title: Twinning of three Fe-PNP pincer complexes interpreted according to order-disorder (OD) theory.
abstract: The systematic twinning of three 2,6-diaminopyridine-based Fe-PNP complexes is interpreted using order-disorder (OD) theory. The monoclinic [Fe(0)(PNP(Et)-(i)Pr)(CO)2] [P112(1)/b, Z' = 4] possesses pseudo-orthorhombic metrics and crystallizes as a reflection twin by pseudo-merohedry with the twin plane (100). The structure is made up of layers with idealized p2(1)a(b) symmetry. The a glide planes of adjacent layers do not overlap, leading to OD polytypism. trans-[Fe(II)(PNP-Et)Br2(CO)] [P2(1)/n, Z' = 1] is systematically twinned via twofold rotation about [001]. It is made up of OD layers with idealized p2(1)2(1)(2) symmetry. OD polytypism is caused by the twofold rotation axes of adjacent layers which do not overlap. [Fe(II)(κ(2)P,N-PNP-(i)Pr,TAD)Cl2]·THF [P1, Z^{\prime} = 2] is systematically twinned via a twofold rotation about [010]. It is made up of layers with idealized p121(1) symmetry. OD polytypism is caused by screw rotations relating adjacent layers with an intrinsic translation along a fourth of a primitive lattice vector. In all three structures the twin individuals are a polytype with a maximum degree of order (MDO) and at the twin interface is located a fragment of the second MDO polytype.
authors.affiliation: Institute of Applied Synthetic Chemistry, Getreidemarkt 9/163, 1060 Vienna, Austria.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Bichler
authors.affiliation: Institute of Applied Synthetic Chemistry, Getreidemarkt 9/163, 1060 Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Holzhacker
authors.affiliation: Institute of Applied Synthetic Chemistry, Getreidemarkt 9/163, 1060 Vienna, Austria.
authors.forename: Mathias
authors.initials: M
authors.lastname: Glatz
authors.affiliation: Institute of Chemical Technologies and Analytics, Division of Structural Chemistry, Getreidemarkt 9/164-SC, 1060 Vienna, Austria.
authors.forename: Berthold
authors.initials: B
authors.lastname: Stöger
authors.affiliation: Institute of Applied Synthetic Chemistry, Getreidemarkt 9/163, 1060 Vienna, Austria.
authors.forename: Karl
authors.initials: K
authors.lastname: Kirchner
keywords: order–disorder polytypism; pincer complexes; twinning