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Acta Crystallogr C. 2010 March 15; 66(Pt 3): m58–m61.
Published online 2010 February 3. doi:  10.1107/S0108270110003033
PMCID: PMC2855585

Tetra­kis(μ2-4-amino­benzoato)di-μ3-oxido-tetra­kis[dibutyl­tin(IV)]

Abstract

The mol­ecule of the title compound, [Sn4(C4H9)8(C7H6NO2)4O2], lies about an inversion centre and is a tetra­nuclear bis­(tetra­butyl­dicarboxyl­ato­distannoxane) complex containing a planar Sn4O2 core in which two μ3-oxide O atoms connect an Sn2O2 ring to two exocyclic Sn atoms. Each Sn atom has a highly distorted octa­hedral coordination. In the mol­ecule, the carboxyl­ate groups of two amino­benzoate ligands bridge the central and exocyclic Sn atoms, while two further amino­benzoate ligands have highly asymmetric bidentate chelation to the exocyclic Sn atoms plus long O(...)Sn inter­actions with the central Sn atoms. Each Sn atom is also coordinated by two pendant n-butyl ligands, which extend roughly perpendicular to the plane of the Sn4O10 core. Only one of the four unique hydrogen-bond donor sites is involved in a classic N—H(...)O hydrogen bond, and the resulting supra­molecular hydrogen-bonded structure is an extended two-dimensional network which lies parallel to the (100) plane and consists of a checkerboard pattern of four-connected mol­ecular cores acting as nodes. The amine groups not involved in the hydrogen-bonding inter­actions have significant N—H(...)π inter­actions with neighbouring amino­benzene rings.

Comment

Bis(dicarboxyl­ato­tetra­organo­distannoxanes), {[R 2Sn(O2CR′)]2O}2, are of inter­est because of their useful applications in biology and catalysis (Blair et al., 1997 [triangle]; Petrosyan et al., 1996 [triangle]; Ribot et al., 1998 [triangle]; Tiekink et al., 1995 [triangle]). We have previously reported the crystal structures of related bis(di­car­boxyl­ato­tetra­organo­distannoxanes) prepared from various carboxyl­ates, viz. β-{[(E)-1-(2-hydr­oxy-3-methyl­phenyl)­ethyl­idene]­amino}­propionate, β-{[(2Z)-(3-hydr­oxy-1-methyl-2-butenyl­idene)]­amino}­propionate (Basu Baul, Masharing et al., 2006 [triangle]), and 5-[(E)-2-aryl-1-diazenyl]-2-hydroxy­benzoates, where aryl is 2-meth­oxy, 3-methyl (Basu Baul et al., 2007 [triangle]) and 4-unsubstituted, 4-methyl, 4-chloro and 4-bromo (Basu Baul, Rynjah et al., 2006 [triangle]). During an extension of these studies into the coordination chemistry of substituted carboxyl­ates with organo­tin species, 4-amino­benzoic acid was reacted with di­butyl­tin(IV) oxide to form the tetra­nuclear title compound, {[Bu2Sn(O2CC6H4-p-NH2)]2O}2 (Bu = n-butyl), (I), and its crystal structure is reported here.

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Object name is c-66-00m58-scheme1.jpg

The mol­ecular structure of (I) is shown in Fig. 1 [triangle]. The mol­ecule lies about an inversion centre and is a tetra­nuclear bis­(tetra­butyl­dicarboxyl­ato­distannoxane) complex containing a planar Sn4O2 core, in which two μ3-oxide O atoms connect an Sn2O2 ring (endocyclic Sn atoms) to two exocyclic Sn atoms to give an R 8Sn4O2 central unit. The central Sn2(...)Sn2(−x + 1, −y, −z + 1) contact is 3.3140 (2) Å, while the two unique exo-Sn(...)endo-Sn distances are 3.6334 (2) and 3.7660 (2) Å. Two symmetry-related amino­benzoate ligands each bridge one endocyclic to one exocyclic Sn centre via the two carboxyl­ate O atoms, with the Sn—O distances being quite similar (Table 1 [triangle]). Two additional amino­benzoate ligands each have highly asymmetric bidentate chelation via the two carboxyl­ate O atoms to an exocyclic Sn atom, with the longer Sn1(...)O5 inter­actions being quite long [2.9053 (18) Å]. Additionally, the other carboxyl­ate O atom in each of these ligands coordinates via a second long Sn2(...)O4(1 − x, −y, 1 − z) bond [2.7841 (17) Å] to an endocyclic Sn atom. Each Sn atom is also coordinated by two pendant Bu ligands, which subtend angles of about 140° at their parent Sn atoms. If the longer Sn(...)O distances are considered as part of the primary coordination environment, each Sn atom has a highly distorted octa­hedral coordination, with some of the distortion arising from bite-angle constraints. Alternatively, ignoring Sn(...)O distances greater than 2.3 Å yields a distorted trigonal–bipyramidal geometry about each Sn atom, with, in each case, the Bu ligands occupying equatorial positions.

Figure 1
A view of the mol­ecule of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. Only one conformation of the disordered amino­benzene ring is shown. H atoms bonded to C atoms have been ...
Table 1
Selected geometric parameters (Å, °)

The Sn4O10 core of the mol­ecule forms an essentially planar system, although the six-membered ring formed by Sn1, Sn2, the μ3-oxide atom O7 and the bridging carboxyl­ate group is somewhat twisted towards a screw boat form, forcing atoms O1 and O2 out of the plane of the remainder of the core atoms by 0.323 (2) and −0.505 (2) Å, respectively. The amino­benzene rings are slightly tilted out of the plane of the Sn4O10 core, with dihedral angles between the benzene ring planes and core plane in the range 12.8 (3)–24.6 (2)° (the presented range includes both disordered conformations of one amino­benzoate ligand). Nonetheless, the Sn4O10 core and associated carboxyl­ate ligands can be considered as a fairly planar entity, with the pendant Bu ligands extending roughly perpendicular to this plane (Fig. 2 [triangle]).

Figure 2
The disposition of the pendant n-butyl ligands perpendicular to the plane of the Sn4O10 core and the carboxyl­ate ligands in the mol­ecule of (I). H atoms bonded to C atoms have been omitted for clarity and only one of the arrangements ...

The amino­benzene moiety of the amino­benzoate ligand containing atoms O1 and O2 is disordered over two conformations. The major conformation is present in approximately 59% of the mol­ecules.

The structures of many dimeric dicarboxyl­atotetra­organo­distannoxanes are known and have been reviewed (Tiekink, 1991 [triangle], 1994 [triangle]). Five predominant patterns of carboxyl­ate ligand coordination about the Sn4O2 core seem to recur, but by far the most common motif is the centrosymmetric variant displayed by compound (I). The Cambridge Structural Database (Version 5.30, update 4 of September 2009; Allen, 2002 [triangle]) contains entries for 135 structures displaying the same basic coordination motif as (I). In structures of this type, the Sn coordination geometry, as well as the distribution of Sn—O distances, is usually much the same.

Although two symmetry-independent amine groups offering four potential hydrogen-bond donor sites are present in the mol­ecule of (I), only one of these is involved in a classic N—H(...)O hydrogen bond (Table 2 [triangle]). This inter­molecular inter­action is with a carboxyl­ate O atom in the same carboxyl­ate ligand of a neighbouring tetra­nuclear mol­ecule related by a c-glide operation, and serves to link the mol­ecules into extended zigzag chains which run parallel to the [001] direction (Fig. 3 [triangle]) and can be described by a graph-set motif of C(8) [see Bernstein et al. (1995 [triangle]) for a description of graph-set motifs]. The path of this motif involves only the atoms of a single unique carboxyl­ate ligand. As the mol­ecule lies about an inversion centre, each mol­ecule accepts and donates two of these hydrogen bonds, so that both sides of the mol­ecule are involved in two anti­parallel adjacent chains. A consequence of this is that the same hydrogen-bonding inter­actions also yield further zigzag chains which run via the core of each mol­ecule parallel to [010] and which can be described by a graph-set motif of C(14). Effectively, the core of each mol­ecule cross­links two adjacent [001] chains, and neighbouring mol­ecules in each such chain crosslink different chains, resulting in a checkerboard pattern of four-connected mol­ecular cores acting as nodes between the chains (Fig. 3 [triangle]). The overall supra­molecular hydrogen-bonded structure arising out of these inter­actions is thus an extended two-dimensional network which lies parallel to the (100) plane. The hydrogen-bonded ring motif within each of the checkerboard squares is An external file that holds a picture, illustration, etc.
Object name is c-66-00m58-efi1.jpg(22).

Figure 3
The supra­molecular hydrogen-bonded layer in the structure of (I). H atoms bonded to C atoms have been omitted for clarity and only one of the arrangements of the disordered amino­benzene ring is shown.
Table 2
Hydrogen-bond geometry (Å, °)

There are no significant π–π inter­actions in the structure of (I), but one unique N—H(...)π inter­action is present between the amine group not involved in the hydrogen-bonding inter­actions described above and the amino­benzene ring defined by atoms C9–C14 (centroid Cg1) in a neighbouring mol­ecule [N1B(...)Cg1i = 3.706 (10) Å, H13(...)Cg1i = 2.84 Å, H13(...)ring plane = 2.67 Å and N1B—H13(...)Cg1i = 168°; symmetry code: (i) −x + 1, y − An external file that holds a picture, illustration, etc.
Object name is c-66-00m58-efi2.jpg, −z + An external file that holds a picture, illustration, etc.
Object name is c-66-00m58-efi3.jpg]. The inter­action appears to involve only the minor conformation of the disordered amino­benzene ring; although the major conformation of the amino­benzene ring has an H atom at a similar distance from the plane of the Cg1i ring, it is significantly offset from the centre of the ring.

Experimental

A suspension of Bu2SnO (1.036 g, 3.64 mmol) and 4-amino­benzoic acid (0.5 g, 3.64 mmol) in anhydrous toluene (50 ml) were refluxed for 3 h in a flask equipped with a Dean–Stark water separator and a water-cooled condenser. After the reaction, a clear solution was obtained and this was filtered while hot. The solvent was evaporated in vacuo, and the white residue was washed thoroughly with hexane and dried in vacuo. The residue was dissolved in chloro­form and the solution was filtered to remove any undissolved particles. The filtrate was left to crystallize at room temperature. The crude product was obtained after evaporation and this was then recrystallized from a chloro­form–hexane solution (1:1 v/v) to give colourless prismatic crystals of (I) in 65% yield (m.p. 379–381 K). Analysis calculated for C60H96N4O10Sn4: C 47.78, H 6.42, N 3.71%; found: C 47.80, H 6.23, N 3.66%. IR (KBr, cm−1): 1621 ν(OCO)asym, 643 ν(Sn—O—Sn); 1H NMR (CDCl3, δ, p.p.m.): 7.91 (br d, 2H, H2), 6.68 (d, 2H, H3), 4.0 (br s, 2H, NH2); Sn–nBu skeleton: 0.80 (br m, 6H, H4*), 1.35 (br m, 4H, H3*), 1.70 (br m, 8H, H1* and H2*); 13C NMR (CDCl3, δ, p.p.m.), ligand skeleton: 113.7 (C3), 123.2 (C1), 131.9 (C2), 150.0 (C4), 172.8 (CO2); Sn–nBu skeleton: 28.1, 27.7, 27.4, 26.8 and 26.1 (C1*, C2* and C3*), 13.6 (C4*). For the 1H and 13C NMR assignments, atoms marked with an asterisk (*) refer to the n-butyl ligand numbered outwards from the Sn atom; the other C atoms belong to the amino­benzene ring, starting from the ring C atom closest to the carboxyl­ate group.

Crystal data

  • [Sn4(C4H9)8(C7H6NO2)4O2]
  • M r = 1507.84
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is c-66-00m58-efi4.jpg
  • a = 12.3017 (1) Å
  • b = 17.1436 (1) Å
  • c = 15.8633 (1) Å
  • β = 103.3015 (5)°
  • V = 3255.75 (4) Å3
  • Z = 2
  • Mo Kα radiation
  • μ = 1.57 mm−1
  • T = 160 K
  • 0.22 × 0.20 × 0.17 mm

Data collection

  • Nonius KappaCCD area-detector diffractometer
  • Absorption correction: multi-scan (Blessing, 1995 [triangle]) T min = 0.646, T max = 0.764
  • 94040 measured reflections
  • 9527 independent reflections
  • 7900 reflections with I > 2σ(I)
  • R int = 0.060

Refinement

  • R[F 2 > 2σ(F 2)] = 0.032
  • wR(F 2) = 0.078
  • S = 1.13
  • 9520 reflections
  • 428 parameters
  • 231 restraints
  • H atoms treated by a mixture of independent and constrained refinement
  • Δρmax = 1.46 e Å−3
  • Δρmin = −0.89 e Å−3

The entire amino­benzene moiety of one of the two symmetry-independent carboxyl­ate ligands is disordered over two conformations. Two sets of overlapping positions were defined for the atoms of this group and the site-occupation factors of each conformation were refined while restraining their sum to unity. The site-occupation factor of the major conformation refined to 0.585 (5). Similarity restraints with tolerance s.u. values of 0.005 Å were applied to the chemically equivalent bond lengths and angles involving all disordered atoms, while neighbouring atoms within and between each conformation were restrained to have similar atomic displacement parameters within a tolerance s.u. of 0.01 Å2. Each conformation of the disordered amino­benzene group was further restrained to be planar, also with a tolerance s.u. of 0.01 Å. The H atoms of the ordered amine group were placed in the positions indicated by a difference electron-density map and their positions were allowed to refine, together with individual isotropic displacement parameters. The methyl H atoms were constrained to an ideal geometry (C—H = 0.98 Å), with U iso(H) = 1.5U eq(C), but were allowed to rotate freely about the adjacent C—C bonds. All other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C—H = 0.95 (aromatic) or 0.99 Å (methyl­ene) and N—H = 0.88 Å, and with U iso(H) = 1.2U eq(C,N). Seven low-angle reflections were omitted from the final cycles of refinement because their observed intensities were much lower than the calculated values as a result of being partially obscured by the beam stop.

Data collection: COLLECT (Nonius, 2000 [triangle]); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997 [triangle]); data reduction: DENZO-SMN and SCALEPACK (Otwinowski & Minor, 1997 [triangle]); program(s) used to solve structure: SIR92 (Altomare et al., 1994 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: ORTEPII (Johnson, 1976 [triangle]); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008 [triangle]) and PLATON (Spek, 2009 [triangle]).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S0108270110003033/fg3152sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S0108270110003033/fg3152Isup2.hkl

Acknowledgments

The financial support of the Department of Science and Technology, New Delhi, India (grant No. SR/S1/IC-03/2005 to TSBB), is gratefully acknowledged.

Footnotes

Supplementary data for this paper are available from the IUCr electronic archives (Reference: FG3152). Services for accessing these data are described at the back of the journal.

References

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