Nitrogen in GaP is an isoelectronic acceptor. Due to its much higher electronegativity than phosphorus, nitrogen forms bound excitons. This had made possible the fabrication of LEDs from an indirect band gap material. A spectrocopic study of N-H complexes in GaP grown by LEC technology shows that two hydrogens and one nitrogen are involved, existing in three different states; two of them corresponding to different charged states. One of this centres does not show gallium isotope shift, resulting that both hydrogens are bonded to the nitrogen, the nitrogen being five fold coordinated. We investigated this new NH2 configuration using ab-initio calculations on a HNHGa22P21H42 cluster. As this centre has C3v symmetry, nitrogen is positioned in a phosphorus site, one hydrogen is antibonding on nitrogen and the other at bond centre, both along a 〈111〉 direction. We found the hydrogen at bond centre prefers to bond to nitrogen for the double positive charged state, with the nitrogen five folded coordinated. This configuration is metastable for the singly positive charged state. The last two states have very similar configurations, being the plane formed by the three Ga atoms and nitrogen perpendicular to the H-N-H direction, very similar to the NH5+2 molecule. A vibrational analysis of the NHNGa3+2 cluster is in a good agreement with experiment.