New cobalt- and sodium-containing heteronuclear phosphonate clusters: Synthesis, structure and properties

Polyhedron 35 (2012) 116–123

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New cobalt- and sodium-containing heteronuclear phosphonate clusters: Synthesis, structure and properties Nataliya P. Burkovskaya a, Marina E. Nikiforova a,⇑, Mikhail A. Kiskin a, Zhanna V. Dobrokhotova a, Artem S. Bogomyakov b, Pavel S. Koroteev a, Vasyl I. Pekhnyo c, Aleksei A. Sidorov a, Vladimir M. Novotortsev a, Igor L. Eremenko a a b c

N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky Prosp. 31, 119991 Moscow, Russian Federation International Tomography Center, Siberian Branch of the Russian Academy of Sciences, Institutskaya Str. 3a, 630090 Novosibirsk, Russian Federation V.I. Vernadsky Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine, 32–34, Palladin Avenue, 03680 Kiev, Ukraine

a r t i c l e

i n f o

Article history: Received 23 September 2011 Accepted 6 January 2012 Available online 28 January 2012 Keywords: Heterometallic clusters Cobalt(II) complexes Phosphonate ligands X-ray diffraction study Thermal decomposition Magnetic properties

a b s t r a c t New polynuclear heteroligand complexes [(g-HPiv)2(l2-Hmhp)4Na6Co5(l6,g2-O3PPh)2(l3,g2-Piv)2 (l3-Piv)3(l-Piv)7]2C10H22 (12C10H22) and [(g-H2O)4Na12Co12(l5,g2-O3PPh)4(l6-O3PPh)4(l3,g2-mhp)8 (l2-Piv)4(l3-Piv)8]1.25C10H22 (21.25C10H22), where Hmhp is 6-methyl-2-pyridone, mhp is the 6methyl-2-piridonate, and Piv is the pivalate anion, were obtained by the self-assembly of {Co(Piv)2}n, Na2O3PPh, and Hmhp in boiling decane (174 °C). The structures of compounds 12C10H22 and 21.25C10H22 were determined by single-crystal X-ray diffraction. The magnetic properties of these compounds and their thermal decomposition were investigated. The removal of coordinated water molecules from complex 21.25C10H22 begins at 470 °C. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction Molecular heteropolynuclear metal phosphonates containing high-spin transition metal atoms are a class of coordination compounds which have attracted great interest primarily due to the fact that they would be expected to form systems with magnetic ordering [1–6]. In addition, these molecules are promising precursors for the preparation of zeolite-like microporous materials [7–9], as well as of other different molecular materials having interesting physicochemical properties [10–13]. Performing the chemical design of phosphonate-bridged heteropolynuclear molecules, researchers often face difficulties in isolating pure compounds because of their low solubility. However, in this case it can be used a heteroligand coordination sphere containing phosphonate bridges together with, for example, pivalate anions or other organic ligands, which substantially increase the solubility of the complexes [14–22]. As for the methods for the synthesis of this class of heteronuclear molecules, we can distinguish the self-assembly method, which provides the possibility of preparing molecules containing a relatively large number of different metal atoms from a set of small

⇑ Corresponding author. E-mail address: [email protected] (M.E. Nikiforova). 0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2012.01.005

starting molecules by varying their ratio and the reaction conditions [15,18,20,21]. However, in this case the ratio of different metal ions in the final heteronuclear molecule not necessarily corresponds to the ratio of these metals in the starting reagents. It should be noted that as a rule the synthesis under drastic conditions, at high temperatures, generally facilitates the formation of metal cores containing a large number of metal centers. To understand the pathways of the assembly of phosphonate-bridged heteronuclear clusters, we investigated a system consisting of the polymeric cobalt pivalate {Co(Piv)2}n, sodium phenylphosphonate, and 6-methyl-2-hydroxypyridine with the aim of assembling {Co–Na} clusters, which could exhibit unusual magnetic properties and serve as the starting compounds for the synthesis of complex oxides. 2. Experimental 2.1. Synthesis New heterometallic clusters were synthesized in a pure argon atmosphere with the use of decane (without the additional purification), the purified solvents MeCN, THF, and EtOH, phenylphosphonic acid (Aldrich), NaOH (97%), HPiv – pivalic acid (2,2-dimethyl propanoic acid by IUPAC or trimethylacetic acid) (Aldrich), and 6-methyl-2-hydroxypyridine (Fluka). Polymeric cobalt pivalate {CoPiv)2}n was synthesized according to a known procedure [23].

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The Na2O3PPh and NaPiv salts were prepared by the neutralization of NaOH with H2O3PPh and HPiv, respectively. 2.1.1. [(g-HPiv)2(l2-Hmhp)4Na6Co5(l6,g2-O3PPh)2(l3,g2-Piv)2(l3Piv)3(l-Piv)7]2C10H22, (12C10H22) Decane (20 ml) was added to a mixture of {Co(Piv)2}n (0.30 g, 1.15 mmol), 6-methyl-2-hydroxypyridine (0.10 g, 0.92 mmol), Na2 O3PPh (0.093 g, 0.46 mmol) in EtOH (5 ml), and NaPiv (0.055 g, 0.46 mmol). The reaction mixture was heated to the boiling point of decane (174 °C) and then kept with continuous stirring under a stream of argon for 15 min. That was accompanied by the partial dissolution of the starting compounds and removal of lower-temperature-boiling EtOH. The mixture was cooled to room temperature and filtered off from the precipitate. The resulting dark-blue solution was kept at room temperature overnight. The resulting rhombic-shaped violet crystals suitable for X-ray diffraction study were separated from the solution by decantation, washed with cold hexane (0 °C), and dried under a stream of argon. The yield of compound 12C10H22 was 0.156 g (59.7% based on the starting {Co (Piv)2}n). Anal. Calc. for C126H210Co5Na6N4O38P2 (12C10H22): C, 52.17; H, 7.33; N, 1.95. Found (taking into account the solvent molecules): C, 52.48; H, 7.34; N, 1.94%. IR (KBr), m/cm1: 3667–3325 m.b, 3278 w, 3252 w, 3245–3093 w.b, 3070–3025 w.b, 2960 s, 2927 m, 2871 m, 1699 m, 1656 v.s, 1622 s, 1592 m, 1569 v.s, 1554 v.s, 1537 m, 1484 v.s, 1460 m, 1418 s, 1361 s, 1309 m, 1228 s, 1199 m, 1161 m, 1138 m, 1092 s, 1069 s, 1032 w, 1004 m, 993 m, 937 w, 893 m, 870 m, 794 s, 751 m, 722 m, 698 m, 608 m, 593 m, 575s, 532 m, 503 w, 477 w, 428 m. 2

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measured on a Quantum Design MPMSXL SQUID magnetometer in the temperature range of 5–300 K at an external magnetic field strength of up to 5 kOe. The molar magnetic susceptibility (v) was calculated taking into account the diamagnetism according to Pascal’s additivity rules. In the paramagnetic region, the effective magnetic moment was calculated by the equation leff = [(3k/NAb2)vT]1/ 2  (8vT)1/2, where k is the Boltzmann constant, NA is Avogadro’s number, and b is the Bohr magneton [24]. 2.3. X-ray diffraction studies The X-ray diffraction data sets for complexes 12C10H22 and 21.25C10H22 were collected on a Bruker APEX II diffractometer equipped with a CCD camera and a graphite-monochromated Mo Ka radiation source (k = 0.71073 Å) [25]. Semiempirical absorption corrections for both compounds were applied [26]. The structures were solved by direct methods and using Fourier techniques and were refined by the full-matrix least squares against F2 with anisotropic thermal parameters for all non-hydrogen atoms. The hydrogen atoms of the carbon-containing ligands and the NH and OH groups were positioned geometrically and refined using the riding model. All calculations were carried out with the use of the SHELX97 program package [27]. Disordered decane solvent molecules in 12C10H22, which could not be located in electron density maps, were removed by the SQUEEZE routine [28]. The crystallographic parameters and the refinement statistics are given in Table 1S. 2.4. Thermal analysis

2

2.1.2. [(g-H2O)4Na12Co12(l5,g -O3PPh)4(l6-O3PPh)4(l3,g -mhp)8(l2Piv)4(l3-Piv)8]1.25C10H22, (21.25C10H22) A mixture of {Co(Piv)2}n (0.30 g, 1.15 mmol), 6-methyl-2hydroxypyridine (0.084 g, 0.77 mmol), and Na2O3PPh (0.156 g, 0.77 mmol) in the presence of a small amount of NaOH (0.01 g, 0.25 mmol) in EtOH (5 ml) and decane (20 ml) was heated to the boiling point (174 °C) and then kept with continuous stirring under a stream of argon for 15 min, which was accompanied by the partial dissolution of the starting compounds and removal of lower-temperature-boiling EtOH. The mixture was cooled to room temperature and filtered off from the precipitate. The resulting dark-blue solution was kept at room temperature for 2–4 days. The needlelike blue-violet crystals suitable for X-ray diffraction study were separated from the solution by decantation, washed with cold hexane (0 °C), and dried under a stream of argon. The yield of compound 21.25C10H22 was 0.0941 g (21.5% based on the starting {Co(Piv)2}n). Anal. Calc. for C168.5H223.5Co12Na12N8O60P8 (21.25C10 H22): C, 44.07; H, 4.85; N, 2.30. Found (taking into account the solvent molecules): C, 44.46; H, 4.95; N, 2.46%. IR (KBr), m/cm1: 3705–3242 m.b, 3166 w, 3055 w, 2963 s, 2938 m, 2870 m, 1734 w, 1654 m, 1598 v.s, 1567 s, 1474 s, 1468 v.s, 1413 s, 1357 s, 1227 s, 1160 m, 1129 s, 1092 s, 1067 s, 1011 m, 980 m, 894 m, 863 w, 801 s, 752 s, 727 m, 703 m, 678 w, 616 s, 594 m, 548 m, 512 w, 486 w, 431 w. 2.2. Methods The IR spectra of compound 12C10H22 and 21.25C10H22 were measured on a Perkin Elmer Spectrum-65 FT–IR spectrometer in the range of 400–4000 cm1 in KBr pellets. The elemental analysis was carried out on an EA1108 automatic C,H,N,S analyzer (Carlo Erba Instruments). The X-ray powder diffraction study of the decomposition products was carried out with a FR-552 monochromator camera (Cu Ka1 radiation) using germanium as the internal standard (X-ray diffraction patterns were processed with an IZA-2 comparator with an accuracy of ±0.01 mm) and with a STOE Powder Diffraction System. The static magnetic susceptibility was

The thermal decomposition of complexes 1 and 2 was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) on NETZSCH instruments. The thermogravimetric measurements were carried out in a flow (20 ml/min) of artificial air (O2, 20.8%; CH4, <0.0001%) (20 ml/min) as well as in argon (Ar, >99.998%; O2, <0.0002%; N2, <0.001%; water vapor, <0.0003%; CH4, <0.0001%) on a TG 209 F1 instrument in alundum crucibles at a heating rate of 10 °C/min. The composition of the gas phase was studied on a QMS 403C Aëolos mass spectrometric unit under TGA conditions. The ionization electrons energy was 70 eV; the maximum determined mass number (the ratio of the ion mass to its charge Z) was 300 amu. The weights of the samples used in thermogravimetric experiments were 0.5–3 mg. The differential scanning calorimetry experiments were performed in a flow of dry artificial air and argon on a DSC 204 F1 calorimeter in aluminum cells at a heating rate of 10 °C/min. The weights of the samples were 1–4 mg. The temperature calibration of the thermobalance and the calorimeter was performed based on the phase transition points of the reference compounds (C6H12, Hg, KNO3, In, Sn, Bi, CsCl; 99.99% purity) according to the ISO/CD 11357-1 standard. The samples used for the TGA and DSC experiments were weighed on a SARTORIUS RESEARCH R 160P analytical balance with an accuracy of 1102 mg. The data obtained by thermal analysis methods were processed according to the ISO 11357-1, ISO 11357-2, ISO 11358, and ASTM E 1269-95 standards using the NETZSCH Proteus Thermal Analysis software. 3. Results and discussion 3.1. Synthesis and structures of phosphonate clusters with cobalt and sodium atoms Available methods for the synthesis of heteronuclear compounds containing sodium and cobalt atoms are based on the reactions of various cobalt(II) salts with R-phosphonic acids in the presence of deprotonating agents and chlorine-substituted 2-hydroxypyridine as an additional bridging ligand [20,21,15].

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Earlier, we have used the similar approach for the system {Co (Piv)2}n:Na2O3PPh:Hmhp = 3:2:2 in MeCN under mild conditions (40–50 °C) and isolated only crystals of the homonuclear cluster containing twelve cobalt atoms, [Co12(l2-Hmhp)6(l3-OH)4(l6O3PPh)4(l2-Piv)12]6.5MeCN (36.5MeCN), in 55% yield [29]. It could be expected that the change in the ratio of the starting reagents and the use of more drastic conditions for the synthesis would make it possible to form heteronuclear molecules. However,it appeared thatthe reactionperformed in acetonitrile at 40–50 °Cwiththeuseofahigherconcentrationofcobaltpivalateinthe startingreactionmixture({Co(Piv)2}n:Na2O3PPh:Hmhp =6:2:3)does not change the character of the reaction product. The complex 36.5MeCN crystallized upon cooling of the solution. In this case, the rise of temperature to 174 °C (due to the use of decane as the reaction medium)playedmoreimportantroleandallowedustoisolatecrystals of the heterometallic cluster [(g-HPiv)2(l2-Hmhp)4Na6Co5(l6, g2-O3PPh)2(l3,g2-Piv)2(l3-Piv)3(l-Piv)7]2C10 H22 (12C10H22) as a solvate with decane in low yield (10–15%). The yield of 12C10H22 substantially increases (to 59.7%) in the case of the addition of sodium pivalate to the reaction mixture to the ratio {Co(Piv)2}n:Na2O3 PPh:Hmhp:NaPiv = 5:2:4:2, which is close to the stoichiometric ratio of the metals according to formula 1. On the other hand, the use of a small amount of NaOH instead of sodium pivalate in the reaction with the use of the main reagents in the ratio {Co(Piv)2}n:Na2O3 PPh: Hmhp = 3:2:2 (see Section 2) results in the formation of crystals of another heterometallic complex of the composition [(g-H2O)4Na12Co12(l5,g2-O3PPh)4(l6-O3PPh)4(l3,g2-mhp)8(l2-Piv)4(l3-Piv)8]1.25 C10H22 (21.25C10H22) in 21% yield. According to the X-ray diffraction data (Fig. 1 and Table 2S), the central cobalt atom Co3 in molecule 1 is in a strongly distorted octahedral coordination environment. Two cobalt atoms, Co1 and Co4, are in a distorted trigonal–bipyramidal ligand environment formed by five O atoms of one chelate-bridging O,O0 ,O00 -phosphonate anion and four O,O0 -pivalate anions. The other cobalt atoms, Co2 and Co5,

are in a tetrahedral ligand environment formed by the O atoms of the phosphonate and pivalate anions. Four neutral 6-methyl-2pyridone molecules act as bridges between the sodium atoms Na1, Na3, Na4, and Na6. The structure of the metal core of compound 1 can be represented as two strongly distorted pentagonal pyramids Na1Na3Co3Na2Co1Co2 and Na6Co4Co5Na4Co3Na5 sharing the Co3 atom, which lies in the base of two pentagonal pyramids (Fig. 2). Each PhPO32 dianion forms bonds with three Co atoms and three Na atoms, both phosphonate anions being coordinated to the central cobalt atom Co3 (Fig. 2), whose octahedral coordination is completed by two chelate-bridging pivalate anions (Fig. 1). In complex 1, the acidic groups of phenylphosphonic acid are in the form of the doubly deprotonated anions characterized by the l6,g2-chelate-bridging coordination mode or 6.322 according to the Harris notation [30] and bind six metal atoms (Fig. 3a). Molecule 1 is stabilized by six intramolecular hydrogen bonds, four of which are formed between the protons of the NH groups of the 6-methyl-2-pyridone molecules and the oxygen atoms of the pivalate and phosphonate ligands. The other two hydrogen bonds are formed between the hydrogens of the carboxyl groups of the axial HPiv molecules and the O atoms of the bridging pivalate anions (Table 3S and Fig. 1). According to the X-ray diffraction data (Figs. 4, 5 and Table 2S), the metal core formed by sodium atoms in molecule 2 can be described as a system of two mutually perpendicular bicapped trigonal prisms Na8Na7Na5Na6Na12Na11Na10Na9 and Na8Na7Na5Na6Na1Na4Na3Na2 sharing the Na5Na6Na7Na8 face (Fig. 5). Four water molecules are coordinated to four Na atoms belonging to the shared face of these polyhedra, are directed into the cavity of molecule 2, and form angles of 23.5–26° with this face. In this system, the phenylphosphonate dianions are structureforming and bind the Co and Na atoms in molecule 2 exhibiting the l6- and l5,g2-chelate-briding coordination mode (6.222 and

Fig. 1. Molecular structure of heteronuclear complex 1 (Ph and Butert groups are not shown for clarity, the displacement ellipsoids are drawn at the 30% probability level).

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Fig. 2. Structure of the metal core of cluster 1.

Fig. 3. Coordination modes of the PhPO32 dianion to the Na and Co atoms: 6.322 (a) for compound 1 and 6.222 (b), 5.222 (c) for compound 2.

5.222 according to the Harris notation) (Figs. 3b, c and 6). The Na atoms are in a distorted tetragonal-pyramidal (Na4, Na5, Na6, Na7, Na8, and Na10) and trigonal–bipyramidal (Na1, Na2, Na3, Na9, Na11, and Na12) ligand environment. The Co1, Co6, Co9, and Co10 atoms are in a tetrahedral coordination environment formed by four O atoms of the chelate-bridging O,O0 ,O00 -phosphonate and O,N-pyridonate anions and by the bridging O,O0 ,O00 -phosphonate and O,O0 -pivalate anions, whereas the other cobalt atoms are in a distorted trigonal–bipyramidal environment. Eight chelating 6-methyl-2-pyridonate anions are related to the Co atoms and, at the same time, act as bridges between the Na and Co atoms. The other twelve pivalate anions exhibit l2- and l3-bridging coordination modes. 3.2. Thermal decomposition of heterometallic phosphonates containing sodium and cobalt atoms 3.2.1. Thermal behavior of complex 12C10H22 Complex 1 destruction begins at 125 ± 5 °C. It should be noted that in the range of 125–240 °C, the decomposition goes in the same way both under an inert atmosphere and in air. It is impossible to separate the steps of the removal of solvent molecules and neutral ligands in this temperature range based on the TGA data (Fig. 7a). The total weight loss is 32.5 ± 2.0%. However, the variation dependence pattern of heat flux on temperature (the DSC curve) suggests that several gaseous products are removed in the temperature range under consideration (Fig. 7b). The mass spectrum of the gas phase shows the following ion peaks: peaks with the maximum intensity in the temperature range of 125–180 °C, C2H3+(27), C2H5+(29), C3H3+(39), C3H5+(41), C3H6+(42), C3H7+(43), CO2+(44), CHO2+(45), C4H9+(57), and C5H11+(71), and peaks with the maximum intensity

in the temperature range of 180–240 °C, C6H4NO+(109), C4H3 NO+(81), C4H2NO+(80), C3H3N+(53), C3H6+(42), and CH2N+ (28). The products in the gas phase were identified based on the analysis of the mass spectrum and the DSC curve. Apparently, the endothermic (Q = 340.2 ± 8.9 kJ/mol) removal of (Dm = 10.3 ± 1.0%) decane molecules of solvation (tboil = 174 °C, DvapH(174) = 38.75 kJ/mol) and (Dm = 7.3 ± 1.0%) coordinated pivalic acid molecules (tboil = 163 °C, DsubH° = 73.2 ± 3.0 kJ/mol) occurs in the range of 125–180 °C [31]. In the range of 180–240 °C, the endothermic (Q = 115.3 ± 7.5 kJ/ mol) removal (Dm = 15.2 ± 1.0%) of 6-methyl-2-pyridone occurs (DsubH° = 92.0 ± 1.3 kJ/mol) [31]. The thermal effect of this step is substantially smaller than the energy of the sublimation of 4 moles of 6-methyl-2-pyridone. This is apparently attributed to the fact that several processes occur in this temperature range, such as the cleavage of the Na–O(L) bonds, the structural reorganization, and the sublimation of the ligand. At temperatures above 240 °C, a gradual enough sample weight loss is observed in argon on the background of several endothermic effects (Fig. 7a). The total weight loss up to 550 °C is 69.0 ± 2.0%. The solid thermal decomposition product is X-ray amorphous. The decomposition processes in air at temperatures above 240 °C are accompanied by significant exothermic effects, which may indicate the occurrence of the processes associated with the formation of new structures (Fig. 7a). The decomposition product is amorphous-crystalline. The X-ray powder diffraction data (experimental error is 3–5 wt%) are given in Table 4S. 3.2.2. Thermal behavior of complex 21.25C10H22 The thermal decomposition of complex 2 proved to be quite interesting and unexpected because of the complicated structure of 2 and the absence of coordinated neutral ligands. Hence, the

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Fig. 4. Molecular structure of heteronuclear complex 2 (Ph and Butert groups are not shown for clarity, the displacement ellipsoids are drawn at the 30% probability level).

Fig. 5. Structure of the Na metal core in complex 2 represented as a system of two mutually perpendicular bicapped trigonal prisms and the arrangement of water molecules with respect to the Na5Na6Na7Na8 face.

interpretation of the thermal analysis data should be considered as the most probable. Based on the DSC, TGA, and DTA data and the

mass spectra of the gas phase under the TGA conditions, several decomposition and structural reorganization steps can be

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Fig. 6. Coordination of the Co and Na atoms in complex 2 by the phosphonate dianions (the phenyl substituents of the phosphonate dianions are not shown).

distinguished. It should be noted that in the range of 125–240 °C, the decomposition occurs in the same way both under an inert atmosphere and in air (Fig. 8). The first step is observed in the range of 125–195 °C. The mass spectrum shows ions C2H3+(27), C2H5+(29), C3H3+(39), C3H5+(41), C3H6+(42), C3H7+(43), C4H9+(57), C5H11+(71), and C6H13+(85) (Fig. 9). This step corresponds to the removal of the adsorbed and solvated decane molecules. All further calculations were carried out for molecule 2 without taking into account the solvate molecules. Further, presumably, the products obtained in thermal decomposition under an inert atmosphere as a result of the successive elimination of pivalate anions from molecule 2 are removed in two steps. In the range of 315–370 °C, Dm = 10.0 ± 1.5% (the percentage of l2-coordinated pivalate anions calculated from the empirical formula is 9.21%). Earlier [32], we have suggested the possible composition for the gas phase that is formed in thermal decomposition of tris-pivalates M2(Piv)6 (M = La, Sm, and Eu). Hence, in the case under consideration the elimination of pivalate anions may result in the formation of the following possible gasphase products:

the gas phase cannot be unambiguously determined from a comparison of these data with the mass spectra of individual gaseous products [31]. However, the preference should be given to compounds 5 and 7. In the temperature range of 390–470 °C, Dm = 20.0 ± 1.5% (the percentage of l2-coordinated pivalate anions calculated from the empirical formula is 18.42%). The mass spectrum of the gas phase is identical to the mass spectrum of the second decomposition step. At temperatures above 470 °C, this process goes into the fourth step. It should be emphasized that the coordinated water molecules begin to be eliminated at this temperature. The mass spectrum of the gas phase also reveals ion currents corresponding to the ionization of 6-methyl-2-pyridone (the protonation of 6methyl-2-pyridonate anions occurs apparently due to the presence of phenylphosphonate dianions): C6H4NO+(109), C4H3NO+(81), C4H2NO+(80), C3H3N+(53), C3H6+(42), CH2N+(28). The complex completely decomposes at temperatures above 540 °C accompanied by the appearance of the ion C5H5+(77) in the mass spectrum. In the experiment performed under an inert atmosphere (below 600 °C), the process is not completed. The thermal decomposition in air in the temperature range from 250 to 575 °C occurs with the release of large amounts of

In the mass spectrum in this temperature range were recorded the following ions: C2H5+(29), CH2O+(30), C3H3+(39), C3H5+(41), C3H7+(43), CO2+(44), C4H8+(56), and C4H9+(57). The composition of

energy and results in the complete redox decomposition accompanied by a weight loss of 47.6 ± 2.0% and the formation of solid

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a

a 100

20

1

90

10

60 5

50

1

40

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500

-1.2

-1.6

-5

t, C

100

200

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o

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500

t, C

b

b

12

-0.3

2

-0.6

10

Q, mW/mg

Q, mW/mg

-1.0

-1.4

0

30 100

Q, mW/mg

70

Q, mW/mg

15

80

m, %

-0.8

2

1

-0.9

8 6 4 2

-1.2

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50

100

150

o

200

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decomposition products (Fig. 8b). The results of the X-ray powder diffraction analysis of the solid decomposition product in air are presented in Table 5S. Hence, we established that the solid product obtained in the experiment without additional annealing contains cobalt oxide Co3O4 and sodium cobaltate, whereas the composition of the sodium- and phosphorus-containing compound remained unclear. 3.3. Magnetic properties of complexes 12C10H22 and 21.25C10H22

c

500

100

2

90 80

m, %

Fig. 7. Weight loss in argon (a) and the change in the heat flux (in the range of 30– 540 °C (a), in the range of 50–270 °C (b); 1, in argon; 2, in air) during heating of complex 1.

400 o

t, C

t, C

1

70 60 50 40 100

200

300

400

500

600

o

The temperature dependences of the effective magnetic moment

leff and inverse magnetic susceptibility (1/v) for the complexes 12C10H22 and 21.25C10H22 are shown in Fig. 1S. The effective magnetic moments of both compounds decrease with temperature lowering. However, the effective magnetic moment of the complex 21.25C10H22 monotonically decreases from 14.68 at 300 K to 8.30 lB at 5 K (Fig. 1Sb), whereas leff of the complex 12C10H22 remains virtually unchanged (decreases from 10.10 to 9.18 lB) in the temperature range of 300–40 K and a more substantial decrease is observed only at lower temperatures (6.52 lB at 5 K) (Fig. 1Sa). The values of leff at 5 K (6.52 lB for 12C10H22 and 8.30 lB for 21.25C10H22) are substantially lower than theoretical spin-only ones (8.66 and 13.42 lB for 12C10H22 and 21.25C10H22, correspondingly). The temperature dependences of the inverse magnetic susceptibility (1/v) for the compounds 12C10H22 and 21.25C10 H22 in the range of 40–300 K obey the Curie–Weiss law with the

t, C Fig. 8. Changes in the heat flux (a, in argon; b, in air) and the weight loss (c) (1, in argon; 2, in air) during heating of complex 2.

parameters C = 13.28 ± 0.09 K cm3/mol, h = 17.9 ± 1 K and C = 29.0 ± 0.2 K cm3/mol, h = 25.9 ± 1 K, respectively (Fig. 1S). The values C = 2.66 for 12C10H22 and 2.42 for 21.25C10H22 (per cobalt atom) are larger than the theoretical spin-only value (C = 1.875 at S = 3/2 and g = 2), which is consistent with the orbital contribution to the magnetic susceptibility typical for CoII ions in the bipyramidal and octahedral ligand environment and the g-factors larger than 2. The negative values of h may also be evidence of antiferromagnetic exchange interactions between the paramagnetic centers in the complexes through the bridging ligands. The values of leff at 5 K is lower than theoretical spin-only ones that also indicate a presence

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m/z = 18

I, A

4.0x10

2.0x10

-12

and Science of the Russian Federation (SC-14.740.11.0363), the Russian Academy of Sciences, and the Siberian Branch of the Russian Academy of Sciences.

m/z = 41

m/z = 43

Appendix A. Supplementary data

-12

m/z = 53

m/z = 57

0.0

m/z = 77

m/z = 71

100

123

200

300

o

400

CCDC 844917 and 844918 contain the supplementary crystallographic data for compound 1 and 21.25C10H22. 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) 1223336-033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.poly.2012.01.005.

500

t, C Fig. 9. Most characteristic peaks of the detected ion currents in the gas phase in the thermogravimetric experiment during heating of complex 2 under an inert atmosphere.

of antiferromagnetic exchange interactions. 4. Conclusions We showed that the formation of polynuclear metal phosphonates is determined not only by the ratio of the starting reagents but also by the reaction conditions. More drastic reaction conditions are favorable for the formation of high-spin compounds 1 and 2 containing no oxo- or hydroxo-bridging groups, which are present in the compounds of the general formula [(l2-L)6Co12(l3OH)4(l6-O3PPh)4(l2-Piv)12] (L = THF, HPiv, or Hmhp), which we have synthesized earlier under mild conditions. In the resulting heteronuclear compounds, the PhPO32 dianion exhibits different bridging and chelate-bridging coordination modes, which were not observed in homonuclear compounds containing twelve cobalt atoms [29]. This is apparently associated with steric difficulties in the process of compounds 1 and 2 metal cores formation. The thermogravimetric study of compounds 1 and 2 showed that their thermal stability is determined by their structures. The thermal stability of complex 2 is substantially higher than that of complex 1 due to the absence of coordinated neutral ligands (complex 2 completely decomposes at temperatures above 540 °C). It should be emphasized that the removal of coordinated water molecules from complex 2 begins at 470 °C. This unexpected effect is apparently attributed to the complex structure of 2 because the coordinated water molecules are located inside a ‘‘multilayer capsule’’ of molecule 2. Acknowledgments This study was supported by the Russian Foundation for Basic Research (Project Nos. 11-03-00642 and 10-03-90410), the Council on Grants of the President of the Russian Federation (Grants NSh3672.2010.3 and NSh-8503.2010.3), the State Department of Science and Innovation Policy (NK-537P_25), the Ministry of Education

References [1] [2] [3] [4]

[5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]

[25] [26] [27] [28] [29]

[30] [31] [32]

D. Gatteschi, R. Sessoli, Angew. Chem., Int. Ed. 42 (2003) 268. D. Gatteschi, A. Caneschi, L. Pardi, R. Sessoli, Science 265 (1994) 1054. O. Kahn, Molecular Magnetism, VCH Publishers, 1993. E.-C. Yang, D.N. Hendrickson, W. Wernsdorfer, M. Nakano, L.N. Zakharov, R.D. Sommer, A.L. Rheingold, M. Ledezma-Gairaud, G. Christou, J. Appl. Phys. 91 (2002) 7382. M. Murrie, S.J. Teat, H. Stöeckli-Evans, H.U. Güdel, Angew. Chem., Int. Ed. 42 (2003) 4653. R. Sessoli, D. Gatteschi, J. Villain, Molecular Nanomagnets, Oxford University Press, Oxford, 2006. J. Le Bideau, C. Payen, P. Palvadeau, B. Bujoli, Inorg. Chem. 33 (1994) 4885. K. Maeda, J. Akimoto, F. Mizukami, Angew. Chem., Int. Ed. 33 (1994) 2335. K. Maeda, J. Akimoto, Y. Kiyozumi, F. Mizukam, Angew. Chem., Int. Ed. 34 (1995) 1199. A. Clearfield, K.D. Karlin, Prog. Inorg. Chem. 47 (1998) 371. B. Zhang, A. Clearfield, J. Chem. Soc. 119 (1997) 2751. G. Alberti, J.M. Lehn, Compr. Supramol. Chem. 7 (1996) 151. C. Arendt, G. Hägele, Comput. Chem. 19 (1995) 263. V. Chandrasekhar, S. Kigsley, Angew. Chem., Int. Ed. 39 (2000) 2320. S. Langley, M. Helliwell, J. Raftery, E.I. Tolis, R.E.P. Winpenny, Chem. Commun. (2004) 142. V. Chandrasekhar, P. Sasikumar, R. Boomishankar, Dalton Trans. (2008) 5189. S. Kingsley, Ph.D. Thesis, Indian Institute of Technology Kanpur, India, 2001. E.K. Brechin, R.A. Coxall, A. Parkin, S. Parsons, P.A. Tasker, R.E.P. Winpenny, Angew. Chem., Int. Ed. 40 (2001) 2700. R. Murugavel, S. Shanmugan, Dalton Trans. (2008) 5358. S.J. Langley, M. Helliwell, R. Sessoli, P. Rosa, W. Wernsdorfer, R.E.P. Winpenny, Chem. Commun. (2005) 5029. S. Langley, M. Helliwell, R. Sessoli, S.J. Teat, R.E.P. Winpenny, Dalton Trans. (2009) 3102. B.A. Breeze, M. Shanmugam, F. Tuna, R.E.P. Winpenny, Chem. Commun. (2007) 5185. I.L. Eremenko, S.E. Nefedov, A.A. Sidorov, I.I. Moiseev, Russ. Chem. Bull. Engl. Transl. 48 (1999) 405. Yu.V. Rakitin, V.T. Kalinnikov, Sovremennaya magnetokhimiya (in Russian, Modern Magnetochemistry, Science, St. Petersburg, 1994), Nauka, St. Petersburg, 1994. SMART (Control) and SAINT (Integration) Software, Version 5.0, Bruker AXS Inc., Madison, WI, 1997. G.M. Sheldrick, SADABS, Program for Scanning and Correction of Area Detector Data, Göttingen University, Göttingen, Germany, 2003. G.M. Sheldrik, Acta Crystallogr., Sect. A 64 (2008) 112. P.v.d. Sluis, A.L. Spek, Acta Crystallogr., Sect. A 46 (1990) 194. N.P. Burkovskaya, M.E. Nikiforova, M.A. Kiskin, A.S. Lermontov, A.S. Bogomyakov, V.S. Mironov, Zh.V. Dobrokhotova, V.I. Pekhnyo, A.A. Sidorov, V.M. Novotortsev, I.L. Eremenko, Polyhedron 30 (2011) 2941. R.A. Coxall, S.G. Harris, D.K. Henderson, S. Parsons, P.A. Tasker, R.E.P. Winpenny, Dalton Trans. (2000) 2349. Available from: . Zh.V. Dobrokhotova, I.G. Fomina, M.A. Kiskin, G.B. Belov, M.A. Bykov, V.M. Novotortsev, Russ. J. Phys. Chem. A 80 (2006) 323.