Phosphor(V)-nitride durch Hochdruck-Hochtemperatur-Synthese

Episode von Fakultät für Chemie und Pharmazie - Digitale Hochschulschriften der LMU - Teil 01/06 von Ludwig-Maximilians-Universität München · 18. Juni 2001

1. Development and establishment of the high-pressure high-temperature synthesis

as a broad approach to nitridophosphates. In this thesis for the first time a broad

access to nitridophosphates was developed and therefore the basis for a systematic

investigation of this class of compounds was established. It was shown, that under high-pressure

conditions (> 3 GPa) using a belt or Walker module crystalline

nitridophosphates can be obtained by reaction of phosphorus(V) nitride with alkaline or

earth alkaline azides at temperatures of 1200-1600 °C. Thus the possibilty to suppress

eliminiation of N2 from nitridophosphates, which occurs at 800 °C under atmospheric

pressure, was proved by use of high-pressure conditions. Thereby the maximum

temperature in synthesis of nitridophosphates was approximately doubled. A raise of the

maximum temperature during the synthesis leads to much better crystallization

conditions. Hence the main problem in synthesis of crystalline nitridophosphates, which

consists of bad crystallisation conditions due to limited maximum reaction temperature,

was solved and the number of the crystallographically well characterized ternary

phosphorus(V) nitrides was doubled from nine to eighteen. Especially the number of

highly condensed nitridophosphates (molar ratio P : N > 1 : 2) could be raised from three

to nine and a second modification of the binary phosphorus(V) nitride P3N5 was obtained.

Consequently the high-pressure high-temperature synthesis can be seen as the first

widely applicable approach to nitridophosphates. Due to the hermetically sealed reaction

cell precise modulation of the P-N framework by systematic variation of the P3N5 : azide

molar ratio in the starting materials. Moreover under high-pressure conditions the

reaction time was reduced dramatically compared to conventional synthesis. While using

conventional methods several hours or days are needed for quantitative reactions,

reactions under high pressure conditions succeed in 5-15 min.

At the beginning of the work the apparatus for the high-pressure experiments did not

exist within the laboratory equipment of our research group. The success of the first

experiments (synthesis of NaP4N7, KP4N7, RbP4N7, CsP4N7), which were performed in

cooperation with Evers, significantly contributed to the aquisition of the 1000 t-press

installed by Huppertz, and the introduction of the multianvil high-pressure technique at

the University of Munich (LMU).

2. NaP4N7, KP4N7, RbP4N7, and CsP4N7. The nitridophosphates NaP4N7, KP4N7, RbP4N7,

and CsP4N7 were synthesized by reaction of P3N5 with the respective alkaline azide in the

molar ratio MN3 : P3N5 = 3 : 4 (M = Na, K, Rb, Cs) at approximately 40 kbar and 1300 °C

using a belt module. NaP4N7 (C2/c, a = 1233.45(4), b = 852.30(3), c = 513.97(1) pm, b = 102.572(2)°, Z = 4, Rp = 0.0772, wRp = 0.1077, RF = 0.0718) crystallizes isotypic to

CaAl4O7 in a three-dimensional network structure of corner-sharing PN4 tetrahedra with

Na + ions in the channels. According to the formula ¥

3

[(P [4]

4 N 5

[2]

N 2

[3]

) - ] N [2] - and N [3] -bridges

exist in a molar ratio 5 : 2. KP4N7 (Pnma, a = 1222.72(2), b = 984.25(2),

c = 466.24(1) pm, Z = 4, Rp = 0.0865, wRp = 0.1113, RF = 0.0821), RbP4N7

(a = 1231.07(2), b = 989.46(1), c = 468.44(1) pm, Z = 4, Rp = 0.0350, wRp = 0.0462,

RF = 0.0589), and CsP4N7 (a = 1242.91(3), b = 997.63(3), c = 471.33(2) pm, Z = 4,

Rp = 0.0524, wRp = 0.0646, RF = 0.0494) crystallize isotypic to the mineral barylite

BaBe2Si2O7 in a three-dimensional network structure from corner-sharing PN4 tetrahedra

with the alkaline ions in the channels. According to the formula ¥

3

[(P [4]

4 N 5

[2]

N 2

[3]

) - ] N [2] -

and N [3] -bridges exist in a molar ratio 5 : 2. Using the obtained crystallographic data of

MP4N7 (M = Na, K, Rb, Cs) MAPLE and CHARDI calculations as well as calculations

based on the bond-length bond-strength concept were carried out and discussed. The

radiographically obtained results were confirmed. The compounds were characterized by

IR- and 31 P-MAS NMR-spectroscopy (d = -23.5, -25.0 (NaP4N7); -0.4, -1.7 (KP4N7), -19.6,

-28.2 (RbP4N7), -21.6, -31.9 ppm (CsP4N7)). Thermogravimetric examinations under inert

gas conditions revealed the thermal decomposition temperature of the compounds, which

is about 850-900 °C.

3. Rb3P6N11 and Cs3P6N11. The nitridophosphates Rb3P6N11 and Cs3P6N11 were

synthesized by reaction of P3N5 with the respective alkaline azide in the molar ratio

MN3 : P3N5 = 3 : 2 (M = Rb, Cs) using a Walker module at approximately 35 kbar and

1300 °C. Rb3P6N11 (P4132, a = 1049.74(1) pm, Z = 4, Rp = 0.0979, wRp = 0.1077,

RF = 0.0612) and Cs3P6N11 (P4132, a = 1065.15(1) pm, Rp = 0.0487, wRp = 0.0618,

RF = 0.0812) crystallize isotypic to K3P6N11 in a three-dimensional network structure of

corner-sharing PN4 tetrahedra with the alkaline ions in the channels. According to the

formula ¥

3

[(P 6

[4]

N 9

[2]

N 2

[3]

) 3- ] N [2] - and N [3] -bridges exist in the molar ratio 9 : 2. Using the

obtained crystallographic data of M3P6N11 (M = Rb, Cs) MAPLE and CHARDI calculations

as well as calculations based on the bond-length bond-strength concept were carried out

and discussed. The radiographically obtained results were confirmed. The compounds

were characterized by IR- and 31 P-MAS NMR-spectroscopy (d = -7.4 (Rb3P6N11), -8.9

ppm (Cs3P6N11)). Thermogravimetric examinations under inert gas conditions revealed

the thermal decomposition temperature of the compounds, which is about 850-900 °C.

Temperature-dependant powder X-ray investigations revealed that Rb3P6N11 shows no

thermal expansion between room temperature and 540 °C.4. NaPN2. The nitridophosphate NaPN2 was synthesized by reaction of P3N5 with NaN3 in

the molar ratio NaN3 : P3N5 = 3 : 1 using a Walker module at approximately 35 kbar and

1300 °C. NaPN2 (I 4 2d, a = 497.21(2), c = 697.60(3) pm, Z = 4, Rp = 0.0502,

wRp = 0.0649, RF = 0.0788) crystallizes isotypic to LiPN2 in a three-dimensional network

structure of corner-sharing PN4 tetrahedra with the Na + ions in the channels. According to

the formula ¥

3

[(P

[4]

N 2

[2]

) - ] N [2] -bridges exist exclusively. Using the obtained

crystallographic data of NaPN2, MAPLE and CHARDI calculations as well as calculations

based on the bond-length bond-strength concept were carried out and discussed. The

radiographically obtained results were confirmed. The compound was characterized by

IR- and 31 P-MAS NMR-spectroscopy (d = -15.0 ppm). Thermogravimetric examinations

under inert gas conditions revealed the thermal decomposition temperature of the

compound, which is about 900 °C.

5. CaP2N4 and SrP2N4. The nitridophosphates CaP2N4 und SrP2N4 were obtained by

reaction of Ca(N3)2 and Sr(N3)2 with P3N5 (molar ratio M(N3)2 : P3N5 = 3 : 2) at 35 kbar

and 1300 °C in a Walker module. A structure model could be obtained from X-ray powder

data. CaP2N4 (P6322, a = 972.11(1) pm, c = 785.90(1) pm, Z = 8, Rp = 0.059,

wRp = 0.079, RF = 0.174) and SrP2N4 (P6322, a = 987.44(1), c = 785.90(1) pm, Z = 8,

Rp = 0.075, wRp = 0.098, RF = 0.115) crystallize isotypic in a network structure from

corner-sharing PN4 tetrahedra with the alkaline earth ions within the channels.

Perpendicular to [001] layers from condensed P6N6 sechser rings exists which are linked

by P4N4 vierer rings and further P6N6 sechser rings forming the network structure.

According to the formula ¥

3

[(P

[4]

N 2

[2]

) - ] N [2] -bridges occur exclusively. Using the obtained

crystallographic data of CaP2N4 and SrP2N4, MAPLE and CHARDI calculations as well as

calculations based on the bond-length bond-strength concept were carried out and

discussed. The radiographically obtained results were confirmed. The compounds were

characterized by IR- and 31 P-MAS NMR-spectroscopy (d = -20.0, -15.9, -5.2, -3.6, -

2.6 (CaP2N4), -27.8, -23.4, -17.1, -15.5, -14.1 ppm (SrP2N4). Thermogravimetric

examinations under inert gas conditions revealed the thermal decomposition temperature

of SrP2N4, which is about 900 °C. CaP2N4 was stable up to 1000 °C.

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