Synthesis and characterization of vanadium(IV)–M (M=Mn, Zn) and vanadium(IV)–Ln (Ln=La, Nd) complexes with nitrilotriacetate ligands: {(NH4)2[(VIVO)2(μ2-O)(nta)2M(H2O)4] · 2H2O}n and NH4[Ln(H2O)9][(VIVO)2 (μ2-O)(nta)2]