Group polyphosphides

From the pioneering work of Rudolph (group 14 Zintl ions) and Baudler (polyphosphide Zintl ions) to the modem multidimensional techniques used in current research, multinuclear NMR has played a central role in evaluating stmctures. 

Coordination to metals follows the usual trends. The transition metals try to achieve octahedral coordination (with a few exceptions), but the cations of the electropositive group 1-3 elements exhibit a rich variety. The coordination polyhedra are determined by radius ratios more than by topological preferences. For polyphosphides in general, all P atoms are involved in M-P interactions according to the number of lone pairs present. The anionic (lb)P and (2b)P as well as the neutral (3b)P° species adopt quasi-tetrahedral coordination, especially if main-group cations are involved. Only a few exceptions are known, for example Li3P7. With more covalent M-P bonds, the number (m + n) of available lone pairs of a polyanion P " is strongly related to the metal coordination number that is, CN(M) < m + n). If CN(M) > m + n), ion-ion and ion-dipole interactions dominate. The relation <7[M-(2b)P] > <7[M-(3b)P] is true in most cases. 

The diversity in structure and bonding possible for phosphides is effectively demonstrated by the monophosphides. Monophosphides MP of the group 1 and 2 elements (El, E2) are polyphosphides with i(P ) chains and P2" dumbbells, respectively. Ell and E12 monophosphides are not known. The E3 and E13 monophosphides are the so-called normal compounds with 3x = (M) (see Section 2). With El3, they form the zinc blende structure with tetrahedral heteroatomic bonds. Ternary derivatives such as MgGeP2 and CuSi2P3 have a random distribution of the M atoms, whereas CdGeP2, crystallizes in the ordered chalcopyrite type with a TO[GeP4/2] tetrahedral net (see Section 6.4). The E3 monophosphides form the NaCl structure. CeP is remarkable because of its physical properties (metal-semiconductor transition heavy-fermion behavior). The E14 monophosphides show the break usually observed when passing the Zintl border. Binary lead phosphides are not known SiP and GeP... 

Baudler s group (and others) continue to make extensive use of alkali-metal polyphosphide reagents in the synthesis of both cyclic " and acyclic polyphosphines. " A wide range of new systems has been described in the past year, and the field as a whole has been reviewed. ... 

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