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Synthesis and structure of a new dinuclear oxomolybdate complex containing a linear OMoOMoO unit
Inorganica Chimica Acta 344 (2003) 61 /64 www.elsevier.com/locate/ica
Synthesis and structure of a new dinuclear oxomolybdate complex containing a linear O Mo O Mo O unit /
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Li-Zhen Cai a, Li-Jun Song a, Hui-Yi Zeng a, Zhen-Chao Dong a,b,*, Guo-Cong Guo a, Jin-Shun Huang a a
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China b National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan Received 17 May 2002
Abstract A new dinuclear oxomolybdate complex [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3] ×/2H2O was obtained as black needle crystals by the reaction of MoCl3 ×/3H2O with a specially designed tetradentate Schiff base ligand under solvothermal conditions. Singlecrystal X-ray diffraction analysis indicates that it crystallizes in a monoclinic P 21/c space group with a rare oxo-bridged dinuclear molybdenum structure. The structure is characterized by two MoO4N2 octahedra sharing a corner oxygen atom in a completely linear Mo /O /Mo arrangement. In addition to being the first example of nearly linear O /Mo /O /Mo/O arrangements, the present structure features a Mo /O single bond at two ends, in sharp contrast with the known O /M/O/M/O (M /W, Re) units that contain M/O double bonds for terminal oxygen, due to the spatial chelating requirement of the long tetradentate Schiff base ligand. ˚ suggests the The completely linear Mo/O/Mo structure together with the relatively short Mo/O distance of 1.8819(7) A involvement of metal /oxygen p bonding. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Oxomolybdates; Linear O/M/O/M/O structures; Schiff base ligands
1. Introduction Coordination complexes of oxomolybdates exhibit varieties of topological structures and are particularly attractive for their application in catalysis [1]. By tuning the protonation ability of donor groups, the coordination of oxomolybdates to multidentate ligands is found to reveal diverse degrees of aggregation and numerous structural types. For the lowest aggregation of a dinuclear structure, bulky multidentate Schiff base ligands play an effective role in space-confining the size of oxomolybdates and many dinuclear oxomolybates have been thus synthesized [2,3]. * Corresponding author. Tel.: /86-591-371 3074; fax: /86-591-371 4946.
In this paper, we report the synthesis and single crystal structure of a new oxo-bridged dinuclear molybdenum complex, [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3] ×/2H2O. To our knowledge, this is the first example of dinuclear oxomolybate complexes containing a nearly linear O /Mo /O /Mo /O moiety, although linear N /Mo /O /Mo/N structures were previously reported [4,5]. Analogous structures were also found in other dinuclear metal complexes, e.g. O /W/ O /W /O in W2O3(CH2CMe3)6 [6], O /Re /O /Re /O in Re2O3L8 [7 /10], Cl /M /O /M /Cl in [M2OCl10]4 (M /W [11], Re [12], Ru [13], Os [14]), and O /Re / O /Re /O in [ReO(salpd)]2O [15] as well as O /Tc /O / Tc /O in m-O[TcO(sal2pn)]2 [16]. Here we shall demonstrate that the present compound reveals novel character in both coordination and bonding.
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 2 7 9 - 3
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2. Experimental 2.1. Synthesis 2.1.1. Materials All materials used in the synthesis were of analytical grade and used as received. 2.1.2. Synthesis of C17H18N2O2 The N ,N ?-bis(salicylidene)-propane-1,3-diamine, hereafter called the tetradentate Schiff base ligand, was prepared according to literature [17]. Salicylaldenhyde (24 ml, 0.22 mol) was added dropwise to a solution of 1,3-diamino propane (8.4 ml, 0.1 mol) in 40 ml benzene. The reaction mixture was then refluxed at 86 8C for 0.5 h. After most of the solvent was removed, the residue was cooled to room temperature followed by the addition of 50 ml methanol. After overnight cooling at 0 8C, yellow precipitate was observed and collected by filtration. The precipitate was washed with 40 ml methanol, filtered off, and dried in vacuo to give 15.02 g of pure C17H18N2O2 (54% yield). Anal. Calc. (%): C, 72.34; H, 6.383; N, 9.929; O, 11.35. Found: C, 72.19; H, 6.199; N, 9.876; O, 12.16%. IR (cm1, KBr): nCH (C6H6) 3050, 3010; nCN 1610; nCH (CH2) 2893, 2870; nOH 3500. 2.1.3. Synthesis of [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3] ×/2H2O The title compound was obtained from a solvothermal reaction of MoCl3 ×/3H2O (0.256 g, 1 mmol), PPh3 (0.262 g, 1 mmol), FeSO4 (0.076 g, 0.5 mmol), and the above-prepared Schiff base (0.705 g, 0.25 mmol) in methanol (15 ml) in a 30 ml Teflon-lined stainless steel autoclave for 96 h at 100 8C. The needle black crystals were separated from the black solution after cooling down to room temperature.
Table 1 Crystal data and structure refinement [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3]×/2H2O Empirical formula Formula weight Temperature (K) ˚ ) Mo Ka Wavelength (A Crystal system Space group ˚) a (A ˚) b (A ˚) c (A b (8) ˚ 3) V (A Z Dcalc (Mg m 3) m (mm1) F (000) Crystal size (mm) u Range (8) Index ranges Reflections collected Independent reflections Reflections observed R1 a wR2 b ˚ 3) rmax (e A ˚ 3) rmin (e A
for
C34H36N4O9Mo2 836.55 293(2) 0.71073 monoclinic P 21/c 8.2070(3) 10.9770(4) 19.5926(1) 92.066(1) 1763.92(9) 2 1.575 0.769 848 0.26 /0.16/0.14 2.08 5/u 5/25.03 /9 5/h 5/7, /135/k 5/10, /13 5/l 5/23 5214 3101 1978 0.0633 0.1506 1.257 /0.796
a
R1 /a½½Fo½/½Fc½/a½Fo½. wR 2/(a(w (F/2o//F/2c )/2)/a(w (F/2o )/2))1/2 (0.0861P )2)], P /(F/2o//2F/2c )//3. b
where
w/1/[(s2(F/2o )//
bonded to carbon were located by geometrical calculation. The hydrogen atoms associated with solvent water molecules were located from difference Fourier maps. All non-hydrogen atoms were refined anisotropically. The final refinement over 223 variables resulted in the agreement factors R1 /0.0633, wR2 /0.1506, S /1.095, (D/s)max /0.001 for 1978 observed reflections. All calculations were performed by using the Siemens SHELXL package [19].
2.2. Crystal structure determination The crystal data of title compound, and the parameters of data collection are summarized in Table 1. A black needle crystal of the title compound with dimensions of 0.26 /0.16 /0.14 mm3 was mounted on the top of a glass fiber. X-ray diffraction data were collected on a Siemens Smart CCD diffractometer equipped with graphite-monochromated Mo Ka radiation (l / ˚ ). A total of 5214 independent reflections 0.71073 A (Rint /0.0455) were collected in the v scan mode in the range of 4.16 5/2u /50.068 at 293 K, of which 1978 reflections with I /2.0s (I ) were considered observed and used in subsequent structural determination and full-matrix least-square refinements. Absorption correction was performed by the SADABS program [18]. The structure was solved by the direct methods and subsequent difference Fourier syntheses. Hydrogen atoms
3. Results and discussion The compound consists of discrete molybdenum complexes and water solvent molecules. According to the charge-balancing requirement for the neutral [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3] complex determined by the single-crystal X-ray diffraction, the formal oxidation state of Mo is /5, which implies the oxidation of the starting material MoCl3 ×/3H2O by atmospheric oxygen in air or dissolved in the solvent. (All starting materials and solvents were handled in air before loaded into an autoclave for solvothermal reactions.) During the reaction, the R /O /H group from the Schiff base ligand was deprotonated and the resulted R / O anion was coordinated to Mo, analogous to the reaction of Schiff bases with other metal ions [20,21].
L.-Z. Cai et al. / Inorganica Chimica Acta 344 (2003) 61 /64
The structure is characterized by the presence of an oxo-bridged or corner-shared double octahedral unit that reveals a completely linear Mo /O /Mo arrangement in a nearly linear O /Mo /O /Mo/O unit, as shown in Fig. 1. Two bulky tetradentate Schiff base ligands, together with three atmospheric oxygen atoms, spatially bind two Mo atoms into a dinuclear complex with the bridged O atom located at an inversion center. To our knowledge, the present compound is the first example featuring a nearly linear O /Mo /O /Mo/O arrangement. Similar structural units were previously reported in the literature, though limited, e.g. N /Mo / O /Mo /N [4,5], O /W/O /W /O [6], O /Re /O /Re /O [7 /10], Cl /M /O /M/Cl (M /W [11], Re [12], Ru [13], Os [14]). In contrast with the known O /M /O /M /O (M /W, Re) units that contain M /O double bonds for terminal oxygen, the present O /Mo /O /Mo /O features a Mo /O single bond at two ends, probably due to the spatial chelating requirement of the tetradentate Schiff base ligand (below). All Mo(V) ions are located in a distorted octahedral coordination environment and are crystallographically equivalent since the dinuclear complex has an inversion center symmetry. Each Schiff base ligand provides four donor sites, two oxygen and two nitrogen, which bind across two Mo atoms non-symmetrically and help to link the complex together. Among six coordinated atoms around each Mo, O1 and O2 are from atmospheric oxygen with O1 serving as a bridging atom and O2 as a terminal atom; N1, N2, O3, and O4 are from Schiff base ligands with O3 acting as the end atoms for the nearly linear O3 /Mo/O1 /Mo /O3 (O1 / Mo /O3 /171.9(1)8, Mo/O1 /Mo /1808). Selected bond lengths and angles were shown in Table 2. The O3 site is usually occupied by a terminal oxygen for small ligands [6 /10]. The lengthy configuration of the present Schiff base ligand is probably responsible for such coordination preference. ˚ , as The Mo /O2 distance is as short as 1.702(5) A commonly observed for terminal oxygen atoms. This bond is of double-bond character in reference with the Mo /O lengths reported in C19H25MoNO6 (1.695(2) / ˚ ), C17H20MoN2O6S2 (1.696(3) /1.700(3) A ˚ ), 1.712(2) A
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Table 2 ˚) Select bond lengths (A and angles [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3]×/2H2O
(8)
for
˚) Bond length (A Mo /O(1) Mo /O(2) Mo /O(3) Mo /O(4) Mo /N(1) Mo /N(2)
1.8816(7) 1.705(5) 2.087(5) 2.031(4) 2.189(7) 2.148(7)
N(1)/C(11) N(1)/C(10) N(2)/C(7) N(2)/C(8) O(4)/C(17)
1.285(9) 1.470(9) 1.297(10) 1.480(10) 1.326(8)
Bond angle (8) Mo /O(1)/Mo a O(1)/Mo/O(3) O(2)/Mo/O(1) O(2)/Mo/O(3) O(1)/Mo/O(3) O(4)/Mo/O(3) O(2)/Mo/O(4) O(1)/Mo/O(4) O(2)/Mo/N(1) O(1)/Mo/N(1)
180 171.86(14) 100.3(2) 87.7(2) 171.86(14) 80.7(2) 166.5(2) 91.57(14) 91.3(2) 95.55(17)
O(4)/Mo/N(1) O(3)/Mo/N(1) N(2)/Mo/N(1) O(2)/Mo/N(2) O(1)/Mo/N(2) O(4)/Mo/N(2) O(3)/Mo/N(2) C(11)/N(1)/Mo C(10)/N(1)/Mo C(17)/O(4)/Mo
81.0(2) 85.7(2) 164.3(2) 100.9(2) 92.03(18) 85.1(2) 84.9(2) 124.3(6) 120.0(5) 129.7(4)
a Symmetry transformations used to generate equivalent atoms: 1/ x , /y , 2/z .
˚) and MoO2{HOC2H4N(C2H4O)2} (1.697(3) /1.721(3) A [22]. The Mo /O3 and Mo /O4 distances are 2.086(6) ˚ , respectively, falling in the range for a and 2.030(4) A typical Mo /O single bond [23]. The Mo /N distances ˚ , in good vary slightly from 2.147(7) to 2.188(7) A agreement with those reported in C68H48MoN4O4 ×/ ˚ ) and [Mo2(NMe2)(OAr2C4H8O [24] (2.129/2.131 A ˚ ) [25]. Of particular 3,5-Me2)6(HNMe2)2] (2.107 /2.236 A ˚, interest is the Mo /O1 bond distance of 1.8819(7) A which lies between the distances for the single-bond and double-bond. Taken into account the completely linear Mo/O /Mo structure, the involvement of metal/oxygen p-bonding character is evident. This is electronically possible since each Mo(V) ion can offer one unpaired d electron, which, together with two p electrons from the central O atom, may form a three-center-four-electron P43 bond and thus shorten the interatomic distance and help to stabilize the structure.
4. Supplementary material
Fig. 1. View of [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3]×/2H2O showing the oxo-bridged dinuclear complex (30% ellipsoids). For clarity, the packing water molecules are omitted. Symmetry codes: a: 1/x , /y , 2/z .
Complete crystallographic data (including structure factors) for the structure reported in this paper have been deposited at the Cambridge Crystallographic Data Centre, CCDC No. 184674. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: /44-1223-336-033; e-mail: [email protected]; www: http://www.ccdc.cam.ac.uk).
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Acknowledgements This work was supported by the Innovative Project (No. IP01007) and the Introduction of Overseas Elitists Program (No. IB990168), Chinese Academy of Sciences.
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[11] T. Glowiak, M. Sabat, B. Jezowska-Trzebiatowska, Acta Crystallogr., B 31 (1975) 1783. [12] J.C. Morrow, Acta Crystallogr. 15 (1962) 851. [13] A.M. Mathieson, D.P. Mellor, N.C. Stephenson, Acta Crystallogr. 5 (1952) 185. [14] K.F. Tebbe, H.G. Schnering, Z. Anorg. Allgem. Chem. 396 (1973) 66. [15] F. Tisato, F. Refosco, Inorg. Chim. Acta 164 (1989) 127. [16] G. Bandoli, U. Mazzi, M. Nicolini, F. Refosco, J. Chem. Soc., Dalton Trans. (1984) 2505. [17] M.L. Tong, X.M. Chen, B.H. Ye, L.N. Ji, Angew. Chem., Int. Ed. 38 (1999) 2237. [18] SADABS, Bruker Smart and Bruker Shelxtl Package, Bruker AXS GmbH, Karlsrute, 1998. [19] G.M. Sheldrick, SHELXL93. Program for the Refinement of Crystal Structure, University of Go¨ttingen, Go¨ttingen, Germany. [20] J.M. Berg, D.J. Spira, K.O. Hodgson, A.E. Bruce, K.F. Miller, J.L. Corbin, E.I. Stiefel, Inorg. Chem. 23 (1984) 3412. [21] J.A. Craig, E.W. Harlan, B.S. Snyder, M.A. Whitener, R.H. Holm, Inorg. Chem. 28 (1989) 2082. [22] S.C. Liu, L.D. Ma, D. Mcgowty, J. Zubieta, Polyhedron 9 (1990) 1541. [23] A.N. Papadopoulos, C.P. Raptopoulou, A. Terzis, A.G. Hatzidimitriou, A. Gourdon, D.P. Kessissoglou, J. Chem. Soc., Dalton Trans. (1995) 2591. [24] E. Solari, C. Maltese, M. Latronico, C. Floriani, A. Chiesi-Villa, C. Rizzoli, J. Chem. Soc., Dalton Trans. (1998) 2395. [25] T.W. Coffindaffer, G.P. Niccolai, D. Powell, I.P. Rothwell, J.C. Huffman, J. Am. Chem. Soc. 105 (1985) 3572.
Synthesis and structure of a new dinuclear oxomolybdate complex containing a linear O Mo O Mo O unit /
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Li-Zhen Cai a, Li-Jun Song a, Hui-Yi Zeng a, Zhen-Chao Dong a,b,*, Guo-Cong Guo a, Jin-Shun Huang a a
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China b National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan Received 17 May 2002
Abstract A new dinuclear oxomolybdate complex [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3] ×/2H2O was obtained as black needle crystals by the reaction of MoCl3 ×/3H2O with a specially designed tetradentate Schiff base ligand under solvothermal conditions. Singlecrystal X-ray diffraction analysis indicates that it crystallizes in a monoclinic P 21/c space group with a rare oxo-bridged dinuclear molybdenum structure. The structure is characterized by two MoO4N2 octahedra sharing a corner oxygen atom in a completely linear Mo /O /Mo arrangement. In addition to being the first example of nearly linear O /Mo /O /Mo/O arrangements, the present structure features a Mo /O single bond at two ends, in sharp contrast with the known O /M/O/M/O (M /W, Re) units that contain M/O double bonds for terminal oxygen, due to the spatial chelating requirement of the long tetradentate Schiff base ligand. ˚ suggests the The completely linear Mo/O/Mo structure together with the relatively short Mo/O distance of 1.8819(7) A involvement of metal /oxygen p bonding. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Oxomolybdates; Linear O/M/O/M/O structures; Schiff base ligands
1. Introduction Coordination complexes of oxomolybdates exhibit varieties of topological structures and are particularly attractive for their application in catalysis [1]. By tuning the protonation ability of donor groups, the coordination of oxomolybdates to multidentate ligands is found to reveal diverse degrees of aggregation and numerous structural types. For the lowest aggregation of a dinuclear structure, bulky multidentate Schiff base ligands play an effective role in space-confining the size of oxomolybdates and many dinuclear oxomolybates have been thus synthesized [2,3]. * Corresponding author. Tel.: /86-591-371 3074; fax: /86-591-371 4946.
In this paper, we report the synthesis and single crystal structure of a new oxo-bridged dinuclear molybdenum complex, [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3] ×/2H2O. To our knowledge, this is the first example of dinuclear oxomolybate complexes containing a nearly linear O /Mo /O /Mo /O moiety, although linear N /Mo /O /Mo/N structures were previously reported [4,5]. Analogous structures were also found in other dinuclear metal complexes, e.g. O /W/ O /W /O in W2O3(CH2CMe3)6 [6], O /Re /O /Re /O in Re2O3L8 [7 /10], Cl /M /O /M /Cl in [M2OCl10]4 (M /W [11], Re [12], Ru [13], Os [14]), and O /Re / O /Re /O in [ReO(salpd)]2O [15] as well as O /Tc /O / Tc /O in m-O[TcO(sal2pn)]2 [16]. Here we shall demonstrate that the present compound reveals novel character in both coordination and bonding.
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 2 7 9 - 3
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2. Experimental 2.1. Synthesis 2.1.1. Materials All materials used in the synthesis were of analytical grade and used as received. 2.1.2. Synthesis of C17H18N2O2 The N ,N ?-bis(salicylidene)-propane-1,3-diamine, hereafter called the tetradentate Schiff base ligand, was prepared according to literature [17]. Salicylaldenhyde (24 ml, 0.22 mol) was added dropwise to a solution of 1,3-diamino propane (8.4 ml, 0.1 mol) in 40 ml benzene. The reaction mixture was then refluxed at 86 8C for 0.5 h. After most of the solvent was removed, the residue was cooled to room temperature followed by the addition of 50 ml methanol. After overnight cooling at 0 8C, yellow precipitate was observed and collected by filtration. The precipitate was washed with 40 ml methanol, filtered off, and dried in vacuo to give 15.02 g of pure C17H18N2O2 (54% yield). Anal. Calc. (%): C, 72.34; H, 6.383; N, 9.929; O, 11.35. Found: C, 72.19; H, 6.199; N, 9.876; O, 12.16%. IR (cm1, KBr): nCH (C6H6) 3050, 3010; nCN 1610; nCH (CH2) 2893, 2870; nOH 3500. 2.1.3. Synthesis of [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3] ×/2H2O The title compound was obtained from a solvothermal reaction of MoCl3 ×/3H2O (0.256 g, 1 mmol), PPh3 (0.262 g, 1 mmol), FeSO4 (0.076 g, 0.5 mmol), and the above-prepared Schiff base (0.705 g, 0.25 mmol) in methanol (15 ml) in a 30 ml Teflon-lined stainless steel autoclave for 96 h at 100 8C. The needle black crystals were separated from the black solution after cooling down to room temperature.
Table 1 Crystal data and structure refinement [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3]×/2H2O Empirical formula Formula weight Temperature (K) ˚ ) Mo Ka Wavelength (A Crystal system Space group ˚) a (A ˚) b (A ˚) c (A b (8) ˚ 3) V (A Z Dcalc (Mg m 3) m (mm1) F (000) Crystal size (mm) u Range (8) Index ranges Reflections collected Independent reflections Reflections observed R1 a wR2 b ˚ 3) rmax (e A ˚ 3) rmin (e A
for
C34H36N4O9Mo2 836.55 293(2) 0.71073 monoclinic P 21/c 8.2070(3) 10.9770(4) 19.5926(1) 92.066(1) 1763.92(9) 2 1.575 0.769 848 0.26 /0.16/0.14 2.08 5/u 5/25.03 /9 5/h 5/7, /135/k 5/10, /13 5/l 5/23 5214 3101 1978 0.0633 0.1506 1.257 /0.796
a
R1 /a½½Fo½/½Fc½/a½Fo½. wR 2/(a(w (F/2o//F/2c )/2)/a(w (F/2o )/2))1/2 (0.0861P )2)], P /(F/2o//2F/2c )//3. b
where
w/1/[(s2(F/2o )//
bonded to carbon were located by geometrical calculation. The hydrogen atoms associated with solvent water molecules were located from difference Fourier maps. All non-hydrogen atoms were refined anisotropically. The final refinement over 223 variables resulted in the agreement factors R1 /0.0633, wR2 /0.1506, S /1.095, (D/s)max /0.001 for 1978 observed reflections. All calculations were performed by using the Siemens SHELXL package [19].
2.2. Crystal structure determination The crystal data of title compound, and the parameters of data collection are summarized in Table 1. A black needle crystal of the title compound with dimensions of 0.26 /0.16 /0.14 mm3 was mounted on the top of a glass fiber. X-ray diffraction data were collected on a Siemens Smart CCD diffractometer equipped with graphite-monochromated Mo Ka radiation (l / ˚ ). A total of 5214 independent reflections 0.71073 A (Rint /0.0455) were collected in the v scan mode in the range of 4.16 5/2u /50.068 at 293 K, of which 1978 reflections with I /2.0s (I ) were considered observed and used in subsequent structural determination and full-matrix least-square refinements. Absorption correction was performed by the SADABS program [18]. The structure was solved by the direct methods and subsequent difference Fourier syntheses. Hydrogen atoms
3. Results and discussion The compound consists of discrete molybdenum complexes and water solvent molecules. According to the charge-balancing requirement for the neutral [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3] complex determined by the single-crystal X-ray diffraction, the formal oxidation state of Mo is /5, which implies the oxidation of the starting material MoCl3 ×/3H2O by atmospheric oxygen in air or dissolved in the solvent. (All starting materials and solvents were handled in air before loaded into an autoclave for solvothermal reactions.) During the reaction, the R /O /H group from the Schiff base ligand was deprotonated and the resulted R / O anion was coordinated to Mo, analogous to the reaction of Schiff bases with other metal ions [20,21].
L.-Z. Cai et al. / Inorganica Chimica Acta 344 (2003) 61 /64
The structure is characterized by the presence of an oxo-bridged or corner-shared double octahedral unit that reveals a completely linear Mo /O /Mo arrangement in a nearly linear O /Mo /O /Mo/O unit, as shown in Fig. 1. Two bulky tetradentate Schiff base ligands, together with three atmospheric oxygen atoms, spatially bind two Mo atoms into a dinuclear complex with the bridged O atom located at an inversion center. To our knowledge, the present compound is the first example featuring a nearly linear O /Mo /O /Mo/O arrangement. Similar structural units were previously reported in the literature, though limited, e.g. N /Mo / O /Mo /N [4,5], O /W/O /W /O [6], O /Re /O /Re /O [7 /10], Cl /M /O /M/Cl (M /W [11], Re [12], Ru [13], Os [14]). In contrast with the known O /M /O /M /O (M /W, Re) units that contain M /O double bonds for terminal oxygen, the present O /Mo /O /Mo /O features a Mo /O single bond at two ends, probably due to the spatial chelating requirement of the tetradentate Schiff base ligand (below). All Mo(V) ions are located in a distorted octahedral coordination environment and are crystallographically equivalent since the dinuclear complex has an inversion center symmetry. Each Schiff base ligand provides four donor sites, two oxygen and two nitrogen, which bind across two Mo atoms non-symmetrically and help to link the complex together. Among six coordinated atoms around each Mo, O1 and O2 are from atmospheric oxygen with O1 serving as a bridging atom and O2 as a terminal atom; N1, N2, O3, and O4 are from Schiff base ligands with O3 acting as the end atoms for the nearly linear O3 /Mo/O1 /Mo /O3 (O1 / Mo /O3 /171.9(1)8, Mo/O1 /Mo /1808). Selected bond lengths and angles were shown in Table 2. The O3 site is usually occupied by a terminal oxygen for small ligands [6 /10]. The lengthy configuration of the present Schiff base ligand is probably responsible for such coordination preference. ˚ , as The Mo /O2 distance is as short as 1.702(5) A commonly observed for terminal oxygen atoms. This bond is of double-bond character in reference with the Mo /O lengths reported in C19H25MoNO6 (1.695(2) / ˚ ), C17H20MoN2O6S2 (1.696(3) /1.700(3) A ˚ ), 1.712(2) A
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Table 2 ˚) Select bond lengths (A and angles [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3]×/2H2O
(8)
for
˚) Bond length (A Mo /O(1) Mo /O(2) Mo /O(3) Mo /O(4) Mo /N(1) Mo /N(2)
1.8816(7) 1.705(5) 2.087(5) 2.031(4) 2.189(7) 2.148(7)
N(1)/C(11) N(1)/C(10) N(2)/C(7) N(2)/C(8) O(4)/C(17)
1.285(9) 1.470(9) 1.297(10) 1.480(10) 1.326(8)
Bond angle (8) Mo /O(1)/Mo a O(1)/Mo/O(3) O(2)/Mo/O(1) O(2)/Mo/O(3) O(1)/Mo/O(3) O(4)/Mo/O(3) O(2)/Mo/O(4) O(1)/Mo/O(4) O(2)/Mo/N(1) O(1)/Mo/N(1)
180 171.86(14) 100.3(2) 87.7(2) 171.86(14) 80.7(2) 166.5(2) 91.57(14) 91.3(2) 95.55(17)
O(4)/Mo/N(1) O(3)/Mo/N(1) N(2)/Mo/N(1) O(2)/Mo/N(2) O(1)/Mo/N(2) O(4)/Mo/N(2) O(3)/Mo/N(2) C(11)/N(1)/Mo C(10)/N(1)/Mo C(17)/O(4)/Mo
81.0(2) 85.7(2) 164.3(2) 100.9(2) 92.03(18) 85.1(2) 84.9(2) 124.3(6) 120.0(5) 129.7(4)
a Symmetry transformations used to generate equivalent atoms: 1/ x , /y , 2/z .
˚) and MoO2{HOC2H4N(C2H4O)2} (1.697(3) /1.721(3) A [22]. The Mo /O3 and Mo /O4 distances are 2.086(6) ˚ , respectively, falling in the range for a and 2.030(4) A typical Mo /O single bond [23]. The Mo /N distances ˚ , in good vary slightly from 2.147(7) to 2.188(7) A agreement with those reported in C68H48MoN4O4 ×/ ˚ ) and [Mo2(NMe2)(OAr2C4H8O [24] (2.129/2.131 A ˚ ) [25]. Of particular 3,5-Me2)6(HNMe2)2] (2.107 /2.236 A ˚, interest is the Mo /O1 bond distance of 1.8819(7) A which lies between the distances for the single-bond and double-bond. Taken into account the completely linear Mo/O /Mo structure, the involvement of metal/oxygen p-bonding character is evident. This is electronically possible since each Mo(V) ion can offer one unpaired d electron, which, together with two p electrons from the central O atom, may form a three-center-four-electron P43 bond and thus shorten the interatomic distance and help to stabilize the structure.
4. Supplementary material
Fig. 1. View of [(C6H4OCHN(CH2)3NHCOC6H4)2Mo2O3]×/2H2O showing the oxo-bridged dinuclear complex (30% ellipsoids). For clarity, the packing water molecules are omitted. Symmetry codes: a: 1/x , /y , 2/z .
Complete crystallographic data (including structure factors) for the structure reported in this paper have been deposited at the Cambridge Crystallographic Data Centre, CCDC No. 184674. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: /44-1223-336-033; e-mail: [email protected]; www: http://www.ccdc.cam.ac.uk).
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L.-Z. Cai et al. / Inorganica Chimica Acta 344 (2003) 61 /64
Acknowledgements This work was supported by the Innovative Project (No. IP01007) and the Introduction of Overseas Elitists Program (No. IB990168), Chinese Academy of Sciences.
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