Synthesis of a new binucleating ligand LH4: synthesis and X-ray structures of anti-[Co2(LH4)(OH2)2](NO3)4·5H2O, anti-[Ni2(LH4)(NCMe)2](PF6)4·4H2O, anti-[Zn2(LH4)(NO3)2](NO3)2 and syn-[Cu2(LH2)](BPh4)2