The structural chemistry of text-book species: The tartrato-cuprates in Fehling's solution

摘要

Fehling's solution is an aqueous alkaline solution (pH ca. 13) of D-, L-, or rac-tartrato-cuprates(II) and both excess tartrate and hydroxide. The isolation of crystalline solids succeeded for rac-tartrate-containing samples. Crystal structure analyses revealed the formulas K_8[Cu _(10)(rac-tartH_(-1))_4(rac-tartH_(-2)) _4(H_2O)_4]·18H_2O (1), Li _4[Cu_2(rac-tartH_(-2)-κ~2O ~1,O~2:κ~2O~3,O~4) _2]·11.75H_2O (2), and Na_6[Cu(rac- tartH_(-2)-κ~2O~2,O~3) _2]·14H_2O (3). The cupric central atom is in a square-planar tetracoordination in the bis(diolato) chelate in 3, and in square-pyramidal 4+1 coordination in the mixed carboxylato-alkoxido chelates 1 and 2. In terms of stoichiometry, 3 is closest to typical Fehling recipes.