The only 4-dimensional non-compact rank one symmetric spaces are CH 2 and RH 4 . By the classical results of Heintze, one can model these spaces by real solvable Lie groups with left invariant metrics. In this paper we classify all possible left invariant Hermitian structures on these Lie groups, i.e., left invariant Riemannian metrics and the corresponding Hermitian complex structures. We show that each metric from the classification on CH 2 admits at least four Hermitian complex structures. One class of metrics on CH 2 and all the metrics on RH 4 admit 2-spheres of Hermitian complex structures. The standard metric of CH 2 is the only Einstein metric from the classification, and also the only metric that admits Kähler structure, while on RH 4 all the metrics are Einstein. Finally, we examine the geometry of these Lie groups: curvature properties, self-duality, and holonomy.2010 Mathematics Subject Classification. Primary 53B35; Secondary 22E60, 53C20.

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