Generation and structural characterisation of a difluorodimethoxyborate-mediated hydrogen-bonded supramolecular synthon

Abstract

Recrystallisation of [CuL^2e][BF₄]₂ [L^2e = 1,2-bis(amidino-O-ethylurea)ethane] from methanol affords [CuL^2e][BF₂(OMe)₂][BF₄], the basic building block of which is a 1-D linear chain of [CuL^2e]²⁺ cations linked by difluorodimethoxyborate-mediated hydrogen-bonded supramolecular synthons. Hydrogen-bonded [BF₄]⁻ anions link the chains to form a 2-D sheet structure; weak co-ordinate interactions between Cu(II) centres and [BF₄]⁻ anions in adjacent sheets generate a 3-D network. Recrystallisation of [CuL^2m][BF₄]₂ [L^2m = 1,2-bis(amidino-O-methylurea)ethane] from methanol leaves it unaltered. The [CuL^2m]²⁺–[BF₄]⁻ system does not give rise to the same sort of supramolecular synthon and linear 1-D chain as the [CuL^2e]²⁺–[BF₂(OMe)₂]⁻ system. Instead the basic building block is a zigzag chain of [CuL^2m]²⁺ cations linked through a different arrangement of hydrogen-bonded [BF₄]⁻ anions. The [BF₄]⁻ anions also act as hydrogen-bonding acceptors to connect the chains, firstly into 2-D sheets and ultimately into a 3-D network.