X-ray Crystal Structure of Thorium Tetrahydroborate, Th(BH₄)₄, and Computational Studies of An(BH₄)₄ (An = Th, U)

Abstract

The crystal structure of Th­(BH4)4 is described. Two of the four BH4 – ions are terminal and tridentate (κ3), whereas the other two bridge between neighboring ThIV centers in a κ2,κ2 (i.e., bis-bidentate) fashion. Thus, each thorium center is bound to six BH4 – groups by 14 Th–H bonds. The six boron atoms describe a distorted octahedron in which the κ3-BH4 – ions are mutually cis; the 14 ligating hydrogen atoms define a highly distorted bicapped hexagonal antiprism. The thorium centers are linked into a polymer consisting of interconnected helical chains wound about 4-fold screw axes. The structures of An­(BH4)4 (An = Th, U) were also investigated by DFT. The geometries of [An­(BH4)6]2–, [An3(BH4)16]4–, and [An5(BH4)26]6– fragments of the polymeric structures were optimized at the B3LYP and/or PBE levels. Most calculated geometries are 14-coordinate and agree with the experimental structures, but isolated [Th­(BH4)6]2– units are predicted to feature 16-coordinate ThIV centers.

Synthesis and Characterization of Chelating Alkyl-borohydride Complexes of Thorium and Uranium: Th(CH2NMe2BH3)4 and U(CH2NMe2BH3)4

“…For example, the average κ 1 BH 3 and κ 2 BH 3 Th···B distances in Th(BH 3 NMe 2 BH 3 ) 4 are 3.193(5) and 2.911(3) Å, respectively (a difference of 0.28 Å) . The latter distance is similar to those seen for κ 2 BH 4 –Th interactions in other compounds: 2.950(8) and 2.879(9) Å in Th(BH 4 ) 4 (dmpe) 2 and 2.895(6) and 2.934(6) Å in homoleptic Th(BH 4 ) 4 . Although to the best of our knowledge no κ 1 borohydride-uranium(IV) interactions have been structurally characterized, several κ 2 BH 4 –U distances have been reported: 2.90(1) and 2.82(2) Å in U(BH 4 ) 4 , 2.89(1) Å U(BH 4 ) 4 (Et 2 O) 2 , 2.87(2) and 2.90(2) Å in U(BH 4 ) 4 (Me 2 O) 2 , and 2.84(5) Å in U(BH 4 ) 4 (OPPh 3 ) 2 …”

“…25 The latter distance is similar to those seen for κ 2 BH 4 −Th interactions in other compounds: 2.950(8) and 2.879(9) Å in Th-(BH 4 ) 4 (dmpe) 2 26 and 2.895(6) and 2.934(6) Å in homoleptic Th(BH 4 ) 4 . 27 Although to the best of our knowledge no κ 1 borohydride-uranium(IV) interactions have been structurally characterized, several κ 2 BH 4 −U distances have been reported: 2.90(1) and 2.82 28 and 2.84(5) Å in U(BH 4 ) 4 (OPPh 3 ) 2 . 29 Although the 0.1 Å difference between the long and short Th•••B bonds in 1 and the 0.19 Å difference between the long and short U•••B distances in 2 are smaller than the ca.…”

A versatile strategy for the formation of hydride-bridged actinide–iridium multimetallics

“…The discrepancy between the uranium and thorium species was unexpected and, to our knowledge, has not been reported in actinide polyhydride complexes, which are often isostructural between their uranium and thorium counterparts. 53–55 In addition, the close average An–Ir distances of 2.954(1) Å (1) and 2.993(1) Å (2) are well within the sum of covalent radii for U/Ir (3.37 Å) and Th/Ir (3.47 Å), 56 suggesting the possibility of An–Ir bonding interactions.…”

Synthesis and Characterization of Ether Adducts of Thorium Tetrahydroborate Th(BH4)4 and Chemical Vapor Deposition of Thorium Boride Thin Films

“…61 We recently reported the first single-crystal X-ray diffraction study of Th(BH 4 ) 4 . 62 In addition, we have described a thorium complex featuring a new type of modified h y d r o b o r a t e l i g a n d , t h e a m i n o d i b o r a n a t e T h -(H 3 BNMe 2 BH 3 ) 4 . 63 Although heating this latter compound under vacuum affords a sublimate, the sublimate consists of the thermolysis products Th(H 3 BNMe 2 BH 3 ) 3 (BH 4 ) and Th-(H 3 BNMe 2 BH 3 ) 2 (BH 4 ) 2 , which are formed by loss of the aminoborane (NMe 2 BH 2 ) 2 .…”

“…Two of the most attractive of these are the binary tetrahydroborate Th­(BH 4 ) 4 , which was first described in 1949, and its methyltrihydroborate analogue Th­(BH 3 CH 3 ) 4 , first reported in 1983 . We recently reported the first single-crystal X-ray diffraction study of Th­(BH 4 ) 4 . In addition, we have described a thorium complex featuring a new type of modified hydroborate ligand, the aminodiboranate Th­(H 3 BNMe 2 BH 3 ) 4 .…”