The use of the terphenyl substituent -C6H3-2,6-Mes(2) (abbreviated Ar) has permitted the synthesis of several new low-coordinate beryllium compounds. Reaction of 1 equiv of LiAr with BeCl2(OEt2)(2) or BeBr2(OEt2)(2) (1) gives the monomeric complexes ArBeX(OE2) (X=Cl (2); Br(3) featuring three-coordinate berylliums. Treatment of 2 with 1 equiv of LiSMes* (Mes*=-C6H2-2,4,6-t-Bu-2) affords the three-coordinate thiolate derivative ArBeSMes* (OEt2) (4). The reaction of 2 with LiNHPh, LiNHSiPh3, or LiN(SiMe3)(2) affords the unstable dimer (ArBeNHPh)(2) (5) or the monomers ArBeNHSiPh3(OEt2) (6) and ArBeN(SiMe3)(2) (7). The last is the first example of a two-coordinate beryllium center in the solid state. The addition of 1 equiv of 2 to NaMo(eta(5)-C5H5)CO)(3) gives the isocarbonyl complex Ar(THF)(2)Be(OC)(3)Mo(eta(5)H(5)) (8), which features four-coordinate beryllium bound to Ar, two THF ligands, and an oxygen from one of the molybdenum-bound carbonyls. Reaction of 2 with a 1:1 mixture of LiN(SiMe3)(2) and PhCN affords the six-membered-ring compound PhC(NSiMe3)(2)(BeCl)(2)N(SiMe3)(2) (9) and the four-coordinate monomer Bd{(NSiMe3)(2)CPh}(2) (10). Compounds 1-10 were characterized by X-ray crystallography, and 1 and 4 and 6-10 were also characterized by H-1, Be-9, and C-13 NMR spectroscopy. X-ray data at 130 K(1-9) or 185 K (10) with Mo K alpha(lambda=0.710 73 Angstrom (1, 2a, 3, 7, 8) or Cu K alpha(lambda=1.541 78 Angstrom) (2b, 4-6, 9, 10). BeBr2(OEt2)(2) (1), a=11.690(5) Angstrom, b=10.191(3) Angstrom, c=12.131(5) Angstrom, beta=114.67(e)degrees, V=1313.3(9) Angstrom(3), space group P2(1)/n, Z=4, R-1=0.062; ArBeCl(OEt2) (2a), a=13.136(3) Angstrom, b=13.877(3) Angstrom, c=28.092(6) Angstrom, V=5121(2) Angstrom(3), space group Pbca, Z=8, R-1=0.058; ArBeCl(OEt2) (2b), a=8.857(1) Angstrom, b=8.8977(9) Angstrom, c=18.198(7) Angstrom, alpha=86.437(8)degrees,