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Supramolecular salts containing the anionic [Ge(C2O4)3]2− complex and heteroaromatic amines
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Inorganica Chimica Acta 362 (2009) 263–270 www.elsevier.com/locate/ica
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Supramolecular salts containing the anionic [Ge(C2O4)3]2 complex and heteroaromatic amines Luı´s Cunha-Silva a, Fa-Nian Shi a, Filipe A. Almeida Paz a,*, Michaele J. Hardie b, Jacek Klinowski c, Tito Trindade a, Joa˜o Rocha a,* a
Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal b School of Chemistry, University of Leeds, Leeds LS2 9JT, UK c Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK
Received 24 December 2007; received in revised form 11 February 2008; accepted 19 February 2008 Available online 26 February 2008
Abstract The crystalline compounds (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2[Ge(C2O4)3] 2(H2O) (2) [Hbipy+ is the 2,20 -bipyridinium cation (C10H9N2), and Hphen+ is the 1,100 -phenathrolinium cation (C12H9N2)] were isolated from mild hydrothermal syntheses and their structures were elucidated from single-crystal X-ray diffraction. The two compounds were further characterised by vibrational spectroscopy (FT-IR and FT-Raman), thermogravimetric analysis (TGA) and CHN elemental composition. Compounds 1 and 2 comprise the tris(oxalato-O,O0 )germanate dianion complex, [Ge(C2O4)3]2, which co-crystallises with Hbipy+ (in 1), or Hphen+ and water molecules (in 2). In 1, the germanium oxalate anionic complex, [Ge(C2O4)3]2, and the Hbipy+ organic residues interact mutually via N–H O hydrogen bonding interactions, leading to supramolecular discrete hydrogen-bonded units which are further interconnected via p–p stacking. Compound 2, on the other hand, exhibits a more complex hydrogen bonding network due to the presence of the water molecules of crystallisation which, along with p–p stacking between neighbouring Hphen+ residues, mediate the crystal packing. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Germanium(IV) oxalate; Organic–inorganic hybrids; Hydrogen bonds; Crystalline structures
1. Introduction Crystalline hybrid materials have been the subject of intensive worldwide research over the last two decades, essentially due to their inherent structural variety (ranging from discrete complexes to multi-dimensional coordination polymers) and interesting properties to be applied in potential functional devices (e.g., magnetic, sensing and separation properties) [1]. In the course of our on-going research efforts towards novel crystalline hybrid materials, (for latest examples see Ref. [2]), we have recently dedicated substantial attention to use of Ge centres [3]. Usually germanium cations exhibit two distinct oxidation states, +2 *
Corresponding authors. E-mail addresses: fi[email protected] (F.A. Almeida Paz), [email protected] (J. Rocha). 0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2008.02.038
and +4, with the latter being the most frequent. In addition, Ge4+ centres exhibit a number of distinct coordination numbers and environments, namely four (often tetrahedral), five (square pyramidal or trigonal bipyramidal) and six (often octahedral), a crucial structural feature to obtain topological diversity in germanate frameworks [4]. We have described a series of complex-based compounds containing the divalent tris(oxalato-O,O0 )germanate anion co-crystallised with a number of isostructural cationic d-transition metallic complexes with 1,100 -phenanthroline (phen), [M(phen)3][Ge(C2O4)3] xH2O. In the same publication, we also reported the first examples of binuclear complexes containing the neutral bis(oxalateO,O0 )germanium fragment [Ge(C2O4)2] connected by two l2-bridging hydroxyl groups to a cationic [M(phen)2]2+ fragment, [MGe(phen)2(l2-OH)2(C2O4)2] [5]. More recently, we have synthesised a novel germanium oxalate anionic
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complex, [Ge(OH)2(C2O4)2]2, which was isolated in the solid state in the form of salts with piperazinium and bipyridinium organic cations [6]. Here, we wish to report the synthesis and structural characterisation of two unprecedented crystalline salts containing the rarely encountered divalent tris(oxalato-O,O0 )germanate dianion complex, [Ge(C2O4)3]2: (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2[Ge(C2O4)3] 2(H2O) (2) [Hbipy+ is the 2,20 -bipyridinium cation (C10H9N2), and Hphen+ is the 1,100 -phenathrolinium cation (C12H9N2)]. The structures were determined by single-crystal X-ray diffraction, and the compounds were characterised by vibrational spectroscopy (FT-IR and FT-Raman), thermogravimetric (TGA) and elemental CHN analysis.
Calc. elemental composition (C26H18GeN4O12; M = 651.03; in %): C, 47.9; N, 8.6; H, 2.8. Found (in %): C, 47.6; N, 8.2; H, 3.0. TGA data (weight losses): 220– 292 °C, 37.4%; 292–330 °C, 43.0%; 330–598 °C, 2.3% (continuous but slow weight loss). Selected FT-IR data (in cm1; FT-Raman data in italics inside the parentheses): m(N–H, from protonated bipy) = 3213w; msym (C– H bipy ring) = 3106m, 3055, 2955w (3109, 3055); m(C@O, uncoordinated carbonyl groups) = 1749s (1769, 1740); masym ð–CO 2 Þ ¼ 1675m, 1591m, 1532m (1612, 1576, 1531); msym ð–CO 2 Þ ¼ 1475m, 1442m, 1333s (1467, 1375); m(C– O) = 1234m, 1184m (1257,1156); m(C–H) = 1092w, 1026w, 992w, 951w, 900m (1055,1019); c(C–H) = 610m (617, 545); q[(C@O)–O] = 476m, 443w (444).
2. Experimental
2.2.2. (Hphen)2[Ge(C2O4)3] 2(H2O) (2) This compound was prepared using a similar experimental procedure to that described for 1, but using instead a mixture containing 0.20 g of GeO2 (1.91 mmol), 0.32 g of H2C2O4 2H2O (2.54 mmol) and 0.25 g of phen (1.26 mmol) in ca. 15 g of distilled water. The duration of the reaction was of 72 h, with 0.48 g of the final product being recovered (yield 77% based on H2C2O4 2H2O). Calc. elemental composition (C30H22GeN4O14, M = 735.11; in %): C, 49.0; N, 7.6; H, 3.0. Found (in %): C, 48.9; N, 7.3; H, 3.0. TGA data (weight losses): 113– 126 °C, 2.0%; 126–313 °C, 54.6%; 313–598 °C, 18.8% (continuous weight loss). Selected FT-IR data (in cm1; FT-Raman data in italics inside the parentheses): m(O–H, crystallisation water) = 3388sb; m(N–H in protonated phen) = 3231m; msym(C–H, phen ring) = 3072w (3073); m(C@O, uncoordinated carbonyl groups) = 1750s (1769, 1740); masym ð–CO 2 Þ ¼ 1683w, 1624m, 1550m (1621, Þ ¼ 1475w, 1424w, 1342s (1458, 1422, 1549); msym ð–CO 2 1384); m(C–O) = 1251m, 1216w (1303, 1248, 1194); m(C– H) = 1142w, 1084w, 1043w, 909m (1102, 1046); c(C– H) = 610m (608, 554, 509); q[(C–O)–O) = 468m (462, 417).
2.1. General details and instrumentation Chemicals were readily available from commercial sources and were used as received without further purification: germanium(IV) oxide amorphous (GeO2, 99.99+%, Aldrich), oxalic acid dihydrate (H2C2O4 2H2O, P99%, Panreac), 2,20 -bipyridine (bipy, C10H8N2, P98%, Fluka), and 1,100 -phenanthroline monohydrate (phen, C12H8N2 H2O, P99.0%, Fluka). FT-IR spectra were collected from KBr pellets (Aldrich 99%+, FT-IR grade) on a Mattson 7000 FT-IR spectrometer. FT-Raman spectra were registered on a Bruker RFS 100 with a Nd:YAG coherent laser (k = 1064 nm). Elemental analyses (EA) for C, H and N were performed with a CHNS-932 Elemental analyser at the Microanalysis Laboratory of the University of Aveiro (Department of Chemistry). Thermogravimetric analyses (TGA) were carried out using a Shimadzu TGA 50, with a heating rate of 5 °C/ min under air. SEM (scanning electron microscopy) and EDS (energy dispersive analysis of X-rays spectroscopy) were performed using a Hitachi S-4100 field emission gun tungsten filament instrument working at 25 kV. 2.2. Synthesis 2.2.1. (Hbipy)2[Ge(C2O4)3] (1) A mixture containing 0.20 g of GeO2 (1.91 mmol), 0.32 g of H2C2O4 2H2O (2.54 mmol) and 0.20 g of bipy (1.28 mmol) in ca. 15 mL of distilled water was stirred through roughly at ambient conditions to a homogeneous suspension which was then transferred to a PTFE-lined stainless steel reaction vessel. The reaction took place under typical hydrothermal conditions (autogeneous pressure and static conditions) at 100 °C over a period of 78 h. After reacting, the vessel was removed from the oven and allowed to cool slowly to ambient temperature before opening. The isolated solid product, composed solely of large single crystals, was filtered off, washed with copious amounts of distilled water and air-dried under ambient conditions (0.45 g, ca. 82% yield based on H2C2O4 2H2O).
2.3. Single-crystal X-ray diffraction Crystals of (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2[Ge (C2O4)3] 2(H2O) (2) suitable for single-crystal X-ray diffraction analysis were manually harvested from the reaction vials (before filtering and air-drying) and mounted on glass fibres using FOMBLIN Y perfluoropolyether vacuum oil (LVAC 25/6) purchased from Aldrich [7]. Data for 1 were collected at 150(2) K on a Bruker X8 Kappa APEX II CCD area-detector diffractometer (Mo Ka graphite˚ ) controlled by monochromated radiation, k = 0.71073 A the APEX2 software package [8], and equipped with an Oxford Cryosystems Series 700 cryostream monitored remotely using the software interface CRYOPAD [9]. Images were processed using the software package SAINT+ [10], and data were corrected for absorption by the multi-scan semi-empirical method implemented in SADABS [11]. Data for 2 were collected on a Bruker Nonius Kappa charge coupled device (CCD) area-detector diffractometer (Mo Ka
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˚ ) congraphite-monochromated radiation, k = 0.71073 A trolled by the Collect software package [12] and equipped with an Oxford Cryosystems cryostream. Images were processed using the software packages Denzo and Scalepack [13], and data were corrected for Lorenztian and polarisation effects. Absorption corrections were applied using the multi-scan semi-empirical method implemented in SORTAV [14,15]. Structures were solved using the direct methods of SHELXS-97 [16], which allowed the immediate location of the heaviest atoms. The remaining non-hydrogen atoms were located from difference Fourier maps calculated from successive full-matrix least squares refinement cycles on F2 using SHELXL-97 [17]. All non-hydrogen atoms were successfully refined using anisotropic displacement parameters. Hydrogen atoms bonded to carbon were located at their idealised positions and included in the structural model in subsequent refinement cycles in riding-motion approximation with isotropic thermal displacements parameters (Uiso) fixed at 1.2 times Ueq of the respective carbon atoms. Hydrogen atoms associated with the nitrogen atoms were markedly visible from difference Fourier maps. These atoms were included in the structural models with the N– ˚ (in 1) and 1.00(1) A ˚ H distances restrained to 0.95(1) A (in 2) and assuming a riding-motion approximation with
Table 1 Crystal and structure refinement data for (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2[Ge(C2O4)3] 2(H2O) (2) Formula Formula weight Crystal system Space group ˚) a (A ˚) b (A ˚) c (A b (°) ˚ 3) Volume (A Z Dcalc (g cm3) l(Mo Ka) (mm1) F(0 0 0) Crystal size (mm) Crystal type h range Index ranges
Reflections collected Independent reflections Final R indices [I > 2r(I)]a,b Final R indices (all data)a,b
1
2
C26H18GeN4O12 651.03 monoclinic C2/c 19.267(4) 13.328(3) 13.662(3) 133.08(3) 2562.5(16) 4 1.688 1.274 1320 0.38 0.31 0.15 colourless prisms 3.56–28.36 25 6 h 6 25, 17 6 k 6 17, 18 6 l 6 18 22 947 3184 (Rint = 0.0392) R1 = 0.0262 wR2 = 0.0574 R1 = 0.0360 wR2 = 0.0624 0.359 and 0.406
C30H22GeN4O14 735.11 monoclinic P21/c 13.285(3) 16.712(3) 13.475(3) 100.95(3) 2937.1(10) 4 1.662 1.127 1496 0.38 0.12 0.10 pink prisms 3.90–27.49 17 6 h 6 16, 19 6 k 6 21, 16 6 l 6 17 24 075 6700 (Rint = 0.0309) R1 = 0.0294 wR2 = 0.0681 R1 = 0.0371 wR2 = 0.0720 0.318 and 0.444
Largest difference in peak and hole P P a R1 ¼ jjF o j jF c jj= jF o j. qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi P P b wR2 ¼ ½wðF 2o F 2c Þ2 = ½wðF 2o Þ2 .
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isotropic thermal displacement parameters fixed at 1.5 Ueq of the nitrogen atom to which they are attached. Hydrogen atoms from the water molecules of crystallisation in 2 were also visible in difference Fourier maps, and were included in the final structural model with the O–H ˚, and H H distances restrained to 0.95(1) and 1.55(1) A respectively, while assuming a riding-motion approximation with an isotropic thermal displacement parameter fixed at 1.5 Ueq of the parent oxygen atom. In 1 the last difference Fourier map synthesis showed the highest peak ˚ from C1, and the deepest hole ˚ 3) at 0.78 A (0.36 e A 3 ˚ from Ge1. In 2 the highest peak ˚ (0.41 e A ) at 0.62 A 3 ˚ from C10 and the deepest hole ˚ (0.32 e A ) is at 0.67 A 3 ˚ ˚ (0.44 e A ) at 0.68 A from Ge1. Table 2 ˚ ) and angles (in °) for the octahedral {GeO6} Selected bond lengths (in A coordination environments present in (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2[Ge(C2O4)3] 2(H2O) (2)a,b 1
2
Ge1–O1 Ge1–O3 Ge1–O5 Ge1–On Ge1–Om Ge1–Oo
1.8641(12) 1.8872(12) 1.8779(13) – – –
O1–Ge1–O3 O1–Ge1–O5 O1–Ge1–On O1–Ge1–Om O1–Ge1–Oo O3–Ge1–O5 O3–Ge1–On O3–Ge1–Om O3–Ge1–Oo O5–Ge1–On O5–Ge1–Om O5–Ge1–Oo On–Ge1–Om On–Ge1–Oo Om–Ge1–Oo
173.65(5) 95.93(6) 86.85(8) 89.30(6) 89.78(6) 89.10(6) 89.30(6) 94.97(8) 85.60(6) 89.78(6) 85.60(6) 172.14(8) 173.65(5) 89.10(6) 89.10(6)
a
b
1.8898(12) 1.8674(12) 1.8795(12) 1.8823(12) 1.8751(12) 1.8876(13) 85.85(6) 90.61(6) 175.64(5) 94.43(6) 88.21(6) 96.38(6) 92.04(6) 88.91(6) 172.05(5) 85.83(5) 172.94(5) 88.94(6) 89.34(5) 94.23(6) 86.29(5)
Legend: On is O1i in 1 and O7 in 2; Om is O3i in 1 and O9 in 2; Oo is O5i in 1 and O11 in 2. Symmetry operation used to generate atoms: (i) x + 1, y, z + 3/2.
Table 3 Geometrical details of the hydrogen bonding interactions present in (Hphen)2[Ge(C2O4)3] 2(H2O) (2)a ˚) D–H A dD A (A \(DHA) (°) N2–H2C O2Wi N3–H3A O1W O1W–H1A O2ii O1W–H1B O6 O2W–H2A O8 O2W–H2B O8
2.760(2) 2.747(2) 2.906(2) 2.063(14) 2.9285(19) 3.070(2)
154.1(2) 157.4(2) 163.8(2) 152(2) 165.1(2) 150.0(2)
a Symmetry operations used to generate atoms: (i) x + 1, y + 1, z + 1; (ii) x + 2, y 1/2, z + 3/2.
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Crystal data collection and refinement details for compounds 1 and 2 are summarised in Table 1. Geometrical details on the Ge4+ octahedral coordination environments for the two compounds are provided in Table 2. Table 3 collects the hydrogen bonding geometrical features for compound 2. Schematic drawings for the two structures have been prepared using the software package Crystal Diamond [18] in combination with the X-seed interface platform [19].
tity and as pure phases composed solely of single crystals found to be stable at ambient conditions. We also note that these two compounds could also be directly isolated by the slow evaporation of the mother liquors from the contents of the reaction vessels. The phase purity and homogeneity of the bulk samples were confirmed by SEM and powder X-ray diffraction (data not shown) in combination with elemental analyses (CHN content) and EDS investigations (qualitative identification of the presence of Ge).
3. Results and discussion
3.1. Crystal structural details
The compounds (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2 [Ge(C2O4)3] 2(H2O) (2) were obtained from hydrothermal syntheses, under mild conditions (at 100 °C), in large quan-
The divalent tris(oxalate-O,O0 )germanate anionic complex, [Ge(C2O4)3]2, is present in the asymmetric units of compounds 1 and 2 (Fig. 1) and, despite its obvious struc-
Fig. 1. Schematic representation of the molecular units of the structures of (a) (Hbipy)2[Ge(C2O4)3] (1) and (b) (Hphen)2[Ge(C2O4)3] 2(H2O) (2), with the atoms composing the respective asymmetric units connected through black-filled bonds and showing the labelling scheme for all non-hydrogen atoms. Thermal ellipsoids are drawn at the 50% probability level and hydrogen atoms are represented as small spheres with arbitrary radius. For selected bond ˚ ) and angles (in °) see Table 2. lengths (in A
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tural simplicity, is relatively uncommon. Indeed, besides our recent report of a series of heterodimetallic crystalline complexes containing this anion [5], searches in the literature and in the Cambridge Structural Database (CSD, Version 5.28 with three updates – August 2007) [20,21] produced only five more related structures containing this anion [22]. The Ge4+ centre is coordinated by six oxygen atoms belonging to three oxalate anions (coordinated via a typical anti,anti-chelate bidentate fashion), originating slightly distorted {GeO6} octahedral coordination environments for the two compounds (Fig. 1): the Ge–O bonds ˚ (for 1) and were found in the 1.8641(12)–1.8872(12) A
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˚ (for 2) ranges; while the cis O– 1.8674(12)–1.8898(12) A Ge–O octahedral angles are in the 85.60(6)–95.93(6)° (for 1) and 85.83(5)–96.38(6)° (for 2) ranges, the trans O–Ge– O angles range instead from 172.14(8)° to 173.65(6)° (for 1) and from 172.05(5)° to 175.64(5)° (for 2) (Table 2). These geometrical features are consistent with those described in related compounds for which the average ˚ , and the average cis Ge–O bond length is of ca. 1.88 A (or chelate bite angle) and trans O–Ge–O octahedral angles are of 85.7° and 173.6°, respectively [5,22]. The asymmetric units of the two compounds are further composed of, in 1, a 2,20 -bipyridinium cation [(C12H9N2)+, (Hbipy+)] or, in 2,
Fig. 2. (a) Crystal packing of (Hbipy)2[Ge(C2O4)3] (1) viewed along the [0 0 1] direction of the unit cell. (b) Schematic representation of a fragment of this crystal structure emphasising the N–H O hydrogen bonding interactions (dashed lines) and the p–p stacking between neighbouring Hbipy+ cations. Symmetry operation used to generate equivalent atoms: (i) x, y 1, z.
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two crystallographically independent 1,100 -phenanthrolinium cations [(C12H9N2)+, (Hphen+)] and two water molecules of crystallisation (O1W and O2W) (Fig. 1). The crystal packing of the two compounds exhibit notably identical features, with the anionic [Ge(C2O4)3]2 complexes being intercalated by the organic cations (Hbipy+ in 1 and Hphen+ in 2) in a typical brick-wall-like fashion in the ab plane of the unit cell (exemplified in Fig. 2a for the crystal packing of 1). In 1, each [Ge(C2O4)3]2 complex interacts with two neighbouring Hbipy+ cations via strong and directional N–H O hydrogen bonds (N1–H1 O4i, ˚ with <(NHO) = 145.9(2)°; symmed(N O) = 2.743(2) A
try operation: (i) x, y 1, z; dashed bonds in Fig. 2b), leading to the formation of a discrete (Hbipy)2[Ge(C2O4)3] supramolecular entity. The close packing of these entities is, on the one hand, mediated by an extensive network of weak intermolecular C–H O hydrogen bonding interac˚ – not shown] tions [d(H O) ranging from 2.39 to 2.71 A and, on the other by p–p off-set stacking interactions between Hbipy+ cations having Cg Cg distances in the ˚ range (average value of 3.73 A ˚ ; Cg rep3.586(2)–4.076(2) A resents the centroids of neighbouring aromatic rings; Fig. 2b). In 2, individual anionic [Ge(C2O4)3]2 complexes are always acceptors in strong O–H O hydrogen bonding
Fig. 3. Schematic representation of the (a) N–H O and O–H O hydrogen bonding interactions (dashed lines) involving the two crystallographically independent water molecules of crystallisation, and (b) the 2D supramolecular hydrogen bonded structure in (Hphen)2[Ge(C2O4)3] 2(H2O) (2). For clarity purposes only the hydrogen atoms involved in hydrogen bonds are shown. Symmetry operations used to generate equivalent atoms: (i) x + 1, y + 1, z + 1; (ii) x + 2, y1/2, z+3/2.
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interactions with the two water molecules of crystallisation (O1W and O2W), which interconnect the anions to the organic cationic Hphen+ residues via N–H O hydrogen bonds (Fig. 3a). This arrangement of N–H O and O– H O intermolecular contacts leads to a 2D supramolecular hydrogen-bonded network as depicted in Fig. 3b (see Table 3 for geometrical details of the hydrogen bonds). As for the previous compound, the crystal packing in 2 is also mediated by the cooperative effect of a considerable number of weak C–H O hydrogen bonding interactions ˚ – not [d(H O) distances ranging from 2.29 to 2.94 A shown] with off-set p–p stacking between adjacent Hphen+ residues [Cg Cg distances ranging from 3.547(2) to ˚ , with an average value of 3.67 A ˚ ]. 3.780(2) A 3.2. Vibrational spectroscopy and thermal behaviour Vibrational (FT-IR and FT-Raman) spectroscopy studies (Figs. S1 and S2 in the Supplementary material) are notably analytical of the structural features of the two compounds, clearly supporting the structural models refined from single-crystal X-ray diffraction (see previous section) [23]. The protonation of the bipy and phen residues in 1 and 2, respectively, gives rise to the typical stretching m(N–H) vibrations appearing as a medium-intensity band centred at 3213 cm1 in the FT-IR spectrum of 1 (at 3110 and 3106 cm1 in the corresponding FT-Raman spectrum), or as a weak (and broad) band centred at ca. 3231 cm1 in the FT-IR spectrum of 2. The spectra are also diagnostic of the presence of the anionic [Ge(C2O4)3]2 complex, in particular of the presence of the O,O-chelation mode of the oxalate groups. Indeed, the typical masym ð–CO 2 Þ and the msym ð–CO2 Þ vibrational modes are markedly evident in the FT-IR spectra with the corre values being sponding D½masym ð–CO 2 Þ msym ð–CO2 Þ] 1 greater than 200 cm [24,25]. The thermal treatment in air of 1 and 2 between room temperature and 600 °C resulted in markedly distinct thermograms (Fig. S3 in the Supplementary material). The thermal decomposition of 1 is not straightforward, occurring in two consecutive steps between 220 and 330 °C. The total weight loss (80.4%) is consistent with the complete oxidation of the organic component and the formation of the stoichiometric amount of GeO(OH)2 (calculated value of 81.2%). For 2, the first weight loss was registered in the 113–165 °C temperature range (2.0%) and can be attributed to the release of one lattice water per formula unit (calculated value of 2.4%). The second weight loss occurs between 258 and 313 °C (54.6%), and is consistent with the release of the remaining water molecule of crystallisation in addition with the phen residues (calculated value of 56.3%). The consecutive weight losses after 313 °C are tentatively attributed to the thermal decomposition of the remnant germanium complex, most likely due to the oxidation of the oxalate anions. Noteworthy, as depicted in Fig. S3, this decomposition is still not complete at 600 °C.
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Acknowledgements We are grateful to FEDER, POCI (Portugal) and to the Portuguese Foundation for Science and Technology (FCT, MCTES) for their general financial support (POCIPPCDT/QUI/58377/2004) and also for the postdoctoral grants SFRH/BPD/14410/2003 (to L.C.-S.) and SFRH/ BPD/9309/2002 (to F.-N.S.). We also wish to thank the EPSRC (UK) and the University of Leeds for equipment funding. Appendix A. Supplementary material CCDC 671247 and 671248 contain the supplementary crystallographic data for compounds 1 and 2. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi: 10.1016/j.ica.2008.02.038. References [1] (a) C.J. Kepert, Chem. Commun. (2006) 695–700; (b) A.P. Cote, A.I. Benin, N.W. Ockwig, M. O’Keeffe, A.J. Matzger, O.M. Yaghi, Science 310 (2005) 1166–1170; (c) S. Kitagawa, K. Uemura, Chem. Soc. Rev. 34 (2005) 109–119; (d) J.L.C. Rowsell, E.C. Spencer, J. Eckert, J.A.K. Howard, O.M. Yaghi, Science 309 (2005) 1350–1354; (e) H.K. Chae, D.Y. Siberio-Perez, J. Kim, Y. Go, M. Eddaoudi, A.J. Matzger, M. O’Keeffe, O.M. Yaghi, Nature 427 (2004) 523–527; (f) S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem., Int. Ed. Engl. 43 (2004) 2334–2375; (g) N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O’Keeffe, O.M. Yaghi, Science 300 (2003) 1127–1129; (h) O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Nature 423 (2003) 705–714; (i) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keefe, O.M. Yaghi, Science 295 (2002) 469–472; (j) B.L. Chen, M. Eddaoudi, S.T. Hyde, M. O’Keeffe, O.M. Yaghi, Science 291 (2001) 1021–1023; (k) H. Li, M. Eddaoudi, M. O’Keeffe, O.M. Yaghi, Nature 402 (1999) 276–279. [2] (a) F.-N. Shi, L. Cunha-Silva, R.A. Sa´ Ferreira, L. Mafra, T. Trindade, L.D. Carlos, F.A.A. Paz, J. Rocha, J. Am. Chem. Soc. 130 (2008) 150–167; (b) L. Cunha-Silva, L. Mafra, D. Ananias, L.D. Carlos, J. Rocha, F.A.A. Paz, Chem. Mater. 19 (2007) 3527–3538; (c) F.A.A. Paz, J. Klinowski, Pure Appl. Chem. 79 (2007) 1097– 1110; (d) P.I. Girginova, F.A.A. Paz, P.C.R. Soares-Santos, R.A.S. Ferreira, L.D. Carlos, V.S. Amaral, J. Klinowski, H.I.S. Nogueira, T. Trindade, Eur. J. Inorg. Chem. (2007) 4238–4246; (e) F.N. Shi, F.A.A. Paz, P.I. Girginova, H.I.S. Nogueira, J. Rocha, V.S. Amaral, J. Klinowski, T. Trindade, J. Solid State Chem. 179 (2006) 1497–1505; (f) P.C.R. Soares-Santos, F.A.A. Paz, R.A.S. Ferreira, J. Klinowski, L.D. Carlos, T. Trindade, H.I.S. Nogueira, Polyhedron 25 (2006) 2471–2482; (g) L. Mafra, F.A.A. Paz, F.N. Shi, C. Fernandez, T. Trindade, J. Klinowski, J. Rocha, Inorg. Chem. Commun. 9 (2006) 34–38; (h) F.A.A. Paz, J. Rocha, J. Klinowski, T. Trindade, F.N. Shi, L. Mafra, Prog. Solid State Chem. 33 (2005) 113–125.
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Inorganica Chimica Acta 362 (2009) 263–270 www.elsevier.com/locate/ica
Note
Supramolecular salts containing the anionic [Ge(C2O4)3]2 complex and heteroaromatic amines Luı´s Cunha-Silva a, Fa-Nian Shi a, Filipe A. Almeida Paz a,*, Michaele J. Hardie b, Jacek Klinowski c, Tito Trindade a, Joa˜o Rocha a,* a
Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal b School of Chemistry, University of Leeds, Leeds LS2 9JT, UK c Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK
Received 24 December 2007; received in revised form 11 February 2008; accepted 19 February 2008 Available online 26 February 2008
Abstract The crystalline compounds (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2[Ge(C2O4)3] 2(H2O) (2) [Hbipy+ is the 2,20 -bipyridinium cation (C10H9N2), and Hphen+ is the 1,100 -phenathrolinium cation (C12H9N2)] were isolated from mild hydrothermal syntheses and their structures were elucidated from single-crystal X-ray diffraction. The two compounds were further characterised by vibrational spectroscopy (FT-IR and FT-Raman), thermogravimetric analysis (TGA) and CHN elemental composition. Compounds 1 and 2 comprise the tris(oxalato-O,O0 )germanate dianion complex, [Ge(C2O4)3]2, which co-crystallises with Hbipy+ (in 1), or Hphen+ and water molecules (in 2). In 1, the germanium oxalate anionic complex, [Ge(C2O4)3]2, and the Hbipy+ organic residues interact mutually via N–H O hydrogen bonding interactions, leading to supramolecular discrete hydrogen-bonded units which are further interconnected via p–p stacking. Compound 2, on the other hand, exhibits a more complex hydrogen bonding network due to the presence of the water molecules of crystallisation which, along with p–p stacking between neighbouring Hphen+ residues, mediate the crystal packing. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Germanium(IV) oxalate; Organic–inorganic hybrids; Hydrogen bonds; Crystalline structures
1. Introduction Crystalline hybrid materials have been the subject of intensive worldwide research over the last two decades, essentially due to their inherent structural variety (ranging from discrete complexes to multi-dimensional coordination polymers) and interesting properties to be applied in potential functional devices (e.g., magnetic, sensing and separation properties) [1]. In the course of our on-going research efforts towards novel crystalline hybrid materials, (for latest examples see Ref. [2]), we have recently dedicated substantial attention to use of Ge centres [3]. Usually germanium cations exhibit two distinct oxidation states, +2 *
Corresponding authors. E-mail addresses: fi[email protected] (F.A. Almeida Paz), [email protected] (J. Rocha). 0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2008.02.038
and +4, with the latter being the most frequent. In addition, Ge4+ centres exhibit a number of distinct coordination numbers and environments, namely four (often tetrahedral), five (square pyramidal or trigonal bipyramidal) and six (often octahedral), a crucial structural feature to obtain topological diversity in germanate frameworks [4]. We have described a series of complex-based compounds containing the divalent tris(oxalato-O,O0 )germanate anion co-crystallised with a number of isostructural cationic d-transition metallic complexes with 1,100 -phenanthroline (phen), [M(phen)3][Ge(C2O4)3] xH2O. In the same publication, we also reported the first examples of binuclear complexes containing the neutral bis(oxalateO,O0 )germanium fragment [Ge(C2O4)2] connected by two l2-bridging hydroxyl groups to a cationic [M(phen)2]2+ fragment, [MGe(phen)2(l2-OH)2(C2O4)2] [5]. More recently, we have synthesised a novel germanium oxalate anionic
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complex, [Ge(OH)2(C2O4)2]2, which was isolated in the solid state in the form of salts with piperazinium and bipyridinium organic cations [6]. Here, we wish to report the synthesis and structural characterisation of two unprecedented crystalline salts containing the rarely encountered divalent tris(oxalato-O,O0 )germanate dianion complex, [Ge(C2O4)3]2: (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2[Ge(C2O4)3] 2(H2O) (2) [Hbipy+ is the 2,20 -bipyridinium cation (C10H9N2), and Hphen+ is the 1,100 -phenathrolinium cation (C12H9N2)]. The structures were determined by single-crystal X-ray diffraction, and the compounds were characterised by vibrational spectroscopy (FT-IR and FT-Raman), thermogravimetric (TGA) and elemental CHN analysis.
Calc. elemental composition (C26H18GeN4O12; M = 651.03; in %): C, 47.9; N, 8.6; H, 2.8. Found (in %): C, 47.6; N, 8.2; H, 3.0. TGA data (weight losses): 220– 292 °C, 37.4%; 292–330 °C, 43.0%; 330–598 °C, 2.3% (continuous but slow weight loss). Selected FT-IR data (in cm1; FT-Raman data in italics inside the parentheses): m(N–H, from protonated bipy) = 3213w; msym (C– H bipy ring) = 3106m, 3055, 2955w (3109, 3055); m(C@O, uncoordinated carbonyl groups) = 1749s (1769, 1740); masym ð–CO 2 Þ ¼ 1675m, 1591m, 1532m (1612, 1576, 1531); msym ð–CO 2 Þ ¼ 1475m, 1442m, 1333s (1467, 1375); m(C– O) = 1234m, 1184m (1257,1156); m(C–H) = 1092w, 1026w, 992w, 951w, 900m (1055,1019); c(C–H) = 610m (617, 545); q[(C@O)–O] = 476m, 443w (444).
2. Experimental
2.2.2. (Hphen)2[Ge(C2O4)3] 2(H2O) (2) This compound was prepared using a similar experimental procedure to that described for 1, but using instead a mixture containing 0.20 g of GeO2 (1.91 mmol), 0.32 g of H2C2O4 2H2O (2.54 mmol) and 0.25 g of phen (1.26 mmol) in ca. 15 g of distilled water. The duration of the reaction was of 72 h, with 0.48 g of the final product being recovered (yield 77% based on H2C2O4 2H2O). Calc. elemental composition (C30H22GeN4O14, M = 735.11; in %): C, 49.0; N, 7.6; H, 3.0. Found (in %): C, 48.9; N, 7.3; H, 3.0. TGA data (weight losses): 113– 126 °C, 2.0%; 126–313 °C, 54.6%; 313–598 °C, 18.8% (continuous weight loss). Selected FT-IR data (in cm1; FT-Raman data in italics inside the parentheses): m(O–H, crystallisation water) = 3388sb; m(N–H in protonated phen) = 3231m; msym(C–H, phen ring) = 3072w (3073); m(C@O, uncoordinated carbonyl groups) = 1750s (1769, 1740); masym ð–CO 2 Þ ¼ 1683w, 1624m, 1550m (1621, Þ ¼ 1475w, 1424w, 1342s (1458, 1422, 1549); msym ð–CO 2 1384); m(C–O) = 1251m, 1216w (1303, 1248, 1194); m(C– H) = 1142w, 1084w, 1043w, 909m (1102, 1046); c(C– H) = 610m (608, 554, 509); q[(C–O)–O) = 468m (462, 417).
2.1. General details and instrumentation Chemicals were readily available from commercial sources and were used as received without further purification: germanium(IV) oxide amorphous (GeO2, 99.99+%, Aldrich), oxalic acid dihydrate (H2C2O4 2H2O, P99%, Panreac), 2,20 -bipyridine (bipy, C10H8N2, P98%, Fluka), and 1,100 -phenanthroline monohydrate (phen, C12H8N2 H2O, P99.0%, Fluka). FT-IR spectra were collected from KBr pellets (Aldrich 99%+, FT-IR grade) on a Mattson 7000 FT-IR spectrometer. FT-Raman spectra were registered on a Bruker RFS 100 with a Nd:YAG coherent laser (k = 1064 nm). Elemental analyses (EA) for C, H and N were performed with a CHNS-932 Elemental analyser at the Microanalysis Laboratory of the University of Aveiro (Department of Chemistry). Thermogravimetric analyses (TGA) were carried out using a Shimadzu TGA 50, with a heating rate of 5 °C/ min under air. SEM (scanning electron microscopy) and EDS (energy dispersive analysis of X-rays spectroscopy) were performed using a Hitachi S-4100 field emission gun tungsten filament instrument working at 25 kV. 2.2. Synthesis 2.2.1. (Hbipy)2[Ge(C2O4)3] (1) A mixture containing 0.20 g of GeO2 (1.91 mmol), 0.32 g of H2C2O4 2H2O (2.54 mmol) and 0.20 g of bipy (1.28 mmol) in ca. 15 mL of distilled water was stirred through roughly at ambient conditions to a homogeneous suspension which was then transferred to a PTFE-lined stainless steel reaction vessel. The reaction took place under typical hydrothermal conditions (autogeneous pressure and static conditions) at 100 °C over a period of 78 h. After reacting, the vessel was removed from the oven and allowed to cool slowly to ambient temperature before opening. The isolated solid product, composed solely of large single crystals, was filtered off, washed with copious amounts of distilled water and air-dried under ambient conditions (0.45 g, ca. 82% yield based on H2C2O4 2H2O).
2.3. Single-crystal X-ray diffraction Crystals of (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2[Ge (C2O4)3] 2(H2O) (2) suitable for single-crystal X-ray diffraction analysis were manually harvested from the reaction vials (before filtering and air-drying) and mounted on glass fibres using FOMBLIN Y perfluoropolyether vacuum oil (LVAC 25/6) purchased from Aldrich [7]. Data for 1 were collected at 150(2) K on a Bruker X8 Kappa APEX II CCD area-detector diffractometer (Mo Ka graphite˚ ) controlled by monochromated radiation, k = 0.71073 A the APEX2 software package [8], and equipped with an Oxford Cryosystems Series 700 cryostream monitored remotely using the software interface CRYOPAD [9]. Images were processed using the software package SAINT+ [10], and data were corrected for absorption by the multi-scan semi-empirical method implemented in SADABS [11]. Data for 2 were collected on a Bruker Nonius Kappa charge coupled device (CCD) area-detector diffractometer (Mo Ka
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˚ ) congraphite-monochromated radiation, k = 0.71073 A trolled by the Collect software package [12] and equipped with an Oxford Cryosystems cryostream. Images were processed using the software packages Denzo and Scalepack [13], and data were corrected for Lorenztian and polarisation effects. Absorption corrections were applied using the multi-scan semi-empirical method implemented in SORTAV [14,15]. Structures were solved using the direct methods of SHELXS-97 [16], which allowed the immediate location of the heaviest atoms. The remaining non-hydrogen atoms were located from difference Fourier maps calculated from successive full-matrix least squares refinement cycles on F2 using SHELXL-97 [17]. All non-hydrogen atoms were successfully refined using anisotropic displacement parameters. Hydrogen atoms bonded to carbon were located at their idealised positions and included in the structural model in subsequent refinement cycles in riding-motion approximation with isotropic thermal displacements parameters (Uiso) fixed at 1.2 times Ueq of the respective carbon atoms. Hydrogen atoms associated with the nitrogen atoms were markedly visible from difference Fourier maps. These atoms were included in the structural models with the N– ˚ (in 1) and 1.00(1) A ˚ H distances restrained to 0.95(1) A (in 2) and assuming a riding-motion approximation with
Table 1 Crystal and structure refinement data for (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2[Ge(C2O4)3] 2(H2O) (2) Formula Formula weight Crystal system Space group ˚) a (A ˚) b (A ˚) c (A b (°) ˚ 3) Volume (A Z Dcalc (g cm3) l(Mo Ka) (mm1) F(0 0 0) Crystal size (mm) Crystal type h range Index ranges
Reflections collected Independent reflections Final R indices [I > 2r(I)]a,b Final R indices (all data)a,b
1
2
C26H18GeN4O12 651.03 monoclinic C2/c 19.267(4) 13.328(3) 13.662(3) 133.08(3) 2562.5(16) 4 1.688 1.274 1320 0.38 0.31 0.15 colourless prisms 3.56–28.36 25 6 h 6 25, 17 6 k 6 17, 18 6 l 6 18 22 947 3184 (Rint = 0.0392) R1 = 0.0262 wR2 = 0.0574 R1 = 0.0360 wR2 = 0.0624 0.359 and 0.406
C30H22GeN4O14 735.11 monoclinic P21/c 13.285(3) 16.712(3) 13.475(3) 100.95(3) 2937.1(10) 4 1.662 1.127 1496 0.38 0.12 0.10 pink prisms 3.90–27.49 17 6 h 6 16, 19 6 k 6 21, 16 6 l 6 17 24 075 6700 (Rint = 0.0309) R1 = 0.0294 wR2 = 0.0681 R1 = 0.0371 wR2 = 0.0720 0.318 and 0.444
Largest difference in peak and hole P P a R1 ¼ jjF o j jF c jj= jF o j. qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi P P b wR2 ¼ ½wðF 2o F 2c Þ2 = ½wðF 2o Þ2 .
265
isotropic thermal displacement parameters fixed at 1.5 Ueq of the nitrogen atom to which they are attached. Hydrogen atoms from the water molecules of crystallisation in 2 were also visible in difference Fourier maps, and were included in the final structural model with the O–H ˚, and H H distances restrained to 0.95(1) and 1.55(1) A respectively, while assuming a riding-motion approximation with an isotropic thermal displacement parameter fixed at 1.5 Ueq of the parent oxygen atom. In 1 the last difference Fourier map synthesis showed the highest peak ˚ from C1, and the deepest hole ˚ 3) at 0.78 A (0.36 e A 3 ˚ from Ge1. In 2 the highest peak ˚ (0.41 e A ) at 0.62 A 3 ˚ from C10 and the deepest hole ˚ (0.32 e A ) is at 0.67 A 3 ˚ ˚ (0.44 e A ) at 0.68 A from Ge1. Table 2 ˚ ) and angles (in °) for the octahedral {GeO6} Selected bond lengths (in A coordination environments present in (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2[Ge(C2O4)3] 2(H2O) (2)a,b 1
2
Ge1–O1 Ge1–O3 Ge1–O5 Ge1–On Ge1–Om Ge1–Oo
1.8641(12) 1.8872(12) 1.8779(13) – – –
O1–Ge1–O3 O1–Ge1–O5 O1–Ge1–On O1–Ge1–Om O1–Ge1–Oo O3–Ge1–O5 O3–Ge1–On O3–Ge1–Om O3–Ge1–Oo O5–Ge1–On O5–Ge1–Om O5–Ge1–Oo On–Ge1–Om On–Ge1–Oo Om–Ge1–Oo
173.65(5) 95.93(6) 86.85(8) 89.30(6) 89.78(6) 89.10(6) 89.30(6) 94.97(8) 85.60(6) 89.78(6) 85.60(6) 172.14(8) 173.65(5) 89.10(6) 89.10(6)
a
b
1.8898(12) 1.8674(12) 1.8795(12) 1.8823(12) 1.8751(12) 1.8876(13) 85.85(6) 90.61(6) 175.64(5) 94.43(6) 88.21(6) 96.38(6) 92.04(6) 88.91(6) 172.05(5) 85.83(5) 172.94(5) 88.94(6) 89.34(5) 94.23(6) 86.29(5)
Legend: On is O1i in 1 and O7 in 2; Om is O3i in 1 and O9 in 2; Oo is O5i in 1 and O11 in 2. Symmetry operation used to generate atoms: (i) x + 1, y, z + 3/2.
Table 3 Geometrical details of the hydrogen bonding interactions present in (Hphen)2[Ge(C2O4)3] 2(H2O) (2)a ˚) D–H A dD A (A \(DHA) (°) N2–H2C O2Wi N3–H3A O1W O1W–H1A O2ii O1W–H1B O6 O2W–H2A O8 O2W–H2B O8
2.760(2) 2.747(2) 2.906(2) 2.063(14) 2.9285(19) 3.070(2)
154.1(2) 157.4(2) 163.8(2) 152(2) 165.1(2) 150.0(2)
a Symmetry operations used to generate atoms: (i) x + 1, y + 1, z + 1; (ii) x + 2, y 1/2, z + 3/2.
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Crystal data collection and refinement details for compounds 1 and 2 are summarised in Table 1. Geometrical details on the Ge4+ octahedral coordination environments for the two compounds are provided in Table 2. Table 3 collects the hydrogen bonding geometrical features for compound 2. Schematic drawings for the two structures have been prepared using the software package Crystal Diamond [18] in combination with the X-seed interface platform [19].
tity and as pure phases composed solely of single crystals found to be stable at ambient conditions. We also note that these two compounds could also be directly isolated by the slow evaporation of the mother liquors from the contents of the reaction vessels. The phase purity and homogeneity of the bulk samples were confirmed by SEM and powder X-ray diffraction (data not shown) in combination with elemental analyses (CHN content) and EDS investigations (qualitative identification of the presence of Ge).
3. Results and discussion
3.1. Crystal structural details
The compounds (Hbipy)2[Ge(C2O4)3] (1) and (Hphen)2 [Ge(C2O4)3] 2(H2O) (2) were obtained from hydrothermal syntheses, under mild conditions (at 100 °C), in large quan-
The divalent tris(oxalate-O,O0 )germanate anionic complex, [Ge(C2O4)3]2, is present in the asymmetric units of compounds 1 and 2 (Fig. 1) and, despite its obvious struc-
Fig. 1. Schematic representation of the molecular units of the structures of (a) (Hbipy)2[Ge(C2O4)3] (1) and (b) (Hphen)2[Ge(C2O4)3] 2(H2O) (2), with the atoms composing the respective asymmetric units connected through black-filled bonds and showing the labelling scheme for all non-hydrogen atoms. Thermal ellipsoids are drawn at the 50% probability level and hydrogen atoms are represented as small spheres with arbitrary radius. For selected bond ˚ ) and angles (in °) see Table 2. lengths (in A
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tural simplicity, is relatively uncommon. Indeed, besides our recent report of a series of heterodimetallic crystalline complexes containing this anion [5], searches in the literature and in the Cambridge Structural Database (CSD, Version 5.28 with three updates – August 2007) [20,21] produced only five more related structures containing this anion [22]. The Ge4+ centre is coordinated by six oxygen atoms belonging to three oxalate anions (coordinated via a typical anti,anti-chelate bidentate fashion), originating slightly distorted {GeO6} octahedral coordination environments for the two compounds (Fig. 1): the Ge–O bonds ˚ (for 1) and were found in the 1.8641(12)–1.8872(12) A
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˚ (for 2) ranges; while the cis O– 1.8674(12)–1.8898(12) A Ge–O octahedral angles are in the 85.60(6)–95.93(6)° (for 1) and 85.83(5)–96.38(6)° (for 2) ranges, the trans O–Ge– O angles range instead from 172.14(8)° to 173.65(6)° (for 1) and from 172.05(5)° to 175.64(5)° (for 2) (Table 2). These geometrical features are consistent with those described in related compounds for which the average ˚ , and the average cis Ge–O bond length is of ca. 1.88 A (or chelate bite angle) and trans O–Ge–O octahedral angles are of 85.7° and 173.6°, respectively [5,22]. The asymmetric units of the two compounds are further composed of, in 1, a 2,20 -bipyridinium cation [(C12H9N2)+, (Hbipy+)] or, in 2,
Fig. 2. (a) Crystal packing of (Hbipy)2[Ge(C2O4)3] (1) viewed along the [0 0 1] direction of the unit cell. (b) Schematic representation of a fragment of this crystal structure emphasising the N–H O hydrogen bonding interactions (dashed lines) and the p–p stacking between neighbouring Hbipy+ cations. Symmetry operation used to generate equivalent atoms: (i) x, y 1, z.
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two crystallographically independent 1,100 -phenanthrolinium cations [(C12H9N2)+, (Hphen+)] and two water molecules of crystallisation (O1W and O2W) (Fig. 1). The crystal packing of the two compounds exhibit notably identical features, with the anionic [Ge(C2O4)3]2 complexes being intercalated by the organic cations (Hbipy+ in 1 and Hphen+ in 2) in a typical brick-wall-like fashion in the ab plane of the unit cell (exemplified in Fig. 2a for the crystal packing of 1). In 1, each [Ge(C2O4)3]2 complex interacts with two neighbouring Hbipy+ cations via strong and directional N–H O hydrogen bonds (N1–H1 O4i, ˚ with <(NHO) = 145.9(2)°; symmed(N O) = 2.743(2) A
try operation: (i) x, y 1, z; dashed bonds in Fig. 2b), leading to the formation of a discrete (Hbipy)2[Ge(C2O4)3] supramolecular entity. The close packing of these entities is, on the one hand, mediated by an extensive network of weak intermolecular C–H O hydrogen bonding interac˚ – not shown] tions [d(H O) ranging from 2.39 to 2.71 A and, on the other by p–p off-set stacking interactions between Hbipy+ cations having Cg Cg distances in the ˚ range (average value of 3.73 A ˚ ; Cg rep3.586(2)–4.076(2) A resents the centroids of neighbouring aromatic rings; Fig. 2b). In 2, individual anionic [Ge(C2O4)3]2 complexes are always acceptors in strong O–H O hydrogen bonding
Fig. 3. Schematic representation of the (a) N–H O and O–H O hydrogen bonding interactions (dashed lines) involving the two crystallographically independent water molecules of crystallisation, and (b) the 2D supramolecular hydrogen bonded structure in (Hphen)2[Ge(C2O4)3] 2(H2O) (2). For clarity purposes only the hydrogen atoms involved in hydrogen bonds are shown. Symmetry operations used to generate equivalent atoms: (i) x + 1, y + 1, z + 1; (ii) x + 2, y1/2, z+3/2.
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interactions with the two water molecules of crystallisation (O1W and O2W), which interconnect the anions to the organic cationic Hphen+ residues via N–H O hydrogen bonds (Fig. 3a). This arrangement of N–H O and O– H O intermolecular contacts leads to a 2D supramolecular hydrogen-bonded network as depicted in Fig. 3b (see Table 3 for geometrical details of the hydrogen bonds). As for the previous compound, the crystal packing in 2 is also mediated by the cooperative effect of a considerable number of weak C–H O hydrogen bonding interactions ˚ – not [d(H O) distances ranging from 2.29 to 2.94 A shown] with off-set p–p stacking between adjacent Hphen+ residues [Cg Cg distances ranging from 3.547(2) to ˚ , with an average value of 3.67 A ˚ ]. 3.780(2) A 3.2. Vibrational spectroscopy and thermal behaviour Vibrational (FT-IR and FT-Raman) spectroscopy studies (Figs. S1 and S2 in the Supplementary material) are notably analytical of the structural features of the two compounds, clearly supporting the structural models refined from single-crystal X-ray diffraction (see previous section) [23]. The protonation of the bipy and phen residues in 1 and 2, respectively, gives rise to the typical stretching m(N–H) vibrations appearing as a medium-intensity band centred at 3213 cm1 in the FT-IR spectrum of 1 (at 3110 and 3106 cm1 in the corresponding FT-Raman spectrum), or as a weak (and broad) band centred at ca. 3231 cm1 in the FT-IR spectrum of 2. The spectra are also diagnostic of the presence of the anionic [Ge(C2O4)3]2 complex, in particular of the presence of the O,O-chelation mode of the oxalate groups. Indeed, the typical masym ð–CO 2 Þ and the msym ð–CO2 Þ vibrational modes are markedly evident in the FT-IR spectra with the corre values being sponding D½masym ð–CO 2 Þ msym ð–CO2 Þ] 1 greater than 200 cm [24,25]. The thermal treatment in air of 1 and 2 between room temperature and 600 °C resulted in markedly distinct thermograms (Fig. S3 in the Supplementary material). The thermal decomposition of 1 is not straightforward, occurring in two consecutive steps between 220 and 330 °C. The total weight loss (80.4%) is consistent with the complete oxidation of the organic component and the formation of the stoichiometric amount of GeO(OH)2 (calculated value of 81.2%). For 2, the first weight loss was registered in the 113–165 °C temperature range (2.0%) and can be attributed to the release of one lattice water per formula unit (calculated value of 2.4%). The second weight loss occurs between 258 and 313 °C (54.6%), and is consistent with the release of the remaining water molecule of crystallisation in addition with the phen residues (calculated value of 56.3%). The consecutive weight losses after 313 °C are tentatively attributed to the thermal decomposition of the remnant germanium complex, most likely due to the oxidation of the oxalate anions. Noteworthy, as depicted in Fig. S3, this decomposition is still not complete at 600 °C.
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Acknowledgements We are grateful to FEDER, POCI (Portugal) and to the Portuguese Foundation for Science and Technology (FCT, MCTES) for their general financial support (POCIPPCDT/QUI/58377/2004) and also for the postdoctoral grants SFRH/BPD/14410/2003 (to L.C.-S.) and SFRH/ BPD/9309/2002 (to F.-N.S.). We also wish to thank the EPSRC (UK) and the University of Leeds for equipment funding. Appendix A. Supplementary material CCDC 671247 and 671248 contain the supplementary crystallographic data for compounds 1 and 2. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi: 10.1016/j.ica.2008.02.038. References [1] (a) C.J. Kepert, Chem. Commun. (2006) 695–700; (b) A.P. Cote, A.I. Benin, N.W. Ockwig, M. O’Keeffe, A.J. Matzger, O.M. Yaghi, Science 310 (2005) 1166–1170; (c) S. Kitagawa, K. Uemura, Chem. Soc. Rev. 34 (2005) 109–119; (d) J.L.C. Rowsell, E.C. Spencer, J. Eckert, J.A.K. Howard, O.M. Yaghi, Science 309 (2005) 1350–1354; (e) H.K. Chae, D.Y. Siberio-Perez, J. Kim, Y. Go, M. Eddaoudi, A.J. Matzger, M. O’Keeffe, O.M. Yaghi, Nature 427 (2004) 523–527; (f) S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem., Int. Ed. Engl. 43 (2004) 2334–2375; (g) N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O’Keeffe, O.M. Yaghi, Science 300 (2003) 1127–1129; (h) O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Nature 423 (2003) 705–714; (i) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keefe, O.M. Yaghi, Science 295 (2002) 469–472; (j) B.L. Chen, M. Eddaoudi, S.T. Hyde, M. O’Keeffe, O.M. Yaghi, Science 291 (2001) 1021–1023; (k) H. Li, M. Eddaoudi, M. O’Keeffe, O.M. Yaghi, Nature 402 (1999) 276–279. [2] (a) F.-N. Shi, L. Cunha-Silva, R.A. Sa´ Ferreira, L. Mafra, T. Trindade, L.D. Carlos, F.A.A. Paz, J. Rocha, J. Am. Chem. Soc. 130 (2008) 150–167; (b) L. Cunha-Silva, L. Mafra, D. Ananias, L.D. Carlos, J. Rocha, F.A.A. Paz, Chem. Mater. 19 (2007) 3527–3538; (c) F.A.A. Paz, J. Klinowski, Pure Appl. Chem. 79 (2007) 1097– 1110; (d) P.I. Girginova, F.A.A. Paz, P.C.R. Soares-Santos, R.A.S. Ferreira, L.D. Carlos, V.S. Amaral, J. Klinowski, H.I.S. Nogueira, T. Trindade, Eur. J. Inorg. Chem. (2007) 4238–4246; (e) F.N. Shi, F.A.A. Paz, P.I. Girginova, H.I.S. Nogueira, J. Rocha, V.S. Amaral, J. Klinowski, T. Trindade, J. Solid State Chem. 179 (2006) 1497–1505; (f) P.C.R. Soares-Santos, F.A.A. Paz, R.A.S. Ferreira, J. Klinowski, L.D. Carlos, T. Trindade, H.I.S. Nogueira, Polyhedron 25 (2006) 2471–2482; (g) L. Mafra, F.A.A. Paz, F.N. Shi, C. Fernandez, T. Trindade, J. Klinowski, J. Rocha, Inorg. Chem. Commun. 9 (2006) 34–38; (h) F.A.A. Paz, J. Rocha, J. Klinowski, T. Trindade, F.N. Shi, L. Mafra, Prog. Solid State Chem. 33 (2005) 113–125.
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