On the interaction between mercury(II) salts and 3-methylpyrazoline-5-one. The first crystal structure of a cyclic organomercuric compound with a dimercurated methylenic carbon atom

Synthesis and characterization of two types of novel organomercury derivatives of 3-methylpyrazoline-5-one (MepzH2-one), (XHg)2(MepzH-one) (X = Cl−, Br−) and Hg(MepzH-one)2 are described. The 1H and 13C NMR data revealed existence of dimercurated compounds in the dimethylsulfoxide-d 6 solution. NMR spectra confirmed that the mercuration took place at the C-4 atom of the pyrazole ring. X-ray crystal structure analysis of 4,4-bis(chloromercurio)-3-methylpyrazoline-5-one revealed almost linear coordination of both mercury atoms [Hg–C 2.099(6) and 2.104(5) ; Hg–Cl 2.330(2) and 2.338(2) ; C–Hg–Cl 171.1(2) and 174.4(2)°]. The slight deviation from linearity is caused by contacts with nitrogen or oxygen atoms from the neighbouring molecule [Hg $$\cdots$$ N 2.768(5) and Hg $$\cdots$$ O 2.748(5) ]. The molecules are interconnected by hydrogen bonds N–H $$\cdots$$ Cl of 3.286(5) .