Potentiometric studies in aqueous solution at 25 degrees C and ionic strength 0.5 mol dm(-3) in NaClO4 show that beryllium(II) with different polyamino carboxylic acids forms the following complexes : EDTA (ethylenediaminetetraacetic), 1,2-PDTA(1,2-propylenediamine-N,N,N’,N’-tetraacetic), and CDTA (trans-1,2-cyclohexanediamine-N,N,N’,N’-tetraacetic) (ligands, H(4)L), [BeHL](-), [BeL](2-), and [Be-3(OH)(3)(HL)]; EDDADP (ethylenediamine-N,N’-diacetic-N,N’-dipropionic) and EDTP (ethylenediamine-N,N,N’,N’-tetrapropionic) (ligands, H(4)L), [BeH(2)L], [BeHL](-), [BeL](2-), and [Be-3(OH)(3)(HL)]; o-PhDTA (o-phenylenediamine-N,N,N’,N’-tetraacetic),3,4-TDTA (3,4-toluenediamine-N,N,N’,N’-tetraacetic) and 4-Cl-o-PhDTA (4-chloro-o-phenylenediamine-N,N,N’,N’-tetraacetic) (ligands, H(4)L), [BeHL](-) and [BeL](2-); NTA (nitrilotriacetic) (ligand H(3)L), [BeL](-) and [Be-3(OH)(3)(HL)](+); NDAP (nitrilodiaceticpropionic) (ligand H(3)L), [BeH(2)L](+), [BeHL], [BeL](-), [Be-3(OH)(3)(HL)](+), and [Be-3(OH)(3)L]; NADP (nitriloaceticdipropionic) (ligand, H(3)L), [BeHL] and [BeL](-); NTP (nitrilotripropionic) (ligand, H(3)L), [BeL](-). The following complexes are formed analogously for magnesium(II) : o-PhDTA, 3,4-TDTA, and 4-Cl-o-PhDTA, [MgHL](-) and [MgL](2-); NADP and NTP, [MgHL] and [MgL](-). The stability constants were determined. From an aqueous solution of Be(OH)(2) and NTP (ratio 1:1), boiled until the Be(OH)(2) was completely dissolved, crystals of the complex sodium (nitrilotripropionato)beryllate(II) trihydrate, Na[Be(NC9H12O6)]. 3H(2)O were obtained. X-ray diffraction structural analysis revealed that, in the chelate complex [Be(NTP)](-) (hexagonal), P6(3), a = 11.4768(7) Angstrom, b = 11.4768(7) Angstrom, c = 6.2807(3) Angstrom, V = 716.44(7) Angstrom(3), Z = 2, R1 = 0.0433, wR2 = 0.1110), the tetrahedron BeNO3 is almost regular with a very slight distortion toward the symmetry C-3v, H-1, C-13, Be-9 NMR, IR spectra, and thermal analyses are studied. : EDTA (ethylenediaminetetraacetic), 1,2-PDTA(1,2-propylenediamine-N,N,N’,N’-tetraacetic), and CDTA (trans-1,2-cyclohexanediamine-N,N,N’,N’-tetraacetic) (ligands, H(4)L), [BeHL](-), [BeL](2-), and [Be-3(OH)(3)(HL)]; EDDADP (ethylenediamine-N,N’-diacetic-N,N’-dipropionic) and EDTP (ethylenediamine-N,N,N’,N’-tetrapropionic) (ligands, H(4)L), [BeH(2)L], [BeHL](-), [BeL](2-), and [Be-3(OH)(3)(HL)]; o-PhDTA (o-phenylenediamine-N,N,N’,N’-tetraacetic),3,4-TDTA (3,4-toluenediamine-N,N,N’,N’-tetraacetic) and 4-Cl-o-PhDTA (4-chloro-o-phenylenediamine-N,N,N’,N’-tetraacetic) (ligands, H(4)L), [BeHL](-) and [BeL](2-); NTA (nitrilotriacetic) (ligand H(3)L), [BeL](-) and [Be-3(OH)(3)(HL)](+); NDAP (nitrilodiaceticpropionic) (ligand H(3)L), [BeH(2)L](+), [BeHL], [BeL](-), [Be-3(OH)(3)(HL)](+), and [Be-3(OH)(3)L]; NADP (nitriloaceticdipropionic) (ligand, H(3)L), [BeHL] and [BeL](-); NTP (nitrilotripropionic) (ligand, H(3)L), [BeL](-). The following complexes are formed analogously for magnesium(II) : o-PhDTA, 3,4-TDTA, and 4-Cl-o-PhDTA, [MgHL](-) and [MgL](2-); NADP and NTP, [MgHL] and [MgL](-). The stability constants were determined. From an aqueous solution of Be(OH)(2) and NTP (ratio 1:1), boiled until the Be(OH)(2) was completely dissolved, crystals of the complex sodium (nitrilotripropionato)beryllate(II) trihydrate, Na[Be(NC9H12O6)]. 3H(2)O were obtained. X-ray diffraction structural analysis revealed that, in the chelate complex [Be(NTP)](-) (hexagonal), P6(3), a = 11.4768(7) Angstrom, b = 11.4768(7) Angstrom, c = 6.2807(3) Angstrom, V = 716.44(7) Angstrom(3), Z = 2, R1 = 0.0433, wR2 = 0.1110), the tetrahedron BeNO3 is almost regular with a very slight distortion toward the symmetry C-3v, H-1, C-13, Be-9 NMR, IR spectra, and thermal analyses are studied.