Nonaqueous synthesis of molecular zinc amide phosphate

Article abstract of DOI:10.1016/j.jorganchem.2013.09.040

Three new molecular zinc compounds were prepared by nonaqueous reactions of Zn[N(SiMe₃)₂]₂ and ZnEt₂ 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 mononuclear complexes [ZnX₂OP(OSiMe₃)₃] (X = N(SiMe ₃)₂ (1), hfacac = hexafluoroacetylacetonate, (2)) and one dinuclear zinc phosphate [(Zn{(py)N(SiMe₃)₂} {μ₂-O₂P(OSiMe₃)₂})₂] (3). Compound 1 is only the second structurally characterized adduct of zinc bisamide with an oxygen donor and a three-coordinate Zn atom. The cyclic inorganic core {Zn(μ₂-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 trimethylsiloxy groups that can be employed in further studies on the formation of extended structures by condensation reactions. Spectroscopic properties and thermal behavior of the molecular products were examined. Compounds 1 and 3 were converted to α-Zn₂P₂O₇ by calcination.

Full text of DOI:10.1016/j.jorganchem.2013.09.040

Journal of Organometallic Chemistry 749 (2014) 197e203
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Nonaqueous synthesis of molecular zinc amide phosphate
a
a
a
b
a,
*
Jan Chyba , Zdenek Moravec , Marek Necas , Sanjay Mathur , Jiri Pinkas
a
Department of Chemistry and CEITEC MU, Masaryk University, Kotlarska 2, CZ-61137 Brno, Czech Republic
Institute of Inorganic Chemistry, University of Cologne, Greinstraße 6, D-50939 Cologne, Germany
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 August 2013
Received in revised form
3 2 2
Three new molecular zinc compounds were prepared by nonaqueous reactions of Zn[N(SiMe ) ] and
ZnEt
ray diffraction analyses of crystalline products revealed molecular structures of two mononuclear
complexes [ZnX OP(OSiMe (1), hfacac ¼ hexafluoroacetylacetonate, (2)) and one
] (X ¼ N(SiMe
dinuclear zinc phosphate [(Zn{(py)N(SiMe -O P(OSiMe }) ] (3). Compound 1 is only the second
structurally characterized adduct of zinc bisamide with an oxygen donor and a three-coordinate Zn atom.
The cyclic inorganic core {Zn( -O PO )} in 3 is a model for the most common single four-ring (S4R)
2 3 3 3 2
with trimethylsilylesters of phosphoric acid, OP(OSiMe ) and OP(OSiMe ) (OH). Single-crystal X-
30 September 2013
2
3
)
3
3 2
)
Accepted 30 September 2013
3
)
2
}{
m
2
2
3
)
2
2
Keywords:
Zinc
Amide
Phosphate
X-ray structure
Nonaqueous
m
2
2
2
2
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 by
condensation reactions. Spectroscopic properties and thermal behavior of the molecular products were
examined. Compounds 1 and 3 were converted to
a-Zn
2
P
2
O
7
by calcination.
Ó 2013 Elsevier B.V. All rights reserved.
1
. Introduction
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 molecular
zinc phosphates and phosphonates have been mainly prepared by
Zinc phosphates [1e5] and phosphonates [6e8] constitute a
very rich and structurally interesting group of compounds that
include species featuring various nuclearity, dimensionality and
architecture modes. The unabated interest in these compounds
spans from their function as open-framework materials to their use
as 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 potential
applications in catalysis, sorption, ion exchange, and luminescence
the reactions of zinc precursors, such as ZnR
2
(R ¼ Me, Et),
Zn(OAc) , ZnCl , ZnO, with phosphoric and phosphonic acids and
2
2
their alkyl and aryl esters and feature a variety of cage structures
[30e33]. The reactions often involve bases with O and N donor
atoms which are then included as co-ligands in the coordination
spheres of zinc atoms or compensate the cluster charge as pro-
tonated cations. One of the frequent structural motifs is a cube-like
double-four-ring (D4R) unit that was used for the assembly of zinc
phosphates with different supramolecular architectures [34e38].
By far the most prevalent molecular units in zinc phosphates are
[11]. The most pertinent for these purposes are 3-dimensional (3D)
zeolite-like networks [12e16] but layer (2D) [17e20] and chain or
ladder (1D) [21,22] structures are also frequently reported. The
mechanism of formation of zinc phosphates was investigated with
considerable effort and it was shown that low dimensional struc-
tures can be converted to higher-dimensionality frameworks upon
changing reaction conditions [23e25]. Analysis of these reactions
suggests that small clusters serve as the starting species that
condense to chains or ladders and subsequently transform to layer
structures to finally form 3D frameworks [26,27]. The major syn-
thetic route to zinc phosphates is the hydrothermal synthesis
employing zinc salts, phosphoric acid and organic amines serving
2 2 4
Zn P O cycles, also called single-four-rings (S4R) [39e41], which
were shown to be important intermediates in the formation of
open-framework structures. These basic units are formed as the
first 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 or
3D-networks [42e45]. The molecular zinc phosphates were also
used directly as precursors in the thermolytic preparation of layer
and ceramic materials [46e48].
Nonaqueous or organometallic synthetic routes to oxide and
phosphate materials offer certain advantages over their aqueous
counterparts, such as a better control of condensation reactions,
residual reactive functional surface groups in products, and a wider
choice of precursors. These nonaqueous condensation reactions
*
Corresponding author. Tel.: þ420 549496493; fax: þ420 549492443.
E-mail address: jpinkas@chemi.muni.cz (J. Pinkas).
0
022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.09.040

198
J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203
provided a large number of molecular and extended-structure
metal phosphates and phosphonates. The reactions of metal am-
ides or metal alkyls with tris(trimethylsilyl)ester of phosphoric acid
CHN elemental analyses were performed at the Institute of
Chemistry, UNAM, Mexico. Thermal analysis (TG/DSC) was
measured on a Netzsch STA 449C Jupiter apparatus from 25 to
ꢁ
3
ꢀ1
[49,50] are based on silylamide or alkylsilane elimination or
1100 C under flowing air (70 cm min ) with a heating rate of
ꢀ
1
treatment of metal alkyls with phosphonic acids [51e53] can be
employed.
Here we report results of our study focused on the nonaqueous
synthesis of molecular zinc phosphates employing reactions of two
5 K min . The Zn and P content was analyzed on an ICP-OES
spectrometer Jobin Yvon 170 Ultrace (generator 40 MHz, ampli-
3
ꢀ1
tude 1.0 kW, plasma gas flow 12 dm min ) with the use of ab-
sorption lines 213.618 nm (P) and 202.548 nm (Zn). The solution
NMR spectra were recorded on a Bruker Avance II 300 NMR spec-
trimethylsilylesters of phosphoric acid, OP(OSiMe
3
)
3
and OP(OSi-
1,1,1,5,5,5-
1
13
Me (OH), with Zn[N(SiMe and/or ZnEt
3
)
2
3
)
2
]
2
2
.
trometer at frequencies 300.1 MHz for H, 75.5 MHz for C,
19
31
29
hexafluoropentan-2,4-dione (hexafluoroacetylacetone, Hhfacac)
was used in a subsequent reaction with bis(trimethylsilyl)amine
groups and modified the Zn coordination sphere. Thermal treat-
282.4 MHz for F, 121.5 MHz for P, 59.6 MHz for Si with
deuterated solvents as the external lock. The H and C{ H} NMR
spectra were referenced to the residual proton signals or carbon
1
13
1
ment was employed to convert molecular products to
a
-Zn
2
P
2
O
7
.
resonances of benzene-d
6
(7.16 and 128.39 ppm, respectively) and
CDCl (7.24 and 77.23 ppm, respectively). EI-MS spectra were ob-
3
2
. Experimental section
tained on TSQ Quantum XLS with use of direct insertion probe
method. The ionization energy was set to 10 eV and the spectra
were scanned for m/z 35e1100 Da. APCI-MS measurement was
performed on Agilent 6224 TOF LC-MS system. Solid samples were
dissolved in toluene. The samples were injected via syringe pump
KDS Model 100 Series (KD Scientific, Inc., USA) into the electrospray
2.1. General methods
All manipulations were performed in a dry nitrogen atmosphere
using combined Schlenk and Stock techniques as well as in an M.
Braun drybox with both H O and O levels below 1 ppm. Zn
N(SiMe was synthesized from ZnCl and LiN(SiMe accord-
ing to literature [54,55]. OP(OSiMe was prepared from H PO
and Me SiCl [56] and vacuum-distilled. OP(OSiMe (OH) was
prepared by the reaction of KH PO with Me SiCl [57]. ZnEt (1 M
ꢀ1
ion source at a flow rate of 30 ml min for two minute long ana-
lyses. The spectra were recorded both in positive and negative
2
2
[
3
)
2
]
2
2
3
)
2
3
)
3
3
4
mode for m/z 30e3200 Da at 4 GHz tuning for high resolution in-
ꢁ
3
3
)
2
strument mode. The drying gas temperature of 200 C and the
drying gas flow of 7 l/min with 30 psig for the nebulizer pressure
were used for ionization of analytes in ion source/ESI. The frag-
mentor was set to 10 V and the capillary voltage was ꢀ2000/4000 V
(þ/ꢀAPCI). A Stoe-Cie transmission diffractometer STADI P oper-
2
4
3
2
solution in heptane) and Hhfacac (1,1,1,5,5,5-hexafluoropentan-2,4-
dione) were purchased from Aldrich and used as received. Toluene
and hexane were freshly distilled from Na/benzophenone under
ꢀ
N
2
; pyridine was predried over KOH and distilled from phosphorus
ating with a Ge monochromatized Co (1.788965 A) radiation (40 kV,
pentoxide before use. Benzene-d was dried over and distilled from
6
30 mA) and equipped with a PSD detector was used for the XRD
data acquisition at ambient temperature.
3 2 5
Na/K alloy and degassed prior to use. CDCl was dried by P O and
vacuum-transferred to an ampoule.
Diffraction data were collected on a KUMA KM-4 k-axis CCD
ꢀ
diffractometer with Mo-K
a
radiation (
l
¼ 0.71073 A). The tem-
2.2. Characterization
perature during data collection was 120(2) K. The structures were
solved by direct methods and refined by standard methods using
ShelXTL software package [58]. Details of the data collection and
structure refinement are listed in Table 1.
The IR spectra (4000e400 cmꢀ1) were recorded on a Bruker
Tensor T27 spectrometer. Samples were prepared as KBr pellets.
Table 1
Crystal data and structure refinement parameters.
Compound number
1
2
3
Empirical formula
fw
Crystal system
Space group
C
21
H
63
N
2
O
4
PSi
7
Zn
C
19
H
29
F
12
O
8
PSi
3
Zn
C
17 41 2 4 4
H N O PSi Zn
700.70
Orthorhombic
Pbca
794.03
Triclinic
P1
546.22
Monoclinic
P2 /n
1
Temperature, K
120(2)
120(2)
0.71073
120(2)
0.71073
ꢀ
l
, A
0.71073
22.0917(6)
21.6835(4)
17.4249(4)
90
90
90
8347.0(3)
8
0.852
ꢀ
a, A
b, A
c, A
10.7368(10)
11.2924(9)
15.5880(14)
76.262(7)
87.483(7)
71.926(7)
1744.4(3)
2
12.3954(17)
13.265(4)
17.876(7)
90
100.458(18)
90
2890.4(15)
4
1.093
ꢀ
ꢀ
a
b
, deg
, deg
, deg
g
ꢀ
3
V, A
Z
m
ꢀ1
, mm
0.953
No. of reflns collected
No. of indep. reflns (Rint
92,270
18,616
18,662
)
7347 (0.0573)
7347/33/398
1.207
0.0424, 0.0948
0.0698, 0.1191
0.731/ꢀ0.622
6112 (0.0170)
6112/0/406
0.884
0.0387, 0.1106
0.0561, 0.1332
0.808/ꢀ0.551
5090 (0.0231)
5090/0/274
1.069
0.0356, 0.0912
0.0626, 0.1194
0.632/ꢀ0.351
No. of data/restraints/parameters
2
GoF on F
a
a
b
b
R
R
1
,
,
wR
wR
2
2
(I > 2
s
(I))
1
(all data)
ꢀ
ꢀ3
Largest diff. peak/hole, e A
a
R
wR
1
¼ SjjF
o
j ꢀ jF
c
jj/SjF
o
j.
b
2
2
2
2)2]1/2.
2
¼ [Sw(F
o
ꢀ F
c
) /S(F
o

J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203
199
3 3
)
). 31P{ H} NMR (124.5 MHz, chloroform-
1
2
.3. Synthesis of [Zn{N(SiMe
3
)
2
}
2
OP(OSiMe
3
)
3
] (1)
(d,2JPSi ¼ 5.8 Hz, POSi(CH
ꢀ1
d
1
): ꢀ19.8 (s, POSi(CH
3
)
3
). IR (KBr pellet, cm ):
n
2963 m, 2947 w,
3
OP(OSiMe
added at room temperature to a toluene solution (5.0 cm ) of Zn
N(SiMe (1.00 mmol, 386 mg). The reaction mixture was stirred
overnight. Single crystals were grown by slow cooling of concen-
3
)
3
(1.00 mmol, 315 mg) in toluene (1.0 cm ) was
2901 w, 1609 w, 1450 w, 1256 s (
dCH
3
), 1207 m, 1101 s, 1057 m, 1015
3
vs, 885 m, 847 vs ( CH ), 756 m (
r
3
r
CH
3
), 698 w, 667 w, 611 w. MS EI
þ
[
3
)
2
]
2
(10 eV, m/z, rel. int.): 275 (100); 299 (15) [OP(OSiMe
3
)
3
ꢀ CH
3
] ;
ꢀ 2py] .
þ
þ
369 (25) [Zn{N(SiMe
3
)
2
}
2
ꢀ CH
3
] ; 919 (10) [M ꢀ CH
3
ꢁ
1
ꢀ
trated reaction mixture to ꢀ25 C. Yield 476 mg (69%). H NMR
APCI(ꢀ): 706 (100) [Zn{N(SiMe
3
)
2
}{O
2
P(OSiMe
3
)
2
}
2
] ; 819/823
2
9
2
13
ꢀ
(
300.1 MHz, benzene-d
6
):
d
0.21 (s, Si satell.
J
SiH ¼ 6.9 Hz,
C
(70) [isotope pattern for 2Zn]; 930/934 (90) [M ꢀ 2py] ; 962/966
1
29
ꢁ
satell.
J
CH ¼ 119.7 Hz, POSi(CH
3
)
3
, 27H); 0.31 (s,
Si satell.
(50). M.p.158e159 C dec. EA failed because of a partial dissociation
2
13
1
, 36H). 13C{ H}
);
ꢀ2.1 (s,
1
J
SiH ¼ 6.4 Hz, C satell. JCH ¼ 117.2 Hz, ZnNSi(CH
3
)
3
of pyridine.
2
NMR (75.5 MHz, benzene-d
6
):
d
1.2 (d, JPC ¼ 1.5 Hz, POSi(CH
3 3
)
29
1
6
.1 (s, NSi(CH
NSi(CH
); 22.4 (d, JPSi ¼ 5.1 Hz, POSi(CH
121.5 MHz, benzene-d ):
ꢀ28.1 (s, POSi(CH
2960 m, 2903 w, 1439 vw, 1259 m ( CH
069 m, 989 m, 937 w, 849 vs ( CH ), 762 w ( CH
3 3 6
) ). Si{ H} NMR (59.6 MHz, benzene-d ): d
2
31
1
3. Results and discussion
3
)
3
3
)
3
).
). IR (KBr pellet,
3
), 1244 m, 1232 w,
P{ H} NMR
(
6
d
3 3
)
ꢀ
1
In the area of zinc phosphate synthesis, many different routes
have been employed, both aqueous [15,25,28,29] and nonaqueous
[30,32,53] with a corresponding array of precursors. To the best of
our knowledge, zinc amides have not yet been used as starting
reagents for the preparation of zinc phosphate molecular com-
plexes or extended structures. We decided to fill an existing gap
cm ):
n
d
1
r
3
r
3
), 669 w, 613 w.
þ H] ; 387 (100)
þ
MS (m/z, rel. int.) APCI(þ): 315 (80) [OP(OSiMe
3
)
3
þ
[
[
1
Zn{N(SiMe
3
)
2
}
2
þ H] ; 419 (50); 530 (50); 629 (25); 683 (1)
þ
ꢀ
M ꢀ CH
3
] ; 1725 (50); APCI(ꢀ): 402 (80); 625 (100) [M ꢀ SiMe
3
] ;
047 (70). EA calcd for C21
63 2 4 7
H N O PSi Zn: C, 36.00; H, 9.06; N, 4.00.
and to explore the utility of Zn[N(SiMe
cursor. The use of a molecule with sterically demanding N(SiMe )
3 2 2
) ] as a reactive zinc pre-
ꢁ
Found C, 35.21; H, 8.17; N, 3.90. M.p. 51.3e51.8 C.
3 2
groups may offer advantages in obtaining molecular products
containing metal centers with a low coordination number and
being soluble in organic solvents.
We expected the reaction pathway to follow the elimination of
tris(trimethylsilyl)amine in analogy to the reactions of Al and Ga
2
.4. Synthesis of [Zn(hfacac)
2 3 3
{OP(OSiMe ) }] (2)
3
Hhfacac (1.00 mmol, 208 mg) in toluene (1.0 cm ) was added at
3
room temperature to the toluene solution (5.0 cm ) of
1
(
0.50 mmol, 350 mg). The reaction mixture was then heated
amides [49]. However, the combination of Zn[N(SiMe
3
)
2
]
2
and
ꢁ
overnight to 50 C. Volatile byproducts were removed under
reduced pressure. A crude product was recrystallized from hexane.
Yield (135 mg, 34%). H NMR (300.1 MHz, chloroform-d
OP(OSiMe
{N(SiMe
3
)
3
in a 1:1 ratio in toluene led to a solid product [Zn
ꢁ
1
3
)
2
}
2
OP(OSiMe
3
)
3
] (1). Compound 1 sublimes at 85 C at
1
):
CH, 2H). H NMR (300.1 MHz,
, 27H); 6.15 (s, (CF CO) CH, 2H).
PC ¼ 1.5 Hz,
d 0.25 (s,
1
1.3 Pa without decomposition. The X-ray diffraction analysis of
single crystals revealed a molecular structure shown in (Fig. 1). The
relevant bond lengths and angles are gathered in Table 2. The
adduct 1 is formed by coordination of phosphate ester through the
terminal phosphoryl oxygen to the zinc atom of the amide mole-
cule. According to CSD [59], this is only the second structurally
characterized 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
POSi(CH
3
)
3
, 27H); 6.04 (s, (CF
): 0.10 (s, POSi(CH
C{ H} NMR (75.5 MHz, benzene-d
POSi(CH ); 90.20 (s, (CF CO) CH); 118.34 (q,
CF ¼ 34.6 Hz, (CF
):
3 2
CO)
benzene-d
6
d
3
)
3
3
2
13
1
3
6
): d 0.32 (d, J
1
3
)
3
3
J
2
J
CF ¼ 284.6 Hz,
2
19 1
(
(
(
CF
282.4 MHz, chloroform-d
124.5 MHz, benzene-d ):
H} NMR (59.6 MHz, chloroform-d
3
CO)
2
CH); 180.70 (q,
3
CO)
2
CH). F{ H}
P{ H} NMR
3
1
1
1
d
ꢀ77.06 (s, 12F).
2
9
29
6
d
ꢀ26.9 (s, Si satell, POSi(CH
3 3
) ). Si
1
2
{
1
):
2966 vw, 1651 s (
CO), 1535 m, 1495 m ( CC), 1261 vs (
CO þ
), 1150 vs ( CH), 1097 m ( PO), 1072 m ( SiO), 853 s
), 800 m, 764 w ( CH ), 669 m, 590 w. MS (EI 10 eV, m/z, rel.
d
25.8 (d, JPSi ¼ 5.8 Hz,
CO), 1611 vw
CF ),
ꢀ
1
POSi(CH
3
)
3
). IR (KBr pellet, cm ):
n
n
(
1
n
CC), 1560 w (
204 s ( CF
CH
n
n
n
n
3
n
3
d
n
n
(r
3
r
3
þ
int.): 585 (100) [Zn(hfacac)OP(OSiMe
3
)
3
] ; 899 (60) [Zn(hfacac)
þ
þ
{
{
OP(OSiMe
OP(OSiMe
3
)
)
3
}
}
2
] ; APCI(þ): 629 (10); 899 (100) [Zn(hfacac)
ꢁ
3
3
2
] ; 1449 (10). M.p. 41.0e42.0 C. EA calculated for
Zn: C, 28.74; H, 3.68. Found: C, 28.46; H, 3.91.
C
H
19 29
F
12
O
8
PSi
3
2
.5. Synthesis of [(Zn{(py)N(SiMe -O
3
)
2
}{
m
2
2 3 2 2
P(OSiMe ) }) ] (3)
To a stirred solution of OP(OSiMe ) OH (1.00 mmol, 242 mg) in
3 2
3
3
pyridine (5.0 cm ), a solution of ZnEt
heptane) was added dropwise. After evolution of gaseous byprod-
ucts ceased, a solution of Zn[N(SiMe (0.50 mmol, 193 mg) in
toluene (1 cm ) was added and the reaction mixture was stirred for
h at room temperature. Volatile compounds were removed under
2
(0.50 mmol, 0.5 cm , 1 M in
3 2 2
) ]
3
1
reduced pressure and the obtained solid residue was redissolved in
ꢁ
hexane. Crystals were grown by slow cooling to ꢀ25 C. Yield
1
24 mg, 23%. 1H NMR (300.1 MHz, chloroform-d
1
):
d
ꢀ0.01 (s,
POSi(CH
(
3
)
3
, 36H); 0.04 (s, ZnNSi(CH
3
)
3
, 36H); 7.44 (m, py, 4H); 7.85
):
3 3 3 3
) , 36H); 0.45 (s, ZnNSi(CH ) , 36H); 6.83 (m, py,
1
m, py, 4H); 8.81 (m, py, 2H). H NMR (300.1 MHz, benzene-d
6
d
0.18 (s, POSi(CH
H); 6.99 (m, py, 4H); 8.93 (m, py, 2H). C{ H} NMR (75.5 MHz,
1
3
1
4
2
chloroform-d
NSi(CH ), 124.71 (s, py); 138.67 (s, py); 149.68 (s, py). Si{ H}
NMR (59.6 MHz, benzene-d ); 16.7
): ꢀ4.5 (s, NSi(CH
1
):
d
1.11 (d, JPSi ¼ 1.4 Hz, POSi(CH
3 3
) ); 5.83 (s,
3 2 2 3 3
Fig. 1. Molecular structure of [Zn{N(SiMe ) } OP(OSiMe ) ] (1). H and C atoms of the
methyl groups were omitted for clarity. Thermal ellipsoids were drawn at the 50%
probability level.
2
9
1
3 3
)
6
3 3
)

200
J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203
Table 2
Selected bond distances (A) and angles ( ) of 1.
ꢀ
ꢁ
Zn1eN2
Zn1eN1
Zn1eO1
P1eO1
P1eO2
P1eO3
P1eO4
1.897(3)
1.900(3)
2.036(3)
1.470(3)
1.530(3)
1.545(3)
1.538(2)
Zn1eO1eP1
167.63(18)
125.46(17)
109.33(11)
141.68(13)
108.93(12)
112.45(17)
104.66(14)
Si1eN1eSi2
N1eZn1eO1
N1eZn1eN2
N2eZn1eO1
O1eP1eO2
O3eP1eO4
ꢁ
valence angles is 359.97 ). The coordinative bond in 1 (ZneO
ꢀ
2
3
.036(3) A) is longer than covalent ZneOPO bonds in compounds
ꢀ
ꢀ
with Zn in a higher coordination (avr. 1.94 A for CN ¼ 4, avr. 2.01 A
for CN ¼ 5) [59]. However, the ZneOeP moiety is only slightly bent
ꢁ
ꢀ
to 167.6 and the phosphoryl P]O bond (1.470(3) A) is elongated
upon coordination to Zn when compared to uncoordinated moiety
ꢀ
in OP(OSiPh
3
)
3
(1.449(2) A) [60]. However, the phosphoryl char-
acter is clearly retained when compared to an average value of Oe
ꢀ
3
PO bonds (avr. 1.52 A) in open-framework zinc phosphates and
zincephosphate complexes [59]. Coordination of phosphate ester
to zinc caused also deviation of amidic N atoms from their original
ꢁ
ꢁ
nearly linear NeZneN arrangement (175.2 ) to 141.7 . The ZneN
ꢀ
2 3 3
Fig. 2. Molecular structure of [Zn(hfacac) OP(OSiMe ) ] (2). H and F atoms were
omitted for clarity. Thermal ellipsoids were drawn at the 50% probability level.
distances (avr. 1.899 A) in 1 are longer than in parent Zn
ꢀ
[
N(SiMe
3
)
2
]
2
(1.833 A) [61].
The adduct 1 was characterized in solution by H, C{ H}, 29Si
1
13
1
{1
H}, and P{ H} NMR spectroscopy. The H NMR spectrum dis-
31
1
1
these properties predestine 1 as a potential CVD precursor for the
fabrication of zinc phosphate films by silylamide elimination re-
action observed previously in aluminum amides [49]. Thermal
analysis TG/DSC in flowing air of 1 revealed an abrupt mass loss
plays two singlet resonances with chemical shifts of 0.21 and
.31 ppm; their 29Si satellites and a correct integral ratio 3:4
correspond with trimethylsiloxy and bis(trimethylsilyl)amido
0
13
1
groups in 1. Similarly, there are two resonances in the C{ H} NMR
starting from 90
and at this point the process slowed down to finish at 350
was no more mass decrease up to 1000 C, however, two broad
exothermic effects appeared at 620 and 950 C that can be attrib-
uted to crystallization and phase transformation events. The total
mass change 87.4% was recorded at 1000 C and the residue was
analyzed by powder XRD to identify resulting crystalline phases. All
reflections in the diffractogram were assigned to -Zn P O (PDF
ꢁ
C. By 189
ꢁ
C, about 64.5% of the weight was lost
3
spectrum. A doublet at 1.2 ppm ( JPC ¼ 1.5 Hz) and a singlet at
ꢁ
C. There
6
.1 ppm represent the methyl groups in POSiMe
3
and NSiMe
3
,
ꢁ
2
9
1
respectively. Two resonances are also present in the Si{ H} NMR
ꢁ
spectrum; a singlet at ꢀ2.1 ppm belongs to bis(trimethylsilyl)am-
2
ides and a doublet at 22.4 ppm ( JPSi ¼ 5.1 Hz) shows coupling to the
ꢁ
31
1
P nucleus in tris(trimethylsiloxy) moieties. The
P{ H} NMR
spectrum features only one resonance at ꢀ28.1 ppm, that points to
a
2
2 7
a higher shielding of the P atom in adduct 1 as compared to the free
card 8-238) which has the same stoichiometric Zn/P ratio as the
precursor 1. The calculated mass loss for the conversion of 1 to
Zn P O would require only 78.3%; the larger experimental value is
ester OP(OSiMe
3
)
3
(
d
¼ ꢀ23.4 ppm). Repeated measurements of
NMR spectra in time confirmed stability of 1 in deuterated solvents
2
2 7
at room temperature.
probably caused by a partial sublimation before decomposition.
The presence of reactive amide groups in the molecular product
1 offers a possibility to further functionalize the molecule. For this
reason we tested the reactions of 1 with protic reagents including
The IR spectrum of 1 displays strong bands of SiCH
bending [62] and rocking vibrations at 1259 and 849/762 cm
respectively, which are characteristic for the SiMe groups [63].
These bands are accompanied by weaker asymmetric and sym-
3
symmetric
ꢀ
1
,
3
i
MeOH, PrOH and Hhfacac. While treatment of 1 with the alcohols
ꢀ
1
metric SiC
3
stretchings at 669 and 613 cm , respectively. The
(2 mol, in toluene) led to insoluble precipitates, the reaction
(Scheme 1) with 2 equiv. of diketone provided a molecular com-
pound [Zn(hfacac) {OP(OSiMe ) }], 2. The crystals were grown by a
ꢀ1
bands at 1069 and 989 cm are consistent with the presence of Pe
O and SieO bonds [64].
2
3 3
þ
Mass spectra display fragments [M ꢀ Me] (in both APCIþ and
slow cooling of concentrated hexane solution of 2 in a freezer
C); the adduct is unstable to dissociation and decomposes on
ꢀ
EI 10 eV ionization modes) and [M ꢀ SiMe
3
]
(in APCIꢀ mode) that
(ꢀ25
ꢁ
attest to the stability of ZneO]P coordination bond in the gas phase.
Coupled with the fact that compound 1 sublimes under vacuum,
heating under vacuum. As shown by the single-crystal X-ray
diffraction measurements (Fig. 2), the adduct 2 is of the same
Scheme 1. Transformation of the zinc amide adduct 1 in the reaction with Hhfacac to adduct 2.

J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203
201
Table 3
Selected bond distances (A) and angles ( ) of 2.
strong stretching bands of the CF
groups as well as of the diket-
3
ꢀ
ꢁ
onate backbone [67]. Thermal analysis of 2 shows an endothermic
ꢁ
Zn1eO4
Zn1eO7
Zn1eO6
Zn1eO5
Zn1eO8
P1eO4
1.951(2)
2.009(2)
2.019(2)
2.055(2)
2.065(2)
1.480(2)
1.538(2)
1.544(2)
1.545(2)
Zn1eO4eP1
O5eZn1eO8
O7eZn1eO6
O4eZn1eO6
O4eZn1eO7
O6eZn1eO5
O7eZn1eO8
O4eP1eO3
O1eP1eO2
139.93(14)
165.60(9)
138.34(9)
109.33(10)
112.33(10)
87.89(9)
87.67(8)
110.33(14)
106.21(13)
effect on a DSC curve at 53.6 C that can be ascribed to melting of
ꢁ
the adduct. Continuous mass loss starts at 171 C and finishes at
ꢁ
2
23 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 (ZnEt
provide molecular zinc phosphates of high nuclearity [47,48]. We
expected similar outcomes from the reaction of Zn[N(SiMe
with OP(OSiMe (OH). However the reaction is probably modified
2 2
and Zn(OAc) )
P1eO1
P1eO2
P1eO3
3 2 2
) ]
3 2
)
by the presence of hexamethyldisilazane which is formed as a
byproduct in the condensation reaction and subsequently silylates
3
1
nuclearity as the starting complex 1. The amide groups were
replaced by two chelating hfacac ligands and the zinc coordination
number increased to five. The relevant bond lengths and angles are
gathered in Table 3.
3 2 3 3
OP(OSiMe ) (OH) to OP(OSiMe ) . The P NMR spectrum of the
reaction mixture featured resonances of OP(OSiMe ) (ꢀ24.3 ppm),
3
3
1 (ꢀ27.3 ppm) and two unidentified lines (ꢀ11.5 and ꢀ15.8 ppm)
that may belong to [Zn{OP(O)(OSiMe ) } ] and [(Me Si) NZn
3
2 2
3
2
The central zinc atom is five-coordinate with a distorted square-
pyramidal geometry. A quantitative measure for comparing real
structural parameters to idealized limiting geometries on the Berry
pathway from a square pyramid to a trigonal bipyramid and
quantifying the degree of stereochemical distortion is the param-
3 2
{OP(O)(OSiMe ) }].
In addition to Zn[N(SiMe ) ] we tested also ZnEt2 as a zinc
precursor in our reactions with tris(trimethylsilyl)ester of phos-
phoric acid. In contrast to a facile formation of 1, H and P NMR
analysis of the reaction mixture containing the ester OP(OSiMe3)3
and ZnEt2 in hexane does not indicate any reaction (adduct for-
mation or condensation) at room temperature; nor even after
refluxing the reaction mixture for 3 h or heating to 110 C in a
sealed NMR tube for 28 h. However, evaporation of the solvent
resulted in an intractable mixture of oily products with a multitude
3
2 2
1
31
eter
s
¼ 100(
b
ꢀ
a)/60, where b > aa are the trans angles not
involving a unique ligand. The parameter adopts values from zero
to 100% for perfectly square-pyramidal and trigonal-bipyramidal
geometries, respectively [65]. Analysis of metric parameters of 2
ꢁ
found
complex [Zn(hfacac)
s
¼ 45.5% which points to a distortion of the tetrahedral
3
1
1
2
] [66] upon coordination of OP(OSiMe
3
)
3
.
of resonances in its P{ H} NMR spectrum. The same results were
obtained by carrying out the reaction in toluene with the exception
that the mixture of products appeared already at room
temperature.
Although the coordination number of zinc atom in 2 is higher than
in complex 1, the corresponding ZneO(P) distance (Table 3) in 2 is
ꢀ
ꢀ
shorter (1.951(2) A) than in 1 (ZneO 2.036(3) A) and shorter than
an average phosphate bond length to five-coordinate Zn (avr.
In contrast to these observations, ZnEt exhibits a high reactivity
2
ꢀ
ꢁ
2
.00 A) [59]. The value of ZneOeP angle in 2 is 139.93(14) and the
P]O distance of 1.480(2) A is longer than 1.470(3) A in 1.
towards OP(OSiMe ) (OH). The combination of both compounds at
3
2
ꢀ
ꢀ
room temperature was accompanied by vigorous evolution of gas.
The results of multinuclear NMR analysis agree with the mo-
lecular structure determined by the X-ray diffraction experiments.
The H NMR spectrum of 2 displays two resonances in a 27:2 ratio
[(Zn{(py)N(SiMe ) }{m2-O P(OSiMe ) }) ] (3) was obtained in a
3
2
2
3 2
2
moderate yield by mixing two equivalents of OP(OSiMe ) (OH)
3
2
1
with one equivalent of ZnEt2 and by subsequent addition of one
equivalent of Zn[N(SiMe ) ] (Scheme 2). The reaction had to be
for trimethylsilyl (0.10 ppm) and methine (6.15 ppm) hydrogen
3
2 2
atoms. The CH resonance of 2 is shifted upfield with respect to
carried out in pyridine because in hexane the product did not
crystallize. The X-ray diffraction experiment established the mo-
lecular structure of 3 which features a centrosymmetric cyclic
inorganic core Zn P O in a chair-like conformation that is remi-
uncoordinated [Zn(hfacac)
to the signal of [Zn(hfacac)
acetone-d (6.02 ppm) [66]. This may imply coordination of the
2
] (6.23 ppm in CD
2 2
Cl ) and is very close
2
] observed in a coordinating solvent
6
2
2 4
1
3
1
ester in solution. Four resonances in the C{ H} NMR spectrum and
niscent of the S4R building units of open-framework zinc phos-
phates (Fig. 3). The relevant metric parameters are summarized in
Table 4. The zinc atoms are connected by two silylphosphate
[O P(OSiMe ) ] bridging units (Zn(1)eO(1) 1.946(2), Zn(1)eO(4)#1
one in both 19F{ H} (ꢀ77.1 ppm) and P{ H} NMR spectrum
1
31
1
(
ꢀ26.9 ppm) are in agreement with the molecular structure of 2
2
and are shifted upfield with respect to uncoordinated [Zn(hfacac) ]
2
3 2
2
9
1
ꢀ
ꢁ
and OP(OSiMe
spectrum is more deshielded (a doublet at 25.8 ppm, JPSi ¼ 5.8 Hz)
then the corresponding resonances in OP(OSiMe and in 1. Also
PSi increases in the order of
< 1 < 2. The mass spectrum (EI, 10 eV) of 2 features
3
)
3
. The resonance of OSiMe
3
in the Si{ H} NMR
1.976(2) A). The intraring OeZneO angle (98.8 ) is much sharper
2
than the corresponding angles found in open-framework zinc
ꢁ
ꢁ
3
)
3
phosphates (av. 114.6 ) or the OeAleO angles (av. 102.3 ) in mo-
lecular S4R aluminophosphates [(R Al{m2-O P(OSiMe ) }) ],
2
the coupling constant
OP(OSiMe
J
2
2
3 2
2
3
)
3
R ¼ Me, Et, t-Bu [50,68] but it is comparable to the OeGaeO angle
ꢁ
signals at m/z 585 and 899 which represent the [Zn(hfacac)
(99.4 ) in gallophosphate [(t-Bu Ga{
m
-O P(OSiMe ) }) ] [69]. The
2
2
2
3 2
2
þ
ꢁ
ꢁ
{
OP(OSiMe
3
)
3
}
n
]
(n ¼ 1, 2) fragments. This attests to a certain
OePeO angles (116.5 ) are similar as in framework (av. 111.2 ) and
molecular (av. 114.6 ) metal phosphates [59,69]. The tetrahedral
ꢁ
stability of the ZneOeP bond. The infrared spectrum of 2 features
Scheme 2. Synthesis of cyclic zinc amide phosphate 3.

202
J. Chyba et al. / Journal of Organometallic Chemistry 749 (2014) 197e203
Thermal behavior of molecular four-ring 3 was 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% by
ꢁ
ꢁ
2
20 C and 19.9% by 600 C). The total mass loss (66.7%) was in a
reasonable agreement with XRD analysis of residual white powder,
which was identified as a crystalline -phase of Zn (PDF card
-238). The theoretical value require 72.1%, the difference is
possibly caused by loss of pyridine during handling the sample.
a
2 2 7
P O
8
4. Conclusions
Our investigation focused on the nonaqueous reactions of tri-
3 3
methylsilylesters of phosphoric acid, OP(OSiMe ) and OP(OSi-
Me (OH), with Zn[N(SiMe and ZnEt brought three new
3
)
2
3
)
2
]
2
2
molecular zinc amide phosphate species soluble in organic sol-
vents. The structures of crystalline molecular products 1, 2, and 3
were determined by the X-ray diffraction analysis. The molecule 1
is only the second structurally characterized adduct of zinc bisa-
mide with an oxygen donor with a three-coordinate Zn atom. This
sublimable solid was converted to a-Zn P O by calcination and
2 2 7
appears to be a promising precursor for CVD of ceramic films. A
high reactivity of the amide groups allowed conversion of 1 to a
chelate complex 2 in the reaction with Hhfacac. OP(OSiMe
reacts with ZnEt and Zn[N(SiMe to form the molecular com-
pound 3 which features a cyclic inorganic core {Zn( -O PO )}
2
3 2
) (OH)
3 2 2 2 3 2 2
Fig. 3. Molecular structure of [(Zn{(py)N(SiMe ) }{m -O P(OSiMe ) }) ] (3). All H and C
atoms of the methyl groups were omitted for clarity. Thermal ellipsoids were drawn at
the 50% probability level.
2
3 2 2
) ]
m
2
2
2
related 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 connecting
points in our further studies on the formation of extended struc-
tures by nonhydrolytic condensation reactions.
coordination sphere of zinc atoms includes one pyridine molecule
ꢀ
(
Zn(1)eN(2) 2.081(3) A) and one amide group N(SiMe
3
)
2
(Zn(1)e
ꢀ
N(1) 1.921(3) A). The two pyridine molecules on the ring are in a
trans arrangement. Although the coordination properties of the
ring could imply the existence of cis/trans isomeric forms of 3 in the
reaction mixture, the NMR analysis of mother liquor revealed only
one set of signals probably corresponding to a fast on NMR time
scale process of pyridine exchange. The static trans isomer would
provide the same number of signals as fast exchange averaged
species but the cis molecule would require doubling the number of
Acknowledgments
Authors thank Dr. V. Vavra (MU) for recording the XRD data and
Dr. V. Jancik (UNAM) for CHN analyses. J.C. thanks to Erasmus
Program for supporting his research stay at University of Würzburg.
Z.M. thanks to Postdoc II CZ.1.07/2.3.00/30.0037. This work was
supported by CEITEC e Central European Institute of Technology
OSiMe
nate from two different zinc precursors. P NMR analysis of the
reaction solution of ZnEt with 2 equiv. of OP(OSiMe (OH) after
evolution of gaseous byproducts showed only a single resonance
that was different from the starting OP(OSiMe (OH). We envisage
the formation of an intermediate mononuclear zinc phosphate
complex [Zn(py) {OP(O)(OSiMe ] with the octahedral zinc
3
resonances. The zinc atoms contained in 3 probably origi-
31
(CZ.1.05/1.1.00/02.0068) and MOBILITY 7AMB13DE006.
2
3 2
)
Appendix A. Supplementary material
3 2
)
CCDC 953618e953620 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
4
3 2 2
) }
atom stabilized by coordinated pyridine molecules. This hypo-
thetical molecule has a precedent in crystallographically charac-
terized [Zn(imz) {OP(O)(O-t-Bu) } ] [48]. However, we failed in
4 2 2
attempts to isolate this intermediate. Moreover, when we evapo-
rated the solvent the obtained solid residue was not soluble to
allow further characterization. This observation could be inter-
preted as a loss of coordinated pyridine molecules at the zinc atom
followed by the formation of insoluble zinc phosphate coordination
polymer. ICP-OES elemental analyses confirmed a Zn:P ratio of
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