Electrochemical and Structural Studies of Nickel(Ii) Complexes with N2O2 Schiff Base Ligands Derived from 2-Hydroxy-1-Naphthaldehyde. Molecular Structure of N,N′-2,3-Dimethylbutane-2,3-Diyl-Bis(2-Hydroxy-1-Naphthylideneiminate) Nickel(Ii)