lable at ScienceDirect

Journal of Organometallic Chemistry 749 (2014) 197e203

Contents lists avai

Journal of Organometallic Chemistry

journal homepage: www.elsevier .com/locate/ jorganchem

Nonaqueous synthesis of molecular zinc amide phosphate

Jan Chyba a, Zdenek Moravec a, Marek Necas a, Sanjay Mathur b, Jiri Pinkas a,*

aDepartment of Chemistry and CEITEC MU, Masaryk University, Kotlarska 2, CZ-61137 Brno, Czech Republicb Institute of Inorganic Chemistry, University of Cologne, Greinstraße 6, D-50939 Cologne, Germany

a r t i c l e i n f o

Article history:Received 6 August 2013Received in revised form30 September 2013Accepted 30 September 2013

Keywords:ZincAmidePhosphateX-ray structureNonaqueous

* Corresponding author. Tel.: þ420 549496493; faxE-mail address: jpinkas@chemi.muni.cz (J. Pinkas)

0022-328X/$ e see front matter � 2013 Elsevier B.V.http://dx.doi.org/10.1016/j.jorganchem.2013.09.040

a b s t r a c t

Three new molecular zinc compounds were prepared by nonaqueous reactions of Zn[N(SiMe3)2]2 andZnEt2 with trimethylsilylesters of phosphoric acid, OP(OSiMe3)3 and OP(OSiMe3)2(OH). Single-crystal X-ray diffraction analyses of crystalline products revealed molecular structures of two mononuclearcomplexes [ZnX2OP(OSiMe3)3] (X ¼ N(SiMe3)2 (1), hfacac ¼ hexafluoroacetylacetonate, (2)) and onedinuclear zinc phosphate [(Zn{(py)N(SiMe3)2}{m2-O2P(OSiMe3)2})2] (3). Compound 1 is only the secondstructurally characterized adduct of zinc bisamide with an oxygen donor and a three-coordinate Zn atom.The cyclic inorganic core {Zn(m2-O2PO2)}2 in 3 is a model for the most common single four-ring (S4R)building unit of open-framework zinc phosphates. The molecule of 3 possesses reactive amide and tri-methylsiloxy groups that can be employed in further studies on the formation of extended structures bycondensation reactions. Spectroscopic properties and thermal behavior of the molecular products wereexamined. Compounds 1 and 3 were converted to a-Zn2P2O7 by calcination.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

Zinc phosphates [1e5] and phosphonates [6e8] constitute avery rich and structurally interesting group of compounds thatinclude species featuring various nuclearity, dimensionality andarchitecture modes. The unabated interest in these compoundsspans from their function as open-framework materials to their useas seeds for spatial control of nucleation and growth of metal-organic framework (MOF) nanostructures [9] to models in nano-particle composition and homogeneity studies by MAS NMR [10].Open-framework zinc phosphates are studied for their potentialapplications in catalysis, sorption, ion exchange, and luminescence[11]. The most pertinent for these purposes are 3-dimensional (3D)zeolite-like networks [12e16] but layer (2D) [17e20] and chain orladder (1D) [21,22] structures are also frequently reported. Themechanism of formation of zinc phosphates was investigated withconsiderable effort and it was shown that low dimensional struc-tures can be converted to higher-dimensionality frameworks uponchanging reaction conditions [23e25]. Analysis of these reactionssuggests that small clusters serve as the starting species thatcondense to chains or ladders and subsequently transform to layerstructures to finally form 3D frameworks [26,27]. The major syn-thetic route to zinc phosphates is the hydrothermal synthesisemploying zinc salts, phosphoric acid and organic amines serving

: þ420 549492443..

All rights reserved.

as the templates. Additionally, the amine phosphate method [23]and nonaqueous routes with organophosphorous precursors,such as esters [28] and amides [29], were devised. The molecularzinc phosphates and phosphonates have been mainly prepared bythe reactions of zinc precursors, such as ZnR2 (R ¼ Me, Et),Zn(OAc)2, ZnCl2, ZnO, with phosphoric and phosphonic acids andtheir alkyl and aryl esters and feature a variety of cage structures[30e33]. The reactions often involve bases with O and N donoratoms which are then included as co-ligands in the coordinationspheres of zinc atoms or compensate the cluster charge as pro-tonated cations. One of the frequent structural motifs is a cube-likedouble-four-ring (D4R) unit that was used for the assembly of zincphosphates with different supramolecular architectures [34e38].By far the most prevalent molecular units in zinc phosphates areZn2P2O4 cycles, also called single-four-rings (S4R) [39e41], whichwere shown to be important intermediates in the formation ofopen-framework structures. These basic units are formed as thefirst oligomers in the reaction process and are also the most com-mon structural motifs in the crystalline higher-dimensional struc-tures where they become connected to chains, ladders, layers or3D-networks [42e45]. The molecular zinc phosphates were alsoused directly as precursors in the thermolytic preparation of layerand ceramic materials [46e48].

Nonaqueous or organometallic synthetic routes to oxide andphosphate materials offer certain advantages over their aqueouscounterparts, such as a better control of condensation reactions,residual reactive functional surface groups in products, and a widerchoice of precursors. These nonaqueous condensation reactions

J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203198

provided a large number of molecular and extended-structuremetal phosphates and phosphonates. The reactions of metal am-ides or metal alkyls with tris(trimethylsilyl)ester of phosphoric acid[49,50] are based on silylamide or alkylsilane elimination ortreatment of metal alkyls with phosphonic acids [51e53] can beemployed.

Here we report results of our study focused on the nonaqueoussynthesis of molecular zinc phosphates employing reactions of twotrimethylsilylesters of phosphoric acid, OP(OSiMe3)3 and OP(OSi-Me3)2(OH), with Zn[N(SiMe3)2]2 and/or ZnEt2. 1,1,1,5,5,5-hexafluoropentan-2,4-dione (hexafluoroacetylacetone, Hhfacac)was used in a subsequent reaction with bis(trimethylsilyl)aminegroups and modified the Zn coordination sphere. Thermal treat-ment was employed to convert molecular products to a-Zn2P2O7.

2. Experimental section

2.1. General methods

All manipulations were performed in a dry nitrogen atmosphereusing combined Schlenk and Stock techniques as well as in an M.Braun drybox with both H2O and O2 levels below 1 ppm. Zn[N(SiMe3)2]2 was synthesized from ZnCl2 and LiN(SiMe3)2 accord-ing to literature [54,55]. OP(OSiMe3)3 was prepared from H3PO4and Me3SiCl [56] and vacuum-distilled. OP(OSiMe3)2(OH) wasprepared by the reaction of KH2PO4 with Me3SiCl [57]. ZnEt2 (1 Msolution in heptane) and Hhfacac (1,1,1,5,5,5-hexafluoropentan-2,4-dione) were purchased from Aldrich and used as received. Tolueneand hexane were freshly distilled from Na/benzophenone underN2; pyridine was predried over KOH and distilled from phosphoruspentoxide before use. Benzene-d6 was dried over and distilled fromNa/K alloy and degassed prior to use. CDCl3 was dried by P2O5 andvacuum-transferred to an ampoule.

2.2. Characterization

The IR spectra (4000e400 cm�1) were recorded on a BrukerTensor T27 spectrometer. Samples were prepared as KBr pellets.

Table 1Crystal data and structure refinement parameters.

Compound number 1

Empirical formula C21H63N2O4PSi7Znfw 700.70Crystal system OrthorhombicSpace group PbcaTemperature, K 120(2)l, �A 0.71073a, �A 22.0917(6)b, �A 21.6835(4)c, �A 17.4249(4)a, deg 90b, deg 90g, deg 90V, �A3 8347.0(3)Z 8m, mm�1 0.852No. of reflns collected 92,270No. of indep. reflns (Rint) 7347 (0.0573)No. of data/restraints/parameters 7347/33/398GoF on F2 1.207R1,a wR2

b (I > 2s(I)) 0.0424, 0.0948R1,a wR2

b (all data) 0.0698, 0.1191Largest diff. peak/hole, e �A�3 0.731/�0.622

a R1 ¼ SjjFoj � jFcjj/SjFoj.b wR2 ¼ [Sw(Fo2 � Fc

2)2/S(Fo2)2]1/2.

CHN elemental analyses were performed at the Institute ofChemistry, UNAM, Mexico. Thermal analysis (TG/DSC) wasmeasured on a Netzsch STA 449C Jupiter apparatus from 25 to1100 �C under flowing air (70 cm3 min�1) with a heating rate of5 K min�1. The Zn and P content was analyzed on an ICP-OESspectrometer Jobin Yvon 170 Ultrace (generator 40 MHz, ampli-tude 1.0 kW, plasma gas flow 12 dm3 min�1) with the use of ab-sorption lines 213.618 nm (P) and 202.548 nm (Zn). The solutionNMR spectra were recorded on a Bruker Avance II 300 NMR spec-trometer at frequencies 300.1 MHz for 1H, 75.5 MHz for 13C,282.4 MHz for 19F, 121.5 MHz for 31P, 59.6 MHz for 29Si withdeuterated solvents as the external lock. The 1H and 13C{1H} NMRspectra were referenced to the residual proton signals or carbonresonances of benzene-d6 (7.16 and 128.39 ppm, respectively) andCDCl3 (7.24 and 77.23 ppm, respectively). EI-MS spectra were ob-tained on TSQ Quantum XLS with use of direct insertion probemethod. The ionization energy was set to 10 eV and the spectrawere scanned for m/z 35e1100 Da. APCI-MS measurement wasperformed on Agilent 6224 TOF LC-MS system. Solid samples weredissolved in toluene. The samples were injected via syringe pumpKDSModel 100 Series (KD Scientific, Inc., USA) into the electrosprayion source at a flow rate of 30 ml min�1 for two minute long ana-lyses. The spectra were recorded both in positive and negativemode for m/z 30e3200 Da at 4 GHz tuning for high resolution in-strument mode. The drying gas temperature of 200 �C and thedrying gas flow of 7 l/min with 30 psig for the nebulizer pressurewere used for ionization of analytes in ion source/ESI. The frag-mentor was set to 10 V and the capillary voltagewas�2000/4000 V(þ/�APCI). A Stoe-Cie transmission diffractometer STADI P oper-atingwith a Gemonochromatized Co (1.788965�A) radiation (40 kV,30 mA) and equipped with a PSD detector was used for the XRDdata acquisition at ambient temperature.

Diffraction data were collected on a KUMA KM-4 k-axis CCDdiffractometer with Mo-Ka radiation (l ¼ 0.71073 �A). The tem-perature during data collection was 120(2) K. The structures weresolved by direct methods and refined by standard methods usingShelXTL software package [58]. Details of the data collection andstructure refinement are listed in Table 1.

2 3

C19H29F12O8PSi3Zn C17H41N2O4PSi4Zn794.03 546.22Triclinic MonoclinicP1 P21/n120(2) 120(2)0.71073 0.7107310.7368(10) 12.3954(17)11.2924(9) 13.265(4)15.5880(14) 17.876(7)76.262(7) 9087.483(7) 100.458(18)71.926(7) 901744.4(3) 2890.4(15)2 40.953 1.09318,616 18,6626112 (0.0170) 5090 (0.0231)6112/0/406 5090/0/2740.884 1.0690.0387, 0.1106 0.0356, 0.09120.0561, 0.1332 0.0626, 0.11940.808/�0.551 0.632/�0.351

Fig. 1. Molecular structure of [Zn{N(SiMe3)2}2OP(OSiMe3)3] (1). H and C atoms of themethyl groups were omitted for clarity. Thermal ellipsoids were drawn at the 50%probability level.

J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203 199

2.3. Synthesis of [Zn{N(SiMe3)2}2OP(OSiMe3)3] (1)

OP(OSiMe3)3 (1.00 mmol, 315 mg) in toluene (1.0 cm3) wasadded at room temperature to a toluene solution (5.0 cm3) of Zn[N(SiMe3)2]2 (1.00mmol, 386mg). The reactionmixturewas stirredovernight. Single crystals were grown by slow cooling of concen-trated reaction mixture to �25 �C. Yield 476 mg (69%). 1H NMR(300.1 MHz, benzene-d6): d 0.21 (s, 29Si satell. 2JSiH ¼ 6.9 Hz, 13Csatell. 1JCH ¼ 119.7 Hz, POSi(CH3)3, 27H); 0.31 (s, 29Si satell.2JSiH ¼ 6.4 Hz, 13C satell. 1JCH ¼ 117.2 Hz, ZnNSi(CH3)3, 36H). 13C{1H}NMR (75.5 MHz, benzene-d6): d 1.2 (d, 2JPC ¼ 1.5 Hz, POSi(CH3)3);6.1 (s, NSi(CH3)3). 29Si{1H} NMR (59.6 MHz, benzene-d6): d �2.1 (s,NSi(CH3)3); 22.4 (d,2JPSi ¼ 5.1 Hz, POSi(CH3)3). 31P{1H} NMR(121.5 MHz, benzene-d6): d �28.1 (s, POSi(CH3)3). IR (KBr pellet,cm�1): n 2960 m, 2903 w, 1439 vw, 1259 m (dCH3), 1244 m, 1232 w,1069 m, 989 m, 937 w, 849 vs (rCH3), 762 w (rCH3), 669 w, 613 w.MS (m/z, rel. int.) APCI(þ): 315 (80) [OP(OSiMe3)3 þ H]þ; 387 (100)[Zn{N(SiMe3)2}2 þ H]þ; 419 (50); 530 (50); 629 (25); 683 (1)[M� CH3]þ; 1725 (50); APCI(�): 402 (80); 625 (100) [M� SiMe3]�;1047 (70). EA calcd for C21H63N2O4PSi7Zn: C, 36.00; H, 9.06; N, 4.00.Found C, 35.21; H, 8.17; N, 3.90. M.p. 51.3e51.8 �C.

2.4. Synthesis of [Zn(hfacac)2{OP(OSiMe3)3}] (2)

Hhfacac (1.00 mmol, 208 mg) in toluene (1.0 cm3) was added atroom temperature to the toluene solution (5.0 cm3) of 1(0.50 mmol, 350 mg). The reaction mixture was then heatedovernight to 50 �C. Volatile byproducts were removed underreduced pressure. A crude product was recrystallized from hexane.Yield (135 mg, 34%). 1H NMR (300.1 MHz, chloroform-d1): d 0.25 (s,POSi(CH3)3, 27H); 6.04 (s, (CF3CO)2CH, 2H). 1H NMR (300.1 MHz,benzene-d6): d 0.10 (s, POSi(CH3)3, 27H); 6.15 (s, (CF3CO)2CH, 2H).13C{1H} NMR (75.5 MHz, benzene-d6): d 0.32 (d, 3JPC ¼ 1.5 Hz,POSi(CH3)3); 90.20 (s, (CF3CO)2CH); 118.34 (q, 1JCF ¼ 284.6 Hz,(CF3CO)2CH); 180.70 (q, 2JCF ¼ 34.6 Hz, (CF3CO)2CH). 19F{1H}(282.4 MHz, chloroform-d1): d �77.06 (s, 12F). 31P{1H} NMR(124.5 MHz, benzene-d6): d �26.9 (s, 29Si satell, POSi(CH3)3). 29Si{1H} NMR (59.6 MHz, chloroform-d1): d 25.8 (d,2JPSi ¼ 5.8 Hz,POSi(CH3)3). IR (KBr pellet, cm�1): n 2966 vw, 1651 s (nCO), 1611 vw(nCC), 1560 w (nCO), 1535 m, 1495 m (nCO þ nCC), 1261 vs (nCF3),1204 s (nCF3), 1150 vs (dCH), 1097 m (nPO), 1072 m (nSiO), 853 s(rCH3), 800 m, 764 w (rCH3), 669 m, 590 w. MS (EI 10 eV, m/z, rel.int.): 585 (100) [Zn(hfacac)OP(OSiMe3)3]þ; 899 (60) [Zn(hfacac){OP(OSiMe3)3}2]þ; APCI(þ): 629 (10); 899 (100) [Zn(hfacac){OP(OSiMe3)3}2]þ; 1449 (10). M.p. 41.0e42.0 �C. EA calculated forC19H29F12O8PSi3Zn: C, 28.74; H, 3.68. Found: C, 28.46; H, 3.91.

2.5. Synthesis of [(Zn{(py)N(SiMe3)2}{m2-O2P(OSiMe3)2})2] (3)

To a stirred solution of OP(OSiMe3)2OH (1.00 mmol, 242 mg) inpyridine (5.0 cm3), a solution of ZnEt2 (0.50 mmol, 0.5 cm3, 1 M inheptane) was added dropwise. After evolution of gaseous byprod-ucts ceased, a solution of Zn[N(SiMe3)2]2 (0.50 mmol, 193 mg) intoluene (1 cm3) was added and the reaction mixture was stirred for1 h at room temperature. Volatile compounds were removed underreduced pressure and the obtained solid residue was redissolved inhexane. Crystals were grown by slow cooling to �25 �C. Yield124 mg, 23%. 1H NMR (300.1 MHz, chloroform-d1): d �0.01 (s,POSi(CH3)3, 36H); 0.04 (s, ZnNSi(CH3)3, 36H); 7.44 (m, py, 4H); 7.85(m, py, 4H); 8.81 (m, py, 2H). 1H NMR (300.1 MHz, benzene-d6):d 0.18 (s, POSi(CH3)3, 36H); 0.45 (s, ZnNSi(CH3)3, 36H); 6.83 (m, py,4H); 6.99 (m, py, 4H); 8.93 (m, py, 2H). 13C{1H} NMR (75.5 MHz,chloroform-d1): d 1.11 (d,2JPSi ¼ 1.4 Hz, POSi(CH3)3); 5.83 (s,NSi(CH3)3), 124.71 (s, py); 138.67 (s, py); 149.68 (s, py). 29Si{1H}NMR (59.6 MHz, benzene-d6): �4.5 (s, NSi(CH3)3); 16.7

(d,2JPSi¼ 5.8 Hz, POSi(CH3)3). 31P{1H} NMR (124.5MHz, chloroform-d1): �19.8 (s, POSi(CH3)3). IR (KBr pellet, cm�1): n 2963 m, 2947 w,2901 w, 1609 w, 1450 w, 1256 s (dCH3), 1207 m,1101 s, 1057 m,1015vs, 885 m, 847 vs (rCH3), 756 m (rCH3), 698 w, 667 w, 611 w. MS EI(10 eV, m/z, rel. int.): 275 (100); 299 (15) [OP(OSiMe3)3 � CH3]þ;369 (25) [Zn{N(SiMe3)2}2 � CH3]þ; 919 (10) [M � CH3 � 2py]þ.APCI(�): 706 (100) [Zn{N(SiMe3)2}{O2P(OSiMe3)2}2]�; 819/823(70) [isotope pattern for 2Zn]; 930/934 (90) [M � 2py]�; 962/966(50). M.p.158e159 �C dec. EA failed because of a partial dissociationof pyridine.

3. Results and discussion

In the area of zinc phosphate synthesis, many different routeshave been employed, both aqueous [15,25,28,29] and nonaqueous[30,32,53] with a corresponding array of precursors. To the best ofour knowledge, zinc amides have not yet been used as startingreagents for the preparation of zinc phosphate molecular com-plexes or extended structures. We decided to fill an existing gapand to explore the utility of Zn[N(SiMe3)2]2 as a reactive zinc pre-cursor. The use of a molecule with sterically demanding N(SiMe3)2groups may offer advantages in obtaining molecular productscontaining metal centers with a low coordination number andbeing soluble in organic solvents.

We expected the reaction pathway to follow the elimination oftris(trimethylsilyl)amine in analogy to the reactions of Al and Gaamides [49]. However, the combination of Zn[N(SiMe3)2]2 andOP(OSiMe3)3 in a 1:1 ratio in toluene led to a solid product [Zn{N(SiMe3)2}2OP(OSiMe3)3] (1). Compound 1 sublimes at 85 �C at1.3 Pa without decomposition. The X-ray diffraction analysis ofsingle crystals revealed a molecular structure shown in (Fig. 1). Therelevant bond lengths and angles are gathered in Table 2. Theadduct 1 is formed by coordination of phosphate ester through theterminal phosphoryl oxygen to the zinc atom of the amide mole-cule. According to CSD [59], this is only the second structurallycharacterized adduct of zinc amide with an oxygen donor pos-sessing a three-coordinate Zn atom. The low-coordination envi-ronment around zinc exhibits trigonal planar geometry (the sum of

Table 2Selected bond distances (�A) and angles (�) of 1.

Zn1eN2 1.897(3) Zn1eO1eP1 167.63(18)Zn1eN1 1.900(3) Si1eN1eSi2 125.46(17)Zn1eO1 2.036(3) N1eZn1eO1 109.33(11)P1eO1 1.470(3) N1eZn1eN2 141.68(13)P1eO2 1.530(3) N2eZn1eO1 108.93(12)P1eO3 1.545(3) O1eP1eO2 112.45(17)P1eO4 1.538(2) O3eP1eO4 104.66(14)

Fig. 2. Molecular structure of [Zn(hfacac)2OP(OSiMe3)3] (2). H and F atoms wereomitted for clarity. Thermal ellipsoids were drawn at the 50% probability level.

J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203200

valence angles is 359.97�). The coordinative bond in 1 (ZneO2.036(3) �A) is longer than covalent ZneOPO3 bonds in compoundswith Zn in a higher coordination (avr. 1.94 �A for CN ¼ 4, avr. 2.01 �Afor CN ¼ 5) [59]. However, the ZneOeP moiety is only slightly bentto 167.6� and the phosphoryl P]O bond (1.470(3) �A) is elongatedupon coordination to Zn when compared to uncoordinated moietyin OP(OSiPh3)3 (1.449(2) �A) [60]. However, the phosphoryl char-acter is clearly retained when compared to an average value of OePO3 bonds (avr. 1.52 �A) in open-framework zinc phosphates andzincephosphate complexes [59]. Coordination of phosphate esterto zinc caused also deviation of amidic N atoms from their originalnearly linear NeZneN arrangement (175.2�) to 141.7�. The ZneNdistances (avr. 1.899 �A) in 1 are longer than in parent Zn[N(SiMe3)2]2 (1.833 �A) [61].

The adduct 1 was characterized in solution by 1H, 13C{1H}, 29Si{1H}, and 31P{1H} NMR spectroscopy. The 1H NMR spectrum dis-plays two singlet resonances with chemical shifts of 0.21 and0.31 ppm; their 29Si satellites and a correct integral ratio 3:4correspond with trimethylsiloxy and bis(trimethylsilyl)amidogroups in 1. Similarly, there are two resonances in the 13C{1H} NMRspectrum. A doublet at 1.2 ppm (3JPC ¼ 1.5 Hz) and a singlet at6.1 ppm represent the methyl groups in POSiMe3 and NSiMe3,respectively. Two resonances are also present in the 29Si{1H} NMRspectrum; a singlet at �2.1 ppm belongs to bis(trimethylsilyl)am-ides and a doublet at 22.4 ppm (2JPSi¼ 5.1 Hz) shows coupling to theP nucleus in tris(trimethylsiloxy) moieties. The 31P{1H} NMRspectrum features only one resonance at �28.1 ppm, that points toa higher shielding of the P atom in adduct 1 as compared to the freeester OP(OSiMe3)3 (d ¼ �23.4 ppm). Repeated measurements ofNMR spectra in time confirmed stability of 1 in deuterated solventsat room temperature.

The IR spectrum of 1 displays strong bands of SiCH3 symmetricbending [62] and rocking vibrations at 1259 and 849/762 cm�1,respectively, which are characteristic for the SiMe3 groups [63].These bands are accompanied by weaker asymmetric and sym-metric SiC3 stretchings at 669 and 613 cm�1, respectively. Thebands at 1069 and 989 cm�1 are consistent with the presence of PeO and SieO bonds [64].

Mass spectra display fragments [M � Me]þ (in both APCIþ andEI 10 eV ionization modes) and [M � SiMe3]� (in APCI�mode) thatattest to the stability of ZneO]P coordination bond in the gas phase.Coupled with the fact that compound 1 sublimes under vacuum,

Scheme 1. Transformation of the zinc amide addu

these properties predestine 1 as a potential CVD precursor for thefabrication of zinc phosphate films by silylamide elimination re-action observed previously in aluminum amides [49]. Thermalanalysis TG/DSC in flowing air of 1 revealed an abrupt mass lossstarting from 90 �C. By 189 �C, about 64.5% of the weight was lostand at this point the process slowed down to finish at 350 �C. Therewas no more mass decrease up to 1000 �C, however, two broadexothermic effects appeared at 620 and 950 �C that can be attrib-uted to crystallization and phase transformation events. The totalmass change 87.4% was recorded at 1000 �C and the residue wasanalyzed by powder XRD to identify resulting crystalline phases. Allreflections in the diffractogram were assigned to a-Zn2P2O7 (PDFcard 8-238) which has the same stoichiometric Zn/P ratio as theprecursor 1. The calculated mass loss for the conversion of 1 toZn2P2O7 would require only 78.3%; the larger experimental value isprobably caused by a partial sublimation before decomposition.

The presence of reactive amide groups in the molecular product1 offers a possibility to further functionalize the molecule. For thisreason we tested the reactions of 1 with protic reagents includingMeOH, iPrOH and Hhfacac. While treatment of 1 with the alcohols(2 mol, in toluene) led to insoluble precipitates, the reaction(Scheme 1) with 2 equiv. of diketone provided a molecular com-pound [Zn(hfacac)2{OP(OSiMe3)3}], 2. The crystals were grown by aslow cooling of concentrated hexane solution of 2 in a freezer(�25 �C); the adduct is unstable to dissociation and decomposes onheating under vacuum. As shown by the single-crystal X-raydiffraction measurements (Fig. 2), the adduct 2 is of the same

ct 1 in the reaction with Hhfacac to adduct 2.

Table 3Selected bond distances (�A) and angles (�) of 2.

Zn1eO4 1.951(2) Zn1eO4eP1 139.93(14)Zn1eO7 2.009(2) O5eZn1eO8 165.60(9)Zn1eO6 2.019(2) O7eZn1eO6 138.34(9)Zn1eO5 2.055(2) O4eZn1eO6 109.33(10)Zn1eO8 2.065(2) O4eZn1eO7 112.33(10)P1eO4 1.480(2) O6eZn1eO5 87.89(9)P1eO1 1.538(2) O7eZn1eO8 87.67(8)P1eO2 1.544(2) O4eP1eO3 110.33(14)P1eO3 1.545(2) O1eP1eO2 106.21(13)

J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203 201

nuclearity as the starting complex 1. The amide groups werereplaced by two chelating hfacac ligands and the zinc coordinationnumber increased to five. The relevant bond lengths and angles aregathered in Table 3.

The central zinc atom is five-coordinate with a distorted square-pyramidal geometry. A quantitative measure for comparing realstructural parameters to idealized limiting geometries on the Berrypathway from a square pyramid to a trigonal bipyramid andquantifying the degree of stereochemical distortion is the param-eter s ¼ 100(b � a)/60, where b > aa are the trans angles notinvolving a unique ligand. The parameter adopts values from zeroto 100% for perfectly square-pyramidal and trigonal-bipyramidalgeometries, respectively [65]. Analysis of metric parameters of 2found s ¼ 45.5% which points to a distortion of the tetrahedralcomplex [Zn(hfacac)2] [66] upon coordination of OP(OSiMe3)3.Although the coordination number of zinc atom in 2 is higher thanin complex 1, the corresponding ZneO(P) distance (Table 3) in 2 isshorter (1.951(2) �A) than in 1 (ZneO 2.036(3) �A) and shorter thanan average phosphate bond length to five-coordinate Zn (avr.2.00�A) [59]. The value of ZneOeP angle in 2 is 139.93(14)� and theP]O distance of 1.480(2) �A is longer than 1.470(3) �A in 1.

The results of multinuclear NMR analysis agree with the mo-lecular structure determined by the X-ray diffraction experiments.The 1H NMR spectrum of 2 displays two resonances in a 27:2 ratiofor trimethylsilyl (0.10 ppm) and methine (6.15 ppm) hydrogenatoms. The CH resonance of 2 is shifted upfield with respect touncoordinated [Zn(hfacac)2] (6.23 ppm in CD2Cl2) and is very closeto the signal of [Zn(hfacac)2] observed in a coordinating solventacetone-d6 (6.02 ppm) [66]. This may imply coordination of theester in solution. Four resonances in the 13C{1H} NMR spectrum andone in both 19F{1H} (�77.1 ppm) and 31P{1H} NMR spectrum(�26.9 ppm) are in agreement with the molecular structure of 2and are shifted upfield with respect to uncoordinated [Zn(hfacac)2]and OP(OSiMe3)3. The resonance of OSiMe3 in the 29Si{1H} NMRspectrum is more deshielded (a doublet at 25.8 ppm, 2JPSi ¼ 5.8 Hz)then the corresponding resonances in OP(OSiMe3)3 and in 1. Alsothe coupling constant 2JPSi increases in the order ofOP(OSiMe3)3 < 1 < 2. The mass spectrum (EI, 10 eV) of 2 featuressignals at m/z 585 and 899 which represent the [Zn(hfacac){OP(OSiMe3)3}n]þ (n ¼ 1, 2) fragments. This attests to a certainstability of the ZneOeP bond. The infrared spectrum of 2 features

Scheme 2. Synthesis of cyclic

strong stretching bands of the CF3 groups as well as of the diket-onate backbone [67]. Thermal analysis of 2 shows an endothermiceffect on a DSC curve at 53.6 �C that can be ascribed to melting ofthe adduct. Continuous mass loss starts at 171 �C and finishes at223 �C with a complete sublimation/evaporation of the sample.

It has been reported recently that the reactions of bis(tertbu-toxy)phosphoric acid with zinc precursors (ZnEt2 and Zn(OAc)2)provide molecular zinc phosphates of high nuclearity [47,48]. Weexpected similar outcomes from the reaction of Zn[N(SiMe3)2]2with OP(OSiMe3)2(OH). However the reaction is probably modifiedby the presence of hexamethyldisilazane which is formed as abyproduct in the condensation reaction and subsequently silylatesOP(OSiMe3)2(OH) to OP(OSiMe3)3. The 31P NMR spectrum of thereaction mixture featured resonances of OP(OSiMe3)3 (�24.3 ppm),1 (�27.3 ppm) and two unidentified lines (�11.5 and �15.8 ppm)that may belong to [Zn{OP(O)(OSiMe3)2}2] and [(Me3Si)2NZn{OP(O)(OSiMe3)2}].

In addition to Zn[N(SiMe3)2]2 we tested also ZnEt2 as a zincprecursor in our reactions with tris(trimethylsilyl)ester of phos-phoric acid. In contrast to a facile formation of 1, 1H and 31P NMRanalysis of the reaction mixture containing the ester OP(OSiMe3)3and ZnEt2 in hexane does not indicate any reaction (adduct for-mation or condensation) at room temperature; nor even afterrefluxing the reaction mixture for 3 h or heating to 110 �C in asealed NMR tube for 28 h. However, evaporation of the solventresulted in an intractable mixture of oily products with a multitudeof resonances in its 31P{1H} NMR spectrum. The same results wereobtained by carrying out the reaction in toluene with the exceptionthat the mixture of products appeared already at roomtemperature.

In contrast to these observations, ZnEt2 exhibits a high reactivitytowards OP(OSiMe3)2(OH). The combination of both compounds atroom temperature was accompanied by vigorous evolution of gas.[(Zn{(py)N(SiMe3)2}{m2-O2P(OSiMe3)2})2] (3) was obtained in amoderate yield by mixing two equivalents of OP(OSiMe3)2(OH)with one equivalent of ZnEt2 and by subsequent addition of oneequivalent of Zn[N(SiMe3)2]2 (Scheme 2). The reaction had to becarried out in pyridine because in hexane the product did notcrystallize. The X-ray diffraction experiment established the mo-lecular structure of 3 which features a centrosymmetric cyclicinorganic core Zn2P2O4 in a chair-like conformation that is remi-niscent of the S4R building units of open-framework zinc phos-phates (Fig. 3). The relevant metric parameters are summarized inTable 4. The zinc atoms are connected by two silylphosphate[O2P(OSiMe3)2] bridging units (Zn(1)eO(1) 1.946(2), Zn(1)eO(4)#11.976(2) �A). The intraring OeZneO angle (98.8�) is much sharperthan the corresponding angles found in open-framework zincphosphates (av. 114.6�) or the OeAleO angles (av. 102.3�) in mo-lecular S4R aluminophosphates [(R2Al{m2-O2P(OSiMe3)2})2],R ¼ Me, Et, t-Bu [50,68] but it is comparable to the OeGaeO angle(99.4�) in gallophosphate [(t-Bu2Ga{m2-O2P(OSiMe3)2})2] [69]. TheOePeO angles (116.5�) are similar as in framework (av. 111.2�) andmolecular (av. 114.6�) metal phosphates [59,69]. The tetrahedral

zinc amide phosphate 3.

Fig. 3. Molecular structure of [(Zn{(py)N(SiMe3)2}{m2-O2P(OSiMe3)2})2] (3). All H and Catoms of the methyl groups were omitted for clarity. Thermal ellipsoids were drawn atthe 50% probability level.

J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203202

coordination sphere of zinc atoms includes one pyridine molecule(Zn(1)eN(2) 2.081(3) �A) and one amide group N(SiMe3)2 (Zn(1)eN(1) 1.921(3) �A). The two pyridine molecules on the ring are in atrans arrangement. Although the coordination properties of thering could imply the existence of cis/trans isomeric forms of 3 in thereaction mixture, the NMR analysis of mother liquor revealed onlyone set of signals probably corresponding to a fast on NMR timescale process of pyridine exchange. The static trans isomer wouldprovide the same number of signals as fast exchange averagedspecies but the cis molecule would require doubling the number ofOSiMe3 resonances. The zinc atoms contained in 3 probably origi-nate from two different zinc precursors. 31P NMR analysis of thereaction solution of ZnEt2 with 2 equiv. of OP(OSiMe3)2(OH) afterevolution of gaseous byproducts showed only a single resonancethat was different from the starting OP(OSiMe3)2(OH). We envisagethe formation of an intermediate mononuclear zinc phosphatecomplex [Zn(py)4{OP(O)(OSiMe3)2}2] with the octahedral zincatom stabilized by coordinated pyridine molecules. This hypo-thetical molecule has a precedent in crystallographically charac-terized [Zn(imz)4{OP(O)(O-t-Bu)2}2] [48]. However, we failed inattempts to isolate this intermediate. Moreover, when we evapo-rated the solvent the obtained solid residue was not soluble toallow further characterization. This observation could be inter-preted as a loss of coordinated pyridine molecules at the zinc atomfollowed by the formation of insoluble zinc phosphate coordinationpolymer. ICP-OES elemental analyses confirmed a Zn:P ratio of1:2.29 in the solid material.

Table 4Selected bond distances (�A) and angles (�) of 3.

Zn1eN1 1.921(3) N1eZn1eN2 109.32(11)Zn1eN2 2.081(3) O1eZn1eO4 98.78(9)Zn1eO1 1.946(2) O1eP1eO4 116.49(13)Zn1eO4 1.976(2) O3eP1eO2 105.34(14)P1eO1 1.486(2) P1eO1eZn1 137.99(14)P1eO2 1.554(2) P1eO4eZn1 133.25(14)P1eO3 1.552(2) Si3eN1eSi4 126.13(16)P1eO4 1.491(2)

Thermal behavior of molecular four-ring 3was examined by TG/DSC analysis to assess its potential as precursor to ceramic mate-rials [36,47,48]. The mass loss occurred in two steps (46.6% by220 �C and 19.9% by 600 �C). The total mass loss (66.7%) was in areasonable agreement with XRD analysis of residual white powder,which was identified as a crystalline a-phase of Zn2P2O7 (PDF card8-238). The theoretical value require 72.1%, the difference ispossibly caused by loss of pyridine during handling the sample.

4. Conclusions

Our investigation focused on the nonaqueous reactions of tri-methylsilylesters of phosphoric acid, OP(OSiMe3)3 and OP(OSi-Me3)2(OH), with Zn[N(SiMe3)2]2 and ZnEt2 brought three newmolecular zinc amide phosphate species soluble in organic sol-vents. The structures of crystalline molecular products 1, 2, and 3were determined by the X-ray diffraction analysis. The molecule 1is only the second structurally characterized adduct of zinc bisa-mide with an oxygen donor with a three-coordinate Zn atom. Thissublimable solid was converted to a-Zn2P2O7 by calcination andappears to be a promising precursor for CVD of ceramic films. Ahigh reactivity of the amide groups allowed conversion of 1 to achelate complex 2 in the reaction with Hhfacac. OP(OSiMe3)2(OH)reacts with ZnEt2 and Zn[N(SiMe3)2]2 to form the molecular com-pound 3 which features a cyclic inorganic core {Zn(m2-O2PO2)}2related to the single four-ring (S4R) building units of open-framework zinc phosphates. The reactive amide and trimethylsi-loxy substituents at the ring of 3 will be employed as connectingpoints in our further studies on the formation of extended struc-tures by nonhydrolytic condensation reactions.

Acknowledgments

Authors thank Dr. V. Vavra (MU) for recording the XRD data andDr. V. Jancik (UNAM) for CHN analyses. J.C. thanks to ErasmusProgram for supporting his research stay at University ofWürzburg.Z.M. thanks to Postdoc II CZ.1.07/2.3.00/30.0037. This work wassupported by CEITEC e Central European Institute of Technology(CZ.1.05/1.1.00/02.0068) and MOBILITY 7AMB13DE006.

Appendix A. Supplementary material

CCDC 953618e953620 contain the supplementary crystallo-graphic data for this paper. These data can be obtained free ofcharge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

References

[1] A.K. Cheetham, G. Ferey, T. Loiseau, Angew. Chem. Int. Ed. 38 (1999) 3268.[2] C.N.R. Rao, S. Natarajan, A. Choudhury, S. Neeraj, A.A. Ayi, Acc. Chem. Res. 34

(2001) 80.[3] W.T.A. Harrison, Curr. Opin. Solid State Mater. Sci. 6 (2002) 407.[4] R. Murugavel, A. Choudhury, M.G. Walawalkar, R. Pothiraja, C.N.R. Rao, Chem.

Rev. 108 (2008) 3549.[5] J. Yu, R. Xu, Acc. Chem. Res. 43 (2010) 1195.[6] A. Clearfield, Curr. Opin. Solid State Mater. Sci. 6 (2002) 495.[7] K. Maeda, Microporous Mesoporous Mater. 73 (2004) 47.[8] K.J. Gagnon, H.P. Perry, A. Clearfield, Chem. Rev. 112 (2012) 1034.[9] P. Falcaro, A.J. Hill, K.M. Nairn, J. Jasieniak, J.I. Mardel, T.J. Bastow, S.C. Mayo,

M. Gimona, D. Gomez, H.J. Whitfield, R. Ricco, A. Patelli, B. Marmiroli,H. Amenitsch, T. Colson, L. Villanova, D. Buso, Nat. Commun. 2 (2011) 237.

[10] M. Roming, C. Feldmann, Y.S. Avadhut, J. Schmedt auf der Günne, Chem.Mater. 20 (2008) 5787.

[11] P.-C. Jhang, N.-T. Chuang, S.-L. Wang, Angew. Chem. Int. Ed. 49 (2010) 4200.[12] T.E. Gier, G.D. Stucky, Nature 349 (1991) 508.[13] G.-Y. Yang, S.C. Sevov, J. Am. Chem. Soc. 121 (1999) 8389.[14] S. Neeraj, S. Natarajan, Chem. Mater. 12 (2000) 2753.[15] M. Wiebcke, Z. Anorg. Allg. Chem. 633 (2007) 98.

J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203 203

[16] S. Drumel, P. Janvier, D. Deniaud, B. Bujoli, J. Chem. Soc. Chem. Commun.(1995) 1051.

[17] Z. Fu, D. Song, Y. Zeng, S. Liao, J. Dai, Dalton Trans. 41 (2012) 10910.[18] A. Clearfield, Chem. Mater. 10 (1998) 2801.[19] R.M.P. Colodrero, A. Cabeza, P. Olivera-Pastor, D. Choquesillo-Lazarte,

J.M. Garcia-Ruiz, A. Turner, G. Ilia, B. Maranescu, K.E. Papathanasiou, G.B. Hix,K.D. Demadis, M.A.G. Aranda, Inorg. Chem. 50 (2011) 11202.

[20] A. Choudhury, S. Natarajan, C.N.R. Rao, J. Solid State Chem. 157 (2001) 110.[21] W.T.A. Harrison, Z. Bircsak, L. Hannooman, Z. Zhang, J. Solid State Chem. 136

(1998) 93.[22] S.-Y. Mao, Y. Xie, Z.-X. Xie, J.-T. Zhao, J. Alloys Compd. 456 (2008) 524.[23] S. Neeraj, S. Natarajan, C.N.R. Rao, Angew. Chem. Int. Ed. 38 (1999) 3480.[24] A. Choudhury, S. Natarajan, C.N.R. Rao, Inorg. Chem. 39 (2000) 4295.[25] R.I. Walton, A.J. Norquist, S. Neeraj, S. Natarajan, C.N.R. Rao, D. O’Hare, Chem.

Commun. (2001) 1990.[26] A.A. Ayi, A. Choudhury, S. Natarajan, S. Neeraj, C.N.R. Rao, J. Mater. Chem. 11

(2001) 1181.[27] A. Choudhury, S. Neeraj, S. Natarajan, C.N.R. Rao, J. Mater. Chem. 11 (2001)

1537.[28] S. Neeraj, C.N.R. Rao, A.K. Cheetham, J. Mater. Chem. (2004) 814.[29] S. Neeraj, A.K. Cheetham, Chem. Commun. (2002) 1738.[30] Y. Yang, J. Pinkas, M. Noltemeyer, H.G. Schmidt, H.W. Roesky, Angew. Chem.

Int. Ed. 38 (1999) 664.[31] V. Chandrasekhar, T. Senapati, A. Dey, S. Hossain, Dalton Trans. 40 (2011) 5394.[32] Z. Fu, T. Chivers, Inorg. Chem. 44 (2005) 7292.[33] C. Lei, J.-G. Mao, Y.-Q. Sun, H.-Y. Zeng, A. Clearfield, Inorg. Chem. 42 (2003)

6157.[34] R. Murugavel, S. Kuppuswamy, R. Boomishankar, A. Steiner, Angew. Chem. Int.

Ed. 45 (2006) 5536.[35] R. Murugavel, S. Shanmugan, Dalton Trans. (2008) 5358.[36] R. Murugavel, S. Kuppuswamy, N. Gogoi, R. Boomishankar, A. Steiner, Chem.

Eur. J. 16 (2010) 994.[37] R. Murugavel, S. Kuppuswamy, N. Gogoi, A. Steiner, Inorg. Chem. 49 (2010)

2153.[38] A.Ch. Kalita, C. Roch-Marchal, R. Murugavel, Dalton Trans. 42 (2013) 9755.[39] W.T.A. Harrison, L. Hannooman, J. Solid State Chem. 131 (1997) 363.[40] C.N.R. Rao, S. Natarajan, S. Neeraj, J. Solid State Chem. 152 (2000) 302.[41] I. Macdonald, W.T.A. Harrison, Inorg. Chem. 41 (2002) 6184.[42] S. Neeraj, S. Natarajan, C.N.R. Rao, J. Solid State Chem. 150 (2000) 417.

[43] C.N.R. Rao, S. Natarajan, S. Neeraj, J. Am. Chem. Soc. 122 (2000) 2810.[44] S. Natarajan, L. van Wullen, W. Klein, M. Jansen, Inorg. Chem. 42 (2003) 6265.[45] L. Li, T. Su, J. Li, J. Xu, J. Yu, R. Xu, Inorg. Chim. Acta 370 (2011) 65.[46] C.G. Lugmair, T.D. Tilley, Inorg. Chem. 37 (1998) 6304.[47] C.G. Lugmair, T.D. Tilley, A.L. Rheingold, Chem. Mater. 9 (1997) 339.[48] R. Murugavel, M. Sathiyendiran, M.G. Walawalkar, Inorg. Chem. 40 (2001)

427.[49] J. Pinkas, H. Wessel, Y. Yang, M.L. Montero, M. Noltemeyer, M. Froba,

H.W. Roesky, Inorg. Chem. 37 (1998) 2450.[50] J. Pinkas, D. Chakraborty, Y. Yang, R. Murugavel, M. Noltemeyer, H.W. Roesky,

Organometallics 18 (1999) 523.[51] Y. Yang, H.G. Schmidt, M. Noltemeyer, J. Pinkas, H.W. Roesky, J. Chem. Soc.

Dalton Trans. (1996) 3609.[52] Y. Yang, M.G. Walawalkar, J. Pinkas, H.W. Roesky, H.G. Schmidt, Angew. Chem.

Int. Ed. 37 (1998) 96.[53] P. Gerbier, C. Guérin, B. Henner, J.-R. Unal, J. Mater. Chem. 9 (1999) 2559.[54] H. Burger, W. Sawodny, U. Wannagat, J. Organomet. Chem. 3 (1965) 113.[55] M. Bochmann, G. Bwembya, K.J. Webb, Inorg. Synth. 31 (1997) 19.[56] Ger. Pat. DE 4323183A1, 1995.[57] K.A. Andrianov, B.N. Rutovskii, A.A. Kazakova, Zh. Obshch. Khim. 26 (1956)

267.[58] G.M. Sheldrick, Acta Crystallogr. A 64 (2008) 112.[59] F.H. Allen, Acta Crystallogr. B 58 (2002) 380.[60] G. Ferguson, B.J. O’Leary, T.R. Spalding, Acta Crystallogr. E 61 (2005) O906.[61] G. Margraf, H.W. Lerner, M. Bolte, M. Wagner, Z. Anorg. Allg. Chem. 630 (2004)

217.[62] H. Niida, M. Takahashi, T. Uchino, T. Yoko, J. Non-Cryst. Solids 306 (2002) 292.[63] Y.Y. Song, Y.N. Huang, E.A. Havenga, I.S. Butler, Vib. Spectrosc. 27 (2001) 127.[64] A. Aronne, M. Turco, G. Bagnasco, P. Pernice, M. Di Serio, N.J. Clayden,

E. Marenna, E. Fanelli, Chem. Mater. 17 (2005) 2081.[65] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, J. Chem. Soc.

Dalton Trans. (1984) 1349.[66] E.V. Dikarev, H.L. Zhang, B. Li, J. Am. Chem. Soc. 127 (2005) 6156.[67] P.M. Visintin, C.A. Bessel, P.S. White, C.K. Schauer, J.M. DeSimone, Inorg. Chem.

44 (2005) 316.[68] M.R. Mason, R.M. Matthews, M.S. Mashuta, J.F. Richardson, Inorg. Chem. 35

(1996) 5756.[69] M.R. Mason, A.M. Perkins, R.M. Matthews, J.D. Fisher, M.S. Mashuta, A. Vij,

Inorg. Chem. 37 (1998) 3734.

本文献由“学霸图书馆-文献云下载”收集自网络，仅供学习交流使用。

学霸图书馆（www.xuebalib.com）是一个“整合众多图书馆数据库资源，

提供一站式文献检索和下载服务”的24 小时在线不限IP

图书馆。

图书馆致力于便利、促进学习与科研，提供最强文献下载服务。

图书馆导航：

图书馆首页 文献云下载 图书馆入口 外文数据库大全 疑难文献辅助工具