Vibrational spectra and torsional barrier of cyclopentadienyl beryllium borohydride, C5H5BeBH4

Abstract

Infrared and Raman spectra are reported for liquid and solid C5H5BeCl, C5H5BeBH4, and C5H5BeBD4 and vibrational assignments of most of the C5H5, BeX, and skeletal modes are made. Conclusive evidence for a double hydrogen bridge configuration is found for C5H5BeBH4 and, in contrast to Be(BH4)2, this structure is unchanged in going from gas to liquid to solid. The C5H5 frequencies are in close accord with those of (C5H5)2Fe while the vibrations of the BeBH4 group are analogous to those reported earlier for the +BeBH4 ion in solid Be(BH4)2. Observation of several transitions for the skeletal torsional motion of C5H5BeBH4 implies that free internal rotation about the symmetry axis does not occur and calculations yield a value of 500 cm−1 for the tenfold torsional barrier. Raman polarization data are consistent with a low energy orientation which places the BeH2bB bridging plane and a Cs molecular symmetry plane in coincidence.

Variable Borohydride Hapticity in Nickel(II) Scorpionate Complexes [(TpR,Me)Ni(ηn‐BH4)]: TpR,Me = hydrotris{3‐R‐5‐methyl‐1‐pyrazolyl}borate; R = Ph, n = 3 vs. R = Me, n = 4

“…Imaginary frequencies were not obtained for either model. Consistent with literature precedent,, , the frequency calculation on C 3 v ‐[(Tp)Ni(η 4 ‐BH 4 )] indicated two additional strong A 1 modes, particularly a symmetric ν s (Ni–H) mode at 1127 cm –1 , and a ν(Ni–BH 4 ) mode at 473 cm –1 (Table ). FTIR spectra of [(Tp Me,Me )Ni(η 4 ‐BH 4 )] and the [(Tp Me,Me )Ni(η 4 ‐BD 4 )] isotopologue were obtained (Figures S8 and S9); because the modes of interest fall in the fingerprint region dominated by scorpionate ligand vibrations (Figure ), difference techniques were utilized to resolve the normal modes of the borohydride ligand from the scorpionate‐centered bands (Figure : raw data were converted to absorption, scalar corrections were applied to adjust the baselines to zero, the isotopologue spectrum was vertically scaled to align the scorpionate‐centered modes and the natural abundance spectrum was subtracted).…”

“…The reduction in complex symmetry and borohydride hapticity in [(Tp Ph,Me )Ni(η 3 ‐BH 4 )] increases the number of bands arising from the borohydride normal modes;, , a complete descent in symmetry from the T d ‐BH 4 free ion to C 3 v ‐[(Tp)Ni(η 4 ‐BH 4 )] and to C s ‐[(Tp)Ni(η 3 ‐BH 4 )] is given in Table S7, wherein a particularly informative comparison is made to the spectrum of [(η 5 ‐C 5 H 5 )Be(η 3 ‐BH 4 )] as previously assigned under ideal C 2 v symmetry (a depiction of all 12 normal modes germane to the BeH 2 BH 2 core is given in the reference) . In addition to the expected ν(B–H) modes, the frequency calculation on [(Tp)Ni(η 3 ‐BH 4 )] yielded a strong δ(BH 2 ) mode at 1086 cm –1 ,, a ν s (Ni–H) mode at 1353 cm –1 , and a ν(Ni–BH 4 ) mode at 430 cm –1 . The fingerprint region of FTIR spectra for [(Tp Ph,Me )Ni(η 3 ‐BH 4 )] and the [(Tp Ph,Me )Ni(η 3 ‐BD 4 )] isotopologue (Figures S10 and S11) were even more complicated by scorpionate‐centered bands (Figure ), but difference techniques again revealed several borohydride bands (Figure and Table ).…”

“…A potential pitfall in assigning the coordination mode of the borohydride ligand lies in the inherent inaccuracy of determining the hydride atom positions adjacent to a heavy transition metal by X‐ray diffraction. For this reason, vibrational spectroscopy has been an important tool to confirm the coordination modes , , , , , , , , , …”

Beryllium-9 NMR Study of Solid Bis(2,4-pentanedionato-O,O‘)beryllium and Theoretical Studies of 9Be Electric Field Gradient and Chemical Shielding Tensors. First Evidence for Anisotropic Beryllium Shielding

“…From ref a. o Geometry from refs and . C−H bond lengths were set to 1.09 Å. p Isotropic chemical shifts are referenced with respect to Be(NO 3 ) 2 (aq) as Be(H 2 O) 4 2+ unless otherwise indicated.…”

Synthesis and spectroscopic properties of cyclopentadienyl(methyl)beryllium and cyclopentadienylberyllium halide complexes

“…A detailed infrared and Raman analysis for liquid and solid C5H5BeCl, C5H5BeBH4, and C5H5BeBD4 has been recently published. 27 The results clearly show that the fundamental frequencies pertaining to the cyclopentadienyl ring must be assigned with local C5" symmetry for the metal-ring species (as apposed to Dih symmetry that would be consistent with an electrostatic ring).…”