# Ytterbium(III) Tricyanomethanides with Sodium and Potassium: Similarities and Differences Between NaYb[C(CN)3]4 and KYb[C(CN)3]4

## TL;DR

This paper compares two ytterbium compounds with tricyanomethanide anions, highlighting structural differences based on sodium or potassium presence.

## Contribution

The study reveals structural and coordination differences in ytterbium(III) tricyanomethanides with sodium and potassium.

## Key findings

- NaYb[C(CN)3]4 and KYb[C(CN)3]4 have distinct crystal structures and coordination geometries.
- Na+ and K+ cations show different bonding distances and interactions with tricyanomethanide anions.
- Raman spectroscopy confirms the pseudo-D3h symmetry of [C(CN)3]− in NaYb[C(CN)3]4.

## Abstract

Metathesis reactions of Ag[C(CN)3] with anhydrous YbCl3 dissolved in water combined with stoichiometric amounts of the alkali-metal salts A[C(CN)3] (A = Na or K) yield the non-isotypic tetragonal compounds NaYb[C(CN)3]4 (P4/nnc with a = 1188.37(9) pm, c = 1232.41(9) pm) and KYb[C(CN)3]4 (P4/nbm with a = 1179.26(9) pm, c = 668.73(5) pm). Both crystal structures contain a three-dimensional framework (Niggli formula: 3∞{(Yb[C(CN)3]8/2)−}) with Yb3+ in square antiprismatic coordination of terminal nitrogen atoms (d(Yb–N) = 241–242 pm) from eight planar star-shaped tricyanomethanide anions [C(CN)3]−. The Na+ or K+ cations occupy vacancies, which provide them with a tetrahedral coordination sphere of nitrogen (d(Na–N) = 239 pm vs. d(K–N) = 276 pm) from four [C(CN)3]− anions. This difference results from secondary contacts with the central carbon atoms (d(Na–C) = 361 pm vs. d(K–C) = 367 pm) of four different [C(CN)3]− units, which do not contribute to NaYb[C(CN)3]4, but effectuate a lot in the case of KYb[C(CN)3]4. The Raman spectrum recorded for NaYb[C(CN)3]4 corroborates the presence of a pseudo-D3h-symmetric tricyanomethanide anion [C(CN)3]− and the absence of water.