The ambidentate dianions [(BuN)-Bu-t(E)P(mu -(NBu)-Bu-t)(2)P(E)(NBu)-Bu-t](2-) (5a, E = S; 5b, E = Se) are obtained as their disodium and dipotassium salts by the reaction of cis-[Bu-t(H)N(E)P(mu -(NBu)-Bu-t)(2)P(E)N(H)Bu-t] (6a, E = S; 6b, E = Se), with 2 equiv of MN(SiMe3)(2) (M = Na, K) in THF at 23 degreesC. The corresponding dilithium derivative is prepared by reacting 6a with 2 equiv of (BuLi)-Bu-t in THF at reflux. The X-ray structures of five complexes of the type [(THF)(x)M](2-)[(BuN)-Bu-t(E)P(mu -(NBu)-Bu-t)(2)P(E)(NBu)-Bu-t] (9, M = Li, E = S, x = 2; 11a/11b, M = Na, E = S/Se, x = 2; 12a, M = K, E = S, x = 1; 12b, M = K, E = Se, x = 1.5) have been determined. In the dilithiated derivative 9 the dianion 5a adopts a bis (N,S)-chelated bonding mode involving four-membered LiNPS rings whereas 11a,b and 12a,b display a preference for the formation of six-membered MNPNPN and MEPNPE rings, i.e., (N,N' and E,E')chelation. The bis-solvated disodium complexes 11a,b and the dilithium complex 9 are monomeric, but the dipotassium complexes 12a,b form dimers with a central K2E2 ring and associate further through weak K E contacts to give an infinite polymeric network of 20-membered K6E6P4N4 rings. The monoanions [Bu-t(H)N(E)P-(mu -(NBu)-Bu-t)(2)P(E)(NBu)-Bu-t)](-) (E = S, Se) were obtained as their lithium derivatives 8a and Sh by the reaction of 1 equiv of (BuLi)-Bu-n with 6a and 6b, respectively. An X-ray structure of the TMEDA-solvated complex 8a and the P-3t NMR spectrum of 8b indicate a N,E coordination mode. The reaction of 6b with excess (BuLi)-Bu-t in THF at reflux results in partial deselenation to give the monolithiated P(III)/P(V) complex {(THF)(2)Li[(BuN)-Bu-t(Se)P(mu -(NBu)-Bu-t)(2)PN-(H)Bu-t]} 10, which adopts a (N,Se) bonding mode.