Hydrothermal Chemistry of Oxomolybdenum-1, 4

Apr 1, 2010 - Research Institute, College of Sciences, University of New Orleans, New Orleans, ... Affiliated with The State University of New York at...
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DOI: 10.1021/cg9014724

Hydrothermal Chemistry of Oxomolybdenum-1,4-Carboxyphenylphosphonates in the Presence of M(II)-Organonitrogen Building Blocks (M(II) = Co, Ni, and Cu).

2010, Vol. 10 2209–2218

Paul DeBurgomaster,† Amanda Aldous,# Hongxue Liu,‡ Charles J. O’Connor,‡ and Jon Zubieta*,† †

Department of Chemistry, Syracuse University, Syracuse, New York 13244, and ‡Advanced Materials Research Institute, College of Sciences, University of New Orleans, New Orleans, Louisiana 70148. # Affiliated with The State University of New York at Potsdam, supported by NSF-REU. Received November 24, 2009

ABSTRACT: Hydrothermal methods were used to prepare a series of materials of the M(II)-L0 /MoxOy/H2O3PC6H4CO2H family, where M(II) = Co, Ni, or Cu and L0 = 2,20 -bipyridine (bpy), o-phenanthroline (phen), or 2,20 :6,200 -terpyridine (terpy). The common {Mo5O15(O3PR)2}4- cluster provided a building block for the one-dimensional (1D) structure of [{Cu(bpy)(H2O)}3{O2CC6H4PO3}2Mo5O15] 3 4.5H2O (1 3 4.5H2O). While the pentamolybdate cluster was observed for [Co(terpy)2][Mo5O14(OH){HO2CC6H4PO3}2] 3 5.25H2O (5 3 5.25H2O) and [Ni(phen)2(H2O)2][Ni(phen)2Mo5O15{HO2CC6H4PO3}2] 3 2H2O (6 3 2H2O), the clusters are present as discrete molecular anions. In contrast, the 1D structure of [Cu(bpy){O3PC6H4CO2H}Mo2O6] (2) exhibits a {Mo2O6}n2nþ chain, decorated with phosphonate and {Cu(phen)}2þ groups. The three-dimensional (3D) structure of [{Cu(phen)}2Mo2O5{O3PC6H4CO2}2] 3 H2O (3 3 H2O) is constructed from {Mo2O5}2þ binuclear units, linked into chains through bridging {Cu(phen)}2þ groups; the chains are in turn connected through the dipodal carboxyphenylphosphonate ligands to produce the overall 3D connectivity. Fluoride incorporation in [Cu(bpy){O3PC6H4CO2}MoO2F] (4) results in mononuclear {MoO5F} octahedra linked through {Cu(bpy)}2þ units and the organophosphonate ligand into a chain. The molecular structure of the second polyoxofluoromolybdate species [Co(bpy)3]2[Mo12F4O34(H2O)4{O3PC6H4CO2H}2] 3 4H2O (7 3 4H2O) consists of discrete {Co(bpy)3}2þ cations and [Mo12F4O34(H2O)4{O3PC6H4CO2H}2]4- anionic clusters. The unique dodecamolybdate unit of 7 consists of two {Mo6F2O17(H2O)2(O3PR)2}2- subunits fused through two bridging oxo-groups.

The extensive contemporary interest in metal-organophosphonate chemistry1-7 reflects their role as prototypical organic-inorganic hybrid materials that exhibit a range of structures, including molecular clusters, chains, networks, and three-dimensional (3D) frameworks. The structural diversity is reflected in a range of physical properties giving rise to applications in catalysis, proton conductivity, ion exchange, intercalation chemistry, and photochemistry.8-15 A significant subclass of these materials is the oxometalorganophosphonates, represented by the oxovanadium- and oxomolybdenum-organophosphonates.16-43 Of particular interest is the design of such organic-inorganic oxide materials with diphosphonate ligands, HO3P-tether-PO3H2, a family of dipodal ligands that characteristically provide “pillared layer” structures with a variety of metals, including oxovanadates (Scheme 1). These are 3D frameworks with alternating inorganic and organic domains. The separations between inorganic layers may be varied by modification of the tether lengths, and the interlamellar domain may be sculpted by appropriate functionalization of the organic linkers.20,44 In contrast, the oxomolybdate chemistry with diphosphonate ligands is characterized by the incorporation of discrete polyoxomolybdate-organophosphonate clusters as building blocks, most notably the {Mo5O15(O3PR)2}4- cluster (Scheme 2). The one-dimensional (1D) {Mo5O15(O3PR)2}n4nchains can undergo spatial expansion through appropriate secondary-metal ligand complexes, such as the dipodal

*Corresponding author. E-mail: [email protected]. r 2010 American Chemical Society

{Cu2(tpyprz)}4þ, to provide two- and three-dimensional (2D and 3D) materials (tpyprz = tetrapyridylpyrazine). This strategy represents a common approach for the preparation of organic-inorganic hybrid materials, one that exploits dipodal ligands, such as 4,40 -bipyridine, dicarboxylic acids, or diphosphonates as the organic tethers. However, a related type of dipodal ligand is one that exhibits different donor group termini, such as 1,4-carboxy-phenylphosphonic acid, H2O3PC6H4CO2H. The incorporation of different donor groups offers the potential for designing materials incorporating two different metals with different donor group preferences. While two-component systems, such as the well-documented metal organic frameworks,45 have revealed some design principles, the chemistry of three-component systems remains relatively unexplored. In the specific case of the oxomolybdate-based materials, our naive expectation was that structural expansion of the anticipated {Mo5O15(O3PR)2}4- cluster would occur through carboxylate coordination of the secondary metal (Scheme 3). While a “conventional” 1D structure with the pentamolybdophosphonate building block was observed for [{Cu(bpy)H2O}3{O2CC6H4PO3}2Mo5O15] 3 4.5H2O (1 3 4.5H2O), the structural chemistry of the M(II)-ligand/MoxOy/{O3PC6H4CO2}3-, M(II) = Co, Ni, or Cu and 2,20 -bipyridine (bpy), system proved more complex than anticipated, reflecting factors such as the hydrothermal conditions, the coordination preferences of the secondary metal, and incorporation of fluoride anions. A preliminary survey of the structural chemistry of this class of materials has provided, in addition to the Published on Web 04/01/2010

pubs.acs.org/crystal

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Crystal Growth & Design, Vol. 10, No. 5, 2010 Scheme 1

DeBurgomaster et al. Scheme 3

and [Co(bpy)3]2[Mo12F4O34(H2O)4(O3PC6H4CO2H)2] 3 4H2O (7 3 4H2O), [2, 20 -bipyridine (bpy), o-phenanthroline (phen), or 2,20 :6,200 -terpyridine (terpy)]. Experimental Section

Scheme 2

Examples of the construction of (a) a two-dimensional network and (b) a three-dimensional framework from the building blocks.

1D 1 3 4H2O, the 1D [Cu(bpy){O3PC6H4CO2H}Mo2O6] (2), the 3D [{Cu(phen)}2Mo2O5{O3PC6H4CO2}2] 3 H2O (3 3 H2O), the oxyfluoromolybdate chain [Cu(bpy){O3PC6H4CO2}MoO2F] (4) and the molecular species [Co(terpy)2][Mo5O14(OH){HO2CC6H4PO3}2] 3 5.25H2O (5 3 5.25H2O), [Ni(phen)2(H2O)2][Ni(phen)2Mo5O15{HO2CC6H4PO3}2] 3 2H2O (6 3 2H2O),

General Considerations. All chemicals were used as obtained without further purification: molybdenum(VI) oxide, copper(II) acetate hydrate, cobalt(II) acetate hydrate, nickel(II) acetate hydrate, 2,20 -dipyridyl, 1,10-phenanthroline, 2,20 :6,200 terpyridine, glacial acetic acid, and hydrofluoric acid (48-51%) were purchased from Aldrich. The ligand 1,4-carboxy-phenyl phosphonic acid was prepared according to the literature method.46 All hydrothermal syntheses were carried out in 23 mL poly(tetrafluoroethylene) lined stainless steel containers under autogenous pressure. The reactants were stirred briefly and initial pH was measured before heating. Water was distilled above 3.0 M Ω in-house using a Barnstead model 525 Biopure Distilled Water Center. The initial and final pH of the reaction was measured using Hydrion pH sticks. Synthesis of [{Cu(bpy)H2O}3{O2CC6H4PO3}2Mo5O15] 3 4.5H2O (1 3 4.5H2O). A mixture of MoO3 (0.204 g, 1.42 mmol), cupric acetate hydrate (0.091 g, 0.50 mmol), 2,20 bipyridine (0.068 g, 0.44 mmol), 1,4-carboxy-phenyl phosphonic acid (0.052 g, 0.26 mmol), and H2O (10.00 mL, 554.94 mmol) in the mole ratio 5.41:1.91:1.66:1.00:2118 was stirred briefly before heating to 120 °C for 48 h. Initial and final pH values of 5.0 and 2.0 were recorded. Blue blocks of 1 3 4.5H2O suitable for X-ray diffraction were isolated in 35% yield. IR (KBr pellet, cm-1): 3434(b), 3081(m), 1605(m), 1576(w), 1530(m), 1498(w), 1474(w), 1445(m), 1400(m), 1316(w), 1129(m), 1057(m), 1033(m), 976(m), 930(s), 913(m), 773(m), 732(m), 691(s), 603(w), 548(w). Synthesis of [Cu(bpy){O3PC6H4CO2H}Mo2O6] (2). A stirred solution of MoO3 (0.200 g, 1.39 mmol), cupric acetate hydrate (0.089 g, 0.49 mmol), 2,20 bipyridine (0.068 g, 0.44 mmol), 1,4carboxy-phenyl phosphonic acid (0.046 g, 0.23 mmol), and H2O (10.00 mL, 554.94 mmol) in the mole ratio 6.09:2.15:1.91:1.00:2434 was heated at 150 °C for 48 h (initial and final pH: 5.0 and 2.0). Green blocks of 2 suitable for X-ray diffraction were isolated in 40% yield. IR (KBr pellet, cm-1): 3436(b), 3104(m), 1600(m), 1536(m), 1445(m), 1399(m), 1313(w), 1251(w), 1147(m), 1094(m), 1029(w), 975(s), 932(s), 881(s), 772(s), 727(m), 628(m), 552(s), 508(m). Synthesis of [{Cu(phen)}2Mo2O5{O3PC6H4CO2}2] 3 H2O (3 3 H2O). A solution of MoO3 (0.203 g, 1.41 mmol), cupric acetate hydrate (0.091 g, 0.50 mmol), 1,10 phenanthroline (0.087 g, 0.48 mmol), 1, 4-carboxy-phenyl phosphonic acid (0.050 g, 0.25 mmol), H2O (10.00 mL, 554.94 mmol), and acetic acid (0.200 mL, 3.49 mmol) in the mole ratio 5.91:2.03:1.96:1.00:2247:14.14 was stirred and heated to 180 °C for 5 days. Blue plates of 3 3 H2O were collected in 20% yield (initial pH: 3.0, final pH: 3.0). IR (KBr pellet, cm-1): 3432(b), 1597(m), 1564(m), 1519(m), 1427(w), 1407(m), 1169(s), 1123(w), 1064(m), 997(m), 934(m), 892(m), 846(m), 778(w), 758(m), 728(w), 599(w), 565(w), 499(w). Synthesis of [Cu(bpy){O3PC6H4CO2}MoO2F] (4). The reaction of MoO3 (0.203 g, 1.41 mmol), cupric acetate hydrate (0.090 g, 0.50 mmol), 2,20 bipyridine (0.066 g, 0.42 mmol), 1,4-carboxy-phenyl phosphonic acid (0.054 g, 0.27 mmol), and H2O (10.00 mL, 554.94 mmol) in the mole ratio 5.28:1.88:1.58:1.00:2078 at 200 °C for 48 h produced blue blocks of 4 in 50% yield (initial pH: 2.0, final pH: 1.0). IR (KBr pellet, cm-1): 3467(b), 3118(m), 3086(m), 1599(m), 1575(w), 1501(m), 1439(s), 1313(w), 1255(w), 1190(s), 1060(s), 984(m), 951(m), 931(m), 897(m), 866(m), 577(s), 559(m), 497(m), 463(w). Synthesis of [Co(terpy)2][Mo5O14(OH){HO2CC6H4PO3}2] 3 5.25H2O (5 3 5.25H2O). MoO3 (0.197 g, 1.37 mmol), cobalt(II) acetate hydrate (0.107 g, 0.43 mmol), 2,20 :6,200 terpyridine (0.047 g, 0.20 mmol), 1, 4-carboxy-phenyl phosphonic acid (0.048 g, 0.24 mmol), H2O

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Table 1. Summary of Crystallographic Data for the Structures of [{Cu(bpy)(H2O)]3(O2CC6H4PO3)2Mo5O15] 3 4.5H2O (1 3 4.5H2O), [Cu(bpy)(O3PC6H4CO2H)Mo2O6] (2), [{Cu(phen)}2Mo2O5(O3PC6H4CO2)2] 3 H2O (3 3 H2O), [Cu(bpy)(O3PC6H4CO2)MoO2F] (4), [Co(terpy)2][Mo5O14(OH)(O3PC6H4CO2H)2] 3 5.25H2O (5 3 5.25H2O), [Ni(phen)2(H2O)2][{Ni(phen)2}Mo5O15(O3PC6H4CO2H)2] 3 2H2O (6 3 2H2O), [Co(bpy)3]2[Mo12F4O34(H2O)4(O3PC6H4CO2H)2] 3 4H2O (7 3 4H2O)a

empirical formula formula weight crystal system space group a (A˚) b (A˚) c (A˚) R (°) β (°) γ (°) V (A˚3) Z Dcalc (g cm-3) μ (mm-1) T (K) wavelength R1 wR2

1

2

3

[{Cu(bpy)H2O}3(O2CC6H4PO3)2Mo5O15] 3 4.5H2O C44H47Cu3Mo5N6O32.50P2 1912.14 monoclinic Cc 17.1352(13) 17.8987(14) 18.6980(15) 90 93.748(2) 90 5722.4(8) 4 2.219 2.312 90(2) 0.71073 0.0358 0.0802

[Cu(bpy)(O3PC6H4CO2H)Mo2O6] C17H13CuMo2N2O11P 707.68 monoclinic P2(1)/n 14.1898(18) 7.6767(10) 19.200(2) 90 97.868(2) 90 2071.8(5) 4 2.269 2.354 90(2) 0.71073 0.0256 0.0597

[{Cu(phen)}2Mo2O5(O3PC6H4CO2)2] 3 H2O C19H14CuMoN2O8P 1177.54 monoclinic C2/c 15.8199(14) 18.6497(17) 13.9062(13) 90 97.240(2) 90 4070.1(6) 8 1.922 1.792 90(2) 0.71073 0.0310 0.0676

4

5

6

7

[Cu(bpy)(O3PC6H4CO2)MoO2F] C17H12CuFMoN2O7P 565.74 triclinic P1 8.3104(12) 9.9495(14) 11.0998(15) 92.146(2) 102.656(2) 93.899(2) 892.1(2) 2 2.106 2.043 90(2) 0.71073 0.0245 0.0576

[Co(terpy)2][Mo5O14(OH) (HO2CC6H4PO3)2] 3 5.25H2O C44H44.50Co Mo5N6O30.25P2 1741.93 monoclinic P2(1)/c 14.9260(10) 16.8088(11) 22.4843(15) 90 99.3130(10) 90 5566.7(6) 4 2.078 1.542 90(2) 0.71073 0.0320 0.0671

[Ni(phen)2(H2O)2][{Ni(phen)2}Mo5O15 (HO2CC6H4PO3)2] 3 2H2O C62H50Mo5N8Ni2O29P2 2030.16 monoclinic P2(1)/n 15.0268(8) 22.5898(11) 20.1845(10) 90 94.1810(10) 90 6833.4(6) 4 1.973 1.569 90(2) 0.71073 0.0403 0.0804

[Co(bpy)3]2[Mo12F4O34(H2O)4{O3P(C6H4)CO2H}2] 3 4H20 C37H35CoF2Mo6N6O26 P 1683.25 triclinic P1 12.3593(11) 12.4558(11) 16.5780(14) 69.636(2) 80.106(2) 89.840(2) 2352.5(4) 2 2.376 2.035 90(2) 0.71073 0.0339 0.0790

a

R1 =

P P P P |Fo| - |Fc|/ |Fo|, wR2 = { [w(Fo2 - Fc2)2)2]/ [w(Fo2)2]}1/2.

(10.00 mL, 554.94 mmol), and HF (0.200 mL, 5.80 mmol) in the mole ratio 6.81:2.14:1.00:1.18:2761:28.86 were combined and briefly stirred before heating to 120 °C for 48 h. The initial and final pH values were 2.0 and 2.0, respectively. Orange blocks of 5 3 5.25H2O suitable for X-ray diffraction were isolated in 65% yield. IR (KBr pellet, cm-1): 3545(b), 1692(m), 1604(m), 1568(w), 1499(w), 1448(s), 1415(m), 1314(m), 1266(m), 1143(w), 1114(w), 1067(s), 993(m), 929(s), 846(m), 803(m), 767(m), 672(s), 516(w). Synthesis of [Ni(phen)2(H2O)2][Ni(phen)2Mo5O15{HO2CC6H4PO3}2] 3 2H2O (6 3 2H2O). The reaction of MoO3 (0.151 g, 1.05 mmol), nickel(II) acetate hydrate (0.148 g, 0.60 mmol), 1,10 phenanthroline (0.085 g, 0.43 mmol), 1,4-carboxy-phenyl phosphonic acid (0.045 g, 0.22 mmol), H2O (5.00 mL, 277.47 mmol), and HF (0.200 mL, 5.80 mmol) with the mole ratio 4.70:2.67:1.93:1.00:1244:26.01 was stirred briefly before heating to 120 °C for 72 h. Initial and final pH values of 2.0 and 1.0, respectively, were recorded. Purple blocks of 6 3 2H2O suitable for X-ray diffraction were isolated in 80% yield. IR (KBr pellet, cm-1): 3340(b), 1699(s), 1625(m), 1585(w), 1516(m), 1425(s), 1343(w), 1274(m), 1145(m), 1119(m), 1062(s), 978(s), 902(m), 862(m), 771(w), 689(s), 600(m), 562(w). Synthesis of [Co(bipy)3]2[Mo12F4O34(H2O)4{O3PC6H4CO2H}2] 3 4H2O (7 3 4H2O). A mixture of MoO3 (0.200 g, 1.39 mmol), cobalt(II) acetate hydrate (0.107 g, 0.43 mmol), 2,20 bipyridine (0.067 g, 0.43 mmol), 1,4-carboxy-phenyl phosphonic acid (0.051 g, 0.25 mmol),

H2O (10.00 mL, 554.94 mmol), and HF (0.200 mL, 5.80 mmol) with the mole ratio 5.51:1.71:1.70:1.00:2202:23.02 was combined. The reaction was stirred briefly before heating to 150 °C for 48 h with an initial and final pH of 2.0 and 1.0, respectively. Yellow blocks of 7 3 4H2O were isolated in 80% yield and were suitable for X-ray diffraction. IR (KBr pellet, cm-1): 3545(b), 1692(m), 1604(m), 1500(w), 1448(s), 1314(m), 1266(m), 1143(w), 1114(w), 1067(s), 993(m), 929(s), 803(m), 767(m), 672(s). X-ray Crystallography. Structural measurements were performed on a Bruker-AXS SMART-CCD diffractometer at low temperature (90 K) using graphite-monochromated Mo KR radiation (λMo KR = 0.71073 A˚).47 The data were corrected for Lorentz and polarization effects and absorption using SADABS.48 The structures were solved by direct methods. All non-hydrogen atoms were refined anisotropically. After all of the non-hydrogen atoms were located, the model was refined against F2, initially using isotropic and later anisotropic thermal displacement parameters. Hydrogen atoms were introduced in calculated positions and refined isotropically. Neutral atom scattering coefficients and anomalous dispersion corrections were taken from the International Tables, Vol. C. All calculations were performed using SHELXTL crystallographic software packages.49,50 Crystallographic details have been summarized in Table 1. Atomic positional parameters, full tables of bond lengths and angles, and anisotropic temperature factors are available in

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Table 2. Selected Bond Length Ranges (A˚) for the Compounds of This Studya Mo-Ot Mo-Odb Mo-OH Mo-Ophosphonate Mo-Ocarboxylate Mo-Oaqua Mo-Ft Mo-Fb M(II)-Ooxo M(II)-Ocarboxylate M(II)-Ophosphonate M(II)-Oaqua M(II)-N

1

2

3

1.694(4)-1.737(4) 1.902(4)-1.971(4)

1.698(2)-1.750(2) 1.863(2)-1.940(2)

1.702(2)-1.719(2) 1.893(2)

2.164(4)-2.436(4)

2.194(2)-2.417(2)

2.008(2) 2.196(2)-2.281(2)

2.281(4)-2.310(4) 1.958(4) 1.986(4) 1.969(4)-1.996(4) 1.992(6)-2.002(6)

1.958(2)-2.188(2)

2.265(2)

1.932(2)

1.910(2)-1.919(2)

1.983(2)-1.997(2)

2.007(2)-2.016(2)

4

5

6

7

1.689(2)-1.714(2)

1.696(2)-1.729(2) 1.861(2)-1.952(2) 2.010(2)-2.052(2) 2.185(2)-2.558(2)

1.698(2)-1.741(2) 1.877(2)-1.927(2)

1.696(3)-1.719(3) 1.886(2)-1.942(2)

2.231(2)-2.474(2)

2.296(3)-2.363(3)

1.967(2) 2.229(2)-2.257(2)

2.331(2)-2.380(2) 1.750(3) 2.201(2)-2.265(2)

1.916(2) 2.329(2)

2.105(2)

1.917(2)-1.934(2)

2.113(2)

1.994(2)-1.998(2) a

1.865(2)-1.950(2)

2.058(3)-2.099(3)

1.920(3)-1.941(3)

Abbreviations: Ot: terminal oxo-group; Odb: doubly bridging oxo-group, Mo-O-Mo; Ft: terminal fluoride; Fb: bridging fluoride, Mo-F-Mo.

Table 3. Summary of Structural Features of the Compounds of This Study name

dimensionality 1-D

[{Cu(bpy)(H2O)}3(O2CC6H4PO3)2Mo5O15] (1) [Cu(bpy)(O3PC6H4CO2H)Mo2O6} (2)

1-D

[{Cu(phen)}2Mo2O5(O3PC6H4CO2)2] (3)

3-D

[Cu(bpy)(O3PC6H4CO2)MoO2F] (4) [Co(terpy)2][Mo5O14(OH)(HO2CC6H4PO3)2] (5) [Ni(phen)2(H2O)2][Ni(phen)2Mo5O15(HO2CC6H4PO3)2] (6) [Co(bpy)3]2[Mo12F4O34(H2O)4(O3PC6H4CO2H)2] (7)

1-D molecular molecular molecular

Supporting Information. Selected bond lengths and angles are given in Table 2.

Results and Discussion Synthesis and Infrared Spectroscopy. The techniques of hydrothermal synthesis are now routinely used for the preparation of metal oxides and organic-inorganic composite materials.51-57 Product composition may depend on several critical factors, including pH of the hydrothermal medium, temperature, and hence pressure, the presence of structuredirection cations, and the use of mineralizers or solubilizing reagents. For compounds 1 and 2, the reaction mixture consisted of MoO3 and 1,4-carboxyphenylphosphonic acid, Cu(CH3CO2)2 3 H2O, and the appropriate organonitrogen ligand. In the case of 3, acetic acid was required for crystal formation. The introduction of HF was required for crystallization in the preparations of compounds 4-7. For compounds 4 and 7, fluoride incorporation was observed. While oxyfluorovanadates are quite common and are an expanding class of materials,58 polyoxofluoromolybdates

inorganic unit {Mo5O15(O3PR)2}4- clusters decorated with {Cu(bpy)(H2O)}2þ groups {Mo2O6}n chains decorated with {Cu(bpy)}2þ groups and {O3PR} tetrahedra Cu-molybdophosphonate chains; binuclear units of corner-sharing {MoO6} octahedra binuclear Cu-oxofluoromolybdate units {Mo5O14(OH)(O3PR)}3- clusters, discrete {Co(terpy)2}2þ cations {Mo5O15(O3PR)2}4- clusters decorated with a {Ni(phen)2}2þ group, discrete {Ni(phen)2(H2O)2þ cations {Mo12F4O34(H2O)4(O3PC6H4CO2H)2}4- cluster, discrete {Co(bpy)3}2þ cations

remain relatively unexplored.58-64 Compound 7 is a unique example of dodecamolybdate incorporating fluoride ligands. It is also curious that the cobalt of the {Co(terpy)2}3þ cation of 5 has been oxidized to the þ3 oxidation state. While this is a unique example for this series of compounds, oxidation of Co(II) to Co(III) in the cationic component of a phosphomolydate had been previously described for [Co(bpy)3][Mo5O14(OH){O3P(CH2)3PO3}],38 a material exhibiting a similar {Mo5O14(OH)(O3PR)2}3- building unit to that of 5. The infrared spectra of the compounds exhibit two medium to strong bands in the 890-935 cm-1 region assigned to the symmetric and antisymmetric stretching frequencies of the cis-{MoO2} groups. X-ray Structures. As shown in Figure 1, the structure of [{Cu(bpy)(H2O)}3{O2CC6H4PO3}2Mo5O15] 3 4.5H2O (1 3 4.5H2O) is one-dimensional. The structure is constructed from the common pentamolybdate clusters {Mo5O15(O3PR)2}4- as building blocks. The cluster consists of a ring of five {MoO6} octahedra linked through four edge-sharing and one cornersharing interactions. The ring is capped on either face by

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Figure 1. A polyhedral representation of the structure of [{Cu(bpy)(H2O)}3(O2CC6H4PO3)2Mo5O15] (1). Bipyridyl carbon atoms have been omitted for clarity. Color scheme: molybdenum, green octahedra; copper, blue polyhedra; phosphorus, yellow tetrahedra; oxygen, red spheres; nitrogen, light blue spheres; carbon, black spheres. The color scheme is used throughout.

Figure 2. Polyhedral view of the one-dimensional structure of [{Cu(bpy)(HO2CC6H4PO3)Mo2O6] (2). The bipyridyl carbon atoms have been omitted for clarity.

tetrahedral {O3PR}2- groups, each sharing three oxygen vertices with the ring. Each pentamolybdate ring is decorated by three {Cu(bpy)(H2O)}2þ groups. Two of these are also coordinated to carboxylate oxygens from carboxyphenylphosphonate ligands whose -PO3 termini bond to adjacent pentamolybdate clusters in the chain. These Cu(II) sites exhibit distorted “4 þ 1” square pyramidal geometries with the bpy nitrogen donors, the aqua ligand and a carboxylate oxygen donor in the basal plane, with a terminal molybdenum oxo-group in the apical position. Curiously, the third Cu(II) center exhibits distorted square planar geometry {CuN2O2} through bonding to the bpy nitrogen donors, an aqua ligand and a phosphonate oxygen that serves as a Cu-O-Mo bridge. This {Cu(bpy)H2O}2þ group nestles in a cavity formed by two adjacent {Mo5O15(O3PR)4- clusters and the two {Cu(bpy)(H2O)(O2CC6H4PO3)} tethers linking them. While the structure of 1 conforms to the naively anticipated structural prototype, the 1D structure of [Cu(bpy)(O3PC6H4CO2H)Mo2O6] (2) is constructed from a {Mo2O6}n chain of molybdenum octahedra, decorated with {Cu(bpy)}2þ groups and (O3PC6H4CO2H)2- ligands (Figure 2). The chains consist of binuclear units of face-sharing {MoO6} octahedra connected through corner-sharing interactions into a molybdate chain. Each phosphonate terminus of the 1,4-carboxyphenylphosphonate contributes a doubly bridging oxygen donor to each of two adjacent binuclear molybdate units of the chain. The third oxygen bonds to a {Cu(bpy)}2þ unit. The Cu(II) sites exhibit the common “4 þ 1” square pyramidal geometry with the bpy nitrogen donors, a phosphonate oxygen and a molybdate oxo-group in the basal

Figure 3. (a) A view of the three-dimensional structure of [{Cu(phen)}2Mo2O5(O3PC6H4CO2)2] (3) in the ab plane; (b) a view of the structure in the bc plane with bipyridyl carbons omitted; (c) a view down an inorganic chains axis showing the dispositions of the 1,4-carboxyphenylphosphonate groups.

plane and an apical oxo-group from a neighboring binuclear molybdate unit. The phenylcarboxylate moieties project outward from the chain at an angle of ca. 79° with respect to the chain axis. The carboxylate group is protonated, with C-O(H) and CdO distances of 1.336(3) and 1.202(4) A˚, respectively. The 3D structure of [{Cu(phen)}2Mo2O5(O3PC6H4CO2)2] 3 H2O (3 3 H2O) is shown in Figure 3a. In this case, the molybdate building block is a binuclear unit of corner-sharing {MoO6} octahedra. These binuclear units are linked through Cu(II) square pyramids and phosphonate tetrahedra to produce a 1D polyhedral chain. Each Mo(VI) site has an uncoordinated terminal oxogroup, an oxo-group bridging to a copper site, an oxo-group bridging to the other molybdenum of the binuclear unit, a phosphonate oxygen donor, and two carboxylate oxygen

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Figure 4. Polyhedral representation of the one-dimensional structure of [{Cu(bpy)}(O3PC6H4CO2)MoO2F] (4) Color scheme: fluorine, green spheres.

donors from different ligands. Consequently, there is a {Mo2(O2CR)2} bridging unit associated with each binuclear building block. Each Cu(II) center is characterized by an apical oxo-group linking to a binuclear molybdate site, and by a basal plane defined by the bpy nitrogen donors and phosphonate oxygen donors from two phosphonate groups. As a result, each {O3PR} terminus bonds to a molybdenum and to two copper sites. The 1,4-carboxyphenylphosphonate ligands project from each copper-phosphomolybdate chain so as to link the chain to four adjacent chains (Figure 3b). The chains project at relative angles of ca. 56° and 145° to produce the overall 3D connectivity. While [Cu(bpy)(O3PC6H4CO2)MoO2F] (4) (Figure 4) is a 1D structure, the incorporation of fluoride into the molybdenum coordination sphere results in a structure quite distinct from those of the 1D materials 1 and 2. In this instance, there is a {MoO5F} octahedral unit with no Mo-O-Mo bridges. The building block is a hexanuclear unit of cornersharing molybdenum octahedra, copper square pyramids, and phosphorus tetrahedra. The coordination geometry at the molybdenum is defined by a terminal oxo-group, an oxogroup bridging to the copper site, a phosphonate oxygen donor, the oxygen donors from a chelating carboxylate group, and a terminal fluoride. The square pyramidal Cu(II) center bridges the molybdenum through an oxo-group and two phosphonate tetrahedra through oxygen donors. The remaining two coordination sites are occupied by the bpy nitrogen donors. Each 1,4-carboxyphenylphosphonate ligand bridges a molybdenum and two copper sites at the {O3PR} terminus and links to an adjacent copper-molybdophosphonate cluster through the phenylcarboxylate group. The remaining structures of the series are molecular species. The structure of [Co(terpy)2][Mo5O14(OH)(O3PC6H4CO2H)2] 3 5.25H2O (5 3 5.25H2O) consists of discrete {Co(terpy)2}3þ cations, {Mo5O14(OH)(O3PC6H4CO2H)2}3cluster anions, and water molecules of crystallization. The structure of the anion, shown in Figure 5, is grossly similar to those of well-documented pentamolybdate-phosphate and -phosphonate clusters, for example, [Mo5O15(O3POH)2]4and [Mo5O15(O3PCH3)2]4-.66,67 The major structural difference is the protonation of one of the doubly bridging oxo-groups. The protonation site is unambiguously identified as O20 from valence sum calculations68 and from a comparison of the molybdenum-doubly bridging bond length of the structure (Mo-O20: 2.031(2) A˚, ave; Mo-O for all other doubly bridging oxo-groups: 1.910(2) A˚, ave). Charge balance considerations require that the cation be {Co(terpy)2}3þ with the cobalt having undergone oxidation to the þ3 oxidation state. The bond distances bear out this observation. The average Co-N bond distance of the {Co(terpy)2}3þ cation of 5 is 1.920(3) A˚, a value similar to that of 1.93(1) A˚ for the Co(III) species {Co(bpy)3}3þ.69

Figure 5. A ball and stick representation of the structure of the molecular anionic cluster {Mo5O14(OH)(O3PC6H4CO2H)2}3- of 5. Color scheme: hydrogen, pink spheres.

Figure 6. Ball and stick representation of the structure of the molecular anionic cluster [{Ni(phen)2}Mo5O15(O3PC6H4CO2H)2]2of 6. Color scheme: nickel, light green sphere.

In contrast, the Co(II) distances would be expected to be significantly longer, as observed for {Co(bpy)3}2þ, which has an average Co-N bond distance of 2.130(5) A˚.70 It should be noted that [Co(bpy)3][Mo5O14(OH){O3P(CH2)3PO3}],38 a material with a similar phosphomolybdate building block to 5, also contains a Co(III) cation. The material was originally formulated as [Co(bpy)3][Mo5O14(OH){HO3P(CH2)3PO3}], with a Co(II) cation, but this is clearly incorrect. The average Co-N bond distance for this latter compound is 1.940(4) A˚, a value consistent with the Co(III) formulation. The carboxylate groups of the 1,4-carboxyphenylphosphonate ligands are also protonated, a feature confirmed by the average C-O bond lengths of 1.209(4) and 1.326(4) A˚ for the CdO and C-O(H) bonds. The structure of [Ni(phen)2(H2O)2][Ni(phen)2Mo5O15(O3PC6H4CO2H)2] 3 2H2O (6 3 2H2O) also consists of molecular cations and anions with water molecules of crystallization. While the anionic cluster exhibits the common pentamolybdate building unit, in this case, the {Mo5O15(O3PR)2}4- cluster is decorated with a {Ni(phen)2}2þ unit as shown in Figure 6. The Ni(II) site displays distorted octahedral geometry defined by the four nitrogen donors of two phenanthroline ligands, an oxo-group bridging to a molybdenum site of the cluster and a phosphonate oxygen donor bridging the nickel and a molybdenum site. In a fashion previously described for compound 5,

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Figure 8. Thermal gravimetric profile for compound 6 in the 25-1000 °C range.

Figure 7. (a) Ball-and-stick view of the structure of the molecular anion {Mo12F4O34(H2O)4(O3PC6H4CO2H)2}4- of 7. The aqua ligands are shown as red spheres with black borders; (b) a polyhedral view of the structure of the polyoxofluoromolybdophosphonate cluster of 7.

the carboxylate groups are protonated to provide charge compensation. The most unusual molecular anion occurs in the structure of [Co(bpy)3]2[Mo12F4O34(H2O)4 (O3PC6H4CO2H)2] 3 4H2O (7 3 4H2O). The structure consists of discrete {Co(bpy)3}2þ cations, {Mo12F4O34(H2O)4(O3PC6H4CO2H)2}4- cluster anions, and water molecules of crystallization. As shown in Figure 7, the structure of the molecular anion is constructed from edge- and corner-sharing {MoO6}, {MoO5F}, and {MoO4F2} octahedra. The cluster sits on a crystallographic inversion center and consequently consists of two equivalent hexamolybdate units linked through two corner-sharing interactions. Each hexanuclear unit contains a ring of molybdenum octahedra linked through four edge-sharing and two corner-sharing interactions and capped by a 1,4-carboxyphenylphosphonate ligand. Each oxygen donor of the phosphonate ligand bridges two molybdenum sites of the ring. Two oxo-groups have been replaced by fluoride anions. One is terminal, while the second adopts a doubly bridging mode. A curious feature of the structure is the presence of two terminal aqua ligands which are unambiguously identified by their bond lengths: Mo-O(H2) of 2.356(3) A˚, ave., in contrast to ModO distances of 1.710(3)A˚, ave. Four molybdate sites exhibit cis-terminal oxo-groups, and one site possesses a cis-terminal oxo-fluoro configuration. The final molybdenum site exhibits a terminal aqua ligand, four doubly bridging oxo-groups, and a bond to a phosphonate oxygen donor. Consequently, within the {Mo12F4O34(H2O)4(O3PC6H4CO2H)2}4- cluster there are 18 terminal oxogroups, 4 terminal aqua ligands, 2 terminal fluorides, 12 bonds to phosphonate oxygen donors, 2 doubly bridging fluorides, and 16 doubly bridging oxo-groups.

The anionic cluster of 7 is unique and affords a new example of the growing class of polyoxofluoromolybdate clusters.59-65 However, the hexanuclear subunit has precedents in [{Cu(terpy)}2Mo6O17(H2O)(O3PCH2NH2CH2PO3)2],71 [{Co2(tpyprz)(H2O)2}Mo6O18{O3PCCH2)5PO3}] 3 2H2O,38 and in the organoarsonates of the type {Mo6O18(O3AsR)2}4-.72 Several observations present themselves with respect to the structural chemistry of this limited series of M(II)organonitrogen ligand/MoxOyFz/H2O3PC6H4CO2H materials (Table 3). The first is that while the unsymmetrical 1,4carboxyphenylphosphonate ligand can provide a linker for constructing 1D structures with alternating pentamolybdate and metal-organic cations nodes, the carboxylate groups are not as effective in this respect as a second phosphonate unit or polyazaheterocyclic groups. In fact, in compounds 2 and 5-7, the carboxylate groups are protonated and nonbonding. In structures 3 and 4, the carboxylate groups chelate molybdenum sites rather than copper sites, resulting in novel and unanticipated structures. When Cu(II) is replaced by Co(II) and Ni(II), there is a tendency to form isolated {M(II)(ligand)x}2þ cations, rather than participation of the M(II) site in structural expansion. Fluoride incorporation into metal oxide structures under hydrothermal conditions is quite common for the oxyfluorovanadates, but, as yet, an unexplored domain of the molybdates. As the field lacks a sufficient structural database, no structural systematic has yet evolved for the polyoxofluoromolybdates. For example, terminal, doubly bridging and quadruply bridging fluorides groups have been observed, and in the case of compound 7 both terminal and doubly bridging in the same structure. The substitution patterns appear random at the time but presumably reflect electronic requirements of the cluster. Likewise, the Mo:F and oxo group:F ratios of the MoxOyFz clusters vary considerably. The Mo:F ratios fall in the range 8:1 for [Mo16O53F2]6- to 1:3 for [Mo3O4F9]5-, while the oxo group:F ratios vary from 26.5:1 in [Mo16O53F2]6- to 1:2.25 in [Mo3O4F9]5-. Seven other examples exhibit values intermediate to these extremes. Thermal Properties. The thermal decompositions of compounds 1 and 5-7 were investigated by thermogravimetric analysis. The behavior of compound 6, shown in Figure 8, is characteristic of the compounds of this series. There is an initial dehydration between 125 and 150 °C, corresponding to the loss of the water of crystallization. This step is followed

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Figure 10. A possible alternating chain axis for 4.

Figure 9. The temperature dependence of the magnetic susceptibility χ (red circles) and of the effective magnetic moment μeff (blue diamonds) of compound 4. The inset shows the behavior of the magnetic susceptibility in the 2-30 K temperature range.

by a plateau of stability, from 150 to 370 °C in the case of compound 6. A second weight loss between 375 to 400 °C appears to be consistent with a second dehydration step that releases the coordinated water molecules. Following these dehydration processes, ligand decomposition occurs between 550 and 700 °C. The total weight loss for 1 is ca. 46% with 48.8% calculated for loss of water and ligand. The amorphous gray residue was not characterized. The loss of water of crystallization below 200 °C, while the coordinated water is not released until 375-400 °C, is consistent with a dehydration mechanism dependent on topological and energetic considerations.73 Water occupying accessible void space in the structure is expected to be released at lower temperatures than coordinated water molecules, buried within the coordination framework of the solid. Magnetism. The temperature-dependent magnetic susceptibilities of three of the copper-containing compounds, the 1D materials 1, 2, and 4, were investigated. The presence of magnetic impurities in all samples of compound 3 precluded meaningful interpretation of its magnetic properties. The magnetic behaviors of compounds 1 and 2 were fit to the Curie-Weiss law, eq 1: χ ¼ χ0 þ χTI þ

Ng2 μ2B SðS þ 1Þ þ χTI 3kðT -ΘÞ

ð1Þ

For compound 1 (Figure S11, Supporting Information), the best fit gave values of g = 2.20, Θ = -0.19 K, and χTI = -0.000169. At 300 K, the effective moment μeff = (8χ0T)1/2 is 3.33μB, corresponding to three Cu(II) sites per formula unit. The absence of any significant magnetic interactions is not unanticipated as the closest through bond interaction Cu2-O-Mo-O-Cu3 involves copper sites with magnetic orbitals poorly aligned for overlap. The best fit of the magnetic data for 2 (Figure S12, Supporting Information) to the Curie-Weiss law gave g = 2.09, Θ = -0.33 K, and χTI = -0.0000612 emu/mol. The effective moment at 300 K is 1.82 μB, consistent with one d9Cu(II) site per formula unit. Once again, the absence of magnetic interactions is consistent with the distance between copper sites, with a closest approach of 7.7 A˚.

In contrast, the magnetic data for compound 4, shown in Figure 9, is best fit to the alternating chain model described by the following equation:74 Ng2 μ2B A þ By þ Cy2 χ ¼ χ0 þ χTI ¼ þ χTI ð2Þ kT 1 þ Dy þ Ey2 þ Fy3 where y = |J|/kT. The values of parameters A, B, C, D, E, and F for 0 e R e 0.4 are A = 0.25, B = -0.12587 þ 0.22752R, C = 0.019111 - 0.13307R þ 0.50967R2 - 1.3167R3 þ 1.0081R4, D = 0.10772 þ 1.4192R, E = -0.0028521 - 0.42346R þ 2.1953R2 0.82412R3, F = 0.37754 - 0.067022R þ 6.9805R2 - 21.678R3 þ 15.838R4. The values of A to F for 0.4 < R e 1 are A = 0.25, B = -0.13695 þ 0.26387R, C = 0.017025 - 0.12668R þ 0.49113R2 - 1.1977R3 þ 0.87257R4, D = 0.070509 þ 1.3042R, E = -0.0035767 - 0.40837R þ 3.4862R2 - 0.73888R3, F = 0.36184 - 0.065528R þ 6.65875R2 - 20.945R3 þ 15.425R4. The best fit gives g = 2.19, J/k = -3.90 K, R = 0.57, χTI = 0.000117 emu/mol. At 300 K, the effective moment μeff = (8χ0T)1/2 is 1.91μB, corresponding to one Cu(II) site per formula unit. The structure of compound 4 does resemble a spin 1/2 Heisenberg ladder. However, as reported in many previous studies, the fits using spin ladder model and alternating chain model can be indistinguishable. The spin ladder model using JR (the exchange along the rungs), JL (the exchange along the legs), g, and χTI as fitting parameters was also attempted.75,76 The best fit gives g = 2.26, JR/k = -2.84 K, JL/k = -6.56 K, and χTI = 0.0001.27 emu/mol (Figure S14, Supporting Information). However, the fitting to alternating chain model is much better, with an agreement factor R = 3.53  10-6, compared to R = 4.36  10-5 for spin ladder model. We conclude that the magnetism of compound 4 is best described as an alternating chain with the chain axis most likely as shown in Figure 10. Conclusions Hydrothermal synthesis has been exploited to prepare a small series of compounds of the M(II)-organonitrogen ligand/MoxOyFz/(H2O3PC6H4CO2H) system. The naive expectation was that the dipodic, unsymmetrical ligand would bridge {Mo5O15(O3PR)2}4- clusters to {M(II)(ligand)x}2þ subunits to form 1D materials. While [{Cu(bpy)(H2O)}3Mo5O15(O3PC6H4CO2)2] 3 4.5H2O (1 3 4.5H2O) did conform to this structural prototype, the remaining copper molybdates exhibited polymeric structures based on unusual molybdate and/or copper building blocks. Thus, the 1D structure of [Cu(bpy)(O3PC6H4CO2H)Mo2O6] (2) contains a {Mo2O6}n chain decorated by phosphonate groups and Cu(II) square pyramids. The carboxylate ligand is protonated and pendant.

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The 3D structure of [{Cu(phen)}2Mo2O5(O3PC6H4CO2)2] 3 H2O (3 3 H2O) is constructed from binuclear units of cornersharing {MoO6} octahedra linked into a chain through phosphonate tetrahedra and copper polyhedra. The 1,4-carboxyphenylphosphonate ligands link the chains into the 3D framework. Fluoride incorporation into [Cu(bpy)(O3PC6H4CO2)MoO2F] (4) provides a 1D structure with 1,4-carboxyphenylphosphonate bridges but with unusual hexanuclear coppermolybdophosphonate nodes. When Cu(II) is replaced with Co(II) or Ni(II), the molecular anions of 5-7 are observed. However, all three structures have certain peculiarities. The pentamolybdate cluster of 5 is in the protonated form {Mo5O14(OH)(O3PR)2}3-, while the cluster in 6 is decorated with a {Ni(phen)2}2þ unit. The polyoxofluoromolybdate cluster of 7 is a unique dodecamolybdate {Mo12F4O34(H2O)4(O3PR)2}2-. It is likely that many additional structures will emerge as the hydrothermal parameter space is explored. In particular, variations in stoichiometries, reaction pH, and temperature are well-known to produce a variety of products. A deeper understanding of the structural systematics of these phases will evolve with the continued careful exploration of the hydrothermal reaction conditions. Acknowledgment. This work was supported by a grant from the National Science Foundation (CHE-0907787). The magnetic studies were supported by a grant from the Louisiana Board of Regents through contract number LEQSF(2007-12)-ENH-PKSFI-PRS-04. Supporting Information Available: Tables of positional parameters, bond lengths, bond angles, anisotropic temperature factors, and calculated hydrogen atom positions for 1-7 in CIF format; ORTEP diagrams for 1-7. This material is available free of charge via the Internet at http://pubs.acs.org.

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