Strukturchemische Verwandtschaft von Kaliumhexahydroxoscandat(III), K₃[Sc(OH)₆] mit den isotypen Hydroxometallaten Rb₃[Sc(OH)₆], K₃[Cr(OH)₆] und Rb₃[Cr(OH)₆]

Abstract

Ternäre Hydroxide M 3I{MIII(OH)6}mit MI  K, Rb und MIII  Sc, Cr wurden analog zu K3[Cr(OH)6] [1] aus Alkalimetallamiden und d‐Metallnitraten durch Komproportionierung von Amid‐ und Nitrationen zu elementarem Stickstoff und Hydroxidionen in überkritischem Ammoniak bei 523 K und 3 ≤ p(NH3) ≤ 6 kbar innerhalb von 1 bis 3 Monaten dargestellt. Die Atomanordnungen der Verbindungen wurden einschließlich der H‐Positionen röntgenographisch an Einkristallen bestimmt. Das Größenverhältnis r(MI)/r(MIII) korreliert mit der Symmetrie dieser Verbindungen. Strukturchemische Beziehungen von K3[Sc(OH)6 zu Rb3[Sc(OH)6], K3[Cr(OH)6], Rb3[Cr(OH)6] zu K4[CdCl6] [4] werden diskutiert.

CaNa[Cr(OH)6] – A Layered Hydroxochromate(III) with Ordered Brucite Structure and its Thermal Decomposition

“…In the following, these positions are named after their main constituent. The chromium(III) cations are octahedrally surrounded by six hydroxide groups with an average Cr–O bond length of 200.8(2) pm, which is well in accordance with known chromium(III) hydroxides . The chromium(III) centered octahedron is slightly distorted with a deviation of only 0.2 pm from the average Cr–O bond length.…”

“…Space ] (A = K, Rb). [4] To the best of our knowledge, the mixed chromium(III) hydroxide CaNa[Cr(OH) 6 ] crystallizes in a new structure type. Yet it is closely related to hexahydroxometalates with the general formula A 2 [M(OH) 6 ], where in most cases A is an alkali metal and M is a tetravalent element.…”

“…The chromium(III) cations are octahedrally surrounded by six hydroxide groups with an average Cr-O bond length of 200.8(2) pm, which is well in accordance with known chromium(III) hydroxides. [1][2][3][4][5] The chromium(III) centered octahedron is slightly distorted with a deviation of only 0.2 pm from the average Cr-O bond length. Using the formula by Brown and Shannon, [21] the degree of distortion is 9.9 ϫ 10 -7 .…”

“…Three bands with equal intensity distribution are well known for isolated [Cr(OH) 6 ] 3-, [1] confirming the crystal structure and the valence state of chromium in CaNa[Cr(OH) 6 ]. Considering the respective Tanabe-Sugano diagram for a d 3 configuration, three allowed transitions can be found based on the ground state 4 A 2g and the two excited states 4 T 1g and 4 T 2g . [36] The transition to the first electronic state ν 1 : 4 A 2g Ǟ 4 T 2g (F) causes the band at 591 nm in the spectrum, whereas the remaining two bands at 420 nm and 264 nm are caused by the transitions ν 2 : 4 A 2g Ǟ 4 T 1g (F) and ν 3 : 4 A 2g Ǟ 4 T 1g (P), respectively.…”

“…In the group of alkalineearth metal hydroxochromates, the two katoite-like hydrogarnets Ca 3 [Cr(OH) 6 ] 2 and Sr 3 [Cr(OH) 6 ] 2 [1] are the only quaternary representatives, whereas Mg 6 [Cr(OH) 6 ] 2 CO 3 (OH) 4 •4H 2 O (stichtite) [2] is worth mentioning as the sole quinary chromium hydroxide with alkaline-earth metals. In combination with alkali metals a few more examples are known, for instance the quaternary compounds K 3 [Cr(OH) 6 ], [3] Rb 3 [Cr(OH) 6 ], [4] and Na 9 [Cr(OH) 6 ] 2 (OH) 3 . [5] In these hydroxometalates, chromium mainly adopts the oxidation state +III and hydrogen bonds are generally observed.…”