Fc (g cm-3) F(000) µ (mm-1) θ range (°) no. data collected no. unique data Rint no. obs data (I > 2σ > (I)) no. parameters no. restraints R1 (obs data) wR2 (all data) S max, min residual e density (e Å3)

formula Mr crystal color and shape crystal size (mm) crystal system space group a (Å) b (Å) c (Å) a (o ) β ( o) γ (o) U (Å3) Z Fc (g cm-3) F(000) µ (mm-1) θ range (°) no. data collected no. unique data Rint no. obs data (I > 2σ > (I)) no. parameters no. restraints R1 (obs data) wR2 (all data) S max, min residual e density (e Å3)

1

2

3

4

C16H14N6O4CuCl2 488.77 pale green block 0.34 × 0.25 × 0.013 triclinic P1j 8.7086(17) 9.990(2) 11.409(2) 99.45(3) 105.88(3) 101.96(3) 907.9(3) 2 1.788 494 1.537 1.91–27.49 13892 4147 0.1336 3216

C16H16N6O5CuBr2 595.71 dark green needle 0.54 × 0.02 × 0.02 triclinic P1j 9.4572(19) 10.011(2) 11.879(2) 103.24(3) 97.97(3) 107.36(3) 1018.7(4) 2 1.942 586 5.037 2.22–28.25 18455 5020 0.0191 4568

C13H13N4O2CuCl3 427.15 pale green needle 0.100 × 0.02 × 0.02 triclinic P1j 8.8005(3) 9.3330(5) 9.9370(6) 80.104(4) 80.399(3) 84.103(3) 790.46(8) 2 1.795 430 1.901 2.10–28.27 16772 3874 0.0461 2909

C20H18CuN6O11 581.94 blue plate 0.12 × 0.12 × 0.01 triclinic P1j 7.0604(8) 11.1943(12) 15.5157(16) 100.739(2) 93.515(2) 108.297(2) 1134.4(2) 2 1.704 594 1.040 3.65–33.12 8438 4638 0.0333 3697

284 5 0.0604 0.1710 1.036 2.160, -1.088

295 0 0.0242 0.0679 1.041 2.050, -0.446

223 4 0.0427 0.1276 1.082 0.746, -0.609

335 2 0.0575 0.1545 1.038 0.870, -0.985

5

6

7

C10H10CuN6O6 373.78 green needle 0.10 × 0.05 × 0.05 orthorhombic Pbcn 14.7440(12) 8.9510(7) 10.0648(8) 90 90 90 1328.29(18) 4 1.869 756 1.691 3.98–33.03 9038 1456 0.0585 1167

C10H10Cl2CuN4 320.66 green block 0.34 × 0.14 × 0.07 monoclinic P21/c 8.7895(2) 19.1727(4) 7.1261(2) 90 108.832(1) 90 1136.59(5) 4 1.874 644 2.370 2.12–27.48 9723 2597 0.1649 2280

C12H12Cl2CuN2O2 350.68 green needle 0.25 × 0.05 × 0.05 monoclinic P21/c 8.4512(17) 22.888(5) 7.1305(14) 90 110.54(3) 90 1291.6(4) 4 1.803 708 2.102 3.13–27.47 11769 2942 0.1117 2412

113 0 0.0389 0.0998 1.022 0.901, -0.545

190 0 0.0600 0.1631 1.042 1.161, -1.775

199 5 0.0556 0.1466 1.042 1.072, -1.404

phase)/cm-1: 3455 m, 3346 and 3209 m, 2167 w, 2014 w, 1942 w, 1628 s, 1558 m, 1504 m, 1367 w, 1321 w, 1273 s, 1150 w, 1025 m, 1012 m, 963 w, 864 m, 818 m, 665 w. ESR (room temperature): g⊥ 2.113. [Cu(bpy5dmol)(Cl)2] (7). CuCl2 · 6H2O (9.6 mg, 0.04 mmol) dissolved in methanol (1 mL) was added to a solution of bpy5dmol (10.0 mg, 0.04 mmol) in hot methanol (10 mL). After three days of slow evaporation pale green needles of complex 7 formed (12.0 mg, 86%). Microanalysis: calculated for C12H12N2O2CuCl2.H2O; C 39.09, H 3.83, N 7.60%; found C 38.75, H 3.35, N 7.20%. IR V max(solid phase)/

cm-1: 3335 br s, 1605 s, 1389 s, 1220 m, 1133 m, 1075 s, 1044 s, 832 m, 724 m, 666 m, 621. ESR (room temperature): g⊥2.088. X-ray Data Collections and Structure Determinations. Single crystals of complexes 1-7 were mounted on glass fibers under oil, and X-ray diffraction data were collected with Mo KR radiation (λ ) 0.71073 Å) at 150(1) K on a Nonius KappaCCD diffractometer with sealed-tube Mo source; on a Bruker Apex IIX8 diffractometer with an Mo rotating-anode source (complexes 2 and 3); or using synchrotron radiation (λ ) 0.84640 Å) at Station 16.2SMX of CCLRC Daresbury laboratory with a Bruker D8 diffractometer fitted with an APEX

646 Crystal Growth & Design, Vol. 8, No. 2, 2008 Scheme 1

II detector (complexes 4 and 5). Data were corrected for Lorentz and polarization effects and absorption corrections were applied using multiscan methods. The structures were solved by direct methods using SHELXS-9724 and refined by full-matrix least-squares on F2 using SHELXL-97,25 using the X-Seed GUI.26 All nonhydrogen atoms were refined anisotropically and, unless stated otherwise, C-H and O-H hydrogen atoms were placed in geometrically estimated positions with a riding refinement. Details of data collections and structure refinements are given in Table 1, with any additional details given below. All O-H hydrogen atoms were fully refined for complexes 1 and 4 with restraints on the bond lengths. All O-H hydrogen atoms were fully refined for complex 2. For complex 3 the N-H and O1-H hydrogen atoms were fully refined with restraints on bond lengths, and the O2-H hydrogen atoms were set at the positions where they first appeared in the difference map with Uiso set at 1.5 times Ueq of O2. Complex 5 N-H hydrogen atoms were fully refined. Complexes 6 and 7, all hydrogen atoms were fully refined although restraints were placed on some C-H and O-H bond distances for 7.

Results and Discussion Phenanthroline-Based Ligands. 1,10-Phenanthroline-5,6[pteridine-2,4-diamine] () phenpte) was synthesized in near quantitative yields by the condensation of 1,10-phenanthroline5,6-dione (phendione) with 2,4,5,6-tetraaminopyrimidine in ethanol, with the free base of 2,4,5,6-tetraaminopyrimidine being generated from its sulfate salt in situ, Scheme 1. Phenpte was characterized by 1H NMR and 13C NMR, IR, mass spectrometry, and elemental analysis. The 1H NMR showed six aromatic protons, the amine protons were not observed by NMR probably due to fast exchange. 13C NMR showed 16 peaks, which is consistent with the structure of the ligand. The infrared absorption spectrum shows N-H stretching and N-H bending of the amine groups at 3316 and 1630 cm-1, respectively. The distinctive CdO stretch of the phendione at 1687 cm-1 is not observed in the spectrum. Ligands pyrazino[2,3-f][1,10]phenanthroline-2,3-diamide () phenpyzda) and pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarboxylic acid () phenpyzdc) were synthesized by acid hydrolyzis of pyrazino[2,3-f][1,10]phenanthroline-2,3-dinitrile, adapting the procedure of Abeywickrama and Baker for similar ligand syntheses.27 Stirring the dinitrile in concentrated sulfuric acid for five days at room temperature gave the diamide ligand phenpyzda as a beige solid in 68% yield, Scheme 2. The diamide ligand was found to be very insoluble in all solvents tried, including various deuterated acids. Hence it was not possible to fully characterize the diamide ligand by NMR. Nevertheless, all other methods of characterization fully support the formation of this ligand. The infrared spectrum shows an N-H stretch, CdO stretch, and N-H bend of the amide group with respective characteristic frequencies of 3387, 1667, and 1591 cm-1. The characteristic CtN stretch from the nitrile group of the starting material is also absent. Heating pyrazino[2,3-f][1,10]phenanthroline-2,3-dinitrile at reflux for 24 h in 50% w/v of sulfuric acid and water results in further hydrolyzis to give phenpyzdc as a orange/brown solid in 88% yield, Scheme 2. The 1H NMR shows three aromatic proton signals, the proton of the carboxylic acid is not observed in the spectrum, probably due to fast exchange on a NMR time

Stephenson et al.

scale, and the 13C{1H} NMR spectrum shows the expected eight signals. Bands are observed in the infrared spectrum which are characteristic of a carboxylic acid functional group, and the CtN stretch from the starting material is not observed. Phenpte was found to be insoluble in most common laboratory solvents, although would dissolve in hot dimethylsulfoxide, and showed slight solubility in 2,2,2,-trifluoroethanol under reflux conditions. The ligand was reacted with a variety of transition metal salts, but reactions did not lead to isolatable or identifiable products, which is no doubt due to the extreme insolubility of the ligand. Phenpyzda is also highly insoluble, but can be dissolved in acidic aqueous solutions, noting that the use of acidic conditions to grow crystals of Cu(II) complexes of similarly insoluble chelating ligands has been utilized by Kruger and co-workers.8 Pale green needles of complex [Cu(phenpyzda)Cl2(H2O)] · H2O (1) were grown from an acidic water/methanol solution of CuCl2 · 6H2O and phenpyzda in 1:2 proportions. The synthesis of this complex was found to be repeatable using other copper(II) salts, including nitrate, acetate, bromide, and tetrafluoroborate, indicating that the chloride ligands originate from the acid. Likewise, dark green crystals of the complex [Cu(phenpyzda)Br2(H2O)] · 2H2O (2) were synthesized in an analogous way from Cu(NO3)2 · 6H2O and phenpyzda but with concentrated HBr as the acid. Again, this complex could be obtained from different Cu(II) salts. A number of other concentrated acids were also tried, including HI, HNO3, HBF4, and HOAc, along with many other transition metal salts, but no other crystalline complexes were obtained with this ligand. The IR spectra of complex 1 and 2 were similar and showed slight shifting of most bands compared with that of the free ligand, and ESR results were typical of square pyramidal Cu(II) with g⊥ values of 2.231 and 2.237 for 1 and 2, respectively. Phenpyzdc was treated in a similar manner to phenpyzda, with a 1:2 mixture of CuCl2 · 6H2O and phenpyzdc in aqueous HCl and MeOH giving green crystals on heating under solvothermal conditions for 5 days and subsequent evaporation. Analysis of the product revealed that the ligand undergoes a metal-mediated conversion to 1H,3H-imidazol[2,3-f][1,10]phenanthroline () imiphen), with the isolation of complex [CuCl3(imiphenH)] · 2H2O (3), Scheme 3. This ligand conversion also occurs if the reaction mixture is simply allowed to evaporate (with no prior heating or solvothermal treatment), and in the absence of methanol, but does not occur in the absence of Cu(II). Microanalysis and infrared spectroscopy indicate that the ligand conversion occurs in the bulk material, and ESR of complex 3 gives a g⊥ value of 2.189. Many other different combinations of acids and metal salts were attempted with phenpyzdc, but none produced crystalline material for analysis. Complexes 1 and 2 have very similar neutral coordination complexes, with both showing square pyramidal Cu(II) coordination geometry, Figure 1. In each case there is one chelating phenpyzda ligand, and the remaining coordination sites are occupied by two halide ions and an aquo ligand, with a halide in the apical position. The two amide groups of the ligands are staggered in relation to one another in both complexes, with torsion angles between the two N-C bonds of 161.7 and 163.1° for complexes 1 and 2, respectively, and one amide group in-plane with the conjugated π-ring of the ligand. Aside from the identity of the halide, the only notable difference between the complexes is the orientation of the aquo ligands; this is due to their differing hydrogen bonding interactions within the crystal lattices.



Scheme 2

Scheme 3

In complex 1 there is one additional water molecule which hydrogen bonds to the [Cu(phenpyzda)Cl2(H2O)] species, which itself acts as a hydrogen bond donor and acceptor through its aquo, amide, and chloride groups. Hence, a complicated 3D network of hydrogen bonds exists. Hydrogen bonding motifs are frequently referred to by graph set notation of generalized form Gda(n) where G is the general form such as R for ring, C for chain, a and d are the numbers of acceptor and donor atoms, respectively, and n is the number of atoms in the pattern.28 The hydrogen bonds in complex 1 involving waters are shown in Figure 2a. The uncomplexed water molecule is a hydrogen bond acceptor from the aquo ligand at a O-H · · · O distance 1.664 Å, (O · · · O 2.633 Å), and a hydrogen bond donor to a Cl group and a OdC amide of two neighboring [Cu(phenpyzda)Cl2(H2O)] molecules, at a OH · · · Cl distance of 2.372 Å (O · · · Cl 3.269 Å) and a O-H · · · OdC distance of 1.856 Å (O · · · O 2.800 Å). The amide involved in this interaction is in-plane with

Figure 1. Molecular complexes from the crystal structures of (a) [Cu(phenpyzda)Cl2(H2O)] · H2O (1) and (b) [Cu(phenpyzda)Br2(H2O)] · 2H2O (2). Ellipsoids are shown at 50% probability levels. Selected bond lengths and angles: Complex 1 Cu1-O1 1.971(3), Cu1-N1 2.040(3), Cu1-N2 2.027(3), Cu1-Cl1 2.5571(11), Cu1-Cl2 2.2664(12) Å, O1-Cu1-N2 159.68(13), O1-Cu1-N1 89.75(13), N2-Cu1-N1 81.02(13), O1-Cu1-Cl2 92.44(10), N2-Cu1-Cl2 93.50(10), N1-Cu1-Cl2 169.25(9), O1-Cu1-Cl1 100.66(10), N2-Cu1-Cl1 97.33(9), N1-Cu1-Cl1 89.45(9), Cl2-Cu1-Cl1 100.48(4)°. Complex 2 Cu-Br1 2.6824(6), Cu1-Br2 2.4109(8), Cu1-O1 1.9724(18), Cu1-N2 2.0326(18), Cu1-N1 2.0482(18) Å; O1-Cu1-N2 166.79(7), O1-Cu1-N1 87.69(8), N2-Cu1-N1 80.84(8), O1-Cu1-Br2 92.09(7), N2-Cu1-Br2 96.34(6), N1-Cu1-Br2 159.38(5),O1-Cu1-Br192.82(6),N2-Cu1-Br195.52(6),N1-Cu1-Br1 99.59(6), Br2-Cu1-Br1 101.01(3)°.

the conjugated π-ring of the ligand. These two neighboring [Cu(phenpyzda)Cl2(H2O)] molecules also hydrogen bond together through the same Cl group and one of the NH groups of the same amide (NH · · · Cl separation 2.392 Å, N · · · Cl 3.256 Å) to form a ring with a R32(8) motif. The aquo ligand also hydrogen bonds to an out-of-plane amide group of a further [Cu(phenpyzda)Cl2(H2O)] molecule at OH · · · OdC distance 1.876 Å (O · · · O 2.778 Å), Figure 2a. The [Cu(phenpyzda)Cl2(H2O)] molecules also form hydrogen bonds between themselves through NH · · · Cl interactions from the amide groups, Figure 2b. The in-plane amide is involved in a second ring motif, this time as a hydrogen bond donor forming an R42(8) motif Cl · · · (NH2) · · · Cl · · · (NH2) ring between four [Cu(phenpyzda)Cl2(H2O)] molecules at NH · · · Cl distances 2.392 and 2.590 Å (N · · · Cl 3.256 and 3.256 Å). The out-of-plane amide only forms one interaction as a hydrogen bond donor, being involved in a pairwise interaction between two [Cu(phenpyzda)Cl2(H2O)] molecules that are inverted with respect to one another, Figure 2b, at a NH · · · Cl distance of 2.459 Å (N · · · Cl 3.282 Å). Interestingly, despite the ability to form homomeric R22(8) hydrogen bonding interactions, there are no amide · · · amide hydrogen bonding interactions within complex 1. The overall 3D hydrogen bonding network is shown in Figure 3a. Despite the extended π-system of the ligand, the network does not show extensive π-stacking interactions with only one face-to-face interaction apparent at a ring centroid separation of 3.791 Å. The network topology is complicated, Figure 3b. Each [Cu(phenpyzda)Cl2(H2O)] complex is connected to six others through hydrogen bonding interactions in a distorted R-Po-related manner. Each [Cu(phenpyzda)Cl2(H2O)] also hydrogen bonds to three uncomplexed water molecules, while each water hydrogen bonds to three different [Cu(phenpyzda)Cl2(H2O)] complexes. Hence, overall the network has 3,9connectivity, that is, contains 3-connecting and 9-connecting nodes. There are few identified examples of such networks, with known examples involving coordination polymers with lanthanide species or copper clusters.29 Complex 2 also shows a complicated 3D network of hydrogen bonds that is quite distinct from that of complex 1 due in part to the larger amount of water in the overall complex. While the single uncomplexed water molecule in complex 1 acted as a 3-connecting node, there are two different uncomplexed waters in complex 2 one of which is a 3-connecting node, with the other a 4-connecting node as it is a bifurcated hydrogen bond acceptor. The uncomplexed waters and the aquo ligand hydrogen bond together to form a hexameric water cluster with coordinate or hydrogen bonding links to six molecules of [Cu(phenpyzda)Br2(H2O)], Figure 4a. The water cluster features an R42(8) hydrogen bonding ring motif and two pendent waters with O-H · · · O distances between the water/aquo groups of 1.811, 1.899, and 2.121 Å (corresponding O · · · O distances 2.701, 2.764, and 2.716 Å). The uncomplexed water molecules also act as hydrogen bond donors to Br and CdO groups of neighboring [Cu(phenpyzda)Br2(H2O)] complexes (OH · · · Br distance 2.549 Å, O · · · Br 3.452 Å; OH · · · OdC distance 1.893 Å, O · · · O 2.771 Å). There are also multiple hydrogen bonding


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Figure 2. Hydrogen bonding interactions in complex [Cu(phenpyzda)Cl2(H2O)] · H2O (1). (a) Interactions involving the uncomplexed water molecule (shown in ball-and-stick); (b) interactions between molecules of [Cu(phenpyzda)Cl2(H2O)].

Figure 3. Representations of the crystal structure of complex 1. (a) 3D hydrogen bonded network; (b) 3,9-connectivity between molecular components. Large spheres represent the center of the [Cu(phenpyzda)Cl2(H2O)] molecules, whereas small spheres are the uncomplexed water molecules.

Figure 4. Hydrogen bonding interactions in complex [Cu(phenpyzda)Br2(H2O)] · 2H2O (2). (a) Interactions involving aquo ligands and uncomplexed water molecules (shown as ball-and-stick). For the sake of clarity, for two [Cu(phenpyzda)Br2(H2O)] molecules only the O atoms of the hydrogen bond acceptor amide group are shown. (b) Hydrogen bonds between the [Cu(phenpyzda)Br2(H2O)] molecules.

interactions directly between the [Cu(2)Br2(H2O)] molecules, Figure 4b. The in-plane amide acts as a hydrogen bond donor to form a R42(8) Br · · · (NH2) · · · Br · · · (NH2) ring similar to that seen in complex 1 (NH · · · Br 2.605 and 2.778 Å, N · · · Br 3.479 and 3.472 Å). The out-of-plane amide is a hydrogen bond donor to a Br and an in-plane OdC group of different neighboring [Cu(phenpyzda)Br2(H2O)] molecules (NH · · · Br 2.687 Å, N · · · Br 3.523 Å; NH · · · OdC 2.167 Å, N · · · O 2.941 Å), and accepts a hydrogen bond from an uncomplexed water molecule within the water cluster. Note that the presence of amide · · · amide hydrogen bonding interactions is a marked

difference to the interactions seen in complex 1. Two amide · · · amide linkages form a R22(14) motif ring between two [Cu(phenpyzda)Br2(H2O)] molecules related by a center of inversion. A section of the overall 3D hydrogen bonded network is shown in Figure 5a. The 3D structure has hydrophilic regions of water and bromide ions, interspersed with hydrophobic ligand regions. Again, there is one face-to-face π-π stacking interaction apparent at a ring centroid separation of 3.847 Å. The network connectivity is complicated, Figure 5b, with the interactions between the [Cu(phenpyzda)Br2(H2O)] com-



Figure 5. Representations of the crystal structure of complex 2. (a) 3D hydrogen bonded network; (b) Connectivity diagram with large spheres representing the center of the [Cu(phenpyzda)Br2(H2O)] molecules, whereas small spheres are the uncomplexed water molecules.

Figure 6. From the crystal structure of [CuCl3(imiphenH)] · 2H2O (3). (a) Molecular structure of [CuCl3(imiphenH)] with ellipsoids shown at 50% probability levels; (b) highlight of hydrogen bonding interactions between the [CuCl3(imiphenH)] molecules and uncomplexed water molecules. Selected bond lengths and angles for 3: Cu1-N1 2.056(3), Cu1-N2 2.046(3), Cu1-Cl1 2.6352(10), Cu1-Cl2 2.2778(8), Cu1-Cl3 2.2830(11) Å; N2-Cu1-N1–80.59(11), N2-Cu1-Cl2 168.19(9), N1-Cu1-Cl2 92.89(8), N2-Cu1-Cl3 92.45(9), N1-Cu1-Cl3 164.30(9), Cl2-Cu1-Cl3 91.37(4), N2-Cu1-Cl1 90.49(9), N1-Cu1-Cl1 92.26(9), Cl2-Cu1-Cl1 99.64(3), Cl3-Cu1-Cl1 101.92(4)°.

Figure 7. Crystal structure of complex 3. (a) 3D hydrogen bonded network; (b) Connectivity diagram with large spheres representing the center of the [CuCl3(imiphenH)] molecules, and small spheres are the uncomplexed water molecules.

plexes themselves forming a honeycomb-like 5-connected network and the waters providing further hydrogen bonding links across the honeycomb channels.

One type is a hydrogen bond donor in a R42(8) motif involving two symmetry related waters and two [CuCl3(imiphenH)] molecules related by a center of inversion, with interactions to

Complex 3 also features a square pyramidal Cu(II) coordination environment with one chelating (imiphenH)+ ligand, and three Cl- anions, Figure 6a. The complex is uncharged as both imidazole nitrogen atoms are protonated giving the ligand a 1+ charge. As for complexes 1 and 2, in complex 3 there are waters of crystallization that play an important role in the overall 3D hydrogen bonding network structure of the complex. There are two crystallographically distinct uncomplexed water molecules.

the apical Cl at OH · · · Cl distance 2.205 Å (O · · · Cl 3.207 Å). The other water molecule is also involved in a ring motif as a hydrogen bond donor, forming a R44(12) pattern with the basal Cl groups of two inversion-related [CuCl3(imiphenH)] molecules at OH · · · Cl distances 2.404 and 2.307 Å (corresponding O · · · Cl separations 3.229 and 3.181 Å). This water also acts as a hydrogen bond acceptor, interacting with an NH of the imiphenH ligand at a NH · · · O distance 2.027 Å (O · · · N 2.734 Å),


Figure 8. Asymmetric unit of the crystal structure of complex [Cu(bpy4diol)2](NO3)2 · H2O (4) with hydrogen bonds shown as dashed lines and ellipsoids shown at 50% probability levels. Selected bond lengths and angles: Cu1-N1 1.967(3), Cu1-N2 2.001(3), Cu1-N3 2.002(3), Cu1-N4 1.988(3) Å; N1-Cu1-N2 81.73(12), N1-Cu1-N3 101.39(12), N1-Cu1-N4 163.73(13), N4-Cu1-N2 103.80(12), N4-Cu1-N3 82.14(12), N2-Cu1-N3 148.01(12)°.

Figure 6b. There is only one hydrogen bond that occurs directly between [CuCl3(imiphenH)] molecules, which is an NH · · · Cl interaction at distance 2.444 Å (N · · · Cl 3.146 Å). There is a single face-to-face π-π stacking interaction between pairs of coordination complexes at an aryl centroid separation of 3.606 Å. Overall, complex 3 forms a 3D hydrogen bonding network, a section of which is shown in Figure 7a. As for complex 2, the 3D structure divides into hydrophilic and hydrophobic regions. The network topology has a 3,6-connectivity, Figure 7b, and is an unusual example of a 3,6-network with equal proportions of 3- and 6-connecting centers: most previously reported examples feature 3,6-centers in 2:1 proportions.30 Bipyridine-Based Ligands. The 2,2′-bipyridine ligands studied were mixed with a variety of metal salts, but, as for the phenanthroline-based ligands, only Cu(II) complexes were isolated as single crystals. 2,2′-Bipyridine-4,4′-diol was insoluble in common laboratory solvents and required the use of a solvothermal vessel to solubilize the ligand sufficiently to afford a coordination complex; however, 2,2′-bipyridine-4,4′-diamine and 2,2′-bipyridine-5,5′-bis(hydroxymethyl) were soluble in common solvents and gave crystals on simple slow evaporation of solutions. Complexes 4, 5, 6, and 7 where thus isolated. All show typical ESR signals for Cu(II) complexes and were further characterized by IR, microanalysis, UV (when soluble), and single crystal–crystallography. Complex 4 features a four-coordinate Cu(II) center with distorted tetrahedral geometry, Figure 8. There are two crystallographically distinct chelating bpy4diol ligands with a torsion angle of 36.3° between the two C2-C2′ type bonds. Both ligands are fully protonated and do not bind other metal centers but rather engage in hydrogen bonding interactions to nitrate counteranions or water. For one ligand, the alcohol groups act as hydrogen bond donors to nitrate anions at OH · · · O distances 1.914 and 1.842 Å (corresponding O · · · O separations 2.751 and 2.665 Å). This nitrate also accepts a hydrogen bond from the uncomplexed water molecule at OH · · · O distance 1.952 Å (O · · · O separation 2.876 Å). The other ligand is a hydrogen bond donor through one alcohol group to a second type of nitrate at OH · · · O distance 1.910 Å (O · · · O separation 2.692 Å) and a hydrogen bond acceptor from the water molecule through its other alcohol group at a OH · · · O distance 1.761 Å (corresponding O · · · O separation is 2.662 Å). There are no direct hydrogen bond interactions between the coordination complexes. These

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Figure 9. 2D hydrogen bonded network of complex 4.

Figure 10. Crystal structure of complex [Cu(bpy4da)(NO3)2] (5). Ellipsoids are shown at 50% probability levels. Selected bond lengths and angles: Cu1-N1 1.951(2), Cu1-O1 2.017(2) Å; N1-Cu1-O1 170.07(8), N1-Cu1-N1I 82.57(13), N1-Cu1-O1I 95.51(9), N1I-Cu1-O1I 170.07(8), N1I-Cu1-O1 95.51(9), O1I-Cu1-O1 88.01(11)°. Symmetry operation I: 1 - X, Y, 3/2 - Z.

hydrogen bonding interactions form a 2D honeycomb network where one of the two types of nitrate anion connects to three [Cu(bpy4diol)2] complexes either directly or via the water, and each [Cu(bpy4diol)2] complexes connects to three of these nitrates, Figure 9. The second type of nitrate anion forms a weak association with Cu center of a second 2D network at Cu · · · O distance 2.510 Å leading to pairwise interactions between the 2D networks. In complex 5 the Cu(II) center sits on a 2-fold axis and has square planar geometry with one chelating bpy4da ligand and two coordinating nitrate anions, Figure 10. The nitrate ligands are oriented such that their trigonal planes are roughly orthogonal to the plane of the bpy6da ligand. Each individual coordination complex has a region of hydrogen bond donor groups (the amines), and a region of hydrogen bond acceptor groups (nitrates) and hence would be expected to form a hydrogen bonding network. Indeed, considering only strong interactions (where the N · · · O distance is

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