Compressed Octahedral Coordination in Chain Compounds Containing Divalent Copper: Structure and Magnetic Properties of CuFAsF₆ and CsCuAlF₆

Abstract

Crystal structures and magnetic investigations of CuFAsF6 and CsCuAlF6 are reported. Together with KCuAlF6, these appear to be the only examples of Jahn-Teller pure Cu(II) compounds containing only one type of ligand that exhibits a compressed octahedral coordination geometry. The Rietveld method has been used for refining the CsCuAlF6 structure based on neutron powder diffraction data at 4 K. The compound crystallizes in space group Pnma (no. 62) with a=7.055(1), b=7.112(1), c=10.153(1) A and Z=4 at 4 K. The structure is built from infinite [CuF5]n(3n-) chains of [CuF6]4- octahedra running along the [1 0 0] direction and (AlF6)3- octahedra connected by corners in the trans position, thus giving rise to chains oriented along the [0 1 0] direction. Single crystals of CuFAsF6 were prepared under solvothermal conditions in AsF5 above its critical temperature. The structure was determined from single-crystal data. CuFAsF6 crystallises in the orthorhombic space group Imma (No. 74) with a=10.732(5), b=6.941(3), c=6.814(3) A and Z=4 at 200 K. The structure can also be described in terms of one-dimensional infinite [CuF5]n(3n-) chains of tilted [CuF6](4-) octahedra linked by trans-vertices running along the b axis. The [CuF5]n(3n-) chains are connected through [AsF6]- units sharing joint vertices. The compressed octahedral coordination of CuII atoms in CuFAsF6 and CsCuAlF6 compounds at room temperature is confirmed by Cu K-edge EXAFS (extended x-ray absorption fine structure) analysis. For both compounds strong antiferromagnetic interactions within the [CuF5]n(3n-) chains were observed (theta(p)=-290+/-10 K and theta(p)=-390+/-10 K for CuFAsF6 and CsCuAlF6, respectively). The peculiar magnetic behaviour of chain compounds containing divalent copper at low temperature could be related to uncompensated magnetic moments in the one-dimensional network.

[XeF5]+/Metal and [XeF5]+/Non‐Metal Mixed‐Cation Salts of Hexafluoridoantimonate(V)

“…Such unusual compressed coordination has been observed before in CuFAsF 6 , H 3 OCuF(AsF 6 ) 2 , KCuAlF 6 , and CsCuAlF 6 17,18. The shape of [XeF 5 ] + is similar to that in NO 2 XeF 5 (SbF 6 ) 2 with an Xe–F ax bond length [1.798(2) Å] shorter than in the case of Xe–F eq [1.827(2)–1.835(2) Å].…”

Homoleptic [M(XeF2)6]2+ cations of copper(II) and zinc(II)—Syntheses and crystal structures of [M(XeF2)6](SbF6)2 (M=Cu, Zn)

“…All Cu-F (Zn-F) bond lengths are identical to 197.9(3) pm (199.4(5) pm). For comparison, in CuF 2 displaying usual elongated Jahn-Teller distortion, Cu-F distances are in the range 191.0-203.5 pm [13], meanwhile Zn-F bond lengths in ZnF 2 are in the range from 201.2 to 204.6 pm [14].…”

Synthesis and crystal structures of HgFAsF6, Hg(HF)2(AsF6)2, Hg(HF)(AsF6)2 and Hg(AsF6)(SO3F)

“…Crystal structure of HgFAsF 6 represents new, sixth structural type of M II FX V F 6 (MF 2 Á XF 5 ) compounds [7,[35][36][37][38][39]. As in AgFAsF 6 [35] and CuFAsF 6 -types [37] the structure consists of zig-zag (M À F) n n þ (M¼ Hg) one dimensional chains interconnected by AsF 6 groups.…”

“…As in AgFAsF 6 [35] and CuFAsF 6 -types [37] the structure consists of zig-zag (M À F) n n þ (M¼ Hg) one dimensional chains interconnected by AsF 6 groups. Crystal structures of Hg(HF) 2 (AsF 6 ) 2 and Hg(HF)(AsF 6 ) 2 are new examples of compounds with HF directly bound to metal centre [28].…”

“…In the second CuFAsF 6 -type, there are also (CuÀ F) n n þ infinite chains interconnected by AsF 6 units, however the copper atom is found in compressed octahedral coordination [37]. In the third AgFRuF 6 -type [36] and fourth PbFAsF 6 -type [38] the geometry of (MÀF) n nþ cation could be describes as one-dimensional ribbon, meanwhile the fifth SnFAsF 6 -type consist from cyclic [(SnÀ F) 3 ] 3 þ cations and [AsF 6 ] À anions [39].…”