The use of the terphenyl substituent -C(6)H(3)-2,6-Mes(2) (abbreviated Ar) has permitted the synthesis of several new low-coordinate beryllium compounds. Reaction of 1 equiv of LiAr with BeCl(2)(OEt(2))(2) or BeBr(2)(OEt(2))(2) (1) gives the monomeric complexes ArBeX(OEt(2)) (X = Cl (2); Br (3) featuring three-coordinate berylliums. Treatment of 2 with 1 equiv of LiSMes (Mes = -C(6)H(2)-2,4,6-t-Bu(3)) affords the three-coordinate thiolate derivative ArBeSMes(OEt(2)) (4). The reaction of 2 with LiNHPh, LiNHSiPh(3), or LiN(SiMe(3))(2) affords the unstable dimer (ArBeNHPh)(2) (5) or the monomers ArBeNHSiPh(3)(OEt(2)) (6) and ArBeN(SiMe(3))(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)-C(5)H(5))(CO)(3) gives the isocarbonyl complex Ar(THF)(2)Be(OC)(3)Mo(eta(5)-C(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(SiMe(3))(2) and PhCN affords the six-membered-ring compound PhC(NSiMe(3))(2)(BeCl)(2)N(SiMe(3))(2) (9) and the four-coordinate monomer Be{(NSiMe(3))(2)CPh}(2) (10). Compounds 1-10 were characterized by X-ray crystallography, and 1 and 4 and 6-10 were also characterized by (1)H, (9)Be, and (13)C NMR spectroscopy. X-ray data at 130 K (1-9) or 185 K (10) with Mo Kalpha (lambda = 0.710 73 Å) (1, 2a, 3, 7, 8) or Cu Kalpha (lambda = 1.541 78 Å) (2b, 4-6, 9, 10). BeBr(2)(OEt(2))(2) (1), a = 11.690(5) Å, b = 10.191(3) Å, c = 12.131(5) Å, beta = 114.67(3) degrees, V = 1313.3(9) Å(3), space group P2(1)/n, Z = 4, R(1) = 0.062; ArBeCl(OEt(2)) (2a), a = 13.136(3) Å, b = 13.877(3) Å, c = 28.092(6) Å, V = 5121(2) Å(3), space group Pbca, Z = 8, R(1) = 0.058; ArBeCl(OEt(2)) (2b), a = 8.857(1) Å, b = 8.8977(9) Å, c = 18.198(7) Å, alpha = 86.437(8) degrees, beta = 82.677(8) degrees, gamma = 62.405(7) degrees, V = 1260.5(2) Å(3), space group P&onemacr;, Z = 2, R(1) = 0.048; ArBeBr(OEt(2)) (3), a = 8.873(5) Å, b = 8.847(5) Å, c = 18.251(7) Å, alpha = 86.54(4) degrees, beta = 83.17(4) degrees, gamma = 64.14(4) degrees, V = 1280(1) Å(3), space group P&onemacr;, Z = 2, R(1) = 0.071; ArBeSMes(OEt(2)).0.5C(6)H(14) (4.0.5C(6)H(14)), a = 9.732(1) Å, b = 11.190(1) Å, c = 21.841(2) Å, alpha = 75.225(7) degrees, beta = 81.137(8) degrees, gamma = 73.382(8) degrees, V = 2195.3(4) Å(3), space group P&onemacr;, Z = 2, R(1) = 0.062; (ArBeNHPh)(2).C(4)H(10)O (5.C(4)H(10)O), a = 11.894(2) Å, b = 12.212(2) Å, c = 18.709(3) Å, beta = 99.24(1) degrees, V = 2682.4(7) Å(3), space group P2(1), Z = 2, R(1) = 0.045; ArBeNHSiPh(3)(OEt(2)) (6), a = 11.959(2) Å, b = 16.655(2) Å, c = 19.718(2) Å, beta = 105.368(9) degrees, V = 3786.9(8) Å(3), space group P2(1)/c, Z = 4, R(1) = 0.047; ArBeN(SiMe(3))(2) (7), a = 12.623(3) Å, b = 15.404(4) Å, c = 15.502(3) Å, V = 3014(1) Å(3), space group Pbcn, Z = 4, R(1) = 0.046; Ar(THF)(2)Be(OC)(3)Mo(eta(5)-C(5)H(5)).2C(7)H(8) (8.2C(7)H(8)), a = 19.111(4) Å, b = 11.976(3) Å, b = 21.241(5) Å, beta = 103.47(2) degrees, V = 4728(2) Å(3), space group P2(1)/c, Z = 4, R(1) = 0.049; PhC(NSiMe(3))(2)(BeCl)(2)N(SiMe(3))(2) (9), a = 19.996(4) Å, b = 14.816(2) Å, c = 20.183(4) Å, V = 5979(2)Å(3), space group Pbca, Z = 8, R(1) = 0.043; Be{(NSiMe(3))(2)CPh}(2) (10), a = 20.022(2) Å, b = 9.7161(9) Å, c = 19.456(2) Å, beta = 11.392(8) degrees, V = 3524.1(6) Å(3), space group P2(1)/c, Z = 4, R(1) = 0.075.