Additive Covalent Radii for Single-, Double-, and Triple-Bonded Molecules and Tetrahedrally Bonded Crystals: A Summary

Abstract

The recent fits of additive covalent radii R(AB) = r(A) + r(B) for the title systems are reviewed and compared with alternative systems of radii by other authors or with further experimental data. The agreement of the predicted R with experiment is good, provided that the A-B bond is not too ionic, or the coordination numbers of the two atoms too different from the original input data, used in the fit. Bonds between transition metals and halides are not included in the single-bond set, because of their partial multiple-bond character.

Terminal Parent Phosphanide and Phosphinidene Complexes of Zirconium(IV)

“…The ∡ ZrPH for Zr3 is very similar to that computed for H 2 Zr=PH (∡ ZrPH =63.8°), despite the very different zirconium coordination numbers and geometries of the two complexes 10. The Zr⋅⋅⋅H distance in Zr3 is considerably longer than the sum of the single bond covalent radii of Zr and H (1.86 Å),13 and the analogous Zr⋅⋅⋅H distance of 2.13 Å in H 2 Zr=PH,10 which can be rationalized by the aforementioned steric and charge differences between Zr3 and H 2 Zr=PH 10…”

Crystalline Diuranium Phosphinidiide and μ‐Phosphido Complexes with Symmetric and Asymmetric UPU Cores

“…A shoulder in the χ vs. T data is apparent at about 25 K which is most likely due to single‐ion crystal field effects rather than any magnetic exchange 12. Confirmation of the formulation of 3 was provided by the solid state crystal structure, Figure 1, which reveals U–P distances of 2.8187(12) and 2.8110(12) Å that, considering steric profiles, compares well to a U–P distance of 2.743(1) Å in [{U(C 5 Me 5 ) 2 (OMe)} 2 (μ‐PH)]11 and the sum of the single‐bond covalent radii of uranium and phosphorus (2.81 Å) 8…”

“…For the ThPTh derivative this ligand combination produced a seemingly optimal balance of steric shielding of the ThPTh core versus inter‐Tren TIPS steric repulsion. We therefore considered whether the analogous diuranium complex might be accessible; however, uranium has potentially deleterious and facile redox chemistry compared to the more redox‐robust thorium, and is smaller than thorium by 0.05–0.18 Å,8 so uranium with the same ligand set might well be too strained to form a stable UPU linkage and could very easily decompose. Herein, however, we report two different methods for the bulk‐scale preparation and subsequent characterization of diuranium μ‐phosphido complexes, utilizing Tren TIPS and the related Tren DMBS (Tren DMBS =N(CH 2 CH 2 NSiMe 2 Bu t ) 3 ) ligands, that are the first examples of uranium phosphido complexes outside of cryogenic spectroscopic experiments 5b,5c.…”

“…The solid‐state crystal structure of 4 , Figure 1, confirms the separated ion pair formulation and reveals U–P distances of 2.653(4) and 2.665(4) Å, which represents a contraction of approximately 0.15 Å from 3 . The U–P distances in 4 can be considered to be short when considering the bridging nature of the phosphido; for example, although the sum of the covalent uranium and phosphorus double bond radii is 2.36 Å,8 the U=P distances in the terminal uranium(IV) phosphinidene complexes [U(Tren TIPS )(PH)][K(B15C5) 2 ]4a and [U(C 5 Me 5 ) 2 (P‐2,4,6‐Bu t 3 C 6 H 2 )(OPMe 3 )]4b are 2.613(2) and 2.562(3) Å, respectively. Furthermore, the Th–P distances in [{Th(Tren TIPS )} 2 (μ‐P)][Na(12C4) 2 ] (12C4=12‐crown‐4 ether)7d are significantly longer [2.735(2)/2.740(2) Å] than the U–P distances in 4 , even when factoring in the covalent radii differences between thorium and uranium 8.…”

Silyl‐Phosphino‐Carbene Complexes of Uranium(IV)

“…The U⋅⋅⋅P distances in 3 – 5 are 2.774(3), 2.8277(5), and 2.8371(13) Å, respectively, and are at the limit of, or exceed, the covalent single bond radii of uranium and phosphorus (2.81 Å) 11. Further, it is clear from the solid‐state structures that owing to the orientations of the Ph 2 P groups the phosphorus lone pairs do not point towards the uranium ions in 3 – 5 .…”