- Email: [email protected]
Maleate ions as ligands in crystal structures of coordination compounds, including two uranyl complexes
Polyhedron 127 (2017) 331–336
Contents lists available at ScienceDirect
Polyhedron journal homepage: www.elsevier.com/locate/poly
Maleate ions as ligands in crystal structures of coordination compounds, including two uranyl complexes Anton V. Savchenkov a,⇑, Mikhail S. Grigoriev b, Pavel A. Udivankin a, Denis V. Pushkin a, Larisa B. Serezhkina a a b
Samara National Research University, Samara, Russian Federation Russian Academy of Sciences A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Moscow, Russian Federation
a r t i c l e
i n f o
Article history: Received 6 January 2017 Accepted 7 February 2017 Available online 22 February 2017 Keywords: Maleate Uranyl Structure elucidation Coordination modes Crystal engineering
a b s t r a c t Synthetic techniques, FTIR spectra and the crystal structures of two new uranyl complexes with maleate ions are reported. The crystal structure of (NH4)2[UO2(C4H2O4)2] (I) is constructed of chains with the [UO2(C4H2O4)2]2 composition. Maleate ions in I have the tridentate bridging and chelating T11-4 coordination mode with the formation of 4-membered U-containing rings. The crystal structure of Cs2[(UO2)3(C4H2O4)4]2H2O (II) is constructed of layers with the [(UO2)3(C4H2O4)4]2 composition. Half of the maleate ions in II have the bridging and chelating Q21-4 coordination mode, with the formation of 4-membered rings, while the other half have the Q21-7 coordination mode with the formation of 7-membered rings. The coordination modes of the maleate ions in all the crystal structures of coordination compounds from the CSD were analyzed. The non-planarity of the maleate ions is confirmed by calculation of different geometric parameters. Though in all crystal structures most of the maleate ions tend to realize coordination modes with the formation of 7-membered rings, geometrical difficulties of 7-membered ring formation are shown. The presented data on the coordination modes of the maleate ions in crystal structures are of particular interest for crystal engineering and crystal structure prediction. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction The maleate ion C4H2O2– 4 is the ionized form of unsaturated dicarboxylic maleic acid HOOC–CH@CH–COOH. Maleate ions are of particular interest in coordination chemistry due to their diverse coordination modes. In known crystal structures, maleate ions act as terminal [1], bridging [2] and chelating [3] ligands. Structural motifs containing maleate ions can be zero [4], one [5], two [6] and three [7] dimensional. To date, only one crystal structure of a uranyl complex with maleate ions has been reported [8]. It is constructed of 1D bands with the [UO2(C4H2O4)(C4H3O4)]– composition, bound into a 3D framework by electrostatic interactions with K+ cations. The authors of the cited article [8] note that coordination of maleate ions to U atoms in the structure of K[UO2(C4H2O4) (C4H3O4)] leads to the formation of 7-membered rings, which are unusual and unstable. They also assumed that ‘‘their [7-membered rings] formation could be due to the particular ligand isomer with a cis configuration”. Another curious thing mentioned by the
⇑ Corresponding author. E-mail address: [email protected] (A.V. Savchenkov). http://dx.doi.org/10.1016/j.poly.2017.02.006 0277-5387/Ó 2017 Elsevier Ltd. All rights reserved.
authors [8] is that the maleate ions in K[UO2(C4H2O4)(C4H3O4)] are not planar. Indeed, although all the C atoms of the maleate ion are sp2 hybridized, the maleate ions are not planar due to repulsion of two O atoms of different carboxylate groups. In crystal structures, a planar geometry is typical for hydrogen maleate ions, C4H3O 4 , in which the H atom prevents repulsion of the two closest O atoms of different carboxylate groups. A planar geometry is also typical for fumarate ions (trans isomers of maleate ions), in which the two carboxylate groups are shielded from each other by the carbon skeleton. In the mentioned K[UO2(C4H2O4)(C4H3O4)] complex [8], the two carboxylate groups form different angles with the carbon skeleton: 67.5 and 25.7°. The authors [8] suggested that such a distortion of the maleate ions is forced by the necessity of the U atoms to form particular coordination polyhedra. This assumption is supported by the presence of strain in the crystal structure: the five equatorial oxygen atoms of the uranyl ion are rather puckered. Despite all the mentioned curious facts about the coordination of maleate ions in the described uranyl complex, we were not able to find in the literature any relevant review of the coordination modes of maleate ions. Thus, we intended to perform an analysis of the coordination modes of maleate ions in all coordination
332
A.V. Savchenkov et al. / Polyhedron 127 (2017) 331–336
compounds from the CSD. We also report the crystal structures of two new uranyl complexes, (NH4)2[UO2(C4H2O4)2] (I) and Cs2[(UO2)3(C4H2O4)4]2H2O (II), with three different coordination modes of the maleate ions.
Table 2 Assignment of absorption bands in the FTIR spectra of (NH4)2[UO2(C4H2O4)2] (I) and Cs2[(UO2)3(C4H2O4)4]2H2O (II).* Wavenumber, cm–1
2. Experimental
2.1. Synthesis Yellow crystals of I and II were obtained after a few days of isothermal evaporation of the reaction mixtures at ambient conditions. UO2(NO3)23.23H2O was synthesized according to the reported procedure [9] and the hydration number was calculated through gravimetric analysis. Maleic acid (C4H4O4), ammonium hydroxide solution (28% NH3 in H2O) and cesium hydroxide (CsOHH2O) of reagent grade were obtained commercially (ALDRICH). (NH4)2[UO2(C4H2O4)2] (I). UO2(NO3)23.23H2O (200 mg, 0.44 mmol) and C4H4O4 (205 mg, 1.77 mmol) were dissolved in distilled water (10 ml). Ammonium hydroxide solution was added to the reaction mixture to give a pH value of 4 (approximately 107 mg of solution, 1.77 mmol of NH3). The final molar ratio of the reagents was 1:4:4 respectively. Yield: 70%. Gravimetric analysis on uranium: 44.4% (calculated 44.6%). Cs2[(UO2)3(C4H2O4)4]2H2O (II). UO2(NO3)23.23H2O (200 mg, 0.44 mmol) and C4H4O4 (103 mg, 0.88 mmol) were dissolved in distilled water (10 ml). CsOHH2O (149 mg, 0.88 mmol) was added to the reaction mixture. The pH of the final solution was equal to 4. The final molar ratio of the reagents was 1:2:2 respectively. Yield: 75%. Gravimetric analysis on uranium: 45.2% (calculated 45.5%). Table 1 Details of data collection and structure refinement parameters for (NH4)2[UO2(C4H2O4)2] (I) and Cs2[(UO2)3(C4H2O4)4]2H2O (II). Compound
I
II
Chemical formula
(NH4)2[UO2(C4H2O4)2]
Crystal system, space group, Z a, b, c (Å)
monoclinic, C2/c, 4
Cs2[(UO2)3(C4H2O4)4] 2H2O 2 triclinic, P 1,
a, b, c (°) V (Å3) Dx (g/cm3) Radiation, k (Å) l (mm–1) T (K) Crystal size (mm) h range (°) h, k, l range
Reflections number: collected/ unique (N1), Rint/with I > 2r (I) (N2) Parameters refined wR2 on N1 R1 on N2 S Dqmaximum/ Dqminimum (e Å3)
12.9752(3), 7.52160(10), 13.5419(3) 90, 100.415(1), 90 1299.84(5) 2.730 Mo Ka, 0.71073 12.544 100(2) 0.20 0.16 0.10 4.182–34.997 20 h 20, 12 k 12, 21 l 18 10 244/2839, 0.0213/2134
110 0.0319 0.0151 1.012 0.765/–0.677
6.8275(2), 14.5728(4), 16.2015(4) 63.753(1), 78.631(1), 82.326(1) 1415.44(7) 3.679 Mo Ka, 0.71073 19.758 100(2) 0.12 0.04 0.03 4.248–29.996 9 h 9, 19 k 20, 22 l 22 14 668/8221, 0.0255/ 6501
406 0.0765 0.0339 1.040 3.602/–2.094
II
–
3519 m., br. 3445 m., br. – 3036 w. 2925 w.
3168 s. 3035 s. 2928 m. 2892 m. 2858 m. 1651 s. 1587 v.s. 1547 v.s. 1534 v.s. 1453 v.s. 1416 v.s. 1388 v.s. 1308 v.s. 1200 s. 935 v.s. 911 s. 851 s. 832 s.
Caution! Although depleted uranium was used in the following experiments, all uranium containing samples must be handled with suitable care and protection.
Assignment
I
744 m. 697 s. 617 s. 549 s.
2854 w. 1648 m. 1589 s. 1541 v.s. 1520 v.s. 1448 s. 1411 s. 1385 m. 1314 s. 1205 w. 926 s. 917 s. 856 m. 840 w. 828 w. 746 w. 694 m. 631 m. 621 m. 583 w. 545 w.
m(OH) m(NH) m(CH)
m(C@C) mas(COO) din-plane(CH), d(NH), ms(COO) din-plane(CH)
m(C–O) mas(UO2) dout-of-plane(CH)
d(COO) c(COO)
x(COO)
*
v.s. – very strong, s. – strong, m. – medium, w. – weak, br. – broad, c – rocking, x – wagging.
2.2. X-ray diffraction analysis An automatic four-circle diffractometer with the area detector Bruker KAPPA APEX II was used for the X-ray experiments. Unit cell parameters were refined over the whole dataset [10]. Experimental intensities were corrected for absorption using the SADABS program [11]. The structures were solved using the direct method (SHELXS97) [12] and refined using the full-matrix least-squares method (SHELXL2014) [13] on F2 over the whole dataset. All non-hydrogen atoms in I and II were refined in an anisotropic approximation. H atoms of maleate anions were placed in geometrically calculated positions with Uiso = 1.2Ueq(C). H atoms of the NH+4 cation in I were located from the difference Fourier map and refined with equal N–H and equal H. . .H distances, and Uiso = 1.2Ueq(N). Two out of three independent Cs atoms and two water molecules in II are disordered over two positions. Details of the data collection and structure refinement parameters are provided in Table 1. 2.3. FTIR spectroscopy FTIR spectra of I and II (provided in the Supplementary Material) were measured in the range 400–4000 cm1 from pressed KBr pellets using a Perkin Elmer Spectrum 100 spectrometer. Assignment of bands (Table 2) was performed in accordance with the established data for other maleate containing compounds [14–16] and other reliable sources [17–19]. Due to the variable coordination modes of the carboxylate groups (see further discussion) we were unable to accurately assign all the bands in the region 1600–1400 cm1. 3. Results and discussion 3.1. Description of the crystal structures (NH4)2[UO2(C4H2O4)2] (I) crystallizes in the monoclinic crystal system (space group C2/c) with Z = 4 and Z0 = 0.5. The only atom
A.V. Savchenkov et al. / Polyhedron 127 (2017) 331–336
in I occupying a special position is U1, with Ci site-symmetry, which makes the uranyl group UO2+ 2 linear with d(U@O) = 1.766 (1) Å. The coordination number (CN) of the U1 atom is equal to 8: two oxygen atoms of the uranyl group and six oxygen atoms in its equatorial plane form a distorted hexagonal bipyramid. The Voronoi–Dirichlet polyhedron of the U1 atom in I has the form of a distorted hexagonal prism. Two ‘-al’ oxygen atoms in trans positions belong to monodentate carboxylate groups of two maleate ions. The remaining four ‘-al’ oxygen atoms in pairs belong to bidentate carboxylate groups of another two maleate ions (Fig. 1). Thus, maleate ions have the tridentate bridging and chelating (with formation of 4-membered U-containing rings) coordination mode T11-4 (notation is given in accordance with the literature [20]). The maleate ions bind the uranyl groups into chains with the [UO2(C4H2O4)2]2 composition, extending along two perpendicular directions: [1 1 0] or [1 –1 0]. Overall the crystallochemical 11 formula of the complex unit in I is A(T11-4)2, where A = UO2+ 2 , T 4 = C4H2O2– forming 4-membered rings. The mentioned chains 4 form a 3D framework structure through electrostatic interactions and hydrogen bonds with ammonium ions. The four hydrogen bonds, formed by every H atom of the ammonium ion, have the following characteristics: d(N–H) = 0.83–0.85 Å, d(H. . .O) = 1.99– 2.10 Å, d(N. . .O) = 2.83–2.88 Å, angle N–H. . .O = 151–171°. According to a previous report [21], these hydrogen bonds have medium strength. Cs2[(UO2)3(C4H2O4)4]2H2O (II) crystallizes in the triclinic crys with Z = 2 and Z‘ = 1. All the atoms in tal system (space group P 1) II occupy general positions. The U1 atom has CN = 8, while the U2 and U3 atoms have CN = 7. All three uranyl groups are equal arms and linear to within the error of the X-ray experiment (d (U@O) varies from 1.766(5) to 1.778(5) Å and O@U@O angle varies from 178.6(2) to 179.7(3)° in the structure of II). The coordination polyhedra of the U atoms in II have the form of hexagonal (U1) or pentagonal (U2 and U3) bipyramids, while dual to them the Voronoi–Dirichlet polyhedra have the forms of hexagonal or pentagonal prisms respectively. The volumes of the Voronoi–Dirichlet polyhedra of the U atoms in I and II are equal to 9.57 (in I) and 9.47 Å3 (in II) for U1 with CN = 8, and to 9.14 and 9.16 Å3 for U2 and U3 with CN = 7, respectively. These values are in a good agreement with the known values of 9.4(2) Å3 for UO8 and 9.2(1) Å3 for UO7 coordination polyhedra [22]. Every maleate ion in II binds four uranyl ions into (0 1 0) layers with the [(UO2)3(C4H2O4)4]2 composition (Fig. 2). Overall the crystallochemical formula of the complex unit in II is A3(Q21-4)2(Q21-7)2 (see further discussion), where A = UO2+ 2 , 21 2– Q21-4 = C4H2O2– 4 forming 4-membered rings and Q -7 = C4H2O4 forming 7-membered rings. The uranyl-maleate layers are bound into a 3D framework through electrostatic interactions with Cs+ cations. In the case of U(1) atoms with CN = 8 in I and II, the UO2+ 2 line strongly tilts from a normal direction of the equatorial plane (84.8 and 84.6° respectively). This is due to repulsion of the ‘-yl’ oxygen atoms and non-coordinated O atoms of two monodentate carboxylate groups of trans coordinated maleate ions (d = 3.11 Å for I, and 2.88 and 3.00 Å for II, Fig. 1). For the U(2) and U(3) atoms
333
Fig. 2. Fragment of the layer with the [(UO2)3(C4H2O4)4]2 composition in the structure of Cs2[(UO2)3(C4H2O4)4]2H2O (II). Six atoms in green together with a U atom represent a 7-membered ring. Three atoms in blue together with a U atom represent a 4-membered ring.
with CN = 7 in II, the UO2+ 2 line is almost at right angles with the equatorial plane (88.5 and 88.8° respectively). In this case, one out of two ‘-yl’ oxygen atoms of the UO2+ 2 group is squeezed from all sides by the atoms of four coordinated maleate ions (Fig. 2), and the other one is squeezed from all sides by other atoms, including cesium. The difference between the U atoms with CN = 7 and 8 is also evident from the type of bonding with maleate ions. The bonding between the U1 atom and maleate ions in II is exactly the same as between the U1 atom and maleate ions in I. On the other hand, the U2 and U3 atoms realize another coordination mode with the maleate ions, which is the same for both U2 and U3. Three O atoms in the equatorial planes of U2 and U3 in II belong to three carboxylate groups of three maleate ions. The remaining two O atoms belong to two different carboxylate groups of the same maleate ion. Thus, all four crystallographically independent maleate ions in II have the Q21 coordination mode, being bridging and chelating at the same time. However, coordination of two maleate ions leads to the formation of the usual 4-membered rings (Q21-4 coordination mode), while coordination of the other two maleate ions leads to the formation of 7-membered rings (Q21-7, Fig. 2). In spite of the fact that 7-membered rings are unusual and should be unstable, they were earlier observed for another known maleate complex of the uranyl ion, K[UO2(C4H2O4)(C4H3O4)] [8]. According to the method of intersecting spheres [23], the Cs1 atom in II forms a CsO8 coordination polyhedron with d(Cs–O) = 3.00–3.52 Å. Three out of eight O atoms of the CsO8 coordination polyhedron belong to three adjacent uranyl ions. Thus, the Cs1 atom is involved in uranyl-cation interactions, which are typical for cesium salts of uranyl complexes [24–26]. The Cs1 atoms form [1 0 0] zigzag chains with the distances between neighboring Cs1 atoms equal to 4.24 and 4.56 Å. The Cs2 and Cs3 atoms are disordered over two positions. Two disordered water molecules occupy the same positions.
Fig. 1. Fragment of a chain with the [UO2(C4H2O4)2]2 composition in the structure of (NH4)2[UO2(C4H2O4)2] (I). Three atoms in blue together with a U atom represent a 4membered ring.
334
A.V. Savchenkov et al. / Polyhedron 127 (2017) 331–336
Fig. 3. Occurrence of 15 coordination modes of maleate ions in the crystal structures of coordination compounds from the CSD.
As was observed earlier in the structure of K[UO2(C4H2O4) (C4H3O4)] [8], the maleate ions in I and II are also not planar as one would think judging on the hybridization of the carbon atoms. For the maleate ions in I and II with T11-4 and Q21-4 coordination modes, the plane of one carboxylate group is quasi parallel (1.8–9.9°) with the almost planar hydrocarbon skeleton, while the other carboxylate group is quasi perpendicular (74.2–81.4°) to the skeleton. For the maleate ions with the Q21-7 coordination mode in II such angles are increased for quasi parallel carboxylate groups (22.1–22.9°) and decreased for quasi perpendicular (57.7–62.3°) groups. In our opinion, such a deviation of the angles for the Q21-7 coordinated maleate ions in comparison with the ‘more relaxed’ ones (with T11-4 and Q21-4 coordination modes) shows possible strain in the maleate ions due to coordination of a rigid ligand with a double C@C bond to the same U atom by both carboxylate groups. This assumption is supported by the fact that the deviation of the oxygen atoms from the equatorial planes of the uranyl groups in I and II reaches 0.19 Å. 3.2. Analysis of the coordination modes of the maleate ions To summarize all the available data on the structure and coordination modes of maleate ions, we performed a crystallochemical analysis of all maleate containing compounds in the CSD [27]. The following requirements were applied for compounds to avoid unreliable data: 1) The crystal structure simultaneously contains maleate ions C4H2O2– 4 and d- or f-metal atoms A with bond valence s of the A–O bonds and with oxygen atoms of maleate ions 0.25 (s = v/CN, where v is the oxidation state of A and CN is the coordination number);
2) The coordinates of all the atoms are defined (structures with undefined coordinates of only H atoms were also taken into account); 3) 0 < R1 0.1; 4) The crystal structure does not possess disorder. Such requirements resulted in 69 compounds with 77 crystallographically independent maleate ions. Note, that neither hydrogen maleate nor fumarate ions were considered in the current research. It was observed that maleate ions realize 15 different coordination modes (Fig. 3), 8 of which are the most abundant and are realized by 90% of all maleate ions: M1, B2, B01-7, T11-4, T11-7, Q21-4, Q21-7 and Q02-44. The observed coordination modes show that maleate ions are able to serve as terminal (M1, B01-4, B01-7) or bridging (all the remaining 12 coordination modes) ligands, may not be chelating (M1, B2) or may form 4 or 7-membered rings with metals (all the remaining 13 coordination modes). Among the 77 studied maleate ions, 33 ions form 7-membered rings, 23 ions form 4membered rings and 2 ions simultaneously form 4- and 7-membered rings (maleate ions with T02-47 and Q12-47 coordination modes with reference codes IJOBIS [28] and QOVXOO [29] in the CSD [27]). The skeleton of the maleate ion is rather rigid due to the double C@C bond in comparison with the malonate ion C3H2O2– 4 , for example [30,31]. This fact leads to almost constant main geometric parameters of the maleate ions in crystal structures. The offset of the C atom from the mean plane of the carbon skeleton in all the maleate ions does not exceed 0.05 Å, and the mean torsion angle, C–C@C–C, is equal to 1(2)°, which means that the carbon skeleton of the maleate ions is almost planar in all the examined compounds. The distance between the C atoms of two carboxylate groups of maleate ions is 3.1(1) Å, on average. The mean value of
A.V. Savchenkov et al. / Polyhedron 127 (2017) 331–336
Fig. 4. Designation of the dihedral angle between the planes of two carboxylate groups, uCOO (a), of the dihedral angle between the plane of a carboxylate group and the mean plane of a carbon skeleton, v (b), and schematic representations of two common types of structures of maleate ions: with both carboxylate groups twisted by 45° with respect to the carbon skeleton (c) and with a quasi parallel and quasi perpendicular arrangement of the carboxylate groups (d).
Fig. 5. Histogram of the uCOO angles between the planes of two carboxylate groups of maleate ions.
the \OCO angle is equal to 123(2)°, which is in a good agreement with the sp2 hybridization of the C atom in the carboxylate group. On the other hand, rotation of the carboxylate groups relative to each other and to the carbon skeleton is very diverse in the examined compounds. The angle between the planes of the two
335
carboxylate groups, uCOO, varies in the range from 37.5 to 88.6°, which proves the non-planar structure of the maleate ions in the crystals (Fig. 4). Moreover, as seen from Fig. 5, the two carboxylate groups of the maleate ions are preferably rotated to each other with the angle uCOO close to 90°. It was observed that lower uCOO values are typical for maleate ions having coordination modes with the formation of 7-membered rings. The mean uCOO values for maleate ions with coordination modes without the formation of rings and with the formation of 4- and 7-membered rings are equal to 74(12), 75 (11) and 67(13)° respectively. Maleate ions having coordination modes with the formation of 7-membered rings also tend to realize wider \CCC angles: 126(2), 126(2) and 128(2)° in the same sequence as above. These two facts show a stronger deformation of the maleate ions in the case of their coordination with the formation of 7-membered rings, which is due to steric hindrance from binding two carboxylate groups of the maleate ion to the same metal atom. The planes of the carboxylate groups of the maleate ion form dihedral angles v with a mean plane of the carbon skeleton in the range 0.4–89.3° (Fig. 4b). However, the histogram of occurrence of different v angles is explicitly symmetric and multimodal, with the highest mode for the range 45–50° (the mean value of v for all the 77 studied maleate ions is equal to 46.0°, Fig. 6). Mode 1 is the only one without a symmetric pair with respect to the highest mode 4 in Fig. 6. It corresponds to the bin 0–5° and includes scores mainly from those maleate ions which do not form rings due to coordination. Symmetric modes 2 and 6 correspond to bins 10–15 and 80–85° respectively and include scores mainly from those maleate ions, which form 4-membered rings due to coordination. In total, modes 1, 2 and 6 correspond to such a geometry of maleate ions where the plane of one carboxylate group almost coincides with the mean plane of the carbon skeleton (v = 0–20°), while the plane of the second carboxylate group is twisted almost perpendicular to the mean plane of the carbon skeleton (v = 75–90°, Fig. 4d). Such a conformation of the maleate ions in the crystal structures should be the most favorable due to common sense. On the other hand, as seen from Fig. 6, most of the carboxylate groups in the maleate ions are twisted to v angles of 20–75° with respect to the carbon skeleton. This region contains three modes and includes scores mainly from those maleate ions which form
Fig. 6. Combined graph showing the occurrence of the dihedral angle v between the planes of the carboxylate groups of the maleate ion and the mean plane of the carbon skeleton. A solid line is drawn for all 77 maleate ions. Each bin for the solid line may include scores from three groups of maleate ions, dependent on their coordination mode: with the formation of 7-membered rings, with the formation of 4-membered rings or without the formation of rings. The drawn bars include scores only from one out of the three groups of maleate ions (marked with gray, orange and blue colors) with the highest N for the current bin. (Color online.)
336
A.V. Savchenkov et al. / Polyhedron 127 (2017) 331–336
7-membered rings due to coordination. Taking into account the height of the modes of the solid line in Fig. 6, one can conclude that the process of coordination of two carboxylate groups of a maleate ion to the same metal atom can be run in two possible ways. The first way is to twist the planes of both carboxylate groups to angles of about 40–55° (mode 4) with respect to the mean plane of the carbon skeleton (Fig. 4c). The second way is to twist the plane of one carboxylate group to an angle of about 20–40° (mode 3) and the plane of the second carboxylate group to an angle of about 55–75° (mode 5). Thus, maleate ions with coordination modes without the formation of rings and with the formation of 4-membered rings have one carboxylate group quasi parallel to the carbon skeleton and the other one quasi perpendicular. Although coordination of carboxylate groups with the formation of 4-membered rings seems favorable and stable, maleate ions more often realize coordination modes with the formation of 7-membered rings when different carboxylate groups of the maleate ion bind to the same metal atom. In that case, both carboxylate groups of the maleate ion have to twist with respect to the carbon skeleton with angles from 20 to 75° to make the bonding with the metal atom sterically possible. As mentioned above, such a deformation of the maleate ions leads to a lowering of the values of the uCOO angles and rising of the values of the \CCC angles with respect with more relaxed maleate ions, which, in our opinion, proves the steric hindrance of the 7membered ring formation. 4. Conclusion Synthetic techniques, FTIR spectra and the crystal structures of two new uranyl complexes with maleate ions are reported. The crystal structure of (NH4)2[UO2(C4H2O4)2] (I) is constructed of chains with the [UO2(C4H2O4)2]2 composition. Maleate ions in I have the tridentate bridging and chelating coordination mode T11-4 with the formation of 4-membered U-containing rings. The crystal structure of Cs2[(UO2)3(C4H2O4)4]2H2O (II) is constructed of layers with the [(UO2)3(C4H2O4)4]2 composition. Half of the maleate ions in II have the bridging and chelating Q21-4 coordination mode with the formation of usual 4-membered rings, while the other half have the Q21-7 coordination mode with the formation of 7-membered rings. The coordination modes of the maleate ions in all the crystal structures of coordination compounds from the CSD were analyzed. It was shown that the maleate ions realize 15 different coordination modes, eight of which are the most abundant: M1, B2, B01-7, T11-4, T11-7, Q21-4, Q21-7 and Q02-44. Calculations of different geometric parameters show that though the carbon skeleton of the maleate ion is rigid, the ion itself is not planar due to rotation of its carboxylate groups. The majority of the maleate ions tend to form uCOO angles close to 90°. For the most relaxed coordination modes (without rings or with the formation of 4-membered rings) one of the carboxylate groups of the maleate ion is quasi parallel to the carbon skeleton, while the other one is quasi perpendicular. The coordination modes with the formation of 7-membered rings force the maleate ions to rotate both their carboxylate groups to angles of 20–75° with respect to the carbon skeleton. Such coordination modes also result in lowering of the uCOO angle values and rising of the \CCC angle values, which in total show geometrical difficulties for 7-membered ring formation. Still, most of the maleate ions in the known crystal structures tend to realize coordination modes with the formation of 7-membered rings. The presented data on the coordination modes of maleate ions in crystal structures are of particular interest for crystal engineering and crystal structure prediction.
Acknowledgements This work was financially supported by the Russian Federation for Basic Research (project no. 15-33-20470). X-ray diffraction experiments were performed at the Center for Shared Use of Physical Methods of Investigation at the Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences. Appendix A. Supplementary data CCDC 1505763 and 1505764 contains the supplementary crystallographic data for I and II. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10. 1016/j.poly.2017.02.006. References [1] D. Krishna Kumar, Amitava Das, Parthasarathi Dastidar, Cryst. Growth Des. 6 (2006) 1903. [2] Zhang Yugen, Jianmin Li, Nishiura Masayoshi, Hou Hongyi, Deng Wei, Imamoto Tsuneo, J. Chem. Soc., Dalton Trans. (2000) 293. [3] M. Mirzaei, H. Eshtiagh-Hosseini, M. Chahkandi, N. Alfi, A. Shokrollahi, N. Shokrollahi, A. Janiak, CrystEngComm 14 (2012) 8468. [4] J.C. Kim, A.J. Lough, J. Chem. Crystallogr. 35 (2005) 535. [5] Ping Liu, Yao-Yu Wang, Dong-Sheng Li, Hai-Rui Ma, Qi-Zhen Shi, Gene-Hsiang Lee, Shie-Ming Peng, Inorg. Chim. Acta 358 (2005) 3807. [6] J.W. Uebler, J.A. Wilson, R.L. LaDuca, CrystEngComm 15 (2013) 1586. [7] Hong-Ye Bai, Jian-Fang Ma, Ying-Ying Liu, Jin Yang, Inorg. Chim. Acta 376 (2011) 332. [8] G. Bombieri, F. Benetollo, R.M. Rojas, M.L. De Paz, J. Inorg. Nucl. Chem. 43 (1981) 3203. [9] Complex compounds of uranium. Ed. I.I. Chernyaev. Jerusalem, Israel: Program for Scientific Translations, 1966. 520 p. [10] SAINT-Plus (Version 7.68) Bruker AXS Inc., Madison, Wisconsin, USA. (2007). [11] G.M. Sheldrick, SADABS, Bruker AXS Inc., Madison, Wisconsin, USA, 2008. [12] G.M. Sheldrick, Acta Cryst. A64 (2008) 112. [13] G.M. Sheldrick, Acta Cryst. C71 (2015) 3. [14] L.P. Nair, B.R. Bijini, S. Prasanna, S.M. Eapen, C.M.K. Nair, M. Deepa, K. RajendraBabu, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 137 (2015) 778. [15] V. Mahalakshmi, A. Lincy, J. Thomas, K.V. Saban, J. Phys. Chem. Solids 73 (2012) 584. [16] R. Omegala Priakumari, S. Grace Sahaya Sheba, M. Gunasekaran, J. Mol. Struct. 1102 (2015) 63. [17] M.F. Ramos Moita, M.L.T.S. Duarte, R. Fausto, Spectrosc. Lett. 27 (1994) 1421. [18] R.M. Silverstein, F.X. Webster, D. Kiemle, Spectrometric identification of organic compounds, Wiley, 2005, 512 p. [19] G.S. Groenewold, W.A. de Jong, J. Oomens, M.J. Van Stipdonk, J. Am. Soc. Mass Spectrom. 21 (2010) 719. [20] V.N. Serezhkin, A.V. Vologzhanina, L.B. Serezhkina, E.S. Smirnova, E.V. Grachova, P.V. Ostrova, M.Y. Antipin, Acta Cryst. B65 (2009) 45. [21] T. Steiner, Angew. Chem. 41 (2002) 48. [22] V.N. Serezhkin, M.O. Karasev, L.B. Serezhkina, Radiochemistry 55 (2013) 137. [23] V.N. Serezhkin, Yu.N. Mikhailov, Yu.A. Buslaev, Rus. J. Inorg. Chem. 42 (1997) 1871. [24] S. Fortier, T.W. Hayton, Coord. Chem. Rev. 254 (2010) 197. [25] V.N. Serezhkin, G.V. Sidorenko, D.V. Pushkin, L.B. Serezhkina, Radiochemistry 56 (2014) 115. [26] A.V. Savchenkov, A.V. Vologzhanina, L.B. Serezhkina, D.V. Pushkin, S.Yu. Stefanovich, V.N. Serezhkin, Z. Anorg. Allg. Chem. 641 (2015) 1182. [27] C.R. Groom, I.J. Bruno, M.P. Lightfoot, S.C. Ward, Acta Cryst. B72 (2016) 171. [28] C.E. Xanthopoulos, C.C. Hadjikostas, G.A. Katsoulos, A. Terzis, M.P. Sigalas, J. Coord. Chem. 55 (2002) 717. [29] Claudia Bromant, Mathias S. Wickleder, Gerd Meyer, Z. Anorg. Allg. Chem. 627 (2001) 768. [30] V.N. Serezhkin, Y.A. Medvedkov, L.B. Serezhkina, D.V. Pushkin, Russ. J. Phys. Chem. 89 (2015) 1018. [31] Y.A. Medvedkov, L.B. Serezhkina, V.N. Serezhkin, Russ. J. Phys. Chem. 90 (2016) 803.
Contents lists available at ScienceDirect
Polyhedron journal homepage: www.elsevier.com/locate/poly
Maleate ions as ligands in crystal structures of coordination compounds, including two uranyl complexes Anton V. Savchenkov a,⇑, Mikhail S. Grigoriev b, Pavel A. Udivankin a, Denis V. Pushkin a, Larisa B. Serezhkina a a b
Samara National Research University, Samara, Russian Federation Russian Academy of Sciences A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Moscow, Russian Federation
a r t i c l e
i n f o
Article history: Received 6 January 2017 Accepted 7 February 2017 Available online 22 February 2017 Keywords: Maleate Uranyl Structure elucidation Coordination modes Crystal engineering
a b s t r a c t Synthetic techniques, FTIR spectra and the crystal structures of two new uranyl complexes with maleate ions are reported. The crystal structure of (NH4)2[UO2(C4H2O4)2] (I) is constructed of chains with the [UO2(C4H2O4)2]2 composition. Maleate ions in I have the tridentate bridging and chelating T11-4 coordination mode with the formation of 4-membered U-containing rings. The crystal structure of Cs2[(UO2)3(C4H2O4)4]2H2O (II) is constructed of layers with the [(UO2)3(C4H2O4)4]2 composition. Half of the maleate ions in II have the bridging and chelating Q21-4 coordination mode, with the formation of 4-membered rings, while the other half have the Q21-7 coordination mode with the formation of 7-membered rings. The coordination modes of the maleate ions in all the crystal structures of coordination compounds from the CSD were analyzed. The non-planarity of the maleate ions is confirmed by calculation of different geometric parameters. Though in all crystal structures most of the maleate ions tend to realize coordination modes with the formation of 7-membered rings, geometrical difficulties of 7-membered ring formation are shown. The presented data on the coordination modes of the maleate ions in crystal structures are of particular interest for crystal engineering and crystal structure prediction. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction The maleate ion C4H2O2– 4 is the ionized form of unsaturated dicarboxylic maleic acid HOOC–CH@CH–COOH. Maleate ions are of particular interest in coordination chemistry due to their diverse coordination modes. In known crystal structures, maleate ions act as terminal [1], bridging [2] and chelating [3] ligands. Structural motifs containing maleate ions can be zero [4], one [5], two [6] and three [7] dimensional. To date, only one crystal structure of a uranyl complex with maleate ions has been reported [8]. It is constructed of 1D bands with the [UO2(C4H2O4)(C4H3O4)]– composition, bound into a 3D framework by electrostatic interactions with K+ cations. The authors of the cited article [8] note that coordination of maleate ions to U atoms in the structure of K[UO2(C4H2O4) (C4H3O4)] leads to the formation of 7-membered rings, which are unusual and unstable. They also assumed that ‘‘their [7-membered rings] formation could be due to the particular ligand isomer with a cis configuration”. Another curious thing mentioned by the
⇑ Corresponding author. E-mail address: [email protected] (A.V. Savchenkov). http://dx.doi.org/10.1016/j.poly.2017.02.006 0277-5387/Ó 2017 Elsevier Ltd. All rights reserved.
authors [8] is that the maleate ions in K[UO2(C4H2O4)(C4H3O4)] are not planar. Indeed, although all the C atoms of the maleate ion are sp2 hybridized, the maleate ions are not planar due to repulsion of two O atoms of different carboxylate groups. In crystal structures, a planar geometry is typical for hydrogen maleate ions, C4H3O 4 , in which the H atom prevents repulsion of the two closest O atoms of different carboxylate groups. A planar geometry is also typical for fumarate ions (trans isomers of maleate ions), in which the two carboxylate groups are shielded from each other by the carbon skeleton. In the mentioned K[UO2(C4H2O4)(C4H3O4)] complex [8], the two carboxylate groups form different angles with the carbon skeleton: 67.5 and 25.7°. The authors [8] suggested that such a distortion of the maleate ions is forced by the necessity of the U atoms to form particular coordination polyhedra. This assumption is supported by the presence of strain in the crystal structure: the five equatorial oxygen atoms of the uranyl ion are rather puckered. Despite all the mentioned curious facts about the coordination of maleate ions in the described uranyl complex, we were not able to find in the literature any relevant review of the coordination modes of maleate ions. Thus, we intended to perform an analysis of the coordination modes of maleate ions in all coordination
332
A.V. Savchenkov et al. / Polyhedron 127 (2017) 331–336
compounds from the CSD. We also report the crystal structures of two new uranyl complexes, (NH4)2[UO2(C4H2O4)2] (I) and Cs2[(UO2)3(C4H2O4)4]2H2O (II), with three different coordination modes of the maleate ions.
Table 2 Assignment of absorption bands in the FTIR spectra of (NH4)2[UO2(C4H2O4)2] (I) and Cs2[(UO2)3(C4H2O4)4]2H2O (II).* Wavenumber, cm–1
2. Experimental
2.1. Synthesis Yellow crystals of I and II were obtained after a few days of isothermal evaporation of the reaction mixtures at ambient conditions. UO2(NO3)23.23H2O was synthesized according to the reported procedure [9] and the hydration number was calculated through gravimetric analysis. Maleic acid (C4H4O4), ammonium hydroxide solution (28% NH3 in H2O) and cesium hydroxide (CsOHH2O) of reagent grade were obtained commercially (ALDRICH). (NH4)2[UO2(C4H2O4)2] (I). UO2(NO3)23.23H2O (200 mg, 0.44 mmol) and C4H4O4 (205 mg, 1.77 mmol) were dissolved in distilled water (10 ml). Ammonium hydroxide solution was added to the reaction mixture to give a pH value of 4 (approximately 107 mg of solution, 1.77 mmol of NH3). The final molar ratio of the reagents was 1:4:4 respectively. Yield: 70%. Gravimetric analysis on uranium: 44.4% (calculated 44.6%). Cs2[(UO2)3(C4H2O4)4]2H2O (II). UO2(NO3)23.23H2O (200 mg, 0.44 mmol) and C4H4O4 (103 mg, 0.88 mmol) were dissolved in distilled water (10 ml). CsOHH2O (149 mg, 0.88 mmol) was added to the reaction mixture. The pH of the final solution was equal to 4. The final molar ratio of the reagents was 1:2:2 respectively. Yield: 75%. Gravimetric analysis on uranium: 45.2% (calculated 45.5%). Table 1 Details of data collection and structure refinement parameters for (NH4)2[UO2(C4H2O4)2] (I) and Cs2[(UO2)3(C4H2O4)4]2H2O (II). Compound
I
II
Chemical formula
(NH4)2[UO2(C4H2O4)2]
Crystal system, space group, Z a, b, c (Å)
monoclinic, C2/c, 4
Cs2[(UO2)3(C4H2O4)4] 2H2O 2 triclinic, P 1,
a, b, c (°) V (Å3) Dx (g/cm3) Radiation, k (Å) l (mm–1) T (K) Crystal size (mm) h range (°) h, k, l range
Reflections number: collected/ unique (N1), Rint/with I > 2r (I) (N2) Parameters refined wR2 on N1 R1 on N2 S Dqmaximum/ Dqminimum (e Å3)
12.9752(3), 7.52160(10), 13.5419(3) 90, 100.415(1), 90 1299.84(5) 2.730 Mo Ka, 0.71073 12.544 100(2) 0.20 0.16 0.10 4.182–34.997 20 h 20, 12 k 12, 21 l 18 10 244/2839, 0.0213/2134
110 0.0319 0.0151 1.012 0.765/–0.677
6.8275(2), 14.5728(4), 16.2015(4) 63.753(1), 78.631(1), 82.326(1) 1415.44(7) 3.679 Mo Ka, 0.71073 19.758 100(2) 0.12 0.04 0.03 4.248–29.996 9 h 9, 19 k 20, 22 l 22 14 668/8221, 0.0255/ 6501
406 0.0765 0.0339 1.040 3.602/–2.094
II
–
3519 m., br. 3445 m., br. – 3036 w. 2925 w.
3168 s. 3035 s. 2928 m. 2892 m. 2858 m. 1651 s. 1587 v.s. 1547 v.s. 1534 v.s. 1453 v.s. 1416 v.s. 1388 v.s. 1308 v.s. 1200 s. 935 v.s. 911 s. 851 s. 832 s.
Caution! Although depleted uranium was used in the following experiments, all uranium containing samples must be handled with suitable care and protection.
Assignment
I
744 m. 697 s. 617 s. 549 s.
2854 w. 1648 m. 1589 s. 1541 v.s. 1520 v.s. 1448 s. 1411 s. 1385 m. 1314 s. 1205 w. 926 s. 917 s. 856 m. 840 w. 828 w. 746 w. 694 m. 631 m. 621 m. 583 w. 545 w.
m(OH) m(NH) m(CH)
m(C@C) mas(COO) din-plane(CH), d(NH), ms(COO) din-plane(CH)
m(C–O) mas(UO2) dout-of-plane(CH)
d(COO) c(COO)
x(COO)
*
v.s. – very strong, s. – strong, m. – medium, w. – weak, br. – broad, c – rocking, x – wagging.
2.2. X-ray diffraction analysis An automatic four-circle diffractometer with the area detector Bruker KAPPA APEX II was used for the X-ray experiments. Unit cell parameters were refined over the whole dataset [10]. Experimental intensities were corrected for absorption using the SADABS program [11]. The structures were solved using the direct method (SHELXS97) [12] and refined using the full-matrix least-squares method (SHELXL2014) [13] on F2 over the whole dataset. All non-hydrogen atoms in I and II were refined in an anisotropic approximation. H atoms of maleate anions were placed in geometrically calculated positions with Uiso = 1.2Ueq(C). H atoms of the NH+4 cation in I were located from the difference Fourier map and refined with equal N–H and equal H. . .H distances, and Uiso = 1.2Ueq(N). Two out of three independent Cs atoms and two water molecules in II are disordered over two positions. Details of the data collection and structure refinement parameters are provided in Table 1. 2.3. FTIR spectroscopy FTIR spectra of I and II (provided in the Supplementary Material) were measured in the range 400–4000 cm1 from pressed KBr pellets using a Perkin Elmer Spectrum 100 spectrometer. Assignment of bands (Table 2) was performed in accordance with the established data for other maleate containing compounds [14–16] and other reliable sources [17–19]. Due to the variable coordination modes of the carboxylate groups (see further discussion) we were unable to accurately assign all the bands in the region 1600–1400 cm1. 3. Results and discussion 3.1. Description of the crystal structures (NH4)2[UO2(C4H2O4)2] (I) crystallizes in the monoclinic crystal system (space group C2/c) with Z = 4 and Z0 = 0.5. The only atom
A.V. Savchenkov et al. / Polyhedron 127 (2017) 331–336
in I occupying a special position is U1, with Ci site-symmetry, which makes the uranyl group UO2+ 2 linear with d(U@O) = 1.766 (1) Å. The coordination number (CN) of the U1 atom is equal to 8: two oxygen atoms of the uranyl group and six oxygen atoms in its equatorial plane form a distorted hexagonal bipyramid. The Voronoi–Dirichlet polyhedron of the U1 atom in I has the form of a distorted hexagonal prism. Two ‘-al’ oxygen atoms in trans positions belong to monodentate carboxylate groups of two maleate ions. The remaining four ‘-al’ oxygen atoms in pairs belong to bidentate carboxylate groups of another two maleate ions (Fig. 1). Thus, maleate ions have the tridentate bridging and chelating (with formation of 4-membered U-containing rings) coordination mode T11-4 (notation is given in accordance with the literature [20]). The maleate ions bind the uranyl groups into chains with the [UO2(C4H2O4)2]2 composition, extending along two perpendicular directions: [1 1 0] or [1 –1 0]. Overall the crystallochemical 11 formula of the complex unit in I is A(T11-4)2, where A = UO2+ 2 , T 4 = C4H2O2– forming 4-membered rings. The mentioned chains 4 form a 3D framework structure through electrostatic interactions and hydrogen bonds with ammonium ions. The four hydrogen bonds, formed by every H atom of the ammonium ion, have the following characteristics: d(N–H) = 0.83–0.85 Å, d(H. . .O) = 1.99– 2.10 Å, d(N. . .O) = 2.83–2.88 Å, angle N–H. . .O = 151–171°. According to a previous report [21], these hydrogen bonds have medium strength. Cs2[(UO2)3(C4H2O4)4]2H2O (II) crystallizes in the triclinic crys with Z = 2 and Z‘ = 1. All the atoms in tal system (space group P 1) II occupy general positions. The U1 atom has CN = 8, while the U2 and U3 atoms have CN = 7. All three uranyl groups are equal arms and linear to within the error of the X-ray experiment (d (U@O) varies from 1.766(5) to 1.778(5) Å and O@U@O angle varies from 178.6(2) to 179.7(3)° in the structure of II). The coordination polyhedra of the U atoms in II have the form of hexagonal (U1) or pentagonal (U2 and U3) bipyramids, while dual to them the Voronoi–Dirichlet polyhedra have the forms of hexagonal or pentagonal prisms respectively. The volumes of the Voronoi–Dirichlet polyhedra of the U atoms in I and II are equal to 9.57 (in I) and 9.47 Å3 (in II) for U1 with CN = 8, and to 9.14 and 9.16 Å3 for U2 and U3 with CN = 7, respectively. These values are in a good agreement with the known values of 9.4(2) Å3 for UO8 and 9.2(1) Å3 for UO7 coordination polyhedra [22]. Every maleate ion in II binds four uranyl ions into (0 1 0) layers with the [(UO2)3(C4H2O4)4]2 composition (Fig. 2). Overall the crystallochemical formula of the complex unit in II is A3(Q21-4)2(Q21-7)2 (see further discussion), where A = UO2+ 2 , 21 2– Q21-4 = C4H2O2– 4 forming 4-membered rings and Q -7 = C4H2O4 forming 7-membered rings. The uranyl-maleate layers are bound into a 3D framework through electrostatic interactions with Cs+ cations. In the case of U(1) atoms with CN = 8 in I and II, the UO2+ 2 line strongly tilts from a normal direction of the equatorial plane (84.8 and 84.6° respectively). This is due to repulsion of the ‘-yl’ oxygen atoms and non-coordinated O atoms of two monodentate carboxylate groups of trans coordinated maleate ions (d = 3.11 Å for I, and 2.88 and 3.00 Å for II, Fig. 1). For the U(2) and U(3) atoms
333
Fig. 2. Fragment of the layer with the [(UO2)3(C4H2O4)4]2 composition in the structure of Cs2[(UO2)3(C4H2O4)4]2H2O (II). Six atoms in green together with a U atom represent a 7-membered ring. Three atoms in blue together with a U atom represent a 4-membered ring.
with CN = 7 in II, the UO2+ 2 line is almost at right angles with the equatorial plane (88.5 and 88.8° respectively). In this case, one out of two ‘-yl’ oxygen atoms of the UO2+ 2 group is squeezed from all sides by the atoms of four coordinated maleate ions (Fig. 2), and the other one is squeezed from all sides by other atoms, including cesium. The difference between the U atoms with CN = 7 and 8 is also evident from the type of bonding with maleate ions. The bonding between the U1 atom and maleate ions in II is exactly the same as between the U1 atom and maleate ions in I. On the other hand, the U2 and U3 atoms realize another coordination mode with the maleate ions, which is the same for both U2 and U3. Three O atoms in the equatorial planes of U2 and U3 in II belong to three carboxylate groups of three maleate ions. The remaining two O atoms belong to two different carboxylate groups of the same maleate ion. Thus, all four crystallographically independent maleate ions in II have the Q21 coordination mode, being bridging and chelating at the same time. However, coordination of two maleate ions leads to the formation of the usual 4-membered rings (Q21-4 coordination mode), while coordination of the other two maleate ions leads to the formation of 7-membered rings (Q21-7, Fig. 2). In spite of the fact that 7-membered rings are unusual and should be unstable, they were earlier observed for another known maleate complex of the uranyl ion, K[UO2(C4H2O4)(C4H3O4)] [8]. According to the method of intersecting spheres [23], the Cs1 atom in II forms a CsO8 coordination polyhedron with d(Cs–O) = 3.00–3.52 Å. Three out of eight O atoms of the CsO8 coordination polyhedron belong to three adjacent uranyl ions. Thus, the Cs1 atom is involved in uranyl-cation interactions, which are typical for cesium salts of uranyl complexes [24–26]. The Cs1 atoms form [1 0 0] zigzag chains with the distances between neighboring Cs1 atoms equal to 4.24 and 4.56 Å. The Cs2 and Cs3 atoms are disordered over two positions. Two disordered water molecules occupy the same positions.
Fig. 1. Fragment of a chain with the [UO2(C4H2O4)2]2 composition in the structure of (NH4)2[UO2(C4H2O4)2] (I). Three atoms in blue together with a U atom represent a 4membered ring.
334
A.V. Savchenkov et al. / Polyhedron 127 (2017) 331–336
Fig. 3. Occurrence of 15 coordination modes of maleate ions in the crystal structures of coordination compounds from the CSD.
As was observed earlier in the structure of K[UO2(C4H2O4) (C4H3O4)] [8], the maleate ions in I and II are also not planar as one would think judging on the hybridization of the carbon atoms. For the maleate ions in I and II with T11-4 and Q21-4 coordination modes, the plane of one carboxylate group is quasi parallel (1.8–9.9°) with the almost planar hydrocarbon skeleton, while the other carboxylate group is quasi perpendicular (74.2–81.4°) to the skeleton. For the maleate ions with the Q21-7 coordination mode in II such angles are increased for quasi parallel carboxylate groups (22.1–22.9°) and decreased for quasi perpendicular (57.7–62.3°) groups. In our opinion, such a deviation of the angles for the Q21-7 coordinated maleate ions in comparison with the ‘more relaxed’ ones (with T11-4 and Q21-4 coordination modes) shows possible strain in the maleate ions due to coordination of a rigid ligand with a double C@C bond to the same U atom by both carboxylate groups. This assumption is supported by the fact that the deviation of the oxygen atoms from the equatorial planes of the uranyl groups in I and II reaches 0.19 Å. 3.2. Analysis of the coordination modes of the maleate ions To summarize all the available data on the structure and coordination modes of maleate ions, we performed a crystallochemical analysis of all maleate containing compounds in the CSD [27]. The following requirements were applied for compounds to avoid unreliable data: 1) The crystal structure simultaneously contains maleate ions C4H2O2– 4 and d- or f-metal atoms A with bond valence s of the A–O bonds and with oxygen atoms of maleate ions 0.25 (s = v/CN, where v is the oxidation state of A and CN is the coordination number);
2) The coordinates of all the atoms are defined (structures with undefined coordinates of only H atoms were also taken into account); 3) 0 < R1 0.1; 4) The crystal structure does not possess disorder. Such requirements resulted in 69 compounds with 77 crystallographically independent maleate ions. Note, that neither hydrogen maleate nor fumarate ions were considered in the current research. It was observed that maleate ions realize 15 different coordination modes (Fig. 3), 8 of which are the most abundant and are realized by 90% of all maleate ions: M1, B2, B01-7, T11-4, T11-7, Q21-4, Q21-7 and Q02-44. The observed coordination modes show that maleate ions are able to serve as terminal (M1, B01-4, B01-7) or bridging (all the remaining 12 coordination modes) ligands, may not be chelating (M1, B2) or may form 4 or 7-membered rings with metals (all the remaining 13 coordination modes). Among the 77 studied maleate ions, 33 ions form 7-membered rings, 23 ions form 4membered rings and 2 ions simultaneously form 4- and 7-membered rings (maleate ions with T02-47 and Q12-47 coordination modes with reference codes IJOBIS [28] and QOVXOO [29] in the CSD [27]). The skeleton of the maleate ion is rather rigid due to the double C@C bond in comparison with the malonate ion C3H2O2– 4 , for example [30,31]. This fact leads to almost constant main geometric parameters of the maleate ions in crystal structures. The offset of the C atom from the mean plane of the carbon skeleton in all the maleate ions does not exceed 0.05 Å, and the mean torsion angle, C–C@C–C, is equal to 1(2)°, which means that the carbon skeleton of the maleate ions is almost planar in all the examined compounds. The distance between the C atoms of two carboxylate groups of maleate ions is 3.1(1) Å, on average. The mean value of
A.V. Savchenkov et al. / Polyhedron 127 (2017) 331–336
Fig. 4. Designation of the dihedral angle between the planes of two carboxylate groups, uCOO (a), of the dihedral angle between the plane of a carboxylate group and the mean plane of a carbon skeleton, v (b), and schematic representations of two common types of structures of maleate ions: with both carboxylate groups twisted by 45° with respect to the carbon skeleton (c) and with a quasi parallel and quasi perpendicular arrangement of the carboxylate groups (d).
Fig. 5. Histogram of the uCOO angles between the planes of two carboxylate groups of maleate ions.
the \OCO angle is equal to 123(2)°, which is in a good agreement with the sp2 hybridization of the C atom in the carboxylate group. On the other hand, rotation of the carboxylate groups relative to each other and to the carbon skeleton is very diverse in the examined compounds. The angle between the planes of the two
335
carboxylate groups, uCOO, varies in the range from 37.5 to 88.6°, which proves the non-planar structure of the maleate ions in the crystals (Fig. 4). Moreover, as seen from Fig. 5, the two carboxylate groups of the maleate ions are preferably rotated to each other with the angle uCOO close to 90°. It was observed that lower uCOO values are typical for maleate ions having coordination modes with the formation of 7-membered rings. The mean uCOO values for maleate ions with coordination modes without the formation of rings and with the formation of 4- and 7-membered rings are equal to 74(12), 75 (11) and 67(13)° respectively. Maleate ions having coordination modes with the formation of 7-membered rings also tend to realize wider \CCC angles: 126(2), 126(2) and 128(2)° in the same sequence as above. These two facts show a stronger deformation of the maleate ions in the case of their coordination with the formation of 7-membered rings, which is due to steric hindrance from binding two carboxylate groups of the maleate ion to the same metal atom. The planes of the carboxylate groups of the maleate ion form dihedral angles v with a mean plane of the carbon skeleton in the range 0.4–89.3° (Fig. 4b). However, the histogram of occurrence of different v angles is explicitly symmetric and multimodal, with the highest mode for the range 45–50° (the mean value of v for all the 77 studied maleate ions is equal to 46.0°, Fig. 6). Mode 1 is the only one without a symmetric pair with respect to the highest mode 4 in Fig. 6. It corresponds to the bin 0–5° and includes scores mainly from those maleate ions which do not form rings due to coordination. Symmetric modes 2 and 6 correspond to bins 10–15 and 80–85° respectively and include scores mainly from those maleate ions, which form 4-membered rings due to coordination. In total, modes 1, 2 and 6 correspond to such a geometry of maleate ions where the plane of one carboxylate group almost coincides with the mean plane of the carbon skeleton (v = 0–20°), while the plane of the second carboxylate group is twisted almost perpendicular to the mean plane of the carbon skeleton (v = 75–90°, Fig. 4d). Such a conformation of the maleate ions in the crystal structures should be the most favorable due to common sense. On the other hand, as seen from Fig. 6, most of the carboxylate groups in the maleate ions are twisted to v angles of 20–75° with respect to the carbon skeleton. This region contains three modes and includes scores mainly from those maleate ions which form
Fig. 6. Combined graph showing the occurrence of the dihedral angle v between the planes of the carboxylate groups of the maleate ion and the mean plane of the carbon skeleton. A solid line is drawn for all 77 maleate ions. Each bin for the solid line may include scores from three groups of maleate ions, dependent on their coordination mode: with the formation of 7-membered rings, with the formation of 4-membered rings or without the formation of rings. The drawn bars include scores only from one out of the three groups of maleate ions (marked with gray, orange and blue colors) with the highest N for the current bin. (Color online.)
336
A.V. Savchenkov et al. / Polyhedron 127 (2017) 331–336
7-membered rings due to coordination. Taking into account the height of the modes of the solid line in Fig. 6, one can conclude that the process of coordination of two carboxylate groups of a maleate ion to the same metal atom can be run in two possible ways. The first way is to twist the planes of both carboxylate groups to angles of about 40–55° (mode 4) with respect to the mean plane of the carbon skeleton (Fig. 4c). The second way is to twist the plane of one carboxylate group to an angle of about 20–40° (mode 3) and the plane of the second carboxylate group to an angle of about 55–75° (mode 5). Thus, maleate ions with coordination modes without the formation of rings and with the formation of 4-membered rings have one carboxylate group quasi parallel to the carbon skeleton and the other one quasi perpendicular. Although coordination of carboxylate groups with the formation of 4-membered rings seems favorable and stable, maleate ions more often realize coordination modes with the formation of 7-membered rings when different carboxylate groups of the maleate ion bind to the same metal atom. In that case, both carboxylate groups of the maleate ion have to twist with respect to the carbon skeleton with angles from 20 to 75° to make the bonding with the metal atom sterically possible. As mentioned above, such a deformation of the maleate ions leads to a lowering of the values of the uCOO angles and rising of the values of the \CCC angles with respect with more relaxed maleate ions, which, in our opinion, proves the steric hindrance of the 7membered ring formation. 4. Conclusion Synthetic techniques, FTIR spectra and the crystal structures of two new uranyl complexes with maleate ions are reported. The crystal structure of (NH4)2[UO2(C4H2O4)2] (I) is constructed of chains with the [UO2(C4H2O4)2]2 composition. Maleate ions in I have the tridentate bridging and chelating coordination mode T11-4 with the formation of 4-membered U-containing rings. The crystal structure of Cs2[(UO2)3(C4H2O4)4]2H2O (II) is constructed of layers with the [(UO2)3(C4H2O4)4]2 composition. Half of the maleate ions in II have the bridging and chelating Q21-4 coordination mode with the formation of usual 4-membered rings, while the other half have the Q21-7 coordination mode with the formation of 7-membered rings. The coordination modes of the maleate ions in all the crystal structures of coordination compounds from the CSD were analyzed. It was shown that the maleate ions realize 15 different coordination modes, eight of which are the most abundant: M1, B2, B01-7, T11-4, T11-7, Q21-4, Q21-7 and Q02-44. Calculations of different geometric parameters show that though the carbon skeleton of the maleate ion is rigid, the ion itself is not planar due to rotation of its carboxylate groups. The majority of the maleate ions tend to form uCOO angles close to 90°. For the most relaxed coordination modes (without rings or with the formation of 4-membered rings) one of the carboxylate groups of the maleate ion is quasi parallel to the carbon skeleton, while the other one is quasi perpendicular. The coordination modes with the formation of 7-membered rings force the maleate ions to rotate both their carboxylate groups to angles of 20–75° with respect to the carbon skeleton. Such coordination modes also result in lowering of the uCOO angle values and rising of the \CCC angle values, which in total show geometrical difficulties for 7-membered ring formation. Still, most of the maleate ions in the known crystal structures tend to realize coordination modes with the formation of 7-membered rings. The presented data on the coordination modes of maleate ions in crystal structures are of particular interest for crystal engineering and crystal structure prediction.
Acknowledgements This work was financially supported by the Russian Federation for Basic Research (project no. 15-33-20470). X-ray diffraction experiments were performed at the Center for Shared Use of Physical Methods of Investigation at the Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences. Appendix A. Supplementary data CCDC 1505763 and 1505764 contains the supplementary crystallographic data for I and II. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10. 1016/j.poly.2017.02.006. References [1] D. Krishna Kumar, Amitava Das, Parthasarathi Dastidar, Cryst. Growth Des. 6 (2006) 1903. [2] Zhang Yugen, Jianmin Li, Nishiura Masayoshi, Hou Hongyi, Deng Wei, Imamoto Tsuneo, J. Chem. Soc., Dalton Trans. (2000) 293. [3] M. Mirzaei, H. Eshtiagh-Hosseini, M. Chahkandi, N. Alfi, A. Shokrollahi, N. Shokrollahi, A. Janiak, CrystEngComm 14 (2012) 8468. [4] J.C. Kim, A.J. Lough, J. Chem. Crystallogr. 35 (2005) 535. [5] Ping Liu, Yao-Yu Wang, Dong-Sheng Li, Hai-Rui Ma, Qi-Zhen Shi, Gene-Hsiang Lee, Shie-Ming Peng, Inorg. Chim. Acta 358 (2005) 3807. [6] J.W. Uebler, J.A. Wilson, R.L. LaDuca, CrystEngComm 15 (2013) 1586. [7] Hong-Ye Bai, Jian-Fang Ma, Ying-Ying Liu, Jin Yang, Inorg. Chim. Acta 376 (2011) 332. [8] G. Bombieri, F. Benetollo, R.M. Rojas, M.L. De Paz, J. Inorg. Nucl. Chem. 43 (1981) 3203. [9] Complex compounds of uranium. Ed. I.I. Chernyaev. Jerusalem, Israel: Program for Scientific Translations, 1966. 520 p. [10] SAINT-Plus (Version 7.68) Bruker AXS Inc., Madison, Wisconsin, USA. (2007). [11] G.M. Sheldrick, SADABS, Bruker AXS Inc., Madison, Wisconsin, USA, 2008. [12] G.M. Sheldrick, Acta Cryst. A64 (2008) 112. [13] G.M. Sheldrick, Acta Cryst. C71 (2015) 3. [14] L.P. Nair, B.R. Bijini, S. Prasanna, S.M. Eapen, C.M.K. Nair, M. Deepa, K. RajendraBabu, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 137 (2015) 778. [15] V. Mahalakshmi, A. Lincy, J. Thomas, K.V. Saban, J. Phys. Chem. Solids 73 (2012) 584. [16] R. Omegala Priakumari, S. Grace Sahaya Sheba, M. Gunasekaran, J. Mol. Struct. 1102 (2015) 63. [17] M.F. Ramos Moita, M.L.T.S. Duarte, R. Fausto, Spectrosc. Lett. 27 (1994) 1421. [18] R.M. Silverstein, F.X. Webster, D. Kiemle, Spectrometric identification of organic compounds, Wiley, 2005, 512 p. [19] G.S. Groenewold, W.A. de Jong, J. Oomens, M.J. Van Stipdonk, J. Am. Soc. Mass Spectrom. 21 (2010) 719. [20] V.N. Serezhkin, A.V. Vologzhanina, L.B. Serezhkina, E.S. Smirnova, E.V. Grachova, P.V. Ostrova, M.Y. Antipin, Acta Cryst. B65 (2009) 45. [21] T. Steiner, Angew. Chem. 41 (2002) 48. [22] V.N. Serezhkin, M.O. Karasev, L.B. Serezhkina, Radiochemistry 55 (2013) 137. [23] V.N. Serezhkin, Yu.N. Mikhailov, Yu.A. Buslaev, Rus. J. Inorg. Chem. 42 (1997) 1871. [24] S. Fortier, T.W. Hayton, Coord. Chem. Rev. 254 (2010) 197. [25] V.N. Serezhkin, G.V. Sidorenko, D.V. Pushkin, L.B. Serezhkina, Radiochemistry 56 (2014) 115. [26] A.V. Savchenkov, A.V. Vologzhanina, L.B. Serezhkina, D.V. Pushkin, S.Yu. Stefanovich, V.N. Serezhkin, Z. Anorg. Allg. Chem. 641 (2015) 1182. [27] C.R. Groom, I.J. Bruno, M.P. Lightfoot, S.C. Ward, Acta Cryst. B72 (2016) 171. [28] C.E. Xanthopoulos, C.C. Hadjikostas, G.A. Katsoulos, A. Terzis, M.P. Sigalas, J. Coord. Chem. 55 (2002) 717. [29] Claudia Bromant, Mathias S. Wickleder, Gerd Meyer, Z. Anorg. Allg. Chem. 627 (2001) 768. [30] V.N. Serezhkin, Y.A. Medvedkov, L.B. Serezhkina, D.V. Pushkin, Russ. J. Phys. Chem. 89 (2015) 1018. [31] Y.A. Medvedkov, L.B. Serezhkina, V.N. Serezhkin, Russ. J. Phys. Chem. 90 (2016) 803.