Bis(4-carboxylpyrazol-1-yl)acetic acid: a scorpionate ligand for complexes with improved water solubility.

Bis(4-carboxylpyrazol-1-yl)acetic acid (Hbcpza) (2), obtained in a one-pot synthesis, contains carboxyl groups that differ in their p values. The ligand exhibits heteroscorpionate κ-N,N,O-coordination whereupon the peripheral carboxyl groups are not involved in metal binding. The corresponding carbonyl complexes [Mn(Hbcpza)(CO)] (4), [Re(Hbcpza)(CO)] (5) and [Ru(Hbcpza)Cl(CO)] (6a/6b) are partially soluble in water but readily soluble in PBS buffer.

-Block metal complexes with bis(pyrazol-1-yl)acetato ligands.

The hetereoscorpionate ligands bis(pyrazol-1-yl)acetic acid (Hbpza) and bis(3,5-dimethylpyrazol-1-yl)acetic acid (Hbdmpza) are reacted with [Sn(OAc)] or [Sn(acac)] to yield the corresponding Sn(II) complexes. A single crystal X-ray determination for the in solution monomeric complex [Sn(bpza)] (1a) revealed a dinuclear molecular structure [Sn(bpza)] (1b), with κ-N,N,O-coordinated bpza ligands at each of the Sn(II) and two bpza ligands μ-bridging between the Sn(II) centres. The molecular structure of [Sn(bdmpza)] (2) exhibits a homoleptic bisligand complex with both ligands displaced by the free electron pair, which is proven by DFT calculations.