Syntheses, Crystal Structures, and Thermal Stabilities of Polymorphs of Cr(thd)3

Mohammed A.K. Ahmed, Helmer Fjellvåg, Arne Kjekshus, Renie K. Birkedal, Poul Norby, David S. Wragg, Nalinava Sen Gupta

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The syntheses, crystal structures, and thermal stabilities of six polymorphs of Cr(thd)3 [(thd)– = anion of H(thd) = C11H20O2 = 2,2,6,6-tetramethylheptane-3,5-dione] were studied using X-ray diffraction and differential scanning calorimetry. Compound 1 is thermodynamically stable below ca. 110 °C and forms plate-shaped crystals [a = 9.927(5), b = 18.010(5), c = 21.427(5) Å, and β = 95.461(5)° at 295 K; space group C2/c]. Its crystal structure is isotypic with Mn(thd)3. Polymorph 4 is metastable to 1, and the only way to prepare 4 appears to be by precipitation from solution. Crystals of 4 are needle shaped [a = 28.54(3), b = 19.14(2), c = 21.92(2) Å, and β = 97.31(2)° at 295 K; space group C2/c] and this structure is isotypic with monoclinic Co(thd)3. Modifications 2, 2*, and 5 also appear as needle-shaped crystals [orthorhombic: a = 18.97(7), b = 18.69(7), and c = 10.62(5) Å for 2 and tetragonal: a = b = 18.93(5) and c = 10.57(4) Å for 5, both at 110 K]. Crystals of 2 and 5 have limited lifetime, which depends on storage temperature and exposure to X-rays. The conversion sequence is: 5 → 2 → 1, where the first step takes 3 to 4 h and the second some 20 h. Attempts to establish detailed accounts of the orthorhombic Co(thd)3-type structure of 2 and 2* by SXD were unsuccessful due to disorder. The structural distinction between 2 and 2* appears to be associated with rotational disorder among the Cr(thd)3 molecules. 2* and 3 are high-temperature modifications with stability range ca. 155–200 and ca. 200–235 °C, respectively [Cr(thd)3 melts at ca. 235 °C]. Quenched 2* can be retained as metastable at room temp. for some weeks, whereas 3 is not quenchable. High-temperature PXD data show that 3 is cubic [a = 13.357(4) Å at 225 °C; with strong rotational disorder of the molecules]. There are only minor variations in bond lengths and angles between 1 and 4 or from 100 to 295 K, and disorder is limited.
Original languageEnglish
JournalZeitschrift fuer Anorganische und Allgemeine Chemie
Volume636
Issue number13-14
Pages (from-to)2422-2432
ISSN0044-2313
DOIs
Publication statusPublished - 2010
Externally publishedYes

Cite this

Ahmed, M. A. K., Fjellvåg, H., Kjekshus, A., Birkedal, R. K., Norby, P., Wragg, D. S., & Gupta, N. S. (2010). Syntheses, Crystal Structures, and Thermal Stabilities of Polymorphs of Cr(thd)3. Zeitschrift fuer Anorganische und Allgemeine Chemie, 636(13-14), 2422-2432. https://doi.org/10.1002/zaac.201000160
Ahmed, Mohammed A.K. ; Fjellvåg, Helmer ; Kjekshus, Arne ; Birkedal, Renie K. ; Norby, Poul ; Wragg, David S. ; Gupta, Nalinava Sen. / Syntheses, Crystal Structures, and Thermal Stabilities of Polymorphs of Cr(thd)3. In: Zeitschrift fuer Anorganische und Allgemeine Chemie. 2010 ; Vol. 636, No. 13-14. pp. 2422-2432.
@article{30f60952c94f4de7bbf0d8f284861afc,
title = "Syntheses, Crystal Structures, and Thermal Stabilities of Polymorphs of Cr(thd)3",
abstract = "The syntheses, crystal structures, and thermal stabilities of six polymorphs of Cr(thd)3 [(thd)– = anion of H(thd) = C11H20O2 = 2,2,6,6-tetramethylheptane-3,5-dione] were studied using X-ray diffraction and differential scanning calorimetry. Compound 1 is thermodynamically stable below ca. 110 °C and forms plate-shaped crystals [a = 9.927(5), b = 18.010(5), c = 21.427(5) {\AA}, and β = 95.461(5)° at 295 K; space group C2/c]. Its crystal structure is isotypic with Mn(thd)3. Polymorph 4 is metastable to 1, and the only way to prepare 4 appears to be by precipitation from solution. Crystals of 4 are needle shaped [a = 28.54(3), b = 19.14(2), c = 21.92(2) {\AA}, and β = 97.31(2)° at 295 K; space group C2/c] and this structure is isotypic with monoclinic Co(thd)3. Modifications 2, 2*, and 5 also appear as needle-shaped crystals [orthorhombic: a = 18.97(7), b = 18.69(7), and c = 10.62(5) {\AA} for 2 and tetragonal: a = b = 18.93(5) and c = 10.57(4) {\AA} for 5, both at 110 K]. Crystals of 2 and 5 have limited lifetime, which depends on storage temperature and exposure to X-rays. The conversion sequence is: 5 → 2 → 1, where the first step takes 3 to 4 h and the second some 20 h. Attempts to establish detailed accounts of the orthorhombic Co(thd)3-type structure of 2 and 2* by SXD were unsuccessful due to disorder. The structural distinction between 2 and 2* appears to be associated with rotational disorder among the Cr(thd)3 molecules. 2* and 3 are high-temperature modifications with stability range ca. 155–200 and ca. 200–235 °C, respectively [Cr(thd)3 melts at ca. 235 °C]. Quenched 2* can be retained as metastable at room temp. for some weeks, whereas 3 is not quenchable. High-temperature PXD data show that 3 is cubic [a = 13.357(4) {\AA} at 225 °C; with strong rotational disorder of the molecules]. There are only minor variations in bond lengths and angles between 1 and 4 or from 100 to 295 K, and disorder is limited.",
author = "Ahmed, {Mohammed A.K.} and Helmer Fjellv{\aa}g and Arne Kjekshus and Birkedal, {Renie K.} and Poul Norby and Wragg, {David S.} and Gupta, {Nalinava Sen}",
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Ahmed, MAK, Fjellvåg, H, Kjekshus, A, Birkedal, RK, Norby, P, Wragg, DS & Gupta, NS 2010, 'Syntheses, Crystal Structures, and Thermal Stabilities of Polymorphs of Cr(thd)3', Zeitschrift fuer Anorganische und Allgemeine Chemie, vol. 636, no. 13-14, pp. 2422-2432. https://doi.org/10.1002/zaac.201000160

Syntheses, Crystal Structures, and Thermal Stabilities of Polymorphs of Cr(thd)3. / Ahmed, Mohammed A.K.; Fjellvåg, Helmer; Kjekshus, Arne; Birkedal, Renie K.; Norby, Poul; Wragg, David S.; Gupta, Nalinava Sen.

In: Zeitschrift fuer Anorganische und Allgemeine Chemie, Vol. 636, No. 13-14, 2010, p. 2422-2432.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Syntheses, Crystal Structures, and Thermal Stabilities of Polymorphs of Cr(thd)3

AU - Ahmed, Mohammed A.K.

AU - Fjellvåg, Helmer

AU - Kjekshus, Arne

AU - Birkedal, Renie K.

AU - Norby, Poul

AU - Wragg, David S.

AU - Gupta, Nalinava Sen

PY - 2010

Y1 - 2010

N2 - The syntheses, crystal structures, and thermal stabilities of six polymorphs of Cr(thd)3 [(thd)– = anion of H(thd) = C11H20O2 = 2,2,6,6-tetramethylheptane-3,5-dione] were studied using X-ray diffraction and differential scanning calorimetry. Compound 1 is thermodynamically stable below ca. 110 °C and forms plate-shaped crystals [a = 9.927(5), b = 18.010(5), c = 21.427(5) Å, and β = 95.461(5)° at 295 K; space group C2/c]. Its crystal structure is isotypic with Mn(thd)3. Polymorph 4 is metastable to 1, and the only way to prepare 4 appears to be by precipitation from solution. Crystals of 4 are needle shaped [a = 28.54(3), b = 19.14(2), c = 21.92(2) Å, and β = 97.31(2)° at 295 K; space group C2/c] and this structure is isotypic with monoclinic Co(thd)3. Modifications 2, 2*, and 5 also appear as needle-shaped crystals [orthorhombic: a = 18.97(7), b = 18.69(7), and c = 10.62(5) Å for 2 and tetragonal: a = b = 18.93(5) and c = 10.57(4) Å for 5, both at 110 K]. Crystals of 2 and 5 have limited lifetime, which depends on storage temperature and exposure to X-rays. The conversion sequence is: 5 → 2 → 1, where the first step takes 3 to 4 h and the second some 20 h. Attempts to establish detailed accounts of the orthorhombic Co(thd)3-type structure of 2 and 2* by SXD were unsuccessful due to disorder. The structural distinction between 2 and 2* appears to be associated with rotational disorder among the Cr(thd)3 molecules. 2* and 3 are high-temperature modifications with stability range ca. 155–200 and ca. 200–235 °C, respectively [Cr(thd)3 melts at ca. 235 °C]. Quenched 2* can be retained as metastable at room temp. for some weeks, whereas 3 is not quenchable. High-temperature PXD data show that 3 is cubic [a = 13.357(4) Å at 225 °C; with strong rotational disorder of the molecules]. There are only minor variations in bond lengths and angles between 1 and 4 or from 100 to 295 K, and disorder is limited.

AB - The syntheses, crystal structures, and thermal stabilities of six polymorphs of Cr(thd)3 [(thd)– = anion of H(thd) = C11H20O2 = 2,2,6,6-tetramethylheptane-3,5-dione] were studied using X-ray diffraction and differential scanning calorimetry. Compound 1 is thermodynamically stable below ca. 110 °C and forms plate-shaped crystals [a = 9.927(5), b = 18.010(5), c = 21.427(5) Å, and β = 95.461(5)° at 295 K; space group C2/c]. Its crystal structure is isotypic with Mn(thd)3. Polymorph 4 is metastable to 1, and the only way to prepare 4 appears to be by precipitation from solution. Crystals of 4 are needle shaped [a = 28.54(3), b = 19.14(2), c = 21.92(2) Å, and β = 97.31(2)° at 295 K; space group C2/c] and this structure is isotypic with monoclinic Co(thd)3. Modifications 2, 2*, and 5 also appear as needle-shaped crystals [orthorhombic: a = 18.97(7), b = 18.69(7), and c = 10.62(5) Å for 2 and tetragonal: a = b = 18.93(5) and c = 10.57(4) Å for 5, both at 110 K]. Crystals of 2 and 5 have limited lifetime, which depends on storage temperature and exposure to X-rays. The conversion sequence is: 5 → 2 → 1, where the first step takes 3 to 4 h and the second some 20 h. Attempts to establish detailed accounts of the orthorhombic Co(thd)3-type structure of 2 and 2* by SXD were unsuccessful due to disorder. The structural distinction between 2 and 2* appears to be associated with rotational disorder among the Cr(thd)3 molecules. 2* and 3 are high-temperature modifications with stability range ca. 155–200 and ca. 200–235 °C, respectively [Cr(thd)3 melts at ca. 235 °C]. Quenched 2* can be retained as metastable at room temp. for some weeks, whereas 3 is not quenchable. High-temperature PXD data show that 3 is cubic [a = 13.357(4) Å at 225 °C; with strong rotational disorder of the molecules]. There are only minor variations in bond lengths and angles between 1 and 4 or from 100 to 295 K, and disorder is limited.

U2 - 10.1002/zaac.201000160

DO - 10.1002/zaac.201000160

M3 - Journal article

VL - 636

SP - 2422

EP - 2432

JO - Zeitschrift fuer Anorganische und Allgemeine Chemie

JF - Zeitschrift fuer Anorganische und Allgemeine Chemie

SN - 0044-2313

IS - 13-14

ER -