X-ray structures are described for the bis-catecholate, bis-dithiocatecholate, and tetraalkoxy diborane(4) compounds B-2(1,2-O2C6H4)(2) (1), B-2(1,2-O-2-4-(BuC6H3)-C-t)(2) (2), B-2(1,2-O-2-3,5-(Bu2C6H2)-C-t)(2) (3), B-2(1,2-S2C6H4)(2) (4), B-2(1,2-S-2-4-MeC6H3)(2) (5), and B-2(OCH2CMe2CH2O)(2) (6). All the compounds adopt structures in the solid-state in which the B2O4 Or B2S4 units are planar or very nearly so. In compounds 2 and 3, the dihedral angles between the two BO2C2 planes are 17.3 and 31.8 degrees respectively whereas in 1. 4 and 5 these angles are exactly 0 degrees. In 6, a 3-fold disorder precluded our obtaining accurate positions for the two boron atoms, yet a dihedral angle of 0 degrees is required by the 3 site symmetry. The structure of the bis(Lewis base) adduct of B2Cl4, [B2Cl4(NHMe2)(2)] (7), is also described and structures of the salt [NH2Me2][B(1,2-O2C6H4)(2)] (8) and the NMe2-bridged dimer [{BCl2(mu-NMe2)}(2)] (9) are available in the Supporting Information. Compound 1 crystallized in the monoclinic space group P2(1)/e with a = 4.746(1) Angstrom, b = 16.427(3) Angstrom, c = 7.053(2) Angstrom, beta = 98.59(2)degrees, and Z = 2. Crystals of 2 were monoclinic, space group P2(1)/e with a = 6.847(1) Angstrom, b = 18.871(5) Angstrom, c 15.270(2) Angstrom, beta = 93.16(2)degrees, and Z = 4. Crystals of 3 were triclinic, space group P (1) over bar with a = 9.478(4) Angstrom, b = 10.355(4) Angstrom, c =15.082(7) Angstrom, a = 105.71(3)degrees beta = 100.31(4)degrees, gamma = 94.58(3)degrees, and Z = 2. Crystals of 4 were monoclinic, space group P21/e with a = 15.364(3) Angstrom, b = 4.0502(4) Angstrom,= 21.532(3) Angstrom, beta = 99.320(7)degrees, and Z = 4. Crystals of 5 were monoclinic, space group P2(1)/e with a =6.0458(9) Angstrom, b = 7.5319(11) Angstrom, c= 16.552(2) Angstrom, beta = 96.291(3)degrees and Z = 2. Compound 6 crystallized in the rhombohedral space group R (3) over bar m with a = 8.876(2) Angstrom, c = 13.821(3) Angstrom and Z = 3. Crystals of 7 were monoclinic, space group P2(1)/e with a 11.831(3) Angstrom, b = 19.458(5) Angstrom, c =14.823(5) Angstrom, beta = 96.63(4)degrees, and Z = 12.